The biology and therapeutic targeting of the proprotein convertases

Key Points

  • The secretory proprotein convertases comprise a family of nine subtilisin-like serine proteases called proprotein convertase 1 (PC1), PC2, furin, PC4, PC5, paired basic amino acid cleaving enzyme 4 (PACE4), PC7, subtilisin kexin isozyme 1 (SKI-1; also known as S1P) and proprotein convertase subtilisin kexin 9 (PCSK9), and their genes have been named PCSK1 to PCSK9.

  • Knowledge gained from in vitro and ex vivo studies, as well as the characterization of the phenotypes of knockout mice and those associated with human mutations showed that these enzymes can have both redundant and unique physiological roles.

  • Furin and PACE4 have a role in cancer and associated metastasis, in arthritis and in viral infections, which makes them attractive therapeutic targets. Small-molecule inhibitors, biologics or antisense silencing of these proprotein convertases are now being considered as therapeutic options.

  • PC1 is implicated in obesity and type 2 diabetes, PC4 in reproduction and PC7 in the regulation of anxiety; these proprotein convertases are therefore attractive targets in these settings.

  • Although SKI-1 has fundamental functions, such as the regulation of steroid and lipid synthesis, it also enhances viral infectivity, suggesting that the short-term use of pharmacological agents to block its activity could be beneficial.

  • Hepatic PCSK9 is a major circulating protein that regulates the half-life of the low-density lipoprotein receptor (LDLR) as well as the very-low-density lipoprotein receptor (VLDLR). It is upregulated by statins and hence its inhibition (in combination with or without statins) is considered to be one of the most promising new treatment approaches to effectively lower levels of LDL-cholesterol.

  • Multiple strategies are now in clinical trials (Phase I–III) to evaluate the efficacy and safety of blocking the function of PCSK9 and/or decrease its levels in the circulation. These include the use of monoclonal antibodies and adnectins, as well as antisense oligonucleotides and small-molecule inhibitors.


The mammalian proprotein convertases constitute a family of nine secretory serine proteases that are related to bacterial subtilisin and yeast kexin. Seven of these (proprotein convertase 1 (PC1), PC2, furin, PC4, PC5, paired basic amino acid cleaving enzyme 4 (PACE4) and PC7) activate cellular and pathogenic precursor proteins by cleavage at single or paired basic residues, whereas subtilisin kexin isozyme 1 (SKI-1) and proprotein convertase subtilisin kexin 9 (PCSK9) regulate cholesterol and/or lipid homeostasis via cleavage at non-basic residues or through induced degradation of receptors. Proprotein convertases are now considered to be attractive targets for the development of powerful novel therapeutics. In this Review, we summarize the physiological functions and pathological implications of the proprotein convertases, and discuss proposed strategies to control some of their activities, including their therapeutic application and validation in selected disease states.

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Figure 1: Schematic representation of the primary structures of the human proprotein convertases.
Figure 2: Subcellular localization of proprotein convertases.
Figure 3: Intracellular versus extracellular pathway and dominant negative effect of proPCSK9.


  1. 1

    Puente, X. S., Sanchez, L. M., Overall, C. M. & Lopez-Otin, C. Human and mouse proteases: a comparative genomic approach. Nature Rev. Genet. 4, 544–558 (2003).

  2. 2

    Long, J. Z. & Cravatt, B. F. The metabolic serine hydrolases and their functions in mammalian physiology and disease. Chem. Rev. 111, 6022–6063 (2011).

  3. 3

    Siezen, R. J. & Leunissen, J. A. Subtilases: the superfamily of subtilisin-like serine proteases. Protein Sci. 6, 501–523 (1997).

  4. 4

    Wright, C. S., Alden, R. A. & Kraut, J. Structure of subtilisin BPN' at 2.5 angstrom resolution. Nature 221, 235–242 (1969).

  5. 5

    Rawlings, N. D., Barrett, A. J. & Bateman, A. MEROPS: the peptidase database. Nucleic Acids Res. 38, D227–D233 (2010).

  6. 6

    Fuller, R. S., Brake, A. & Thorner, J. Yeast prohormone processing enzyme (KEX2 gene product) is a Ca2+-dependent serine protease. Proc. Natl Acad. Sci. USA 86, 1434–1438 (1989).

  7. 7

    Seidah, N. G. The proprotein convertases, 20 years later. Methods Mol. Biol. 768, 23–57 (2011). This is a historical perspective of the proprotein convertases, from the intensive search that led to their discovery to the present-day understanding of their functions.

  8. 8

    Artenstein, A. W. & Opal, S. M. Proprotein convertases in health and disease. N. Engl. J. Med. 365, 2507–2518 (2011).

  9. 9

    Creemers, J. W. & Khatib, A. M. Knock-out mouse models of proprotein convertases: unique functions or redundancy? Front. Biosci. 13, 4960–4971 (2008).

  10. 10

    Seidah, N. G. et al. The activation and physiological functions of the proprotein convertases. Int. J. Biochem. Cell Biol. 40, 1111–1125 (2008).

  11. 11

    Seidah, N. G. What lies ahead for the proprotein convertases? Ann. NY Acad. Sci. 1220, 149–161 (2011).

  12. 12

    Mesnard, D., Donnison, M., Fuerer, C., Pfeffer, P. L. & Constam, D. B. The microenvironment patterns the pluripotent mouse epiblast through paracrine Furin and Pace4 proteolytic activities. Genes Dev. 25, 1871–1880 (2011).

  13. 13

    Sakai, J. et al. Molecular identification of the sterol-regulated luminal protease that cleaves SREBPs and controls lipid composition of animal cells. Mol. Cell 2, 505–514 (1998).

  14. 14

    Seidah, N. G. et al. Mammalian subtilisin/kexin isozyme SKI-1: a widely expressed proprotein convertase with a unique cleavage specificity and cellular localization. Proc. Natl Acad. Sci. USA 96, 1321–1326 (1999).

  15. 15

    Rawson, R. B., Cheng, D., Brown, M. S. & Goldstein, J. L. Isolation of cholesterol-requiring mutant Chinese hamster ovary cells with defects in cleavage of sterol regulatory element-binding proteins at site 1. J. Biol. Chem. 273, 28261–28269 (1998).

  16. 16

    Ye, J. et al. ER stress induces cleavage of membrane-bound ATF6 by the same proteases that process SREBPs. Mol. Cell 6, 1355–1364 (2000).

  17. 17

    Patra, D. et al. Site-1 protease is essential for endochondral bone formation in mice. J. Cell Biol. 179, 687–700 (2007).

  18. 18

    Gorski, J. P. et al. Inhibition of proprotein convertase SKI-1 blocks transcription of key extracellular matrix genes regulating osteoblastic mineralization. J. Biol. Chem. 286, 1836–1849 (2011).

  19. 19

    Tassew, N. G., Charish, J., Seidah, N. G. & Monnier, P. P. SKI-1 and Furin generate multiple RGMa fragments that regulate axonal growth. Dev. Cell 22, 391–402 (2012).

  20. 20

    Marschner, K., Kollmann, K., Schweizer, M., Braulke, T. & Pohl, S. A key enzyme in the biogenesis of lysosomes is a protease that regulates cholesterol metabolism. Science 333, 87–90 (2011).

  21. 21

    Lenz, O., ter Meulen, J., Klenk, H. D., Seidah, N. G. & Garten, W. The Lassa virus glycoprotein precursor GP-C is proteolytically processed by subtilase SKI-1/S1P. Proc. Natl Acad. Sci. USA 98, 12701–12705 (2001). This was the first report on the broad implication of SKI-1 in the activation of surface glycoproteins of haemorrhagic fever viruses, including Lassa virus and other arenaviruses.

  22. 22

    Maxwell, K. N. & Breslow, J. L. Adenoviral-mediated expression of Pcsk9 in mice results in a low-density lipoprotein receptor knockout phenotype. Proc. Natl Acad. Sci. USA 101, 7100–7105 (2004). This work presented the first evidence that PCSK9 enhances the degradation of the LDLR, thereby rationalizing the effect of PCSK9 on the regulation of circulating LDL-C levels.

  23. 23

    Benjannet, S. et al. NARC-1/PCSK9 and its natural mutants: zymogen cleavage and effects on the low density lipoprotein (LDL) receptor and LDL cholesterol. J. Biol. Chem. 279, 48865–48875 (2004).

  24. 24

    Park, S. W., Moon, Y. A. & Horton, J. D. Post-transcriptional regulation of low density lipoprotein receptor protein by proprotein convertase subtilisin/kexin type 9a in mouse liver. J. Biol. Chem. 279, 50630–50638 (2004).

  25. 25

    Steiner, D. F. The proprotein convertases. Curr. Opin. Chem. Biol. 2, 31–39 (1998).

  26. 26

    Seidah, N. G. & Prat, A. The proprotein convertases are potential targets in the treatment of dyslipidemia. J. Mol. Med. 85, 685–696 (2007).

  27. 27

    Espenshade, P. J., Cheng, D., Goldstein, J. L. & Brown, M. S. Autocatalytic processing of site-1 protease removes propeptide and permits cleavage of sterol regulatory element-binding proteins. J. Biol. Chem. 274, 22795–22804 (1999).

  28. 28

    Seidah, N. G. et al. The secretory proprotein convertase neural apoptosis-regulated convertase 1 (NARC-1): liver regeneration and neuronal differentiation. Proc. Natl Acad. Sci. USA 100, 928–933 (2003). This was the first report on the discovery of PCSK9. Its high expression in the liver and localization on human chromosome 1p33–34.3, close to that of a major locus (the FH3 locus) for ADH (located at 1p34.1–p32), and its upregulation after partial hepatectomy in a coordinated fashion with apolipoprotein B suggested that it may be implicated in cholesterol regulation.

  29. 29

    Seidah, N. G. PCSK9 as a therapeutic target of dyslipidemia. Expert Opin. Ther. Targets 13, 19–28 (2009).

  30. 30

    Seidah, N. G. & Chretien, M. Proprotein and prohormone convertases: a family of subtilases generating diverse bioactive polypeptides. Brain Res. 848, 45–62 (1999).

  31. 31

    Turpeinen, H. et al. Identification of proprotein convertase substrates using genome-wide expression correlation analysis. BMC Genomics 12, 618 (2011).

  32. 32

    Pasquato, A. et al. The proprotein convertase SKI-1/S1P: in vitro analysis of Lassa virus glycoprotein-derived substrates and ex vivo validation of irreversible peptide inhibitors. J. Biol. Chem. 281, 23471–23481 (2006).

  33. 33

    Abifadel, M. et al. Mutations in PCSK9 cause autosomal dominant hypercholesterolemia. Nature Genet. 34, 154–156 (2003). This was the first report on the genetic evidence that PCSK9 represents the third locus of ADH.Single point mutations (S127R and F216L) in two French families were shown to be associated with a gain of function of PCSK9. This was the first indication that targeting PCSK9 may be beneficial for the treatment of dyslipidaemia and associated atherosclerosis.

  34. 34

    Naureckiene, S. et al. Functional characterization of Narc 1, a novel proteinase related to proteinase K. Arch. Biochem. Biophys. 420, 55–67 (2003).

  35. 35

    McNutt, M. C., Lagace, T. A. & Horton, J. D. Catalytic activity is not required for secreted PCSK9 to reduce low density lipoprotein receptors in HepG2 cells. J. Biol. Chem. 282, 20799–20803 (2007). This was the first evidence that the catalytic activity of PCSK9 is not needed for its functional enhancement of LDLR degradation.

  36. 36

    Horton, J. D., Cohen, J. C. & Hobbs, H. H. Molecular biology of PCSK9: its role in LDL metabolism. Trends Biochem. Sci. 32, 71–77 (2007).

  37. 37

    Horton, J. D., Cohen, J. C. & Hobbs, H. H. PCSK9: a convertase that coordinates LDL catabolism. J. Lipid Res. 50, S172–S177 (2009).

  38. 38

    Hsi, K. L., Seidah, N. G., De Serres, G. & Chretien, M. Isolation and NH2-terminal sequence of a novel porcine anterior pituitary polypeptide. Homology to proinsulin, secretin and Rous sarcoma virus transforming protein TVFV60. FEBS Lett. 147, 261–266 (1982).

  39. 39

    Mbikay, M., Seidah, N. G. & Chretien, M. Neuroendocrine secretory protein 7B2: structure, expression and functions. Biochem. J. 357, 329–342 (2001).

  40. 40

    Benjannet, S. et al. Proprotein conversion is determined by a multiplicity of factors including convertase processing, substrate specificity, and intracellular environment. Cell type-specific processing of human prorenin by the convertase PC1. J. Biol. Chem. 267, 11417–11423 (1992).

  41. 41

    Elagoz, A., Benjannet, S., Mammarbassi, A., Wickham, L. & Seidah, N. G. Biosynthesis and cellular trafficking of the convertase SKI-1/S1P: ectodomain shedding requires SKI-1 activity. J. Biol. Chem. 277, 11265–11275 (2002).

  42. 42

    Feliciangeli, S. F. et al. Identification of a pH sensor in the furin propeptide that regulates enzyme activation. J. Biol. Chem. 281, 16108–16116 (2006).

  43. 43

    Basak, A. et al. Enzymic characterization in vitro of recombinant proprotein convertase PC4. Biochem. J. 343, 29–37 (1999).

  44. 44

    Rousselet, E., Benjannet, S., Hamelin, J., Canuel, M. & Seidah, N. G. The proprotein convertase PC7: unique zymogen activation and trafficking pathways. J. Biol. Chem. 286, 2728–2738 (2010).

  45. 45

    Mayer, G. et al. The regulated cell surface zymogen activation of the proprotein convertase PC5A directs the processing of its secretory substrates. J. Biol. Chem. 283, 2373–2384 (2008).

  46. 46

    Cunningham, D. et al. Structural and biophysical studies of PCSK9 and its mutants linked to familial hypercholesterolemia. Nature Struct. Mol. Biol. 14, 413–419 (2007). This study reported the first crystal structure of PCSK9, which revealed the molecular details of the interaction of the prodomain with the catalytic subunit, as well as the topography of the three repeats of the C-terminal Cys-His-rich domain. This work provided the first clue to explain the gain-of-function D374Y mutation and the pH-dependent interaction of PCSK9 with LDLR.

  47. 47

    Thomas, G. Furin at the cutting edge: from protein traffic to embryogenesis and disease. Nature Rev. Mol. Cell Biol. 3, 753–766 (2002).

  48. 48

    Malide, D., Seidah, N. G., Chretien, M. & Bendayan, M. Electron microscopic immunocytochemical evidence for the involvement of the convertases PC1 and PC2 in the processing of proinsulin in pancreatic β-cells. J. Histochem. Cytochem. 43, 11–19 (1995).

  49. 49

    Day, R., Schafer, M. K., Watson, S. J., Chretien, M. & Seidah, N. G. Distribution and regulation of the prohormone convertases PC1 and PC2 in the rat pituitary. Mol. Endocrinol. 6, 485–497 (1992).

  50. 50

    Plaimauer, B. et al. 'Shed' furin: mapping of the cleavage determinants and identification of its C-terminus. Biochem. J. 354, 689–695 (2001).

  51. 51

    Seidah, N. G. et al. Testicular expression of PC4 in the rat: molecular diversity of a novel germ cell-specific Kex2/subtilisin-like proprotein convertase. Mol. Endocrinol. 6, 1559–1570 (1992).

  52. 52

    Gyamera-Acheampong, C. et al. Sperm from mice genetically deficient for the PCSK4 proteinase exhibit accelerated capacitation, precocious acrosome reaction, reduced binding to egg zona pellucida, and impaired fertilizing ability. Biol. Reprod. 74, 666–673 (2006).

  53. 53

    Gyamera-Acheampong, C. & Mbikay, M. Proprotein convertase subtilisin/kexin type 4 in mammalian fertility: a review. Hum. Reprod. Update 15, 237–247 (2009).

  54. 54

    Lusson, J. et al. cDNA structure of the mouse and rat subtilisin/kexin-like PC5: a candidate proprotein convertase expressed in endocrine and nonendocrine cells. Proc. Natl Acad. Sci. USA 90, 6691–6695 (1993).

  55. 55

    Essalmani, R. et al. Deletion of the gene encoding proprotein convertase 5/6 causes early embryonic lethality in the mouse. Mol. Cell. Biol. 26, 354–361 (2006).

  56. 56

    Nakagawa, T. et al. Identification and functional expression of a new member of the mammalian Kex2-like processing endoprotease family: its striking structural similarity to PACE4. J. Biochem. 113, 132–135 (1993).

  57. 57

    Nakagawa, T., Murakami, K. & Nakayama, K. Identification of an isoform with an extremely large Cys-rich region of PC6, a Kex2-like processing endoprotease. FEBS Lett. 327, 165–171 (1993).

  58. 58

    Dong, W. et al. Distinct mRNA expression of the highly homologous convertases PC5 and PACE4 in the rat brain and pituitary. J. Neurosci. 15, 1778–1796 (1995).

  59. 59

    Nour, N. et al. The cysteine-rich domain of the secreted proprotein convertases PC5A and PACE4 functions as a cell surface anchor and interacts with tissue inhibitors of metalloproteinases. Mol. Biol. Cell 16, 5215–5226 (2005).

  60. 60

    Tsuji, A. et al. Secretory proprotein convertases PACE4 and PC6A are heparin-binding proteins which are localized in the extracellular matrix. Potential role of PACE4 in the activation of proproteins in the extracellular matrix. Biochim. Biophys. Acta 1645, 95–104 (2003).

  61. 61

    Sun, X., Essalmani, R., Susan-Resiga, D., Prat, A. & Seidah, N. G. Latent TGF-β binding proteins-2 and -3 inhibit the proprotein convertase 5/6A. J. Biol. Chem. 286, 29063–29073 (2011).

  62. 62

    Seidah, N. G. et al. cDNA structure, tissue distribution, and chromosomal localization of rat PC7, a novel mammalian proprotein convertase closest to yeast kexin-like proteinases. Proc. Natl Acad. Sci. USA 93, 3388–3393 (1996).

  63. 63

    Meerabux, J. et al. A new member of the proprotein convertase gene family (LPC) is located at a chromosome translocation breakpoint in lymphomas. Cancer Res. 56, 448–451 (1996).

  64. 64

    Constam, D. B., Calfon, M. & Robertson, E. J. SPC4, SPC6, and the novel protease SPC7 are coexpressed with bone morphogenetic proteins at distinct sites during embryogenesis. J. Cell Biol. 134, 181–191 (1996).

  65. 65

    Bruzzaniti, A. et al. PC8 [corrected], a new member of the convertase family. Biochem. J. 314, 727–731 (1996).

  66. 66

    Rousselet, E., Benjannet, S., Hamelin, J., Canuel, M. & Seidah, N. G. The proprotein convertase PC7: unique zymogen activation and trafficking pathways. J. Biol. Chem. 286, 2728–2738 (2011).

  67. 67

    Van de Loo, J. W. et al. Biosynthesis, distinct post-translational modifications, and functional characterization of lymphoma proprotein convertase. J. Biol. Chem. 272, 27116–27123 (1997).

  68. 68

    Xiang, Y., Molloy, S. S., Thomas, L. & Thomas, G. The PC6B cytoplasmic domain contains two acidic clusters that direct sorting to distinct trans-Golgi network/endosomal compartments. Mol. Biol. Cell 11, 1257–1273 (2000).

  69. 69

    Declercq, J., Meulemans, S., Plets, E. & Creemers, J. W. Internalization of the proprotein convertase PC7 from the plasma membrane is mediated by a novel motif. J. Biol. Chem. 287, 9052–9060 (2012).

  70. 70

    Pullikotil, P., Benjannet, S., Mayne, J. & Seidah, N. G. The proprotein convertase SKI-1/S1P: alternate translation and subcellular localization. J. Biol. Chem. 282, 27402–27413 (2007).

  71. 71

    Zaid, A. et al. Proprotein convertase subtilisin/kexin type 9 (PCSK9): hepatocyte-specific low-density lipoprotein receptor degradation and critical role in mouse liver regeneration. Hepatology 48, 646–654 (2008).

  72. 72

    Maxwell, K. N., Fisher, E. A. & Breslow, J. L. Overexpression of PCSK9 accelerates the degradation of the LDLR in a post-endoplasmic reticulum compartment. Proc. Natl Acad. Sci. USA 102, 2069–2074 (2005).

  73. 73

    Nassoury, N. et al. The cellular trafficking of the secretory proprotein convertase PCSK9 and its dependence on the LDLR. Traffic 8, 718–732 (2007).

  74. 74

    Kwon, H. J., Lagace, T. A., McNutt, M. C., Horton, J. D. & Deisenhofer, J. Molecular basis for LDL receptor recognition by PCSK9. Proc. Natl Acad. Sci. USA 105, 1820–1825 (2008).

  75. 75

    Surdo, P. L. et al. Mechanistic implications for LDL receptor degradation from the PCSK9/LDLR structure at neutral pH. EMBO Rep. 12, 1300–1305 (2011).

  76. 76

    Holla, O. L., Strom, T. B., Cameron, J., Berge, K. E. & Leren, T. P. A chimeric LDL receptor containing the cytoplasmic domain of the transferrin receptor is degraded by PCSK9. Mol. Genet. Metab. 99, 149–156 (2010).

  77. 77

    Strom, T. B. et al. Disrupted recycling of the low density lipoprotein receptor by PCSK9 is not mediated by residues of the cytoplasmic domain. Mol. Genet. Metab. 101, 76–80 (2010).

  78. 78

    Zhang, D. W., Garuti, R., Tang, W. J., Cohen, J. C. & Hobbs, H. H. Structural requirements for PCSK9-mediated degradation of the low-density lipoprotein receptor. Proc. Natl Acad. Sci. USA 105, 13045–13050 (2008).

  79. 79

    Poirier, S. et al. Dissection of the endogenous cellular pathways of PCSK9-induced LDLR degradation: evidence for an intracellular route. J. Biol. Chem. 284, 28856–28864 (2009). This work demonstrated the existence of the intracellular and extracellular pathways used by PCSK9 to enhance the degradation of LDLR.

  80. 80

    Zhang, X. et al. Neuropeptidomic analysis establishes a major role for prohormone convertase-2 in neuropeptide biosynthesis. J. Neurochem. 112, 1168–1179 (2010).

  81. 81

    Wardman, J. H. et al. Analysis of peptides in prohormone convertase 1/3 null mouse brain using quantitative peptidomics. J. Neurochem. 114, 215–225 (2010).

  82. 82

    van den Ouweland, A. M., Van Groningen, J. J., Roebroek, A. J., Onnekink, C. & Van de Ven, W. J. Nucleotide sequence analysis of the human fur gene. Nucleic Acids Res. 17, 7101–7102 (1989).

  83. 83

    Klenk, H. D. & Garten, W. Host cell proteases controlling virus pathogenicity. Trends Microbiol. 2, 39–43 (1994).

  84. 84

    Garten, W. & Klenk, H. D. Understanding influenza virus pathogenicity. Trends Microbiol. 7, 99–100 (1999).

  85. 85

    Moulard, M. & Decroly, E. Maturation of HIV envelope glycoprotein precursors by cellular endoproteases. Biochim. Biophys. Acta 1469, 121–132 (2000).

  86. 86

    Day, P. M. & Schiller, J. T. The role of furin in papillomavirus infection. Future Microbiol. 4, 1255–1262 (2009).

  87. 87

    Paquet, L. et al. The neuroendocrine precursor 7B2 is a sulfated protein proteolytically processed by a ubiquitous furin-like convertase. J. Biol. Chem. 269, 19279–19285 (1994).

  88. 88

    Young, J. A. & Collier, R. J. Anthrax toxin: receptor binding, internalization, pore formation, and translocation. Annu. Rev. Biochem. 76, 243–265 (2007).

  89. 89

    Sucic, J. F., Moehring, J. M., Inocencio, N. M., Luchini, J. W. & Moehring, T. J. Endoprotease PACE4 is Ca2+-dependent and temperature-sensitive and can partly rescue the phenotype of a furin-deficient cell strain. Biochem. J. 339, 639–647 (1999).

  90. 90

    Gordon, V. M., Klimpel, K. R., Arora, N., Henderson, M. A. & Leppla, S. H. Proteolytic activation of bacterial toxins by eukaryotic cells is performed by furin and by additional cellular proteases. Infect. Immun. 63, 82–87 (1995).

  91. 91

    Jin, W. et al. Proprotein convertases are responsible for proteolysis and inactivation of endothelial lipase. J. Biol. Chem. 280, 36551–36559 (2005).

  92. 92

    Essalmani, R. et al. In vivo evidence that furin from hepatocytes inactivates PCSK9. J. Biol. Chem. 286, 4257–4263 (2011).

  93. 93

    Scamuffa, N. et al. Regulation of prohepcidin processing and activity by the subtilisin-like proprotein convertases furin, PC5, PACE4 and PC7. Gut 57, 1573–1582 (2008).

  94. 94

    Benjannet, S., Rhainds, D., Hamelin, J., Nassoury, N. & Seidah, N. G. The proprotein convertase PCSK9 is inactivated by furin and/or PC5/6A: functional consequences of natural mutations and post-translational modifications. J. Biol. Chem. 281, 30561–30572 (2006). This was the first evidence that furin inactivates PCSK9 by cleavage after Arg218↓ and explains the gain-of-function mechanism of the R218S mutant that is resistant to furin.

  95. 95

    Henrich, S. et al. The crystal structure of the proprotein processing proteinase furin explains its stringent specificity. Nature Struct. Biol. 10, 520–526 (2003).

  96. 96

    Henrich, S., Lindberg, I., Bode, W. & Than, M. E. Proprotein convertase models based on the crystal structures of furin and kexin: explanation of their specificity. J. Mol. Biol. 345, 211–227 (2005). This study reported the first crystal structure of furin, which formed the basis for the development of small-molecule inhibitors of furin-like convertases.

  97. 97

    Basak, S., Chretien, M., Mbikay, M. & Basak, A. In vitro elucidation of substrate specificity and bioassay of proprotein convertase 4 using intramolecularly quenched fluorogenic peptides. Biochem. J. 380, 505–514 (2004).

  98. 98

    Essalmani, R. et al. In vivo functions of the proprotein convertase PC5/6 during mouse development: Gdf11 is a likely substrate. Proc. Natl Acad. Sci. USA 105, 5750–5755 (2008).

  99. 99

    Szumska, D. et al. VACTERL/caudal regression/Currarino syndrome-like malformations in mice with mutation in the proprotein convertase Pcsk5. Genes Dev. 22, 1465–1477 (2008).

  100. 100

    Tortorella, M. D. et al. ADAMTS-4 (aggrecanase-1): N-terminal activation mechanisms. Arch. Biochem. Biophys. 444, 34–44 (2005).

  101. 101

    Liu, J., Afroza, H., Rader, D. J. & Jin, W. Angiopoietin-like protein 3 inhibits lipoprotein lipase activity through enhancing its cleavage by proprotein convertases. J. Biol. Chem. 285, 27561–27570 (2010).

  102. 102

    Xiao, Y. et al. Cell-surface processing of extracellular human immunodeficiency virus type 1 Vpr by proprotein convertases. Virology 372, 384–397 (2008).

  103. 103

    Rousselet, E. et al. The proprotein convertase PC7 enhances the activation of the EGF receptor pathway through processing of the EGF precursor. J. Biol. Chem. 286, 9185–9195 (2011).

  104. 104

    Oexle, K. et al. Novel association to the proprotein convertase PCSK7 gene locus revealed by analysing soluble transferrin receptor (sTfR) levels. Hum. Mol. Genet. 20, 1042–1047 (2011).

  105. 105

    Goldstein, J. L., DeBose-Boyd, R. A. & Brown, M. S. Protein sensors for membrane sterols. Cell 124, 35–46 (2006).

  106. 106

    Llarena, M., Bailey, D., Curtis, H. & O'Hare, P. Different mechanisms of recognition and ER retention by transmembrane transcription factors CREB-H and ATF6. Traffic 11, 48–69 (2010).

  107. 107

    Seidah, N. G. & Prat, A. Precursor convertases in the secretory pathway, cytosol and extracellular milieu. Essays Biochem. 38, 79–94 (2002).

  108. 108

    Poirier, S. et al. The proprotein convertase PCSK9 induces the degradation of low density lipoprotein receptor (LDLR) and its closest family members VLDLR and ApoER2. J. Biol. Chem. 283, 2363–2372 (2008).

  109. 109

    Labonte, P. et al. PCSK9 impedes hepatitis C virus infection in vitro and modulates liver CD81 expression. Hepatology 50, 17–24 (2009). This study provided the first evidence that PCSK9 can protect the liver against hepatitis C virus infection by enhancing the degradation of two hepatitis C virus receptors:LDLR and CD81.

  110. 110

    Dubuc, G. et al. A new method for measurement of total plasma PCSK9: clinical applications. J. Lipid Res. 51, 140–149 (2010).

  111. 111

    Scamuffa, N., Calvo, F., Chretien, M., Seidah, N. G. & Khatib, A. M. Proprotein convertases: lessons from knockouts. FASEB J. 20, 1954–1963 (2006).

  112. 112

    Seidah, N. G., Khatib, A. M. & Prat, A. The proprotein convertases and their implication in sterol and/or lipid metabolism. Biol. Chem. 387, 871–877 (2006).

  113. 113

    Zhu, X. et al. Severe block in processing of proinsulin to insulin accompanied by elevation of des-64,65 proinsulin intermediates in islets of mice lacking prohormone convertase 1/3. Proc. Natl Acad. Sci. USA 99, 10299–10304 (2002).

  114. 114

    Furuta, M. et al. Severe defect in proglucagon processing in islet A-cells of prohormone convertase 2 null mice. J. Biol. Chem. 276, 27197–27202 (2001).

  115. 115

    Dey, A. et al. Furin and prohormone convertase 1/3 are major convertases in the processing of mouse pro-growth hormone-releasing hormone. Endocrinology 145, 1961–1971 (2004).

  116. 116

    Posner, S. F. et al. Stepwise posttranslational processing of progrowth hormone-releasing hormone (proGHRH) polypeptide by furin and PC1. Endocrine 23, 199–213 (2004).

  117. 117

    Zhu, X. et al. Disruption of PC1/3 expression in mice causes dwarfism and multiple neuroendocrine peptide processing defects. Proc. Natl Acad. Sci. USA 99, 10293–10298 (2002).

  118. 118

    Furuta, M. et al. Defective prohormone processing and altered pancreatic islet morphology in mice lacking active SPC2. Proc. Natl Acad. Sci. USA 94, 6646–6651 (1997).

  119. 119

    Berman, Y. et al. Defective prodynorphin processing in mice lacking prohormone convertase PC2. J. Neurochem. 75, 1763–1770 (2000).

  120. 120

    Furuta, M. et al. Incomplete processing of proinsulin to insulin accompanied by elevation of Des-31,32 proinsulin intermediates in islets of mice lacking active PC2. J. Biol. Chem. 273, 3431–3437 (1998).

  121. 121

    Peinado, J. R. et al. Strain-dependent influences on the hypothalamo–pituitary–adrenal axis profoundly affect the 7B2 and PC2 null phenotypes. Endocrinology 146, 3438–3444 (2005).

  122. 122

    Westphal, C. H. et al. The neuroendocrine protein 7B2 is required for peptide hormone processing in vivo and provides a novel mechanism for pituitary Cushing's disease. Cell 96, 689–700 (1999).

  123. 123

    Jackson, R. S. et al. Obesity and impaired prohormone processing associated with mutations in the human prohormone convertase 1 gene. Nature Genet. 16, 303–306 (1997). This was the first evidence that loss of function of the PCSK1 geneis associated with the onset of early childhood obesity.

  124. 124

    Farooqi, I. S. et al. Hyperphagia and early-onset obesity due to a novel homozygous missense mutation in prohormone convertase 1/3. J. Clin. Endocrinol. Metab. 92, 3369–3373 (2007).

  125. 125

    Benzinou, M. et al. Common nonsynonymous variants in PCSK1 confer risk of obesity. Nature Genet. 40, 943–945 (2008).

  126. 126

    Corpeleijn, E. et al. Obesity-related polymorphisms and their associations with the ability to regulate fat oxidation in obese Europeans: the NUGENOB study. Obesity 18, 1369–1377 (2010).

  127. 127

    Creemers, J. W. et al. Heterozygous mutations causing partial prohormone convertase 1 deficiency contribute to human obesity. Diabetes 61, 383–390 (2012).

  128. 128

    Lloyd, D. J., Bohan, S. & Gekakis, N. Obesity, hyperphagia and increased metabolic efficiency in Pc1 mutant mice. Hum. Mol. Genet. 15, 1884–1893 (2006).

  129. 129

    Roebroek, A. J. et al. Failure of ventral closure and axial rotation in embryos lacking the proprotein convertase Furin. Development 125, 4863–4876 (1998).

  130. 130

    Constam, D. B. & Robertson, E. J. Tissue-specific requirements for the proprotein convertase furin/SPC1 during embryonic turning and heart looping. Development 127, 245–254 (2000).

  131. 131

    Susan-Resiga, D. et al. Furin is the major processing enzyme of the cardiac-specific growth factor bone morphogenetic protein 10. J. Biol. Chem. 286, 22785–22794 (2011).

  132. 132

    Chen, H. et al. BMP10 is essential for maintaining cardiac growth during murine cardiogenesis. Development 131, 2219–2231 (2004).

  133. 133

    Roebroek, A. J. et al. Limited redundancy of the proprotein convertase furin in mouse liver. J. Biol. Chem. 279, 53442–53450 (2004). This was the first genetic evidence that furin exhibits redundant functions in the liver.

  134. 134

    Louagie, E. et al. Role of furin in granular acidification in the endocrine pancreas: identification of the V-ATPase subunit Ac45 as a candidate substrate. Proc. Natl Acad. Sci. USA 105, 12319–12324 (2008).

  135. 135

    Pesu, M. et al. T-cell-expressed proprotein convertase furin is essential for maintenance of peripheral immune tolerance. Nature 455, 246–250 (2008).

  136. 136

    De Vos, L. et al. MMTV-cre-mediated fur inactivation concomitant with PLAG1 proto-oncogene activation delays salivary gland tumorigenesis in mice. Int. J. Oncol. 32, 1073–1083 (2008).

  137. 137

    Mbikay, M. et al. Impaired fertility in mice deficient for the testicular germ-cell protease PC4. Proc. Natl Acad. Sci. USA 94, 6842–6846 (1997). This was the first evidence that lack of PC4 results in impaired fertility in male mice, opening the door to the development of contraceptives for males.

  138. 138

    Li, M., Mbikay, M., Nakayama, K., Miyata, A. & Arimura, A. Prohormone convertase PC4 processes the precursor of PACAP in the testis. Ann. NY Acad. Sci. 921, 333–339 (2000).

  139. 139

    Qiu, Q., Basak, A., Mbikay, M., Tsang, B. K. & Gruslin, A. Role of pro-IGF-II processing by proprotein convertase 4 in human placental development. Proc. Natl Acad. Sci. USA 102, 11047–11052 (2005).

  140. 140

    McPherron, A. C., Lawler, A. M. & Lee, S. J. Regulation of anterior/posterior patterning of the axial skeleton by growth/differentiation factor 11. Nature Genet. 22, 260–264 (1999).

  141. 141

    Marchesi, C. et al. Inactivation of endothelial proprotein convertase 5/6 decreases collagen deposition in the cardiovascular system: role of fibroblast autophagy. J. Mol. Med. 89, 1103–1111 (2011).

  142. 142

    Iatan, I. et al. Genetic variation at the proprotein convertase subtilisin/kexin type 5 gene modulates high-density lipoprotein cholesterol levels. Circ. Cardiovasc. Genet. 2, 467–475 (2009).

  143. 143

    Sun, X., Essalmani, R., Seidah, N. G. & Prat, A. The proprotein convertase PC5/6 is protective against intestinal tumorigenesis: in vivo mouse model. Mol. Cancer 8, 73 (2009).

  144. 144

    Constam, D. B. & Robertson, E. J. SPC4/PACE4 regulates a TGFβ signaling network during axis formation. Genes Dev. 14, 1146–1155 (2000).

  145. 145

    Blanchet, M. H. et al. Cripto recruits Furin and PACE4 and controls Nodal trafficking during proteolytic maturation. EMBO J. 27, 2580–2591 (2008).

  146. 146

    Scerri, T. S. et al. PCSK6 is associated with handedness in individuals with dyslexia. Hum. Mol. Genet. 20, 608–614 (2011).

  147. 147

    Constam, D. B. Running the gauntlet: an overview of the modalities of travel employed by the putative morphogen Nodal. Curr. Opin. Genet. Dev. 19, 302–307 (2009).

  148. 148

    Villeneuve, P. et al. Altered processing of the neurotensin/neuromedin N precursor in PC2 knock down mice: a biochemical and immunohistochemical study. J. Neurochem. 82, 783–793 (2002).

  149. 149

    Mitchell, K. J. et al. Functional analysis of secreted and transmembrane proteins critical to mouse development. Nature Genet. 28, 241–249 (2001).

  150. 150

    Schlombs, K., Wagner, T. & Scheel, J. Site-1 protease is required for cartilage development in zebrafish. Proc. Natl Acad. Sci. USA 100, 14024–14029 (2003).

  151. 151

    Yang, J. et al. Decreased lipid synthesis in livers of mice with disrupted site-1 protease gene. Proc. Natl Acad. Sci. USA 98, 13607–13612 (2001).

  152. 152

    Patra, D., DeLassus, E., Hayashi, S. & Sandell, L. J. Site-1 protease is essential to growth plate maintenance and is a critical regulator of chondrocyte hypertrophic differentiation in postnatal mice. J. Biol. Chem. 286, 29227–29240 (2011).

  153. 153

    Rashid, S. et al. Decreased plasma cholesterol and hypersensitivity to statins in mice lacking Pcsk9. Proc. Natl Acad. Sci. USA 102, 5374–5379 (2005).

  154. 154

    Roubtsova, A. et al. Circulating proprotein convertase subtilisin/kexin 9 (PCSK9) regulates VLDLR protein and triglyceride accumulation in visceral adipose tissue. Arterioscler. Thromb. Vasc. Biol. 31, 785–791 (2011). This is the first evidence that lack of circulating PCSK9 originating from hepatocytes results in adipocyte hypertrophy, in part because of increased levels of the cell surface VLDLR protein.

  155. 155

    Denis, M. et al. Gene inactivation of proprotein convertase subtilisin/kexin type 9 reduces atherosclerosis in mice. Circulation 125, 894–901 (2012). This is the first evidence that lack of PCSK9 protects against the development of atherosclerosis in mice lacking either apolipoprotein E or LDLR.

  156. 156

    Herbert, B. et al. Increased secretion of lipoproteins in transgenic mice expressing human D374Y PCSK9 under physiological genetic control. Arterioscler. Thromb. Vasc. Biol. 30, 1333–1339 (2010).

  157. 157

    Timms, K. M. et al. A mutation in PCSK9 causing autosomal-dominant hypercholesterolemia in a Utah pedigree. Hum. Genet. 114, 349–353 (2004).

  158. 158

    Cohen, J. et al. Low LDL cholesterol in individuals of African descent resulting from frequent nonsense mutations in PCSK9. Nature Genet. 37, 161–165 (2005). This was the first evidence that lower levels of PCSK9 are associated with hypocholesterolaemia in individuals exhibiting heterozygous or homozygous loss-of-function mutations.

  159. 159

    Kotowski, I. K. et al. A spectrum of PCSK9 alleles contributes to plasma levels of low-density lipoprotein cholesterol. Am. J. Hum. Genet. 78, 410–422 (2006).

  160. 160

    Bassi, D. E., Fu, J., Lopez, D. C. & Klein-Szanto, A. J. Proprotein convertases: “master switches” in the regulation of tumor growth and progression. Mol. Carcinog. 44, 151–161 (2005).

  161. 161

    Scamuffa, N. et al. Selective inhibition of proprotein convertases represses the metastatic potential of human colorectal tumor cells. J. Clin. Invest. 118, 352–363 (2008).

  162. 162

    Couture, F., D'Anjou, F. & Day R. On the cutting edge of proprotein convertase pharmacology: from molecular concepts to clinical applications. Biomol. Concepts 2, 421–438 (2011).

  163. 163

    Anderson, E. D., Thomas, L., Hayflick, J. S. & Thomas, G. Inhibition of HIV-1 gp160-dependent membrane fusion by a furin-directed α1-antitrypsin variant. J. Biol. Chem. 268, 24887–24891 (1993).

  164. 164

    Zhong, M. et al. The prosegments of furin and PC7 as potent inhibitors of proprotein convertases. In vitro and ex vivo assessment of their efficacy and selectivity. J. Biol. Chem. 274, 33913–33920 (1999).

  165. 165

    Khatib, A. M. et al. Inhibition of proprotein convertases is associated with loss of growth and tumorigenicity of HT-29 human colon carcinoma cells: importance of insulin-like growth factor-1 (IGF-1) receptor processing in IGF-1-mediated functions. J. Biol. Chem. 276, 30686–30693 (2001). This study showed that inhibition of furin is associated with lower levels of tumour formation owing to the lack of processing of growth factors such as proIGF1.

  166. 166

    Lopez, D. C., Bassi, D. E., Zucker, S., Seidah, N. G. & Klein-Szanto, A. J. Human carcinoma cell growth and invasiveness is impaired by the propeptide of the ubiquitous proprotein convertase furin. Cancer Res. 65, 4162–4171 (2005).

  167. 167

    Bassi, D. E. et al. Proprotein convertase inhibition results in decreased skin cell proliferation, tumorigenesis, and metastasis. Neoplasia 12, 516–526 (2010).

  168. 168

    Jiao, G. S. et al. Synthetic small molecule furin inhibitors derived from 2,5-dideoxystreptamine. Proc. Natl Acad. Sci. USA 103, 19707–19712 (2006).

  169. 169

    Komiyama, T. et al. Inhibition of furin/proprotein convertase-catalyzed surface and intracellular processing by small molecules. J. Biol. Chem. 284, 15729–15738 (2009).

  170. 170

    Coppola, J. M., Bhojani, M. S., Ross, B. D. & Rehemtulla, A. A small-molecule furin inhibitor inhibits cancer cell motility and invasiveness. Neoplasia 10, 363–370 (2008).

  171. 171

    Becker, G. L. et al. Potent inhibitors of furin and furin-like proprotein convertases containing decarboxylated P1 arginine mimetics. J. Med. Chem. 53, 1067–1075 (2010).

  172. 172

    Mercapide, J. et al. Inhibition of furin-mediated processing results in suppression of astrocytoma cell growth and invasiveness. Clin. Cancer Res. 8, 1740–1746 (2002).

  173. 173

    Lapierre, M. et al. Opposing function of the proprotein convertases furin and PACE4 on breast cancer cells' malignant phenotypes: role of tissue inhibitors of metalloproteinase-1. Cancer Res. 67, 9030–9034 (2007).

  174. 174

    Dragulescu-Andrasi, A., Liang, G. & Rao, J. In vivo bioluminescence imaging of furin activity in breast cancer cells using bioluminogenic substrates. Bioconjug. Chem. 20, 1660–1666 (2009).

  175. 175

    Mesnard, D. & Constam, D. B. Imaging proprotein convertase activities and their regulation in the implanting mouse blastocyst. J. Cell Biol. 191, 129–139 (2010).

  176. 176

    Senzer, N. et al. Phase I trial of “bi-shRNAifurin/GMCSF DNA/autologous tumor cell” vaccine (FANG) in advanced cancer. Mol. Ther. 20, 679–686 (2012).

  177. 177

    Steinman, R. M. Dendritic cells: understanding immunogenicity. Eur. J. Immunol. 37, S53–S60 (2007). This was the first report of the application of silencing furin (in primary human tumours isolated from patients with the combined expression of GM-CSF), in the production of tumour vaccines that prolonged the life of patients with cancer.

  178. 178

    Zou, T., Satake, A., Ojha, P. & Kambayashi, T. Cellular therapies supplement: the role of granulocyte macrophage colony-stimulating factor and dendritic cells in regulatory T-cell homeostasis and expansion. Transfusion 51, 160S–168S (2011).

  179. 179

    D'Anjou, F. et al. Molecular validation of PACE4 as a target in prostate cancer. Transl. Oncol. 4, 157–172 (2011).

  180. 180

    Komiyama, T., Swanson, J. A. & Fuller, R. S. Protection from anthrax toxin-mediated killing of macrophages by the combined effects of furin inhibitors and chloroquine. Antimicrob. Agents Chemother. 49, 3875–3882 (2005).

  181. 181

    Ozden, S. et al. Inhibition of Chikungunya virus infection in cultured human muscle cells by furin inhibitors: impairment of the maturation of the E2 surface glycoprotein. J. Biol. Chem. 283, 21899–21908 (2008).

  182. 182

    Malfait, A. M. et al. Proprotein convertase activation of aggrecanases in cartilage in situ. Arch. Biochem. Biophys. 478, 43–51 (2008).

  183. 183

    Wylie, J. D., Ho, J. C., Singh, S., McCulloch, D. R. & Apte, S. S. Adamts5 (aggrecanase-2) is widely expressed in the mouse musculoskeletal system and is induced in specific regions of knee joint explants by inflammatory cytokines. J. Orthop. Res. 30, 226–233 (2012).

  184. 184

    Byun, S. et al. Transport and equilibrium uptake of a peptide inhibitor of PACE4 into articular cartilage is dominated by electrostatic interactions. Arch. Biochem. Biophys. 499, 32–39 (2010).

  185. 185

    Kowalska, D. et al. Synthetic small-molecule prohormone convertase 2 inhibitors. Mol. Pharmacol. 75, 617–625 (2009).

  186. 186

    Vivoli, M. et al. Inhibition of prohormone convertases PC1/3 and PC2 by 2,5-dideoxystreptamine derivatives. Mol. Pharmacol. 81, 440–454 (2012).

  187. 187

    Majumdar, S. et al. Proprotein convertase inhibitory activities of flavonoids isolated from oroxylum indicum. Curr. Med. Chem. 17, 2049–2058 (2010).

  188. 188

    Pullikotil, P., Vincent, M., Nichol, S. T. & Seidah, N. G. Development of protein-based inhibitors of the proprotein of convertase SKI-1/S1P: processing of SREBP-2, ATF6, and a viral glycoprotein. J. Biol. Chem. 279, 17338–17347 (2004).

  189. 189

    Hawkins, J. L. et al. Pharmacologic inhibition of site 1 protease activity inhibits sterol regulatory element-binding protein processing and reduces lipogenic enzyme gene expression and lipid synthesis in cultured cells and experimental animals. J. Pharmacol. Exp. Ther. 326, 801–808 (2008).

  190. 190

    Urata, S. et al. Antiviral activity of a small-molecule inhibitor of arenavirus glycoprotein processing by the cellular site 1 protease. J. Virol. 85, 795–803 (2011).

  191. 191

    De Windt, A. et al. Gene set enrichment analysis reveals several globally affected pathways due to SKI-1/S1P inhibition in HepG2 cells. DNA Cell Biol. 26, 765–772 (2007).

  192. 192

    Pasquato, A. et al. Evaluation of the anti-arenaviral activity of the subtilisin kexin isozyme-1/site-1 protease inhibitor PF-429242. Virology 423, 14–22 (2012).

  193. 193

    Olmstead, A. D., Knecht, W., Lazarov, I., Dixit, S. B. & Jean, F. Human subtilase SKI-1/S1P is a master regulator of the HCV lifecycle and a potential host cell target for developing indirect-acting antiviral agents. PLoS Pathog. 8, e1002468 (2012).

  194. 194

    Bastianelli, G. et al. Computational reverse-engineering of a spider-venom derived peptide active against Plasmodium falciparum SUB1. PLoS ONE 6, e21812 (2011).

  195. 195

    Duff, C. J. & Hooper, N. M. PCSK9: an emerging target for treatment of hypercholesterolemia. Expert Opin. Ther. Targets 15, 157–168 (2011).

  196. 196

    Konrad, R. J., Troutt, J. S. & Cao, G. Effects of currently prescribed LDL-C-lowering drugs on PCSK9 and implications for the next generation of LDL-C-lowering agents. Lipids Health Dis. 10, 38 (2011).

  197. 197

    Cariou, B., Le, M. C. & Costet, P. Clinical aspects of PCSK9. Atherosclerosis 216, 258–265 (2011).

  198. 198

    Awan, Z. et al. Rosuvastatin, proprotein convertase subtilisin/kexin type 9 concentrations, and LDL cholesterol response: the JUPITER trial. Clin. Chem. 58, 183–189 (2012).

  199. 199

    Crunkhorn, S. Trial watch: PCSK9 antibody reduces LDL cholesterol. Nature Rev. Drug Discov. 11, 11 (2012).

  200. 200

    Davignon, J., Dubuc, G. & Seidah, N. G. The influence of PCSK9 polymorphisms on serum low-density lipoprotein cholesterol and risk of atherosclerosis. Curr. Atheroscler. Rep. 12, 308–315 (2010).

  201. 201

    Lakoski, S. G., Lagace, T. A., Cohen, J. C., Horton, J. D. & Hobbs, H. H. Genetic and metabolic determinants of plasma PCSK9 levels. J. Clin. Endocrinol. Metab. 94, 2537–2543 (2009).

  202. 202

    Briel, M., Nordmann, A. J. & Bucher, H. C. Statin therapy for prevention and treatment of acute and chronic cardiovascular disease: update on recent trials and metaanalyses. Curr. Opin. Lipidol. 16, 601–605 (2005).

  203. 203

    Dubuc, G. et al. Statins upregulate PCSK9, the gene encoding the proprotein convertase neural apoptosis-regulated convertase-1 implicated in familial hypercholesterolemia. Arterioscler. Thromb. Vasc. Biol. 24, 1454–1459 (2004). This was the first evidence that statins upregulate levels of PCSK9 mRNA via activation of SREBP2.

  204. 204

    Attie, A. D. & Seidah, N. G. Dual regulation of the LDL receptor — some clarity and new questions. Cell Metab. 1, 290–292 (2005).

  205. 205

    Thompson, J. F. et al. Comprehensive whole-genome and candidate gene analysis for response to statin therapy in the treating to new targets (TNT) cohort. Circ. Cardiovasc. Genet. 2, 173–181 (2009).

  206. 206

    Naoumova, R. P. et al. Severe hypercholesterolemia in four British families with the D374Y mutation in the PCSK9 gene: long-term follow-up and treatment response. Arterioscler. Thromb. Vasc. Biol. 25, 2654–2660 (2005).

  207. 207

    Berge, K. E., Ose, L. & Leren, T. P. Missense mutations in the PCSK9 gene are associated with hypocholesterolemia and possibly increased response to statin therapy. Arterioscler. Thromb. Vasc. Biol. 26, 1094–1100 (2006).

  208. 208

    Chan, J. C. et al. A proprotein convertase subtilisin/kexin type 9 neutralizing antibody reduces serum cholesterol in mice and nonhuman primates. Proc. Natl Acad. Sci. USA 106, 9820–9825 (2009). This was the first evidence that an injectable inhibitory mAb can reduce the levels of active PCSK9 in circulation, resulting in a substantial reduction in the levels of LDL-C in mice and non-human primates. This seminal manuscript has led to the wider use of biologics to lower PCSK9 levels.

  209. 209

    Ni, Y. G. et al. A PCSK9-binding antibody that structurally mimics the EGF(A) domain of LDL-receptor reduces LDL cholesterol in vivo. J. Lipid Res. 52, 78–86 (2011).

  210. 210

    Liang, H. et al. Proprotein convertase substilisin/kexin type 9 antagonism reduces low-density lipoprotein cholesterol in statin-treated hypercholesterolemic nonhuman primates. J. Pharmacol. Exp. Ther. 340, 228–236 (2012).

  211. 211

    Ni, Y. G. et al. A proprotein convertase subtilisin-like/kexin type 9 (PCSK9) C-terminal domain antibody antigen-binding fragment inhibits PCSK9 internalization and restores low density lipoprotein uptake. J. Biol. Chem. 285, 12882–12891 (2010).

  212. 212

    McNutt, M. C. et al. Antagonism of secreted PCSK9 increases low-density lipoprotein receptor expression in HEPG2 cells. J. Biol. Chem. 284, 10551–10570 (2009).

  213. 213

    Frank-Kamenetsky, M. et al. Therapeutic RNAi targeting PCSK9 acutely lowers plasma cholesterol in rodents and LDL cholesterol in nonhuman primates. Proc. Natl Acad. Sci. USA 105, 11915–11920 (2008). This was the first evidence that an injectable RNAi lipidformulation against PCSK9 can reduce the levels of circulating PCSK9 and LDL-C in rodents and non-human primates.

  214. 214

    Gupta, N. et al. A locked nucleic acid antisense oligonucleotide (LNA) silences PCSK9 and enhances LDLR expression in vitro and in vivo. PLoS ONE 5, e10682 (2010). This was the first evidence that an injectable antisense LNA against PCSK9 can reduce the levels of circulating PCSK9 and LDL-C in mice.

  215. 215

    Lindholm, M. W. et al. PCSK9 LNA antisense oligonucleotides induce sustained reduction of LDL cholesterol in nonhuman primates. Mol. Ther. 20, 376–381 (2012).

  216. 216

    Chretien, M., Seidah, N. G., Basak, A. & Mbikay, M. Proprotein convertases as therapeutic targets. Expert Opin. Ther. Targets 12, 1289–1300 (2008).

  217. 217

    Mbikay, M., Sirois, F., Yao, J., Seidah, N. G. & Chretien, M. Comparative analysis of expression of the proprotein convertases furin, PACE4, PC1 and PC2 in human lung tumours. Br. J. Cancer 75, 1509–1514 (1997).

  218. 218

    Khatib, A. M., Siegfried, G., Chretien, M., Metrakos, P. & Seidah, N. G. Proprotein convertases in tumor progression and malignancy: novel targets in cancer therapy. Am. J. Pathol. 160, 1921–1935 (2002).

  219. 219

    Abifadel, M. et al. Mutations and polymorphisms in the proprotein convertase subtilisin kexin 9 (PCSK9) gene in cholesterol metabolism and disease. Hum. Mutat. 30, 520–529 (2009).

  220. 220

    Li, N. et al. Associations between genetic variations in the FURIN gene and hypertension. BMC Med. Genet. 11, 124 (2010).

  221. 221

    Ehret, G. B. et al. Genetic variants in novel pathways influence blood pressure and cardiovascular disease risk. Nature 478, 103–109 (2011).

  222. 222

    Kitamura, K. & Tomita, K. Proteolytic activation of the epithelial sodium channel and therapeutic application of a serine protease inhibitor for the treatment of salt-sensitive hypertension. Clin. Exp. Nephrol. 16, 44–48 (2012).

  223. 223

    Croissandeau, G. et al. Increased stress-induced analgesia in mice lacking the proneuropeptide convertase PC2. Neurosci. Lett. 406, 71–75 (2006).

  224. 224

    Espinosa, V. P. et al. Differential regulation of prohormone convertase 1/3, prohormone convertase 2 and phosphorylated cyclic-AMP-response element binding protein by short-term and long-term morphine treatment: implications for understanding the “switch” to opiate addiction. Neuroscience 156, 788–799 (2008).

  225. 225

    Hallenberger, S. et al. Inhibition of furin-mediated cleavage activation of HIV-1 glycoprotein gp160. Nature 360, 358–361 (1992). This was the first evidence that inhibition of furin may lead to the development of a powerful antiviralas it would prevent viral entry (for example, of HIV) by blocking the processing of its surface glycoprotein and hence exposure of its fusiogenic sequence.

  226. 226

    Hatta, M., Gao, P., Halfmann, P. & Kawaoka, Y. Molecular basis for high virulence of Hong Kong H5N1 influenza A viruses. Science 293, 1840–1842 (2001).

  227. 227

    Gordon, V. M., Rehemtulla, A. & Leppla, S. H. A role for PACE4 in the proteolytic activation of anthrax toxin protective antigen. Infect. Immun. 65, 3370–3375 (1997).

  228. 228

    Abrami, L. et al. The pore-forming toxin proaerolysin is activated by furin. J. Biol. Chem. 273, 32656–32661 (1998).

  229. 229

    Mbikay, M. et al. PCSK9-deficient mice exhibit impaired glucose tolerance and pancreatic islet abnormalities. FEBS Lett. 584, 701–706 (2010).

  230. 230

    Seidah, N. G., Day, R., Marcinkiewicz, M., Benjannet, S. & Chretien, M. Mammalian neural and endocrine pro-protein and pro-hormone convertases belonging to the subtilisin family of serine proteinases. Enzyme 45, 271–284 (1991).

  231. 231

    Seidah, N. G. & Chretien, M. Pro-protein convertases of subtilisin/kexin family. Methods Enzymol. 244, 175–188 (1994).

  232. 232

    Steiner, D. F. On the discovery of precursor processing. Methods Mol. Biol. 768, 3–11 (2011).

  233. 233

    Chretien, M. The prohormone theory and the proprotein convertases: it is all about serendipity. Methods Mol. Biol. 768, 13–19 (2011).

  234. 234

    Mizuno, K., Nakamura, T., Ohshima, T., Tanaka, S. & Matsuo, H. Yeast KEX2 genes encodes an endopeptidase homologous to subtilisin-like serine proteases. Biochem. Biophys. Res. Commun. 156, 246–254 (1988).

  235. 235

    Julius, D., Brake, A., Blair, L., Kunisawa, R. & Thorner, J. Isolation of the putative structural gene for the lysine-arginine-cleaving endopeptidase required for processing of yeast prepro-α-factor. Cell 37, 1075–1089 (1984). This was the first seminal genetic evidence that yeast contains a protease called kexin that can act as a proprotein convertase.

  236. 236

    Van de Ven, W. J. et al. Furin is a subtilisin-like proprotein processing enzyme in higher eukaryotes. Mol. Biol. Rep. 14, 265–275 (1990).

  237. 237

    Seidah, N. G. et al. cDNA sequence of two distinct pituitary proteins homologous to Kex2 and furin gene products: tissue-specific mRNAs encoding candidates for pro-hormone processing proteinases. DNA Cell Biol. 9, 414–424 (1990).

  238. 238

    Smeekens, S. P., Avruch, A. S., LaMendola, J., Chan, S. J. & Steiner, D. F. Identification of a cDNA encoding a second putative prohormone convertase related to PC2 in AtT20 cells and islets of Langerhans. Proc. Natl Acad. Sci. USA 88, 340–344 (1991).

  239. 239

    Smeekens, S. P. & Steiner, D. F. Identification of a human insulinoma cDNA encoding a novel mammalian protein structurally related to the yeast dibasic processing protease Kex2. J. Biol. Chem. 265, 2997–3000 (1990).

  240. 240

    Nakayama, K., Hosaka, M., Hatsuzawa, K. & Murakami, K. Cloning and functional expression of a novel endoprotease involved in prohormone processing at dibasic sites. J. Biochem. 109, 803–806 (1991).

  241. 241

    Kiefer, M. C. et al. Identification of a second human subtilisin-like protease gene in the fes/fps region of chromosome 15. DNA Cell Biol. 10, 757–769 (1991).

  242. 242

    Leigh, S. E., Leren, T. P. & Humphries, S. E. Commentary PCSK9 variants: a new database. Atherosclerosis 203, 32–33 (2009).

  243. 243

    Zhang, L. et al. An anti-PCSK9 antibody reduces LDL-cholesterol on top of a statin and suppresses hepatocyte SREBP-regulated genes. Int. J. Biol. Sci. 8, 310–327 (2012).

  244. 244

    Stein, E. A. et al. Effect of a monoclonal antibody to PCSK9 on LDL cholesterol. N. Engl. J. Med. 366, 1108–1118 (2012).

  245. 245

    Mayne, J. et al. Novel loss-of-function PCSK9 variant is associated with low plasma LDL cholesterol in a French-Canadian family and with impaired processing and secretion in cell culture. Clin. Chem. 57, 1415–1423 (2011).

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This research was supported by: Canadian Institutes of Health Research grants MOP-44363, MOP-93792 and MOP-102741; CTP-82946; and a Canada Chair grant 216684 (to N.G.S.). We would like to dedicate this article to M. Chretien who has been our mentor and a major driver in the discovery of the prohormone theory. He was the first to report that cleavage at pairs of basic residues of the inactive hormone precursor β-LPH (lipotropin) generates the active secretory products γ-LPH and β-MSH (melanocyte-stimulating hormone).

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Correspondence to Nabil G. Seidah.

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Related links

Related links


Nabil G. Seidah's homepage

Alnylam Pharmaceuticals website — 4 January 2012 press release

Amgen website — 25 March 2012 press release

MEROPS Peptidase Database

MEROPS Peptidase Database (search results for 'S08.071: furin')

MEROPS Peptidase Database (search results for 'S08.077: PCSK7 peptidase')

Regeneron website — 26 March 2012 press release

Santaris Pharma website — 4 May 2011 press release

Serometrix website

UCL website (PCSK9 database information)

World Intellectual Property Organization (WIPO) website (WO/2011/051961)


Proprotein convertases

Mammalian secretory serine proteases related to bacterial subtilases. They process various precursor proteins, mostly resulting in the release of more active products, but sometimes they inactivate some of their substrates.

Subtilisin kexin isozyme 1

(SKI-1). Also called site 1 protease. The eighth member of the proprotein convertase family; SKI-1 is responsible for the activation of various membrane-bound transcription factors (for example, sterol regulatory element-binding proteins, activating transcription factor 6 and cyclic AMP-responsive element binding proteins) and other proteins transiting through the Golgi apparatus.

Proprotein convertase subtilisin kexin 9

The ninth member of the proprotein convertase family, which is mostly implicated in regulating the levels of circulating low-density lipoprotein (LDL) cholesterol via the induction of the intracellular degradation of the LDL receptor in endosomes and lysosomes.

Low-density lipoprotein receptor

(LDLR). The main receptor of circulating LDL-cholesterol.


The aminoterminal inhibitory domain of the proprotein convertases. This domain acts as an intramolecular chaperone assisting the folding of the convertase in the endoplasmic reticulum, and also keeps the enzyme in an inhibited state until it is separated from the active convertase either in the trans-Golgi network, in immature secretory granules or at the cell surface.

Transforming growth factor-β

(TGFβ). A growth factor that regulates multiple physiological functions.

PCSK9–LDLR complex

The complex formed by the binding of the catalytic subunit of proprotein convertase subtilisin kexin 9 (PCSK9) to the epidermal growth factor A domain of low-density lipoprotein receptor (LDLR). The formation of this complex leads to the degradation of the LDLR in endosomes and lysosomes.

Cys-His-rich domain

Carboxy-terminal domain of proprotein convertase subtilisin kexin 9 (PCSK9) that is crucial for the sorting of the PCSK9–LDLR to endosomes and/or lysosomes.

Knockout mice

Gene knockout in mice. The availability of these genetically engineered mice allowed the characterization of some of the physiological functions of the proprotein convertases.

Genome-wide association study

(GWAS). A genome study that allows the identification of genes associated with disease states.

Sterol regulatory element binding proteins

(SREBPs). Membrane-bound transcription factors that are cleaved first by subtilisin kexin isozyme 1 in the cis- and medial-Golgi and then by site 2 protease to release their aminoterminal cytosolic fragment, which acts as a transcription factor activating the production of various proteins and enzymes implicated in cholesterol and fatty acid synthesis. The activated SREBP2 upregulates the transcription of mRNA encoding proprotein convertase subtilisin kexin 9.

Very-low-density lipoprotein receptor

(VLDLR). The main receptor of circulating VLDL-cholesterol.


(POMC). The precursor of adrenocorticotropic hormone, α-melanocyte-stimulating hormone and β-endorphin. These products produced by proprotein convertase 1 and/or proprotein convertase 2 regulate cortisol and corticosterone production, food intake and skin colour, as well as pain sensitivity.

Autosomal dominant hypercholesterolaemia

(ADH). A single-gene dominant disorder in hypercholesterolemia, where a mutation in one allele is sufficient to cause the disease.

Coronary artery disease

The end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium (the muscle of the heart) with oxygen and nutrients. Coronary artery disease is the leading cause of death worldwide.

Granulocyte–macrophage colony-stimulating factor

(GM-CSF). A cytokine that functions as an activator of the immune system by acting as a white blood cell growth factor and by stimulating stem cells to produce granulocytes (neutrophils, eosinophils and basophils) and monocytes. Monocytes exit the circulation and migrate into tissues, whereupon they mature into macrophages and dendritic cells.

Familial hypercholesterolaemia

A genetic disorder characterized by high cholesterol levels, specifically very high levels of low-density lipoprotein (LDL; also known as 'bad cholesterol') in the blood, and early cardiovascular disease. Many patients have mutations in the gene that encodes the LDL receptor (LDLR) protein, which normally removes LDL from circulation, or in the gene encoding apolipoprotein B, which is the part of LDL that binds to the receptor; mutations in other genes such as proprotein convertase subtilisin kexin 9 are less common.

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Seidah, N., Prat, A. The biology and therapeutic targeting of the proprotein convertases. Nat Rev Drug Discov 11, 367–383 (2012).

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