FBXL2- and PTPL1-mediated degradation of p110-free p85β regulatory subunit controls the PI(3)K signalling cascade


F-box proteins are the substrate-recognition subunits of SCF (Skp1/Cul1/F-box protein) ubiquitin ligase complexes. Purification of the F-box protein FBXL2 identified the PI(3)K regulatory subunit p85β and tyrosine phosphatase PTPL1 as interacting proteins. FBXL2 interacts with the pool of p85β that is free of p110 PI(3)K catalytic subunits and targets this pool for ubiquitylation and subsequent proteasomal degradation. FBXL2-mediated degradation of p85β is dependent on the integrity of its CaaX motif. Whereas most SCF substrates require phosphorylation to interact with their F-box proteins, phosphorylation of p85β on Tyr 655, which is adjacent to the degron, inhibits p85β binding to FBXL2. Dephosphorylation of phospho-Tyr-655 by PTPL1 stimulates p85β binding to and degradation through FBXL2. Finally, defects in the FBXL2-mediated degradation of p85β inhibit the binding of p110 subunits to IRS1, attenuate the PI(3)K signalling cascade and promote autophagy. We propose that FBXL2 and PTPL1 suppress p85β levels, preventing the inhibition of PI(3)K by an excess of free p85 that could compete with p85–p110 heterodimers for IRS1.

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Figure 1: FBXL2 binds p110-free p85 regulatory subunits.
Figure 2: p85β is targeted for ubiquitylation and degradation by SCFFBXL2.
Figure 3: Identification of p85β degron.
Figure 4: p85β interaction with FBXL2 is negatively regulated by Tyr phosphorylation.
Figure 5: PTPL1 dephosphorylates p85β, promoting its binding to FBXL2 and degradation.
Figure 6: Failure to degrade p85β results in PI(3)K activation defects.
Figure 7: p85β degradation regulates cell autophagy.
Figure 8: A model of the FBXL2- and PTPL1-dependent regulation of the PI(3)K pathway.


  1. 1

    Petroski, M. D. & Deshaies, R. J. Function and regulation of cullin-RING ubiquitin ligases. Nat. Rev. Mol. Cell Biol. 6, 9–20 (2005).

    CAS  Article  Google Scholar 

  2. 2

    Skaar, J. R., Pagan, J. K. & Pagano, M. SnapShot: F box proteins I. Cell 137, 1160–1161 (2009).

    CAS  Article  Google Scholar 

  3. 3

    Skaar, J. R., D’Angiolella, V., Pagan, J. K., Pagano, M. & SnapShot, F Box Proteins II. Cell 137, 1358 (2009).

    Article  Google Scholar 

  4. 4

    Wang, C. et al. Identification of FBL2 as a geranylgeranylated cellular protein required for hepatitis C virus RNA replication. Mol. Cell 18, 425–434 (2005).

    CAS  Article  Google Scholar 

  5. 5

    Chen, B. B., Coon, T. A., Glasser, J. R. & Mallampalli, R. K. Calmodulin antagonizes a calcium-activated SCF ubiquitin E3 ligase subunit, FBXL2, to regulate surfactant homeostasis. Mol. Cell Biol. 31, 1905–1920 (2011).

    CAS  Article  Google Scholar 

  6. 6

    Chen, B. B. et al. F-box protein FBXL2 targets cyclin D2 for ubiquitination and degradation to inhibit leukemic cell proliferation. Blood 119, 3132–3141 (2012).

    CAS  Article  Google Scholar 

  7. 7

    Cantley, L. C. The phosphoinositide 3-kinase pathway. Science 296, 1655–1657 (2002).

    CAS  Article  Google Scholar 

  8. 8

    Katso, R. et al. Cellular function of phosphoinositide 3-kinases: implications for development, homeostasis, and cancer. Annu. Rev. Cell Dev. Biol. 17, 615–675 (2001).

    CAS  Article  Google Scholar 

  9. 9

    Vanhaesebroeck, B., Guillermet-Guibert, J., Graupera, M. & Bilanges, B. The emerging mechanisms of isoform-specific PI3K signalling. Nat. Rev. Mol. Cell Biol. 11, 329–341 (2010).

    CAS  Article  Google Scholar 

  10. 10

    Engelman, J. A., Luo, J. & Cantley, L. C. The evolution of phosphatidylinositol 3-kinases as regulators of growth and metabolism. Nat. Rev. Genet. 7, 606–619 (2006).

    CAS  Article  Google Scholar 

  11. 11

    Klippel, A., Kavanaugh, W. M., Pot, D. & Williams, L. T. A specific product of phosphatidylinositol 3-kinase directly activates the protein kinase Akt through its pleckstrin homology domain. Mol. Cell Biol. 17, 338–344 (1997).

    CAS  Article  Google Scholar 

  12. 12

    Franke, T. F., Kaplan, D. R., Cantley, L. C. & Toker, A. Direct regulation of the Akt proto-oncogene product by phosphatidylinositol-3,4-bisphosphate. Science 275, 665–668 (1997).

    CAS  Article  Google Scholar 

  13. 13

    Sarbassov, D. D., Guertin, D. A., Ali, S. M. & Sabatini, D. M. Phosphorylation and regulation of Akt/PKB by the rictor-mTOR complex. Science 307, 1098–1101 (2005).

    CAS  Article  Google Scholar 

  14. 14

    Mora, A., Komander, D., van Aalten, D. M. & Alessi, D. R. PDK1, the master regulator of AGC kinase signal transduction. Semin. Cell Dev. Biol. 15, 161–170 (2004).

    CAS  Article  Google Scholar 

  15. 15

    Luo, J., Field, S. J., Lee, J. Y., Engelman, J. A. & Cantley, L. C. The p85 regulatory subunit of phosphoinositide 3-kinase down-regulates IRS-1 signalling via the formation of a sequestration complex. J. Cell Biol. 170, 455–464 (2005).

    CAS  Article  Google Scholar 

  16. 16

    Mauvais-Jarvis, F. et al. Reduced expression of the murine p85α subunit of phosphoinositide 3-kinase improves insulin signalling and ameliorates diabetes. J. Clin. Invest. 109, 141–149 (2002).

    CAS  Article  Google Scholar 

  17. 17

    Geering, B., Cutillas, P. R. & Vanhaesebroeck, B. Regulation of class IA PI3Ks: is there a role for monomeric PI3K subunits? Biochem. Soc. Trans. 35, 199–203 (2007).

    CAS  Article  Google Scholar 

  18. 18

    Fruman, D. A. et al. Hypoglycaemia, liver necrosis and perinatal death in mice lacking all isoforms of phosphoinositide 3-kinase p85α. Nat. Genet. 26, 379–382 (2000).

    CAS  Article  Google Scholar 

  19. 19

    Ueki, K. et al. Molecular balance between the regulatory and catalytic subunits of phosphoinositide 3-kinase regulates cell signalling and survival. Mol. Cell Biol. 22, 965–977 (2002).

    CAS  Article  Google Scholar 

  20. 20

    Florens, L. & Washburn, M. P. Proteomic analysis by multidimensional protein identification technology. Methods Mol. Biol. 328, 159–175 (2006).

    CAS  PubMed  Google Scholar 

  21. 21

    Emberley, E. D., Mosadeghi, R. & Deshaies, R. J. Deconjugation of Nedd8 from Cul1 is directly regulated by Skp1-Fbox and substrate, and CSN inhibits deneddylated SCF by a non-catalytic mechanism. J. Biol. Chem. 287, 29679–29689 (2012).

    CAS  Article  Google Scholar 

  22. 22

    Park, S. W. et al. The regulatory subunits of PI3K, p85α and p85β, interact with XBP-1 and increase its nuclear translocation. Nat. Med. 16, 429–437 (2010).

    CAS  Article  Google Scholar 

  23. 23

    Abaan, O. D. & Toretsky, J. A. PTPL1: a large phosphatase with a split personality. Cancer Metast. Rev. 27, 205–214 (2008).

    CAS  Article  Google Scholar 

  24. 24

    Huang, J. & Manning, B. D. A complex interplay between Akt, TSC2 and the two mTOR complexes. Biochem. Soc. Trans. 37, 217–222 (2009).

    CAS  Article  Google Scholar 

  25. 25

    Long, X., Lin, Y., Ortiz-Vega, S., Yonezawa, K. & Avruch, J. Rheb binds and regulates the mTOR kinase. Curr. Biol. 15, 702–713 (2005).

    CAS  Article  Google Scholar 

  26. 26

    Zhang, H. et al. Loss of Tsc1/Tsc2 activates mTOR and disrupts PI3K-Akt signalling through downregulation of PDGFR. J. Clin. Invest. 112, 1223–1233 (2003).

    CAS  Article  Google Scholar 

  27. 27

    Zoncu, R., Efeyan, A. & Sabatini, D. M. mTOR: from growth signal integration to cancer, diabetes and ageing. Nat. Rev. Mol. Cell Biol. 12, 21–35 (2011).

    CAS  Article  Google Scholar 

  28. 28

    Songyang, Z. et al. SH2 domains recognize specific phosphopeptide sequences. Cell 72, 767–778 (1993).

    CAS  Article  Google Scholar 

  29. 29

    Yu, J., Wjasow, C. & Backer, J. M. Regulation of the p85/p110α phosphatidylinositol 3’-kinase. Distinct roles for the n-terminal and c-terminal SH2 domains. J. Biol. Chem. 273, 30199–30203 (1998).

    CAS  Article  Google Scholar 

  30. 30

    Wu, H. et al. Regulation of Class IA PI 3-kinases: C2 domain-iSH2 domain contacts inhibit p85/p110α and are disrupted in oncogenic p85 mutants. Proc. Natl Acad. Sci. USA 106, 20258–20263 (2009).

    CAS  Article  Google Scholar 

  31. 31

    Burke, J. E. et al. Dynamics of the phosphoinositide 3-kinase p110delta interaction with p85α and membranes reveals aspects of regulation distinct from p110α. Structure 19, 1127–1137 (2011).

    CAS  Article  Google Scholar 

  32. 32

    Zhang, X. et al. Structure of lipid kinase p110β/p85β elucidates an unusual SH2-domain-mediated inhibitory mechanism. Mol. Cell 41, 567–578 (2011).

    CAS  Article  Google Scholar 

  33. 33

    Chen, D. et al. p50α/p55α phosphoinositide 3-kinase knockout mice exhibit enhanced insulin sensitivity. Mol. Cell Biol. 24, 320–329 (2004).

    CAS  Article  Google Scholar 

  34. 34

    Terauchi, Y. et al. Increased insulin sensitivity and hypoglycaemia in micelacking the p85α subunit of phosphoinositide 3-kinase. Nat. Genet. 21, 230–235 (1999).

    CAS  Article  Google Scholar 

  35. 35

    Ueki, K. et al. Increased insulin sensitivity in mice lacking p85β subunit of phosphoinositide 3-kinase. Proc. Natl Acad. Sci. USA 99, 419–424 (2002).

    CAS  Article  Google Scholar 

  36. 36

    Burke, J. E. & Williams, R. L. Dynamic steps in receptor tyrosine kinase mediated activation of class IA phosphoinositide 3-kinases (PI3K) captured by H/D exchange (HDX-MS). Adv. Biol. Regul. 53, 97–110 (2013).

    CAS  Article  Google Scholar 

  37. 37

    Kok, K., Geering, B. & Vanhaesebroeck, B. Regulation of phosphoinositide 3-kinase expression in health and disease. Trends Biochem. Sci. 34, 115–127 (2009).

    CAS  Article  Google Scholar 

  38. 38

    Chagpar, R. B. et al. Direct positive regulation of PTEN by the p85 subunitof phosphatidylinositol 3-kinase. Proc. Natl Acad. Sci. USA 107, 5471–5476 (2010).

    CAS  Article  Google Scholar 

  39. 39

    Bandyopadhyay, G. K., Yu, J. G., Ofrecio, J. & Olefsky, J. M. Increased p85/55/50 expression and decreased phosphotidylinositol 3-kinase activity in insulin-resistant human skeletal muscle. Diabetes 54, 2351–2359 (2005).

    CAS  Article  Google Scholar 

  40. 40

    Ueki, K., Algenstaedt, P., Mauvais-Jarvis, F. & Kahn, C. R. Positive and negative regulation of phosphoinositide 3-kinase-dependent signalling pathways by three different gene products of the p85α regulatory subunit. Mol. Cell Biol. 20, 8035–8046 (2000).

    CAS  Article  Google Scholar 

  41. 41

    Myers, M. G. Jr et al. IRS-1 activates phosphatidylinositol 3’-kinase by associating with src homology 2 domains of p85. Proc. Natl Acad. Sci. USA 89, 10350–10354 (1992).

    CAS  Article  Google Scholar 

  42. 42

    Otsu, M. et al. Characterization of two 85 kd proteins that associate with receptor tyrosine kinases, middle-T/pp60c-src complexes, and PI3-kinase. Cell 65, 91–104 (1991).

    CAS  Article  Google Scholar 

  43. 43

    Dromard, M. et al. The putative tumour suppressor gene PTPN13/PTPL1 induces apoptosis through insulin receptor substrate-1 dephosphorylation. Cancer Res. 67, 6806–6813 (2007).

    CAS  Article  Google Scholar 

  44. 44

    McDonald, W. H. et al. Comparison of three directly coupled HPLC MS/MS strategies for identification of proteins from complex mixtures: single-dimension LCMS/MS, 2-phase MudPIT, and 3-phase MudPIT. Mass Spectrom 219, 245–251 (2002).

    CAS  Google Scholar 

  45. 45

    Eng, J. et al. An approach to correlate tandem mass spectral data of peptides with amino acid sequences in a protein database. J. Amer. Mass Spectrom 5, 976–989 (1994).

    CAS  Article  Google Scholar 

  46. 46

    Tabb, D. L., McDonald, W. H. & Yates, J. R. 3rd DTASelect and Contrast: tools for assembling and comparing protein identifications from shotgun proteomics. J. Proteome. Res. 1, 21–26 (2002).

    CAS  Article  Google Scholar 

  47. 47

    Zhang, Y. et al. Refinements to label free proteome quantitation: how to deal with peptides shared by multiple proteins. Anal. Chem. 82, 2272–2281 (2010).

    CAS  Article  Google Scholar 

  48. 48

    D’Angiolella, V. et al. SCF(Cyclin F) controls centrosome homeostasis and mitotic fidelity through CP110 degradation. Nature 466, 138–142 (2010).

    Article  Google Scholar 

  49. 49

    Duan, S. et al. mTOR generates an auto-amplification loop by triggering theβTrCP- and CK1α-dependent degradation of DEPTOR. Mol. Cell 44, 317–324 (2011).

    CAS  Article  Google Scholar 

  50. 50

    D’Angiolella, V. et al. Cyclin F-mediated degradation of ribonucleotide reductase M2 controls genome integrity and DNA repair. Cell 149, 1023–1034 (2012).

    Article  Google Scholar 

  51. 51

    Duan, S. et al. FBXO11 targets BCL6 for degradation and is inactivated in diffuse large B-cell lymphomas. Nature 481, 90–93 (2012).

    CAS  Article  Google Scholar 

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The authors thank J. Backer, J. H. Lee and R. K. Mallampalli for reagents, and J. Backer, J. R. Skaar and E. Skolnik for critical reading of the manuscript. M.P. is grateful to T. M. Thor for continuous support. This work was financially supported by grants from the National Institutes of Health (R01-GM057587, R37-CA076584 and R21-CA161108) to M.P. and a grant from Susan G. Komen for the Cure to S.D. A.S., L.F. and M.P.W. are supported by the Stowers Institute for Medical Research. M.P. is an Investigator with the Howard Hughes Medical Institute.

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S.K. planned and performed most experiments and helped to write the manuscript. M.P. coordinated the study, oversaw the results, and wrote the manuscript. S.D., E.S. and A.P. helped with some experiments. A.S., L.F. and M.P.W. performed the mass spectrometry analysis of the FBXL2 complex purified by S.K. All authors discussed the results and commented on the manuscript.

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Correspondence to Michele Pagano.

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Kuchay, S., Duan, S., Schenkein, E. et al. FBXL2- and PTPL1-mediated degradation of p110-free p85β regulatory subunit controls the PI(3)K signalling cascade. Nat Cell Biol 15, 472–480 (2013). https://doi.org/10.1038/ncb2731

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