Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Aspergillus fumigatus CalA binds to integrin α5β1 and mediates host cell invasion

This article has been updated


Aspergillus fumigatus is an opportunistic fungal pathogen that invades pulmonary epithelial cells and vascular endothelial cells by inducing its own endocytosis, but the mechanism by which this process occurs is poorly understood. Here, we show that the thaumatin-like protein CalA is expressed on the surface of the A. fumigatus cell wall, where it mediates invasion of epithelial and endothelial cells. CalA induces endocytosis in part by interacting with integrin α5β1 on host cells. In corticosteroid-treated mice, a ΔcalA deletion mutant has significantly attenuated virulence relative to the wild-type strain, as manifested by prolonged survival, reduced pulmonary fungal burden and decreased pulmonary invasion. Pretreatment with an anti-CalA antibody improves survival of mice with invasive pulmonary aspergillosis, demonstrating the potential of CalA as an immunotherapeutic target. Thus, A. fumigatus CalA is an invasin that interacts with integrin α5β1 on host cells, induces endocytosis and enhances virulence.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: A. fumigatus CalA functions as an invasin.
Figure 2: CalA is required for normal germination and hyphal morphology.
Figure 3: β1 integrin binds to A. fumigatus and is required for maximal endocytosis.
Figure 4: Integrin α5β1 interacts with A. fumigatus CalA.
Figure 5: CalA is required for normal virulence and lung invasion in the mouse model of invasive aspergillosis.
Figure 6: An anti-CalA antibody inhibits host cell invasion and protects mice from lethal invasive aspergillosis.

Change history

  • 14 July 2017

    In the PDF version of this article previously published, the year of publication provided in the footer of each page and in the 'How to cite' section was erroneously given as 2017, it should have been 2016. This error has now been corrected. The HTML version of the article was not affected.


  1. 1

    Maschmeyer, G., Haas, A. & Cornely, O. A. Invasive aspergillosis: epidemiology, diagnosis and management in immunocompromised patients. Drugs 67, 1567–1601 (2007).

    CAS  Article  Google Scholar 

  2. 2

    Taccone, F. S. et al. Epidemiology of invasive aspergillosis in critically ill patients: clinical presentation, underlying conditions, and outcomes. Crit. Care 19, 7 (2015).

    Article  Google Scholar 

  3. 3

    Filler, S. G. & Sheppard, D. C. Fungal invasion of normally non-phagocytic host cells. PLoS Pathog. 2, e129 (2006).

    Article  Google Scholar 

  4. 4

    DeHart, D. J., Agwu, D. E., Julian, N. C. & Washburn, R. G. Binding and germination of Aspergillus fumigatus conidia on cultured A549 pneumocytes. J. Infect. Dis. 175, 146–150 (1997).

    CAS  Article  Google Scholar 

  5. 5

    Kamai, Y., Lossinsky, A. S., Liu, H., Sheppard, D. C. & Filler, S. G. Polarized response of endothelial cells to invasion by Aspergillus fumigatus. Cell Microbiol. 11, 170–182 (2009).

    CAS  Article  Google Scholar 

  6. 6

    Lopes-Bezerra, L. M. & Filler, S. G. Interactions of Aspergillus fumigatus with endothelial cells: internalization, injury, and stimulation of tissue factor activity. Blood 103, 2143–2149 (2004).

    Article  Google Scholar 

  7. 7

    Paris, S. et al. Internalization of Aspergillus fumigatus conidia by epithelial and endothelial cells. Infect. Immun. 65, 1510–1514 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8

    Wasylnka, J. A. & Moore, M. M. Uptake of Aspergillus fumigatus conidia by phagocytic and nonphagocytic cells in vitro: quantitation using strains expressing green fluorescent protein. Infect. Immun. 70, 3156–3163 (2002).

    CAS  Article  Google Scholar 

  9. 9

    Wasylnka, J. A. & Moore, M. M. Aspergillus fumigatus conidia survive and germinate in acidic organelles of A549 epithelial cells. J. Cell Sci. 116, 1579–1587 (2003).

    CAS  Article  Google Scholar 

  10. 10

    Sheppard, D. C. & Filler, S. G. Host cell invasion by medically important fungi. Cold Spring Harb. Perspect. Med. 5, a019687 (2014).

    Article  Google Scholar 

  11. 11

    Upadhyay, S. K. et al. Identification and characterization of a laminin-binding protein of Aspergillus fumigatus: extracellular thaumatin domain protein (AfCalAp). J. Med. Microbiol. 58, 714–722 (2009).

    CAS  Article  Google Scholar 

  12. 12

    Gravelat, F. N. et al. Aspergillus galactosaminogalactan mediates adherence to host constituents and conceals hyphal β-glucan from the immune system. PLoS Pathog. 9, e1003575 (2013).

    CAS  Article  Google Scholar 

  13. 13

    Phan, Q. T. et al. Als3 is a Candida albicans invasin that binds to cadherins and induces endocytosis by host cells. PLoS Biol. 5, e64 (2007).

    Article  Google Scholar 

  14. 14

    Fu, Y. et al. Expression of the Candida albicans gene ALS1 in Saccharomyces cerevisiae induces adherence to endothelial and epithelial cells. Infect Immun. 66, 1783–1786 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  15. 15

    Sheppard, D. C. et al. Functional and structural diversity in the Als protein family of Candida albicans. J. Biol. Chem. 279, 30840–30849 (2004).

    Article  Google Scholar 

  16. 16

    Belaish, R. et al. The Aspergillus nidulans cetA and calA genes are involved in conidial germination and cell wall morphogenesis. Fungal Genet. Biol. 45, 232–242 (2008).

    CAS  Article  Google Scholar 

  17. 17

    Zhu, W. et al. EGFR and HER2 receptor kinase signaling mediate epithelial cell invasion by Candida albicans during oropharyngeal infection. Proc. Natl Acad. Sci. USA 109, 14194–14199 (2012).

    CAS  Article  Google Scholar 

  18. 18

    Wennerberg, K. et al. Beta 1 integrin-dependent and -independent polymerization of fibronectin. J. Cell Biol. 132, 227–238 (1996).

    CAS  Article  Google Scholar 

  19. 19

    Hemler, M. E., Huang, C. & Schwarz, L. The VLA protein family. Characterization of five distinct cell surface heterodimers each with a common 130,000 molecular weight beta subunit. J. Biol. Chem. 262, 3300–3309 (1987).

    CAS  PubMed  Google Scholar 

  20. 20

    Secott, T. E., Lin, T. L. & Wu, C. C. Mycobacterium avium subsp. paratuberculosis fibronectin attachment protein facilitates M-cell targeting and invasion through a fibronectin bridge with host integrins. Infect. Immun. 72, 3724–3732 (2004).

    CAS  Article  Google Scholar 

  21. 21

    Sinha, B. et al. Fibronectin-binding protein acts as Staphylococcus aureus invasin via fibronectin bridging to integrin α5β1 . Cell. Microbiol. 1, 101–117 (1999).

    CAS  Article  Google Scholar 

  22. 22

    Cue, D., Dombek, P. E., Lam, H. & Cleary, P. P. Streptococcus pyogenes serotype M1 encodes multiple pathways for entry into human epithelial cells. Infect. Immun. 66, 4593–4601 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  23. 23

    Livant, D. L. et al. Anti-invasive, antitumorigenic, and antimetastatic activities of the PHSCN sequence in prostate carcinoma. Cancer Res. 60, 309–320 (2000).

    CAS  PubMed  Google Scholar 

  24. 24

    Isberg, R. R. & Leong, J. M. Multiple β1 chain integrins are receptors for invasin, a protein that promotes bacterial penetration into mammalian cells. Cell 60, 861–871 (1990).

    CAS  Article  Google Scholar 

  25. 25

    Al-Bader, N. et al. Role of trehalose biosynthesis in Aspergillus fumigatus development, stress response, and virulence. Infect. Immun. 78, 3007–3018 (2010).

    CAS  Article  Google Scholar 

  26. 26

    Hohl, T. M. & Feldmesser, M. Aspergillus fumigatus: principles of pathogenesis and host defense. Eukaryot. Cell. 6, 1953–1963 (2007).

    CAS  Article  Google Scholar 

  27. 27

    Liu, J. J., Sturrock, R. & Ekramoddoullah, A. K. The superfamily of thaumatin-like proteins: its origin, evolution, and expression towards biological function. Plant Cell Rep. 29, 419–436 (2010).

    CAS  Article  Google Scholar 

  28. 28

    Greenstein, S. et al. Analysis of the Aspergillus nidulans thaumatin-like cetA gene and evidence for transcriptional repression of pyr4 expression in the cetA-disrupted strain. Fungal Genet. Biol. 43, 42–53 (2006).

    CAS  Article  Google Scholar 

  29. 29

    Masuda, T. et al. Five amino acid residues in cysteine-rich domain of human T1R3 were involved in the response for sweet-tasting protein, thaumatin. Biochimie 95, 1502–1505 (2013).

    CAS  Article  Google Scholar 

  30. 30

    Sun, J. N. et al. Host cell invasion and virulence mediated by Candida albicans Ssa1. PLoS Pathog. 6, e1001181 (2010).

    Article  Google Scholar 

  31. 31

    Liu, Y., Mittal, R., Solis, N. V., Prasadarao, N. V. & Filler, S. G. Mechanisms of Candida albicans trafficking to the brain. PLoS Pathog. 7, e1002305 (2011).

    CAS  Article  Google Scholar 

  32. 32

    Lowin, T. et al. Glucocorticoids increase α5 integrin expression and adhesion of synovial fibroblasts but inhibit ERK signaling, migration, and cartilage invasion. Arthritis Rheum. 60, 3623–3632 (2009).

    CAS  Article  Google Scholar 

  33. 33

    Schmidt, C. S. et al. NDV-3, a recombinant alum-adjuvanted vaccine for Candida and Staphylococcus aureus, is safe and immunogenic in healthy adults. Vaccine 30, 7594–7600 (2012).

    CAS  Article  Google Scholar 

  34. 34

    Catlett, N. L., Lee, B.-N., Yoder, O. C. & Turgeon, B. G. Split-marker recombination for efficient targeted deletion of fungal genes. Fungal Genet. News 50, 9–11 (2002).

    Google Scholar 

  35. 35

    Gravelat, F. N., Askew, D. S. & Sheppard, D. C. Targeted gene deletion in Aspergillus fumigatus using the hygromycin-resistance split-marker approach. Methods Mol. Biol. 845, 119–130 (2012).

    CAS  Article  Google Scholar 

  36. 36

    Richie, D. L. et al. The Aspergillus fumigatus metacaspases CasA and CasB facilitate growth under conditions of endoplasmic reticulum stress. Mol. Microbiol. 63, 591–604 (2007).

    CAS  Article  Google Scholar 

  37. 37

    Lee, M. J. et al. Overlapping and distinct roles of Aspergillus fumigatus UDP-glucose 4-epimerases in galactose metabolism and the synthesis of galactose-containing cell wall polysaccharides. J. Biol. Chem. 289, 1243–1256 (2014).

    CAS  Article  Google Scholar 

  38. 38

    Campoli, P. et al. Concentration of antifungal agents within host cell membranes: a new paradigm governing the efficacy of prophylaxis. Antimicrob. Agents Chemother. 55, 5732–5739 (2011).

    CAS  Article  Google Scholar 

  39. 39

    Pongpom, M. et al. Divergent targets of Aspergillus fumigatus AcuK and AcuM transcription factors during growth in vitro versus invasive disease. Infect. Immun. 83, 923–933 (2015).

    Article  Google Scholar 

  40. 40

    Bouchara, J. P. et al. Sialic acid-dependent recognition of laminin and fibrinogen by Aspergillus fumigatus conidia. Infect. Immun. 65, 2717–2724 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  41. 41

    Gravelat, F. N. et al. Aspergillus fumigatus MedA governs adherence, host cell interactions and virulence. Cell. Microbiol. 12, 473–488 (2010).

    CAS  Article  Google Scholar 

  42. 42

    Fontaine, T. et al. Galactosaminogalactan, a new immunosuppressive polysaccharide of Aspergillus fumigatus. PLoS Pathog. 7, e1002372 (2011).

    CAS  Article  Google Scholar 

  43. 43

    Liu, H. et al. Aspergillus fumigatus AcuM regulates both iron acquisition and gluconeogenesis. Mol. Microbiol. 78, 1038–1054 (2010).

    CAS  Article  Google Scholar 

  44. 44

    Collins, S. J. The HL-60 promyelocytic leukemia cell line: proliferation, differentiation, and cellular oncogene expression. Blood 70, 1233–1244 (1987).

    CAS  PubMed  Google Scholar 

  45. 45

    Phan, Q. T., Fratti, R. A., Prasadarao, N. V., Edwards, J. E. Jr & Filler, S. G. N-cadherin mediates endocytosis of Candida albicans by endothelial cells. J. Biol. Chem. 280, 10455–10461 (2005).

    CAS  Article  Google Scholar 

  46. 46

    Van Nhieu, G. T. & Isberg, R. R. The Yersinia pseudotuberculosis invasin protein and human fibronectin bind to mutually exclusive sites on the α5β1 integrin receptor. J. Biol. Chem. 266, 24367–24375 (1991).

    CAS  PubMed  Google Scholar 

  47. 47

    Ejzykowicz, D. E. et al. The Aspergillus fumigatus transcription factor Ace2 governs pigment production, conidiation and virulence. Mol. Microbiol. 72, 155–169 (2009).

    CAS  Article  Google Scholar 

  48. 48

    Williamson, E. C. et al. Diagnosis of invasive aspergillosis in bone marrow transplant recipients by polymerase chain reaction. Br. J. Haematol. 108, 132–139 (2000).

    CAS  Article  Google Scholar 

Download references


The authors thank D. Villarreal for assistance with tissue culture. This work was supported by National Institutes of Health (NIH) grants R01AI073829 and R56AI111836, by UCLA CTSI grant UL1TR000124 and by operating grants 81361 and 123306 from the Canadian Institutes of Health Research. A.S.I. is supported by NIH grant R01AI063503. D.C.S. is supported by a Chercheur–Boursier Award from the Fonds de Recherche Quebec Santé (FRQS).

Author information




H.L., M.J.L., N.V.S., Q.T.P., A.S.I., D.C.S. and S.G.F. designed the experiments. H.L., M.J.L., N.V.S., Q.T.P., M.S. and B.R. performed the experiments. H.L., M.J.L., D.C.S. and S.G.F. analysed the data. H.L., D.C.S. and S.G.F. wrote the paper.

Corresponding author

Correspondence to Scott G. Filler.

Ethics declarations

Competing interests

Ashraf Ibrahim and Scott Filler are co-founders of and hold equity in NovaDigm Therapeutics, Inc.

Supplementary information

Supplementary Information

Supplementary Tables 1,2, Supplementary Figures 1–14 (PDF 1591 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Liu, H., Lee, M., Solis, N. et al. Aspergillus fumigatus CalA binds to integrin α5β1 and mediates host cell invasion. Nat Microbiol 2, 16211 (2017).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing