EGFR-MAPK adaptor proteins mediate the epithelial response to Candida albicans via the cytolytic peptide toxin, candidalysin

Abstract

Candida albicans (C. albicans) is a dimorphic human fungal pathogen that can cause severe oropharyngeal candidiasis (OPC, oral thrush) in susceptible hosts. During invasive infection, C. albicans hyphae invade oral epithelial cells (OECs) and secrete candidalysin, a pore-forming cytolytic peptide that is required for fungal pathogenesis at mucosal surfaces. Candidalysin induces cell damage and activates multiple MAPK-based innate signaling events that collectively drive the production of downstream inflammatory mediators. The activities of candidalysin are also dependent on the epidermal growth factor receptor (EGFR), but how these signals are integrated is undefined. Here, we identified five essential adaptor proteins as key mediators of the epithelial response to C. albicans infection on cultured OECs, including growth factor receptor bound protein 2 (Grb2), Grb2-associated-binding protein 1 (Gab1), Src homology and collagen (Shc), SH2 containing protein tyrosine phosphatase-2 (Shp2) and casitas B-lineage lymphoma (c-Cbl). All these signaling effectors were inducibly phosphorylated in response to C. albicans, in a candidalysin-dependent mechanism but additionally required EGFR phosphorylation, matrix metalloproteinases (MMPs) and cellular calcium flux. Of these, Gab1, Grb2 and Shp2 were the dominant drivers of ERK1/2 signaling and production of downstream cytokines. Together, these results identify the key adaptor proteins that drive EGFR signaling mechanisms, which determine oral epithelial responses to C. albicans.