Activation of EphA2-EGFR signaling in oral epithelial cells by Candida albicans virulence factors

Abstract

During oropharyngeal candidiasis (OPC), Candida albicans invades and damages oral epithelial cells, which respond by producing proinflammatory mediators that recruit phagocytes to foci of infection. The ephrin type-A receptor 2 (EphA2) detects β-glucan and plays a central role in stimulating epithelial cells to release proinflammatory mediators during OPC. The epidermal growth factor receptor (EGFR) also interacts with C. albicans and is known to be activated by the Als3 adhesin/invasin and the candidalysin pore-forming toxin. Here, we investigated the interactions among EphA2, EGFR, Als3 and candidalysin during OPC. We found that EGFR and EphA2 constitutively associate with each other as part of a heteromeric physical complex and are mutually dependent for C. albicans-induced activation. Als3-mediated endocytosis of a C. albicans hypha leads to the formation of an endocytic vacuole where candidalysin accumulates at high concentration. Thus, Als3 potentiates targeting of candidalysin, and both Als3 and candidalysin are required for C. albicans to cause maximal damage to oral epithelial cells, sustain activation of EphA2 and EGFR, and stimulate pro-inflammatory cytokine and chemokine secretion. In the mouse model of OPC, C. albicans-induced production of CXCL1/KC and CCL20 is dependent on the presence of candidalysin and EGFR, but independent of Als3. The production of IL-1α and IL-17A also requires candidalysin but is independent of Als3 and EGFR. The production of TNFα requires Als1, Als3, and candidalysin. Collectively, these results delineate the complex interplay among host cell receptors EphA2 and EGFR and C. albicans virulence factors Als1, Als3 and candidalysin during the induction of OPC and the resulting oral inflammatory response.

Candidalysin delivery to the invasion pocket is critical for host epithelial damage induced byCandida albicans

“…The data support our previous studies (Murciano et al, 2012; Wachtler et al, 2011) and indicate that candidalysin needs to be delivered to the invasion pocket in order to accumulate at sufficient concentrations to induce epithelial cell damage. Furthermore, our data are supported by a recent study showing that Als3 promotes the targeting of candidalysin to host cells by inducing the formation of an endocytic vacuole (the “invasion pocket”) in which candidalysin accumulates (Swidergall et al, 2021).…”

Trans-cellular tunnels induced by the fungal pathogen Candida albicans facilitate invasion through successive epithelial cells without host damage

“…As CaTCT occurs without direct contact between invading hyphae and the host cytosol (with the exclusion of the inflation-glycogen store interface) and without host damage, from an immunological standpoint, CaTCT may be perceived by host cells as an entirely extracellular process. Thus, both innate immune recognition of C.a pathogen-associated molecular patterns (PAMPs) and the activation of epithelial damage-associated molecular patterns (DAMPs) may be similar to those triggered by non-invading adherent C.a hyphae (Cohen-Kedar et al, 2014;Altmeier et al, 2016;d'Enfert et al, 2021;Swidergall et al, 2021). This hypothesis is supported by a study showing that C.a infection of Caco-2 produces only low levels of both host cellular stress responses and proinflammatory cytokines during the first hours of infection (Böhringer et al, 2016).…”

“…How C.a intracellular invasion can proceed without damaging host cells is currently not well understood (Westman, Hube and Fairn, 2019). While hyphal extension and the resulting invagination of the host plasma membrane into the so-called 'invasion pocket' can account for at least a portion of intracellular invasion, further hyphal extension within the host, and even more so into neighbouring host cells, is expected to lead to eventual host membrane breaching and damage due to Lachat et al 2021 3 increased membrane stretching (Mogavero et al, 2021;Swidergall et al, 2021). Current models hypothesize the presence of a non-damaging intracellular invasion route, though the mechanism underlying such a route has not been described (Allert et al, 2018;Basmaciyan et al, 2019).…”

A variant ECE1 allele contributes to reduced pathogenicity of Candida albicans during vulvovaginal candidiasis

“…Given results obtained from our isogenic strain construction approach, it was initially surprising to find that cytokine and damage biomarkers from vaginal epithelial cells did not differ between treatment with WT or variant candidalysin peptide. While candidalysin has been recently shown to accumulate in the "invasion pocket" during hyphal invasion of oral epithelium, the actual quantity of candidalysin released into the external environment or locally is not currently known [13,34]. Therefore, we cannot rule out the possibility that potentially supraphysiologic concentrations of these candidalysins used in cell culture assays may not show differential activity, but the distinction could become more obvious at natural levels released by C. albicans during infection.…”