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

Marc Swidergall,Aaron P Mitchell,Quynh T Phan,Michael R Yeaman,Zeping Wang,Jianfeng Lin,Michael D Lazarus,Scott G Filler,Norma V Solis,Manning Y Huang,Nicolas Millet

doi:10.1371/journal.ppat.1009221

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.

Highlights

Oropharyngeal candidiasis is characterized by superficial fungal invasion of the oral mucosa, epithelial cell death, and leukocyte recruitment to the focus of infection [1]
Two C. albicans virulence factors contribute to the pathogenesis of oropharyngeal candidiasis (OPC), Als3 which enables the organism to adhere to and invade host cells, and candidalysin which is a pore-forming toxin that damages host cells
Exposure of oral epithelial cells to purified β-glucan induces only transient ephrin type-A receptor 2 (EphA2) phosphorylation, does not activate epidermal growth factor receptor (EGFR), and is insufficient to induce a significant inflammatory response [10,15]. These results suggest that stimulation of a proinflammatory response in epithelial cells requires the sustained activation of EphA2 and/or activation of a second epithelial cell receptor such as EGFR

Summary

Introduction

Oropharyngeal candidiasis is characterized by superficial fungal invasion of the oral mucosa, epithelial cell death, and leukocyte recruitment to the focus of infection [1]. In addition to producing host defense peptides that have direct antifungal activity, oral epithelial cells secrete alarmins, proinflammatory cytokines, and chemokines that recruit phagocytes to foci of infection and enhance their candidacidal activity to limit the growth of the invading fungus [8,9,10]. This epithelial cell response is amplified by interleukin (IL)-17, which is secreted by γδ T cells, innate TCRαβ+ cells, and type-3 innate lymphoid cells [11,12,13]

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