The fungal peptide toxin candidalysin induces distinct membrane repair mechanisms compared to bacterial pore-forming toxins

Abstract

The common fungal pathogen, Candida albicans, relies on the pore-forming toxin candidalysin to damage host cells. Cells counteract pore-forming toxins by Ca2+-dependent mechanisms, such as microvesicle shedding and annexin recruitment to resist cholesterol-dependent cytolysins like streptolysin O (SLO), or annexin involvement and patch repair in the case of aerolysin. However, the specific Ca2+-dependent repair pathways engaged in response to candidalysin remain poorly understood. Here, we determined the involvement of different Ca2+-dependent repair mechanisms to candidalysin and compared responses to SLO and aerolysin using flow cytometry and high-resolution microscopy. We report that candidalysin triggered Ca2+-dependent repair, but patch repair and ceramide failed to provide significant protection. MEK-dependent repair and annexins A1, A2 and A6 contributed partially to repairing damage caused by candidalysin. However, annexin translocation after candidalysin challenge was delayed compared to SLO or aerolysin challenge. Surprisingly, extracellular Cl- improved cell survival after candidalysin challenge, but not after challenge with SLO or aerolysin. Finally, we found that candidalysin is removed via extracellular vesicle shedding. These findings reveal that Ca2+-dependent microvesicle shedding protects cells from candidalysin and can be engaged by multiple molecular mechanisms during membrane repair. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/653080v2_figa1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@433b3aorg.highwire.dtl.DTLVardef@1e583f3org.highwire.dtl.DTLVardef@139f086org.highwire.dtl.DTLVardef@de07b0_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Abstract.C_FLOATNO Candidalysin is resisted by distinct repair mechanisms compared to bacterial PFTs.After pore formation and membrane damage by each toxin, multiple repair pathways are triggered downstream of Ca{superscript 2} flux. Candidalysin induces a protective Cl- influx and activates MEK-dependent repair, which contributes to cell protection. Annexin translocation occurs slowly and provides minor protection, while patch repair is ineffective. In contrast, aerolysin does not benefit from Cl- influx or MEK protection. Aerolysin triggers moderate annexin translocation and relies primarily on patch repair as the main protective mechanism. Streptolysin O elicits rapid annexin translocation and activates MEK signaling, both of which contribute to robust protection. Patch repair plays only a minor protective role against SLO. The figure was created using BioRender. C_FIG