Retrograde signaling disruption influences ABC superfamily transporter, ergosterol and chitin levels along with biofilm formation in Candida albicans

Abstract

Objective: The rise in fungal infections is alarming due to emergence of multidrug drug resistance (MDR). Hence elucidating novel drug targets to circumvent the problem of MDR warrants immediate attention. This study analyzes the effect of retrograde (RTG) signaling disruption on major MDR mechanisms and virulence of the human pathogenic fungal species Candida albicans. Material and methods: Drug transporter activity was measured by rhodamine 6G (R6G) efflux. Membrane damage was studied by propidium iodide intake and ergosterol level determination. Cell wall effect was estimated by quantifying chitin levels and cell sedimentation rate. Biofilm formation was visualized by calcoflour white and crystal violet staining and measured by dry mass and MTT assay. Cell adherence to buccal epithelial cell was determined by trypan blue staining and MTT assay. Virulence was studied using nematode model Caenorhabditis elegans. Result: We demonstrated that mutant of transcription factor CaRTG3 leads to impaired efflux activity of ATP Binding Cassette (ABC) superfamily multidrug transporters. We further uncover that rtg3 mutant exhibited a disrupted membrane, decreased ergosterol levels and increased chitin content. Furthermore, RTG signaling disruption leads to inhibited biofilm formation and cell adherence to buccal epithelial cells. Lastly, rtg3 mutant displayed a reduced infectivity in C. elegans illustrating its vulnerability as antifungal target. Interestingly, all the abrogated phenotypes could be rescued in the revertant strain of rtg3 mutant. Conclusion: Present study establishes a link between RTG signaling, drug efflux and biofilm formation and validates CaRTG3 as antifungal target. Intricate studies are needed to further understand and exploit this therapeutic opportunity.