Regulation of phosphatidylinositol-(4,5)-bisphosphate and active-Rho1p levels and distribution is crucial for correct spatio-temporal cytokinesis and echinocandin responses in Candida albicans.

Abstract

Candida species cause severe infections like invasive candidiasis, which annually affects 1.5 million people worldwide and causes close to 1 million deaths. Candida albicans is the predominant cause of candidiasis. We previously showed that Eps15-Homology domain-containing protein Irs4p binds 5-phosphatase enzyme Inp51p to regulate plasma membrane levels of phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P₂) in C. albicans. Indeed, deletion of IRS4 or INP51 led to elevated levels of PI(4,5)P₂ and the presence of abnormal intracellular membranous PI(4,5)P₂ patches. We demonstrated an interplay between PI(4,5)P₂ and septins to regulate the PKC-Mkc1 cell wall integrity pathway, echinocandin and cell wall stress responses, and virulence during candidiasis. To gain insights into the nature of these abnormal patches, we used fluorescent protein tagging and live-cell imaging to follow their nascency. We show that these abnormal patches tightly correlate with cytokinesis, as they predominantly arise close to the site and time of cell division. We further demonstrate that these patches colocalize PI(4,5)P₂ with actomyosin ring components Act1p and Myo1p, which form its core, and active Rho1p, a small GTPase that plays a regulatory role. Additionally, activation of Rho1p was altered in irs4 and inp51 mutants compared to wild-type strain, with over-activation or down-activation during early exponential or stationary phase, respectively. Wild-type cells exposed to 4× MIC of the echinocandin caspofungin show abnormal PI(4,5)P₂ patches that colocalize with the same cytokinesis components as above, except that they are transient. Taken together, our results support a model in which PI(4,5)P₂ plays a pivotal role, along with Rho1p, in the correct execution of cytokinesis and response to caspofungin.