Rapid Redistribution of Phosphatidylinositol-(4,5)-Bisphosphate and Septins during the Candida albicans Response to Caspofungin

Abstract

ABSTRACTWe previously showed that phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] and septin regulation play major roles in maintainingCandida albicanscell wall integrity in response to caspofungin and other stressors. Here, we establish a link between PI(4,5)P2 signaling and septin localization and demonstrate that rapid redistribution of PI(4,5)P2 and septins is part of the natural response ofC. albicansto caspofungin. First, we studied caspofungin-hypersusceptibleC. albicans irs4andinp51mutants, which have elevated PI(4,5)P2 levels due to loss of PI(4,5)P2-specific 5′-phosphatase activity. PI(4,5)P2 accumulated in discrete patches, rather than uniformly, along surfaces of mutants in yeast and filamentous morphologies, as visualized with a green fluorescent protein (GFP)-pleckstrin homology domain. The patches also contained chitin (calcofluor white staining) and cell wall protein Rbt5 (Rbt5-GFP). By transmission electron microscopy, patches corresponded to plasma membrane invaginations that incorporated cell wall material. Fluorescently tagged septins Cdc10 and Sep7 colocalized to these sites, consistent with well-described PI(4,5)P2-septin physical interactions. Based on expression patterns of cell wall damage response genes,irs4andinp51mutants were firmly positioned within a group of caspofungin-hypersusceptible, septin-regulatory protein kinase mutants.irs4andinp51were linked most closely to thegin4mutant by expression profiling, PI(4,5)P2-septin-chitin redistribution and other phenotypes. Finally, sublethal 5-min exposure of wild-typeC. albicansto caspofungin resulted in redistribution of PI(4,5)P2 and septins in a manner similar to those ofirs4,inp51, andgin4mutants. Taken together, our data suggest that theC. albicansIrs4-Inp51 5′-phosphatase complex and Gin4 function upstream of PI(4,5)P2 and septins in a pathway that helps govern responses to caspofungin.