Candida albicans Responds To Caspofungin By Dynamically Regulating A Novel PI(4,5)P2-Septin Cell Wall Integrity Pathway

Ref ID: 19261

Author:

H. Badrane, M. Nguyen, C. Clancy

Author address:

Univ. of Pittsburgh, Pittsburgh, PA

Full conference title:

53rd Interscience Conference on Antimicrobial Agents and Chemotherapy

Date: 10 September 2014

Abstract:

Background: We showed that phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2) regulation by C. albicans Irs4-Inp51 is involved in PKC-MAPK cell wall integrity pathway activation and caspofungin resistance. C. albicans delocalizes PI(4,5)P2 and septins to aberrant plasma membrane sites as part of the natural response to caspofungin. We characterized temporal PI(4,5)P2-septin responses to caspofungin. Methods: We exposed C. albicans SC5314 to caspofungin (0x, 0.25x, 1x and 4xMIC; MIC=0.125 μg/mL), and performed time-lapse, live-cell imaging of PI(4,5)P2 (CaPH-GFP) and septins (Cdc10- and Sep7-RFP; Nikon A1 laser microscope). PKC-MAPK pathway activation was measured by Mkc1 phosphorylation.Results: Five dramatic findings were apparent after imaging cells for two hours. First, the amount of plasma membrane PI(4,5)P2 increased steadily beginning at 30 minutes in all cells after exposure to caspofungin, as measured by CaPH-GFP signal per yeast cell (mean GFP intensity at MIC increased from 100 to 210). Second, aberrant accumulations and co-localization of PI(4,5)P2 and septins occurred in a subpopulation of cells (~50% at the MIC), in which foci assembled and disassembled at multiple plasma membrane sites throughout the imaging period. The remaining cells had increased PI(4,5)P2 levels without delocalization. Third, PI(4,5)P2-septin effects were caspofungin dose-dependent.
PI(4,5)P2 levels and PI(4,5)P2-septin distributions were
not altered appreciable at caspofungin concentrations
8804;0.25x MIC. At 1x and 4xMIC, however, PI(4,5)P2 levels
and the percentage of cells with PI(4,5)P2-septin
delocalization increased progressively. Fourth, the
percentage of cells with PI(4,5)P2-septin delocalization
corresponded to the percentage of inviable cells at 2 hours.
Fifth, PI(4,5)P2 levels correlated with the level of PKCMAPK
pathway activation. Conclusions: C.
albicans increases PI(4,5)P2 as part of the protective
response to caspofungin, which activates the PKC-MAPK
cell wall integrity pathway. Failure to activate or overactivation
of PI(4,5)P2-septin responses, as
in irs4 and inp51mutants and in response to lethal
caspofungin concentrations, is deleterious. Taken with our
previous data, the findings support a novel PI(4,5)P2-

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Conference Year: 2013

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