PKC Signaling Regulates Drug Resistance of the Fungal Pathogen Candida albicans via Circuitry Comprised of Mkc1, Calcineurin, and Hsp90
Figure 1
Pharmacological inhibition of PKC signaling enhances the efficacy of antifungal drugs targeting the cell membrane.
(A) A drug screen identifies compounds that abrogate fluconazole (FL) resistance of a Candida albicans clinical isolate (CaCi-2). Seven compounds from the LOPAC1280 Navigator library had little toxicity on their own but enhanced the efficacy of FL against CaCi-2 when tested at 12.5 µM in RPMI medium with 2% glucose in the presence or absence of 8 µg/ml FL. Growth was measured by absorbance at 600 nm after 48 hours at 30°C. Optical densities were averaged for duplicate measurements and normalized relative to the no compound control (-) or FL-only control. Data was quantitatively displayed with colour using Treeview (see colour bar). The target or mode of action of each compound is indicated in blue. 1CAT = choline acetyltransferase; 2JAK3 = Janus kinase family protein; and 3KDO-8-P = 3-deoxy-D-manno-2-octulosonate-8-phosphate. (B) Pharmacological inhibition of Pkc1 with cercosporamide abrogates azole resistance and reduces echinocandin tolerance of CaCi-2 in an MIC assay. Assays were done in yeast peptone dextrose (YPD) with a fixed concentration of 2 µg/ml micafungin (MF) or 8 µg/ml FL, as indicated. Data was analyzed after 48 hours at 30°C as in part A. (C) Pkc1 inhibitors confer increased sensitivity to other ergosterol biosynthesis inhibitors. A fixed concentration of CaCi-2 cells was incubated in YPD with no antifungal (-), 2 µg/ml MF, 8 µg/ml FL, 2.5 µg/ml fenpropimorph (FN), or 2 µg/ml terbinafine (TB) and with the PKC inhibitors cercosporamide (100 µg/ml) or staurosporine (37.5 ng/ml), as indicated. Data was analyzed after 48 hours at 30°C as in part A.