Functional characterization of the CgPGS1 gene reveals a link between mitochondrial phospholipid homeostasis and drug resistance in Candida glabrata

Abstract

Cardiolipin and its precursor phosphatidylglycerol are two anionic phospholipids that are essential for the biogenesis of functional mitochondria. To assess their role in mitochondrial and cellular functions in the pathogenic yeast Candida glabrata, a functional characterization of the CgPGS1 gene encoding the phosphatidylglycerolphosphate synthase has been carried out. Transposon insertion mutation in CgPGS1 resulted in the loss of phosphatidylglycerolphosphate synthase activity and in deficiency of both phosphatidylglycerol and cardiolipin. The Cgpgs1 Delta mutant cells displayed reduced amounts of cytochrome b and cytochrome a, and had impaired growth on minimal media containing non-fermentable carbon and energy sources. They did not grow at elevated temperatures and failed to form colonies after induction of mitochondrial DNA deletions. The mutant cells also displayed a decreased susceptibility to fluconazole, ketoconazole, clotrimazole, voriconazole and posaconazole. In the Cgpgs1 Delta mutant, a quantitative real time PCR revealed enhanced mRNA levels for multidrug resistance associated genes such as CgPDR1 encoding transcriptional activator and CgCDR1, CgPDH1 and CgSNQ2 coding for drug efflux transporters. These results indicate that CgPGS1 and anionic phospholipids are required for optimal mitochondrial functions and maintenance of yeast susceptibility to azole antifungals.

Mitochondria and Fungal Pathogenesis: Drug Tolerance, Virulence, and Potential for Antifungal Therapy

“…In the S. cerevisiae oxa1⌬ mutants, respiratory complexes in the inner membrane are inappropriately assembled (7,43) and the mutants display lower levels of another important phospholipid in mitochondrial membranes, phosphatidylethanolamine (63). In pgs1⌬ mutants of C. glabrata, both phosphatidylglycerol and cardiolipin are absent from mitochondrial membranes (3). Taken together, these data suggest that changes to the structure of mitochondrial membranes could be the trigger for activation of the drug resistance pathway.…”

“…2). Consistently, deletion of the phosphatidylglycerol synthase gene PGS1 leads to cell wall defects in S. cerevisiae and C. glabrata (3,90,91) and to caspofungin sensitivity in S. cerevisiae (76). Moreover, the C. albicans mutants with deletions of the genes for the phospholipid-biosynthetic enzymes phosphatidylserine synthase FIG.…”

“…With antifungal drugs that target cell membranes, such as the azoles and the polyenes, both resistance and sensitivity of mitochondrial mutants have been reported (9,10,18,22,45,75,85,86). In contrast, only sensitivity has been observed with agents that target the cell wall, which includes the echinocandin class of antifungal drugs (3,15,17,22,38,90). A similarly complex picture is observed in regard to virulence of mitochondrial mutants, with both hypo-and hypervirulence of Candida spp.…”

“…Mitochondrial mutants of C. albicans, Candida parapsilosis, and S. cerevisiae are sensitive to the echinocandins (15,17,22,38,76). Mitochondrial dysfunction leads to cell wall defects in C. glabrata (3,10). While sensitivity to the echinocandins has not been tested directly yet, the close relationship between C. glabrata and S. cerevisiae predicts that mitochondria will be required for echinocandin tolerance in C. glabrata also.…”

“…In any case, activation of the drug resistance pathway by deletion of OXA1 appears to be distinct from that which occurs in cells that have lost mtDNA (35,89). Another example is the inactivation of the phosphatidylglycerol synthase gene CgPGS1 in C. glabrata, which is necessary for synthesis of the phospholipids phosphatidylglycerol and cardiolipin in mitochondria (3). pgs1⌬ mutants of S. cerevisiae tend to lose mtDNA (90), but activation of the drug resistance genes of figure).…”