Two Pathways Diverge: Glycerophosphocholine Impacts Both Phosphate and Lipid Metabolism in Candida albicans

Candida albicans (C. albicans)is a leading source of fungal infections in humans, resulting in over 250,000 deaths annually. C. albicanscolonizes multiple host niches and causes invasive disease, requiring its adaptation to wide variations in nutrient availability. Phosphate is an essential nutrient, and several genes associated with phosphate acquisition are differentially expressed during infection. In addition to inorganic phosphate (Pi ), C. albicans utilizes the abundant lipid metabolite, glycerophosphocholine (GPC), as a phosphate source. GPC is transported into the cell via the Git3 and Git4 transporters. The Git transporters are required for full virulence in a mouse model of disseminated candidiasis, but the mechanism for that virulence defect is unknown. Here, we probe the importance of GPC uptake to cellular metabolism by examining two aspects of its metabolic fate: i) its catabolism to liberate Pi ), and ii) its potential conversion to phosphatidylcholine (PC) via reacylation. To query its role in phosphate homeostasis, we employed a knockout strain of the high affinity phosphate transporter, Pho84. Cells lacking Pho84 display sensitivity to several host-related stressors and decreased virulence. Our results show that provision of cells with GPC as phosphate source alleviates hypersensitivity of pho84∆/∆ mutants to osmotic, oxidative, and cell wall stress. The rate at which GPC and Pi are transported into the cell varies depending upon the total level of phosphate provided, with Pi transport exceeding GPC transport by a maximum of two-fold at 500 µM total phosphate. The effect of exogenous GPC on induction of the PHO regulon, the cellular system of phosphate homeostasis, is complex and concentration dependent. Beyond its role in phosphate metabolism, GPC has other physiologically relevant metabolic fates, namely its reacylation to form a phosphatidylcholine (PC) molecule. In Saccharomyces cerevisiae, the first step of this novel reacylation pathway is catalyzed by the acyltransferase, Gpc1, which converts GPC to lyso-PC. Initial in vivo labeling studies under phosphate replete conditions indicate that the C. albicans homolog of Gpc1 is a GPC acyltransferase and that the reacylation pathway is functional in C. albicans. In vitro assays in strains lacking or containing Gpc1 are underway. Taken together, our results indicate that C. albicans can utilize the abundant lipid metabolite, GPC, via at least two metabolic pathways to promote its growth and survival in the human host.