The Vacuolar Ca²⁺ ATPase Pump Pmc1p Is Required for Candida albicans Pathogenesis

ABSTRACT

Calcium is a critically important secondary messenger of intracellular signal transduction in eukaryotes but must be maintained at low levels in the cytoplasm of resting cells to avoid toxicity. This is achieved by several pumps that actively transport excess cytoplasmic Ca²⁺ out of the cell across the plasma membrane and into other intracellular compartments. In fungi, the vacuole serves as the major storage site for excess Ca²⁺, with two systems actively transporting cytoplasmic calcium ions into the vacuole. The H⁺/Ca²⁺ exchanger, Vcx1p, harnesses the proton-motive force across the vacuolar membrane (generated by the V-ATPase) to drive Ca²⁺ transport, while the P-type ATPase Pmc1p uses ATP hydrolysis to translocate Ca²⁺ into the vacuole. Ca²⁺-dependent signaling is required for the prevalent human fungal pathogen Candida albicans to endure exposure to the azole antifungals and to cause disease within the mammalian host. The purpose of this study was to determine if the Pmc1p or Vcx1p Ca²⁺ pumps are required for C. albicans pathogenicity and if these pumps impact antifungal resistance. Our results indicate that Pmc1p is required by C. albicans to transition from yeast to hyphal growth, to form biofilms in vitro, and to cause disease in a mouse model of disseminated infection. Moreover, loss of Pmc1p function appears to enhance C. albicans azole tolerance in a temperature-dependent manner.

IMPORTANCE Maintenance of Ca²⁺ homeostasis is important for fungal cells to respond to a multitude of stresses, as well as antifungal treatment, and for virulence in animal models. Here, we demonstrate that a P-type ATPase, Pmc1p, is required for Candida albicans to respond to a variety of stresses, affects azole susceptibility, and is required to sustain tissue invasive hyphal growth and to cause disease in a mouse model of disseminated infection. Defining the mechanisms responsible for maintaining proper Ca²⁺ homeostasis in this important human pathogen can ultimately provide opportunities to devise new chemotherapeutic interventions that dysregulate intracellular signaling and induce Ca²⁺ toxicity.