Regulatory Mechanisms Of CaRch1 On Cytosolic Calcium Homeostasis And Drug Tolerance In Candida Albicans

Candida albicans is an important human opportunistic fungal pathogen, and its cytosolic calcium homeostasis plays a role in its durg tolerance, hyphal development and virulence in a mouse systemic model. Our previous study shows that the plasma membrane protein Ca Rch1 is a novel regulator of calcium homeostasis in C. albicans. Deletion of Ca RCH1 leads to increased calcium uptake, increased cytosolic calcium concentration and activation of calcium/calcineurin signaling, which causes a calcium hypersensitivity of C. albicans cells. The high-affinity calcium influx system(HACS; also called calcium channel) consisted of Ca Cch1, Ca Mid1 and Ca Ecm7 controls calcium influx into the cell in response to depletion of extracellular calcium or environmental stimuli. Previous studies from other laboratories demonstrate that lack of each of the HACS components reduces calcium uptake and leads to a sensitivtyof C. albicans cells to both antifungal drugs and oxidative stress as well as defects in hyphal development and reduced virulence in a mouse systemic model. In this study, we show that cells lacking Ca CCH1 and Ca MID1, but not Ca ECM7, are sensitive to tunicamycin. Cells lacking Ca RCH1 are sensitive to tunicamycin. Deletion of Ca RCH1 increases the tunicamycin sensitivity of cells lacking Ca ECM7 or Ca MID1, but not Ca CCH1. In addition, deletion of each HACS component suppresses the calcium hypersensitivity of, and the elevated activation level of calcium/calcineurin signaling in, C. albicans cells lacking Ca RCH1. Ca RCH1 is epistatic to the HACS system in the tolerance of antifungal drugs. In addition, cells lacking Ca RCH1 show a delay in in vitro filamentation and attenuated virulence in the mouse systemic model. Furthermore, deletion of Ca RCH1 suppresses the defect in hyphal development due to the deletion of Ca CCH1 or Ca ECM7, and increases the virulence of cells lacking any of the HACS components. Therefore, Ca Rch1 and the HACS system regulate the calcium homeostasis negatively and positively, respectively, and thereby affect the calcium sensitivity, durg tolerance, hyphal development and virulence of C. albicans cells. A previous study shows that the ER/Golgi calcium pump Ca Pmr1 is required for cell wall maintenance and virulence. We show here that deletion of Ca RCH1 increases the calcium hypersensitivity of, and the elevated activation level of calcium/calcineurin signaling in, C. albicans cells lacking Ca PMR1. Disruption of Ca RCH1 alone results in reduced chitin levels. Further deletion of Ca RCH1 leads to decreased chitin and mannan contents and worsens the filamentation defect of C. albicans cells lacking Ca PMR1. Therefore, Ca Rch1 genetically interacts with Ca Pmr1 in the regulation of calcium homeostasis, stress response, cell wall integrity and hyphal development.