Vcx1 and ESCRT components regulate intracellular pH homeostasis in the response of yeast cells to calcium stress

Endosomal sorting complexes required for transport (ESCRTs) are involved in the formation of multivesicular bodies and sorting of targeted proteins to the yeast vacuole. The deletion of seven genes encoding components of the ESCRT machinery render Saccharomyces cerevisiae cells sensitive to high extracellular CaCl2 concentrations as well as to low pH in media. In this work, we focused on intracellular pH (pH(in)) homeostasis of these mutants. None of the studied ESCRT mutants exhibited an altered pH(in) level compared to the wild type under standard growth conditions. Nevertheless, 60 min of CaCl2 treatment resulted in a more significant drop in pH(in) levels in these mutants than in the wild type, suggesting that pH(in) homeostasis is affected in ESCRT mutants upon the addition of calcium. Similarly, CaCl2 treatment caused a bigger pH(in) decrease in cells lacking the vacuolar Ca2+/H+ antiporter Vcx1 which indicates a role for this protein in the maintenance of proper pH(in) homeostasis when cells need to cope with a high CaCl2 concentration in media. Importantly, ESCRT gene deletions in the vcx1 Delta strain did not result in an increase in the CaCl2-invoked drop in the pH(in) levels of cells, which demonstrates a genetic interaction between VCX1 and studied ESCRT genes.