CALCINEURIN INHIBITS VCX1-DEPENDENT H+ CA2+ EXCHANGE AND INDUCES CA2+ATPASES IN SACCHAROMYCES-CEREVISIAE/

The PMC1 gene in Saccharomyces cerevisiae encodes a vacuolar Ca2+ ATPa se required for growth in high-Ca2+ conditions. Previous work showed t hat Ca2+ tolerance can be restored to pmc1 mutants by inactivation of calcineurin, a Ca2+/calmodulin-dependent protein phosphatase sensitive to the immunosuppressive drug FK506. We now report that calcineurin d ecreases Ca2+ tolerance of pmc1 mutants by inhibiting the function of VCX1, which encodes a vacuolar H+/Ca2+ exchanger related to vertebrate Na+/Ca2+ exchangers. The contribution of VCX1 in Ca2+ tolerance is lo w in strains with a functional calcineurin and is high in strains whic h lack calcineurin activity. In contrast, the contribution of PMC1 to Ca2+ tolerance is augmented by calcineurin activation. Consistent with these positive and negative roles of calcineurin, expression of a vcx 1::lacZ reporter was slightly diminished and a pmc1::lacZ reporter was induced up to 500-fold by processes dependent on calcineurin, calmodu lin, and Ca2+. It is likely that calcineurin inhibits VCX1 function ma inly by posttranslational mechanisms, Activities of VCX1 and PMC1 help to control cytosolic free Ca2+ concentrations because their function can decrease pmc1::lacZ induction by calcineurin, Additional studies w ith reporter genes and mutants indicate that PMR1 and PMR2A, encoding P-type ion pumps required for Mn2+ and Na+ tolerance, may also be indu ced physiologically in response to high-Mn2+. and -Na+ conditions thro ugh calcineurin-dependent mechanisms. In these situations, inhibition of VCX1 function may be important for the production of Ca2+ signals, We propose that elevated cytosolic free Ca2+ concentrations, calmoduli n, and calcineurin regulate at least four ion transporters in S. cerev isiae in response to several environmental conditions.