Novel role for known and unknown calcium transport involved proteins in Saccharomyces cerevisiae

In budding yeast calcium is an important second messenger involved in controlling many fundamental cellular processes. Hypotonic shock in S. cerevisiae triggers a raise in cytosolic Ca2+ that seems to depend both on calcium influx and on calcium release from internal stores. Calcium signal is still present in strains carrying the deletion of all known calcium channels, allowing us to suppose the involvement of still unknown calcium channel. Computational data (JBC 2002 277:31079–88) suggested to consider Yor365c and Yal053w, two putative TRP ion channels. Surprisingly, during the response to hypotonic shock in YPD growing yeast we did not observe the typical calcium induced calcium release that characterize calcium signalling in response to other stresses but we noticed a great sensitivity to calcium and a higher signal in the absence of extracellular calcium, indicating that calcium raise is due to an intracellular calcium release. Our data suggest that yeast response to hypotonic shock is mediated by Mid1 and Yal053w that release calcium from internal stores and by Cch1 that drives the influx of calcium from extracellular environment.