Protein phosphatase type 2B (calcineurin)-mediated, FK506-sensitive regulation of intracellular ions in yeast is an important determinant for adaptation to high salt stress conditions.

Abstract

To assess the physiological function of Ca(2+)‐dependent protein phosphatase (PP2B) in the yeast Saccharomyces cerevisiae, the phenotypes of PP2B‐deficient mutants were investigated. Although PP2B was dispensable for growth under normal conditions, the mutations did, however, cause growth inhibition under certain stress circumstances. The growth of the mutants was inhibited by NaCl and LiCl, but not by KCl, CaCl2, MgCl2 or nonspecific osmotic stresses. Upon shift to high NaCl medium, intracellular Na+ levels of both wild type yeast and the mutants initially increased at a comparable rate. However, internal Na+ in wild type cells started to decline more rapidly than the mutant cells during cultivation in high NaCl medium, indicating that PP2B is important in maintaining a gradient across the membrane. The protection against salt stress was achieved, at least in part, by the stimulation of Na+ export. The maintenance of a high level of internal K+ in high NaCl medium was also PP2B‐dependent. In the presence of the immunosuppressant FK506, the growth behaviour and intracellular Na+ and K+ of wild type cells in high NaCl medium became very similar to those of the PP2B‐deficient mutant in a manner dependent on the presence of the FK506 binding protein.

Characterization of the Calcium-mediated Response to Alkaline Stress in Saccharomyces cerevisiae

“…Activated calcineurin dephosphorylates and activates the transcriptional factor Crz1/Tcn1 (10, 11), which enters the nucleus (12) and, in turn, activates a set of responsive genes by binding to calcineurin-dependent responsive elements (CDRE) 1 (10, 13). It has been documented that most of the transcriptional responses driven by activation of calcineurin are mediated by Crz1/Tcn1 (13).Recent evidence from our laboratory (14) supports early data (15,16) showing that calcineurin might be involved in the tolerance to alkaline pH. We showed (14) that a significant part of the alkaline response of the ENA1 promoter, and most of the PHO89 response, was blocked by the calcineurin inhibitor FK506 as well as by the absence of Cnb1 or Crz1/Tcn1, suggesting that the transcriptional response of certain genes to alkalinization of the medium could be, at least in part, dependent on calcineurin.…”

Evidence for Antagonistic Regulation of Cell Growth by the Calcineurin and High Osmolarity Glycerol Pathways in Saccharomyces cerevisiae

“…Calcineurin, essential only under specific environmental conditions, is an important mediator of the Ca 2ϩ signal. Calcineurin is required for the recovery from the G 1 arrest induced by mating pheromones and for homeostasis of ions, including Na ϩ /Li ϩ , Mn 2ϩ , and OH Ϫ (13)(14)(15)(16). Calcineurin regulates the expression of ion transporter genes by a mechanism mediated by Crz1, a calcineurin-dependent transcription factor (17,18).…”

An Osmotically Induced Cytosolic Ca2+ Transient Activates Calcineurin Signaling to Mediate Ion Homeostasis and Salt Tolerance of Saccharomyces cerevisiae

“…The Ca 2ϩ /calmodulin-dependent type 2B phosphatase calcineurin is the pivotal intermediate in this signal pathway that mediates cellular Na ϩ , K ϩ , and Ca 2ϩ homeostasis (7,8). Hypersaline stress causes Ca 2ϩ activation of calmodulin, which in turn activates calcineurin (7,8).…”

“…Hypersaline stress causes Ca 2ϩ activation of calmodulin, which in turn activates calcineurin (7,8). Signaling through calcineurin regulates the expression of ENA1/PMR2A, which encodes the P-type ATPase that is primarily responsible for Na ϩ efflux across the plasma membrane, and of PMC1 and PMR1, which encode endomembrane-localized Ca 2ϩ -ATPase pumps.…”