OSMO-STRESS-INDUCED CHANGES IN NEUTRAL TREHALASE ACTIVITY OF THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

Exposure of repressed growing cultures of Schizosaccharomyces pombe to various extracellular concentrations of NaCl, sorbitol or glycerol re sulted in a reversible increase in neutral trehalase activity which wa s maintained while the cells were in the presence of high environmenta l osmolarity. Treatment of osmo-stress-induced trehalase by phosphatas e lead to a decreased activity indicating that the active enzyme is ph osphorylated. The stress response following the osmotic shock required protein synthesis and was independent of the cAMP-dependent protein k inase pathway. Cells disrupted for wis1 or phh1 (identical to sty1 and spell, which encode members of the mitogen-activated protein kinase ( MAPK) cascade, showed that the osmo-stress-induced increase in trehala se markedly diminished. In contrast, the heat shock-induced increase i n trehalase remained unchanged in these cells. Taken together, the dat a suggest that the elevation of trehalase activity in Schiz. pombe und er conditions of high osmolarity is due to de novo synthesis of the en zyme and that this process is modulated through a MAPK signal transduc tion pathway as part of the physiological response to the osmotic stre ss. The wis1-phh1 MAPK cascade, however, does not appear to form part of the mechanism underlaying the increase in trehalase after heat stre ss. (C) 1997 Elsevier Science B.V.