GLUCOSE-INDUCED, CYCLIC-AMP-INDEPENDENT SIGNALING PATHWAY FOR ACTIVATION OF NEUTRAL TREHALASE IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

The addition of glucose to derepressed cells of Schizosaccharomyces po mbe provokes a cAMP signal and activation of the cytoplasmic neutral t rehalase. This transduction pathway does not require functional RAS pr otein since RAS1-disrupted cells exhibited a glucose response similar to that shown by control cells. Treatment of activated trehalase by al kaline phosphatase resulted in enzyme deactivation suggesting that tre halase may be modulated in vivo by reversible phosphorylation through cAMP-dependent protein kinase (PKA1). However, the addition of glucose to derepressed growing cells of Schiz. pombe lacking the catalytic su bunit of protein kinase A (Delta pka1::URA4(+) strains) induced stimul ation of trehalase as well as phosphorylation of the enzyme protein. T his glucose-induced response was absent in PKA1-deficient cells from r esting cultures. Addition of exogenous cAMP activated trehalase in nor mal growing cells but failed to produce any effect on trehalase in PKA 1-disrupted growing cells. These results confirm the occurrence of a P KA1-dependent pathway for trehalase activation and imply the existence of another glucose-induced phosphorylation pathway capable of activat ing trehalase during growth by a distinct, cAMP-independent protein ki nase. At least one of the upstream components playing a role in the tr ansduction of this alternative signal is either absent or inactive in cells from stationary phase and sporulated cultures. Cells harbouring the disrupted PKA1 gene responded also to a heat-shock signal by incre asing trehalase activity, thus revealing that this enzyme may be a tar get common to various signalling pathways in the fission yeast.