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 pombe provokes a cAMP signal and activation of the cytoplasmic neutral trehalase. This transduction pathway does not require functional RAS protein since RAS1-disrupted cells exhibited a glucose response similar to that shown by control cells. Treatment of activated trehalase by alkaline phosphatase resulted in enzyme deactivation suggesting that trehalase 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 subunit of protein kinase A (Delta pka1::URA4(+) strains) induced stimulation of trehalase as well as phosphorylation of the enzyme protein. This glucose-induced response was absent in PKA1-deficient cells from resting cultures. Addition of exogenous cAMP activated trehalase in normal growing cells but failed to produce any effect on trehalase in PKA1-disrupted growing cells. These results confirm the occurrence of a PKA1-dependent pathway for trehalase activation and imply the existence of another glucose-induced phosphorylation pathway capable of activating trehalase during growth by a distinct, cAMP-independent protein kinase. At least one of the upstream components playing a role in the transduction 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 increasing trehalase activity, thus revealing that this enzyme may be a target common to various signalling pathways in the fission yeast.