Cyclic AMP signalling pathway and trehalase activation in the fission yeast Schizosaccharomyces pombe

Abstract

The response of derepressed cells of Schizosaccharomyces pombe to the addition of glucose included a marked and reversible activation of neutral trehalase that was not produced in repressed cells. The protein synthesis inhibitor cycloheximide, the protonophore 2,4dinitrophenol or the uncoupler sodium azide also enhanced trehalase activity in derepressed cells provided glucose was present in the incubation assays. However, only 2,4=dinitrophenol or cycloheximide was able to induce trehalase activation in repressed cells. Stimulation of trehalase by these compounds was preceded in all cases by a rapid increase in adenosine 3'-5'-cyclic monophosphate (CAMP) content. Since exogenous CAMP can activate trehalase both in repressed and derepressed growing cells, the results provide evidence for the existence of an induced CAMP signalling pathway in the fission yeast with several entries for trehalase activation. The correlation between CAMP increase and trehalase activation was not maintained when the enzyme was heat-shock-activated, supporting the concept that trehalase activity can be also enhanced in cells by another mechanism in which CAMP does not act as second messenger.

Activation of neutral trehalase by glucose and nitrogen source in Schizosaccharomyces pombe strains deficient in cAMP‐dependent protein kinase activity

“…The cells were pulsed then for 40 min with 10 mM asparagine and cell extracts obtained. Enzyme samples were treated as described in section 2. repressed in glucose-grown PKA 1 cells [4,11]. Such explanation is consistent with the notion that the expression of a whole set of genes, whose transcription is under regulatory control by the cAMP-PKA pathway, is allowed in the absence of PKA function.…”

“…Since nitrogen sources alone fail to induce trehalase activation in Schiz. pombe, but they increase the activity of the enzyme in the presence of glucose [4], we analysed the effect of nitrogen source by adding 10 mM asparagine to cells suspended in buffer after a previous activation by glucose in the presence of remaining sugar (20-35 mM). A clear nitrogen-source-induced activation of trehalase was thus found in both growing and resting derepressed cells (Fig.…”

“…Before and after addition of glucose or nitrogen-source as inducers of trehalase activation samples were removed at timed intervals and the cells washed as above in the cold. Cell-free extracts were obtained, centrifuged and analysed for trehalase and protein as previously described [11]. Specific activity of trehalase is expressed as nmol glucose liberated rain i mg protein -~ .…”

“…Specific activity of trehalase is expressed as nmol glucose liberated rain i mg protein -~ . Fructose-1,6-bisphosphatase activity was assayed spectrophotometrically as indicated in [12] except that imidazole buffer was replaced by 10 mM MES/KOH at pH 7. cAMP was determined as previously indicated [11].…”

“…Glucose and nitrogen sources are also able to trigger activation of trehalase in the fission yeast Schizosaccharomyces pombe [4], an organism which has diverged markedly from the budding yeast S. cerevisiae [5]. Schiz.…”