Protein kinase Sck1 is involved in trehalase activation by glucose and nitrogen source in the fission yeast Schizosaccharomyces pombe

Abstract

Summary: Trehalase activity is markedly enhanced upon addition of glucose and a nitrogen source to cells of the fission yeast Schizosaccharomyces pombe. This increase corresponds to a post-translational activation of the enzyme, which is controlled by cAMP-dependent and cAMP-independent pathways. Recent work has shown that overexpression of SCK1 in Schiz. pombe is able to suppress mutations that result in reduced Pka1 (cAMP-dependent protein kinase A activity, suggesting that Sck1 (suppressor of loss of cAMP-dependent protein kinase) might be a functional analogue of Pka1 in the fission yeast. Here, an analysis of the possible role of Sck1 in the activation of trehalase triggered by glucose and a nitrogen source is reported in cells that were deficient in either Pka1, Sck1 or both protein kinases. The results showed that, except in repressed cells, Sck1 probably mediates a cAMP-independent activation of trehalase following the signal(s) triggered by glucose and the nitrogen source. The absence of functional Sck1 in derepressed cells renders trehalase insensitive to activation by glucose and the nitrogen source even in the presence of Pka1, indicating that the Sck1-dependent, cAMP-independent pathway is the main signalling pathway controlling trehalase activation under derepression conditions. It is proposed that, during the activation of trehalase induced by glucose or a nitrogen source, the cAMP-Pka1 activation pathway previously characterized is to some extent parallel to this newly described one which includes Sck1 as ohosphorylating enzyme. Neither of these two pathways, however, plays a key role in the heat-induced increase in trehalase activity.

Enhancement of Neutral Trehalase Activity by Oxidative Stress in the Fission YeastSchizosaccharomyces pombe

“…Several reports have shown that trehalase can be posttranslationally activated in this yeast by enzyme phosphorylation (Soto et al, 1997). Thus, we investigated whether the increase in trehalase induced by oxidative stress could be due, at least in part, to modification of the enzyme protein by phosphorylation.…”

Characterization of tpp1 + as Encoding a Main Trehalose-6P Phosphatase in the Fission Yeast Schizosaccharomyces pombe

“…In the absence of such "extra" phosphatase activity, ⌬tpp1 spores should be phenotypically similar to ⌬tps1 spores (4), i.e., unable to mobilize trehalose and therefore unable to germinate, since neutral trehalase of S. pombe does not recognize trehalose-6P as a substrate (data not shown). Besides, all the known routes for neutral trehalase activation previously described in S. pombe (8,10,24,25,27) were shown to be fully functional in ⌬tpp1 strains, which is clearly different from ⌬tps1 strains, where neutral trehalase is activated only by osmostress (6).…”

“…Thus, basal expression of the genes involved in either synthesis or degradation of trehalose appears to be repressed by Pka1 activity. However, in a double disruptant for Pka1 and Sck1 (a protein kinase that supresses some defects of ⌬pka1 mutants and regulates neutral-trehalase activation under different conditions) (17,25), tpp1 ϩ expression recovered the wild-type basal levels (Fig. 3D).…”

Sck1 Negatively Regulates Gpa2-Mediated Glucose Signaling in Schizosaccharomyces pombe

“…4). Further support for a downstream role in nutrient signaling by Sck1 and its budding yeast homolog Sch9p comes from studies of trehalose mobilization as a function of nitrogen signaling (27,28). The study of Sch9p identified it as a negative regulator of PKA and the likely target of activation by nitrogen via the fermentable-growth-medium induced pathway (27).…”