Nutrient-induced activation of trehalase in nutrient-starved cells of the yeast Saccharomyces cerevisiae: cAMP is not involved as second messenger

Abstract

Starvation of Saccharomyces cerevisiae cells for spec& nutrients such as nitrogen, phosphate or sulphate causes arrest in the GI phase of the cell cycle at a specific point called 'start'. Re-addition of different nitrogen sources, phosphate or sulphate to such starved cells causes activation of trehalase within a few minutes. Nitrogen-sourceand sulphate-induced activation of trehalase were not associated with any change in the cAMP level, but in the case of phosphate there was a small transient increase. When nitrogen-source-activated trehalase was isolated by immuno-affinity chromatography from crude extracts, the puridied enzyme showed the same activity profile as in the original crude extracts, indicating that post-translational modification is responsible for the activation. In the yeast mutants cdc25-5 and cdc35-10, which are temperature sensitive for cAMP synthesis, incubation at the restrictive temperature lowered but did not prevent nitrogen-, phosphate-or sulphate-induced activation of trehalase. Since under these conditions the cAMP level in the cells is very low, it is unlikely that cAMP acts as a second messenger in this nutrient-induced effect. Nitrogen-source-induced activation of trehalase requires the presence of glucose at a concentration similar to that able to stimulate the RAS-adenylate cyclase pathway. This indicates that the same glucose-sensing system might be involved in both phenomena. Nitrogen-starved cells fractionated according to cell size all showed nitrogen-source-induced activation of trehalase to the same extent, indicating that the nitrogen-induced signalling pathway involved is not dependent on the well-known cell size requirement for progression over the start point of the cell cycle.

The lag phase rather than the exponential-growth phase on glucose is associated with a higher cAMP level in wild-type and cAPK-attenuated strains of the yeast Saccharomyces cerevisiae

“…We have called this pathway the ' Fermentable-growth-medium-induced pathway' (Thevelein, 1991. This suggestion was based on the glucose-repressible character of glucose-induced activation of cAMP synthesis (Argiielles et al, 1990;Beullens et al, 1988;Dumortier et al, 1995), the observation that other nutrients in the presence of glucose can trigger activation of trehalase without effect on cAMP (Hirimburegama et al, 1992) and by the demonstration that several targets of cAPK are still regulated during diauxic growth in strains lacking the regulatory subunit of cAPK (Belazzi et al, 1991;Cameron et al, 1988;Durnez et al, 1994).…”

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

“…Congruent with the presumed function of PKA in resting cells, and lending support to a possible role of cAMP as second messenger in the nitrogensource-induced signaling pathway for trehalase activation, the addition of asparagine to these cells causes a transient cAMP signal that is even more pronounced than that triggered by glucose (3-fold vs. 12-fold increase above a basal level of 250 pmol cAMP.g wet weight-I). A similar nitrogen-induced cAMP signal has never been seen in S. cerevisiae [2]. Therefore, in resting PKA1 cells of the fission yeast, the mechanism causing trehalase activation by nitrogen sources could be somewhat similar to that occuring after glucose addition, i.e.…”

“…The activation of trehalase by glucose and nitrogen source in cells of Schiz. pombe devoid of PKA indicates that the mechanisms underlying these stimulations do not fit entirely the models previously propossed for the increase in trehalase induced by the same sources in S. cerevisiae [1][2][3]. Although the action of a kinase different to PKA has to be assumed to account for the induced activations in PKAl-disrupted cells, this observation does not invalidate previous findings on the existence of a glucose-induced cAMP-PKA-mediated phosphorylation pathway causing trehalase activation in this yeast [4,11].…”

“…This stimulation of trehalase appears to be due to phosphorylation of the enzyme protein but, contrariwise to the glucose-induced activation of trehalase, is not associated with changes in the cAMP level [2]. A model has been suggested for this yeast in which nitrogen sources activate trehalase by means of a novel signaling pathway which includes direct stimulation of free catalytic subunits of cAMP-dependent protein kinase (cAPK, protein kinase A or PKA) without any role of cAMP as second messenger [3].…”

Stability of neutral trehalase during heat stress in Saccharomyces cerevisiae is dependent on the activity of the catalytic subunits of cAMP‐dependent protein kinase, Tpk1 and Tpk2

“…The stabilization of neutral trehalase during heat stress mediated by Tpk1p and Tpk2p may be different from the known post-translational regulation of neutral trehalase by cAPK-dependent phosphorylation, such as activation by nutrients and cAMP [15,16]. Two consensus cAPK phosphorylation sites [RRX(SorT)] [45] have been found at the N-terminal region of the sequence predicted for Nth1p [22,27].…”