Role of the fission yeast cell integrity MAPK pathway in response to glucose limitation

Abstract

BackgroundGlucose is a signaling molecule which regulates multiple events in eukaryotic organisms and the most preferred carbon source in the fission yeast Schizosaccharomyces pombe. The ability of this yeast to grow in the absence of glucose becomes strongly limited due to lack of enzymes of the glyoxylate cycle that support diauxic growth. The stress-activated protein kinase (SAPK) pathway and its effectors, Sty1 MAPK and transcription factor Atf1, play a critical role in the adaptation of fission yeast to grow on alternative non-fermentable carbon sources by inducing the expression of fbp1+ gene, coding for the gluconeogenic enzyme fructose-1,6-bisphosphatase. The cell integrity Pmk1 pathway is another MAPK cascade that regulates various processes in fission yeast, including cell wall construction, cytokinesis, and ionic homeostasis. Pmk1 pathway also becomes strongly activated in response to glucose deprivation but its role during glucose exhaustion and ensuing adaptation to respiratory metabolism is currently unknown.ResultsWe found that Pmk1 activation in the absence of glucose takes place only after complete depletion of this carbon source and that such activation is not related to an endogenous oxidative stress. Notably, Pmk1 MAPK activation relies on de novo protein synthesis, is independent on known upstream activators of the pathway like Rho2 GTPase, and involves PKC ortholog Pck2. Also, the Glucose/cAMP pathway is required operative for full activation of the Pmk1 signaling cascade. Mutants lacking Pmk1 displayed a partial growth defect in respiratory media which was not observed in the presence of glucose. This phenotype was accompanied by a decreased and delayed expression of transcription factor Atf1 and target genes fbp1+ and pyp2+. Intriguingly, the kinetics of Sty1 activation in Pmk1-less cells was clearly altered during growth adaptation to non-fermentable carbon sources.ConclusionsUnknown upstream elements mediate Pck2-dependent signal transduction of glucose withdrawal to the cell integrity MAPK pathway. This signaling cascade reinforces the adaptive response of fission yeast to such nutritional stress by enhancing the activity of the SAPK pathway.

The critical glucose concentration for respiration-independent proliferation of fission yeast, Schizosaccharomyces pombe

“…Specific growth rates were calculated from growth curves. Hatano et al, 2015;Madrid et al, 2013;Hoffman, 2005). Our present study may have close relation to the results of these earlier studies.…”

Multiple regulatory levels influence cell integrity control by PKC ortholog Pck2 in fission yeast

“…S3D), thus supporting the notion that Tor1-dependent regulation of Pck2 levels is likely exerted at a translational level. Cycloheximide pre-treatment suppresses Pmk1 activation during glucose exhaustion (Madrid et al, 2013), implying that progressive MAPK activation under these conditions also requires de novo Pck2 synthesis. Remarkably, in the absence of glucose, the amounts of both total and T842-phosphorylated Pck2 were significantly reduced in tor1D cells, together with decreased Pmk1 activation (Fig.…”

“…However, whereas the Rho2-Pck2 branch is fully responsible for MAPK activation in response to hyper-and hypo-osmotic stress, both Rho1 and Rho2 target Pck2 for signaling cell wall damage to the CIP (Barba et al, 2008;Sánchez-Mir et al, 2014b). In addition, Pmk1 activation under osmotic stress is quick and transient, whereas MAPK activation induced by cell wall stress or glucose deprivation is delayed and progressive (Barba et al, 2008;Madrid et al, 2013), suggesting the existence of specific factors determining the kinetics and magnitude of the response.…”

Multiple crosstalk between TOR and the cell integrity MAPK signaling pathway in fission yeast

“…Its core member, ERK ortholog MAPK Pmk1, is activated by adverse conditions such as hyperosmotic stress, cell wall damage or glucose withdrawal112728. Rho GTPases Rho1 and Rho2 are the main positive regulators of the CIP through Pck2, one of the two orthologs of protein kinase C (PKC) in this organism28.…”