Although the identification of the upstream activator/s of the cell integrity pathway during glucose limitation remains so far elusive, our results indicate that Pck2 is a key element Combretastatin A4 for signal reception and transduction to the Pmk1 cascade under these conditions. This conclusion is consistent with the fact that Pck2 is critical for Pmk1 activation in most of the stresses which activate this signaling pathway [18]. However, the detection of some Pmk1 phosphorylation

in pck2Δ cells suggests that alternative element/s might be able to transduce the activation signal to the MAPK module independently on this particular kinase. Pck1 might be such element, due to the slight defect in MAPK activation observed in pck1Δ cells. However, considering that Pck1 negatively regulates both basal and osmostress-induced Pmk1 activity [18], this would imply that it might be playing either a positive or negative role during signal transmission to the cell integrity pathway depending of the nature of the stressing

stimulus. An interesting finding is the observation that de novo protein synthesis is necessary to allow Pmk1 activation in response to glucose limitation. Importantly, this appears to be a specific requirement, because translational inhibition did not MK0683 purchase preclude MAPK https://www.selleckchem.com/products/DAPT-GSI-IX.html activation in response to other stimuli like osmostress. In attempts to find out the identity of inducible element/s we focussed our attention on the SAPK pathway, whose activity is essential in fission yeast to promote cellular adaptation and growth in the absence of glucose [13]. However, mutant strains lacking either MAPK Sty1 or Atf1 transcription factor displayed strong Pmk1 activation in response to glucose withdrawal, suggesting that the SAPK pathway

does not perform a significant role in this response. On the other hand, the defective Pmk1 phosphorylation shown in strains deleted in key members of the cAMP pathway gives support to the idea that this signaling cascade contributes positively to Pmk1 activation in conditions of glucose deprivation. PAK5 However, this interpretation is difficult to understand taking into account that both intracellular cAMP levels and Pka1 activity decrease dramatically with shortage of glucose [27]. Moreover, Pmk1 activation during glucose deprivation was still evident in cells lacking Rst2, a transcription factor whose activity is repressed by glucose via Pka1 [14]. In absence of glucose, lack of Pka1-dependent phosphorylation promotes Rst2 nuclear entry to activate the transcription of a specific set of genes whose products are involved in cellular adaptation to stress (e.g. ctt1 +) and growth in non-fermentable carbon sources (i.e. fbp1 +) [14].