PKA AND HOG1 ROLE IN GENE EXPRESSION AND CELL SURVIVAL IN RESPONSE TO OSMOSTRESS IN SACCHAROMYCES CEREVISIAE

OJEDA L; DUNAYEVICH P; ROSSI S ; COLMAN LERNER A; PORTELA P

Salta

Congreso; Reunión Anual de SAIB-PABMB 2019; 2019

SAIB-PABMB

The stress-adaptation response involves several signalling pathways that couple (combine) stimuli to coordinate responses ensuring cellular homeostasis. We focus on crosstalk between HOG1-MAPK and cAMP-PKA pathways in osmostress cellular responses. We compared the growth rate, glucose consumption rate and CLS (chronological lifespan) under osmotic stress of the hog1∆tpk2∆ and hog1∆tpk1∆ double mutant strains with WT and single mutant hog1∆, tpk2∆ and tpk1∆. The hog1∆ strain shows growth defects, reduced efficiency -of glucose metabolism and reduced CLS under osmotic stress. The hog1∆tpk2∆ double mutant -shows an improved duplication time similar to WT cells when compared to hog1∆ and hog1∆ tpk1∆. However, the hog1∆ tpk2∆ double mutant strain shows a maximum growth level similar to hog1∆, hog1∆ tpk1∆ under osmotic stress conditions that was about 50% less than WT strain. The hog1∆ tpk2∆ double mutant improved the glucose consumption rate and CLS compared to hog1∆ strain. These results indicate that TPK2 deletion improves the stress tolerance of hog1 mutant strain. An increase in external osmolarity causes loss of turgor pressure and cell volume due to water efflux, which triggers a homeostatic response activated by the HOG pathway .Consequently there are a glycerol accumulation and cell volume recovery during osmostress-adaptation. HOG pathway activation requires a transient phosphorylation of the activation loop and the subsequent nuclear accumulation of Hog1. In the nucleus Hog1 controls the expression of several stress-response genes. Neither the levels of Hog1 activation loop phosphorylation, nor Hog1 nuclear accumulation, nor cell volume recovery are affected in TPK2 mutant strain during osmotic stress. Using a transcriptional reporter of Hog1 activation, we found that, unlike to the WT strain, there was no transcriptional induction in hog1∆ and hog1∆tpk2∆ strains upon osmotic stress indicating that osmostress-dependent activation of HOG-MAPK pathway is independent of PKA. The in vivo kinetic recruitment of Hog1 to the STL1 (an osmostress-activated gene) promoter was slightly affected in strains lacking Tpk2. Then, we analyzed the Hog1 contribution on gene expression of two osmostress genes HSP42 and RPS29B that were previously described as target of PKA binding. Analysis of the transcriptional Time curse was performed in WT, hog1Δ, tpk2Δ, tpk2Δ hog1Δ strains. Our results suggest that the adaptive response to transient stress could be regulated by opposite roles of Hog1 and PKA. Tpk2 recruitment on HSP42 and RPS29B promoters (?) was also assessed in response to osmotic stress. Tpk2 binding was affected in cells lacking Hog1, suggesting a crosstalk between the chromatin recruitment of Tpk2 and Hog1. Altogether, our results suggest that both Tpk2 and Hog1 are key regulators in osmostress adaptation, that could act in parallel in order to perform opposite roles in this stress response.