Signal flow between CWI/TOR and CWI/RAS in budding yeast under conditions of oxidative stress and glucose starvation

Abstract

The CWI pathway cross-talks with TOR and RAS in both the oxidative and glucose starvation responses. Mtl1 is the cell-wall protein in charge of sensing and regulating this response. Rom2 and Rho1, which are the upper elements in the pathway, mediate this signal. Several outputs are involved and required for this response, one of which, ribosomal gene expression, seems to be regulated by Sfp1, amongst other possible transcription factors. Moreover, cross-talk also occurs in a reverse flow from TOR and RAS to the CWI pathway. Thus Tor1 and Ras2 inhibition also activates Slt2 in the absence of the Mtl1 protein and assures the proper adaptive response to oxidation and glucose deprivation.

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Acknowledgements

This work was supported by Ministerio de Educacion y Ciencia (Spanish Government) Grant BFU2009-11215. N.P. was founded by a contract associated to the former Grant. M.I.P was supported by a fellowship from the Generalitat de Catalunya (Spain).

Figures and Tables

Figure 1 Sfp1 overexpression is toxic in the absence of Mtl1 when cells are exposed to hydrogen peroxide treatment. (A) Serial dilutions of wt, mtl1, wt⁺pSfp1, mt1l⁺pSfp1 were plated onto SD plates containing or not containing hydrogen peroxide 1 mM. Sfp1 was cloned in pUG35 plasmid containing the URA3 gene. Sfp1 ORF is under the MET25 promoter in this plasmid. (B) A temptative model depicting the possible interactions between Mtl1, TOR1, RAS2 and Sfp1.

Figure 2 The simultaneous absence of Mtl1-Tor1 and Mtl1-Ras2 induces Slt2 phosphorylation in response to hydrogen peroxide treatment and in response to glucose depletion. (A) western blot analysis of Slt2 activity using the p44/42 polyclonal antibody in samples from wt, mtl1, mtl1ras2 and mtl1tor1 growing exponentially and treated with 1 mM hydrogen peroxide for the indicated times. (B) The same as in (A) but the strains were exponentially grown in SD, washed four times with minimum medium without glucose, and then transferred to SD minus glucose for incubation at 25°C. Samples were collected at the indicated times for western blot analysis. Anti-GSTSlt2 antibody was used to detect total Slt2 protein; this was equivalent in all the samples taken in the experiment (not shown for simplification).

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