Truman AW, et al. (2007) In the yeast heat shock response, Hsf1-directed induction of Hsp90 facilitates the activation of the Slt2 (Mpk1) mitogen-activated protein kinase required for cell integrity. Eukaryot Cell 6(4):744-52
Abstract: Yeast is rendered temperature-sensitive with loss of the C-terminal (CT) domain of heat shock transcription factor (Hsf1). This domain loss was found to abrogate heat-stimulation of Slt2(Mpk1), the mitogen-activated protein kinase (MAPK) that directs the reinforced cell integrity gene expression needed for high temperature growth. In Hsf1 CT domain-deficient cells Slt2 still undergoes Mkk1/2-directed dual-Thr/Tyr-phosphorylation in response to the heat stimulation of cell integrity pathway signaling, but the low Hsp90 expression level suppresses any corresponding increase in Slt2 kinase activity, due to Slt2 being a "client" of the Hsp90 chaperone. A non-Hsf1-directed Hsp90 overexpression restored the heat induction of Slt2 activity in these cells, as well as both Slt2-dependent (Rlm1, Swi4) and Slt2-independent (MBF) transcriptional activities. Their high temperature growth was also rescued, not just by this Hsp90 overexpression, but by osmotic stabilization, by the expression of a Slt2-independent form of the Rlm1 transcriptional regulator of cell integrity genes, and by a multicopy SLT2 gene vector. In providing the elevated Hsp90 needed for an efficient activation of Slt2, heat-activation of Hsf1 indirectly facilitates (Slt2-directed) heat-activation of yet another transcription factor (Rlm1). This provides an explanation as to why - in earlier transcript analysis as compared to chromatin immunoprecipitation studies - many more genes of yeast displayed a Hsf1-dependent transcriptional activation by heat than bound Hsf1 directly. The levels of Hsp90 expression affecting transcription factor regulation by Hsp90 client protein kinases also provides a mechanistic model for how heat shock factor can influence the expression of several non-hsp genes in higher organisms.
|Status: Published||Type: Journal Article||PubMed ID: 17293484|
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