Activation of
Heat shock trnacription factor Hsf1 by Snf1-dependent phosphorylation under
glucose starvation conditions.
Ji-Sook Hahn,
Dennis Thiele
Biological Chemistry, University of Michigan, 1301 Catherine Rd, Ann Arbor, MI
48109, USA (hahnjs@umich.edu)
Heat shock transcription factor (HSF) is an evolutionarily conserved transcriptional regulator that mediates the response of eukaryotic cells to heat shock and other environmental and pathophysiological stresses. We have identified around 150 in vivo targets of Hsf1 in Saccharomyces cerevisiae using microarray combined with immunoprecipitation and anti-Hsf1 antibody. According to the genome-wide expression data, most of the Hsf1 targets are induced by heat shock and about 30% of them are also induced by diauxic shift. We demonstrated that induction of Hsf1 target genes by heat shock and glucose starvation is mediated via different signal transduction pathways and Snf1 kinase is involved in activation of Hsf1 only under glucose starvation conditions. Phosphorylation of Hsf1 was detected in vivo upon glucose starvation in a Snf1-dependent manner. We also showed phosphorylation of Hsf1 by Snf1 in vitro. DNA binding activity of Hsf1, determined by chromatin immunoprecipitation assay, was slightly increased upon glucose starvation especially to the low affinity target promoters such as SSA3 and HSP30. The increase in DNA binding activity of Hsf1 was not observed in a snf1 deletion mutant. Induction of mRNA expression of a subset of Hsf1 targets by glucose starvation was dependent on Snf1 and C terminal activation domain of Hsf1, suggesting the Snf1-dependent phosphorylation of Hsf1 as an activation mechanism of Hsf1 under glucose starvation conditions.