Analysis of the phosphorylation of human heat shock transcription factor-1 by MAP kinase family members

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Abstract
The activation of heat shock transcription factor‐1 (HSF‐1) after treatment of mammalian cells with stresses such as heat shock, heavy metals, or ethanol induces the synthesis of heat shock proteins. HSF‐1 is phosphorylated at normal growth temperature and is hyperphosphorylated upon stress. We recently presented evidence that HSF‐1 can be phosphorylated by the mitogen activated protein kinase, ERK1, and that such phosphorylation appears to negatively regulate the activity of HSF‐1. In this report, we have tested the ability of ERK1 to phosphorylate various HSF‐1 deletion mutants. Our results show that ERK1 phosphorylation is dependent on a region of HSF‐1 extending from amino acids 280 to 308. This region contains three serine residues that are potential ERK1 phosphorylation sites. The region falls within a previously defined regulatory domain of HSF‐1. The possibility of protein kinases other than ERK1 phosphorylating HSF‐1 was also examined using in‐gel kinase assays. The results show that HSF‐1 can be phosphorylated in a ras‐dependent manner by other members of the MAP kinase family such as JNK and p38 protein kinases and possibly others. J. Cell. Biochem. 67:43–54, 1997.

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