Phosphorylation of HSF1 by MAPK-Activated Protein Kinase 2 on Serine 121, Inhibits Transcriptional Activity and Promotes HSP90 Binding

Abstract

Heat shock transcription factor 1 (HSF1) monitors the structural integrity of intracellular proteins and its regulation is essential for the health and longevity of eukaryotic organisms. HSF1 also plays a role in the acute inflammatory response in the negative regulation of cytokine gene transcription. Here we show, for the first time, that HSF1 is regulated by the proinflammatory protein kinase MAPKAP kinase 2 (MK2). We have shown that MK2 directly phosphorylates HSF1 and inhibits activity by decreasing its ability to bind the heat shock elements (HSE) found in the promoters of target genes encoding the HSP molecular chaperones and cytokine genes. We show that activation of HSF1 to bind HSE in hsp promoters is inhibited through the phosphorylation of a specific residue, serine 121 by MK2. A potential mechanism for MK2-induced HSF1 inactivation is suggested by the findings that phosphorylation of serine 121 enhances HSF1 binding to HSP90, a major repressor of HSF1. Dephosphorylation of serine 121 in cells exposed to non-steroidal anti-inflammatory drugs leads to HSP90 dissociation from HSF1, which then forms active DNA binding trimers. These experiments indicate a novel mechanism for the regulation of HSF1 by proinflammatory signaling and may permit HSF1 to respond rapidly to extracellular events, permitting optimal physiological regulation.Heat shock factor 1 (HSF1) 3 is the transcriptional activator of HSP molecular chaperone genes during stress (1, 2). The hsf1 gene plays an essential role in protection of cells from heat shock by regulating the induction of cytoprotective HSP and in protection against the effects of endotoxins through its ability to repress the transcription of proinflammatory cytokines through inhibition of factors involved in cytokine transcription such as 4). Aging is associated with the degeneration of HSP expression with time and the loss of resistance to cellular oxidants; elevated HSF1 leads to significant increase in lifespan in Caenorhabditis elegans (5-7). In cancer, the converse situation applies, and malignant transformation is associated with aberrantly high levels of HSP (8, 9). These clinical phenomena reflect the role of HSP molecular chaperones in cellular regulation, as either up-or downregulation of HSP expression can profoundly modulate multiple key proteins within the cell (10). It is therefore clear that elucidating the molecular mechanisms that control HSP expression in mammalian cells is essential.Under normal conditions, most HSF1 is inactive and maintained in a compacted monomeric form (11-13). Inactive HSF1 lacks the ability to bind to the heat shock elements (HSE) in hsp promoters, is unable to trans-activate hsp genes and fails to repress the promoters of proinflammatory cytokines (13-16). Activation of HSF1 is a complex process involving monomer to trimer transition and DNA binding; hyperphosphorylation, and capacity to activate target promoters (12,(17)(18)(19). Trimerization of HSF1 is governed by leucine zipper domains in the amino terminus and is subject to ...

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