c-Jun NH2-terminal kinase targeting and phosphorylation of heat shock factor-1 suppress its transcriptional activity

The mammalian heat shock transcription factor HSF-1 regulates the expressio n of the heat shock proteins, molecular chaperones that are involved in cel lular processes from higher order assembly to protein degradation. HSF-1 is a phosphorylated monomer under physiological growth conditions and is loca ted mainly in the cytoplasm. Upon activation by a variety of environmental stresses, HSF-I is translocated into the nucleus, forms trimers, acquires D NA binding activity, is hyperphosphorylated, appears as punctate granules, and increases transcriptional activity of target genes. As cells recover fr om stress, the punctate granules gradually disappear, and HSF-I appears in a diffused staining pattern in the cytoplasm and nucleus. We have previousl y shown that the mitogen-activated protein kinase ERK phosphorylates and su ppresses HSF-l-driven transcription. Here, Re show that c-Jun NH2-terminal kinase (JNK) also phosphorylates and inactivates HSF-I. Overexpression of J NK facilitates the rapid disappearance of HSF-1 punctate granules after hea t shock Similar to ERE, JNK binds to HSF-1 in the conserved mitogen-activat ed protein kinases binding motifs and phosphorylates HSF-1 in the regulator y domain. The overexpression of an HSF-l-green fluorescent protein fusion c onstruct lacking JNK phosphorylation sites causes this HSF-1 mutant to form nuclear granules that remain longer in the nucleus after heat shock. Taken together, these findings indicate that JNK phosphorylates HSF-1 and suppre sses its transcriptional activity by rapidly clearing HSF-1 hom the sites o f transcription.