Glycogen synthase kinase 3 beta negatively regulates both DNA-binding and transcriptional activities of heat shock factor 1

Stress activation of heat shock factor (HSF1) involves the conversion of re pressed monomers to DNA-binding homotrimers with increased transcriptional capacity and results in transcriptional up-regulation of the heat shock pro tein (hsp) gene family. Cells tightly control the activity of HSF1 through interactions with hsp90 chaperone complexes and through integration into a number of different signaling cascades. A number of studies have shown that HSF1 transcriptional activity is negatively regulated by constitutive phos phorylation in the regulatory domain by glycogen synthase kinase (GSK3) iso forms alpha/beta. However, previous studies have not examined the ability o f GSK3 to regulate the DNA-binding activity of native HSF1 in vivo under he at shock conditions. Here we show that GSK3 beta inhibits both DNA-binding and transcriptional activities of HSF1 in heat-shocked cells. Specific inhi bition of GSK3 increased the levels of DNA binding and transcription after heat shock and delayed the attenuation of HSF1 during recovery. In contrast , the overexpression of GSK3 beta resulted in significant reduction in heat -induced HSF1 activities. These results confirm the role of GSK3 beta as a negative regulator of HSF1 transcription in cells during heat shock and dem onstrate for the first time that GSK3 beta functions to repress DNA binding .