Xavier I J, Mercier P A, McLoughlin C M, Ali A, Woodgett J R, Ovsenek N
Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada.
J Biol Chem. 2000 Sep 15;275(37):29147-52. doi: 10.1074/jbc.M002169200.
Stress activation of heat shock factor (HSF1) involves the conversion of repressed monomers to DNA-binding homotrimers with increased transcriptional capacity and results in transcriptional up-regulation of the heat shock protein (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 phosphorylation in the regulatory domain by glycogen synthase kinase (GSK3) isoforms alpha/beta. However, previous studies have not examined the ability of GSK3 to regulate the DNA-binding activity of native HSF1 in vivo under heat shock conditions. Here we show that GSK3beta inhibits both DNA-binding and transcriptional activities of HSF1 in heat-shocked cells. Specific inhibition 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 GSK3beta resulted in significant reduction in heat-induced HSF1 activities. These results confirm the role of GSK3beta as a negative regulator of HSF1 transcription in cells during heat shock and demonstrate for the first time that GSK3beta functions to repress DNA binding.
热休克因子（HSF1）的应激激活涉及将受抑制的单体转化为具有增强转录能力的DNA结合同源三聚体，并导致热休克蛋白（hsp）基因家族的转录上调。细胞通过与hsp90伴侣复合物相互作用以及整合到多种不同的信号级联反应中来严格控制HSF1的活性。许多研究表明，糖原合酶激酶（GSK3）α/β亚型在调节域中的组成型磷酸化对HSF1转录活性具有负调控作用。然而，先前的研究尚未考察GSK3在热休克条件下体内调节天然HSF1 DNA结合活性的能力。在此我们表明，GSK3β在热休克细胞中抑制HSF1的DNA结合和转录活性。特异性抑制GSK3可增加热休克后DNA结合和转录水平，并延迟恢复过程中HSF1的衰减。相反，GSK3β的过表达导致热诱导的HSF1活性显著降低。这些结果证实了GSK3β在热休克期间作为细胞中HSF1转录负调节因子的作用，并首次证明GSK3β起到抑制DNA结合的作用。
