Tanabe M, Sasai N, Nagata K, Liu X D, Liu P C, Thiele D J, Nakai A
Department of Molecular and Cell Biology, Institute for Frontier Medical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8397, Japan.
J Biol Chem. 1999 Sep 24;274(39):27845-56. doi: 10.1074/jbc.274.39.27845.
The expression of heat shock genes is controlled at the level of transcription by members of the heat shock transcription factor family in vertebrates. HSF4 is a mammalian factor characterized by its lack of a suppression domain that modulates formation of DNA-binding homotrimer. Here, we have determined the exon structure of the human HSF4 gene and identified a major new isoform, HSF4b, derived by alternative RNA splicing events, in addition to a previously reported HSF4a isoform. In mouse tissues HSF4b mRNA was more abundant than HSF4a as examined by reverse transcription-polymerase chain reaction, and its protein was detected in the brain and lung. Although both mouse HSF4a and HSF4b form trimers in the absence of stress, these two isoforms exhibit different transcriptional activity; HSF4a acts as an inhibitor of the constitutive expression of heat shock genes, and hHSF4b acts as a transcriptional activator. Furthermore HSF4b but not HSF4a complements the viability defect of yeast cells lacking HSF. Moreover, heat shock and other stresses stimulate transcription of target genes by HSF4b in both yeast and mammalian cells. These results suggest that differential splicing of HSF4 mRNA gives rise to both an inhibitor and activator of tissue-specific heat shock gene expression.
在脊椎动物中，热休克基因的表达在转录水平上受热休克转录因子家族成员的控制。HSF4是一种哺乳动物因子，其特征在于缺乏调节DNA结合同型三聚体形成的抑制结构域。在此，我们确定了人类HSF4基因的外显子结构，并鉴定出一种主要的新亚型HSF4b，它是通过选择性RNA剪接事件产生的，此外还有先前报道的HSF4a亚型。通过逆转录-聚合酶链反应检测发现，在小鼠组织中HSF4b mRNA比HSF4a更丰富，并且在脑和肺中检测到了其蛋白。尽管小鼠HSF4a和HSF4b在无应激条件下均形成三聚体，但这两种亚型表现出不同的转录活性；HSF4a作为热休克基因组成型表达的抑制剂，而hHSF4b作为转录激活剂。此外，HSF4b而非HSF4a可弥补缺乏HSF的酵母细胞的生存力缺陷。而且，热休克和其他应激可刺激酵母和哺乳动物细胞中HSF4b对靶基因的转录。这些结果表明，HSF4 mRNA的差异剪接产生了组织特异性热休克基因表达的抑制剂和激活剂。
