Goodson M L, Sarge K D
Department of Biochemistry, Chandler Medical Center, University of Kentucky, Lexington 405036-0084, USA.
Biochem Biophys Res Commun. 1995 Jun 26;211(3):943-9. doi: 10.1006/bbrc.1995.1903.
HSF1 mediates the stress induced expression of heat shock proteins, referred to as the cellular stress response. Previous results indicated that mammalian cells express two distinct HSF1 protein isoforms, with molecular sizes of 69 kDa (HSF1-beta) and 71 kDa (HSF1-alpha). The purpose of this study was to determine the mechanism by which these two HSF1 protein isoforms are generated. Our results show that mammalian cells express two distinct HSF1 mRNA isoforms which arise via alternative splicing of the HSF1 pre-mRNA. The two HSF1 mRNA isoforms differ by a single 66 bp exon of the HSF1 gene which is spliced into the HSF1-alpha mRNA isoform but skipped in the HSF1-beta mRNA isoform. This 66 bp exon encodes a 22 amino acid sequence, whose molecular weight (2.3 kDa) matches the difference in size between the HSF1-beta and HSF1-alpha protein isoforms (69 and 71 kDa). Further analysis reveals that this extra 22 amino acid sequence, whose insertion site in the HSF1-alpha isoform is located immediately adjacent to a C-terminal leucine zipper motif (leucine zipper 4) previously shown to be involved in maintenance of HSF1 in the non-DNA-binding control form, contains an additional, previously unidentified leucine zipper motif (leucine zipper 5). Our results also show that the levels of the two HSF1 isoforms are regulated in a tissue dependent manner, with testis expressing higher levels of the HSF1-beta isoform while heart and brain express higher levels of the HSF1-alpha isoform. These results demonstrate a new mechanism by which HSF1 expression is regulated in mammalian cells and suggest a potential role for the HSF1 isoforms in mediating tissue-dependent regulation of the cellular stress response.
热休克因子1（HSF1）介导应激诱导的热休克蛋白表达，即细胞应激反应。先前的研究结果表明，哺乳动物细胞表达两种不同的HSF1蛋白异构体，分子量分别为69 kDa（HSF1-β）和71 kDa（HSF1-α）。本研究的目的是确定这两种HSF1蛋白异构体的产生机制。我们的研究结果表明，哺乳动物细胞表达两种不同的HSF1 mRNA异构体，它们是通过HSF1前体mRNA的可变剪接产生的。这两种HSF1 mRNA异构体的区别在于HSF1基因的一个66 bp外显子，该外显子被剪接到HSF1-α mRNA异构体中，但在HSF1-β mRNA异构体中被跳过。这个66 bp外显子编码一个22个氨基酸的序列，其分子量（2.3 kDa）与HSF1-β和HSF1-α蛋白异构体（69和71 kDa）之间的大小差异相匹配。进一步的分析表明，这个额外的22个氨基酸序列，其在HSF1-α异构体中的插入位点紧邻先前显示参与维持HSF1非DNA结合控制形式的C末端亮氨酸拉链基序（亮氨酸拉链4）包含一个额外的、先前未鉴定的亮氨酸拉链基序（亮氨酸拉链5）。我们的研究结果还表明，这两种HSF1异构体的水平以组织依赖性方式调节，睾丸中HSF1-β异构体的表达水平较高，而心脏和大脑中HSF1-α异构体的表达水平较高。这些结果证明了一种在哺乳动物细胞中调节HSF1表达的新机制，并提示HSF1异构体在介导细胞应激反应的组织依赖性调节中可能发挥作用。
