Liu X D, Liu P C, Santoro N, Thiele D J
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606, USA.
EMBO J. 1997 Nov 3;16(21):6466-77. doi: 10.1093/emboj/16.21.6466.
Heat shock factors (HSF) are important eukaryotic stress responsive transcription factors which are highly structurally conserved from yeast to mammals. HSFs bind as homotrimers to conserved promoter DNA recognition sites called HSEs. The baker's yeast Saccharomyces cerevisiae possesses a single essential HSF gene, while distinct HSF isoforms have been identified in humans. To ascertain the degree of functional similarity between the yeast and human HSF proteins, human HSF1 and HSF2 were expressed in yeast cells lacking the endogenous HSF gene. We demonstrate that human HSF2, but not HSF1, homotrimerizes and functionally complements the viability defect associated with a deletion of the yeast HSF gene. However, derivatives of hHSF1 that give rise to a trimerized protein, through disruption of a carboxyl- or aminoterminal coiled-coil domain thought to engage in intramolecular interactions that maintain the protein in a monomeric state, functionally substitute for yeast HSF. Surprisingly, hHSF2 expressed in yeast activates target gene transcription in response to thermal stress. Moreover, hHSF1 and hHSF2 exhibit selectivity for transcriptional activation of two distinct yeast heat shock responsive genes, which correlate with previously established mammalian HSF DNA binding preferences in vitro. These results provide new insight into the function of human HSF isoforms, and demonstrate the remarkable functional conservation between yeast and human HSFs, critical transcription factors required for responses to physiological, pharmacological and environmental stresses.
热休克因子（HSF）是重要的真核生物应激反应转录因子，从酵母到哺乳动物，其结构高度保守。HSF以同源三聚体形式结合到称为热休克元件（HSE）的保守启动子DNA识别位点上。酿酒酵母拥有一个单一的必需HSF基因，而在人类中已鉴定出不同的HSF亚型。为了确定酵母和人类HSF蛋白之间的功能相似程度，将人类HSF1和HSF2在缺乏内源性HSF基因的酵母细胞中表达。我们证明，人类HSF2而非HSF1能形成同源三聚体，并在功能上弥补与酵母HSF基因缺失相关的生存力缺陷。然而，通过破坏被认为参与分子内相互作用以维持蛋白质处于单体状态的羧基或氨基末端卷曲螺旋结构域而产生三聚体化蛋白的hHSF1衍生物，在功能上可替代酵母HSF。令人惊讶的是，在酵母中表达的hHSF2在热应激反应中激活靶基因转录。此外，hHSF1和hHSF2对两个不同的酵母热休克反应基因的转录激活表现出选择性，这与先前在体外确定的哺乳动物HSF DNA结合偏好相关。这些结果为人类HSF亚型的功能提供了新的见解，并证明了酵母和人类HSF之间显著的功能保守性，它们是对生理、药理和环境应激反应所需的关键转录因子。
