Differential roles of heat shock transcription factors

脊椎动物基因组编码一个热休克因子家族（HSF1 -4），其中HSF1和HSF3的DNA结合和转录活性在热休克时被激活。HSF1具有经典热休克因子的特性，并在暴露于热休克和其他应激条件下表现出DNA结合和转录活性的快速激活，而HSF3通常在更高的温度下被激活，并具有明显的延迟动力学。虽然这些数据表明HSF3是一种冗余的应激激活剂，但相对于HSF1，它在热休克反应调节中的作用尚不确定。为了研究HSF3在热休克反应中的作用，我们在禽类淋巴样细胞系中通过体细胞重组破坏HSF3基因，构建了缺乏HSF3基因的空细胞。缺乏HSF3的空细胞，表达正常水平的HSF1，表现出热休克反应的严重减少，通过诱导表达热休克g…更多基因。因此，缺乏HSF3的细胞不表现出耐热性。这些结果表明HSF3在热休克反应的调控中起主导作用。HSF4是一种哺乳动物因子，其特征是缺乏调节dna结合同源三聚体形成的抑制结构域。我们已经确定了人类HSF4基因的外显子结构，并鉴定了一个主要的新异构体HSF4b，除了先前报道的HSF4a异构体之外，它是通过替代RNA剪接事件衍生的。RT-PCR检测小鼠组织中HSF4b mRNA含量高于HSF4a，脑组织和肺中均检测到HSF4b蛋白。虽然小鼠HSF4a和HSF4b在没有应激的情况下都能形成三聚体，但这两种异构体表现出不同的转录活性，HSF4a是热休克基因组成表达的抑制剂，而hHSF4b是转录激活剂。此外，HSF4b而不是HSF4a可以弥补缺乏HSF的酵母细胞的活力缺陷。此外，热休克和其他应激刺激HSF4b在酵母和哺乳动物细胞中靶基因的转录。这些结果表明，HSF4 mRNA的不同剪接导致了组织特异性热休克基因表达的抑制剂和激活剂。少

The vertebrate genome encodes a family of heat shock factors (HSFs 1-4) of which the DNA binding and transcriptional activities of HSF1 and HSF3 are activated upon heat shock. HSF1 has the properties of the classical heat shock factor and exhibits rapid activation of DNA binding and transcriptional activity upon exposure to conditions of heat shock and other stresses, whereas HSF3 is typically activated at higher temperatures and with distinct delayed kinetics. While these data suggest that HSF3 functions as a redundant stress activator, its role relative to HSF1, in the regulation of the heat shock response, was uncertain. To address the role of HSF3 in the heat shock response, null cells lacking the HSF3 gene were constructed by disruption of the resident gene by somatic recombination in an avian lymphoid cell line. Null cells lacking HSF3, yet expressing normal levels of HSF1, exhibited a severe reduction in the heat shock response as measured by inducible expression of heat shock g … More enes. Consequently, cells lacking HSF3 did not exhibit thermotolerance. These results reveal that HSF3 has a dominant role in the regulation of the heat shock response.HSF4 is a mammalian factor characterized by its lack of a suppression domain that modulates formation of DNA-binding homotrimer. 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 RT-PCR, 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 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. Less