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(HSFs1-4)，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，在热休克和其他应激条件下表现出快速激活DNA结合和转录活性，而HSF3通常在更高的温度下激活，并具有明显的延迟动力学。虽然这些数据表明，HSF3作为一种多余的应激激活剂发挥作用，但它相对于HSF1在调节热休克反应中的作用尚不确定。为了研究HSF3在热休克反应中的作用，在禽类淋巴细胞系中，通过体细胞重组破坏驻留基因，构建了缺失HSF3基因的空细胞。缺乏hsf3但表达hsf1正常水平的空细胞表现出热休克反应的严重降低，通过热休克g…的诱导表达来衡量。更多的烯。因此，缺乏HSF3的细胞不表现出耐热性。这些结果表明，HSF3在热休克反应的调节中起主导作用。HSF4是一种哺乳动物因子，其特点是缺乏调节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异构体外，还通过选择性RNA剪接获得了HSF4b。RT-PCR检测到HSF4b在小鼠组织中的表达比HSF4a丰富，在脑和肺中检测到HSF4b的蛋白。虽然小鼠HSF4a和HSF4b在无应激条件下都形成三聚体，但这两种异构体表现出不同的转录活性，HSF4a作为热休克基因结构性表达的抑制因子，而hHSF4b作为转录激活因子。此外，HSF4b而不是HSF4a弥补了缺乏HSFF的酵母细胞的活性缺陷。此外，热休克和其他应激刺激通过HSF4b在酵母和哺乳动物细胞中转录靶基因。这些结果表明，HSF4 mRNA的差异剪接既是组织特异性热休克基因表达的抑制者，也是组织特异性热休克基因表达的激活者。较少

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