The heat shock transcription factor (HSF) family consists of three members in mammals and regulates expression of heat shock genes via a heat shock element. HSF1 and HSF2 are required for some developmental processes, but it is unclear how they regulate these processes. To elucidate the mechanisms of developmental regulation by HSFs, we generated mice in which the HSF4 gene is mutated. HSF4-null mice had cataract with abnormal lens fiber cells containing inclusion-like structures, probably due to decreased expression of gamma-crystallin, which maintains protein stability. Furthermore, we found increased proliferation and premature differentiation of the mutant lens epithelial cells, which is associated with increased expression of growth factors, FGF-1, FGF-4, and FGF-7. Unexpectedly, HSF1 competed with HSF4 for the expression of FGFs not only in the lens but also in other tissues. These findings reveal the lens-specific role of HSF4, which activates gamma-crystallin genes, and also indicate that HSF1 and HSF4 are involved in regulating expression of growth factor genes, which are essential for cell growth and differentiation.

Elevation of activeE levels in Escherichia coli by either repressing the expression of rseA encoding an anti-E factor or cloning rpoE in a multicopy plasmid, led to a large decrease in the number of dead cells and the accumulation of cellular proteins in the medium in the stationary phase. The numbers of CFU, however, were nearly the same as those of the wild type or cells devoid of the cloned gene. In the wild-type cells, rpoE expression was increased in the stationary phase and a low-level release of intracellular proteins was observed. These results suggest that dead cell lysis in stationary-phase E. coli occurs in a E -dependent fashion. We propose there is a novel physiological function of the E regulon that may guarantee cell survival in prolonged stationary phase by providing nutrients from dead cells for the next generation.Escherichia coli undergoes a decrease in viable cell number in the early stationary phase when grown in rich media (28). Our previous study suggested that the ssnA gene helps promote the decline in cell viability (27). Disruption of ssnA caused a significant retardation of this decline, while increased expression gave rise to cell growth inhibition. Since the expression was not extensive enough to have a physical effect on cell structure, the growth inhibition seems to be due to the increase in the cellular activity of ssnA.Here, we have identified the rpoE gene, encoding E , as the gene that suppresses growth inhibition by ssnA. RpoE, first identified as a transcription factor for the rpoH gene encoding a main heat shock factor (6, 25), is involved in the expression of several genes (4, 19) whose products deal with unfolded periplasmic or membrane proteins, caused by heat shock or environmental stresses in E. coli (15,18,19).E is an essential sigma factor in E. coli, not only at high temperatures but also at low temperatures (5, 7, 11). The active E molecules are increased in response to unfolded extracytoplasmic proteins (13) via a unique mechanism of E modulation, in which RseA, RseB, and RseC encoded by the rpoE-rseABC operon are involved (4,15,16). RseA, an inner membrane protein, functions as an anti-E factor. RseB, a periplasmic protein, binds to RseA and is thought to function as a sensor for unfolded proteins. RseC is an inner membrane protein that positively modulates E activity, although the mechanism of this interaction remains unclear. When unfolded proteins are accumulated in the periplasm in response to stress, such as high temperature or chemicals, RseB separates from the complex consisting of RseB, RseA, and E , releasing E as an active form in the cytoplasm. The active E then induces transcription from the rpoE P2 promoter to allow its autoinduction and expression of the genes of the E regulon (18,19). Among these genes, htrA and fkpA are known to encode periplasmic serine protease (11,12,24) and periplasmic peptidyl prolyl isomerase (3), respectively, which mediate protein turnover or protein folding in the extracytoplasmic compartments. No other genes of the E regu...

Heat shock response, which is characterized by the induction of a set of heat shock proteins, is essential for induced thermotolerance and is regulated by heat shock transcription factors (HSFs). Curiously, HSF1 is essential for heat shock response in mammals, whereas in avian HSF3, an avian-specific factor is required for the burst activation of heat shock genes. Amino acid sequences of chicken HSF1 are highly conserved with human HSF1, but those of HSF3 diverge significantly. Here, we demonstrated that chicken HSF1 lost the ability to activate heat shock genes through the amino-terminal domain containing an alanine-rich sequence and a DNA-binding domain. Surprisingly, chicken and human HSF1 but not HSF3 possess a novel function that protects against a single exposure to mild heat shock, which is not mediated through the activation of heat shock genes. Overexpression of HSF1 mutants that could not bind to DNA did not restore the susceptibility to cell death in HSF1-null cells, suggesting that the new protective role of HSF1 is mediated through regulation of unknown target genes other than heat shock genes. These results uncover a novel role of vertebrate HSF1, which has been masked underthe roles of heat shock proteins.All living organisms respond to elevated temperatures by inducing a set of highly conserved proteins, heat shock proteins (Hsps). This response is called the heat shock response and is believed to be a universal and fundamental mechanism for cell protection against stresses such as heat shock. The heat shock response is regulated mainly at the level of transcription by heat shock transcription factors (HSFs) in eukaryotes, which bind to heat shock elements on upstream sequences of heat shock genes (45). It is well known that cells can survive an exposure to lethal temperatures when cells are preincubated at sublethal high temperatures. This phenomenon is now called induced thermotolerance. Numerous studies suggest that Hsp induction is crucial to the acquisition of the induced thermotolerance (19). Finally, heat shock response regulated by HSF is shown to be necessary for acquisition of the induced thermotolerance in the fruit fly (15), mouse embryo fibroblast cells (21), and chicken B lymphocyte DT40 cells (42).HSFs do more than activate heat shock genes in response to elevated temperatures. It was shown that in Drosophila HSF is required under normal growth conditions for oogenesis and early development (15). Mice deficient in HSF1 show abnormal placental development, growth retardation, and female infertility (7, 46). Furthermore, mice deficient in HSF2 exhibit abnormalities in brain development and defects in spermatogenesis and oogenesis (16). In all of these cases, developmental functions of HSFs are not mediated through the induction of Hsps, suggesting that HSFs regulate unknown genes related to development. Recently, it was found that HSFs can regulate only a specific heat shock gene under normal growth conditions. In chicken DT40 cells, HSF1 and HSF3 regulate only Hsp90␣ expression in a...

Heat shock response is an adoptive response to proteotoxic stress, and a major heat shock transcription factor 1 (HSF1) has been believed to protect cells from cell death by inducing heat shock proteins (Hsps) that assist protein folding and prevent protein denaturation. However, it is revealed recently that HSF1 also promotes cell death of male germ cells. Here, we found a proapoptotic Tdag51 (T-cell death associated gene 51) gene as a direct target gene of HSF1. Heat shock and other stresses induced different levels of Hsps and Tdag51, which depend on cell types. Hsps bound directly to the N-terminal pleckstrin-homology like (PHL) domain of Tdag51, and suppressed death activity of the C-terminal proline/ glutamine/histidine-rich domain. Tdag51, but not major Hsps, were induced in male germ cells exposed to high temperatures. Analysis of Tdag51-null testes showed that Tdag51 played substantial roles in promoting heat shockinduced cell death in vivo. These data suggest that cell fate on proteotoxic condition is determined at least by balance between Hsp and Tdag51 levels, which are differently regulated by HSF1.

Heat shock factor 1 (HSF1) is a major transactivator of heat shock proteins in response to heat shock, and it is also involved in oogenesis, spermatogenesis, and placental development. However, we do not know the molecular mechanisms controlling developmental processes. In this study, we found that HSF1-null mice exhibited a significant decrease in the T cell-dependent B cell response. When mice were immunized intraperitoneally with sheep red blood cells, the sheep red blood cellspecific IgG production, especially IgG2a production, in HSF1-null mice was about 50% lower than that in wildtype mice at 6 days after the immunization, whereas IgM production was normal. The number of bromodeoxyuridine-incorporated spleen cells in immunized HSF1-null mice was one-third that in immunized wild-type mice, indicating reduced proliferation of the spleen cells. We analyzed levels of cytokines and chemokines in spleen cells and in peritoneal macrophages stimulated with lipopolysaccharide and interferon-␥ and found that expression levels of interleukin-6 and CCL5 were significantly lower in HSF1-null cells than those in wild-type cells. Furthermore, we demonstrated that the IL-6 gene is a direct target gene of HSF1. These results revealed a novel molecular link between HSF1 and a gene related to immune response and inflammation.