Heat Shock Transcription Factor 2 Is Significantly Involved in Neurodegenerative Diseases, Inflammatory Bowel Disease, Cancer, Male Infertility, and Fetal Alcohol Spectrum Disorder: The Novel Mechanisms of Several Severe Diseases

HSF (heat shock transcription factor or heat shock factor) was discovered as a transcription factor indispensable for heat shock response. Although four classical HSFs were discovered in mammals and two major HSFs, HSF1 and HSF2, were cloned in the same year of 1991, only HSF1 was intensively studied because HSF1 can give rise to heat shock response through the induction of various HSPs' expression. On the other hand, HSF2 was not well studied for some time, which was probably due to an underestimate of HSF2 itself. Since the beginning of the 21st century, HSF2 research has progressed and many biologically significant functions of HSF2 have been revealed. For example, the roles of HSF2 in nervous system protection, inflammation, maintenance of mitosis and meiosis, and cancer cell survival and death have been gradually unveiled. However, we feel that the fact HSF2 has a relationship with various factors is not yet widely recognized; therefore, the biological significance of HSF2 has been underestimated. We strongly hope to widely communicate the significance of HSF2 to researchers and readers in broad research fields through this review. In addition, we also hope that many readers will have great interest in the molecular mechanism in which HSF2 acts as an active transcription factor and gene bookmarking mechanism of HSF2 during cell cycle progression, as is summarized in this review.

Polymorphisms in the HSF2, LRRC6, MEIG1 and PTIP genes correlate with sperm motility in idiopathic infertility

The aim of this study was to investigate the association of 24 functionally important single nucleotide polymorphisms (SNPs) with male infertility. In this cross-sectional study, we genotyped 24 functionally important single nucleotide polymorphisms in 24 infertility candidate genes in 500 oligo-/astheno-/oligoastheno-/normo-zoospermic infertile men with idiopathic infertility. Sequenom iPlex gold assay was used for genotyping. Sperm count and motility were compared between prevalent genotypes at each test locus. We did not observe any significant difference in the average sperm count between the alternate genotypes for the loci in the KLK3, LRRC6, MEIG1, HSF2, ESR2 and PTIP genes. However, we observed a significant difference in sperm motility between the alternate genotypes for the loci in the LRRC6, MEIG1, HSF2 and PTIP genes. Polymorphisms in the LRRC6 (rs200321595), MEIG1 (rs150031795), HSF2 (rs143986686) and PTIP (rs61752013) genes show association with sperm motility.

Heat shock transcription factor HSF2 modulates the autophagy response through the BTG2-SOD2 axis

The heat shock transcription factor HSF1 regulates the inducible Hsp gene transcription, whereas HSF2 is involved in the constitutive transcription. HSFs can work for the non-heat shock genes transcription in a case-specific manner to facilitate normal cellular functions. Here, we demonstrate that HSF2 acts as an upstream regulator of heat shock-induced autophagy response in a rat histiocytoma. The heat-induced HSF2 transactivates the B-cell translocation gene-2 (BTG2) transcription, and the latter acts as a transcriptional coactivator for superoxide dismutase (SOD2). The altered HSF2 promoter occupancy on the BTG2 promoter enhances BTG2 transcription. Since SOD2 regulation is linked to mitochondrial redox sensing, HSF2 appears to act as a redox sensor in deciding the cell fate. The HSF2 shRNA or NFE2L2/BTG2 siRNA treatments have interfered with the autophagy response. We demonstrate that HSF2 is an upstream activator of autophagy response, and the HSF2-BTG2-SOD2 axis acts as a switch between the non-selective (micro/macro) and selective (chaperone-mediated) autophagy.

Cell Cycle Regulation by Heat Shock Transcription Factors

Cell division and cell cycle mechanism has been studied for 70 years. This research has revealed that the cell cycle is regulated by many factors, including cyclins and cyclin-dependent kinases (CDKs). Heat shock transcription factors (HSFs) have been noted as critical proteins for cell survival against various stresses; however, recent studies suggest that HSFs also have important roles in cell cycle regulation-independent cell-protective functions. During cell cycle progression, HSF1, and HSF2 bind to condensed chromatin to provide immediate precise gene expression after cell division. This review focuses on the function of these HSFs in cell cycle progression, cell cycle arrest, gene bookmarking, mitosis and meiosis.

Integrated Bioinformatics Analysis Identifies Heat Shock Factor 2 as a Prognostic Biomarker Associated With Immune Cell Infiltration in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies and ranks as the second leading cause of cancer-related mortality worldwide. Heat shock factor 2 (HSF2) is a transcription factor that plays a critical role in development, particularly corticogenesis and spermatogenesis. However, studies examining the expression and prognostic value of HSF2 and its association with tumor-infiltrating immune cells in HCC are still rare. In the present study, we found that HSF2 expression was significantly upregulated in HCC tissues compared with normal liver tissues using the TCGA, ICGC, GEO, UALCAN, HCCDB and HPA databases. High HSF2 expression was associated with shorter survival of patients with HCC. Cox regression analyses and nomogram were used to evaluate the association of HSF2 expression with the prognosis of patients with HCC. Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and gene set enrichment analysis (GSEA) revealed that HSF2 was associated with various signaling pathways, including the immune response. Notably, HSF2 expression was significantly correlated with the infiltration levels of different immune cells using the TIMER database and CIBERSORT algorithm. HSF2 expression also displayed a significant correlation with multiple immune marker sets in HCC tissues. Knockdown of HSF2 significantly inhibited the proliferation, migration, invasion and colony formation ability of HCC cells. In summary, we explored the clinical significance of HSF2 and provided a therapeutic basis for the early diagnosis, prognostic judgment, and immunotherapy of HCC.

Role of heat shock transcription factor 2 in the NMDA-dependent neuroplasticity induced by chronic ethanol intake in mouse hippocampus

Ethanol consumption impairs learning and memory through disturbances of NMDA-type glutamate receptor-dependent synaptic plasticity (long-term depression [LTD] and long-term potentiation [LTP]) in the hippocampus. Recently, we demonstrated that two ethanol binge-like episodes in young adult rats selectively blocked NMDA-LTD in hippocampal slices, increased NMDA receptor sensitivity to a GluN2B subunit antagonist, and induced cognitive deficits. Here, using knockout adult mice, we show that a stress-responsive transcription factor of the heat shock factor family, HSF2, which is involved in the perturbation of brain development induced by ethanol, participates in these processes. In the absence of ethanol, hsf2^-/- mice show a selective loss of LTD in the hippocampus, which is associated with an increased sensitivity of NMDA-field excitatory postsynaptic potentials (fEPSPs) to a GluN2B antagonist, compared with wild-type (WT) mice. These results suggest that HSF2 is required for proper glutamatergic synaptic transmission and LTD plasticity. After 1 month of chronic ethanol consumption in a two-bottle choice paradigm, WT mice showed an increase in hippocampal synaptic transmission, an enhanced sensitivity to GluN2B antagonist, and a blockade of LTD. In contrast, such modulation of synaptic transmission and plasticity were absent in hsf2^-/- mice. We conclude that HSF2 is an important mediator of both glutamatergic neurotransmission and synaptic plasticity in basal conditions and also mediates ethanol-induced neuroadaptations of the hippocampus network after chronic ethanol intake.

The proteostasis guardian HSF1 directs the transcription of its paralog and interactor HSF2 during proteasome dysfunction

Protein homeostasis is essential for life in eukaryotes. Organisms respond to proteotoxic stress by activating heat shock transcription factors (HSFs), which play important roles in cytoprotection, longevity and development. Of six human HSFs, HSF1 acts as a proteostasis guardian regulating stress-induced transcriptional responses, whereas HSF2 has a critical role in development, in particular of brain and reproductive organs. Unlike HSF1, that is a stable protein constitutively expressed, HSF2 is a labile protein and its expression varies in different tissues; however, the mechanisms regulating HSF2 expression remain poorly understood. Herein we demonstrate that the proteasome inhibitor anticancer drug bortezomib (Velcade), at clinically relevant concentrations, triggers de novo HSF2 mRNA transcription in different types of cancers via HSF1 activation. Similar results were obtained with next-generation proteasome inhibitors ixazomib and carfilzomib, indicating that induction of HSF2 expression is a general response to proteasome dysfunction. HSF2-promoter analysis, electrophoretic mobility shift assays, and chromatin immunoprecipitation studies unexpectedly revealed that HSF1 is recruited to a heat shock element located at 1.397 bp upstream from the transcription start site in the HSF2-promoter. More importantly, we found that HSF1 is critical for HSF2 gene transcription during proteasome dysfunction, representing an interesting example of transcription factor involved in controlling the expression of members of the same family. Moreover, bortezomib-induced HSF2 was found to localize in the nucleus, interact with HSF1, and participate in bortezomib-mediated control of cancer cell migration. The results shed light on HSF2-expression regulation, revealing a novel level of HSF1/HSF2 interplay that may lead to advances in pharmacological modulation of these fundamental transcription factors.

Mitochondrial ROS-induced ERK1/2 activation and HSF2-mediated AT1 R upregulation are required for doxorubicin-induced cardiotoxicity

Doxorubicin (DOX), one useful chemotherapeutic agent, is limited in clinical use because of its serious cardiotoxicity. Growing evidence suggests that angiotensin receptor blockers (ARBs) have cardioprotective effects in DOX-induced cardiomyopathy. However, the detailed mechanisms underlying the action of ARBs on the prevention of DOX-induced cardiomyocyte cell death have yet to be investigated. Our results showed that angiotensin II receptor type I (AT₁ R) plays a critical role in DOX-induced cardiomyocyte apoptosis. We found that MAPK signaling pathways, especially ERK1/2, participated in modulating AT₁ R gene expression through DOX-induced mitochondrial ROS release. These results showed that several potential heat shock binding elements (HSE), which can be recognized by heat shock factors (HSFs), located at the AT₁ R promoter region. HSF2 markedly translocated from the cytoplasm to the nucleus when cardiomyocytes were damaged by DOX. Furthermore, the DNA binding activity of HSF2 was enhanced by DOX via deSUMOylation. Overexpression of HSF2 enhanced DOX-induced cardiomyocyte cell death as well. Taken together, we found that DOX induced mitochondrial ROS release to activate ERK-mediated HSF2 nuclear translocation and AT₁ R upregulation causing DOX-damaged heart failure in vitro and in vivo.

Fluoride exposure changed the structure and the expressions of Y chromosome related genes in testes of mice

It is known that during spermatogenesis, pluripotent germ cells differentiate to become efficient delivery vehicles to the oocyte of paternal DNA, and the process is easily damaged by external poison. In this study, the effects of fluoride on the body weight, fluoride content in femur, testosterone levels in serum and testis, sperm quality, and the expressions of Y chromosome microdeletion genes and protein levels were examined in testes of Kunming male mice treated with different concentrations of 0, 25, 50, 100 mg/L of NaF in drinking water for 11 weeks, respectively. The results showed that compared with the control group, fluoride contents in three treatment groups were significantly increased and the structure of testes was seriously injured. The testosterone contents and the sperm count were decreased. Sperm malformation ratio was distinctly elevated. The expressions of Sly and HSF2 mRNA were markedly reduced in 100 mg/L NaF group and Ssty2 mRNA expression was dramatically decreased in 50 and 100 mg/L NaF groups. Meanwhile, the protein levels of Ssty2 and Sly were significantly reduced in 50 and 100 mg/L NaF groups and HSF2 protein levels were significantly decreased in 100 mg/L NaF group. These studies indicated that fluoride had toxic effects on male reproductive system by reducing the testosterone and sperm count, and increasing the sperm malformation ratio, supported by the damage of testicular structure, as a consequence of depressed HSF2 level, which resulted in the down-regulation of Ssty2 and Sly mRNA and protein.

Purification, crystallization and X-ray diffraction analysis of the DNA-binding domain of human heat-shock factor 2

Cells respond to various proteotoxic stimuli and maintain protein homeostasis through a conserved mechanism called the heat-shock response, which is characterized by the enhanced synthesis of heat-shock proteins. This response is mediated by heat-shock factors (HSFs). Four genes encoding HSF1-HSF4 exist in the genome of mammals. In this protein family, HSF1 is the orthologue of the single HSF in lower eukaryotic organisms and is the major regulator of the heat-shock response, while HSF2, which shows low sequence homology to HSF1, serves as a developmental regulator. Increasing evidence has revealed biochemical properties and functional roles that are unique to HSF2, such as its DNA-binding preference and sumoylation patterns, which are distinct from those of HSF1. The structural basis for such differences, however, is poorly understood owing to the lack of available mammalian HSF structures. The N-terminal DNA-binding domain (DBD) is the most conserved functional module and is the only crystallizable domain in HSFs. To date, only HSF1 homologue structures from yeast and fruit fly have been determined. Along with extensive studies of the HSF family, more structural information, particularly from members with a remoter phylogenic relationship to the reported structures, e.g. HSF2, is needed in order to better understand the detailed mechanisms of HSF biology. In this work, the recombinant DBD (residues 7-112) from human HSF2 was produced in Escherichia coli and crystallized. An X-ray diffraction data set was collected to 1.32 Å resolution from a crystal belonging to space group P212121 with unit cell-parameters a = 65.66, b = 67.26, c = 93.25 Å. The data-evaluation statistics revealed good quality of the collected data, thus establishing a solid basis for the determination of the first structure at atomic resolution in this protein family.

Set1/MLL complex is indispensable for the transcriptional ability of heat shock transcription factor 2

Heat shock transcription factor 2 (HSF2) is one of four mammalian HSFs, and it is essential in neurogenesis and gametogenesis. However, other aspects of this transcription factor have not been thoroughly characterized. We recently demonstrated that HSF2 suppresses the aggregation caused by polyglutamine (polyQ) protein, and that the cell protective ability of HSF2 is mediated through the induction of the small HSP alphaB-crystallin (CRYAB). In the present study, we investigated the mechanism of HSF2-induced CRYAB expression. We demonstrated that HSF2 interacted with the core component of the Set1/MLL H3K4 histone methyltransferase complex, WDR5. Indeed, HSF2 up-regulated the H3K4me3, H3K14Ac, and H3K27Ac (active histone marks) of the CRYAB promoter. WDR5 bound to the HSF2 central domain (Domain X) in vitro and in vivo, and Cys278 of HSF2 was indispensable for HSF2-WDR5 interaction. HSF2 also interacted with the Set1/MLL complex. These results suggest that the interaction with the Set1/MLL complex via binding to WDR5 is critical for the transcriptional ability of HSF2.

The long noncoding RNA TUG1 regulates blood-tumor barrier permeability by targeting miR-144

Blood-tumor barrier (BTB) limits the delivery of chemotherapeutic agent to brain tumor tissues. Long non-coding RNAs (lncRNAs) have been shown to play critical regulatory roles in various biologic processes of tumors. However, the role of lncRNAs in BTB permeability is unclear. LncRNA TUG1 (taurine upregulated gene 1) was highly expressed in glioma vascular endothelial cells from glioma tissues. It also upregulated in glioma co-cultured endothelial cells (GEC) from BTB model in vitro. Knockdown of TUG1 increased BTB permeability, and meanwhile down-regulated the expression of the tight junction proteins ZO-1, occludin, and claudin-5. Both bioinformatics and luciferase reporter assays demonstrated that TUG1 influenced BTB permeability via binding to miR-144. Furthermore, Knockdown of TUG1 also down-regulated Heat shock transcription factor 2 (HSF2), a transcription factor of the heat shock transcription factor family, which was defined as a direct and functional downstream target of miR-144. HSF2 up-regulated the promoter activities and interacted with the promoters of ZO-1, occludin, and claudin-5 in GECs. In conclusion, our results indicate that knockdown of TUG1 increased BTB permeability via binding to miR-144 and then reducing EC tight junction protein expression by targeting HSF2. Thus, TUG1 may represent a useful future therapeutic target for enhancing BTB permeability.

Novel polymorphisms in UTR and coding region of inducible heat shock protein 70.1 gene in tropically adapted Indian zebu cattle (Bos indicus) and riverine buffalo (Bubalus bubalis)

Due to evolutionary divergence, cattle (taurine, and indicine) and buffalo are speculated to have different responses to heat stress condition. Variation in candidate genes associated with a heat-shock response may provide an insight into the dissimilarity and suggest targets for intervention. The present work was undertaken to characterize one of the inducible heat shock protein genes promoter and coding regions in diverse breeds of Indian zebu cattle and buffaloes. The genomic DNA from a panel of 117 unrelated animals representing 14 diversified native cattle breeds and 6 buffalo breeds were utilized to determine the complete sequence and gene diversity of HSP70.1 gene. The coding region of HSP70.1 gene in Indian zebu cattle, Bos taurus and buffalo was similar in length (1,926 bp) encoding a HSP70 protein of 641 amino acids with a calculated molecular weight (Mw) of 70.26 kDa. However buffalo had a longer 5' and 3' untranslated region (UTR) of 204 and 293 nucleotides respectively, in comparison to Indian zebu cattle and Bos taurus wherein length of 5' and 3'-UTR was 172 and 286 nucleotides, respectively. The increased length of buffalo HSP70.1 gene compared to indicine and taurine gene was due to two insertions each in 5' and 3'-UTR. Comparative sequence analysis of cattle (taurine and indicine) and buffalo HSP70.1 gene revealed a total of 54 gene variations (50 SNPs and 4 INDELs) among the three species in the HSP70.1 gene. The minor allele frequencies of these nucleotide variations varied from 0.03 to 0.5 with an average of 0.26. Among the 14 B. indicus cattle breeds studied, a total of 19 polymorphic sites were identified: 4 in the 5'-UTR and 15 in the coding region (of these 2 were non-synonymous). Analysis among buffalo breeds revealed 15 SNPs throughout the gene: 6 at the 5' flanking region and 9 in the coding region. In bubaline 5'-UTR, 2 additional putative transcription factor binding sites (Elk-1 and C-Re1) were identified, other than three common sites (CP2, HSE and Pax-4) observed across all the analyzed animals. No polymorphism was found within the 3'-UTR of Indian cattle or buffalo as it was found to be monomorphic. The promoter sequences generated in 117 individuals showed a rich array of sequence elements known to be involved in transcription regulation. A total of 11 nucleotide changes were observed in the promoter sequence across the analyzed species, 3 of these changes were located within the potential transcription factor binding domains. We also identified 4 microsatellite markers within the buffalo HSP70.1 gene and 3 microsatellites within bovine HSP70.1. The present study identified several distinct changes across indicine, taurine and bubaline HSP70.1 genes that could further be evaluated as molecular markers for thermotolerance.