In vivo growth of a murine lymphoma cell line alters regulation of expression of HSP72

Impact of heat shock transcription factor 1 on global gene expression profiles in cells which induce either cytoprotective or pro-apoptotic response following hyperthermia

Background

Elevated temperatures induce activation of the heat shock transcription factor 1 (HSF1) which in somatic cells leads to heat shock proteins synthesis and cytoprotection. However, in the male germ cells (spermatocytes) caspase-3 dependent apoptosis is induced upon HSF1 activation and spermatogenic cells are actively eliminated.

Results

To elucidate a mechanism of such diverse HSF1 activity we carried out genome-wide transcriptional analysis in control and heat-shocked cells, either spermatocytes or hepatocytes. Additionally, to identify direct molecular targets of active HSF1 we used chromatin immunoprecipitation assay (ChIP) combined with promoter microarrays (ChIP on chip). Genes that are differently regulated after HSF1 binding during hyperthermia in both types of cells have been identified. Despite HSF1 binding to promoter sequences in both types of cells, strong up-regulation of Hsps and other genes typically activated by the heat shock was observed only in hepatocytes. In spermatocytes HSF1 binding correlates with transcriptional repression on a large scale. HSF1-bound and negatively regulated genes encode mainly for proteins required for cell division, involved in RNA processing and piRNA biogenesis.

Conclusions

Observed suppression of the transcription could lead to genomic instability caused by meiotic recombination disturbances, which in turn might induce apoptosis of spermatogenic cells. We propose that HSF1-dependent induction of cell death is caused by the simultaneous repression of many genes required for spermatogenesis, which guarantees the elimination of cells damaged during heat shock. Such activity of HSF1 prevents transmission of damaged genetic material to the next generation.

Inducible heat shock protein 70 expression as a potential predictive marker of metastasis in breast tumors

Heat shock protein (Hsp)-peptide complexes purified from tumors can prime the immune system against tumor antigens, but how they contribute to the generation of immune responses against naturally occurring tumors is unknown. Murine tumors expressing high amounts of Hsp70 are preferentially rejected by the immune system, suggesting that low Hsp70 expression is advantageous for tumor growth in the host. To determine whether Hsp70 was differentially expressed in human tumors, inducible Hsp70 expression was quantitatively (by Western blot) and qualitatively (by immunohistology) analyzed in 53 biopsies of tumor and normal breast tissue. The mean expression of inducible Hsp70 was significantly higher in tumor compared with normal tissue (U = 899.0; P = 0.0033). However, a significant negative association of the amount of Hsp70 expressed by tumor tissue was found with metastasis (r = -0.309; P = 0.05). After 3 years, follow-up analysis determined that 7 of the 53 patients relapsed, and 5 died. Hsp70 expression in tumor (but not normal) cells was significantly lower in relapse patients and patients with metastatic disease than in patients with no relapse or metastasis. Together, these observations support the hypothesis that Hsp70 plays a role in tumor expansion in vivo, and tumors that downregulate it may be able to evade immunosurveillance and grow.

HSP70.1 and -70.3 are required for late-phase protection induced by ischemic preconditioning of mouse hearts

We investigated the role of inducible heat shock proteins 70.1 and 70.3 (HSP70.1 and HSP70.3, respectively) in myocardial ischemic preconditioning (IP) in mice. Wild-type (WT) mice and HSP70.1- and HSP70.3-null [HSP70.1/3(-/-)] mice were subjected to IP and examined 24 h later during the late phase of protection. IP significantly increased steady-state levels of HSP70.1 and HSP70.3 mRNA and expression of inducible HSP70 protein in WT myocardium. To assess protection against tissue injury, mice were subjected to 30 min of regional ischemia and 3 h of reperfusion. In WT mice, IP reduced infarct size by 43% compared with sham IP-treated mice. In contrast, IP did not reduce infarct size in HSP70.1/3(-/-) mice. Absence of inducible HSP70.1 and HSP70.3 had no effect, however, on classical or early-phase protection produced by IP, which significantly reduced infarct size in HSP70.1/3(-/-) mice. We conclude that inducible HSP70.1 and HSP70.3 are required for late-phase protection against infarction following IP in mice.

JNK phosphorylates the HSF1 transcriptional activation domain: role of JNK in the regulation of the heat shock response

The role of c-Jun NH2-terminal kinase (JNK) signaling cascade in the stress-inducible phosphorylation of heat shock factor 1 (HSF1) was investigated using known agonists and antagonists of JNK. We showed that treatment of HeLa cells with MG132, a proteasome inhibitor and known INK activator, caused the transcriptional activation domain of HSF1 to be targeted and phosphorylated by JNK2 in vivo. Dose-response and time course studies of the effects of heat shock and anisomycin treatment showed a close correlation of the activation of JNK and hyperphosphorylation of HSF1. SB203580 inhibited INK at the 100 microM concentration and significantly reduced the amount of hyperphosphorylated HSF1 upon heat shock or anisomycin treatment. SB203580 and dominant-negative JNK suppress hsp70 promoter-driven reporter gene expression selectively at 45 degrees C but not at 42 degrees C heat stress, suggesting that JNK would be preferentially associated with the protective heat shock response against severe heat stress. The possibility that JNK-mediated phosphorylation of HSF1 may selectively stabilize the HSF1 protein and confers protection to cells under conditions of severe stress is discussed.

A natural extracellular factor that induces Hsp72, inhibits apoptosis, and restores stress resistance in aged human cells

Experiments with cultured cells showed that most cellular stress resistance components are specialized for certain types of damage. For example, superoxide dismutase protects from oxidative damage; DNA repair enzymes guard against mutagens and other DNA-damaging agents. On the other hand, the major inducible heat shock protein Hsp72 protects cells from a large variety of stresses and thus represents a generalized repair/stress resistance component. Hsp72 not only refolds damaged proteins but also interferes with programmed cell death signaling pathways, thus providing cells with time to repair the damage, hence its universality as a stress protector. In the present study we demonstrate the occurrence in murine and human ascites fluids (AF) of a natural nontoxic extracellular factor (ascites Hsp72-inducing factor, AHIF) capable of activating Hsp72 expression in different types of cells via a pathway distinct from the heat shock response pathway. AHIF is unique in that it is the first physiological factor capable of inducing synthesis of Hsp72 not only in young cells but, remarkably, also in aged human cells that largely have lost the ability to express Hsp72 in response to stresses, a manifestation at the cellular level of a progressive impairment in the ability to adapt to environmental changes which characterizes aging. Pretreatment of aged human cells with AF triggers Hsp72 expression at levels seen in young stressed cells and protects cells from a variety of otherwise lethal stressful treatments such as heat shock, TNF, UV irradiation, etoposide, and menadione. Activation of Hsp72 expression is essential for antiapoptotic action of AHIF because specific inhibition of Hsp72 expression by antisense RNA abolishes the cytoprotective effect of AF. In view of an important link between stress resistance and longevity in different organisms, the abilities of AHIF make it a unique candidate for the role of a systemic regulator of the aging process. While a cell-autonomous stress response diminishes with aging, aged cells retain the ability to respond to an extracellular factor which induces the expression of Hsp72. This finding opens up exciting possibilities for using AF factor to restore stress resistance to old cells and organisms and the possibility of interfering with the aging process. The ability to induce stress resistance in young cells and to restore it in aged cells could serve as a basis for developing effective antiapoptotic therapies.

Evidence for a hsp25-specific mechanism involved in transcriptional activation by heat shock

Transcriptional stimulation of heat shock genes is generally due to the activation of heat shock transcription factor (HSF) 1. We demonstrate that in the murine leucemic cell line, P388, trimerization of HSF1, transcriptional activation of the hsp70 gene, and expression of Hsp70 are achieved as a result of heat shock. In contrast, the small heat shock proteins Hsp25 and alpha B-crystallin are not expressed in these cells and cannot be induced upon heat shock. Furthermore, no hsp25 transcript can be detected, indicating that there is a defect in the hsp25 gene or a block in its expression. Comparison of the hsp25 gene structure between P388 and Hsp25-expressing Ehrlich ascites tumor (EAT) cells by Southern blot analysis revealed no differences in the structural organization of the gene and no changes in its localization in the genome. However, sequence analysis of the hsp25 promoter region in P388 cells demonstrates minor differences. Despite these differences, the hsp25 promoter from P388 cells mediates heat shock-induced activation of a reporter gene when transfected into human HeLa cells which is comparable to that of the hsp25 promoter from EAT cells. Furthermore, the hsp25 gene isolated from EAT or P388 cells can both be expressed in HeLa cells and lead to a similar heat shock-stimulated accumulation of Hsp25. Silencing of the hsp25 and alpha B-crystallin genes in P388 cells by DNA-methylation could also be excluded since 5-azacytidine treatment does not influence expression of these genes. Interestingly, when expressed in P388 cells the hsp25 promoter from EAT cells is not activated upon heat shock, whereas the human hsp70 promoter is activated. Taken together, the data suggest cell line-specific differences in a mechanism of regulation of hsp25 transcription, which interferes with the activation of the promoter by HSF1 and which may also affect the alpha B-crystallin gene.

Cell Signaling and Heat Shock Protein Expression

Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance. Copyright 1996 S. Karger AG, Basel

Methylation-associated transcriptional silencing of the major histocompatibility complex-linked hsp70 genes in mouse cell lines

The MHC-linked hsp70 locus consists of duplicated genes, hsp70.1 and hsp70.3, which in primary mouse embryo cells are highly heat shock-inducible. Several mouse cell lines in which hsp70 expression is not activated by heat shock have been described previously, but the basis for the deficiency has not been identified. In this study, genomic footprinting analysis has identified a common basis for the deficient response of the hsp70.1 gene to heat shock in four such cell lines, viz., the promoter is inaccessible to transcription factors, including heat shock transcription factor. Southern blot analyses reveal extensive CpG methylation of a 1.2-kilobase region spanning the hsp70.1 transcription start site and hypermethylation of the adjacent hsp70.3 gene, which is presumably also inaccessible to regulatory factors. Of four additional, randomly chosen mouse cell lines, three show no or minimal hsp70.3 heat shock responsiveness and CpG methylation of both hsp70 genes, and two of the three lines exhibit a suboptimal hsp70.1 response to heat shock as well. In all three lines, the accessibility of the hsp70.1 promoter to transcription factors is detectable but clearly diminished (relative to that in primary mouse cells). Our results suggest that the tandem hsp70 genes are concomitantly methylated and transcriptionally repressed with high frequency in cultured mouse cells.