Modulation of HSP70 and HSP27 gene expression by the differentiation inducer sodium butyrate in U-937 human promonocytic leukemia cells

Role of heat shock proteins in stem cell behavior

Stress response is well appreciated to induce the expression of heat shock proteins (Hsps) in the cell. Numerous studies have demonstrated that Hsps function as molecular chaperones in the stabilization of intracellular proteins, repairing damaged proteins, and assisting in protein translocation. Various kinds of stem cells (embryonic stem cells, adult stem cells, or induced pluripotent stem cells) have to maintain their stemness and, under certain circumstances, undergo stress. Therefore, Hsps should have an important influence on stem cells. Actually, numerous studies have indicated that some Hsps physically interact with a number of transcription factors as well as intrinsic and extrinsic signaling pathways. Importantly, alterations in Hsp expression have been demonstrated to affect stem cell behavior including self-renewal, differentiation, sensitivity to environmental stress, and aging. This chapter summarizes recent findings related to (1) the roles of Hsps in maintenance of stem cell dormancy, proliferation, and differentiation; (2) the expression signature of Hsps in embryonic/adult stem cells and differentiated stem cells; (3) the protective roles of Hsps in transplanted stem cells; and (4) the possible roles of Hsps in stem cell aging.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

Short-chain fatty acid mediated phosphorylation of heat shock protein 25: effects on camptothecin-induced apoptosis

Although short-chain fatty acid (SCFA)-induced heat shock protein 25 (Hsp25) is associated with increased cellular resistance to injury, withdrawal of lumenal butyrate in vivo is associated with intestinal epithelial injury and apoptosis. Recognizing that SCFA-dependent posttranslational modification of Hsp25 may involve altered Hsp25 phosphorylation, we hypothesized that butyrate regulates Hsp25 phosphorylation and secondarily affects cellular responses to apoptosis-inducing agents. Intestinal epithelial crypt IEC-18 cells were treated with butyrate, propionate, or the histone deacetylase inhibitor trichostatin A for 6-24 h. Immunolocalization of Hsp25 was examined by confocal laser microscopy. Hsp25 phosphorylation was characterized using two-dimensional isoelectric focusing gel electrophoresis. Hsp25 accumulation in cytoskeletal- and mitochondrial-enriched fractions was examined by immunoblotting. The activation of p38 MAP kinase was determined using phospho-specific antibodies and MAPKAPK 2 kinase assays. The effects of SCFA on apoptosis were studied by ELISA detection of cleaved DNA and using antibodies recognizing cleaved caspase-3. Five-millimolar butyrate induced no significant injury to IEC-18 cells. Hsp25 did not accumulate in Triton X-100-insoluble cytoskeletal fractions with butyrate treatment but did localize to mitochondria in a p38 MAP kinase-dependent manner. Hsp25 phosphorylation was induced by butyrate, propionate, and trichostatin A. Butyrate-mediated changes in Hsp25 phosphorylation coincide with the activation of the p38 MAP kinase and MAPKAPK 2. Butyrate, propionate, and low-dose trichostatin A confer significant protection from camptothecin-induced apoptosis, which was not reversed by the p38 inhibitor SB203580. We conclude that butyrate-mediated phosphorylation of Hsp25 is associated with significant resistance to apoptosis, which appears to be independent of p38-mediated targeting of Hsp25 to mitochondria.

Induction of HSP70 promotes DeltaF508 CFTR trafficking

The DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) is a temperature-sensitive trafficking mutant that is detected as an immature 160-kDa form (band B) in gel electrophoresis. The goal of this study was to test the hypothesis that HSP70, a member of the 70-kDa heat shock protein family, promotes DeltaF508 CFTR processing to the mature 180-kDa form (band C). Both pharmacological and genetic techniques were used to induce HSP70. IB3-1 cells were treated with sodium 4-phenylbutyrate (4PBA) to promote maturation of DeltaF508 CFTR to band C. A dose-dependent increase in band C and total cellular HSP70 was observed. Under these conditions, HSP70-CFTR complexes were increased and 70-kDa heat shock cognate protein-CFTR complexes were decreased. Increased DeltaF508 CFTR maturation was also seen after transfection with an HSP70 expression plasmid and exposure to glutamine, an inducer of HSP70. With immunofluorescence techniques, the increased appearance of CFTR band C correlated with CFTR distribution beyond the perinuclear regions. These data suggest that induction of HSP70 promotes DeltaF508 CFTR maturation and trafficking.

Regulation of multidrug resistance 1 (MDR1)/P-glycoprotein gene expression and activity by heat-shock transcription factor 1 (HSF1)

Infection of HeLa cells with adenovirus-carrying HSF1(+) cDNA, which encodes a mutated form of HSF1 with constitutive transactivation capacity, increased multidrug resistance 1 (MDR1) mRNA level and P-glycoprotein (P-gp) cell surface content and stimulated rhodamine 123 accumulation and vinblastine efflux activity. On the other hand, infection with adenovirus-carrying HSP70 and HSP27 cDNAs did not increase MDR1/P-gp expression. HSF1 regulates MDR1/P-gp expression at the transcriptional level, since HSF1(+) bound the heat-shock consensus elements (HSEs) in the MDR1 gene promoter and also activated the expression of an MDR1 promoter-driven reporter plasmid (pMDR1(-1202)). In addition, heat-shock increased pMDR1(-1202) promoter activity but not the activity of a similar reporter plasmid with point mutations at specific HSEs, and the heat-induced increase was totally inhibited by co-transfection with an expression plasmid carrying HSF1(-), a dominant negative mutant of HSF1. The stress inducers arsenite, butyrate, and etoposide also increased pMDR1(-1202) promoter activity, but the increase was not inhibited (in the case of butyrate) or was only partially inhibited (in the case of arsenite and etoposide) by HSF1(-). These results demonstrate that HSF1 regulates MDR1 expression, and that the HSEs present in the -315 to -285 region mediate the heat-induced activation of the MDR1 promoter. However, other factors may also participate in MDR1 induction by stressing agents.

The expression of glucose regulated protein-94 in colorectal carcinoma cells treated by sodium butyrate

The expression of glucose regulated protein 94 (GRP94) during the treatment of human colorectal carcinoma cell line-Clone A cells with sodium butyrate was studied. Sodium butyrate (SB) can cause functional and morphological effects on Clone A cells including growth arrest at G0/G1 stage and cell differentiation as observed by morphological changes, MTT and flow cytometry assays, as well as reduced Grp94 gene expression as shown by Northern blot and Western blot assays. The possible mechanism of the correlation between Grp94 gene expression and tumor growth inhibition and cell differentiation is briefly discussed.

Activation of protein kinase A by dibutyryl cAMP treatment of NIH 3T3 cells inhibits proliferation but fails to induce Ser-133 phosphorylation and transcriptional activation of CREB

The cAMP analogue dibutyryl cAMP (dbcAMP) is often used to activate the protein kinase A pathway and to study the expression of cAMP-responsive genes. Here we show that in NIH 3T3 cells dbcAMP is able to activate PKA, but fails to stimulate expression of the cAMP-inducible c-fos gene. Co-expression of A-kinase anchoring protein 75, previously shown to amplify cAMP signalling and to stimulate c-fos expression, could not restore cAMP responsiveness of the c-fos promoter. DbcAMP-induced activation of PKA may result in poor translocation of the catalytic sub-units of PKA to the nucleus, indicated by the lack of both Ser-133 phosphorylation of the cAMP-response element binding factor CREB and stimulation of the transcriptional activity of this factor. DbcAMP treatment, however, inhibited cell proliferation. These results suggest that cAMP-mediated inhibition of proliferation may be independent of translocation of the catalytic sub-units into the nucleus.

Role of butyric acid and its derivatives in the treatment of colorectal cancer and hemoglobinopathies

Butyric acid, a short chain fatty acid (SCFA), is a natural component of the animal metabolism. Physiological concentrations induce multiple and reversible biological effects. They concern regulatory mechanisms of gene expression conducing to promote markers of cell differentiation, apoptosis and cell growth control. The described hyperacetylation of histones and the induction of several immune or non-immune cell-activating mediators are consistent with the pleiotropic stimulatory effect of the agent. Butyric acid is considered as a biological response modifier (BRM) and is an interesting tool for biological studies. The history of butyric acid as a putative medication in human health is spanning since 60 years and is confusing in part because of conflicting data between exciting experimental results and clinical trials. In light of minimal impact of systemic therapy and the short half-life of the saline molecule used, it is evident that continuous infusions of butyrate are required to improve the efficacy of the treatment. Butyric acid has been viewed with skepticism because of less convenient for long-term chronic therapy. New experimental data from several studies conduced within the past decade with butyric derivatives, delivery systems, and long-acting prodrugs, have demonstrated the practical value of the therapeutic concept. To support issues regarding clinical development, it was of interest to evaluate the recent information, showing butyric acid currently considered as therapeutic purposes in the treatment of colorectal cancer and hemoglobinopathies.

Inhibition of cellular proliferation by the Wilms tumor suppressor WT1 requires association with the inducible chaperone Hsp70

The Wilms tumor suppressor WT1 encodes a zinc finger transcription factor that is expressed in glomerular podocytes during a narrow window in kidney development. By immunoprecipitation and protein microsequencing analysis, we have identified a major cellular protein associated with endogenous WT1 to be the inducible chaperone Hsp70. WT1 and Hsp70 are physically associated in embryonic rat kidney cells, in primary Wilms tumor specimens and in cultured cells with inducible expression of WT1. Colocalization of WT1 and Hsp70 is evident within podocytes of the developing kidney, and Hsp70 is recruited to the characteristic subnuclear clusters that contain WT1. The amino-terminal transactivation domain of WT1 is required for binding to Hsp70, and expression of that domain itself is sufficient to induce expression of Hsp70 through the heat shock element (HSE). Substitution of a heterologous Hsp70-binding domain derived from human DNAJ is sufficient to restore the functional properties of a WT1 protein with an amino-terminal deletion, an effect that is abrogated by a point mutation in DNAJ that reduces binding to Hsp70. These observations indicate that Hsp70 is an important cofactor for the function of WT1, and suggest a potential role for this chaperone during kidney differentiation.

Modulation of heat-shock protein 70 (HSP70) gene expression by sodium butyrate in U-937 promonocytic cells: relationships with differentiation and apoptosis

The administration of sodium butyrate at 0.75 mM induced the functional differentiation of U-937 human promonocytic leukemia cells with negligible cell mortality. However, the drug rapidly caused cell death with characteristics of apoptosis when used at concentrations of 5 mM and above. In addition, butyrate stimulated the expression of the stress-responsive heat-shock protein 70 (HSP70) gene when applied at both differentiation-inducing and apoptosis-inducing concentrations. The induction of HSP70 by butyrate was inhibited by the simultaneous addition of cAMP-increasing agents (dibutyryl cAMP or the combination of forskolin plus theophylline). However, these agents did not prevent differentiation and only partially reduced apoptosis. Moreover, the DNA topoisomerase II inhibitor etoposide, which provoked U-937 cell differentiation and apoptosis with the same or greater efficiency than butyrate, failed to stimulate HSP70 expression. Finally, it was observed that cAMP-increasing agents also abrogated the induction of HSP70 and reduced the apoptosis caused by cadmium chloride, a typical inducer of the stress response. Taken together, these results indicate that HSP70 expression is not required for differentiation of promonocytic cells, as earlier proposed, and that butyrate probably triggers the stress response in these cells.

Molecular Events as Targets of Anticancer Drug Therapy

The aim of this review is to introduce some molecular targets for cancer chemotherapy, with comments on their mode of action, preclinical and clinical results. The representatives of the following groups are covered: phosphorylation inhibitors, protein kinase modulators, receptor antagonists, immunomodulators, differentiating agents, multidrug resistance modulation, telomerase inhibitors, and bioreductive agents.