Induction of GRP78 by valproic acid is dependent upon histone deacetylase inhibition

Valproic (2-propylpentanoic) acid is a commonly used drug in the treatment of bipolar disorder and epilepsy. The molecular mechanism that underlies its clinical efficacy remains controversial and is complicated by the broad range of intracellular effects of valproic acid, including its ability to inhibit histone deacetylase (HDAC) and induce protein chaperone expression. Here we show that an established HDAC inhibitor, trichostatin A, promotes ER chaperone expression in HEK293 cells. Furthermore, we use chemical derivatives of valproic acid to show that the ability to promote GRP78 levels directly correlates with the induction of histone H4 hyperacetylation. These results suggest that exposure to valproic acid enhances chaperone expression by a mechanism that involves histone hyperacetylation.     

Protective effects of valproic acid against airway hyperresponsiveness and airway remodeling in a mouse model of allergic airways disease

Airway remodeling and airway hyperresponsiveness are major aspects of asthma pathology that are not targeted optimally by existing anti-inflammatory drugs. Histone deacetylase inhibitors have a wide range of effects that may potentially abrogate aspects of remodeling. One such histone deacetylase inhibitor is valproic acid (2-propylvaleric acid). Valproic acid is used clinically as an anti-epileptic drug and is a potent inhibitor of class I histone deacetylases but also inhibits class II histone deacetylases. We used valproic acid as a molecular model of histone deacetylase inhibition in vivo in chronic allergic airways disease mice with airway remodeling and airway hyperresponsiveness. Wild-type Balb/c mice with allergic airways disease were treated with valproic acid or vehicle control. Airway inflammation was assessed by bronchoalveolar lavage fluid cell counts and examination of lung tissue sections. Remodeling was assessed by morphometric analysis of histochemically stained slides and lung function was assessed by invasive plethysmography measurement of airway resistance. Valproic acid treatment did not affect inflammation parameters; however, valproic acid treatment resulted in reduced epithelial thickness as compared to vehicle treated mice

(p < 0.01), reduced subepithelial collagen deposition (p < 0.05) and attenuated airway hyperresponsiveness (p < 0.05 and p < 0.01 for the two highest doses of methacholine, respectively). These findings show that treatment with valproic acid can reduce structural airway remodeling changes and hyperresponsiveness, providing further evidence for the potential use of histone deacetylase inhibitors for the treatment of asthma.     

Protective effects of valproic acid against airway hyperresponsiveness and airway remodeling in a mouse model of allergic airways disease

Airway remodeling and airway hyperresponsiveness are major aspects of asthma pathology that are not targeted optimally by existing anti-inflammatory drugs. Histone deacetylase inhibitors have a wide range of effects that may potentially abrogate aspects of remodeling. One such histone deacetylase inhibitor is valproic acid (2-propylvaleric acid). Valproic acid is used clinically as an anti-epileptic drug and is a potent inhibitor of class I histone deacetylases but also inhibits class II histone deacetylases. We used valproic acid as a molecular model of histone deacetylase inhibition in vivo in chronic allergic airways disease mice with airway remodeling and airway hyperresponsiveness. Wild-type Balb/c mice with allergic airways disease were treated with valproic acid or vehicle control. Airway inflammation was assessed by bronchoalveolar lavage fluid cell counts and examination of lung tissue sections. Remodeling was assessed by morphometric analysis of histochemically stained slides and lung function was assessed by invasive plethysmography measurement of airway resistance. Valproic acid treatment did not affect inflammation parameters; however, valproic acid treatment resulted in reduced epithelial thickness as compared to vehicle treated mice (p < 0.01), reduced subepithelial collagen deposition (p < 0.05) and attenuated airway hyperresponsiveness (p < 0.05 and p < 0.01 for the two highest doses of methacholine, respectively). These findings show that treatment with valproic acid can reduce structural airway remodeling changes and hyperresponsiveness, providing further evidence for the potential use of histone deacetylase inhibitors for the treatment of asthma.     

Histone Deacetylase Inhibitor Valproic Acid Promotes the Differentiation of Human Induced Pluripotent Stem Cells into Hepatocyte-Like Cells

In this study, we aimed to elucidate the effects and mechanism of action of valproic acid on hepatic differentiation from human induced pluripotent stem cell-derived hepatic progenitor cells. Human induced pluripotent stem cells were differentiated into endodermal cells in the presence of activin A and then into hepatic progenitor cells using dimethyl sulfoxide. Hepatic progenitor cells were matured in the presence of hepatocyte growth factor, oncostatin M, and dexamethasone with valproic acid that was added during the maturation process. After 25 days of differentiation, cells expressed hepatic marker genes and drug-metabolizing enzymes and exhibited drug-metabolizing enzyme activities. These expression levels and activities were increased by treatment with valproic acid, the timing and duration of which were important parameters to promote differentiation from human induced pluripotent stem cell-derived hepatic progenitor cells into hepatocytes. Valproic acid inhibited histone deacetylase activity during differentiation of human induced pluripotent stem cells, and other histone deacetylase inhibitors also enhanced differentiation into hepatocytes. In conclusion, histone deacetylase inhibitors such as valproic acid can be used to promote hepatic differentiation from human induced pluripotent stem cell-derived hepatic progenitor cells.     

The Epigenetic Modifier,Valproic Acid,Enhances Radiation Sensitivity

Valproic acid is an established therapeutic for a variety of seizure disorders and incertain cases for depression and anxiety. In addition, valproic acid has been shown topossess histone deacetylase inhibition activity and is currently being investigated asan anti-cancer agent, either alone or in combination with other conventional cancertherapies such as ionizing radiation. In this study, we investigated whether valproicacid modulates cellular responses to radiation in human erythroleukemic, K562 cells.Hyperacetylation of nuclear histones 3 and 4 was used to correlate the effects ofvalproic acid to inhibition of histone deacetylase activity, clonogenic survival,apoptosis and apoptosis. The findings from the clonogenic survival and caspaseinduction assays indicated that pre-treatment of cells with valproic acid for 24 hours,markedly enhanced radiation induced cell-death and apoptosis in K562 cells,respectively. Mechanisms involving drug-mediated cytotoxicity and changes in cellcycle distribution were associated with the radiation sensitizing properties of valproicacid, particularly at the higher concentrations. Overall, our findings are consistentwith the general consensus that HDAC inhibitors efficiently sensitize cancer cells tothe effects of ionizing radiation and support the idea of developing clinically relevantcombinations of HDAC inhibitors and radiotherapy.     

Casein kinase 2 inhibition differentially modulates apoptotic effect of trichostatin A against epithelial ovarian carcinoma cell lines

Histone deacetylase inhibitors and casein kinase 2 inhibitors have been shown to induce apoptosis. However, the combined effect of casein kinase 2 inhibition on the apoptotic effect of histone deacetylase inhibitor is unknown. We assessed the effect of casein kinase 2 inhibition on the apoptotic effect of trichostatin A in human epithelial carcinoma cell lines with respect to cell death signaling pathways. At concentrations that did not induce cell death, the casein kinase 2 inhibitor 4,5,6,7-tetrabromobenzotriazole inhibited activation of apoptotic proteins and changes in mitochondrial membrane permeability induced by the histone deacetylase inhibitor trichostatin A. These results suggest that casein kinase 2 inhibition may reduce trichostatin A-induced apoptosis in ovarian carcinoma cell lines by suppressing activation of apoptotic proteins and changes in mitochondrial membrane permeability, which both lead to caspase-3 activation. Casein kinase 2 inhibition, which does not induce a cytotoxic effect, may prevent histone deacetylase inhibitor-mediated apoptosis.     

Effect of valproic acid on radiation-induced DNA damage in euchromatic and heterochromatic compartments

The distinction between heterochromatin and euchromatin in the double-strand break (DSB) damage pathway is of interest, recent reports indicate that chromatin is not created equally nor is it acquiescent to DSBs. Using the classical histone deacetylase inhibitor, Trichostatin A, we have previously demonstrated that chromatin represents a heterogeneous substrate with respect to histone tail modification by histone deacetylase inhibitors and consequent responses to DNA damage and repair. Here, we extended the initial findings by investigating the radiation sensitizing properties of the widely used antiepileptic, valproic acid. Clonogenic survival assays confirm that valproic acid is an efficient sensitizer of radiation-induced cell death. The radiosensitizing effect is correlated with valproic acid-mediated histone hyperacetylation, chromatin decondensation and enhanced formation of radiation-induced γH2AX preferentially on euchromatic alleles. Heterochromatin was much more resistant to histone tail modification, changes in chromatin architecture and DNA damage. These findings are consolidated by studies with the structurally related analogue, valpromide, which does not inhibit histone deacetylase enzymes. At a relatively low concentration (1 mM) valpromide did not cause chromatin modifications and radiation sensitivity, providing further evidence that the radiation sensitizing properties of valproic acid are at least in part, due to histone modification-dependent effects on euchromatin. When higher concentrations (5 mM) were used, both compounds resulted in significant radiation sensitivity, albeit, with differing efficacy (dose modifying factors of 1.5 and 1.2 for valproic acid and valpromide, respectively). The findings imply that histone-modification independent mechanisms also contribute to the radiation sensitizing properties of valproic acid. Overall, our findings are consistent with the emerging interest in the use histone deacetylase inhibitors in combination with radiotherapy for the treatment of cancer.     

Interaction between dexamethasone and butyrate in apoptosis induction: non-additive in thymocytes and synergistic in a T cell-derived leukemia cell line.

In thymocytes butyrate and trichostatin A are unable to augment dexamethasone-induced apoptosis. In cultured rat thymocytes the extent of apoptosis induced by dexamethasone alone did not increase by addition of 0.1 - 10 mM butyrate. Even more pronounced was the non-additive interrelationship between dexamethasone and trichostatin A, as trichostatin A-induced apoptosis was not only blocked by the presence of dexamethasone but dexamethasone-induced apoptosis was also partially inhibited in the presence of 0.1 - 0.5 microM trichostatin A. The fact that the non-additive relationship with dexamethasone for apoptosis induction was observed with both histone deacetylase inhibitors suggests that in thymocytes this phenomenon is related to histone acetylation. In contrast to this, in the human T cell-derived leukemia cell line CEM-C7H2, dexamethasone did not block butyrate- or trichostatin A-induced apoptosis; moreover, butyrate, in the concentration range of 0.1 - 1 mM, had a marked synergistic effect on dexamethasone-induced apoptosis. This synergism, however, was not mimicked by trichostatin A, indicating that the effect is not related to histone acetylation but rather due to a pleiotropic effect of butyrate. Furthermore, in CEM-C7H2 cells, at higher concentrations of butyrate (5 - 10 mM) or trichostatin A (0.4 - 0.8 microM), there was a minor but reproducible antagonistic effect of dexamethasone on apoptosis induced by each of the two histone deacetylase inhibitors, suggesting that this antagonistic effect too, is related to histone hyperacetylation.