Histone deacetylase is a direct target of valproic acid, a potent anticonvulsant, mood stabilizer, and teratogen

Valproate regulates GSK-3-mediated axonal remodeling and synapsin I clustering in developing neurons

Valproate (VPA) and lithium have been used for many years in the treatment of manic depression. However, their mechanisms of action remain poorly understood. Recent studies suggest that lithium and VPA inhibit GSK-3beta, a serine/threonine kinase involved in the insulin and WNT signaling pathways. Inhibition of GSK-3beta by high concentrations of lithium has been shown to mimic WNT-7a signaling by inducing axonal remodeling and clustering of synapsin I in developing neurons. Here we have compared the effect of therapeutic concentrations of lithium and VPA during neuronal maturation. VPA and, to a lesser extent, lithium induce clustering of synapsin I. In addition, lithium and VPA induce similar changes in the morphology of axons by increasing growth cone size, spreading, and branching. More importantly, both mood stabilizers decrease the level of MAP-1B-P, a GSK-3beta-phosphorylated form of MAP-1B in developing neurons, suggesting that therapeutic concentrations of these mood stabilizers inhibit GSK-3beta. In vitro kinase assays show that therapeutic concentrations of VPA do not inhibit GSK-3beta but that therapeutic concentrations of lithium partially inhibit GSK-3beta activity. Our results support the idea that both mood stabilizers inhibit GSK-3beta in developing neurons through different pathways. Lithium directly inhibits GSK-3beta in contrast to VPA, which inhibits GSK-3beta indirectly by an as-yet-unknown pathway. These findings may have important implications for the development of new strategies to treat bipolar disorders.

Stage-specific modulation of skeletal myogenesis by inhibitors of nuclear deacetylases

Nuclear acetyltransferases promote and deacetylases inhibit skeletal muscle-gene expression, suggesting the potential effectiveness of deacetylase inhibitors (DIs) in modulating skeletal myogenesis. Surprisingly, previous studies have indicated that DIs suppress myogenesis. The recent observations that histone deacetylases associate with the muscle-regulatory proteins MyoD and MEF2C only in undifferentiated myoblasts prompted us to evaluate the effect of DIs at distinct stages of the myogenic program. We found that exposure of established rodent and human muscle cells to distinct DIs has stage-specific effects. Exposure of undifferentiated skeletal myoblasts to DIs, followed by incubation in differentiation medium, enhanced the expression of muscle-specific reporters and increased the levels of endogenous muscle proteins, leading to a dramatic increase in the formation of multinucleated myotubes. By contrast, simultaneous exposure of muscle cells to differentiation medium and DIs inhibited the myogenic program. Likewise, embryos exposed in utero to nonteratogenic doses of DI at the early stages of somitic myogenesis (embryonic day 8.5) exhibited an increased number of somites and augmented expression of a muscle-specific transgene as well as endogenous muscle genes. The functional effects induced by DIs were mirrored by changes in the state of acetylation of histones present at a muscle-gene enhancer and of MyoD itself. These results represent the first evidence that DIs can enhance muscle differentiation and suggest the rationale for their use in manipulating adult and embryonic skeletal myogenesis.

A common mechanism of action for three mood-stabilizing drugs

Lithium, carbamazepine and valproic acid are effective mood-stabilizing treatments for bipolar affective disorder. The molecular mechanisms underlying the actions of these drugs and the illness itself are unknown. Berridge and colleagues suggested that inositol depletion may be the way that lithium works in bipolar affective disorder, but others have suggested that glycogen synthase kinase (GSK3) may be the relevant target. The action of valproic acid has been linked to both inositol depletion and to inhibition of histone deacetylase (HDAC). We show here that all three drugs inhibit the collapse of sensory neuron growth cones and increase growth cone area. These effects do not depend on GSK3 or HDAC inhibition. Inositol, however, reverses the effects of the drugs on growth cones, thus implicating inositol depletion in their action. Moreover, the development of Dictyostelium is sensitive to lithium and to valproic acid, but resistance to both is conferred by deletion of the gene that codes for prolyl oligopeptidase, which also regulates inositol metabolism. Inhibitors of prolyl oligopeptidase reverse the effects of all three drugs on sensory neuron growth cone area and collapse. These results suggest a molecular basis for both bipolar affective disorder and its treatment.

Differential effects of histone deacetylase inhibitors on interleukin-18 gene expression in myeloid cells

Histone deacetyrase (HDAC) inhibitors induce growth arrest and differentiation of leukemia cell lines and tumor cells derived from a large variety of human tissues. Here we showed that HDAC inhibitors sodium butyrate, TSA, and valproate regulated the expression of Interleukin-18 (IL-18), a cytokine with antitumor and proinflammatory properties, in human acute myeloid leukemia cell lines U937 and HEL. Sodium butyrate increased expression of IL-18 protein and mRNA and activated 1357bp IL-18 gene promoter construct. IL-18 mRNA level was up-regulated by TSA or valproate, which also activated IL-18 full-length promoter. While sodium butyrate or TSA stimulated the 108-bp IL-18 minimal promoter, valproate failed to activate it, indicating that valproate may use a distinct mechanism from sodium butyrate and TSA to activate IL-18 gene expression.

Histone-deacetylase inhibitors: novel drugs for the treatment of cancer

The opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs) allow gene expression to be exquisitely regulated through chromatin remodelling. Aberrant transcription due to altered expression or mutation of genes that encode HATs, HDACs or their binding partners, is a key event in the onset and progression of cancer. HDAC inhibitors can reactivate gene expression and inhibit the growth and survival of tumour cells. The remarkable tumour specificity of these compounds, and their potency in vitro and in vivo, underscore the potential of HDAC inhibitors as exciting new agents for the treatment of cancer.

Valproic acid defines a novel class of HDAC inhibitors inducing differentiation of transformed cells

Histone deacetylases (HDACs) play important roles in transcriptional regulation and pathogenesis of cancer. Thus, HDAC inhibitors are candidate drugs for differentiation therapy of cancer. Here, we show that the well-tolerated antiepileptic drug valproic acid is a powerful HDAC inhibitor. Valproic acid relieves HDAC-dependent transcriptional repression and causes hyperacetylation of histones in cultured cells and in vivo. Valproic acid inhibits HDAC activity in vitro, most probably by binding to the catalytic center of HDACs. Most importantly, valproic acid induces differentiation of carcinoma cells, transformed hematopoietic progenitor cells and leukemic blasts from acute myeloid leukemia patients. More over, tumor growth and metastasis formation are significantly reduced in animal experiments. Therefore, valproic acid might serve as an effective drug for cancer therapy.

Histone deacetylases and cancer: causes and therapies

Together, histone acetyltransferases and histone deacetylases (HDACs) determine the acetylation status of histones. This acetylation affects the regulation of gene expression, and inhibitors of HDACs have been found to cause growth arrest, differentiation and/or apoptosis of many tumours cells by altering the transcription of a small number of genes. HDAC inhibitors are proving to be an exciting therapeutic approach to cancer, but how do they exert this effect?