Histone deacetylase inhibitors such as sodium butyrate and trichostatin A induce apoptosis through an increase of the bcl-2-related protein Bad

Sodium 4-phenylbutyrate induces apoptosis of human lung carcinoma cells through activating JNK pathway

Sodium 4-phenylbutyrate (PB) has been used in the therapy of urea cycle defects for many years. Recently, it has been shown to cause cellular differentiation, growth arrest, and apoptosis in certain malignancies. We have analyzed the effects of PB on human lung carcinoma cells. PB has distinct patterns of effects on different lung carcinoma cells, inducing apoptosis in NCI-H460 and NCI-H1792 cells, causing G1 arrest in A549 and SK-LU-1 cells, but having no effect on a non-transformed bronchial epithelial cell line HBE4-E6/E7. We investigated the role of MAP kinase family members, extracellular signal-regulated kinase (ERK), JNK, and p38 mitogen-activated protein kinase (MAPK), as well as other important cell survival signaling molecules in PB-induced apoptosis. We observed activation of JNK and ERK by PB in the lung cancer cells. JNK was activated only in the two apoptotic cells, whereas ERK was activated in both the apoptotic and the growth-arrested cells, demonstrating a correlation between apoptosis and activation of JNK in response to PB. Both JNK inhibitor and JNK RNA interference (RNAi) inhibited PB-induced apoptosis, whereas MEK inhibitor did not, supporting that apoptosis induced by PB is through activation of JNK. De novo protein synthesis is required for the PB-induced JNK activation and induction of apoptosis. However, the production of known upstream activators of JNK, namely Fas/Fas ligand, tumor necrosis factor (TNF)-alpha, TNF-beta, and TRAIL, are not altered by PB treatment. Therefore, PB activates JNK through an unidentified and cell type-specific mechanism. Understanding of this mechanism is of therapeutic value in treating cancer patients with PB.

Synergistic induction of apoptosis in breast cancer cells by cotreatment with butyrate and TNF-alpha, TRAIL, or anti-Fas agonist antibody involves enhancement of death receptors' signaling and requires P21waf1

Inhibitors of histone deacetylase (HDAC) are considered as potential anticancer agents. We have previously demonstrated that an inhibitor of HDAC, sodium butyrate (NaB), induces apoptosis of breast cancer cells in a P53-independent and P21(waf1)-dependent manner. In this study, we showed that tumor necrosis factor-alpha (TNF-alpha), TNF-related apoptosis-inducing ligand (TRAIL), and anti-Fas agonist antibody potentiated NaB-induced growth inhibition through synergistic induction of apoptosis in breast cancer cell lines (MCF-7, T47-D, and BT-20). In MCF-7 cells, NaB increased the expression of death receptors; NaB alone or in combination with TNF-alpha, TRAIL, and anti-Fas agonist antibody increased the levels of Bid, tBid, and that of cytosolic cytochrome c. Synergistic induction of apoptosis was strongly inhibited by dominant-negative Fas-associated death domain (FADD) and inhibitors of caspases-8 and -9, indicating that potentiation of apoptosis involved key elements of death receptors' signaling pathways. Moreover, cotreatment of NaB and ligands of death receptors up-regulated the levels of P21(waf1) and that of proliferating cell nuclear antigen (PCNA) associated with P21(waf1). Transient transfections of p21(waf1) antisense or p21(waf1) deficient for its interaction with PCNA abolished synergistic induction of apoptosis. This suggested that potentiation of apoptosis by cotreatments required P21(waf1) and its interaction with PCNA. Since breast tumors contain rarely p21 mutations, our results may open interesting prospects in the fight against breast cancer.

Role of RB and RB2/P130 genes in marrow stromal stem cells plasticity

Marrow stromal cells (MSCs) are stem-like cells having a striking somatic plasticity. In fact, besides differentiating into mesenchymal lineages (bone, cartilage, and fat), they are capable of differentiating into neurons and astrocytes in vitro and in vivo. The RB and RB2/P130 genes, belonging to the retinoblastoma gene family, play a key role in neurogenesis, and for this reason, we investigated their role in neural commitment and differentiation of MSCs. In MSCs that were either uncommitted or committed toward neural differentiation, we ectopically expressed RB and RB2/P130 genes and analyzed their role in regulating the cell cycle, apoptosis and differentiation. In uncommitted MSCs, the activity of RB and RB2/P130 appeared limited to negatively regulating cell cycle progression, having no role in apoptosis and differentiation (toward either mesenchymal or neural lineages). On the other hand, in MSCs committed toward the neural phenotype, both RB and RB2/P130 reduced cell proliferation rate and affected the apoptotic process. RB protected differentiating cells from programmed cell death. On the contrary, RB2/P130 increased the percentage of cells in apoptosis. All of these activities were accomplished mainly in an HDAC-independent way. The retinoblastoma genes also influenced differentiation in neural committed MSCs. RB2/P130 contributes mainly to the induction of generic neural properties, while RB triggers cholinergic differentiation. These differentiating activities are HDAC-dependent. Our research shows that there is a critical temporal requirement for the RB genes during neuronal differentiation of MSCs: they are not required for cell commitment but play a role in the maturation process. For the above reasons, RB and RB2/P130 may have a role in neural differentiation but not in neural determination.

Selective regulation of class I and class II histone deacetylases expression by inhibitors of histone deacetylases in cultured mouse neural cells

The expression of 10 histone deacetylases (HDAC1-10) mRNAs in mouse neuroblastoma Neuro-2a and microglia N9 cell cultures after treatment by inhibitors of HDACs, sodium butyrate and trichostatin A was studied to elucidate whether HDAC inhibitors affect the gene expression of HDACs themselves. Northern blot analysis demonstrated two- to four-fold elevated levels of mRNAs for HDAC1, -3, -5, and -6 after drug treatment in comparison with untreated cells, while mRNA levels for HDAC2 and -7 did not change significantly. In both Neuro-2a and N9 cells the highest increase was observed for HDAC5 and -6 mRNA, whereas, HDAC4 had a prominent increase in mRNA levels after drug treatment only in N9 microglia cell line but not in Neuro-2a. Immunocytochemical examination confirmed that changes in protein levels of HDACs were similar to changes in their mRNA levels. There exists an auto-regulatory feedback loop to the expression levels of several HDACs after inhibition of their biochemical activity, adding several HDAC genes to the list of genes regulated by HDAC inhibitors.

Sodium butyrate enhances Fas-mediated apoptosis of human hepatoma cells

BACKGROUND/AIMS

Human hepatoma cells have been reported to be resistant to Fas-mediated apoptosis. Sodium butyrate (SB) induced apoptosis of several cancer cells. We investigated the effects of SB on Fas-mediated apoptosis of hepatoma cells.

METHODS

In hepatoma cells (HuH-6, HuH-7, Hep-G2, and PLC/PRF/5), susceptibility to Fas-mediated apoptosis and Fas expression were assessed. Caspase-3 activation and cell cycle progression were evaluated in HuH-6. A cDNA microarray assay was performed to screen the changes in the expression of mRNAs.

RESULTS

Pretreatment with SB caused an enhancement of the sensitivity to anti-Fas-mediated cytotoxicity, though it did not increase the expression of Fas. The cDNA microarray assay revealed up-regulation of pro-apoptotic Bik, Bak, Bid and c-Jun N-terminal protein kinase-1, and down-regulation of anti-apoptotic Bag-1 and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitor protein. In some molecules, expression of the proteins was confirmed by Western blotting. An increase in truncated-Bid accompanying the reduction in Bid was also observed.

CONCLUSIONS

SB enhances the susceptibility of hepatoma cells to anti-Fas-mediated cytotoxicity by altering the mRNA and protein expression and/or the activation status of proteins that could be involved in the Fas signaling pathway. SB may have an important role in the elimination of hepatoma cells.

P21(WAF1/CIP1) is dispensable for G1 arrest, but indispensable for apoptosis induced by sodium butyrate in MCF-7 breast cancer cells

Sodium butyrate (NaB) has been proposed as a potential anticancer agent. However, its mechanism of action is not totally elucidated. Here, we showed that NaB-induced cell cycle arrest and apoptosis were associated with an increase of P21(waf1/cip1) in MCF-7 breast cancer cells. This increase was more important in the nuclei, as revealed by immunofluorescence analysis. Transient transfections of MCF-7 cells with p21 deficient for interaction with CDK, but not with p21 deficient for interaction with PCNA (p21PCNA-), abrogated NaB-induced cell cycle arrest. This indicated that cell cycle blockage involved the interaction of P21(waf1/cip1) with CDK. However, P21(waf1/cip1) was dispensable, since p21 antisense did not modify cell cycle arrest. On the other hand, NaB-induced apoptosis was abolished by p21 antisense or p21PCNA-. In addition, NaB decreased PCNA levels, but increased the association of PCNA with P21(waf1/cip1). These results suggested that NaB-induced apoptosis required P21(waf1/cip1) and its interaction with PCNA.

The histone deacetylase inhibitor Trichostatin A modulates CD4+ T cell responses

Background

Histone deacetylase inhibitors (HDACIs) induce hyperacetylation of core histones modulating chromatin structure and affecting gene expression. These compounds are also able to induce growth arrest, cell differentiation, and apoptotic cell death of tumor cells in vitro as well as in vivo. Even though several genes modulated by HDAC inhibition have been identified, those genes clearly responsible for the biological effects of these drugs have remained elusive. We investigated the pharmacological effect of the HDACI and potential anti-cancer agent Trichostatin A (TSA) on primary T cells.

Methods

To ascertain the effect of TSA on resting and activated T cells we used a model system where an enriched cell population consisting of primary T-cells was stimulated in vitro with immobilized anti-CD3/anti-CD28 antibodies whilst exposed to pharmacological concentrations of Trichostatin A.

Results

We found that this drug causes a rapid decline in cytokine expression, accumulation of cells in the G₁ phase of the cell cycle, and induces apoptotic cell death. The mitochondrial respiratory chain (MRC) plays a critical role in the apoptotic response to TSA, as dissipation of mitochondrial membrane potential and reactive oxygen species (ROS) scavengers block TSA-induced T-cell death. Treatment of T cells with TSA results in the altered expression of a subset of genes involved in T cell responses, as assessed by microarray gene expression profiling. We also observed up- as well as down-regulation of various costimulatory/adhesion molecules, such as CD28 and CD154, important for T-cell function.

Conclusions

Taken together, our findings indicate that HDAC inhibitors have an immunomodulatory potential that may contribute to the potency and specificity of these antineoplastic compounds and might be useful in the treatment of autoimmune disorders.

Trichostatin A, an inhibitor of histone deacetylases, strongly suppresses growth of pancreatic adenocarcinoma cells

In cells with an altered p53 gene, the expression of p21(WAF1/CIP1), a potent inhibitor of cyclin-dependent kinases, can be induced by histone deacetylase (HDAC) inhibitors via a p53-independent pathway, which may play a critical role in arrest of cell growth. Accordingly, HDAC inhibitors such as trichostatin A (TSA) have potential utility in pancreatic cancer, as most of these tumors possess mutations in p53, which in fact is the main cause of chemoresistance to 5-fluorouracil. We have analyzed the effect of TSA on the proliferation of nine pancreatic adenocarcinoma cell lines, all containing a mutated p53 gene. TSA strongly inhibited the cellular growth of all these cell lines at submicromolar concentrations. The cellular mechanisms underlying this effect consisted of cell cycle arrest at the G2 phase and apoptotic cell death. The expression of p21(WAF1/CIP1) normally induced at the transcriptional level by p53 was also strongly activated by TSA. These findings suggest that inhibitors of HDAC may represent a novel therapeutic strategy for treatment of pancreatic cancer.

Apoptotic pathways activated by histone deacetylase inhibitors: implications for the drug-resistant phenotype

Histones are abundant proteins that coordinate the organization of eukaryotic nucleosomes. Post-translational modifications of histones-acetylation, phosphorylation and methylation-locally modulate the higher order nucleosome structure. Acetylation and deacetylation of histones occur at their N-terminal tails in a dynamic fashion and influence DNA accessibility to factors regulating replication, repair and transcription. Acetylation, catalyzed by histone acetyltransferases (HATs) on the epsilon-NH(2) group of lysine residues, neutralizes the positive charge and thereby triggers transcriptional activation. Deacetylation, catalyzed by histone deacetylases (HDACs) on the same lysine residues, unmasks the charge and triggers transcriptional repression. Inhibition of HDACs has thus a broad effect on chromatin architecture, and possibly on protein function, and multiple effects on cell growth. HDAC inhibitors (HDIs) are promising as single anti-cancer agents and in combination therapies. Understanding of the molecular basis for HDIs action is needed to better design the clinical antitumor treatments. The apoptotic pathways induced by HDIs are emerging and we provide an overview of the recent findings that regard apoptotic key elements. We also propose that transformed cells discern the widespread effect of HDIs on chromatin architecture as a genotoxic insult to respond to through induction of apoptosis.

Role of caspases, Bid, and p53 in the apoptotic response triggered by histone deacetylase inhibitors trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA)

Histone deacetylase activity is potently inhibited by hydroaximc acid derivatives such as suberoylanilide hydroxamic acid (SAHA) and trichostatin-A (TSA). These inhibitors specifically induce differentiation/apoptosis of transformed cells in vitro and suppress tumor growth in vivo. Because of its low toxicity, SAHA is currently evaluated in clinical trials for the treatment of cancer. SAHA and TSA induce apoptosis, which is characterized by mitochondrial stress, but so far, the critical elements of this apoptotic program remain poorly defined. To characterize in more detail this apoptotic program, we used human cell lines containing alterations in important elements of apoptotic response such as: p53, Bcl-2, caspase-9, and caspase-3. We demonstrate that caspase-9 is critical for apoptosis induced by SAHA and TSA and that efficient proteolytic activation of caspase-2, caspase-8, and caspase-7 strictly depends on caspase-9. Bcl-2 efficiently antagonizes cytochrome c release and apoptosis in response to both histone deacetylase inhibitors. We provide evidences that translocation into the mitochondria of the Bcl-2 family member Bid depends on caspase-9 and that this translocation is a late event during TSA-induced apoptosis. We also demonstrate that the susceptibility to TSA- and SAHA-induced cell death is regulated by p53.

Histone deacetylase inhibitors such as sodium butyrate and trichostatin A inhibit vascular endothelial growth factor (VEGF) secretion from human glioblastoma cells

We investigated the effects of histone deacetylase (HDAC) inhibitors such as sodium butyrate (SB) and trichostatin A (TSA) on the expression of vascular endothelial growth factor (VEGF) by human glioblastoma T98G, U251MG, and U87MG cells. The glioblastoma cells secreted three VEGF isoforms, VEGF (189), (165), and (121), although the expression levels of VEGF differed between the cell types. Treatment with either 5mM SB or 100 ng/ml TSA reduced VEGF secretion in conditioned media and reduced VEGF mRNA expression. We also studied the expression of VEGF-B, -C, and -D mRNA in human glioblastoma cells and their modulation by HDAC inhibitors. The PCR products of VEGF-B (357bp), VEGF-C (501bp), and VEGF-D (484bp) were amplified in all glioblastoma cells examined. Treatment with SB reduced the expression of VEGF-D mRNA in U251MG cells and the expression of VEGF-B mRNA in U87MG cells. TSA treatment reduced the expression of VEGF-D in U251MG cells. These results suggest that HDAC inhibitors reduce VEGF secretion and modulate the expression of the other VEGF family members, and therefore may inhibit angiogenesis in glioblastoma tissues.

Histone deacetylases: unique players in shaping the epigenetic histone code

The epigenome is defined by DNA methylation patterns and the associated posttranslational modifications of histones. This histone code determines the expression status of individual genes dependent upon their localization on the chromatin. The silencing of gene expression is associated with deacetylated histones, which are often found to be associated with regions of DNA methylation as well as methylation at the lysine 4 residue of histone 3. In contrast, the activation of gene expression is associated with acetylated histones and methylation at the lysine 9 residue of histone 3. The histone deactylases play a major role in keeping the balance between the acetylated and deacetylated states of chromatin. Histone deacetylases (HDACs) are divided into three classes: class I HDACs (HDACs 1, 2, 3, and 8) are similar to the yeast RPD3 protein and localize to the nucleus; class II HDACs (HDACs 4, 5, 6, 7, 9, and 10) are homologous to the yeast HDA1 protein and are found in both the nucleus and cytoplasm; and class III HDACs form a structurally distinct class of NAD-dependent enzymes that are similar to the yeast SIR2 proteins. Since inappropriate silencing of critical genes can result in one or both hits of tumor suppressor gene (TSG) inactivation in cancer, theoretically the reactivation of affected TSGs could have an enormous therapeutic value in preventing and treating cancer. Indeed, several HDAC inhibitors are currently being developed and tested for their potency in cancer chemotherapy. Importantly, these agents are also potentially applicable to chemoprevention if their toxicity can be minimized. Despite the toxic side effects and lack of specificity of some of the inhibitors, progress is being made. With the elucidation of the structures, functions and modes of action of HDACs, finding agents that may be targeted to specific HDACs and potentially reactivate expression of only a defined set of affected genes in cancer will be more attainable.