Combinations of proteasome inhibitors and histone deacetylases (HDAC) inhibitors appear to be the most potent to produce synergistic cytotoxicity in preclinical trials. We have recently confirmed that L-carnitine (LC) is an endogenous HDAC inhibitor. In the current study, the anti-tumor effect of LC plus proteasome inhibitor bortezomib (velcade, Vel) was investigated both in cultured hepatoma cancer cells and in Balb/c mice bearing HepG2 tumor. Cell death and cell viability were assayed by flow cytometry and MTS, respectively. Gene, mRNA expression and protein levels were detected by gene microarray, quantitative real-time PCR and Western blot, respectively. The effect of Vel on the acetylation of histone H3 associated with the p21cip1 gene promoter was examined by using ChIP assay and proteasome peptidase activity was detected by cell-based chymotrypsin-like (CT-like) activity assay. Here we report that (i) the combination of LC and Vel synergistically induces cytotoxicity in vitro; (ii) the combination also synergistically inhibits tumor growth in vivo; (iii) two major pathways are involved in the synergistical effects of the combinational treatment: increased p21cip1 expression and histone acetylation in vitro and in vivo and enhanced Vel-induced proteasome inhibition by LC. The synergistic effect of LC and Vel in cancer therapy should have great potential in the future clinical trials.
Histone deacetylase (HDAC) inhibitors are currently undergoing clinical evaluation as anti-cancer agents. Dietary constituents share certain properties of HDAC inhibitor drugs, including the ability to induce global histone acetylation, turn-on epigenetically-silenced genes, and trigger cell cycle arrest, apoptosis, or differentiation in cancer cells. One such example is sulforaphane (SFN), an isothiocyanate derived from the glucosinolate precursor glucoraphanin, which is abundant in broccoli. Here, we examined the time-course and reversibility of SFN-induced HDAC changes in human colon cancer cells.
Cells underwent progressive G2/M arrest over the period 6-72 h after SFN treatment, during which time HDAC activity increased in the vehicle-treated controls but not in SFN-treated cells. There was a time-dependent loss of class I and selected class II HDAC proteins, with HDAC3 depletion detected ahead of other HDACs. Mechanism studies revealed no apparent effect of calpain, proteasome, protease or caspase inhibitors, but HDAC3 was rescued by cycloheximide or actinomycin D treatment. Among the protein partners implicated in the HDAC3 turnover mechanism, silencing mediator for retinoid and thyroid hormone receptors (SMRT) was phosphorylated in the nucleus within 6 h of SFN treatment, as was HDAC3 itself. Co-immunoprecipitation assays revealed SFN-induced dissociation of HDAC3/SMRT complexes coinciding with increased binding of HDAC3 to 14-3-3 and peptidyl-prolyl cis/trans isomerase 1 (Pin1). Pin1 knockdown blocked the SFN-induced loss of HDAC3. Finally, SFN treatment for 6 or 24 h followed by SFN removal from the culture media led to complete recovery of HDAC activity and HDAC protein expression, during which time cells were released from G2/M arrest.
The current investigation supports a model in which protein kinase CK2 phosphorylates SMRT and HDAC3 in the nucleus, resulting in dissociation of the corepressor complex and enhanced binding of HDAC3 to 14-3-3 or Pin1. In the cytoplasm, release of HDAC3 from 14-3-3 followed by nuclear import is postulated to compete with a Pin1 pathway that directs HDAC3 for degradation. The latter pathway predominates in colon cancer cells exposed continuously to SFN, whereas the former pathway is likely to be favored when SFN has been removed within 24 h, allowing recovery from cell cycle arrest.
Over the last decade, several drugs that inhibit class I and/or class II histone deacetylases (HDACs) have been identified, including trichostatin A, the cyclic depsipeptide FR901228 and the antibiotic apicidin. These compounds have had immediate application in cancer research because of their ability to reactivate aberrantly silenced tumour suppressor genes and/or block tumour cell growth. Although a number of HDAC inhibitors are being evaluated in preclinical cancer models and in clinical trials, little is known about the differences in their specific mechanism of action and about the unique determinants of cancer cell sensitivity to each of these inhibitors.
Using a combination of cell viability assays, HDAC enzyme activity measurements, western blots for histone modifications, microarray gene expression analysis and qRT–PCR, we have characterised differences in trichostatin A vs depsipeptide-induced phenotypes in lung cancer, breast cancer and skin cancer cells and in normal cells and have then expanded these studies to other HDAC inhibitors.
Cell viability profiles across panels of lung cancer, breast cancer and melanoma cell lines showed distinct sensitivities to the pan-inhibitor TSA compared with the class 1 selective inhibitor depsipeptide. In several instances, the cell lines most sensitive to one inhibitor were most resistant to the other inhibitor, demonstrating these drugs act on at least some non-overlapping cellular targets. These differences were not explained by the HDAC selectivity of these inhibitors alone since apicidin, which is a class 1 selective compound similar to depsipeptide, also showed a unique drug sensitivity profile of its own. TSA had greater specificity for cancer vs normal cells compared with other HDAC inhibitors. In addition, at concentrations that blocked cancer cell viability, TSA effectively inhibited purified recombinant HDACs 1, 2 and 5 and moderately inhibited HDAC8, while depsipeptide did not inhibit the activity of purified HDACs in vitro but did in cellular extracts, suggesting a potentially indirect action of this drug. Although both depsipeptide and TSA increased levels of histone acetylation in cancer cells, only depsipeptide decreased global levels of transcriptionally repressive histone methylation marks. Analysis of gene expression profiles of an isogenic cell line pair that showed discrepant sensitivity to depsipeptide, suggested that resistance to this inhibitor may be mediated by increased expression of multidrug resistance genes triggered by exposure to chemotherapy as was confirmed by verapamil studies.
Although generally thought to have similar activities, the HDAC modulators trichostatin A and depsipeptide demonstrated distinct phenotypes in the inhibition of cancer cell viability and of HDAC activity, in their selectivity for cancer vs normal cells, and in their effects on histone modifications. These differences in mode of action may bear on the future therapeutic and research application of these inhibitors.
trichostatin A; depsipeptide; HDAC inhibitors; cancer cell viability; drug sensitivity
Proliferation of smooth muscle cells (SMC) in response to vascular injury is central to neointimal vascular remodeling. There is accumulating evidence that histone acetylation constitutes a major epigenetic modification for the transcriptional control of proliferative gene expression; however, the physiological role of histone acetylation for proliferative vascular disease remains elusive.
Methods and Results
In the present study, we investigated the role of histone deacetylase (HDAC) inhibition in SMC proliferation and neointimal remodeling. We demonstrate that mitogens induce transcription of HDAC 1, 2 and 3 in SMC. siRNA-mediated knock-down of either HDAC 1, 2 or 3 and pharmacologic inhibition of HDAC prevented mitogen-induced SMC proliferation. The mechanisms underlying this reduction of SMC proliferation by HDAC inhibition involve a growth arrest in the G1-phase of the cell cycle due to an inhibition of retinoblastoma protein phosphorylation. HDAC inhibition resulted in a transcriptional and posttranscriptional regulation of the cyclin-dependent kinase inhibitors p21Cip1 and p27Kip. Furthermore, HDAC inhibition repressed mitogen-induced cyclin D1 mRNA expression and cyclin D1 promoter activity. As a result of this differential cell cycle-regulatory gene expression by HDAC inhibition, the retinoblastoma protein retains a transcriptional repression of its downstream target genes required for S phase entry. Finally, we provide evidence that these observations are applicable in vivo by demonstrating that HDAC inhibition decreased neointima formation and expression of cyclin D1 in a murine model of vascular injury.
These findings identify HDAC as a critical component of a transcriptional cascade regulating SMC proliferation and suggest that HDAC might play a pivotal role in the development of proliferative vascular diseases, including atherosclerosis and in-stent restenosis.
Vascular smooth muscle cells; HDAC; cell cycle; proliferation; cyclin D1
Histone deacetylases (HDACs) are known to play a central role in the regulation of several cellular properties interlinked with the development and progression of cancer. Recently, HDAC1 has been reported to be overexpressed in hepatocellular carcinoma (HCC), but its biological roles in hepatocarcinogenesis remain to be elucidated. In this study, we demonstrated overexpression of HDAC1 in a subset of human HCCs and liver cancer cell lines. HDAC1 inactivation resulted in regression of tumor cell growth and activation of caspase-independent autophagic cell death, via LC3B-II activation pathway in Hep3B cells. In cell cycle regulation, HDAC1 inactivation selectively induced both p21WAF1/Cip1 and p27Kip1 expressions, and simultaneously suppressed the expression of cyclin D1 and CDK2. Consequently, HDAC1 inactivation led to the hypophosphorylation of pRb in G1/S transition, and thereby inactivated E2F/DP1 transcription activity. In addition, we demonstrated that HDAC1 suppresses p21WAF1/Cip1 transcriptional activity through Sp1-binding sites in the p21WAF1/Cip1 promoter. Furthermore, sustained suppression of HDAC1 attenuated in vitro colony formation and in vivo tumor growth in a mouse xenograft model. Taken together, we suggest the aberrant regulation of HDAC1 in HCC and its epigenetic regulation of gene transcription of autophagy and cell cycle components. Overexpression of HDAC1 may play a pivotal role through the systemic regulation of mitotic effectors in the development of HCC, providing a particularly relevant potential target in cancer therapy.
Lung cancer is the leading cause of cancer mortality worldwide, yet the therapeutic strategy for advanced non-small cell lung cancer (NSCLC) is limitedly effective. In addition, validated histone deacetylase (HDAC) inhibitors for the treatment of solid tumors remain to be developed. Here, we propose a novel HDAC inhibitor, OSU-HDAC-44, as a chemotherapeutic drug for NSCLC.
The cytotoxicity effect of OSU-HDAC-44 was examined in three human NSCLC cell lines including A549 (p53 wild-type), H1299 (p53 null), and CL1-1 (p53 mutant). The antiproliferatative mechanisms of OSU-HDAC-44 were investigated by flow cytometric cell cycle analysis, apoptosis assays and genome-wide chromatin-immunoprecipitation-on-chip (ChIP-on-chip) analysis. Mice with established A549 tumor xenograft were treated with OSU-HDAC-44 or vehicle control and were used to evaluate effects on tumor growth, cytokinesis inhibition and apoptosis. OSU-HDAC-44 was a pan-HDAC inhibitor and exhibits 3–4 times more effectiveness than suberoylanilide hydroxamic acid (SAHA) in suppressing cell viability in various NSCLC cell lines. Upon OSU-HDAC-44 treatment, cytokinesis was inhibited and subsequently led to mitochondria-mediated apoptosis. The cytokinesis inhibition resulted from OSU-HDAC-44-mediated degradation of mitosis and cytokinesis regulators Auroroa B and survivin. The deregulation of F-actin dynamics induced by OSU-HDAC-44 was associated with reduction in RhoA activity resulting from srGAP1 induction. ChIP-on-chip analysis revealed that OSU-HDAC-44 induced chromatin loosening and facilitated transcription of genes involved in crucial signaling pathways such as apoptosis, axon guidance and protein ubiquitination. Finally, OSU-HDAC-44 efficiently inhibited A549 xenograft tumor growth and induced acetylation of histone and non-histone proteins and apoptosis in vivo.
OSU-HDAC-44 significantly suppresses tumor growth via induction of cytokinesis defect and intrinsic apoptosis in preclinical models of NSCLC. Our data provide compelling evidence that OSU-HDAC-44 is a potent HDAC targeted inhibitor and can be tested for NSCLC chemotherapy.
The polyphenolic alcohol resveratrol has demonstrated promising activities for the prevention and treatment of cancer. Different modes of action have been described for resveratrol including the activation of sirtuins, which represent the class III histone deacetylases (HDACs). However, little is known about the activity of resveratrol on the classical HDACs of class I, II and IV, although these classes are involved in cancer development or progression and inhibitors of HDACs (HDACi) are currently under investigation as promising novel anticancer drugs. We could show by in silico docking studies that resveratrol has the chemical structure to inhibit the activity of different human HDAC enzymes. In vitro analyses of overall HDAC inhibition and a detailed HDAC profiling showed that resveratrol inhibited all eleven human HDACs of class I, II and IV in a dose-dependent manner. Transferring this molecular mechanism into cancer therapy strategies, resveratrol treatment was analyzed on solid tumor cell lines. Despite the fact that hepatocellular carcinoma (HCC) is known to be particularly resistant against conventional chemotherapeutics, treatment of HCC with established HDACi already has shown promising results. Testing of resveratrol on hepatoma cell lines HepG2, Hep3B and HuH7 revealed a dose-dependent antiproliferative effect on all cell lines. Interestingly, only for HepG2 cells a specific inhibition of HDACs and in turn a histone hyperacetylation caused by resveratrol was detected. Additional testing of human blood samples demonstrated a HDACi activity by resveratrol ex vivo. Concluding toxicity studies showed that primary human hepatocytes tolerated resveratrol, whereas in vivo chicken embryotoxicity assays demonstrated severe toxicity at high concentrations. Taken together, this novel pan-HDACi activity opens up a new perspective of resveratrol for cancer therapy alone or in combination with other chemotherapeutics. Moreover, resveratrol may serve as a lead structure for chemical optimization of bioavailability, pharmacology or HDAC inhibition.
R306465 is a novel hydroxamate-based histone deacetylase (HDAC) inhibitor with broad-spectrum antitumour activity against solid and haematological malignancies in preclinical models. R306465 was found to be a potent inhibitor of HDAC1 and -8 (class I) in vitro. It rapidly induced histone 3 (H3) acetylation and strongly upregulated expression of p21waf1,cip1, a downstream component of HDAC1 signalling, in A2780 ovarian carcinoma cells. R306465 showed class I HDAC isotype selectivity as evidenced by poor inhibition of HDAC6 (class IIb) confirmed by the absence of downregulation of Hsp90 chaperone c-raf protein expression and tubulin acetylation. This distinguished it from other HDAC inhibitors currently in clinical development that were either more potent towards HDAC6 (e.g. vorinostat) or had a broader HDAC inhibition spectrum (e.g. panobinostat). R306465 potently inhibited cell proliferation of all main solid tumour indications, including ovarian, lung, colon, breast and prostate cancer cell lines, with IC50 values ranging from 30 to 300 nM. Haematological cell lines, including acute lymphoblastic leukaemia, acute myeloid leukaemia, chronic lymphoblastic leukaemia, chronic myeloid leukaemia, lymphoma and myeloma, were potently inhibited at a similar concentration range. R306465 induced apoptosis and inhibited angiogenesis in cell-based assays and had potent oral in vivo antitumoral activity in xenograft models. Once-daily oral administration of R306465 at well-tolerated doses inhibited the growth of A2780 ovarian, H460 lung and HCT116 colon carcinomas in immunodeficient mice. The high activity of R306465 in cell-based assays and in vivo after oral administration makes R306465 a promising novel antitumoral agent with potential applicability in a broad spectrum of human malignancies.
HDAC; HDAC inhibitor; R306465; JNJ-16241199; anticancer agent; small molecule
Histone acetylation is an epigenetic modification involved in the regulation of gene expression, balanced by histone acetyl transferases and histone deacetylase (HDAC) enzymes. HDAC inhibitors (HDACi) induce growth arrest and cell death in transformed cells, and are currently in many clinical cancer trials. The transcriptional response to HDACi is complex, as is the response to HDAC isoform knockdown (KD). Here, we describe for the first time in a human cancer cell line, a transcriptional comparison of treatment by two structurally unrelated HDACi; belinostat and valproic acid with the KD of HDAC1, 2 and 3 isoforms.
HDAC KD showed anti-proliferative effects, although to a lesser extent than HDACi treatment. Moreover, we found a 2-fold increased resistance of HDAC1 knockdown cells to belinostat, suggesting this isoenzyme as a selective target. While both HDACi treatment and individual class I HDAC KD produce significant transcriptional effects, three-times higher for HDACi, the gene-expression profiles of class I HDAC KD compared with that obtained by HDACi treatment exhibited less than 4% of altered genes in common between the two modes of inhibition. Further, cell-specific effects of HDAC KD are evident by comparison with a recent study in a different cell line.
The increased resistance to belinostat in response to HDAC1 depletion indicates the possibility of using this isoform as a predictive biomarker of response to HDACi treatment. Further, the transcriptional response to chemical inhibition of HDACs is very different from that of KD of individual class I HDAC isoforms. These data suggest that the anti-tumor effect of HDACi is indeed linked to class I inhibition, but may be more complex than simply targeting individual HDAC enzymes.
Histone deacetylase (HDAC) inhibitors have the potential to derepress epigenetically silenced genes in cancer cells, leading to cell cycle arrest and apoptosis. In the present study, we screened several garlic-derived small organosulfur compounds for their ability to inhibit HDAC activity in vitro. Among the organosulfur compounds examined, allyl mercaptan (AM) was the most potent HDAC inhibitor. Molecular modeling, structure activity and enzyme kinetics studies with purified human HDAC8 provided evidence for a competitive mechanism (Ki = 24 μM AM). In AM-treated human colon cancer cells, HDAC inhibition was accompanied by a rapid and sustained accumulation of acetylated histones in total cellular chromatin. Chromatin immunoprecipitation assays confirmed the presence of hyperacetylated histone H3 on the P21WAF1 gene promoter within 4 h of AM exposure, and there was increased binding of the transcription factor Sp3. At a later time, 24 h after AM treatment, there was enhanced binding of p53 in the distal enhancer region of the P21WAF1 gene promoter. These findings suggest a primary role for Sp3 in driving P21 gene expression after HDAC inhibition by AM, followed by the subsequent recruitment of p53. Induction of p21Waf1 protein expression was detected at time points between 3 and 72 h after AM treatment and coincided with growth arrest in G1 of the cell cycle. The results are discussed in the context of other anticarcinogenic mechanisms ascribed to garlic organosulfur compounds and the metabolic conversion of such compounds to potential HDAC inhibitors in situ.
Histone deacetylases (HDACs) are enzymes involved in the remodelling of chromatin, and have a key role in the epigenetic regulation of gene expression. Histone deacetylase (HDAC) inhibitors are emerging as an exciting new class of potential anti-cancer agents. In recent years, a number of structurally diverse HDAC inhibitors have been identified and these HDAC inhibitors induce growth arrest, differentiation and/or apoptosis of cancer cells in vitro and in vivo. However, the underlying molecular mechanisms remain unclear. This study aimed at investigating the anti-tumor activity of various HDAC inhibitors, IN-2001, using T47D human breast cancer cells. Moreover, the possible mechanism by which HDAC inhibitors exhibit anti-tumor activity was also explored. In estrogen receptor positive T47D cells, IN-2001, HDAC inhibitor showed anti-proliferative effects in dose-and time-dependent manner. In T47D human breast cancer cells showed anti-tumor activity of IN-2001 and the growth inhibitory effects of IN-2001 were related to the cell cycle arrest and induction of apoptosis. Flow cytometry studies revealed that IN-2001 showed accumulation of cells at G2/M phase. At the same time, IN-2001 treatment time-dependently increased sub-G1 population, representing apoptotic cells. IN-2001-mediated cell cycle arrest was associated with induction of cdk inhibitor expression. In T47D cells, IN-2001 as well as other HDAC inhibitors treatment significantly increased p21WAF1 and p27KIP1 expression. In addition, thymidylate synthase, an essential enzyme for DNA replication and repair, was down-regulated by IN-2001 and other HDAC inhibitors in the T47D human breast cancer cells. In summary, IN-2001 with a higher potency than other HDAC inhibitors induced growth inhibition, cell cycle arrest, and eventual apoptosis in human breast cancer possibly through modulation of cell cycle and apoptosis regulatory proteins, such as cdk inhibitors, cyclins, and thymidylate synthase.
IN-2001; T47D; histone deacetylase
Histone deacetylase 2 (HDAC2) is crucial for embryonic development, affects cytokine signaling relevant for immune responses and is often significantly overexpressed in solid tumors; but little is known about its role in human hepatocellular carcinoma (HCC). In this study, we showed that targeted-disruption of HDAC2 resulted in reduction of both tumor cell growth and de novo DNA synthesis in Hep3B cells. We then demonstrated that HDAC2 regulated cell cycle and that disruption of HDAC2 caused G1/S arrest in cell cycle. In G1/S transition, targeted-disruption of HDAC2 selectively induced the expression of p16INK4A and p21WAF1/Cip1, and simultaneously suppressed the expression of cyclin D1, CDK4 and CDK2. Consequently, HDAC2 inhibition led to the down-regulation of E2F/DP1 target genes through a reduction in phosphorylation status of pRb protein. In addition, sustained suppression of HDAC2 attenuated in vitro colony formation and in vivo tumor growth in a mouse xenograft model. Further, we found that HDAC2 suppresses p21WAF1/Cip1 transcriptional activity via Sp1-binding site enriched proximal region of p21WAF1/Cip1 promoter. In conclusion, we suggest that the aberrant regulation of HDAC2 may play a pivotal role in the development of HCC through its regulation of cell cycle components at the transcription level providing HDAC2 as a relevant target in liver cancer therapy.
Methylselenocysteine (MSC) and selenomethionine (SM) are two organoselenium compounds receiving interest for their potential anticancer properties. These compounds can be converted to β-methylselenopyruvate (MSP) and α-keto-γ-methylselenobutyrate (KMSB), α-keto acid metabolites that share structural features with the histone deacetylase (HDAC) inhibitor butyrate. We tested the organoselenium compounds in an in vitro assay with human HDAC1 and HDAC8; whereas SM and MSC had little or no activity up to 2 mM, MSP and KMSB caused dose-dependent inhibition of HDAC activity. Subsequent experiments identified MSP as a competitive inhibitor of HDAC8, and computational modeling supported a mechanism involving reversible interaction with the active site zinc atom. In human colon cancer cells, acetylated histone H3 levels were increased during the period 0.5–48 h after treatment with MSP and KMSB, and there was dose-dependent inhibition of HDAC activity. The proportion of cells occupying G2/M of the cell cycle was increased at 10–50 μM MSP and KMSB, and apoptosis was induced, as evidenced by morphological changes, Annexin V staining and increased cleaved caspase-3, -6, -7, -9 and poly(adenosine diphosphate-ribose)polymerase. P21WAF1, a well-established target gene of clinically used HDAC inhibitors, was increased in MSP- and KMSB-treated colon cancer cells at both the messenger RNA and protein level, and there was enhanced P21WAF1 promoter activity. These studies confirm that in addition to targeting redox-sensitive signaling molecules, α-keto acid metabolites of organoselenium compounds alter HDAC activity and histone acetylation status in colon cancer cells, as recently observed in human prostate cancer cells.
Histone Arg methylation and Lys acetylation have been found to cooperatively regulate the expression of p53 target genes. Peptidylarginine deiminase 4 (PAD4) is an enzyme that citrullinates histone arginine and monomethyl-arginine residues thereby regulating histone Arg methylation. We have recently found that PAD4 serves as a p53 corepressor to regulate histone Arg methylation at the p53 target gene p21/WAF1/CIP1 promoter. However, it has not been tested whether histone Arg citrullination coordinates with other histone modifications to repress transcription. Here, we show that HDAC2 and PAD4 interact with p53 via distinct domains and simultaneously associate with the p21 promoter to regulate gene expression. After DNA damage, PAD4 and HDAC2 dissociate from several p53-target gene promoters (e.g., p21, GADD45, and PUMA) with a concomitant increase in histone Lys acetylation and Arg methylation at these promoters. Furthermore, PAD4 promoter association and histone Arg modifications are regulated by p53 and HDAC activity. In contrast, HDAC2 promoter association and histone Lys acetylation are affected by p53 and PAD4 activity at minor degrees. Importantly, PAD4 inhibitor Cl-amidine and HDAC inhibitor SAHA demonstrate additive effects in inducing p21, GADD45, and PUMA expression and inhibiting cancer cell growth in a p53-dependent manner. Our results unveil an important crosstalk between histone deacetylation and citrullination, suggesting that a combination of PAD4 and HDAC2 inhibitors as a potential strategy for cancer treatment.
Histone citrullination; Histone deacetylation; PAD4; HDAC2; p53
The RAS association domain family protein 1 (RASSF1) has been implicated in a tumor-suppressive function through the induction of acetylated α-tubulin and modulation of cell migration. However, the mechanisms of how RASSF1A is associated with acetylation of α-tubulin for controlling cell migration have not yet been elucidated. In this study, we found that RASSF1A regulated cell migration through the regulation of histon deacetylase 6 (HDAC6), which functions as a tubulin deacetylase.
Materials and Methods
The cell migration was assessed using wound-healing and transwell assays. The role of RASSF1A on cell migration was examined by immunofluorescence staining, HDAC activity assay and western blot analysis.
Cell migration was inhibited and cell morphology was changed in RASSF1A-transfected H1299 cells, compared with controls, whereas HDAC6 protein expression was not changed by RASSF1A transfection in these cells. However, RASSF1A inhibited deacetylating activity of HDAC6 protein and induced acetylated α-tubulin expression. Furthermore, acetylated α-tubulin and HDAC6 protein were co-localized in the cytoplasm in RASSF1A-transfected H1299 cells. Conversely, when the endogenous RASSF1A expression in HeLa cells was blocked with RASSF1A siRNA treatment, acetylated α-tubulin was co-localized with HDAC6 protein throughout the whole cells, including the nucleus, compared with scramble siRNA-treated HeLa cells. The restoration of RASSF1A by 5-Aza-dC treatment also induced acetylated α-tubulin through inhibition of HDAC6 activity that finally resulted in suppressing cell migration in H1299 cells. To further confirm the role of HDAC6 in RASSF1A-mediated cell migration, the HDAC6 expression in H1299 cells was suppressed by using HDAC6 siRNA, and cell motility was found to be decreased through enhanced acetylated α-tubulin.
The results of this study suggest that the inactivation of HDAC6 by RASSF1A regulates cell migration through increased acetylated α-tubulin protein.
Cell movement; HDAC6; Lung neoplasms; RASSF1A; Tumor suppressor genes
We have previously demonstrated amelioration of Huntington's disease (HD)-related phenotypes in R6/2 transgenic mice in response to treatment with the novel histone deacetylase (HDAC) inhibitor 4b. Here we have measured the selectivity profiles of 4b and related compounds against class I and class II HDACs and have tested their ability to restore altered expression of genes related to HD pathology in mice and to rescue disease effects in cell culture and Drosophila models of HD. R6/2 transgenic and wild-type (wt) mice received daily injections of HDAC inhibitors for 3 days followed by real-time PCR analysis to detect expression differences for 13 HD-related genes. We find that HDACi 4b and 136, two compounds showing high potency for inhibiting HDAC3 were most effective in reversing the expression of genes relevant to HD, including Ppp1r1b, which encodes DARPP-32, a marker for medium spiny striatal neurons. In contrast, compounds targeting HDAC1 were less effective at correcting gene expression abnormalities in R6/2 transgenic mice, but did cause significant increases in the expression of selected genes. An additional panel of 4b-related compounds was tested in a Drosophila model of HD and in STHdhQ111 striatal cells to further distinguish HDAC selectivity. Significant improvement in huntingtin-elicited Drosophila eye neurodegeneration in the fly was observed in response to treatment with compounds targeting human HDAC1 and/or HDAC3. In STHdhQ111 striatal cells, the ability of HDAC inhibitors to improve Htt-elicited metabolic deficits correlated with the potency at inhibiting HDAC1 and HDAC3, although the IC50 values for HDAC1 inhibition were typically 10-fold higher than for inhibition of HDAC3. Assessment of HDAC protein localization in brain tissue by Western blot analysis revealed accumulation of HDAC1 and HDAC3 in the nucleus of HD transgenic mice compared to wt mice, with a concurrent decrease in cytoplasmic localization, suggesting that these HDACs contribute to a repressive chromatin environment in HD. No differences were detected in the localization of HDAC2, HDAC4 or HDAC7. These results suggest that inhibition of HDACs 1 and 3 can relieve HD-like phenotypes in model systems and that HDAC inhibitors targeting these isotypes might show therapeutic benefit in human HD.
neurodegenerative; striatum; disease; epigenetic; therapeutic; chromatin; gene expression
The role of histone deacetylases (HDAC) and the potential of these enzymes as therapeutic targets for cancer, neurodegenerative diseases and a number of other disorders is an area of rapidly expanding investigation. There are 18 HDACs in humans. These enzymes are not redundant in function. Eleven of the HDACs are zinc dependent, classified on the basis of homology to yeast HDACs: Class I includes HDACs 1, 2, 3, and 8; Class IIA includes HDACs 4, 5, 7, and 9; Class IIB, HDACs 6 and 10; and Class IV, HDAC11. Class III HDACs, sirtuins 1–7, have an absolute requirement for NAD+, are not zinc dependent and generally not inhibited by compounds that inhibit zinc dependent deacetylases.
In addition to histones, HDACs have many nonhistone protein substrates which have a role in regulation of gene expression, cell proliferation, cell migration, cell death, and angiogenesis. HDAC inhibitors (HDACi) have been discovered of different chemical structure. HDACi cause accumulation of acetylated forms of proteins which can alter their structure and function. HDACi can induce different phenotypes in various transformed cells, including growth arrest, apoptosis, reactive oxygen species facilitated cell death and mitotic cell death. Normal cells are relatively resistant to HDACi induced cell death. Several HDACi are in various stages of development, including clinical trials as monotherapy and in combination with other anti-cancer drugs and radiation. The first HDACi approved by the FDA for cancer therapy is suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza), approved for treatment of cutaneous T-cell lymphoma.
Vorinostat; Histone deacetylase; apoptosis
Interleukin-13 Receptor α2 (IL-13Rα2) is a tumor-associated antigen and target for cancer therapy. Since IL-13Rα2 is heterogeneously overexpressed in a variety of human cancers, it would be highly desirable to uniformly upregulate IL-13Rα2 expression in tumors for optimal targeting.
We examined epigenetic regulation of IL-13Rα2 in a murine model of human pancreatic cancer by Bisulfite-PCR, sequencing for DNA methylation and chromatin immunoprecipitation for histone modification. Reverse transcription-PCR was performed for examining changes in IL-13Rα2 mRNA expression after treatment with histone deacetylase (HDAC) and c-jun inhibitors. In vitro cytotoxicity assays and in vivo testing in animal tumor models were performed to determine whether HDAC inhibitors could enhance anti-tumor effects of IL-13-PE in pancreatic cancer. Mice harboring subcutaneous tumors were treated with HDAC inhibitors systemically and IL-13-PE intratumorally.
We found that CpG sites in IL-13Rα2 promoter region were not methylated in all pancreatic cancer cell lines studied including IL-13Rα2-positive and IL-13Rα2-negative cell lines and normal cells. On the other hand, histones at IL-13Rα2 promoter region were highly-acetylated in IL-13Rα2-positive but much less in receptor-negative pancreatic cancer cell lines. When cells were treated with HDAC inhibitors, not only histone acetylation but also IL-13Rα2 expression was dramatically enhanced in receptor-negative pancreatic cancer cells. In contrast, HDAC inhibition did not increase IL-13Rα2 in normal cell lines. In addition, c-jun in IL-13Rα2-positive cells was expressed at higher level than in negative cells. Two types of c-jun inhibitors prevented increase of IL-13Rα2 by HDAC inhibitors. HDAC inhibitors dramatically sensitized cancer cells to immunotoxin in the cytotoxicity assay in vitro and increased IL-13Rα2 in the tumors subcutaneously implanted in the immunodeficient animals but not in normal mice tissues. Combination therapy with HDAC inhibitors and immunotoxin synergistically inhibited growth of not only IL-13Rα2-positive but also IL-13Rα2-negative tumors.
We have identified a novel function of histone modification in the regulation of IL-13Rα2 in pancreatic cancer cell lines in vitro and in vivo. HDAC inhibition provides a novel opportunity in designing combinatorial therapeutic approaches not only in combination with IL-13-PE but with other immunotoxins for therapy of pancreatic cancer and other cancers.
Squamous cell carcinoma (SCC) is a treatment-refractory subtype of human cancer arising from stratified epithelium of the skin, lung, esophagus, oropharynx and other tissues. A unifying feature of SCC is high-level expression of the p53-related protein p63 (TP63) in 80% of cases. The major protein isoform of p63 expressed in SCC is ΔNp63α, an N-terminally truncated form which functions as a key SCC cell survival factor by mechanisms that are unclear. In this study we demonstrate that ΔNp63α associates with HDAC1 and HDAC2 to form an active transcriptional repressor complex that can be targeted to therapeutic advantage. Repression of pro-apoptotic Bcl-2 family member genes including PUMA by p63/HDAC is required for survival of SCC cells. Cisplatin chemotherapy, a mainstay of SCC treatment, promotes dissociation of p63 and HDAC from the PUMA promoter, leading to increased histone acetylation, PUMA activation and apoptosis. These effects are recapitulated upon targeting the p63/HDAC complex selectively with class I/II HDAC inhibitors using both in vitro and in vivo models. Sensitivity to HDAC inhibition is directly correlated with p63 expression and is abrogated in tumor cells that overexpress endogenous Bcl-2. Together, our results elucidate a mechanism of p63-mediated transcriptional repression and they identify the ΔNp63α/HDAC complex as an essential tumor maintenance factor in SCC. Additionally, our findings offer a rationale to apply HDAC inhibitors for SCC treatment.
p63; HDAC1; HDAC2; BCL2; Vorinostat; Squamous Cell Carcinoma
3,3′-Diindolylmethane (DIM) is an anti-cancer agent that induces cell cycle arrest and apoptosis through unknown mechanisms. Here, we report that DIM selectively induced proteasome-mediated degradation of the class I histone deacetylases (HDAC1, HDAC2, HDAC3, and HDAC8) in colon cancer cells, without affecting the class II HDAC proteins. DIM-induced down-regulation of the class I HDACs was also observed in vivo in tumor xenografts in nude mice. The depletion of the HDACs as the result of DIM treatment caused a reduction of the HDAC activity on the promoters of CDKN1A/WAF1/CIP1 and CDKN1B/KIP1 genes (encoding cyclin-dependent kinase inhibitors p21 and p27, respectively) and significantly increased the expression of p21 and p27, which arrested cells at the G2 phase of the cell cycle. The degradation of the HDACs also caused DNA damage and triggered apoptosis. Thus, DIM acts by selectively targeting the class I HDACs to promote their degradation.
3,3′-Diindolylmethane; histone deacetylase; protein degradation; cell cycle arrest; apoptosis
An ETS family member, ETS Related Gene (ERG) is involved in the Ewing family of tumors as well as leukemias. Rearrangement of the ERG gene with the TMPRSS2 gene has been identified in the majority of prostate cancer patients. Additionally, overexpression of ERG is associated with un- favorable prognosis in prostate cancer patients similar to leukemia patients. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) regulate transcription as well as epigenetic status of genes through acetylation of both histones and transcription factors. Deregulation of HATs and HDACs is frequently seen in various cancers, including prostate cancer. Many cellular oncogenes as well as tumor viral proteins are known to target either or both HATs and HDACs. Several studies have demonstrated that there are alterations of HDAC activity in prostate cancer cells. Recently, we found that ERG binds and inhibits HATs, which suggests that ERG is involved in deregulation of protein acetylation. Additionally, it has been shown that ERG is associated with a higher expression of HDACs. In this study, we tested the effect of the HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) on ERG-positive prostate cancer cells (VCaP). We found that VPA and TSA induce apoptosis, upregulate p21/Waf1/CIP1, repress TMPRSS2-ERG expression and affect acetylation status of p53 in VCaP cells. These results suggest that HDAC inhibitors might restore HAT activity through two different ways: by inhibiting HDAC activity and by repressing HAT targeting oncoproteins such as ERG.
valproic acid; trichostatin A; histone deacetylase; histone acetyltransferase; CBP/p300; p53; ETS related gene; prostate cancer
Histone deacetylases (HDACs) play critical roles in silencing tumor suppressor genes. HDAC inhibitors reactivate tumor suppressor genes and inhibit tumor cell growth in vitro and in vivo, and several HDAC inhibitors are currently being evaluated in clinical trials for cancer therapy. A comprehensive analysis of proteins regulated by HDAC inhibitors would enhance our ability to define and characterize their essential therapeutic targets. Here, we employed SILAC (stable isotope labeling with amino acids in cell culture)-based quantitative proteomics to identify acetylated proteins in human breast cancer cells. Treatment with the clinically relevant HDAC inhibitor, SAHA (vorinostat), induces lysine acetylation of 61 proteins in MDA-MB-231 human breast cancer cells. SAHA not only induces lysine acetylation in chromatin-associated proteins, but also acetylates previously unrecognized non-histone proteins, including transcriptional factors and regulators, chaperones, cell structure proteins, and glycolytic enzymes in a time-dependent manner. Knowledge of the full repertoire of acetylated proteins will provide a foundation for further defining the functions of HDACs in cancer cells.
Although numerous studies have underlined the role of HDACs in breast physiology and tumorigenesis, little is known on the particular contribution of the various classes of HDACs in these processes. Using ERα-positive MCF-7 breast cancer cells, the effects of MC1575 and MC1568, two novel class II specific HDAC inhibitors (HDI), were analyzed on cell proliferation, apoptosis and estrogen signalling. The specificity of these HDIs was validated by measuring histone and α-tubulin acetylation and by the specific in vitro inhibition of recombinant HDAC4 using histone and non histone substrates, contrasting with the lack of inhibition of class I HDACs. In addition, MC1575 did not inhibit class I HDAC gene expression thus confirming the specific targeting of class II enzymes. Similar to TSA, MC1575 displayed a dose-dependent anti-proliferative effect and induced cell cycle arrest although this blockade occurred at a different level than TSA. Moreover, and in contrast to TSA, MC1575 had no effect on MCF-7 cells apoptosis. Interestingly, MC1575 was able to increase p2lwaf1/CIP1 mRNA levels but did not regulate the expression of other genes such as cyclin D1, p27, p14ARF, Bcl2, Baxα, Trail-R1 and -R2. Finally, MC1575 strongly induced ERβ gene expression but did not decrease ERα expression nor did it switch hydroxy-tamoxifen to an agonist activity. Altogether, these data suggest that the class II HDAC sub-family may exert specific roles in breast cancer progression and estrogen-dependence.
Apoptosis; physiology; Breast Neoplasms; genetics; metabolism; pathology; Cell Cycle; physiology; Cell Division; physiology; Cell Line, Tumor; Estrogen Receptor alpha; metabolism; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Histone Deacetylases; genetics; metabolism; Humans; Repressor Proteins; genetics; metabolism; Signal Transduction; physiology; Histone deacetylase; histone deacetylase inhibitor; breast cancer; estrogen receptor; cell proliferation
Heat shock protein (hsp) 90 is an ATP-dependent molecular chaperone, which maintains the active conformation of client oncoproteins in cancer cells. An isoform, hsp90α, promotes extra-cellular maturation of matrix metalloproteinase (MMP)-2 involved in tumor invasion and metastasis. Knockdown of histone deacetylase (HDAC) 6, which deacetylates lysine residues in hsp90, induces reversible hyper-acetylation and attenuates ATP binding and chaperone function of hsp90. Here, utilizing mass spectrometry, we identified seven lysine residues in hsp90α that are hyper-acetylated, following treatment of eukaryotic cells with a pan-HDAC inhibitor that also inhibits HDAC6. Depending on the specific lysine residue in the middle domain involved, while acetylation affects ATP, co-chaperone and client protein binding to hsp90α, acetylation of all seven lysines increased the binding of hsp90α to 17-allyl-amino-demethoxy geldanamycin (17-AAG). Notably, following treatment with the pan-HDAC inhibitor panobinostat (LBH589), the extra-cellular hsp90α was hyper-acetylated and it bound to MMP-2, which was associated with increased in vitro tumor cell invasiveness. Treatment with anti-acetylated hsp90α antibody inhibited in vitro invasion by tumor cells. Thus, reversible hyper-acetylation modulates the intra- and extra-cellular chaperone function of hsp90, and targeting extra-cellular hyper-acetylated hsp90α may undermine tumor invasion and metastasis.
Apigenin (4′,5,7,-trihydroxyflavone), an anticancer agent, selectively toxic to cancer cells induces cell cycle arrest and apoptosis through mechanisms that have not been fully elucidated. Our studies indicate that apigenin-mediated growth inhibitory responses are due to inhibition of class I histone deacetylases (HDACs) in prostate cancer cells. Treatment of PC-3 and 22Rv1 cells with apigenin (20–40μM) resulted in the inhibition of HDAC enzyme activity, specifically HDAC1 and HDAC3 at the protein and message level. Apigenin-mediated HDAC inhibition resulted in global histone H3 and H4 acetylation, as well as localized hyperacetylation of histone H3 on the p21/waf1 promoter. A corresponding increase was observed in p21/waf1 and bax protein and mRNA expression after apigenin exposure, consistent with the use of HDAC inhibitor, trichostatin A. The downstream events demonstrated cell cycle arrest and induction of apoptosis in both cancer cells. Studies of PC-3 xenografts in athymic nude mice further demonstrated that oral intake of apigenin at doses of 20 and 50μg/mouse/day over an 8-week period resulted in a marked reduction in tumor growth, HDAC activity, and HDAC1 and HDAC3 protein expression at both doses of apigenin. An increase in p21/waf1 expression was observed in apigenin-fed mice, compared to the control group. Furthermore, apigenin intake caused a significant decrease in bcl2 expression with concomitant increase in bax, shifting the bax/bcl2 ratio in favor of apoptosis. Our findings confirm for the first time that apigenin inhibits class I HDACs, particularly HDAC1 and HDAC3 and its exposure results in reversal of aberrant epigenetic events that promote malignancy.
prostate cancer; apigenin; epigenetics; histone modification; chromatin remodeling