Acetylation of histones associated with the p21WAF1/CIP1 gene by butyrate is not sufficient for p21WAF1/CIP1 gene transcription in human colorectal adenocarcinoma cells

Mediterranean diet and health status: Active ingredients and pharmacological mechanisms

The Mediterranean diet (MedDiet) is one of the most widely described and evaluated dietary patterns in scientific literature. It is characterized by high intakes of vegetables, legumes, fruits, nuts, grains, fish, seafood, extra virgin olive oil, and a moderate intake of red wine. A large body of observational and experimental evidence suggests that higher adherence to the MedDiet is associated with lower risk of mortality, cardiovascular disease, metabolic disease, and cancer. Current mechanisms underlying the beneficial effects of the MedDiet include reduction of blood lipids, inflammatory and oxidative stress markers, improvement of insulin sensitivity, enhancement of endothelial function, and antithrombotic function. Most likely, these effects are attributable to bioactive ingredients such as polyphenols, monounsaturated and polyunsaturated fatty acids, or fibre. This review will focus on both established and less established mechanisms of action of biochemical compounds contained in a MedDiet. LINKED ARTICLES: This article is part of a themed section on The Pharmacology of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.6/issuetoc.

Mediterranean Diet: Prevention of Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer diagnosis and the second and third leading cause of cancer mortality in men and women, respectively. However, the majority of CRC cases are the result of sporadic tumorigenesis via the adenoma–carcinoma sequence. This process can take up to 20 years, suggesting an important window of opportunity exists for prevention such as switching toward healthier dietary patterns. The Mediterranean diet (MD) is a dietary pattern associated with various health benefits including protection against cardiovascular disease, diabetes, obesity, and various cancers. In this article, we review publications available in the PubMed database within the last 10 years that report on the impact of a MD eating pattern on prevention of CRC. To assist the reader with interpretation of the results and discussion, we first introduce indexes and scoring systems commonly used to experimentally determine adherence to a MD, followed by a brief introduction of the influence of the MD pattern on inflammatory bowel disease, which predisposes to CRC. Finally, we discuss key biological mechanisms through which specific bioactive food components commonly present in the MD are proposed to prevent or delay the development of CRC. We close with a discussion of future research frontiers in CRC prevention with particular reference to the role of epigenetic mechanisms and microbiome related to the MD eating pattern.

Physiological TLR5 expression in the intestine is regulated by differential DNA binding of Sp1/Sp3 through simultaneous Sp1 dephosphorylation and Sp3 phosphorylation by two different PKC isoforms

Toll-like receptor 5 (TLR5) expression in the intestinal epithelial cells (IECs) is critical to maintain health, as underscored by multiple intestinal and extra-intestinal diseases in mice genetically engineered for IEC-specific TLR5 knockout. A gradient of expression exists in the colonic epithelial cells from the cecum to the distal colon. Intriguingly, an identical gradient for the dietary metabolite, butyrate also exists in the luminal contents. However, both being critical for intestinal homeostasis and immune response, no studies examined the role of butyrate in the regulation of TLR5 expression. We showed that butyrate transcriptionally upregulates TLR5 in the IECs and augments flagellin-induced immune responses. Both basal and butyrate-induced transcription is regulated by differential binding of Sp-family transcription factors to the GC-box sequences over the TLR5 promoter. Butyrate activates two different protein kinase C isoforms to dephosphorylate/acetylate Sp1 by serine/threonine phosphatases and phosphorylate Sp3 by ERK-MAPK, respectively. This resulted in Sp1 displacement from the promoter and binding of Sp3 to it, leading to p300 recruitment and histone acetylation, activating transcription. This is the first study addressing the mechanisms of physiological TLR5 expression in the intestine. Additionally, a novel insight is gained into Sp1/Sp3-mediated gene regulation that may apply to other genes.

Histone deacetylase inhibitors induce attenuation of Wnt signaling and TCF7L2 depletion in colorectal carcinoma cells

Histone deacetylase inhibitors (HDIs) specifically affect cancer cells by inducing cell cycle arrest, activate apoptotic pathways and re-activate epigenetically silenced tumor suppressor genes, but their pleiotropic mode of action is not fully understood. Despite the clinical effects of HDIs in the treatment of hematological malignancies, their potency against solid tumors is still unclear. We investigated the effects and mechanisms of HDI action in colorectal carcinoma cell lines with an activated Wnt signaling pathway, which is implicated in different aspects of tumorigenesis, including cell proliferation, apoptosis, angiogenesis and metastasis. We assessed the effects of HDI treatment in colorectal carcinoma cell lines by measuring histone hyperacetylation, cell viability and expression of Wnt target genes. Upon treatment with HDIs of the hydroxamate class, we found attenuation of Wnt signaling with concomitant induction of apoptosis and colorectal cancer cell death. Strikingly, the effects of HDIs on Wnt signaling were independent of histone hyperacetylation, thus we investigated the role of non-histone target proteins of histone deacetylases (HDACs). The compounds TSA and SAHA induced a rapid proteasome-dependent depletion of the Wnt transcription factor TCF7L2, which may be mediated by inhibition of HDAC 6 and 10. Our findings provide a molecular rationale for the use of HDIs against colorectal carcinomas with activated Wnt signaling.

Superior antimitogenic and chemosensitization activities of the combination treatment of the histone deacetylase inhibitor apicidin and proteasome inhibitors on human colorectal cancer cells

Despite the effectiveness of histone deacetylase inhibitors, proteasome inhibitors and cytotoxic drugs on human cancers, none of these types of treatments by themselves has been sufficient to eradicate the disease. The combination of different modalities may hold enormous potential for eliciting therapeutic results. In the current study, we examined the effects of treatment with the histone deacetylase inhibitor (HDACI) apicidin (APC) in combination with proteasome inhibitors on human colorectal cancer cells. The molecular mechanisms of the combined treatments and their potential to sensitize colorectal cancer cells to chemotherapies were also investigated. Cancer cells were exposed to the agents alone and in combination, and cell growth inhibition was determined by MTT and colony formation assays. HDAC, proteasome and NF-κB activities as well as reactive oxygen species (ROS) were monitored. Cell cycle perturbation and induction of apoptosis were assessed by flow cytometry. The expression of cell cycle/apoptosis- and cytoprotective/stress-related genes was determined by quantitative PCR and EIA, respectively. The potentiation of cancer cell sensitivity to chemotherapies upon APC/PI combination treatment was also studied. The combination of APC and MG132, PI-1 or epoxomicin potently inhibited cancer cell growth, disrupted the cell cycle, induced apoptosis, decreased NF-κB activity and increased ROS production. These events were accompanied by the altered expression of genes associated with the cell cycle, apoptosis and cytoprotection/stress regulation. The combination treatment markedly enhanced the chemosensitivity of colorectal cancer cells (50-3.7 x 10(4)-fold) in a drug-, APC/PI combination- and colorectal cancer subtype-dependent manner. The results of this study have implications for the development of com-binatorial treatments that include HDACIs, PIs and conventional chemotherapeutic drugs, suggesting a potential therapeutic synergy with general applicability to various types of cancers.

The transition from proliferation to differentiation in colorectal cancer is regulated by the calcium activated chloride channel A1

Breaking the balance between proliferation and differentiation in animal cells can lead to cancer, but the mechanisms maintaining this balance remain largely undefined. The calcium activated chloride channel A1 (CLCA1) is a member of the calcium sensitive chloride conductance family of proteins and is expressed mainly in the colon, small intestine and appendix. We show that CLCA1 plays a functional role in differentiation and proliferation of Caco-2 cells and of intestinal tissue. Caco-2 cells spontaneously differentiate either in confluent culture or when treated with butyrate, a molecule present naturally in the diet. Here, we compared CLCA1 expressional levels between patients with and without colorectal cancer (CRC) and determined the functional role of CLCA1 in differentiation and proliferation of Caco-2 cells. We showed that: 1) CLCA1 and CLCA4 expression were down-regulated significantly in CRC patients; 2) CLCA1 expression was up-regulated in Caco-2 cells induced to differentiate by confluent culture or by treatment with sodium butyrate (NaBT); 3) Knockdown of CLCA1 with siRNA significantly inhibited cell differentiation and promoted cell proliferation in Caco-2 confluent cultures, and 4) In Caco-2 3D culture, suppression of CLCA1 significantly increased cell proliferation and compromised NaBT-induced inhibition of proliferation. In conclusion, CLCA1 may contribute to promoting spontaneous differentiation and reducing proliferation of Caco-2 cells and may be a target of NaBT-induced inhibition of proliferation and therefore a potential diagnostic marker for CRC prognosis.

HDAC1 inhibition by maspin abrogates epigenetic silencing of glutathione S-transferase pi in prostate carcinoma cells

Both maspin and glutathione S-transferase pi (GSTp) are implicated as tumor suppressors and downregulated in human prostate cancer. It is well established that GSTp downregulation is through DNA methylation-based silencing. We report here that maspin expression in prostate cancer cell line DU145 reversed GSTp DNA methylation, as measured by methylation- specific PCR, MethyLight assay, and bisulfite sequencing. The effect of maspin on GSTp expression was similar to that of the combination of a synthetic histone deacetylase (HDAC) inhibitor and DNA methylation inhibitor 5-aza-2'-deoxycytidine. Maspin expression also led to an increased level of acetylated histone 3, decreased level of methyl transferase, and methyl-CpG-binding domain proteins at the site of demethylated GSTp promoter DNA. Earlier, we have shown that maspin inhibits HDAC1. In PC3 cells, where both maspin and GSTp are expressed at a reduced level, maspin knockdown led to a significant reduction in GSTp expression, whereas dual knockdown of maspin and HDAC1 barely increased the level of GSTp expression. Thus, HDAC1 may play an essential role in cellular response to maspin-mediated GSTp desilencing. Maspin has been shown to increase tumor cell sensitivity to drug-induced apoptosis. Interestingly, GSTp reexpression in the absence of maspin expression perturbation blocked the phosphorylation of histone 2A.X, the induction of hypoxia-induced factor 1α (HIF-1α), and cell death of LNCaP cells under oxidative stress. Because DNA hypermethylation-based silencing may couple with and depend on histone deacetylation, our study suggests that endogenous HDAC inhibition by maspin may prevent pathologic gene silencing in prostate tumor progression.

The G1 phase arrest and apoptosis by intrinsic pathway induced by valproic acid inhibit proliferation of BGC-823 gastric carcinoma cells

Recent studies have demonstrated that the histone deacetylation level was closely related to the genesis and development of tumors. Thus, activating histone acetyltransferases and/or suppressing histone deacetylases (HDACs) can become an approach for tumor chemotherapy. The histone acetylation regulation often results in the inhibition of cell proliferation, induction of cell apoptosis or differentiation, and cell cycle arrest in G1 phase. It has been demonstrated recently that the traditional anticonvulsant valproic acid was an efficient class I HDAC inhibitor (HDACI); however, its antitumor effect and mechanisms on gastric cancers so far has not been elucidated clearly. In the present study, gastric carcinoma cell lines BGC-823, HGC-27, and SGC-7901 were cultured with valproic acid (VPA) in vitro. The cell morphology was observed by invert microscope, the proliferation was detected by MTT assay, the apoptosis and cell cycle were analyzed by flow cytometry assay with Annexin V/PI and PI, the activities and protein expressions of Caspase 3, Caspase 8, Caspase 9 of BGC-823 cells were detected by spectrophotometry and indirect immunofluorescence technique, respectively. The protein expressions of Cyclin A, Cyclin D1, Cyclin E, P21(Waf/cip1) of BGC-823 cells were analyzed by indirect immunofluorescence assay, and messenger ribonucleic acid (mRNA) expressions were detected by RT-PCR assay. The results showed that the proliferation of three kinds of gastric carcinoma cells could be inhibited obviously by VPA, which was related to the apoptosis induction and cell cycle arrest in G1 phase. The intrinsic pathway (cytochrome C pathway) was chiefly involved in the mechanism of apoptosis, which was indicated by activation of Caspase 9 and Caspase 3. The extrinsic pathway was partially involved, with slight activation of Caspase 8. The mechanism underlying its effect on cell cycle arrest in G1 phase induction was due to the upregulation of P21(Waf/cip1), Mad1 expression and downregulation of Cyclin A, c-Myc expression.

A phosphorylation switch regulates the transcriptional activation of cell cycle regulator p21 by histone deacetylase inhibitors

Histone deacetylase inhibitors induce cell cycle arrest and apoptosis in tumor cells and are, therefore, promising anti-cancer drugs. The cyclin-dependent kinase inhibitor p21 is activated in histone deacetylase (HDAC) inhibitor-treated tumor cells, and its growth-inhibitory function contributes to the anti-tumorigenic effect of HDAC inhibitors. We show here that induction of p21 by trichostatin A involves MAP kinase signaling. Activation of the MAP kinase signaling pathway by growth factors or stress signals results in histone H3 serine 10 phosphorylation at the p21 promoter and is crucial for acetylation of the neighboring lysine 14 and recruitment of activated RNA polymerase II in response to trichostatin A treatment. In non-induced cells, the protein phosphatase PP2A is associated with the p21 gene and counteracts its activation. Induction of p21 is linked to simultaneous acetylation and phosphorylation of histone H3. The dual modification mark H3S10phK14ac at the activated p21 promoter is recognized by the phospho-binding protein 14-3-3ζ, which protects the phosphoacetylation mark from being processed by PP2A. Taken together we have revealed a cross-talk of reversible phosphorylation and acetylation signals that controls the activation of p21 by HDAC inhibitors and identify the phosphatase PP2A as chromatin-associated transcriptional repressor in mammalian cells.

Allyl mercaptan, a garlic-derived organosulfur compound, inhibits histone deacetylase and enhances Sp3 binding on the P21WAF1 promoter

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 (K(i) = 24 microM 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 G(1) 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.

Nucleophosmin/B23 negatively regulates GCN5-dependent histone acetylation and transactivation

Nucleophosmin/B23 is a multifunctional phosphoprotein that is overexpressed in cancer cells and has been shown to be involved in both positive and negative regulation of transcription. In this study, we first identified GCN5 acetyltransferase as a B23-interacting protein by mass spectrometry, which was then confirmed by in vivo co-immunoprecipitation. An in vitro assay demonstrated that B23 bound the PCAF-N domain of GCN5 and inhibited GCN5-mediated acetylation of both free and mononucleosomal histones, probably through interfering with GCN5 and masking histones from being acetylated. Mitotic B23 exhibited higher inhibitory activity on GCN5-mediated histone acetylation than interphase B23. Immunodepletion experiments of mitotic extracts revealed that phosphorylation of B23 at Thr 199 enhanced the inhibition of GCN5-mediated histone acetylation. Moreover, luciferase reporter and microarray analyses suggested that B23 attenuated GCN5-mediated transactivation in vivo. Taken together, our studies suggest a molecular mechanism of B23 in the mitotic inhibition of GCN5-mediated histone acetylation and transactivation.

Down-regulation of p21 (CDKN1A/CIP1) is inversely associated with microsatellite instability and CpG island methylator phenotype (CIMP) in colorectal cancer

p21 (CDKN1A/CIP1/WAF1), one of the cyclin-dependent kinase inhibitors, plays a key role in regulating the cell cycle and is transcriptionally regulated by p53. Down-regulation of p21 is caused by TP53 mutations in colorectal cancer. CpG island methylator phenotype (CIMP) appears to be a distinct subtype of colorectal cancer with concordant methylation of multiple gene promoters and is associated with a high degree of microsatellite instability (MSI-H) and BRAF mutations. However, no study to date has evaluated the relationship between p21 expression and CIMP in colorectal cancer. The purpose of this study was to examine the inter-relationships between p21, p53, CIMP, MSI and KRAS/BRAF status in colorectal cancer. We utilized 737 relatively unbiased samples of colorectal cancers from two large prospective cohort studies. Using quantitative real-time PCR (MethyLight), we measured DNA methylation in five CIMP-specific gene promoters [CACNA1G, CDKN2A (p16/INK4A), CRABP1, MLH1 and NEUROG1]. CIMP-high (>or=4/5 methylated promoters) was diagnosed in 118 (16%) of the 737 tumours. We also assessed expression of p21 and p53 by immunohistochemistry. Among the 737 tumours, 371 (50%) showed p21 loss. Both p21 loss and p53 positivity were inversely associated with CIMP-high, MSI-H and BRAF mutations. The associations of p21 with these molecular features were still present after tumours were stratified by p53 status. In contrast, the associations of p53 positivity with the molecular features were no longer present after tumours were stratified by p21 status. When CIMP-high and non-CIMP-high tumours were stratified by MSI or KRAS/BRAF status, CIMP-high and MSI-H (but not BRAF mutations) were still inversely associated with p21 loss. In conclusion, down-regulation of p21 is inversely correlated with CIMP-high and MSI-H in colorectal cancer, independent of TP53 and BRAF status.

Molecular mechanism of rat NHE3 gene promoter regulation by sodium butyrate

Sodium butyrate (NaB) stimulates sodium and water absorption by inducing colonic Na+/H+exchange. NaB induces Na+/H+exchanger (NHE)3 activity and protein and mRNA expression both in vivo and in vitro. Our previously published observations indicated that this induction is Ser/Thr kinase dependent and that NaB-responsive elements were localized within −320/−34 bp of the rat NHE3 promoter. Here we further delineate the mechanism of NaB-mediated NHE3 gene transcription. Transient and stable transfection of Caco-2 cells with NHE3 gene reporter constructs identified Sp binding site SpB at position −58/−55 nt as critical for NaB-mediated induction. Gel mobility shift (GMSA) and DNA affinity precipitation assays indicated NaB-induced binding of Sp3 and decreased binding of Sp1 to SpB element. While no changes in expression of Sp1 or Sp3 were noted, NaB induced phosphorylation of Sp1 and acetylation of Sp3. Sp3 was a more potent inducer of NHE3 gene transcription, which suggested that change in balance, favoring binding of Sp3 to the SpB site, would result in significant increase in NHE3 promoter activity. Small interfering RNA studies in Caco-2 cells and data from NaB-treated SL2 cells used as a reconstitution model confirmed this hypothesis. In addition to the SpB site, which played a permissive role, an upstream novel butyrate response element located at −196/−175 nt was necessary for maximal induction. GMSA identified a protein-DNA complex with a −196/−175 nt probe; this interaction was not affected by NaB treatment, thus suggesting that in response to NaB Sp3 binding to site SpB precedes and results in recruitment of the putative factor to this upstream site.

Diallyl disulfide increases CDKN1A promoter-associated histone acetylation in human colon tumor cell lines

Diallyl disulfide (DADS) is an organosulfur compound from garlic, which inhibits colon tumor cell proliferation. In a previous study, we have shown that in Caco-2 and HT-29 cells DADS (200 microM) increases global histone acetylation, CDKN1A mRNA, and p21(waf1) protein levels and induces G2/M cell cycle arrest. These results suggested that DADS could inhibit cell proliferation through at least in part a transcriptional activation of CDKN1A expression involving histone acetylation. In this study, using chromatin immunoprecipitation assays, we demonstrate that in Caco-2 and HT-29 cells histone H4 and/or H3 acetylation is increased within CDKN1A promoter after 3 and 6 h treatments with DADS. These results strongly suggest that histone acetylation, a molecular mechanism implicated in the regulation of gene expression, could account for the induction of CDKN1A expression and the antiproliferating effects of DADS in colon tumor cells.

Involvement of HDAC1 and the PI3K/PKC signaling pathways in NF-κB activation by the HDAC inhibitor apicidin

Histone deacetylase (HDAC) inhibitors are appreciated as one of promising anticancer drugs, but they exert differential responses depending on the cell type. We recently reported the critical role of NF-kappaB as a modulator in determining cell fate for apoptosis in response to an HDAC inhibitor. In this study, we investigate a possible signaling pathway required for NF-kappaB activation in response to the HDAC inhibitor apicidin. Treatment of HeLa cells with apicidin leads to an increase in transcriptional activity of NF-kappaB and the expression of its target genes, IL-8 and TNF-alpha. TNF-alpha expression by apicidin is induced at earlier time points than NF-kappaB activation or IL-8 expression. In addition, our data show that the early expression of TNF-alpha does not lead to activation of NF-kappaB, because disruption of TNF-alpha activity by a neutralizing antibody does not affect nuclear translocation of NF-kappaB, IkappaBalpha degradation or reporter gene activation by apicidin. However, this activation of NF-kappaB requires the PI3K and PKC signaling pathways, but not ERK or JNK. Furthermore, apicidin activation of NF-kappaB seems to result from HDAC1 inhibition, as evidenced by the observation that overexpression of HDAC1, but not HDAC2, 3 or 4, dramatically inhibits NF-kappaB reporter gene activity. Collectively, our results suggest that activation of NF-kappaB signaling by apicidin requires both the PI3K/PKC signaling pathways and HDAC1, and functions as a critical modulator in determining the cellular effect of apicidin.

Activation of NF-κB by HDAC inhibitor apicidin through Sp1-dependent de novo protein synthesis: its implication for resistance to apoptosis

Histone deacetylase (HDAC) inhibitors are promising anti-cancer drugs, but these exert differential responses depending on the cell types. Here, we demonstrate a new mechanism for activation of nuclear factor-kappaB (NF-kappaB) by HDAC inhibitor apicidin and the role of NF-kappaB signaling pathway for mediating differential cellular responses, especially, apoptosis. Treatment of HeLa cells with apicidin increases transcriptional activity of NF-kappaB and its target gene IL-8 and cIAP-1 induction, which involves the activation of IKK-IkappaBalpha signaling pathway through Sp1-dependent de novo protein synthesis. In parallel, apicidin treatment leads to histone hyperacetylation in the IL-8 promoter region independent of NF-kappaB signaling pathway, which is not sufficient for full transcription of IL-8 gene. This NF-kappaB activation contributes to resistance of HeLa cells to apoptotic potential of apicidin. Collectively, our results suggest that activation of NF-kappaB signaling cascade functions as a critical modulator to determine cell fate on apoptosis in response to HDAC inhibitors.

Sulforaphane inhibits histone deacetylase in vivo and suppresses tumorigenesis in Apc-minus mice

Sulforaphane (SFN) is an isothiocyanate from broccoli that induces phase 2 detoxification enzymes. We recently reported that SFN acts as a histone deacetylase (HDAC) inhibitor in human colon cancer cells in vitro, and the present study sought to extend these findings in vivo. In mice treated with a single oral dose of 10 mumol SFN, there was significant inhibition of HDAC activity in the colonic mucosa after 6 h, and immunoblots revealed a concomitant increase in acetylated histones H3 and H4, which returned to control levels by 48 h. Longer-term treatment with SFN in the diet resulted in levels of acetylated histones and p21(WAF1) in the ileum, colon, prostate, and peripheral blood mononuclear cells that were elevated compared with controls. Consistent with these findings, SFN suppressed tumor development in Apc(min) mice, and there was an increase in acetylated histones in the polyps, including acetylated histones specifically associated with the promoter region of the P21 and bax genes. These results provide the first evidence for HDAC inhibition by SFN in vivo and imply that such a mechanism might contribute to the cancer chemoprotective and therapeutic effects of SFN, alone or in combination with other HDAC inhibitors currently undergoing clinical trials.

Sulforaphane inhibits histone deacetylase activity in BPH-1, LnCaP and PC-3 prostate epithelial cells

Sulforaphane (SFN), an isothiocyanate first isolated from broccoli, exhibits chemopreventive properties in prostate cancer cells through mechanisms that are poorly understood. We recently reported on a novel mechanism of chemoprotection by SFN in human colon cancer cells, namely the inhibition of histone deacetylase (HDAC). Here, we show that addition of 15 microM SFN also inhibited HDAC activity by 40, 30 and 40% in BPH-1, LnCaP and PC-3 prostate epithelial cells, respectively. The inhibition of HDAC was accompanied by a 50-100% increase in acetylated histones in all three prostate cell lines, and in BPH-1 cells treated with SFN there was enhanced interaction of acetylated histone H4 with the promoter region of the P21 gene and the bax gene. A corresponding 1.5- to 2-fold increase was seen for p21Cip1/Waf1 and Bax protein expression, consistent with previous studies using HDAC inhibitors, such as trichostatin A. The downstream events included cell cycle arrest and activation of apoptosis, as evidenced by changes in cell cycle kinetics and induction of multi-caspase activity. These findings provide new insight into the mechanisms of SFN action in benign prostate hyperplasia, androgen-dependent prostate cancer and androgen-independent prostate cancer cells, and they suggest a novel approach to chemoprotection and chemotherapy of prostate cancer through the inhibition of HDAC.

Chromatin modification by lipids and lipoprotein components: an initiating event in atherogenesis?

PURPOSE OF REVIEW

This review examines recent evidence proposing that lipids and lipoproteins can act as nuclear factors regulating chromatin structure. These novel data broaden our understanding of the mechanisms by which lipoproteins can affect basic biological phenomena such as transcription, genome stability, and cell differentiation. Furthermore, they provide novel insights into the mechanisms of diseases associated with abnormal lipid levels, such as atherosclerosis and diabetes.

RECENT FINDINGS

Data consistent with a role for lipids and lipoprotein components as nuclear factors, as well as initiators of cytoplasmic signalling events resulting in chromatin modification, have been published in the past year. In particular, new insights into the mechanisms of interaction between chromatin and small lipid molecules such as short-chain fatty acids and cholesterol, and endogenous lipid peroxidation products have been obtained. Furthermore, it has been shown that hyperlipidaemic lipoprotein profiles are associated with aberrant DNA methylation patterns at early stages of atherosclerosis in mice and in cultured human macrophages, suggesting that a rearrangement of DNA methylation patterns is among early molecular changes associated with atherogenesis.

SUMMARY

The findings described here are prompting efforts to understand further how lipids and lipoprotein components can affect gene expression in normal and pathological cell behaviour through regulation of the chromatin structure. It is possible that novel candidate therapeutic tools will emerge from these studies.

Histone deacetylase inhibitors, anticancerous mechanism and therapy for gastrointestinal cancers

Histone acetylation regulates gene transcription. Histone acetylation is a reversible process: histone acetyltransferases (HAT) transfer the acetyl moiety from acetyl coenzyme A to the lysine, and histone deacetylases (HDAC) remove the acetyl groups re-establishing the positive charge in the histones. HDAC inhibitors have antiproliferative activity against human cancer cells via cell cycle arrest, pro-differentiation, and pro-apoptosis. In recent years, many studies have shown that specific HDAC inhibitors are helpful for gastrointestinal cancer therapy.

Cell type-specific regulation of the TGF-beta-responsive alpha2(I) collagen gene by CpG methylation

The alpha2(I) collagen gene shows cell type-specific expression, however, the mechanism behind this specificity remains to be determined. We demonstrate here that transforming growth factor-beta (TGF-beta)-mediated induction of alpha2(I) collagen gene is regulated by DNA methylation in a cell type-specific manner. Human alpha2(I) collagen mRNA and type I collagen protein were expressed in normal human fibroblasts (NHF), and also strongly enhanced by TGF-beta; they were not detected in HaCaT, HeLa, or HepG2 cells (termed "collagen-induction resistant (CIR) cells") even following stimulation with TGF-beta. On the other hand, the transcriptional activity of exogenously transfected alpha2(I) collagen promoter was clearly up-regulated by TGF-beta in the CIR cells as well as in NHF. In the CIR cells, CpG clusters around the transcription start site of the alpha2(I) collagen gene were heavily methylated, whereas no methylation was detected in NHF. Moreover, alpha2(I) collagen gene was reactivated in the CIR cells by 5-Aza-2-deoxycytidine (5-AdC) treatment to some extent. However, demethylation by 5-AdC was limited and it was unable to recover the TGF-beta responsiveness. In NHF, the alpha2(I) collagen gene has a Smad3-accessible chromatin structure and acetylated histones in the promoter regions. By contrast, in the CIR cells, Smad3 failed to bind to the chromatin and histones were not acetylated in this area. Furthermore, in vitro methylation of the reporter gene containing the alpha2(I) collagen promoter significantly reduced both basal and TGF-beta-induced enhancement of the transcriptional activity in NHF. Thus, we propose that alpha2(I) collagen gene provides the first example of the TGF-beta responsive gene whose cell type-specificity is regulated by CpG methylation.

An Sp1 response element in the Kaposi's sarcoma-associated herpesvirus open reading frame 50 promoter mediates lytic cycle induction by butyrate

Kaposi's sarcoma-associated herpesvirus (KSHV) can be driven into the lytic cycle in vitro by phorbol esters and sodium butyrate. This report begins to analyze the process by which butyrate activates the promoter of KSHV open reading frame 50 (ORF50), the key viral regulator of the KSHV latency to lytic cycle switch. A short fragment of the promoter, 134 nucleotides upstream of the translational start of ORF50, retained basal uninduced activity and conferred maximal responsiveness to sodium butyrate. The butyrate response element was mapped to a consensus Sp1-binding site. By means of electrophoretic mobility shift assays, both Sp1 and Sp3 were shown to form complexes in vitro with the ORF50 promoter at the Sp1 site. Butyrate induced the formation of a group of novel complexes, including several Sp3-containing complexes, one Sp1-containing complex, and several other complexes that were not identified with antibodies to Sp1 or Sp3. Formation of all butyrate-induced DNA-protein complexes was mediated by the consensus Sp1 site. In insect and mammalian cell lines, Sp1 significantly activated the ORF50 promoter linked to luciferase. Chromatin immunoprecipitation experiments in a PEL cell line showed that butyrate induced Sp1, CBP, and p300 binding to the ORF50 promoter in vivo in an on-off manner. The results suggest that induction of the KSHV lytic cycle by butyrate is mediated through interactions at the Sp1/Sp3 site located 103 to 112 nucleotides upstream of the translational initiation of ORF50 presumably by enhancing the binding of Sp1 to this site.

Histone Deacetylase Inhibitors Up-Regulate the Expression of Tight Junction Proteins

Histone deacetylase (HDAC) inhibitors promote cell maturation, differentiation, and apoptosis through changes in gene expression. Differentiated epithelial cells are characterized by apical tight junctions (TJ), which play a role in cell-cell adhesion, polarity, and the permeability barrier function of epithelia. The relationship between cellular differentiation and expression of TJ-associated proteins is not known. Here, we investigated whether HDAC inhibitors affect the expression of TJ proteins in cultured cells by immunoblotting, immunofluorescence, and quantitative real-time, reverse transcription-PCR. We find that the HDAC inhibitor sodium butyrate significantly up-regulates the protein levels of cingulin, ZO-1, and ZO-2 in Rat-1 fibroblasts, cingulin in COS-7 cells, and cingulin and occludin in HeLa cells. Levels of mRNA for cingulin, ZO-1, and ZO-2 are also increased in sodium butyrate–treated Rat-1 fibroblasts. Up-regulation of cingulin is reversible and dose dependent and requires de novo protein synthesis and protein kinase activity, because it is inhibited by cycloheximide and by the protein kinase inhibitor H-7. Up-regulation of TJ proteins by sodium butyrate is linked to the ability of sodium butyrate to inhibit HDAC activity, because suberoylanilide hydroxamic acid, a HDAC inhibitor of a different structural class, also up-regulates cingulin, ZO-1, and ZO-2 expression in Rat-1 fibroblasts. These results indicate that cellular differentiation correlates with kinase-dependent up-regulation of the expression of specific TJ proteins.

A novel mechanism of chemoprotection by sulforaphane: inhibition of histone deacetylase

Sulforaphane (SFN), a compound found at high levels in broccoli and broccoli sprouts, is a potent inducer of phase 2 detoxification enzymes and inhibits tumorigenesis in animal models. SFN also has a marked effect on cell cycle checkpoint controls and cell survival and/or apoptosis in various cancer cells, through mechanisms that are poorly understood. We tested the hypothesis that SFN acts as an inhibitor of histone deacetylase (HDAC). In human embryonic kidney 293 cells, SFN dose-dependently increased the activity of a beta-catenin-responsive reporter (TOPflash), without altering beta-catenin or HDAC protein levels. Cytoplasmic and nuclear extracts from these cells had diminished HDAC activity, and both global and localized histone acetylation was increased, compared with untreated controls. Studies with SFN and with media from SFN-treated cells indicated that the parent compound was not responsible for the inhibition of HDAC, and this was confirmed using an inhibitor of glutathione S-transferase, which blocked the first step in the metabolism of SFN, via the mercapturic acid pathway. Whereas SFN and its glutathione conjugate (SFN-GSH) had little or no effect, the two major metabolites SFN-cysteine and SFN-N-acetylcysteine were effective HDAC inhibitors in vitro. Finally, several of these findings were recapitulated in HCT116 human colorectal cancer cells: SFN dose-dependently increased TOPflash reporter activity and inhibited HDAC activity, there was an increase in acetylated histones and in p21(Cip1/Waf1), and chromatin immunoprecipitation assays revealed an increase in acetylated histones bound to the P21 promoter. Collectively, these findings suggest that SFN may be effective as a tumor-suppressing agent and as a chemotherapeutic agent, alone or in combination with other HDAC inhibitors currently undergoing clinical trials.

The butyrate story: old wine in new bottles?

PURPOSE OF REVIEW

Short-chain fatty acids are important end products of bacterial carbohydrate fermentation in the colon. In particular, n-butyrate is thought to play a regulatory role in the maintenance of a physiological environment. Disturbances in the interplay between the microflora and the lining epithelium may lead to mucosal inflammation and promote carcinogenesis. The purpose of this article is to review the literature between March 2003 and February 2004 and to determine if recent studies have improved the understanding of butyrate effects in health and disease.

RECENT FINDINGS

Preclinical studies (cell culture experiments, animal studies) using modern molecular biological tools (including cDNA arrays) have provided new insights into the action of butyrate on colonic epithelial, vascular endothelial and extracolonic cell types. The new information adds pieces of evidence to the assumption that butyrate may ameliorate colonic inflammation and may be chemopreventive in carcinogenesis. In contrast, new data from clinical studies have been limited in the review period.

SUMMARY

In the era of molecular biology our understanding of subcellular processes that ultimately lead to inflammatory bowel disease or colorectal cancer has widened considerably. The new powerful technology of genomics and proteomics, however, raises new questions without easy answers. With this new information in mind, we will have to go back to human intervention trials to test the hypotheses generated in vitro. The preclinical data from the review period justify the need for carefully designed clinical trials to test the benefits derived from butyrate production.