Cancer-type regulation of MIG-6 expression by inhibitors of methylation and histone deacetylation

Epigenetic silencing is one of the mechanisms leading to inactivation of a tumor suppressor gene, either by DNA methylation or histone modification in a promoter regulatory region. Mitogen inducible gene 6 (MIG-6), mainly known as a negative feedback inhibitor of the epidermal growth factor receptor (EGFR) family, is a tumor suppressor gene that is associated with many human cancers. To determine if MIG-6 is inactivated by epigenetic alteration, we identified a group of human lung cancer and melanoma cell lines in which its expression is either low or undetectable and studied the effects of methylation and of histone deacetylation on its expression. The DNA methyltransferase (DNMT) inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) induced MIG-6 expression in melanoma cell lines but little in lung cancer lines. By contrast, the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) induced MIG-6 expression in lung cancer lines but had little effect in melanoma lines. However, the MIG-6 promoter itself did not appear to be directly affected by either methylation or histone deacetylation, indicating an indirect regulatory mechanism. Luciferase reporter assays revealed that a short segment of exon 1 in the MIG-6 gene is responsible for TSA response in the lung cancer cells; thus, the MIG-6 gene can be epigenetically silenced through an indirect mechanism without having a physical alteration in its promoter. Furthermore, our data also suggest that MIG-6 gene expression is differentially regulated in lung cancer and melanoma.     

Discovery and SAR of 1,3,4-thiadiazole derivatives as potent Abl tyrosine kinase inhibitors and cytodifferentiating agents

A series of substituted benzoylamino-2-[(4-benzyl)thio]-1,3,4-thiadiazoles has been discovered as potent Abl tyrosine kinase inhibitors. Molecular docking simulations on the Abl tyrosine kinase were conducted in order to rationalize the SAR of the synthesized inhibitors. The most active compound identified from the enzymatic screening (6a) showed interesting inhibitory activity on Imatinib-sensitive murine myeloid 3B clone and Bcr-Abl-independent Imatinib-resistant leukemia cells. Surprisingly, 6a was also proved to act as differentiating inducers in human promyelocytic leukemia cells (HL-60).     

Benzothiazole-containing hydroxamic acids as histone deacetylase inhibitors and antitumor agents

Data from clinical studies indicate that inhibitors of Class I and Class II histone deacetylase (HDAC) enzymes show great promise for the treatment of cancer. Zolinza (SAHA, Zolinza) was recently approved by the FDA for the treatment of the cutaneous manifestations of cutaneous T-cell lymphoma. As a part of our ongoing effort to identify novel small molecules to target these important enzymes, we have prepared two series of benzothiazole-containing analogues of SAHA. It was found that several compounds with 6C-bridge linking benzothiazole moiety and hydroxamic functional groups showed good inhibition against HDAC3 and 4 at as low as 1 μg/ml and exhibited potent cytotoxicity against five cancer cell lines with average IC₅₀ values of as low as 0.81 μg/ml, almost equipotent to SAHA.     

组蛋白乙酰化／脱乙酰化与DNA甲基化的关系

组蛋白乙酰化和脱乙酰化与DNA甲基化有密切的关系,本文介绍了DNA甲基化对组蛋白乙酰化／脱乙酰化影响,组蛋白乙酰化／脱乙酰化对DNA甲基化的影响,以及组蛋白乙酰化／脱乙酰化和DNA甲基化协同效应。     

Kinetics of histone hyperacetylation and deacetylation in human diploid fibroblasts

We have utilized sodium butyrate-treated normal human diploid fibroblasts to study core histone hyperacetylation kinetics. We report a small, distinct population of core histone characterized by a very rapid rate of hyperacetylation ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈10–15}\text{min}$ for monoacetylated histone H4) compared to the slower rate ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈140–200}\text{min}$ for monoacetylated H4) observed for bulk histone. Two rates of core histone deacetylation were also detected and we demonstrated that the rapidly hypermodified histone H4 population was also rapidly deacetylated. The kinetics of histone H4 hyperacetylation and deacetylation in these cells were not significantly altered, regardless of whether cultures were exponentially growing, confluent or arrested in an essentially non-mitotic state.     

A SANT motif in the SMRT corepressor interprets the histone code and promotes histone deacetylation

Nuclear receptor corepressors SMRT (silencing mediator of retinoid and thyroid receptors) and N-CoR (nuclear receptor corepressor) recruit histone deacetylase (HDAC) activity to targeted regions of chromatin. These corepressors contain a closely spaced pair of SANT motifs whose sequence and organization is highly conserved. The N-terminal SANT is a critical component of a deacetylase activation domain (DAD) that binds and activates HDAC3. Here, we show that the second SANT motif functions as part of a histone interaction domain (HID). The HID enhances repression by increasing the affinity of the DAD-HDAC3 enzyme for histone substrate. The two SANT motifs synergistically promote histone deacetylation and repression through unique functions. The HID contribution to repression is magnified by its ability to inhibit histone acetyltransferase enzyme activity. Remarkably, the SANT-containing HID preferentially binds to unacetylated histone tails. This implies that the SMRT HID participates in interpreting the histone code in a feed-forward mechanism that promotes and maintains histone deacetylation at genomic sites of SMRT recruitment.     

A selective inhibitor of N8-acetylspermidine deacetylation in mice and HeLa cells without effects on histone deacetylation

The inhibitory effects of 7-[N-(3-aminopropyl)amino]heptan-2-one (APAH) on N8-acetylspermidine deacetylation were studied. In in vitro studies, APAH produced inhibition (apparent Ki of 0.18 microM) of N8-acetylspermidine deacetylation by the 100,000g supernatant fraction of rat liver. This apparent Ki was 60-fold less than the apparent Km (11 microM) for deacetylation of the substrate, N8-acetylspermidine, suggesting that APAH could be a potent, effective inhibitor in vivo. APAH was administered to mice by intraperitoneal injection at a dose of 200 mg/kg, and polyamine and acetylpolyamine levels in liver and spleen were measured. In tissues of control mice, N8-acetylspermidine was not detectable but increased to detectable levels 30-360 min after APAH treatment. These data are consistent with inhibition of the deacetylase by APAH. Increases in putrescine and N1-acetylspermidine levels occurred in liver after APAH treatment with increases in N1-acetylspermidine levels observed in spleen. In HeLa cells, a significant increase in N8-acetylspermidine was observed following 24 h exposure to 10 microM APAH while no change occurred in the acetylation level of HeLa cell histones. In contrast, 24 h exposure to 10 mM sodium butyrate produced no change in N8-acetylspermidine levels and an increase in the acetylation level of histones H4 and H2B. These results suggest that APAH has a relatively selective inhibitory effect on N8-acetylspermidine but not histone deacetylation. This is the first report of significant levels of N8-acetylspermidine in animal tissues and of the effects of in vivo inhibition of N8-acetylspermidine deacetylase.