脱氧氮杂胞苷诱导HepG2细胞表达主要组织相容性复合体Ⅰ类分子A

目的 观察主要组织相容性复合体Ⅰ类分子A(MICA)在HepG2与L02细胞株中表达的差异及脱氧氮杂胞苷(5-aza-dC)对HepG2细胞株MICA表达的影响,探讨毛细血管扩张性共济失调突变蛋白(ATM)依赖的DNA损伤途径与5-aza-dC调节MICA表达的关系. 方法同时接种并培养L02和HepG2细胞,在同一时间点收取细胞,流式细胞仪检测细胞膜MICA蛋白表达水平;不同浓度5-aza-dC(0.1,1.0,5.0mmol/L)作用于HepG2细胞不同时间(24、48、72、96h)后,定量PCR检测MICA mRNA水平以寻找5-aza-dC最佳作用浓度和时间;ATM特异性抑制剂咖啡因或RNA干扰技术干扰ATM表达,定量PCR检测细胞mRNA水平,流式细胞术检测细胞膜MICA蛋白表达水平.结果 数据比较采用Kruskal-Wallis和Mean-Whitney U方差分析.结果 流式细胞结果显示,HepG2细胞高水平表达MICA,而正常肝细胞L02几乎不表达MICA;5-aza-dC处理可上调HepG2细胞MICA的表达(X2=7.20,P＜0.05),这种上调作用可被ATM特异性阻滞剂咖啡因和ATM特异的小分子干扰RNA所阻断(U=0.00,P＜0.05).结论 MICA在正常肝细胞株中无表达,在肝癌细胞株中高表达;5-aza-dC可诱导HepG2细胞MICA的表达,其机制可能与5-aza-dC引起的ATM依赖的DNA损伤途径有关.     

MYO5B Is Epigenetically Silenced and Associated with MET Signaling in Human Gastric Cancer

Background

Our previous study has shown that MYO5B is downregulated in gastric cancer. However, the mechanism by which the expression of MYO5B was inhibited remains unknown.

Methods

Inspection of the human MYO5B locus uncovered a large and dense CpG island within the 5′ region of this gene. Methylation-specific PCR (MSP) and bisulfite sequencing (BSP) were used for determination of MYO5B promoter methylation in gastric cancer cell lines and gastric cancer samples. Involvement of histone H3 methylation in those cell lines were examined by ChIP assay.

Results

The densely methylated MYO5B promoter region was confirmed by MSP and BSP. Enhanced gene expression was detected when the cells were treated with the DNA-demethylating agent 5-aza-2′-deoxycytidine (DAC) and trichostatin A (TSA), a histone deacetylase inhibitor. Knockdown of MYO5B expression in gastric cancer cells expressing endogenous MYO5B inhibits HGF-stimulated MET degradation, concomitant with sustained c-MET levels and signaling.

Conclusion

The results of our study showed for the first time that MYO5B is epigenetically silenced in gastric cancer cells by aberrant DNA methylation and histone modification. Inactivation of MYO5B expression in gastric cancer cells expressing endogenous MYO5B inhibits HGF-stimulated MET degradation, concomitant with sustained c-MET levels and signaling.     

ADH1B*1, ADH1C*2, DRD2 (-141C Ins), and 5-HTTLPR are associated with alcoholism in Mexican American men living in Los Angeles

BACKGROUND: The aim of the present study was to use a candidate gene approach to identify the genetic risk factors for alcoholism in Mexican Americans residing in the Los Angeles area. The genes selected include alcohol metabolizing genes and neurotransmitter genes, which have been shown in the literature to be associated with alcoholism in other ethnic groups. METHODS: Thirteen allelic variants from seven genes were evaluated for their role in alcoholism using alcoholic (n = 200) and nonalcoholic (n = 251) Mexican Americans. Those polymorphic sites include alcohol dehydrogenase (ADH1B, ADH1C), aldehyde dehydrogenase (ALDH2), cytochrome P-450 2E1 (CYP2E1) TaqI, DraI, RsaI, dopamine D2 receptor (DRD2) TaqI A, B, intron 6, exon 7, -141C Ins/Del, serotonin transporter (5-HTTLPR), and GABAA receptor beta3 subunit (GABRbeta3). RESULTS: The results demonstrate that Mexican Americans have extremely low allele frequency for both ALDH2*2 and ADH1B*2 and a relatively high frequency of ADH1C*2 and CYP2E1 c2 alleles. ADH1B*1, ADH1C*2, DRD2 (-141C Ins), and 5-HTTLPR were associated with alcoholism in Mexican Americans (p < 0.05). DRD2 Ins was associated with alcoholism in those alcoholics who carried the ADH1B*2 or ADH1C*1 protective alleles (p = 0.032 in genotype level and p = 0.015 in allele level). DRD2 TaqI A and B alleles were associated with early age of onset for drinking (p = 0.016 for TaqI A1 and p = 0.049 for TaqI B1 allele). CONCLUSIONS: Together, the data reveal unique genetic patterns in Mexican Americans that may be in part responsible for the heightened risk for alcoholism and alcohol-associated health problems in this population.     

Hepatitis B viral DNA is methylated in liver tissues

The mechanisms that regulate hepatitis B virus (HBV) replication within the liver are poorly understood. Given that methylation of CpG islands regulates gene expression in human tissues, we sought to identify CpG islands in HBV-DNA and to determine if they are methylated in human tissues. In silico analysis demonstrated three CpG islands in HBV genotype A sequences, two of which were of particular interest because of their proximity to the HBV surface gene start codon (island 1) and to the enhancer 1/X gene promoter region (island 2). Human sera with intact virions that were largely unmethylated were used to transfect HepG2 cells and HBV-DNA became partially methylated at both islands 1 and 2 by day 6 following exposure of HepG2 to virus. Examination of three additional human sera and 10 liver tissues showed no methylation in sera but tissues showed methylation of island 1 in six of 10 cases and of island 2 in five of 10 cases. The cell line Hep3B, with integrated HBV, showed complete methylation of island 1 but no methylation of island 2. In conclusion, HBV-DNA can be methylated in human tissues and methylation may play an important role in regulation of HBV gene expression.     

The histone-deacetylase inhibitor Trichostatin A blocks proliferation and triggers apoptotic programs in hepatoma cells

BACKGROUND/AIMS: Effective treatment for hepatocellular carcinoma is urgently needed. The histone-deacetylase inhibitor Trichostatin A (TSA) was shown to induce apoptosis in non-hepatic cells at submicromolar concentrations. However, the effect of TSA on hepatoma cells is unknown. METHODS: The hepatoma cells HepG2, MH1C1, Hepa1-6 and Hep1B as well as human fibroblasts (control cells) were exposed to TSA (10(-6) to 10(-9)M). Cell proliferation was assessed by measuring DNA-synthesis and cell numbers. Apoptosis was quantified by flow cytometry and by the TdT-mediated dUTP nick-end labeling method. Expression patterns of cell cycle- and/or apoptosis-associated p27, p21(cip/waf), bax, bcl-2, cyclin A and (pro)-caspase 3 were studied using quantitative Western blotting. Activation of caspase 3 was analyzed via a colorimetric assay. RESULTS: 10(-6)M TSA inhibited DNA-synthesis by 46% (HepG2) to 64% (MH1C1) after 24h, inducing a G(2)/M-phase arrest and apoptosis. TSA increased activation of caspase 3 and expression of cyclin A, p2l(cip/waf), bax and (pro)-caspase 3, while bcl-2 was downregulated. Human fibroblasts remained unaffected. CONCLUSIONS: TSA inhibits hepatoma cell growth in vitro, which are otherwise particularly resistant to chemotherapy. Its anti-proliferative activity is paralleled by a comparable rate of apoptosis. TSA may be a promising agent for treatment of hepatocellular carcinoma in vivo.     

肝癌细胞对5-氮杂-2'-脱氧胞苷的敏感性与细胞总DNA甲基化水平无关

目的 比较不同肝癌细胞株对5-氮杂-2'-脱氧胞苷(5-aza-dC)的敏感性,探讨肝癌细胞对5-aza-dC的敏感性是否与细胞总DNA甲基化水平有关.方法 用不同剂量(0.5、5.0、10.0μmol/L)的5-aza-dC处理肝癌细胞株(HepG2、QGY7701和HepG2.2.15细胞)及正常肝细胞株L02,比较不同浓度处理前后的细胞增殖抑制率,比较10 μmol/L 5-aza-dC处理前后的Caspase-3活性及细胞DNA片段化水平(5-溴脱氧尿嘧啶核苷掺入率),比较不同细胞总DNA甲基化水平.组间检测结果比较采用t检验.结果 5-aza-dC对HepG2、QGY7701、HepG2.2.15、L02细胞的半数抑制浓度分别为0.5、0.5、4.5、11.4μmol/L,与HepG2细胞和QGY7701细胞相比,HepG2.2.15绌胞和L02细胞对5-aza-dC不敏感.HepG2和QGY7701细胞中Caspase-3的活性升高较L02和HepG2.2.15细胞明显(P值均＜0.05),QGY7701细胞中5-溴脱氧尿嘧啶核苷掺入率升高较L02细胞明显(P＜0.05).L02、HepG2、QGY7701和HepG 2.2.15细胞的DNA总甲基化水平分别为11.7%±0.9%、10.9%±1.3%、11.7%±1.7%和12.2%±1.0%,差异无统计学意义(P值均＞0.05).结论 细胞对5-aza-dC的敏感性与细胞总DNA甲基化水平无关.     

5-aza—dC和丁酸钠对人胃癌细胞株MKN28细胞周期、凋亡以及抑癌基因表达的影响

背景：表遗传修饰的主要方式DNA甲基化和组蛋白乙酰化是胃癌发生机制研究中的热点内容。目的：探讨表遗传学调控对人胃癌细胞株MKN28细胞周期、凋广以及抑癌基因Runx3、p21^WAF1表达的影响。方法：培养人胃癌细胞株MKN28,并分为5-氮-2’-脱氧胞苷（5-aza—dC）组、丁酸钠组、5-aza—dC＋丁酸钠组和对照组。以Annexin V—FITC／PI双染法检测细胞周期和凋亡,以逆转录聚合艏链反应（RT—PCR）检测Runx3、p21^WAF1 mRNA表达,以甲基化特异性PCR（MSP）检测Runx3基因启动于区甲基化状态。结果：与对照组相比,5-aza—dC对细胞周期无明显影响,丁酸钠可使细胞周期阻滞于G0／G1期（P〈0．05）;5-aza—dC组和丁酸钠组细胞凋亡率均显著增高（8．3％±1．3％、20．8％±2．4％对2．0％±0．5％,P〈0．05）5-aza—dC可诱导Runx3mRNA重新表达（P〈0．05）,但对p21^WAF1 mRNA表达无影响。丁酸钠可增强p21^WAF1 mRNA表达（P〈0．05）,但不能诱导Runx3 mRNA表达。联合5-aza—dC和丁酸钠可显著绣导细胞凋亡和增强抑癌基因Runx3、p21^WAF1Ⅲ mRNA表达（P〈0．05）．5-azgt—dC十预后,Runx3基因启动子区呈去甲基化状态：结论：去甲基化制剂5-aza-dC或组生白去乙酰化酶抑制剂丁酸钠通过重新表达Runx3或增强p21^WAF1表达而诱导胃癌MKN28细胞凋亡,从而发挥抗肿瘤的作用。     

Effect of ADH1B genotype on alcohol consumption in young Israeli Jews

BACKGROUND: The alcohol dehydrogenase 1B (ADH1B) genotype affects the risk for alcoholism, with elevated prevalence of a protective allele in Jews. Alcohol consumption is increasing among younger Israeli Jews, reflecting environmental influences. We investigated whether the relationship of ADH1B genotype with alcohol consumption differed between younger and older adult Israelis. METHODS: Israeli community residents aged 22 to 65 participated in a structured interview that included questions on the maximum number of drinks on an occasion (Maxdrinks). The ADH1B genotype was determined for 68 participants and dichotomized into nonprotective (ADH1B(*)1/1) and protective (ADH1B(*)1/2 or ADH1B(*)2/2) genotypes. Using Maxdrinks as the dependent variable, Poisson's regression was used to test an age x genotype interaction. RESULTS: The ADH1B genotype interacted significantly with age (p=0.01) in a Poisson's model with Maxdrinks as the outcome. Among participants >or=33 years, Maxdrinks was low and unrelated to the ADH1B genotype. Among participants <33 years with ADH1B(*)1/2 or ADH1B(*)2/2, Maxdrinks was also low (mean, 2.6 drinks) but among those with ADH1B(*)1/1, Maxdrinks was substantially higher (mean, 6.2 drinks). CONCLUSION: Maximum lifetime drinking among younger adult Israelis without genetic protection exceeded thresholds for risky and unsafe drinking (>or=5 drinks). Environmental influences promoting greater drinking among younger Israelis may particularly affect those with the nonprotective, more common ADH1B genotype.     

Aberrant epigenetic modifications in hepatocarcinogenesis induced by hepatitis B virus X protein

BACKGROUND & AIMS: The involvement of the hepatitis B virus X (HBx) protein in epigenetic modifications during hepatocarcinogenesis has not been previously characterized. The aim of the present study was to identify the involvement of HBx in regional hypermethylation and global hypomethylation during the formation of hepatocellular carcinoma (HCC). METHODS: Liver cell lines were transiently or stably transfected with an HBx-expressing vector. DNA methyltransferase (DNMT) promoter activity changes were examined by luciferase assay and chromatin immunoprecipitation. The methylation status of insulin-like growth factor binding protein-3 was examined by methyl-specific polymerase chain reaction and bisulfite sequencing. Global DNA methylation levels were examined using 5-methylcytosine dot blot and methylation-sensitive Southern blot analysis. HBx-mediated DNA methylation abnormalities were confirmed in patient HCC samples using methyl-specific polymerase chain reaction and 5-methylcytosine dot blot analysis. RESULTS: HBx expression increased total DNMT activities by up-regulation of DNMT1, DNMT3A1, and DNMT3A2 and selectively promoted regional hypermethylation of specific tumor suppressor genes. HBx specifically repressed insulin-like growth factor-3 expression through de novo methylation via DNMT3A1 and DNMT3A2 and by inhibiting SP1 binding via recruiting methyl CpG binding protein 2 to the newly methylated SP1 binding element. HBx also induced global hypomethylation of satellite 2 repeat sequences by down-regulating DNMT3B. The prevalence of these specific methylation abnormalities by HBx was significantly correlated with HBx expression in HBV-infected HCC patients. CONCLUSIONS: Targeted deregulation of DNMTs by HBx promotes both specific regional hypermethylation and global hypomethylation. These epigenetic modulations by HBx may suggest a mechanism for epigenetic tumorigenesis during HBV-mediated hepatocarcinogenesis.     

DNA methylation of developmental genes in pediatric medulloblastomas identified by denaturation analysis of methylation differences

DNA methylation might have a significant role in preventing normal differentiation in pediatric cancers. We used a genomewide method for detecting regions of CpG methylation on the basis of the increased melting temperature of methylated DNA, termed denaturation analysis of methylation differences (DAMD). Using the DAMD assay, we find common regions of cancer-specific methylation changes in primary medulloblastomas in critical developmental regulatory pathways, including Sonic hedgehog (Shh), Wingless (Wnt), retinoic acid receptor (RAR), and bone morphogenetic protein (BMP). One of the commonly methylated loci is the PTCH1-1C promoter, a negative regulator of the Shh pathway that is methylated in both primary patient samples and human medulloblastoma cell lines. Treatment with the DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine (5-aza-dC) increases the expression of PTCH1 and other methylated loci. Whereas genetic mutations in PTCH1 have previously been shown to lead to medulloblastoma, our study indicates that epigenetic silencing of PTCH1, and other critical developmental loci, by DNA methylation is a fundamental process of pediatric medulloblastoma formation. This finding warrants strong consideration for DNA demethylating agents in future clinical trials for children with this disease.