Expression of mRNA for DNA methyltransferases and methyl-CpG-binding proteins and DNA methylation status on CpG islands and pericentromeric satellite regions during human hepatocarcinogenesis

To evaluate the significance of alterations in DNA methylation during human hepatocarcinogenesis, we examined levels of mRNA for DNA methyltransferases and methyl-CpG-binding proteins and the DNA methylation status in 67 hepatocellular carcinomas (HCCs). The average level of mRNA for DNMT1 and DNMT3a was significantly higher in noncancerous liver tissues showing chronic hepatitis or cirrhosis than in histologically normal liver tissues, and was even higher in HCCs. Significant overexpression of DNMT3b and reduced expression of DNMT2 were observed in HCCs compared with the corresponding noncancerous liver tissues. DNA hypermethylation on CpG islands of the p16 (8% and 66%) and hMLH1 (0% and 0%) genes and methylated in tumor (MINT) 1 (6% and 34%), 2 (24% and 58%), 12 (21% and 33%), 25 (0% and 5%), and 31 (0% and 23%) clones, and DNA hypomethylation on satellites 2 and 3 (18% and 67%), were detected in noncancerous liver tissues and HCCs, respectively. There was no significant correlation between the expression level of any DNA methyltransferase and DNA methylation status. Reduced expression of DNA repair protein, MBD4, was significantly correlated with poorer tumor differentiation and involvement of portal vein. Slightly reduced expression of MBD2 was detected in HCCs, and the expression of MeCP2 was particularly reduced in HCCs with portal vein involvement. These data suggest that overexpression of DNMT1 and DNMT3a, DNA hypermethylation on CpG islands, and DNA hypomethylation on pericentromeric satellite regions are early events during hepatocarcinogenesis, and that reduced expression of MBD4 may play a role in malignant progression of HCC.     

Genetic instability and aberrant DNA methylation in chronic hepatitis and cirrhosis--A comprehensive study of loss of heterozygosity and microsatellite instability at 39 loci and DNA hypermethylation on 8 CpG islands in microdissected specimens from patients with hepatocellular carcinoma

A study was conducted to examine the significance of genetic instability and aberrant DNA methylation during hepatocarcinogenesis. Genomic DNA was extracted from 196 microdissected specimens of noncancerous liver tissue that showed no marked histologic findings or findings compatible with chronic hepatitis or cirrhosis, and 80 corresponding microdissected specimens of hepatocellular carcinoma (HCC) from 40 patients. Loss of heterozygosity (LOH) and microsatellite instability (MSI) were examined by polymerase chain reaction (PCR) using 39 microsatellite markers, and DNA methylation status on 8 CpG islands was examined by bisulfite-PCR. In noncancerous liver tissues, LOH, MSI, and DNA hypermethylation were found in 15 (38%), 6 (15%), and 33 (83%) of 40 cases, respectively. The incidence of DNA hypermethylation in histologically normal liver was similar to that in chronic hepatitis and cirrhosis, although neither LOH nor MSI was found in histologically normal liver. In cancerous tissues, LOH, MSI, and DNA hypermethylation were found in 39 (98%), 8 (20%), and 40 (100%) of 40 cases, respectively. CpG islands of the p16 gene and methylated in tumor 1, 2, 12, and 31 clones were frequently methylated in cancerous tissues, although neither the thrombospondin-1 nor the human Mut L homologue (hMLH1) gene was methylated. Absence of silencing of the hMLH1 gene by DNA hypermethylation is consistent with the low incidence of MSI in HCCs. The results of this study indicate that LOH and aberrant DNA methylation contribute to hepatocarcinogenesis; DNA hypermethylation in particular, which precedes or may even cause LOH, is as an early event during hepatocarcinogenesis.     

胃癌组织中肿瘤相关基因甲基化及其表达与叶酸和代谢酶MTHFR基因多态性的关系

目的:探讨人胃癌组织中癌基c-myc,抑癌基因p16INK4A,p21WAF1,错配修复基NhMLH1和hM2SH2的甲基化状态及其表达与叶酸、MTHFR基因多态性的关系．方法:胃癌38例手术切除标本的癌区、癌旁和外周正常黏膜组织,运用FOL ACS:180自动化学发光系统测定叶酸含量,PCR-RFLP技术检测MTHFR基因677(C→T)和1298(A→C)两个常见多态,并分别以Real—time RT-PCR和甲基化特异性PCR (MSP)技术检测肿瘤相关基因的表达和甲基化状态．结果:c-myc表达升高,p16INK4A,hMLH1和hMSH2表达降低的胃癌黏膜组织其基因启动子区异常甲基化．p21WAF1,hMSH2表达降低, p16INK4A高甲基化者叶酸水平明显降低,c-myc低甲基化和表达升高者中均存在低叶酸水平．MTHFR 677CC基因型的胃癌黏膜组织p16INK4A甲基化升高且表达降低,而其余肿瘤相关基因的甲基化及其表达与MTHFR两个常见多态均无明显相关性．结论:DNA甲基化在胃癌的发生、发展中具有重要作用,叶酸水平和MTHFR基因多态性通过影响部分肿瘤相关基因的甲基化状态而调控其表达．     

Tissue microarray for high-throughput analysis of gene expression profiles in hepatocellular carcinoma

AIM: To study the expression profiles of HBsAg, HBcAg, p21WAF1/CIP1 (p21), Rb genes in hepatocellular carcinoma (HCC) and to investigate their roles in the hepatocar-cinogenesis. METHODS: HCC tissue microarray containing 120-min tissues of 40 HCC cases was constructed. HBsAg, HBcAg, p21 and Rb proteins were immunohistochemically stained by streptavidin-peroxidase conjugated method (S-P). The expression loss of these genes in cancerous, para-cancerous tissues and adjacent normal liver tissues of 40 HCCs were comparatively examined. RESULTS: The positive rate of HBsAg expression in cancerous tissues of 40 HCCs was 7.5%, which was lower than that in para-cancerous and adjacent normal liver tissues (X2=12.774, P<0.01; X2=18.442, P<0.01). The positive rate of HBcAg expression in cancerous tissues of 40 HCCs was 20.0%, which was also lower than that in para-cancerous and adjacent normal liver tissues (X2=9.482, P<0.01; X2=14.645, P<0.01). p21 protein deletion rate in cancerous tissues of 40 HCCs was 27.5%, which was higher than that in para-cancerous and adjacent normal liver tissues (X2=7.439, P<0.01; X2=11.174, P<0.01). p21 protein deletion correlated remarkably with the pathological grade of HCC (X2=0.072, P<0.05). Rb protein deletion rate in cancerous tissues of 40 HCCs was 42.5%, which was also higher than that in para-cancerous and adjacent normal liver tissues (X2=10.551, P<0.01; X2=18.353, P<0.01). Rb protein deletion rate did not correlate remarkably with tumor size or pathological grade of HCC (X2=0.014, P>0.05; X2=0.017, P>0.05). CONCLUSION: Expression deletion of HBsAg, HBcAg, p21 and Rb proteins in HCCs may play important roles in the carcinogenesis of HCC. Tissue microarray is an effective high-throughput technique platform for cancer research.     

Detection of hypermethylation of the p16(INK4A) gene promoter in chronic hepatitis and cirrhosis associated with hepatitis B or C virus

BACKGROUND/AIM: Inactivation of the p16(INK4A) (p16) tumour suppressor gene by promoter region hypermethylation has been demonstrated not only in many types of tumours, including hepatocellular carcinoma (HCC), but also in early preneoplastic lesions in the lung, colon, oesophagus, and pancreas. The aim of this study was to examine the methylation status of the p16 promoter in pre- and/or non-neoplastic liver diseases. PATIENTS/SUBJECTS/METHODS: The methylation status of p16 was evaluated in 22 HCC, 17 cirrhosis, 17 chronic hepatitis, nine primary biliary cirrhosis (PBC), eight autoimmune hepatitis, seven drug induced liver disease, six fatty liver, and three normal liver tissues using methylation specific polymerase chain reaction (MSP). p16 protein expression was also examined by immunohistochemical staining. RESULTS: Methylation of the p16 promoter was detected in HCC (72.7%, 16/22) and also in cirrhosis (29.4%, 5/17) and chronic hepatitis (23.5%, 4/17), all of which were positive for hepatitis B or C virus infections. Methylation was not detected in any of the other samples. All methylation positive HCC, cirrhosis, and chronic hepatitis samples showed loss of p16 expression, and a significant correlation was found between methylation and loss of expression. Analysis of serial samples from individual patients with methylation positive HCC revealed that loss of p16 expression with promoter methylation occurred in 18 of 20 patients at the stage of chronic hepatitis without clinically detectable carcinoma. CONCLUSIONS: Our results suggest that methylation of the p16 promoter and the resulting loss of p16 protein expression are early events in a subset of hepatocarcinogenesis and that their detection is useful in the follow up of patients with a high risk of developing HCC, such as those with hepatitis B or C viral infections.     

Hypermethylation and aberrant expression of Wnt-antagonist family genes in gastric cardia adenocarcinoma

The canonical Wnt signalling pathway plays a key role during embryogenesis and pathogenesis of various types of tumors. Recently, several studies have shown that the promoter hypermethylation of Wnt-antagonist genes, including sFRP-1, sFRP-2, sFRP-4, sFRP-5, Wif-1 and Dkk-3, have been certified to contribute to the tumorigenesis of several cancers. The aim of this study was to investigate the promoter methylation of Wnt-antagonist genes in gastric cardia adenocarcinoma (GCA) and corresponding adjacent non-cancerous tissues, and to establish the possible relationship between DNA methylation status and the pathogenesis of GCA. MSP, RT-PCR methods were applied respectively to examine the CpG methylation of the Wnt-antagonist genes and its mRNA expression in tumors and corresponding non-cancerous tissues, and immunohistochemistry method was used to determine protein expression of β-catenin(the key factor of the Wnt signalling pathway) and cyclin D1(the target gene of this pathway). The frequency of promoter methylation of sFRP-1, sFRP-2, sFRP-4, sFRP-5, Wif-1 and Dkk-3 genes in GCA tumor tissues were 78.7%(74/94), 76.6%(72/94), 70.2%(66/94), 77.1%(73/94), 61.7%(58/94) and 21.3%(20/94), respectively, which were significantly higher than those in adjacent non-cancerous tissues. Furthermore, the frequencies of silenced mRNA expression of these six genes in GCA tumor tissues were significantly higher than those in adjacent non-cancerous tissues. Methylation levels of these six genes were all correlated with loss of mRNA expression. The ectopic expression of β-catenin and cyclin D1 was significantly more frequent in GCA tumor tissues than that in adjacent non-cancerous tissues and correlated with each Wnt-antagonist genes hypermethylation status. Epigenetic silencing of Wnt-antagonist genes expression by promoter hypermethylation may play an important role in gastric cardia adenocarcinoma.     

胃癌TIMP3基因启动子甲基化及其蛋白表达的研究

目的:探讨组织金属蛋白酶抑制因子-3(tissue inhibitor of metalloproteinase 3,TIMP3)基因启动子甲基化与其蛋白表达的相关性,并分析 TIMP3基因CpG岛异常甲基化与胃腺癌及其临床病理特征的关联性．方法:应用甲基化特异性PCR(MSP)技术和免疫组织化学方法分别检测78例患者的胃正常黏膜组织、胃癌组织及转移淋巴结中,TIMP3 基因启动子甲基化和蛋白表达情况．结果:胃正常黏膜组织、早期、进展期胃癌组织和转移淋巴结中TIMP3基因启动子均有甲基化修饰,其阳性率分别为35．9％(28／78); 85．0％(17／20),89．7％(52／58);转移淋巴结 100％(78／78)．胃癌组TIMP3基因启动子甲基化率明显高于胃正常黏膜组(尸<0．05)．胃正常黏膜组织TIMP3蛋白表达全部为阳性(100％), 20例早期胃癌中,6例阳性(30％),58例进展期胃癌中,2例阳性(3．4％),在转移淋巴结中全部不表达(0％)．胃癌70例蛋白表达阴性的标本中,64例TIMP3基因启动子甲基化阳性 (91．4％),TIMP3蛋白表达与启动子甲基化呈明显负相关(P<0．01)．结论:启动子区CpG岛高甲基化是胃癌组织中TIMP3基因表达失活的主要机制,可能成为胃癌分子诊断与病期评估的标志之一．     

p16基因启动子区甲基化在人嗜铬细胞瘤和副神经节瘤中的变化

目的 检测嗜铬细胞瘤(PHEO)和副神经节瘤(PGL)中p16基因突变和启动子区DNA甲基化改变,分析其与患者临床特征之间的关系.方法收集34例(PHEO 20例、PGL14例)组织标本及患者临床资料,通过甲基化特异性PCR(MSP)测定p16基因启动子区甲基化状态,DNA测序检测基因序列以及RT-PCR方法测定其mRNA表达.结果 (1)34例肿瘤组织中未发现p16基因纯合缺失及点突变;(2)35.3%(12/34)的患者存在p16基因高甲基化,p16基因甲基化阳性标本中,PHEO和PGL分别占25%和75%,两者差异有统计学意义(P=0.005);p16基因甲基化在恶性、单发肿瘤、发病年龄早的亚组中有增高趋势(P＞0.05);(3)甲基化与非甲基化肿瘤组织之间p16 mRNA表达无统计学差异;不同特点的肿瘤中其mRNA表达亦无统计学差异,但恶性肿瘤p16 mRNA表达与良性肿瘤相比有下降的趋势(0.83±0.65对1.12±0.81,P=0.278).结论人PHEO和PGL中,p16基因纯合缺失和突变并不常见,但p16基因启动子区甲基化是其失活的主要形式.     

p16基因高甲基化在胃癌发展中的作用

目的:通过检测胃癌、癌前病变和正常对照组中p16基因启动子区CpG岛甲基化水平及其表达,并结合临床病理资料,分析他们在胃癌发生、发展中的作用.方法:用甲基化特异性聚合酶链反应(methylation-specific PCR,MSP)检测41例胃癌组织、40例癌前病变组织和38例正常对照组织中p16基因启动子5′CpG岛甲基化;应用免疫组化检测基因的蛋白表达.结果:胃癌组织中p16基因甲基化阳性率为56.1%(23/41),癌前病变组织中为17.5%(7/40),而正常对照组织中为2.6%(1/38),前组与后两组之间的差异有显著性(P<0.05).胃癌组织中p16基因表达阳性率为51.2%,癌前病变组织中为90.0%,正常对照组织中为100.0%,前组与后两组之间的差异有显著性(P<0.05).低分化型胃癌组织中的p16基因甲基化阳性率明显高于高分化型(81.3%vs 40.0%,P<0.05).有淋巴结转移的胃癌组织中,p16基因甲基化阳性率与无转移组的差异有显著性(81.0%vs 30.0%,P<0.05).浸润深达浆膜层的胃癌组织中,甲基化阳性率与未达浆膜层组无统计学差异(60.0%vs 52.4%,P>0.05).胃癌组织中p16基因甲基化阳性组的蛋白表达阳性率显著低于甲基化阴性组(26.1%vs 83.3%,P<0.01).结论:胃癌组织中存在有p16基因启动子5′CpG岛高甲基化,并导致其基因表达率显著低于正常对照及癌前病变组织.p16基因的高甲基化与胃癌分化程度、淋巴结转移相关.p16基因甲基化的发生,从正常、癌前病变到胃癌有逐渐增加的趋势,提示其基因CpG岛高甲基化有可能作为诊断早期胃癌的一项较为敏感的指标.     

AXIN2基因在肝细胞癌中的表达及甲基化研究

目的 观察肝细胞癌(HCC)中AXIN2 mRNA表达水平,分析AXIN2基因甲基化水平对mRNA表达的影响及在HCC发生、发展中的意义.方法 收集手术切除的53例HCC和配对癌旁组织标本、7例正常肝组织标本和5种人肝癌细胞系.应用荧光定量PCR方法检测AXIN2mRNA水平的表达和AXIN2基因启动子区甲基化状态.结果 AXIN2在癌组织中的mRNA表达水平(0.1629±0.0679)低于癌旁组织(0.4155±0.2330),差异有统计学意义(Z=-2.567,P=0.010).HCC和癌旁组织中AXIN2基因甲基化水平(39.77%±3.89%和36.92%±2.81%)均高于正常肝组织(7.38%±2.40%,t 值分别=-3.663和-4.591,P值分别=0.009和0.007).5种人肝癌细胞系中AXIN2基因均呈高甲基化状态.AXIN2 mRNA表达水平与甲基化程度呈负相关(r=-0.458,P=0.032).TNMⅢ期HCC患者的AXIN2甲基化水平高于TNM Ⅰ和Ⅱ期患者(P=0.008).结论 AXIN2 mRNA表达水平下降与其高甲基化状态相关,AXIN2 mRNA低表达和启动子区异常甲基化可能是HCC发生、发展的重要机制之一.

Abstract：

Objective To investigate AXIN2 mRNA expression level in hepatocellular carcinoma (HCC) , and to analyze the effect of AXIN2 gene methylation status on its mRNA expression and HCC genesis and development. Methods Fifty-three surgical excised HCC specimens and paired adjacent non-cancerous specimens, seven normal liver specimens and five HCC cell lines were collected. The expression of AXIN2 at mRNA level and the methylation status of AXIN2 gene promoter were determined by quantitative PCR. Results The expression of AXIN2 mRNA was lower in HCC tissues (0.1629 + 0.0679) than that in adjacent non-cancerous tissues (0. 4155 + 0. 2330), and there was significant difference (Z= -2. 567, P = 0. 010). The methylation level of AXIN2 gene in HCC and adjacent non-cancerous tissues (39. 77% ±3. 89%, and 36. 92% ±2. 81%) was significantly higher than that in normal liver tissues (7. 38% ±2. 40% , t=-3. 663 ,P = 0. 009;t= -4. 591 ,P = 0. 007).AXIN2 gene was hypermethylated in all five HCC cell lines. There was a negative correlation between AXIN2 mRNA expression level and the degree of methylation ( r = -0. 458, P = 0. 032). The methylation level was higher in TNM Ⅲ patients of HCC than that in TNM Ⅰ and Ⅱ patients (P =0.008). Conclusion The down-regulation of AXIN2 gene mRNA expression is correlated with its hypermethylation status. The low expression of AXIN2 mRNA and the abnormal methylation of promoter may be one of the important mechanism of HCC genesis and development.