胃癌中ABCG2的表达及其甲基化探讨

Expression and methylation of ABCG2 gene in gastric carcinoma

目的观察胃癌中三磷酸腺苷结合转运蛋白G超家族成员2(ATP binding cassette transpoter G2,ABCG2)基因的表达及其启动子区CpG岛甲基化水平,探讨其在胃癌发生、发展中的作用。方法采用实时荧光定量RT-PCR法检测6株胃癌细胞株和76例胃癌组织标本及其对应的癌旁组织中ABCG2 mRNA表达,应用免疫组化SP法检测ABCG2蛋白表达。应用甲基化特异性PCR(MSP)法检测ABCG2基因启动子区的甲基化状态。结果 (1)实时荧光定量RT-PCR结果显示ABCG2在低分化胃癌细胞系HGC-27、MKN-45中呈高表达,而在高分化胃癌细胞系AGS及低分化胃癌细胞系MGC-803中呈低表达。胃癌组织中ABCG2 mRNA的表达下调,与患者性别、年龄、浸润深度、肿瘤大小、淋巴结转移无明显相关,但与胃癌分化程度相关。(2)免疫组化结果显示胃癌组织中ABCG2阳性率为41%,癌旁组织中ABCG2阳性率为35%,两组间差异无统计学意义。有淋巴结转移与无淋巴结转移的胃癌组织中ABCG2阳性率分别为54.5%、21.8%,差异有统计学意义。低分化腺癌与高+中分化腺癌组织中ABCG2阳性率分别为62.5%、16.7%,差异有统计学意义。(3)甲基化结果显示仅在胃癌细胞系MGC-803检测到ABCG2基因甲基化,胃癌组织中未检测到甲基化。结论 ABCG2的表达与胃癌的分化程度及侵袭能力有关,其甲基化不参与胃癌的发生、发展。

Purpose To study the expression and the DNA methylation of of ABCG2 gene in gastric cancer and their roles in the onco-genesis of gastric cancer. Methods Real-time fluorescent quantitative reverse transcription-PCR was used to measure the expression level of ABCG2 mRNA in several gastric cancer cell lines and paired samples of primary gastric cancer and corresponding tumor-adja- cent gastric mucosa taken from surgical specimens of 76 gastric cancer patients. The protein expression of ABCG2 was detected by im-munohistoehemistry. Methylation status of the ABCG2 promoter region was assayed by methylation-specific polymerase chain reaction （MSP）. Results （ 1 ） RT-PCR results showed that ABCG2 mRNA in low-differentiated gastric cancer cell lines HGC-27 and MKN-45 was significantly higher than that in well-differentiation gastric cancer cell line AGS. （2） The down-regulation of ABCG2 mRNA was found in 76 cases of gastric cancer and expression of ABCG2 mRNA showed no correlation to sex, age, tumor size, lymph node metastasis and infiltrative depth, but a significant correlation to tumor differentiation. （3） Immunohistoehemistry results showed that the positive rate of ABCG2 expression in tumor-adjacent tissues and gastric cancer was 35% and 41%, respectively. There were no significant difference between them. ABCG2 expression in lymph node metastasis was much higher than that in no lymph node metasta-sis （ 54. 5% vs 21.8% , P 〈 0. 05 ）. ABCG2 expression in low-differentiated ones were much higher than well-differentiated ones （62. 5% vs 16. 7% , P 〈0. 05）. （4） CpG island methylation of ABCG2 was only observed in gastric cancer cell MGC-803, and no methylation in gastric cancer tissues. Conclusion ABCG2 is related to the invasion and differentiation of gastric cancer, and CpG is-land methylation of ABCG2 leads to loss of the ABCG2 gene expression in human gastric cancer, but no correlaion with the oncogenesis of gastric cancer.