抑癌基因RAS启动子甲基化与乳头状甲状腺癌的关系

目的观察抑癌基因RAS在乳头状甲状腺癌(papillary thyroid carcinoma,PTC)中的表达,分析其启动子甲基化与肿瘤发生的关系。方法 选择50例PTC和32例良性甲状腺肿瘤(对照组,包括20例结节性甲状腺肿,12例甲状腺腺瘤)患者,对2组患者手术获取的标本提取RNA后,反转录为cDNA,进行多聚酶链反应(polymerase chain reaction,PCR),检测RAS基因的表达情况;运用甲基化特异性PCR(methylation-specific PCR,MSP)检测上述组织中RAS基因启动子区甲基化的情况,并对2种抑癌基因甲基化和未甲基化的组织随机进行测序。结果 PTC组患者中,有30例(60%)RAS基因启动子发生甲基化;对照组患者中,有10例(31.3%)RAS基因启动子发生甲基化;PTC组织RAS基因启动子甲基化率均显著高于对照组,差异有统计学意义(χ2=6.46,P<0.05)。乳头状甲状腺癌mRNA的半定量的值为0.56±0.10,对照组mRNA半定量的值为0.67±0.16,乳头状甲状腺癌mRNA的表达明显低于对照组,两者差异具有统计学意义(t=2.83,P<0.05)。经DNA测序证实,RAS基因启动子发生甲基化的其CpG岛的碱基未发生改变,仍为CG;未发生甲基化的,碱基由CG变为TG。结论 PTC患者RAS基因启动子甲基化发生率显著高于良性甲状腺肿瘤患者,而RAS基因mRNA的表达则较良性甲状腺肿瘤降低;推测RAS基因启动子甲基化可能与PTC的发生、发展相关。

Relationship between the Promoter Hypermethylation of RAS Gene and Human Papillary Thyroid Carcinoma

Objective To study the expression of the tumor suppressor gene RAS in papillary thyroid carcinoma(PTC) and the correlation between the expression and the aberrant promoter methylation of RAS gene. Methods RT-PCR was used to detect the mRNA expression of RAS in 50 cases of PTC, 20 cases of nodular goiter and 12 cases of thyroid adenoma tissue. We examined the promoter methylation status of RAS gene by using methylation-specific PCR technique(MSP). Results Hypermethylation of RAS gene in promoter region was detected in 30 of 50 cases with PTC(60%) and in 10 of 32 cases of control group(31.3%), the difference in methylation of RAS promoter was significantly higher in PTC patients than that in controls(χ²=6.46, P<0.05). The mRNA expression of RAS genes was significantly lower in PTCs than that in controls(the t value was 2.83, P<0.05). The sequencing confirmed that there was the CG →TG transmission in promoter of RAS genes. Conclusion Methylation of RAS gene in promoter region is a common molecular event and may be involved in the genesis and development of human PTC.