Tsujiuchi T, Tsutsumi M, Sasaki Y, Takahama M, Konishi Y
Department of Oncological Pathology, Cancer Center, Nara Medical University, Kashihara.
Jpn J Cancer Res. 1999 Sep;90(9):909-13. doi: 10.1111/j.1349-7006.1999.tb00834.x.
We have investigated aberrant methylation of CpG nucleotides (CpG sites) and gene expression of c-myc during hepatocarcinogenesis induced by a choline-deficient, L-amino acid-defined (CDAA) diet in rats. Male Fischer 344 rats, 6 weeks old, were continuously given a CDAA diet for 50 and 75 weeks and then killed. Macroscopically detectable nodules, which were histologically confirmed to be hyperplastic nodules (HNs) or well-differentiated hepatocellular carcinomas (HCCs), were dissected free from the surrounding tissue. Normal control liver was obtained from 6-week-old rats. Methylation of CpG sites of the c-myc gene was investigated in bisulfite-treated DNA isolated from normal liver, HNs and HCCs. All 33 cytosines in the 5'-upstream region of the c-myc gene were fully methylated in control liver and the 4 HNs. In contrast, these cytosines were completely unmethylated in 5 HCCs. Examination of the c-myc expression by reverse transcription-polymerase chain reaction (RT-PCR) analysis also showed a marked increase as compared to the low levels in normal livers and HNs. These results suggest that hypomethylation of the c-myc gene might play a critical role in malignant transformation from HN to HCC during CDAA diet-induced hepatocarcinogenesis in rats.
我们研究了在大鼠胆碱缺乏、L-氨基酸限定(CDAA)饮食诱导的肝癌发生过程中,CpG核苷酸(CpG位点)的异常甲基化和c-myc基因的表达情况。6周龄的雄性Fischer 344大鼠连续给予CDAA饮食50周和75周后处死。将肉眼可检测到的结节从周围组织中分离出来,这些结节经组织学证实为增生性结节(HNs)或高分化肝细胞癌(HCCs)。正常对照肝脏取自6周龄大鼠。在从正常肝脏、HNs和HCCs中分离的亚硫酸氢盐处理的DNA中研究c-myc基因CpG位点的甲基化情况。c-myc基因5'上游区域的所有33个胞嘧啶在对照肝脏和4个HNs中均完全甲基化。相比之下,这些胞嘧啶在5个HCCs中完全未甲基化。通过逆转录聚合酶链反应(RT-PCR)分析检测c-myc表达,结果也显示与正常肝脏和HNs中的低水平相比有显著增加。这些结果表明c-myc基因的低甲基化可能在CDAA饮食诱导的大鼠肝癌发生过程中从HN向HCC的恶性转化中起关键作用。