Ding V D, Cameron R, Pickett C B
Department of Molecular Pharmacology and Biochemistry, Merck Sharp & Dohme Research Laboratories, Rahway, New Jersey 07065.
Cancer Res. 1990 Jan 15;50(2):256-60.
We have utilized a DNA clone complementary to epoxide hydrolase mRNA as a probe to examine the level of the mRNA in persistent hepatocyte nodules and hepatomas induced by the Solt-Farber chemical carcinogenesis procedure. Epoxide hydrolase mRNA is increased 14-fold in nodules as compared to the level in normal liver. When rats with liver nodules were administered phenobarbital, an inducer of epoxide hydrolase mRNA in normal animals, a superinduction in epoxide hydrolase mRNA was observed in the nodules (22-fold) as compared to normal liver. Surprisingly, nodule induction in conjunction with phenobarbital administration also produced marked elevation in epoxide hydrolase mRNA levels in the tissue surrounding the nodules. Using HpaII and MspI to assess the degree of methylation of CCGG sites, we have found that the epoxide hydrolase gene is hypomethylated in nodules and hepatomas compared to the gene in normal liver tissue. Phenobarbital treatment alone increased epoxide hydrolase mRNA levels but did not result in hypomethylation of the epoxide hydrolase gene. These data further support the observation that hypomethylation of specific gene sequences occurs during chemical carcinogenesis and is correlated with an elevation in the steady state level of epoxide hydrolase mRNA in persistent hepatocyte nodules.
我们利用与环氧水解酶mRNA互补的DNA克隆作为探针，来检测Solt-Farber化学致癌程序诱导产生的持续性肝细胞结节和肝癌中该mRNA的水平。与正常肝脏中的水平相比，环氧水解酶mRNA在结节中的含量增加了14倍。当给患有肝结节的大鼠注射苯巴比妥（正常动物中环氧水解酶mRNA的诱导剂）时，与正常肝脏相比，在结节中观察到环氧水解酶mRNA的超诱导现象（22倍）。令人惊讶的是，结节诱导结合苯巴比妥给药还导致结节周围组织中环氧水解酶mRNA水平显著升高。使用HpaII和MspI评估CCGG位点的甲基化程度，我们发现与正常肝组织中的基因相比，环氧水解酶基因在结节和肝癌中发生了低甲基化。单独的苯巴比妥处理可增加环氧水解酶mRNA水平，但不会导致环氧水解酶基因的低甲基化。这些数据进一步支持了这样的观察结果，即特定基因序列的低甲基化发生在化学致癌过程中，并且与持续性肝细胞结节中环氧水解酶mRNA稳态水平的升高相关。
