Takahashi S, Hall J, Montesano R
Unit of Mechanisms of Carcinogenesis, International Agency for Research on Cancer, Lyon, France.
Am J Pathol. 1996 Feb;148(2):497-507.
The intercellular distribution of O6-methylguanine-DNA methyltransferase (MGMT) mRNA expression has been investigated at the individual cell level in the liver of rats treated with dimethylnitrosamine using in situ hybridization. Male BDIV rats were orally administered with a single dose of dimethylnitrosamine (5 or 10 mg/kg) and were killed at 24, 48, and 96 hours after exposure. Constitutive MGMT mRNA expression was found in bile duct cells, vascular endothelial cells, and fibrous cells; however, weak or negative expression was detected in hepatocytes and Kupffer cells. On the other hand, after exposure to dimethylnitrosamine, inducible MGMT mRNA was rapidly expressed in hepatocytes, especially in the centrilobular area at earlier time points, confirming our previous studies in which enzymatic activity has been measured in different purified cell populations obtained by differential centrifugation. Immunohistochemical detection of the O6-methylguanine-DNA adduct formation was demonstrated in a dose-dependent fashion and was mainly found in the centrilobular hepatocytes where high levels of MGMT mRNA were present. These results suggest a correlation between the induction of this repair activity and DNA damage; however, the relationship between MGMT mRNA and enzyme activity remains to be fully established for all cell types.
利用原位杂交技术，在细胞水平上研究了经二甲基亚硝胺处理的大鼠肝脏中O6-甲基鸟嘌呤-DNA甲基转移酶（MGMT）mRNA表达的细胞间分布情况。雄性BDIV大鼠经口给予单剂量二甲基亚硝胺（5或10mg/kg），并在暴露后24、48和96小时处死。在胆管细胞、血管内皮细胞和纤维细胞中发现有组成型MGMT mRNA表达；然而，在肝细胞和库普弗细胞中检测到弱表达或阴性表达。另一方面，暴露于二甲基亚硝胺后，诱导型MGMT mRNA在肝细胞中迅速表达，尤其是在早期时间点的小叶中央区域，这证实了我们之前的研究，即在通过差速离心获得的不同纯化细胞群体中测量了酶活性。O6-甲基鸟嘌呤-DNA加合物形成的免疫组织化学检测呈剂量依赖性，主要在存在高水平MGMT mRNA的小叶中央肝细胞中发现。这些结果表明这种修复活性的诱导与DNA损伤之间存在相关性；然而，对于所有细胞类型，MGMT mRNA与酶活性之间的关系仍有待充分确立。
