CLONING OF THE RAT MDR GENE FAMILY AND REGULATION IN NORMAL AND NEOPLASTIC LIVER

多药耐药是一种细胞交叉感染的现象。 对一系列无关化合物的抗药性 单剂；这种抗药性是170 kD蛋白过度表达的结果 膜蛋白，P-糖蛋白，由多药耐药基因编码(S)。 此前，我们已经表明，大鼠暴露在异物介质中，如 致癌物质黄曲霉毒素B1、异黄樟素和2-乙酰氨基荧烯 (2-AAF)可引起肝脏MDR基因表达增加。为了进一步 研究外源生物调节MDR基因表达的机制，我们 采用了原代肝细胞培养系统。暴露于隔离的 肝细胞对甲基胆蒽(MC)，2-AAF，而不是2，3，7，8- 四氯二苯并对二恶英(TCDD)增加MDR基因表达 表达；伴随细胞色素P4501A基因(S)表达的增加 在这些药物中也观察到了。抑制蛋白质合成 并增加MDR基因在这些细胞中的表达。增强版 这些化合物引起的MDR表达是增加的结果 抄写。这些数据表明，MDR的表达受一种 一种不同于ah受体的蛋白质。进一步调查 多药耐药调控机制的研究需要分离大鼠多药耐药细胞 基因。我们已经确定大鼠多药耐药基因家族由以下部分组成 三个成员；这些基因中的一个已经被分离和鉴定。 对大鼠多药耐药基因的全长cDNA进行了序列分析，结果表明 与小鼠mdrlb基因(Mdrl)的同源性；因此，这个大鼠的cdna 被命名为mdrlb基因。关于5‘端启动子和 可能的3‘m RNA稳定区正在执行中。我们观察到 正常肝脏有轻微但显著的地带性分布差异 多药耐药记录(第1区和第3区)。多药耐药性显著增加 再生过程中的转录本主要在1区观察到 肝细胞。我们的数据表明，MDR表达的增加可能 代表癌前结节的一个亚群，可能 比GST-P阳性更特异地经历恶变 结节。

Multidrug resistance is the phenomenon by which cells become cross- resistant to a range of unrelated compounds in response to exposure to a single agent; this resistance is the result of overexpression of a 170 Kd membrane protein, p-glycoprotein, which is encoded by the mdr gene(s). Previously, we have shown that exposure of rats to xenobiotic agents such as the carcinogens aflatoxin B1, isosafrole and 2-acetylaminofluorene (2-AAF) causes increased expression of mdr mRNA in the liver. To further study the mechanism by which xenobiotics regulate mdr gene expression, we have employed a primary hepatocyte culture system. Exposure of isolated hepatocytes to methycholanthrene (MC), 2-AAF but not 2,3,7,8 - tetrachlorodibenzo-p-dioxin (TCDD) increased the expression of mdr mRNA expression; concomitant increases in cytochrome P4501A gene(s) expression were also observed with these agents. Inhibition of protein synthesis also increased the expression of mdr mRNA in these cells. The enhanced mdr expression caused by these compounds is a result of increased transcription. These data suggest that mdr expression is regulated by a protein that is distinct from the Ah receptor. To further investigate the mechanism of mdr regulation it was necessary to isolate the rat mdr genes. We have identified that the rat mdr gene family is comprised of three members; one of these genes has been isolated and characterized. Sequence analysis of a complete cDNA for a rat mdr cDNA indicated a high degree of identity to the mouse mdrlb gene (mdrl); thus, this rat cDNA was designated the mdrlb gene. Further studies on the 5' promoter and possible 3' mRNA stability regions are being performed. We observed in normal liver a slight but significant zonal difference of distribution of mdr transcripts (zone 1 > zone 3). Significant increase of mdr transcripts during regeneration was observed mainly in zone 1 hepatocytes. Our data suggest that the increased mdr expression might represent a subpopulation of preneoplastic nodules which possibly undergoes malignant transformation more specifically than GST-P positive nodules.