Regulation mechamism of gene expression on the early stage of carcinogenesis.

在多步骤的肿瘤发生中，基因表达模式的改变可能是一个重要的步骤，以及癌基因激活和/或反基因失活的步骤。为了研究肿瘤转化过程中基因表达模式可能发生的改变，探索造瘤基因可能是有用的工具之一。从这个角度出发，我一直在研究谷胱甘肽转移酶P （GST-P）基因在大鼠化学性肝癌发生过程中的调控机制。强增强子元件GPEI和位于GST-P基因65处的另一个类似于TRE的序列既可以被Jun激活，也可以被最近报道的致癌基因产物Maf激活。糖皮质激素被认为是jun的抑制剂。TPA刺激GST-P基因的表达和过表达的c-Jun的表达都被地塞米松（Dex）抑制到基础水平。然而，该基因的基础表达并未被Dex所抑制。在试管中进行的交叉实验……更多的细胞也显示出基本相同的结果。这些结果表明GPEI可以被Jun激活，但这种增强子的组成活性是由一些未知的机制引起的，gst - p在癌前病变和化学致癌物诱导的肝癌中特异性表达，而过氧化物酶体增殖体（PP）除外。为了确定PP抑制GST-P表达的分子机制，我分析了PP及其受体PPAR对GST-P表达的影响。经转染的gst - p5 '侧链报告基因的表达被PPAR和PP、clofibrate特异性抑制。抑制的响应元件是位于帽位上游-65nt的TRE。虽然AP-1（Jun/Fos）和Maf激活了该元件，但被Jun激活的表达被PPAR和clofibrate特异性抑制。相反，共转染Jun表达质粒可抑制含有PPAR应答元件的CAT基因的表达。这些结果表明PPAR和Jun相互作用，抑制Jun和糖皮质激素受体的活性。少

In multi-step tumorigenesis, change in the pattern of gene expression might be an important step, as well as the steps of oncogene activation and/or inactivation of antioncogene. To investigate the possible alteration of the cellular pattern of gene expression during neoplastic transformation, it may be useful to explore tumor maker gene as one of the tools. Form this view point, I have been studying the regulation mechanism of glutathione transferase P (GST-P) gene during chemical hepatocarcinogenesis of the rat. The strong enhancer element, GPEI, and another TRE like sequence located at-65 of the GST-P gene are both activated by Jun and also activated by recently reported oncogene product, Maf. Glucocorticoide is known as an inhibitor of Jun. Both the stimulated expressions of GST-P gene by TPA and that by over-expressed c-Jun were suppressed to the basal level by Dexamethasone(Dex). Basal expression of this gene, however, was not ingibited by Dex. Transgection experiments in the cul … More tured cells also show the essentially the same results. These results indicate that the GPEI is activated by Jun but constitutive activity of this enhancer is due to some unknown mechanism other than Jun.GST-P is specifically expressed in precancerous lesions and in hepatomas induced by chemicalcarcinogens except that by peroxisome proliferator(PP). Moreover, the GST-P expression in pre-neoplastic lesion is suppressed by PP.To determine the molecular mechanism of suppression of the GST-P expression by PP, I have analyzed the effects of PP and their receptor, PPAR on the expression of GST-P.The expression of transfected reporter gene having GST-P 5' flanking sequence was specifically suppressed by PPAR and PP, clofibrate. The responsive element of suppression was the TRE located on -65nt upstream from the cap site. Although AP-1(Jun/Fos) and Maf are bing and activate this element, the expression activated by Jun was specifically inhibited by PPAR and clofibrate. Oppositelly, the expression of transfected CAT gene containing PPAR responsive elements was inhibited by co-transfection of Jun expression plasmid. These results suggest that PPAR and Jun were mutually interact and inhibit both activities, like Jun and glucocorticoide receptor. Less