p53 null mice and chemical oncogenesis for promotion study

本研究旨在探讨DNA氧化损伤、细胞凋亡诱导和细胞间隙连接通讯(GJIC)之间可能的相互作用和协同作用，这似乎是五氯苯酚(PCP)促进小鼠肝癌发生的机制。本研究利用P53基因缺失小鼠的以下特点：1)DNA损伤累积，2)细胞凋亡抑制，3)GJIC抑制。结果如下：1)在P53基因缺陷小鼠实验中，饲料中给予PCP 2周后，P53基因缺陷小鼠的肝脏中既没有DNA氧化损伤的增强，也没有细胞增殖的加速，没有明确的证据表明P53参与抑制了PeP的促肿瘤作用。2)体外肝上皮细胞株(WB细胞)实验证明PCP对WB细胞的GJIC有双相抑制作用。PCP还抑制v-myc基因转导的WB细胞的凋亡，并抑制GJIC。GJIC1期抑制WB细胞与氧化应激激活的丝裂原活化蛋白激酶有关，第2期抑制被抗氧化剂表没食子儿茶素没食子酸酯上调。3)我们的体内GJIC分析方法显示，PCP处理后的小鼠肝组织中GJIC受到抑制，这支持了我们先前的体外发现。这些研究表明，PCP既抑制GJIC又抑制细胞凋亡，这表明氧化应激可能参与了这两种现象，并表明这些生物事件在POP的促肿瘤活性中存在显著的交互作用，尽管本研究未证实抑制P53和这些事件的作用。

This research aimes to investigate possible interaction and co-ordination among the oxidative DNA damage, an induction of apoptosis, and the gap junctional intercellular communication (GJIC), which seems to be the mechanism of promoting action in the murine hepatocarcinogenesis by pentachlorophenol (PCP). P53-null mice were applied in this research, because of its following characteristics ; 1)accumulation of DNA damages, 2)inhibition of apoptosis and 3)inhibition of GJIC.Results obtained are as follows : 1)In the study using p53-deficient mouse, there was neither enhancement of oxidative DNA damage nor accelerated cell proliferation in the liver of p53-deficient mouse after treatment with PCP in diet for 2 weeks, showing no clear evidence of involvement of p53 to suppress the tumor-promoting action by PeP.2) In vitro study using hepatic epithelial cell line (WB cell) demonstrated the bi-phasic inhibitory effects of PCP on GJIC in WB cells. PCP also inhibited apoptosis induced in v-myc-transfected WB cells, accompanying an inhibition of GJIC.Inhibition of GJICon WB cell at the first-phase was correlated with the activation of mitogen activated protein kinase which is activated by oxidative stress, and the second inhibition was up-regulated by antioxidant, epigallocatechin gallate. 3) Our method of in vivo GJIC-analysis showed the inhibition of GJIC in the mouse hepatic tissue after treatment with PCP, supporting our previous in vitro findings.Theses studies demonstrated that PCP inhibited both GJIC and apoptosis, showing a possible involvement of oxidative stress in both phenomena, and suggest significant interaction of those biological events in tumor-promoting activity in POP, although the role of suppression in p53 along with theses events was not proven in the present research.