p53 null mice and chemical oncogenesis for promotion study

本研究旨在探讨DNA氧化损伤、细胞凋亡诱导和间隙连接细胞间通讯（GJIC）之间可能的相互作用和协调，这可能是五氯酚（PCP）促进小鼠肝癌发生的机制。本研究采用P53-null小鼠，因为其具有以下特点：1) DNA损伤积累，2)抑制细胞凋亡，3)抑制GJIC。结果如下：1)在p53缺失小鼠的研究中，PCP在饮食中治疗2周后，p53缺失小鼠肝脏中DNA氧化损伤没有增强，细胞增殖也没有加速，没有明确证据表明p53参与抑制PeP的促瘤作用。2)肝上皮细胞系（WB细胞）体外实验表明，PCP对WB细胞GJIC具有双相抑制作用。PCP还能抑制v-myc转染的WB细胞诱导的凋亡，同时抑制GJIC。GJICon WB细胞的第一期抑制与氧化应激激活丝裂原活化蛋白激酶的激活有关，第二期抑制则与抗氧化剂表没食子儿茶素没食子酸酯上调有关。3)我们的体内GJIC分析方法显示PCP处理后小鼠肝组织中GJIC的抑制作用，支持我们之前的体外研究结果。这些研究表明，PCP抑制GJIC和细胞凋亡，表明氧化应激可能参与了这两种现象，并提示这些生物事件在POP促肿瘤活性中有显著的相互作用，尽管在本研究中未证实p53与这些事件的抑制作用。

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.