Dietary Regulation of Biochemical/Molecular Changes in Carcinogen Resistant Cell

我们研究的主要焦点是研究与致癌物耐药性相关的生化和分子变化对癌症预防的影响。我们通过连续接触苯并[a]芘(BP)发展了一系列抗癌细胞。这些细胞是研究早期生化和分子变化的模型，这些变化可能会预防环境致癌物和外源物质造成的癌症。我们的BP抗性细胞也对DMBA具有共同耐药性，DMBA是一种啮齿动物的乳腺癌致癌物。据我们所知，这是第一次对致癌物耐药性的整体机制进行系统检查，包括致癌物外排、激活和解毒。虽然某些解毒酶，谷胱甘肽-S-转移酶、谷胱甘肽过氧化物酶和谷胱甘肽还原酶没有变化，但在BP抗性细胞中观察到还原型谷胱甘肽水平显著增加。我们的观察表明，氧化还原介导的通路级联可能参与了致癌物耐药性的产生。因此，我们检测了戊糖磷酸分流的主要途径酶葡萄糖-6-磷酸脱氢酶(G6PD)的活性。我们发现BP耐药细胞的G6PD活性明显高于WT.我们认为抗癌细胞的主要变化之一是氧化还原介导的机制.蛋白质和RNA表达的分子研究进一步支持了我们的假设。G6PD在人乳腺癌细胞中的表达随耐药程度的增加而增加。我们进一步研究了饮食化学保护剂对人肝癌细胞G6PD的调节作用，发现白藜芦醇和二苯甲酰甲烷能增强G6PD的活性。我们的结果提示，某些化学保护剂的作用机制可能是通过氧化还原循环酶G6PD介导的。氧化还原变化在防止致癌物在乳腺或肝脏肿瘤中的启动中是否重要，我们目前正在调查中。

The primary focus of our study is to investigate the biochemical and molecular changes associated with carcinogen resistance toward cancer prevention. We developed a series of carcinogen-resistant cells by continuous exposure to benzo[a]pyrene (BP). These cells are a model for studying the early biochemical and molecular changes which may prevent cancer due to environmental carcinogens and xenobiotics. Our BP resistant cells are also co-resistant to DMBA, a mammary carcinogen in rodents. To our knowledge this is the first systematic examination of the overall mechanisms involved in carcinogen resistance, including carcinogen efflux, activation,and detoxification. Although certain detoxification enzymes, glutathione-s-transferase, glutathione peroxidase and glutathione reductase were unchanged, a significant increase in reduced glutathione levels was observed in BP resistant cells.Our observation suggested a redox mediated pathway cascade may be involved in carcinogen resistance. Therefore, we examined the major pathway enzyme of the pentose phosphate shunt, glucose-6-phosphate dehydrogenase (G6PD) activity. We found G6PD activities were markedly increased in BP resistant cells compared to WT.We proposed that one of the major changes in carcinogen resistant cells are in redox mediated mechanisms. Our hypothesis was further supported by molecular studies of protein and RNA expressions. The expressions of G6PD were increased with increasing resistance in human breast cancer cells. We further examined the G6PD regulation by dietary chemoprevention agents in human hepatoma cells and we found G6PD activity was enhanced by resveratrol and dibenzoylmethane. Our resultes suggested that the mechanism of action of certain chemoprevention agents may mediated by the redox cycle enzyme G6PD. Whether the redox changes are important in preventing carcinogen initiation in mammary or liver tumors are under our current investigation.