O'Brian C A, Fan D, Ward N E, Dong Z, Iwamoto L, Gupta K P, Earnest L E, Fidler I J
Department of Cell Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Biochem Pharmacol. 1991 Mar 1;41(5):797-806. doi: 10.1016/0006-2952(91)90083-h.
Recent studies have implicated protein kinase C (PKC) activation in drug resistance in vitro. PKC can be activated directly by phorbol-ester tumor promoters as well as by the bile acid deoxycholate. In this report, we demonstrate that deoxycholate, at concentrations that are chronically present in the lumen of the colon in vivo, mimicked phorbol-ester tumor promoters by protecting Adriamycin (ADR)-sensitive and multidrug-resistant (MDR) murine fibrosarcoma UV-2237M cells from ADR cytotoxicity. Deoxycholate also enhanced the resistance of the MDR cell line UV-2237M-ADRR to the cytotoxic effects of vincristine and vinblastine. In contrast to cytotoxic drug-selected MDR phenotypes, deoxycholate-induced drug resistance was transient and required continuous exposure to the bile acid. The protein kinase inhibitor H7 completely reversed the protection against ADR cytotoxicity conferred on UV-2237M-ADRR cells by deoxycholate, providing evidence that deoxycholate exerts its protective effects by a mechanism that involves stimulation of protein phosphorylation and not merely by detergent effects on membrane permeability. PKC consists of a family of at least seven isozymes with distinct modes of activation and substrate specificities. We previously reported that MDR UV-2237M cell lines contain higher levels of PKC activity than the parental ADR-sensitive UV-2237M cell line (O'Brian et al., FEBS Lett 246: 78-82, 1989). The present report shows that PKC-III is a major PKC isozyme in ADR-sensitive and MDR UV-2237M cell lines. Thus, the resistance to ADR induced by the phorbol esters in UV-2237M cell lines provides strong evidence that PKC-III activation confers protection against ADR on ADR-sensitive and MDR UV-2237M cell lines. Furthermore, since deoxycholate is an endogenous molecule in the colonic epithelium, our finding that physiological concentrations of deoxycholate can render cells more resistant to chemotherapeutic drugs in vitro may have implications for the biology and therapy of intestinal cancers.
最近的研究表明，蛋白激酶C（PKC）的激活与体外耐药性有关。PKC可被佛波酯肿瘤启动子以及胆汁酸脱氧胆酸盐直接激活。在本报告中，我们证明，脱氧胆酸盐在体内结肠腔中长期存在的浓度下，通过保护阿霉素（ADR）敏感和多药耐药（MDR）的小鼠纤维肉瘤UV-2237M细胞免受ADR细胞毒性，从而模拟佛波酯肿瘤启动子的作用。脱氧胆酸盐还增强了MDR细胞系UV-2237M-ADRR对长春新碱和长春花碱细胞毒性作用的抗性。与细胞毒性药物选择的MDR表型不同，脱氧胆酸盐诱导的耐药性是短暂的，并且需要持续暴露于胆汁酸。蛋白激酶抑制剂H7完全逆转了脱氧胆酸盐赋予UV-2237M-ADRR细胞对ADR细胞毒性的保护作用，这表明脱氧胆酸盐通过一种涉及刺激蛋白磷酸化的机制发挥其保护作用，而不仅仅是通过对膜通透性的去污剂作用。PKC由至少七种同工酶组成的家族，具有不同的激活模式和底物特异性。我们之前报道过，MDR的UV-2237M细胞系比亲本ADR敏感的UV-2237M细胞系含有更高水平的PKC活性（O'Brian等人，《欧洲生物化学学会联合会快报》246：78-82，1989）。本报告表明，PKC-III是ADR敏感和MDR的UV-2237M细胞系中的主要PKC同工酶。因此，UV-2237M细胞系中佛波酯诱导的对ADR的抗性提供了强有力的证据，即PKC-III的激活赋予ADR敏感和MDR的UV-2237M细胞系对ADR的保护作用。此外，由于脱氧胆酸盐是结肠上皮中的内源性分子，我们发现生理浓度的脱氧胆酸盐可使细胞在体外对化疗药物更具抗性，这可能对肠道癌症的生物学和治疗具有重要意义。
