Bartles J R, Khuon S, Lin X H, Zhang L Q, Reddy J K, Rao M S, Isoye S T, Nehme C L, Fayos B E
Department of Cell Molecular, Northwestern University Medical School, Chicago, Illinois 60611.
Cancer Res. 1990 Feb 1;50(3):669-76.
Rats were fed the peroxisome proliferator ciprofibrate (0.025%), and the effects on the expression, modification, and localization of seven domain-specific integral proteins of the rat hepatocyte plasma membrane were assessed using a combination of immunoblotting, -precipitation, and -fluorescence. Ciprofibrate caused the down-regulation of five of the plasma membrane proteins (the epidermal growth factor receptor, the asialoglycoprotein receptor, HA 321, HA 4, and dipeptidylpeptidase IV) and induced the expression of a more basic, lower-Mr isoform of the basolateral plasma membrane protein CE 9. Pulse labeling, chemical deglycosylation, and 125I-wheat germ lectin blotting suggested that the ciprofibrate-induced isoform of CE 9 differed in the posttranslational modification of its oligosaccharides and contained more sialic acid. These changes in hepatocyte surface differentiation were first observed between Days 1 and 5 on the ciprofibrate-containing diet, coincident with other aspects of the pleiotropic response of the hepatocyte to peroxisome proliferators, e.g., the induction of the Mr 78,000 peroxisome proliferation-associated protein. The effects were reversed within 2-3 weeks upon removal of ciprofibrate. The three other peroxisome proliferators tested, di(2-ethylhexyl)phthalate, clofibrate, and Wy-14,643, were found to exert most of these same effects on the expression and modification of the hepatocyte plasma membrane proteins, but the compounds differed in relative potency. The ciprofibrate-induced decreases in the concentrations of the epidermal growth factor receptor, the asialoglycoprotein receptor, HA 321, and HA 4 were similar to the selective down-regulation of these proteins observed transiently during the period of hepatocyte proliferation following two-thirds hepatectomy. Other compounds frequently used in studies of liver enzyme induction and carcinogenesis, the antioxidants ethoxyquin and butylated hydroxyanisole and the liver tumor promoter phenobarbital, were not as effective as ciprofibrate or two-thirds hepatectomy at causing the down-regulation of these proteins. The induction of the lower-Mr isoform of the basolateral plasma membrane protein CE 9 was not observed following two-thirds hepatectomy or upon the feeding of the antioxidants or phenobarbital but was specific to the feeding of the peroxisome proliferators.
给大鼠喂食过氧化物酶体增殖剂环丙贝特（0.025%），并结合免疫印迹、免疫沉淀和免疫荧光法，评估其对大鼠肝细胞膜七种结构域特异性整合蛋白的表达、修饰和定位的影响。环丙贝特导致五种质膜蛋白（表皮生长因子受体、去唾液酸糖蛋白受体、HA 321、HA 4和二肽基肽酶IV）表达下调，并诱导基底外侧质膜蛋白CE 9产生一种碱性更强、分子量更低的同工型。脉冲标记、化学去糖基化和125I-麦胚凝集素印迹分析表明，环丙贝特诱导产生的CE 9同工型在其寡糖的翻译后修饰方面存在差异，且含有更多的唾液酸。肝细胞表面分化的这些变化最早在喂食含环丙贝特饲料的第1天至第5天之间观察到，这与肝细胞对过氧化物酶体增殖剂多效性反应的其他方面同时出现，例如诱导产生分子量为78,000的过氧化物酶体增殖相关蛋白。在去除环丙贝特后2至3周内，这些影响会逆转。所测试的其他三种过氧化物酶体增殖剂，邻苯二甲酸二（2-乙基己基）酯、氯贝丁酯和Wy-14,643，对肝细胞质膜蛋白的表达和修饰也有大多数相同的影响，但这些化合物的相对效力有所不同。环丙贝特诱导的表皮生长因子受体、去唾液酸糖蛋白受体、HA 321和HA 4浓度降低，与在三分之二肝切除术后肝细胞增殖期间短暂观察到的这些蛋白的选择性下调相似。其他常用于肝酶诱导和致癌研究的化合物，抗氧化剂乙氧喹和丁基羟基茴香醚以及肝肿瘤促进剂苯巴比妥，在导致这些蛋白下调方面不如环丙贝特或三分之二肝切除术有效。在三分之二肝切除术后或喂食抗氧化剂或苯巴比妥后，未观察到基底外侧质膜蛋白CE 9的低分子量同工型的诱导，但其诱导是过氧化物酶体增殖剂喂食所特有的。
