King I, Sartorelli A C
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
Cancer Res. 1989 Oct 15;49(20):5677-81.
A number of epidermal growth factor (EGF)-resistant clones have been isolated from human epidermoid carcinoma A431 cells (I. King and A. C. Sartorelli, Biochem. Biophys. Res. Commun., 140: 837, 1986). These cells had a higher capacity to enter a pathway of terminal differentiation, as determined by their ability to form cornified envelopes. Thus, after 6 days in culture, 10% of parental A431 cells expressed a differentiated phenotype, while more than 50% of each of the EGF-resistant variants (M1, A5, and A7) formed cornified envelopes. These EGF-resistant clones expressed fewer EGF receptors and had a lower capacity for EGF receptor autophosphorylation than parental A431 cells. Clone M1 had the highest capacity to form cornified cell envelopes and expressed about 10% of the EGF receptor autophosphorylation activity of parental cells. The decrease in the level of EGF receptor autophosphorylation appeared to be due to a decrease in EGF receptor number rather than to a lowering of enzyme activity per se. Southern analysis demonstrated that all of the EGF-resistant variants contained fewer copies of the EGF receptor gene and no apparent gene rearrangement was detected in these variant cells. A corresponding decrease in EGF receptor mRNA was also observed in M1, A5, and A7 cells, with a ratio of 18:1:10:5 for A431, M1, A5, and A7 cells, respectively. In addition, two other malignant epithelial cell lines, SqCC/Y1 and FaDu, contained relatively few copies of EGF receptor genes, had low EGF receptor kinase activity and showed a relatively high capacity to form cornified envelopes. These findings suggest that the level of the EGF receptor was critical to the regulation of the degree of maturation of malignant epidermal cells.
已从人表皮样癌A431细胞中分离出多个表皮生长因子（EGF）抗性克隆（I. 金和A. C. 萨托雷利，《生物化学与生物物理研究通讯》，140: 837, 1986）。这些细胞进入终末分化途径的能力更强，这是通过它们形成角质化包膜的能力来确定的。因此，培养6天后，10%的亲本A431细胞表现出分化表型，而每个EGF抗性变体（M1、A5和A7）中超过50%形成了角质化包膜。与亲本A431细胞相比，这些EGF抗性克隆表达的EGF受体较少，EGF受体自身磷酸化的能力也较低。克隆M1形成角质化细胞包膜的能力最强，其表达的EGF受体自身磷酸化活性约为亲本细胞的10%。EGF受体自身磷酸化水平的降低似乎是由于EGF受体数量的减少，而不是酶活性本身的降低。Southern分析表明，所有EGF抗性变体所含的EGF受体基因拷贝数较少，在这些变体细胞中未检测到明显的基因重排。在M1、A5和A7细胞中也观察到EGF受体mRNA相应减少，A431、M1、A5和A7细胞的比例分别为18:1:10:5。此外，另外两种恶性上皮细胞系SqCC/Y1和FaDu所含的EGF受体基因拷贝数相对较少，EGF受体激酶活性较低，且形成角质化包膜的能力相对较高。这些发现表明，EGF受体水平对于恶性表皮细胞成熟程度的调节至关重要。
