Ballard F J, Wong S S, Knowles S E, Partridge N C, Martin T J, Wood C M, Gunn J M
J Cell Physiol. 1980 Nov;105(2):335-46. doi: 10.1002/jcp.1041050216.
Protein degradation has been measured in confluent monolayers of eleven lines of contact-inhibited cells and ten transformed lines as the rate of release of trichloroacetic acid-soluble radioactivity after prelabeling cell protein with [3H]leucine. Insulin, at contrations from 10(-12) M to 10(-6) M, has been added at the beginning of the 4-hour degradation period to detect selective effects of this hormone as an inhibitor of the inducible proteolysis occurring in serum-free medium. In addition insulin binding measurements have been performed on selected cell lines in an attempt to relate receptor properties to insulin action. Substantial effects of insulin are found in most cells with a selective inhibition at low insulin concentrations noted in several of the transformed lines. The difference in insulin sensitivity is not entirely definitive because temperature-sensitive transformation mutants of NRK cells are not more sensitive to insulin at a temperature where they show the transformed phenotype. Although insulin receptors on different cell lines have similar binding properties, two of the hepatomas used, H35 and MH1C1, show inhibition of protein degradation at insulin concentrations where receptor occupancy is extremely low. Calvarial osteoblast-like cells have a high rate of protein degradation which can be reduced by growth factors but not by insulin. The lack of an insulin response is a consequence of poor insulin binding to the cells. Insulin binds to the osteogenic sarcoma cells in substantial amounts. However, its normal action to inhibit the induced proteolysis is restricted because with these cells no increase of proteolysis occurs in serum-free medium. Generally higher rates of protein degradation are observed in the contact-inhibited lines than the transformed cells. We suggest that this difference may provide a selective growth advantage to transformed cells.
在用[3H]亮氨酸预标记细胞蛋白后，以三氯乙酸可溶性放射性物质的释放速率为指标，对11株接触抑制细胞系和10株转化细胞系的汇合单层细胞进行了蛋白质降解的测定。在4小时降解期开始时加入浓度从10（-12）M到10（-6）M的胰岛素，以检测该激素作为无血清培养基中诱导性蛋白水解抑制剂的选择性作用。此外，还对选定的细胞系进行了胰岛素结合测量，试图将受体特性与胰岛素作用联系起来。在大多数细胞中发现了胰岛素的显著作用，在一些转化细胞系中观察到低胰岛素浓度下的选择性抑制。胰岛素敏感性的差异并不完全确定，因为NRK细胞的温度敏感转化突变体在表现出转化表型的温度下对胰岛素并不更敏感。虽然不同细胞系上的胰岛素受体具有相似的结合特性，但所用的两种肝癌细胞系H35和MH1C1在受体占有率极低的胰岛素浓度下显示出蛋白质降解的抑制作用。颅盖成骨样细胞的蛋白质降解率很高，生长因子可降低其降解率，但胰岛素不能。缺乏胰岛素反应是胰岛素与细胞结合不良的结果。胰岛素大量结合到骨肉瘤细胞上。然而，其抑制诱导性蛋白水解的正常作用受到限制，因为在这些细胞中，无血清培养基中不会发生蛋白水解增加。一般来说，接触抑制细胞系中的蛋白质降解率高于转化细胞。我们认为这种差异可能为转化细胞提供选择性生长优势。
