Selective control of the degradation of normal and aberrant proteins in Reuber H35 hepatoma cells.
Selective control of the degradation of normal and aberrant proteins in Reuber H35 hepatoma cells.
复制标题
选择性控制 Reuber H35 肝癌细胞中正常和异常蛋白质的降解。
作者：
S. E. Knowles;F. Ballard
1.用[~（14）C]亮氨酸加L-精氨酸标记肝癌细胞16小时，再用[~3H]-亮氨酸加精氨酸类似物L-刀豆氨酸标记肝癌细胞3小时，测定正常和异常蛋白质的降解率。2.在降解期的前2小时内，含刀豆氨酸的蛋白质以约5倍于正常蛋白质的平均降解速率降解。3.胰岛素、放线菌酮、嘌呤霉素、亮抑酶肽、抗痛剂和胎牛血清可抑制正常蛋白质降解约30%，而这些药物对含刀豆氨酸的蛋白质的降解影响可忽略不计。4.其他化合物抑制这两类蛋白质的降解到相同的程度。5.组合实验显示，与在单一选择性抑制剂存在下测量的降解相比，对正常蛋白质的降解没有额外的抑制作用。6.与16 h标记期的结果相反，仅标记3 h的正常蛋白质的降解不受胰岛素抑制。7.这些结果解释了两个不同的蛋白质周转途径的模型。这些途径中的第一个涉及自噬空泡的形成，并且将被每种选择性抑制剂完全抑制。正常和含刀豆氨酸的蛋白质将通过该途径以相等的速率被分解代谢。我们认为，第二种途径的降解不受测试试剂的调节，而是受每种蛋白质固有稳定性的调节。
1. Rates of degradation of normal and abnormal protein were measured in hepatoma cells after labelling first for 16h with [14C]leucine plus L-arginine and then for 3h with [3H]-leucine plus the arginine analogue, L-canavanine. 2. Over the first 2h of the degradation period, canavanine-containing proteins were degraded at approximately 5 times the average degradation rate of normal proteins. 3. Degradation of normal proteins was inhibited by about 30% by insulin, cycloheximide, puromycin, leupeptin, antipain and foetal calf serum, whereas these agents had a negligible effect on the breakdown of canavanine-containing proteins. 4. Other compounds inhibited degradation of both classes of protein to equal extents. 5. Combination experiments showed no additional inhibitory effects on the degradation of normal proteins over degradation measured in the presence of a single selective inhibitor. 6. In contrast with the results with a 16 h labelling period, the degradation of normal proteins labelled for only 3 h was not inhibited by insulin. 7. These results are explained by a model with two distinct pathways of protein turnover. The first of these pathways involves the formation of autophagic vacuoles and would be completely inhibited by each of the selective inhibitors. Normal and canavanine-containing proteins would be catabolized by this pathway at equal rates. We propose that degradation by a second pathway is not regulated by the agents tested, but by the inherent stability of each protein.