RESTRICTION POINT CONTROL OF CELL-GROWTH BY A LABILE PROTEIN - EVIDENCE FOR INCREASED STABILITY IN TRANSFORMED-CELLS
RESTRICTION POINT CONTROL OF CELL-GROWTH BY A LABILE PROTEIN - EVIDENCE FOR INCREASED STABILITY IN TRANSFORMED-CELLS
复制标题
DOI：
10.1073/pnas.79.2.436
复制
发表时间：
1982-01-01
期刊：
影响因子：
--
通讯作者：
PARDEE, AB
中科院分区：
文献类型：
--
作者：
CAMPISI, J;MEDRANO, EE;PARDEE, AB
动物细胞显然必须积累一种不稳定的蛋白质，然后才能通过细胞周期G1期的限制（R）点。这种R蛋白可以在转化的3T3细胞中获得增加的稳定性，从而允许这些细胞在阻止未转化细胞的条件下继续生长。低剂量的放线菌酮或组氨醇大大降低了正常的3T3（A31）成纤维细胞在早期G1可以进入DNA合成的速度。这些药物对2种致瘤性A31衍生物BP[苯并[a]芘转化]A31和SV[SV 40转化]A31进入S的影响较小，尽管[3H]亮氨酸掺入的测量显示抑制剂在3种细胞系中同样有效。转化系似乎不太敏感，因为它们的R蛋白合成的适度抑制被较低的蛋白降解速率所补偿。为了验证这一观点，在A31和BPA 31细胞达到R点之前不久，细胞质蛋白质合成被完全抑制了几个小时。去除抑制剂后，A31细胞显示S的发作延迟超过抑制剂脉冲，与脉冲期间不稳定蛋白的衰变一致。BPA 31细胞没有表现出过多的延迟，这表明一个更稳定的R蛋白。在A31细胞中，R蛋白的半衰期估计为2.5小时，表明R蛋白的合成开始于G1的开始。在BPA 31细胞中，R蛋白至少8小时没有显示出衰减的迹象。
Animal cells apparently must accumulate a labile protein(s) before they can pass the restriction (R) point in the G1 phase of the cell cycle. This R protein may acquire increased stability in transformed 3T3 cells, thereby allowing these cells to continue growth under conditions that arrest untransformed cells. Low doses of cycloheximide or histidinol drastically reduced the rate at which normal 3T3 (A31) fibroblasts in early G1 could enter DNA synthesis. These drugs had less effect on entry of 2 tumorigenic A31 derivatives, BP[benzo[a]pyrene-transformed]A31 and SV[SV40-transformed]A31, into S, although measurement of [3H]leucine incorporation showed that the inhibitors were equally effective in the 3 cell lines. The transformed lines appears to be less sensitive because moderate inhibition of their R protein synthesis is compensated by lower rates of protein degradation. To test this idea, cytoplasmic protein synthesis was completely inhibited for several hours shortly before A31 and BPA31 cells had reached the R point. After removal of inhibitor, A31 cells showed delays in the onset of S that were in excess of the inhibitor pulse, consistent with decay of labile protein during the pulse. BPA31 cells showed no excess delays, suggesting a much more stable R protein. The half-life of the R protein was estimated as 2.5 h in A31 cells, indicating that R protein synthesis starts at the beginning of G1. In BPA31 cells, the R protein showed no signs of decay for at least 8 h.