Erhardt J A, Pittman R N
Department of Pharmacology, University of Pennsylvania, School of Medicine, Philadelphia 19104, USA.
Oncogene. 1998 Jan 29;16(4):443-51. doi: 10.1038/sj.onc.1201577.
p21WAF1 cyclin-dependent kinase inhibitor has been implicated in the control of proliferation, differentiation, and death in various cell lines. To further examine p21 regulation of the transitions between these cellular processes, an inducible p21 vector (lac operon system) was transfected into the rat pheochromocytoma (PC12) neural cell line. Induction of p21 led to permanent growth arrest, as evidenced by cell counts, FACS analysis, and thymidine incorporation. This arrest was maintained, even after removal of the inducing signal (IPTG). Northern analysis revealed that endogenous p21 mRNA increased following IPTG removal, which may be responsible for the continued growth arrest despite the decrease in ectopic p21 expression. p21 overexpression did not directly lead to a differentiated phenotype; however, differentiation in response to nerve growth factor (NGF) was greatly accelerated. To examine effects on cell death, and specifically test the hypothesis that apoptosis caused by withdrawal of trophic support results from inappropriate entry into cell cycle, serum was removed from proliferating and p21-arrested PC12 cells. The rate of apoptotic death was not affected by p21, nor was it effective in altering the extent of death following other apoptotic stimuli.
p21WAF1细胞周期蛋白依赖性激酶抑制剂已被证明参与多种细胞系的增殖、分化和死亡调控。为了进一步研究p21对这些细胞过程之间转变的调控，将一种可诱导的p21载体（乳糖操纵子系统）转染到大鼠嗜铬细胞瘤（PC12）神经细胞系中。p21的诱导导致永久性生长停滞，细胞计数、流式细胞术分析和胸腺嘧啶核苷掺入实验均证明了这一点。即使去除诱导信号（异丙基-β-D-硫代半乳糖苷，IPTG）后，这种停滞仍持续存在。Northern分析显示，去除IPTG后内源性p21 mRNA增加，这可能是尽管异位p21表达减少但生长停滞仍持续的原因。p21的过表达并未直接导致分化表型；然而，对神经生长因子（NGF）的分化反应大大加速。为了研究对细胞死亡的影响，并特别检验营养支持撤除导致的凋亡是由于不适当进入细胞周期这一假说，从增殖的和p21停滞的PC12细胞中去除血清。凋亡死亡的速率不受p21影响，在改变其他凋亡刺激后的死亡程度方面也无效。
