Effects of p21Cip1/Waf1 at both the G1/S and the G2/M cell cycle transitions:: pRb is a critical determinant in blocking DNA replication and in preventing endoreduplication
Effects of p21Cip1/Waf1 at both the G1/S and the G2/M cell cycle transitions:: pRb is a critical determinant in blocking DNA replication and in preventing endoreduplication
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DOI：
10.1128/mcb.18.1.629
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发表时间：
1998-01-01
影响因子：
5.3
通讯作者：
Reed, SI
中科院分区：
文献类型：
--
作者：
Niculescu, AB;Chen, XB;Reed, SI
周期蛋白依赖性激酶抑制剂p21（Cip/Waf1）和p27（Kip1）的功能仅限于G(1)/ s期转变的细胞周期控制和细胞静止的维持。为了验证这一假设的有效性，我们在多种细胞系中表达了p21，从而将p21活性的影响与通常诱导p21表达的上游信号通路的多效性作用分离开来。结果表明，在生理积累水平上，p21除负调控G(1)/S转化外，还参与调控G(2)/M转化。在所有细胞类型中均观察到G(1)和G(2)阻滞细胞，但其优势程度不同。p21表达的优势G(1)阻滞与功能性pRb的存在相关。G(2)阻滞在prb阴性细胞中更为突出，阻滞分布与p53状态无关，p21的增殖细胞核抗原（PCNA）结合活性似乎没有参与，因为p27缺乏PCNA结合结构域，产生类似的阻滞b。此外，DNA内复制发生在pRb阴性细胞中，而在pRb阳性细胞中则没有发生，这表明在p21 G(2)阻滞细胞中，功能性pRb对于阻止DNA复制是必要的。这些结果表明，Cip/Kip抑制剂家族的主要目标是导致有效的G(1)阻滞以及阻断G(1)或G(2)期DNA复制的是pRb调节系统。最后，当p21表达时，rb阴性细胞经历内复制周期的倾向可能对rb阴性癌症的治疗有负面影响，基因毒性药物可以激活p53/p21途径。
It has been proposed that the functions of the cyclin-dependent kinase inhibitors p21(Cip/Waf1) and p27(Kip1) are limited to cell cycle control at the G(1)/S-phase transition and in the maintenance of cellular quiescence. To test the validity of this hypothesis, p21 was expressed in a diverse panel of cell lines, thus isolating the effects of p21 activity from the pleiotropic effects of upstream signaling pathways that normally induce p21 expression. The data show that at physiological levels of accumulation, p21, in addition to its role in negatively regulating the G(1)/S transition, contributes to regulation of the G(2)/M transition. Both G(1)- and G(2)-arrested cells were observed in all cell types, with different preponderances. Preponderant G(1) arrest in response to p21 expression correlated with the presence of functional pRb. G(2) arrest was more prominent in pRb-negative cells, The arrest distribution did not correlate with the p53 status, and proliferating-cell nuclear antigen (PCNA) binding activity of p21 did not appear to be involved, since p27, which lacks a PCNA binding domain, produced similar arrest Bs. In addition, DNA endoreduplication occurred in pRb-negative but not in pRb-positive cells, suggesting that functional pRb is necessary to prevent DNA replication in p21 G(2)-arrested cells. These results suggest that the primary target of the Cip/Kip family of inhibitors leading to efficient G(1) arrest as well as to blockade of DNA replication from either G(1) or G(2) phase is the pRb regulatory system, Finally, the tendency of Rb-negative cells to undergo endoreduplication cycles when p21 is expressed may have negative implications in the therapy of Rb-negative cancers,vith genotoxic agents that activate the p53/p21 pathway.