Rousseau D, Cannella D, Boulaire J, Fitzgerald P, Fotedar A, Fotedar R
Institut de Biologie Structurale J-P Ebel, Grenoble, France.
Oncogene. 1999 May 27;18(21):3290-302. doi: 10.1038/sj.onc.1202681.
The CDK inhibitor, p21(WAF1/Cip1) blocks cell cycle progression. In vitro, the N-terminus of p21 binds and inhibits CDK-cyclin kinase activity, whereas the C-terminus binds and inhibits PCNA (proliferating cell nuclear antigen) function. PCNA is essential for processivity of both DNA polymerase delta and epsilon. We have performed a detailed analysis of growth inhibition by the N- and C-terminal regions of p21, and determined whether the N- and C-terminal regions mediate this effect by different mechanisms. Expression of either the N- or the C-terminal region of p21 inhibits DNA synthesis and cell growth, but not as efficiently as full length p21. The effectiveness of the two p21 domains is dependent on their stability which is determined by the ubiquitin-proteasome pathway. The stabilization of the N- and C-terminal region of p21 increases their effectiveness as inhibitors of DNA synthesis to levels comparable to full length p21. Inhibition of DNA synthesis by the N-terminal region of p21 involves suppression of E2F activity. In contrast, inhibition by the C-terminal region of p21 is not accompanied by suppression of E2F activity, but is mediated via PCNA binding. The C-terminal region of p21 therefore inhibits cell growth by a mechanism distinct from that of the N-terminal region containing the CDK-cyclin inhibitory domain.
细胞周期蛋白依赖性激酶（CDK）抑制剂p21（WAF1/Cip1）可阻断细胞周期进程。在体外，p21的N端结合并抑制CDK-细胞周期蛋白激酶活性，而C端结合并抑制增殖细胞核抗原（PCNA）的功能。PCNA对于DNA聚合酶δ和ε的持续合成能力至关重要。我们对p21的N端和C端区域的生长抑制作用进行了详细分析，并确定N端和C端区域是否通过不同机制介导这种效应。p21的N端或C端区域的表达均抑制DNA合成和细胞生长，但效率不如全长p21。p21两个结构域的有效性取决于其稳定性，而稳定性由泛素-蛋白酶体途径决定。p21的N端和C端区域的稳定性增加，使其作为DNA合成抑制剂的有效性提高到与全长p21相当的水平。p21的N端区域对DNA合成的抑制涉及E2F活性的抑制。相比之下，p21的C端区域的抑制作用并不伴随着E2F活性的抑制，而是通过与PCNA结合介导的。因此，p21的C端区域通过一种不同于含有CDK-细胞周期蛋白抑制结构域的N端区域的机制来抑制细胞生长。
