Funk J O, Waga S, Harry J B, Espling E, Stillman B, Galloway D A
Program in Cancer Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
Genes Dev. 1997 Aug 15;11(16):2090-100. doi: 10.1101/gad.11.16.2090.
p21 inhibits cyclin-dependent kinase (CDK) activity and proliferating cell nuclear antigen (PCNA)-dependent DNA replication by binding to CDK/cyclin complexes and to PCNA through distinct domains. The human papillomavirus (HPV)-16 E7 oncoprotein (16E7) abrogated a DNA damage-induced cell cycle arrest in vivo, despite high levels of p21. Using cell lysates and purified proteins we show that 16E7 prevented p21 both from inhibiting CDK2/cyclin E activity and PCNA-dependent DNA replication, whereas the nononcogenic HPV-6 E7 had reduced effects. Inactivation of both inhibitory functions of p21 was attained through binding between 16E7 and sequences in the carboxy-terminal end of p21 that overlap with the PCNA-binding site and the second p21 cyclin-binding motif. These data imply that the carboxyl terminus of p21 simultaneously modulates both CDK activity and PCNA-dependent DNA replication and that a single protein, 16E7, can override this modulation to disrupt normal cell cycle control.
p21通过不同结构域与细胞周期蛋白依赖性激酶（CDK）复合物及增殖细胞核抗原（PCNA）结合，从而抑制CDK活性和PCNA依赖性DNA复制。人乳头瘤病毒（HPV）-16 E7癌蛋白（16E7）在体内可消除DNA损伤诱导的细胞周期停滞，尽管p21水平很高。利用细胞裂解物和纯化蛋白，我们发现16E7既能阻止p21抑制CDK2/细胞周期蛋白E活性，又能阻止其抑制PCNA依赖性DNA复制，而非致癌性HPV-6 E7的作用则较弱。通过16E7与p21羧基末端与PCNA结合位点及第二个p21细胞周期蛋白结合基序重叠的序列之间的结合，实现了p21两种抑制功能的失活。这些数据表明，p21的羧基末端同时调节CDK活性和PCNA依赖性DNA复制，并且单一蛋白16E7可以克服这种调节，破坏正常的细胞周期控制。
