Zhang Weifang, Liu Yingwang, Zhao Ning, Chen Hanxiang, Qiao Lijun, Zhao Weiming, Chen Jason J
Institute of Pathogenic Biology, School of Medicine, Shandong University, Jinan, Shandong, China Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
J Virol. 2015 Mar;89(5):2553-62. doi: 10.1128/JVI.02269-14. Epub 2014 Dec 17.
Specific types of human papillomavirus (HPV) are strongly associated with the development of cervical carcinoma. The HPV E6 oncoprotein from HPV degrades p53 and abrogates cell cycle checkpoints. Nonetheless, functional p53 has been observed in cervical cancer. We have previously identified a p53-independent function of E6 in attenuating the postmitotic G1-like checkpoint that can lead to polyploidy, an early event during cervical carcinogenesis that predisposes cells to aneuploidy. How E6 promotes cell cycle progression in the presence of p53 and its target, p21, remains a mystery. In this study, we examined the expression of cell cycle-related genes in cells expressing wild-type E6 and the mutant that is defective in p53 degradation but competent in abrogating the postmitotic checkpoint. Our results demonstrated an increase in the steady-state levels of G1- and G2-related cyclins/Cdks in E6-expressing keratinocytes. Interestingly, only Cdk1 remained active in E6 mutant-expressing cells while bypassing the postmitotic checkpoint. Furthermore, the downregulation of Cdk1 impaired the ability of both wild-type and mutant E6 to induce polyploidy. Our study thus demonstrated an important role for Cdk1, which binds p21 with lower affinity than Cdk2, in abrogating the postmitotic checkpoint in E6-expressing cells. We further show that E2F1 is important for E6 to upregulate Cdk1. Moreover, reduced nuclear p21 localization was observed in the E6 mutant-expressing cells. These findings shed light on the mechanisms by which HPV induces genomic instability and hold promise for the identification of drug targets.
HPV infection is strongly associated with the development of cervical carcinoma. HPV encodes an E6 oncoprotein that degrades the tumor suppressor p53 and abrogates cell cycle checkpoints. Nonetheless, functional p53 has been observed in cervical cancer. We have recently demonstrated a p53-independent abrogation of the postmitotic checkpoint by HPV E6 that induces polyploidy. However, the mechanism is not known. In this study, we provide evidence that Cdk1 plays an important role in this process. Previously, Cdk2 was thought to be essential for the G1/S transition, while Cdk1 only compensated its function in the absence of Cdk2. Our studies have demonstrated a novel role of Cdk1 at the postmitotic G1-like checkpoint in the presence of Cdk2. These findings shed light on the mechanisms by which HPV induces genomic instability and hold promise for the identification of drug targets.
特定类型的人乳头瘤病毒（HPV）与宫颈癌的发生密切相关。HPV的E6癌蛋白可降解p53并消除细胞周期检查点。尽管如此，在宫颈癌中仍观察到功能性p53。我们之前已经确定E6具有一种不依赖p53的功能，可减弱有丝分裂后类似G1期的检查点，这可能导致多倍体形成，这是宫颈癌发生过程中的一个早期事件，使细胞易发生非整倍体。在存在p53及其靶点p21的情况下，E6如何促进细胞周期进程仍是一个谜。在本研究中，我们检测了表达野生型E6和在p53降解方面有缺陷但在消除有丝分裂后检查点方面有能力的突变体的细胞中细胞周期相关基因的表达。我们的结果表明，在表达E6的角质形成细胞中，G1期和G2期相关细胞周期蛋白/细胞周期蛋白依赖性激酶（Cdk）的稳态水平增加。有趣的是，在表达E6突变体的细胞中，只有Cdk1在绕过有丝分裂后检查点时仍保持活性。此外，Cdk1的下调损害了野生型和突变型E6诱导多倍体的能力。因此，我们的研究证明了Cdk1在消除表达E6的细胞中有丝分裂后检查点方面的重要作用，Cdk1与p21的结合亲和力低于Cdk2。我们进一步表明，E2F1对E6上调Cdk1很重要。此外，在表达E6突变体的细胞中观察到核内p21定位减少。这些发现揭示了HPV诱导基因组不稳定的机制，并为确定药物靶点带来了希望。
HPV感染与宫颈癌的发生密切相关。HPV编码一种E6癌蛋白，可降解肿瘤抑制因子p53并消除细胞周期检查点。尽管如此，在宫颈癌中仍观察到功能性p53。我们最近证明了HPV E6可在不依赖p53的情况下消除有丝分裂后检查点，从而诱导多倍体形成。然而，其机制尚不清楚。在本研究中，我们提供证据表明Cdk1在此过程中起重要作用。以前，人们认为Cdk2对G1/S期转换至关重要，而Cdk1仅在没有Cdk2的情况下补偿其功能。我们的研究证明了在有Cdk2存在的情况下，Cdk1在有丝分裂后类似G1期检查点处具有新的作用。这些发现揭示了HPV诱导基因组不稳定的机制，并为确定药物靶点带来了希望。
