Department of Microbiology and Immunology, Western University, London, Ontario, Canada.
J Virol. 2012 Dec;86(24):13313-23. doi: 10.1128/JVI.01637-12. Epub 2012 Sep 26.
The human papillomavirus (HPV) E7 oncoprotein binds cellular factors, preventing or retargeting their function and thereby making the infected cell conducive for viral replication. A key target of E7 is the product of the retinoblastoma susceptibility locus (pRb). This interaction results in the release of E2F transcription factors and drives the host cell into the S phase of the cell cycle. E7 binds pRb via a high-affinity binding site in conserved region 2 (CR2) and also targets a portion of cellular pRb for degradation via the proteasome. Evidence suggests that a secondary binding site exists in CR3, and that this interaction influences pRb deregulation. Additionally, evidence suggests that CR3 also participates in the degradation of pRb. We have systematically analyzed the molecular mechanisms by which CR3 contributes to deregulation of the pRb pathway by utilizing a comprehensive series of mutations in residues predicted to be exposed on the surface of HPV16 E7 CR3. Despite differences in the ability to interact with cullin 2, all CR3 mutants degrade pRb comparably to wild-type E7. We identified two specific patches of residues on the surface of CR3 that contribute to pRb binding independently of the high-affinity CR2 binding site. Mutants within CR3 that affect pRb binding are less effective than the wild-type E7 in overcoming pRb-induced cell cycle arrest. This demonstrates that the interaction between HPV16 E7 CR3 and pRb is functionally important for alteration of the cell cycle.
人乳头瘤病毒（HPV）E7 癌蛋白结合细胞因子，阻止或重新靶向其功能，从而使受感染的细胞有利于病毒复制。E7 的一个关键靶标是视网膜母细胞瘤易感基因座（pRb）的产物。这种相互作用导致 E2F 转录因子的释放，并促使宿主细胞进入细胞周期的 S 期。E7 通过保守区域 2（CR2）中的高亲和力结合位点与 pRb 结合，并且还通过蛋白酶体靶向一部分细胞 pRb 进行降解。有证据表明 CR3 中存在第二个结合位点，并且这种相互作用影响 pRb 的失调。此外，有证据表明 CR3 还参与 pRb 的降解。我们通过利用预测在 HPV16 E7 CR3 表面暴露的残基的综合系列突变，系统地分析了 CR3 对 pRb 途径失调的分子机制。尽管与 cullin 2 相互作用的能力存在差异，但所有 CR3 突变体与野生型 E7 相比降解 pRb 的能力相当。我们确定了 CR3 表面上两个独立于高亲和力 CR2 结合位点的特定残基斑块，这些残基斑块有助于 pRb 结合。影响 pRb 结合的 CR3 突变体比野生型 E7 更有效地克服 pRb 诱导的细胞周期阻滞。这表明 HPV16 E7 CR3 与 pRb 之间的相互作用对于改变细胞周期具有功能重要性。
