Zhang Benyue, Chen Wei, Roman Ann
Department of Microbiology and Immunology and The Walther Oncology Center, Indiana University School of Medicine and The Walther Cancer Institute, Indianapolis, IN 46202, USA.
Proc Natl Acad Sci U S A. 2006 Jan 10;103(2):437-42. doi: 10.1073/pnas.0510012103. Epub 2005 Dec 28.
High-risk human papillomaviruses (HPVs) (e.g., HPV-16) cause anogenital and head and neck cancers, and low-risk HPVs (e.g., HPV-6) cause benign hyperproliferative disease. The E7 protein of HPV-16 binds all retinoblastoma tumor suppressor protein (pRB) family members with higher affinity than HPV-6E7. The HPV-16 E7 protein has been reported to target pRB family members for degradation and to immortalize cells. Here we tested the hypothesis that the low-risk E7 protein has an intrinsic ability to decrease expression of pRB family members. First, we introduced a high-affinity pRB-binding site into HPV-6 E7 (6E7G22D) and showed that, in human foreskin keratinocytes, HPV-6 E7G22D decreased the level of pRB protein but not pRB mRNA. Second, we analyzed the ability of wild-type HPV-6 E7 to destabilize the other pRB family members, p107 and p130. HPV-6 E7, like HPV-16 E7, decreased the level of p130 protein. This decrease was inhibited by MG132, a proteasome inhibitor. Binding of HPV-6 E7 to p130 was necessary but not sufficient to decrease the level of p130. Furthermore, the destabilization of p130 correlated with a decrease in the expression of involucrin, a differentiation marker. We suggest that the shared activity of HPV-16 E7 and HPV-6 E7 to destabilize p130 and decrease or delay differentiation may be related to the role of E7 in the HPV life cycle. The added ability of HPV-16 E7 to regulate pRB and p107 may be related to oncogenic activity.
高危型人乳头瘤病毒（HPV）（如HPV-16）可引发肛门生殖器癌和头颈癌，而低危型HPV（如HPV-6）会导致良性增殖性疾病。HPV-16的E7蛋白与所有视网膜母细胞瘤肿瘤抑制蛋白（pRB）家族成员的结合亲和力高于HPV-6E7。据报道，HPV-16 E7蛋白以pRB家族成员为靶点进行降解并使细胞永生化。在此，我们验证了低危型E7蛋白具有降低pRB家族成员表达的内在能力这一假说。首先，我们在HPV-6 E7中引入了一个高亲和力的pRB结合位点（6E7G22D），结果表明，在人包皮角质形成细胞中，HPV-6 E7G22D降低了pRB蛋白水平，但未降低pRB mRNA水平。其次，我们分析了野生型HPV-6 E7使其他pRB家族成员p107和p130失稳（降解）的能力。与HPV-16 E7一样，HPV-6 E7降低了p130蛋白水平。蛋白酶体抑制剂MG132可抑制这种降低。HPV-6 E7与p130的结合是降低p130水平所必需的，但并不充分。此外，p130的失稳与一种分化标志物内披蛋白表达的降低相关。我们认为，HPV-16 E7和HPV-6 E7在使p130失稳以及降低或延迟分化方面的共同活性可能与E7在HPV生命周期中的作用有关。HPV-16 E7调节pRB和p107的额外能力可能与致癌活性有关。
