Liu Y, Chen J J, Gao Q, Dalal S, Hong Y, Mansur C P, Band V, Androphy E J
Department of Dermatology, New England Medical Center and Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Virol. 1999 Sep;73(9):7297-307. doi: 10.1128/JVI.73.9.7297-7307.1999.
The E6 proteins from cervical cancer-associated human papillomavirus (HPV) types such as HPV type 16 (HPV-16) induce proteolysis of the p53 tumor suppressor protein through interaction with E6-AP. We have previously shown that human mammary epithelial cells (MECs) immortalized by HPV-16 E6 display low levels of p53. HPV-16 E6 as well as other cancer-related papillomavirus E6 proteins also binds the cellular protein E6BP (ERC-55). To explore the potential functional significance of these interactions, we created and analyzed a series of E6 mutants for their ability to interact with E6-AP, p53, and E6BP in vitro. While there was a similar pattern of binding among these E6 targets, a subset of mutants differentiated E6-AP binding, p53 binding, and p53 degradation activities. These results demonstrated that E6 binding to E6-AP is not sufficient for binding to p53 and that E6 binding to p53 is not sufficient for inducing p53 degradation. The in vivo activity of these HPV-16 E6 mutants was tested in MECs. In agreement with the in vitro results, most of these p53 degradation-defective E6 mutants were unable to reduce the p53 level in early-passage MECs. Interestingly, several mutants that showed severely reduced ability for interacting with E6-AP, p53, and E6BP in vitro efficiently immortalized MECs. These immortalized cells exhibited low p53 levels at late passage. Furthermore, mutants defective for p53 degradation but able to immortalize MECs were also identified, and the immortal cells retained normal levels of p53 protein. These results imply that multiple functions of HPV-16 E6 contribute to MEC immortalization.
来自宫颈癌相关人乳头瘤病毒（HPV）类型（如16型HPV，即HPV - 16）的E6蛋白通过与E6 - AP相互作用诱导p53肿瘤抑制蛋白的蛋白水解。我们之前已经表明，由HPV - 16 E6永生化的人乳腺上皮细胞（MEC）显示出低水平的p53。HPV - 16 E6以及其他与癌症相关的乳头瘤病毒E6蛋白也结合细胞蛋白E6BP（ERC - 55）。为了探究这些相互作用的潜在功能意义，我们构建并分析了一系列E6突变体在体外与E6 - AP、p53和E6BP相互作用的能力。虽然这些E6靶点之间存在相似的结合模式，但一部分突变体区分了E6 - AP结合、p53结合和p53降解活性。这些结果表明，E6与E6 - AP的结合不足以与p53结合，并且E6与p53的结合不足以诱导p53降解。在MEC中测试了这些HPV - 16 E6突变体的体内活性。与体外结果一致，大多数这些p53降解缺陷型E6突变体无法降低早期传代MEC中的p53水平。有趣的是，几个在体外与E6 - AP、p53和E6BP相互作用能力严重降低的突变体有效地使MEC永生化。这些永生化细胞在传代后期显示出低水平的p53。此外，还鉴定出了p53降解缺陷但能够使MEC永生化的突变体，并且永生化细胞保留了正常水平的p53蛋白。这些结果表明，HPV - 16 E6的多种功能有助于MEC的永生化。
