Destabilization of the retinoblastoma tumor suppressor by human papillomavirus type 16 E7 is not sufficient to overcome cell cycle arrest in human keratinocytes.
نویسندگان
چکیده
The E7 oncoprotein of human papillomavirus type 16 promotes cell proliferation in the presence of antiproliferative signals. Mutagenesis of E7 has revealed that this activity requires three regions, conserved regions 1 and 2 and a C-terminal zinc finger. Binding to the retinoblastoma tumor repressor (Rb) through an LxCxE motif in conserved region 2 is necessary, but not sufficient, for E7 to induce proliferation. We tested the hypothesis that binding to Rb is not sufficient because conserved region 1 and/or the C terminus are required for E7 to functionally inactivate Rb and thus induce proliferation. One mechanism proposed for how E7 inactivates Rb is by blocking Rb-E2F binding. Either conserved region 1 or the C terminus was necessary, in combination with the LxCxE motif, for E7 to block Rb-E2F binding in vitro. While all full-length E7 proteins with mutations outside of the LxCxE motif inhibited Rb-E2F binding, some failed to abrogate cell cycle arrest, demonstrating that blocking Rb-E2F binding is not sufficient for abrogating antiproliferative signals. Another mechanism proposed for how E7 inactivates Rb is by promoting the destabilization of Rb protein. Mutations in conserved region 1 or the LxCxE motif prevented E7 from reducing the half-life of Rb. Though no specific C-terminal residues of E7 were essential for destabilizing Rb, a novel class of mutations that uncouple the destabilization of Rb from the deregulation of keratinocyte proliferation was discovered. Destabilization of Rb correlated with the abrogation of Rb-induced quiescence but was not sufficient for overriding DNA damage-induced cell cycle arrest or for increasing keratinocyte life span. Finally, the same regions of E7 required for destabilizing Rb were required for reducing p107 and p130 levels. Together, these results suggest that inactivation of all three Rb family members is not sufficient to deregulate keratinocyte cell cycle control.
منابع مشابه
Inactivation of both the retinoblastoma tumor suppressor and p21 by the human papillomavirus type 16 E7 oncoprotein is necessary to inhibit cell cycle arrest in human epithelial cells.
The human papillomavirus (HPV) type 16 E7 oncoprotein must inactivate the retinoblastoma tumor suppressor (Rb) pathway to bypass G(1) arrest. However, E7 C-terminal mutants that were able to inactivate Rb were unable to bypass DNA damage-induced G(1) arrest and keratinocyte senescence, suggesting that the E7 C terminus may target additional G(1) regulators. The E7 C-terminal mutant proteins E7 ...
متن کاملAbrogation of the retinoblastoma tumor suppressor checkpoint during keratinocyte immortalization is not sufficient for induction of centrosome-mediated genomic instability.
Deregulation of the retinoblastoma (pRB) tumor suppressor pathway and telomerase activation have been identified as rate-limiting steps for immortalization of primary human epithelial cells. However, additional molecular aberrations including p53 inactivation, ras activation, and deregulation of protein phosphatase 2A activity are necessary for full transformation of immortalized epithelial cel...
متن کاملHuman Papillomavirus E7 Oncoprotein Overrides the Tumor Suppressor Activity of p21 in Cervical Carcinogenesis
The E7 oncoprotein of the high-risk human papillomaviruses (HPV) is thought to contribute to cervical carcinogenesis at least in part by abrogating cell cycle regulation. E7 can dysregulate the cell cycle through its interaction with several cellular proteins including the retinoblastoma suppressor protein pRb, as well as the cyclin-dependent kinase inhibitor p21. Inactivation of pRb in cervica...
متن کاملType 16 E7 in Cervical Carcinogenesis Critical Roles for Non-pRb Targets of Human Papillomavirus
High-risk human papillomaviruses (HPV) encode two oncogenes, E6 and E7, expressed in nearly all cervical cancers. In vivo , HPV-16 E7 has been shown to induce multiple phenotypes in the context of transgenic mice, including cervical cancer. E7 is a multifunctional protein known best for its ability to inactivate the tumor suppressor pRb. To determine the importance of pRb inactivation by E7 in ...
متن کاملCritical roles for non-pRb targets of human papillomavirus type 16 E7 in cervical carcinogenesis.
High-risk human papillomaviruses (HPV) encode two oncogenes, E6 and E7, expressed in nearly all cervical cancers. In vivo, HPV-16 E7 has been shown to induce multiple phenotypes in the context of transgenic mice, including cervical cancer. E7 is a multifunctional protein known best for its ability to inactivate the tumor suppressor pRb. To determine the importance of pRb inactivation by E7 in c...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Journal of virology
دوره 75 15 شماره
صفحات -
تاریخ انتشار 2001