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Human papillomavirus type 16 E7 binds to E2F1 and activates E2F1-driven transcription in a retinoblastoma
Sun Gwan Hwang1, Daeyoup Lee, Jiyun Kim
1Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
Abstract:
The human papillomavirus (HPV) E7 oncoprotein can immortalize primary human cells and induce tumor formation. These properties of E7 depend on its ability to inhibit the activity of retinoblastoma protein (pRB), which in turn affects E2F function. E2F proteins control the expression of genes involved in differentiation, development, cell proliferation, and apoptosis. By using genetic and biochemical approaches, the present study shows that E7 binds to E2F1 in vivo and in vitro and that both proteins co-localize in the nucleus. Importantly, the binding of the high risk group HPV E7 to E2F1 is tighter than the binding of the low risk group HPV E7 to E2F1. Although E7 of the high risk group HPVs activates E2F1-dependent transcription strongly in C33A or 293T cells, E7 of the low risk group HPVs activates transcription only weakly. By using electrophoretic mobility shift assay, we also showed that E7 binds to E2F1-DNA complexes. Furthermore, we show that these activities of E7 are independent of pRB by using E7 and E2F1 mutants that cannot bind to pRB. Taken together, these data suggest that E7 contributes to the deregulation of pRB-dependent E2F1 repression and to the further activation of E2F1 independently of pRB.
Insights
Human papillomavirus (HPV) E7 protein binds to E2F1, impacting cell cycle regulation. This interaction, crucial for tumor formation, occurs independently of retinoblastoma protein (pRB).
Area of Science:
- Molecular Biology
- Oncology
- Virology
Background:
- The human papillomavirus (HPV) E7 oncoprotein is known to immortalize cells and induce tumors.
- E7's oncogenic activity is linked to its inhibition of retinoblastoma protein (pRB), affecting E2F transcription factors.
- E2F proteins regulate critical cellular processes including proliferation, differentiation, and apoptosis.
Purpose of the Study:
- To investigate the direct interaction between HPV E7 and E2F1.
- To determine if this interaction is dependent on pRB.
- To elucidate the role of E7-E2F1 binding in transcriptional regulation.
Main Methods:
- Genetic and biochemical approaches were employed.
- In vivo and in vitro binding assays were performed.
- Co-localization studies in the nucleus were conducted.
- Electrophoretic mobility shift assays (EMSA) were used.
- Mutant proteins deficient in pRB binding were utilized.
Main Results:
- HPV E7 directly binds to E2F1 both in vivo and in vitro.
- E7 and E2F1 co-localize within the cell nucleus.
- High-risk HPV E7 exhibits tighter binding to E2F1 compared to low-risk HPV E7.
- High-risk HPV E7 strongly activates E2F1-dependent transcription, while low-risk HPV E7 activates it weakly.
- E7 was shown to bind to E2F1-DNA complexes.
- These E7 activities were demonstrated to be independent of pRB.
Conclusions:
- HPV E7 directly interacts with E2F1, contributing to the deregulation of E2F1 repression.
- E7 promotes E2F1 activation independently of pRB, suggesting a novel mechanism in HPV-induced oncogenesis.
- The differential binding affinity and transcriptional activation by high-risk versus low-risk HPV E7 highlight distinct oncogenic potentials.