title: Conserved region 3 of human papillomavirus 16 E7 contributes to deregulation of the retinoblastoma tumor suppressor.
abstract: 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.
authors.affiliation: Department of Microbiology and Immunology, Western University, London, Ontario, Canada.
authors.forename: Biljana
authors.initials: B
authors.lastname: Todorovic
authors.forename: Katherine
authors.initials: K
authors.lastname: Hung
authors.forename: Paola
authors.initials: P
authors.lastname: Massimi
authors.forename: Nikita
authors.initials: N
authors.lastname: Avvakumov
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Dick
authors.forename: Gary S
authors.initials: GS
authors.lastname: Shaw
authors.forename: Lawrence
authors.initials: L
authors.lastname: Banks
authors.forename: Joe S
authors.initials: JS
authors.lastname: Mymryk
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002453:Cell Cycle; D002460:Cell Line; D017931:DNA Primers; D006801:Humans; D008958:Models, Molecular; D050725:Papillomavirus E7 Proteins / Q000737:chemistry / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D016160:Retinoblastoma Protein / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D017931:DNA Primers; D050725:Papillomavirus E7 Proteins; D016160:Retinoblastoma Protein; C059731:oncogene protein E7, Human papillomavirus type 16