E7 Dependent modulation of cell cycle (A) HPV E7 oncoprotein forms a complex with cyclin dependent kinase inhibitor p21 leading to increased expression of cyclin dependent kinase (CDK). (B) HPV E7 oncoprotein binds to phosphorylated retinoblastoma protein (Rb) causing separation of Rb from elongation factor (E2F) complex. The Rb protein is then degraded through the ubiquitin proteosome pathway. (C) HPV E7 oncoprotein associates with histone deacetylases (HDACs) resulting in an increased expression of transcription factors E2F/DP1 inducible genes.