Association of the human papillomavirus type 16 E7 protein with the S-phase-specific E2F-cyclin A complex.
The transcription factor E2F has been shown to be involved in the expression of several cell cycle-regulated genes, and the activity of this factor is controlled by cellular proteins such as pRB and p107. E2F is also a target of the DNA virus oncoproteins (adenovirus E1A, simian virus 40 T antigen, and human papillomavirus [HPV] E7) (see the review by J. R. Nevins [Science 258: 424-429, 1992]). These viral oncoproteins dissociate an inactive complex between E2F and the retinoblastoma tumor suppressor protein (pRB), and this dissociation of the E2F-pRB complex correlates with a stimulation of the E2F-dependent transcription. In the S phase of the cell cycle, E2F forms a complex with p107, cyclin A, and the cdk2 kinase (E2F-cyclin A complex). The cellular function of this S-phase-specific complex is unclear. The adenovirus E1A protein dissociates the E2F-cyclin A complex. The HPV type 16 (HPV-16) E7 protein, which possesses significant sequence homology with E1A, does not dissociate the E2F-cyclin A complex. We find that the HPV-16 E7 protein associates very efficiently with the E2F-cyclin A complex. This association is dependent on the sequences that are also necessary for the transforming activity of E7. Moreover, the E7 protein of a low-risk HPV (type 6b) is much less efficient in binding to the E2F-cyclin A complex compared with that of the high-risk type. We also find that the E2F-cyclin A complex remains endogenously associated with the E7 protein in extracts of Caski cells, which express high levels of HPV-16 E7 protein. Finally, we have extensively purified the E2F-cyclin A complex from mouse L-cell extracts and show that, in cell extracts, the E2F-cyclin A complex remains associated with other cellular proteins.
Arroyo
M
M
Department of Biochemistry, University of Illinois at Chicago 60612.
Bagchi
S
S
Raychaudhuri
P
P
D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins / Q000378:metabolism*; D004247:DNA; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D027383:Papillomaviridae / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins; D016133:Polymerase Chain Reaction; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism*
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; C059731:oncogene protein E7, Human papillomavirus type 16; D004247:DNA