Anchorage-independent transcription of the cyclin A gene induced by the E7 oncoprotein of human papillomavirus type 16.
To develop an experimental model for E7-mediated anchorage-independent growth, we studied the ability of E7-expressing NIH 3T3 subclones to enter S phase when they were cultured in suspension. We found that expression of E7 prevents the inhibition of cyclin E-associated kinase and also triggers activation of cyclin A gene expression in suspension cells. A point mutation in the amino terminus of E7 prevented E7-driven rescue of cyclin E-associated kinase activity in suspension cells; however, cells with this mutation retained some ability to activate cyclin A gene expression and promote S-phase entry. Activation of cyclin A gene expression by E7 was correlated with an increased binding of free E2F to a regulatory element in the cyclin A promoter which mediates both repression of cyclin A upon loss of adhesion and its reactivation by E7. Surprisingly, expression of E7 led to a nuclear accumulation of one species of free E2F, namely, an E2F-4-DP-1 heterodimer, that is exclusively cytoplasmic in the absence of E7. Taken together, the data reported here indicate that several different E7-dependent changes of cellular-growth-regulating pathways can cooperate to allow adhesion-independent entry into S phase.
Schulze
A
A
Forschungsschwerpunkt Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Mannhardt
B
B
Zerfass-Thome
K
K
Zwerschke
W
W
Jansen-Dürr
P
P
D016475:3T3 Cells; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D019925:Cyclin A / Q000235:genetics*; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; D006801:Humans; D051379:Mice; D009856:Oncogene Proteins, Viral / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D027383:Papillomaviridae / Q000235:genetics / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019927:Cyclin E; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; C493763:E2f4 protein, mouse; 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; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases