Bovine papillomavirus E2 protein activates a complex growth-inhibitory program in p53-negative HT-3 cervical carcinoma cells that includes repression of cyclin A and cdc25A phosphatase genes and accumulation of hypophosphorylated retinoblastoma protein.
The bovine papillomavirus E2 protein can inhibit the proliferation of HT-3 cells, a p53-negative cervical carcinoma cell line containing integrated human papillomavirus type 30 DNA. Here, we analyzed HT-3 cells to explore the mechanism of p53-independent E2-mediated growth inhibition. Expression of the E2 protein repressed expression of the endogenous human papillomavirus type 30 E6/E7 genes. This was accompanied by hypophosphorylation and increased accumulation of p105Rb and repression of E2F1 expression. The E2 protein also caused reduced cyclin-dependent kinase (cdk) 2 activity, but this did not appear to be due to increased expression of cdk inhibitors. Rather, expression of cyclin A, which regulates cdk2 activity, and the cdc25A and cdc25B phosphatases, which are thought to activate cdk2, was significantly reduced at both the RNA and protein levels in response to E2 expression. The E2 protein reduced expression of cdc25A and cdc25B in both HT-3 and HeLa cells, but not in cells that were not growth-inhibited by the E2 protein. E2 point mutants unable to inhibit cell growth did not repress cdc25A and cdc25B expression, nor did the cell cycle inhibitors hydroxyurea and mimosine. Based on these results and the known properties of cell cycle components, we propose a model to account for E2-induced growth inhibition of cervical carcinoma cell lines.
Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
L K
LK
Naeger
E C
EC
Goodwin
E S
ES
Hwang
R A
RA
DeFilippis
H
H
Zhang
D
D
DiMaio
D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins; D002417:Cattle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division; D019925:Cyclin A / Q000235:genetics*; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000235:genetics; D016213:Cyclins / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004791:Enzyme Inhibitors; D005260:Female; D005786:Gene Expression Regulation; D006131:Growth Inhibitors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D017027:Protein Tyrosine Phosphatases / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000096:biosynthesis*; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53; D002583:Uterine Cervical Neoplasms; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D020687:cdc25 Phosphatases
C493956:CDKN1A protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; C051550:E2 protein, Bovine papillomavirus; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D004791:Enzyme Inhibitors; D006131:Growth Inhibitors; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D014764:Viral Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D010749:Phosphoprotein Phosphatases; C517004:CDC25A protein, human; C517008:CDC25B protein, human; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases