Analysis of the p53-mediated G1 growth arrest pathway in cells expressing the human papillomavirus type 16 E7 oncoprotein.
Cells expressing human papillomavirus type 16 (HPV-16) E7, similar to those which express HPV-16 E6, are resistant to a p53-mediated G1 growth arrest. We examined the p53-mediated DNA damage response pathway in E7-expressing cells to determine the mechanism by which E7-containing cells continue to cycle. In response to DNA damage, no dramatic difference was detected in G1- or S-phase cyclin or cyclin-dependent kinase (Cdk) levels when E7-expressing cells were compared to the parental cell line, RKO. Furthermore, Cdk2 kinase activity was inhibited in both RKO cells and E7-expressing cells, while Cdk2 remained active in E6-expressing cells. However, the steady-state levels of pRB and p107 protein were substantially lower in E7-expressing cells than in the parental RKO cells or E6-expressing cells. There was no reduction in pRB mRNA levels, but the half-life of pRB in E7-expressing cells was markedly shorter. Infection of primary human foreskin keratinocytes with recombinant retroviruses expressing HPV-16 E7 resulted in a decrease in pRB protein levels, indicating this phenomenon is a consequence of E7 expression, not of immortalization or transformation. These data strongly suggest E7 interferes with the stability of pRB and p107 protein. We propose that the removal of these components of the p53-mediated G1 growth arrest pathway in E7-expressing cells contributes to the ability of E7 to overcome a p53-mediated G1 growth arrest.
Jones
D L
DL
Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Münger
K
K
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000032:analysis / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004249:DNA Damage; D003609:Dactinomycin / Q000494:pharmacology; D016193:G1 Phase; D006801:Humans; D009842:Oligopeptides / Q000494:pharmacology; D009856:Oncogene Proteins, Viral / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D027383:Papillomaviridae / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
D000590:Amino Acid Chloromethyl Ketones; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D015853:Cysteine Proteinase Inhibitors; C068651:E6 protein, Human papillomavirus type 16; C098738:N-acetyl-tyrosyl-valyl-alanyl-aspartyl chloromethyl ketone; D009842:Oligopeptides; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; C059731:oncogene protein E7, Human papillomavirus type 16; C096429:L 709049; D003609:Dactinomycin; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases