Repression of Human Papillomavirus Oncogenes in HeLa Cervical Carcinoma Cells Causes the Orderly Reactivation of Dormant Tumor Suppressor Pathways

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-11, Vol.97 (23), p.12513-12518
• Main Authors: Goodwin, Edward C., DiMaio, Daniel
• Format: Article
• Language: English
• Subjects: Animals; Biochemistry; Biological Sciences; Bovine papillomavirus 1 - genetics; Bovine papillomavirus 1 - metabolism; Cancer; Carcinoma; Carrier Proteins; Cattle; Cell cycle; Cell Cycle Proteins; Cell lines; Cells; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Cyclins - biosynthesis; DNA; DNA - biosynthesis; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; E2F Transcription Factors; E6 gene; E6 protein; E7 gene; E7 protein; Female; Gene Expression Regulation, Viral; Genes, Tumor Suppressor; HeLa Cells; Human papillomavirus; human papillomavirus 18; Humans; Infections; Messenger RNA; Nuclear Proteins - genetics; Oncogene Proteins, Viral - genetics; Oncogenes; p53 protein; Papillomaviridae - genetics; Papillomavirus E7 Proteins; Phosphoproteins - genetics; Proteins; Proto-Oncogene Proteins - biosynthesis; Proto-Oncogene Proteins c-mdm2; RB gene; Repression; Repressor Proteins - genetics; Repressor Proteins - metabolism; Retinoblastoma Protein - genetics; Retinoblastoma-Binding Protein 1; Retinoblastoma-Like Protein p107; Retinoblastoma-Like Protein p130; RNA; Signal Transduction; Transcription Factor DP1; Transcription Factors - metabolism; Tumor Suppressor Protein p53 - biosynthesis; Tumors; Uterine Cervical Neoplasms; Viral Proteins - genetics; Viral Proteins - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.23.12513

Most cervical carcinomas express high-risk human papillomaviruses (HPVs) E6 and E7 proteins, which neutralize cellular tumor suppressor function. To determine the consequences of removing the E6 and E7 proteins from cervical cancer cells, we infected HeLa cells, a cervical carcinoma cell line that contains HPV18 DNA, with a recombinant virus that expresses the bovine papillomavirus E2 protein. Expression of the E2 protein resulted in rapid repression of HPV E6 and E7 expression, followed ≈ 12 h later by profound inhibition of cellular DNA synthesis. Shortly after E6/E7 repression, there was dramatic posttranscriptional induction of p53. Two p53-responsive genes, mdm2 and p21, were induced with slightly slower kinetics than p53 and appeared to be functional, as assessed by inhibition of cyclin-dependent kinase activity and p53 destabilization. There was also dramatic posttranscriptional induction of p105Rband p107 after E6/E7 repression, followed shortly thereafter by induction of p130. By 24 h after infection, only hypophosphorylated p105Rbwas detectable and transcription of several Rb/E2F-regulated genes was dramatically repressed. Constitutive expression of the HPV16 E6/E7 genes alleviated E2-induced growth inhibition and impaired activation of the Rb pathway and repression of E2F-responsive genes. This dynamic response strongly suggests that the p53 and Rb tumor suppressor pathways are intact in HeLa cells and that repression of HPV E6 and E7 mobilizes these pathways in an orderly fashion to deliver growth inhibitory signals to the cells. Strikingly, the major alterations in the cell cycle machinery underlying cervical carcinogenesis can be reversed by repression of the endogenous HPV oncogenes.