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J Virol, May 1998, p. 3925-3934, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Transactivation-Competent Bovine Papillomavirus E2 Protein Is Specifically Required for Efficient Repression of Human Papillomavirus Oncogene Expression and for Acute Growth Inhibition of Cervical Carcinoma Cell Lines

Edward C. Goodwin,1 Lisa Kay Naeger,1,dagger David E. Breiding,2 Elliot J. Androphy,2 and Daniel DiMaio1,*

Department of Genetics, Yale University School of Medicine, New Haven, Connecticut,1 and Departments of Dermatology, Molecular Biology, and Microbiology, Tufts University School of Medicine and New England Medical Center, Boston, Massachusetts2

Received 10 October 1997/Accepted 10 February 1998

The papillomavirus E2 proteins can function as sequence-specific transactivators or transrepressors of transcription and as cofactors in viral DNA replication. We previously demonstrated that acute expression of the bovine papillomavirus type 1 (BPV1) E2 protein in HeLa and HT-3 cervical carcinoma cell lines greatly reduced cellular proliferation by imposing a specific G1/S phase growth arrest. In this report, we analyzed the effects of a panel of point mutations in the BPV1 E2 protein to identify the functional requirements for acute growth inhibition. Disruption of E2-specific transactivation by mutations within either the transactivation domain or the DNA binding domain severely impaired E2-mediated growth inhibition in HeLa and HT-3 cells, even though these mutants retain various other E2 activities. This result indicates that functional transactivation activity is required for acute E2-mediated growth inhibition. HeLa cells, which contain a wild-type p53 gene, and HT-3 cells, which contain a transactivation-defective p53 gene, exhibited similar responses to the E2 mutants, suggesting that identical functions of the E2 protein were required for growth arrest regardless of p53 status. Replacement of the E2 transactivation domain with that of the herpes simplex virus VP16 generated a chimeric transactivator that efficiently stimulated expression of an E2-responsive reporter plasmid yet was completely defective for growth inhibition, suggesting that an E2-specific transactivation function is required for growth arrest. Surprisingly, the transactivation-defective E2 mutants were also markedly defective in their ability to repress transcription of the native human papillomavirus type 18 (HPV18) E6/E7 oncogenes in HeLa cells and of the HPV18 promoter present in a transfected reporter plasmid. These mutants were also defective in their ability to increase p53 levels. Therefore, efficient repression of the HPV18 promoter in HeLa cells is not merely a consequence of the binding of an E2 protein to appropriately situated binding sites in the promoter.

* Corresponding author. Mailing address: Department of Genetics, Yale University School of Medicine, P.O. Box 208005, New Haven, CT 06520-8005. Phone: (203) 785-2684. Fax: (203) 785-7023. E-mail: daniel.dimaio{at}yale.edu.

dagger Present address: Tularik, Inc., South San Francisco, CA 94080.

J Virol, May 1998, p. 3925-3934, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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Copyright © 1998 by the American Society for Microbiology. All rights reserved.