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J Virol, May 1998, p. 3925-3934, Vol. 72, No. 5
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.
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

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