Journal of Virology, October 2001, p. 10005-10013, Vol. 75, No. 20
Department of Microbiology-Immunology,
Northwestern University Medical School, Chicago, Illinois 60611
Received 29 May 2001/Accepted 13 July 2001
The life cycle of human papillomaviruses (HPVs) is tightly linked
to the differentiation status of the host cell. While early genes are
expressed during the initial stages of viral infection, late gene
expression occurs in the suprabasal layers of the cervical epithelium.
Late genes encode E1^E4, a cytosolic
protein, and capsid proteins L1 and L2. We have mapped over 30 initiation sites for late transcripts and show that the transcripts
initiate in a 200-nucleotide region within the E7 open reading frame.
The mechanisms regulating the activation of late gene expression, however, are not yet understood. DNase I hypersensitivity analysis of
HPV-31 chromatin in cell lines that maintain viral genomes extrachromosomally indicates that a major shift in nuclease digestion occurs upon differentiation. In undifferentiated cells, hypersensitive regions exist in the upstream regulatory region proximal to the E6 open
reading frame. Upon differentiation, a region between nucleotides 659 and 811 in the E7 open reading frame becomes accessible to DNase I. These results indicate that the late transcript initiation region
becomes accessible to transcription factor binding upon differentiation. Several complexes mediate chromatin rearrangement, and
we tested whether histone acetylation was sufficient for late transcript activation. Treatment with the histone deacetylase inhibitor
trichostatin A was found to be insufficient to activate late gene
expression in undifferentiated cells. However, it did activate
expression of early transcripts. These results suggest that chromatin
remodeling around the late promoter occurs upon epithelial
differentiation and that mechanisms in addition to histone
deacetylation contribute to activation of late gene expression.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.20.10005-10013.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Differentiation-Dependent Chromatin Rearrangement
Coincides with Activation of Human Papillomavirus Type 31 Late
Gene Expression
*
Corresponding author. Mailing address: Department of
Microbiology-Immunology, Northwestern University Medical School, 303 E. Chicago Ave., Chicago, IL 60611. Phone: (312) 503-0648. Fax: (312)
503-0649. E-mail: l-laimins{at}northwestern.edu.
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