J Virol, June 1998, p. 5016-5024, Vol. 72, No. 6
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
andDepartment of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611
Received 21 January 1998/Accepted 5 March 1998
The life cycle of the papillomaviruses is closely linked to host
cell differentiation, as demonstrated by the fact that amplification of
viral DNA and transcription of late genes occur only in the suprabasal
cells of a differentiated epithelium. Previous studies examining the
pathogenesis of papillomavirus infections have relied on the use of
organotypic raft cultures or lesions from patients to examine these
differentiation-dependent viral activities. In this study, we used a
simple system for epithelial differentiation to study human
papillomavirus (HPV) late functions. We demonstrate that the suspension
of HPV-infected keratinocytes in semisolid medium containing 1.6%
methylcellulose for 24 h was sufficient for the activation of the
late promoter, transcription of late genes, and amplification of viral
DNA. These activities were shown to be linked to and coincide with
cellular differentiation. Expression of the late protein
E1
E4 and amplification of viral DNA were detected in the
identical set of cells after suspension in methylcellulose. This
technique was also used to analyze the differentiation properties of
the cells which expressed the late protein E1
E4. While
induction of the spinous layer markers involucrin and transglutaminase
was compatible with late promoter induction, expression of the
differentiation-specific keratin-10 was shown not to be required for
HPV late functions. Interestingly, while the majority of normal human
keratinocytes induced filaggrin expression by 24 h, this marker of
the granular layer was induced in a smaller subset of HPV type 31 (HPV-31)-positive cells at this time point. The HPV-31-positive cells
which expressed filaggrin did not induce the late protein
E1
E4. Use of the methylcellulose system to induce
epithelial differentiation coupled with the ability to perform a
genetic analysis of HPV functions by using transfection of cloned viral
DNA will facilitate the study of the regulation of the papillomavirus
life cycle.
Present address: Universität Tübingen, Tübingen,
Germany.
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