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J. Virol., 05 1995, 2989-2997, Vol 69, No. 5
S Jeon, BL Allen-Hoffmann and PF Lambert
Integration of human papillomavirus type 16 (HPV-16) DNA into a host
chromosome has been hypothesized to result in altered expression of two
viral transforming genes, E6 and E7, in cervical cancers. In order to
investigate the role that changes in viral genomic state and gene
expression play in cervical carcinogenesis, we have derived clonal
populations of human cervical epithelial cells which harbor multiple copies
of either extrachromosomal or integrated viral DNA. The clonal populations
harboring extrachromosomal HPV-16 DNA stably maintained approximately 1,000
viral copies for at least 15 passages (approximately 100 cell doublings),
which contrasted with the unstable HPV-16 replicons in the parental
counterpart. In the clonal populations harboring integrated viral DNA, 3 to
60 copies of HPV-16 DNA were found integrated in either of two forms: type
1, in which all the copies of HPV-16 DNA were disrupted in the E2 open
reading frame upon integration, and type 2, in which intact viral copies
were flanked by disrupted viral copies and cellular sequences. Despite the
lower HPV-16 DNA copy number, the clonal populations with integrated viral
DNA had levels of E7 protein that were in most cases higher than those
found in the clonal populations harboring extrachromosomal viral DNA.
Irrespective of viral genomic state, the clonal populations were capable of
undergoing terminal differentiation and unable to form colonies in soft
agar, which is indicative of the nontumorigenic nature of these cells.
Importantly, a cell population with integrated viral DNA was found to
outgrow another with extrachromosomal DNA when these cells were cocultured
over a period of time. Thus, integration of human papillomaviral DNA
correlates with increased viral gene expression and cellular growth
advantage. These observations are consistent with the hypothesis that
integration provides a selective advantage to cervical epithelial
precursors of cervical carcinoma.
Copyright © 1995, American Society for Microbiology
Integration of human papillomavirus type 16 into the human genome correlates with a selective growth advantage of cells
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison 53706, USA.
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