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J. Virol., Apr 1997, 2905-2912, Vol 71, No. 4
DL Jones and K Munger
Cells expressing human papillomavirus type 16 (HPV-16) E7, similar to those
which express HPV-16 E6, are resistant to a p53-mediated G1 growth arrest.
We examined the p53-mediated DNA damage response pathway in E7-expressing
cells to determine the mechanism by which E7- containing cells continue to
cycle. In response to DNA damage, no dramatic difference was detected in
G1- or S-phase cyclin or cyclin- dependent kinase (Cdk) levels when
E7-expressing cells were compared to the parental cell line, RKO.
Furthermore, Cdk2 kinase activity was inhibited in both RKO cells and
E7-expressing cells, while Cdk2 remained active in E6-expressing cells.
However, the steady-state levels of pRB and p107 protein were substantially
lower in E7- expressing cells than in the parental RKO cells or
E6-expressing cells. There was no reduction in pRB mRNA levels, but the
half-life of pRB in E7-expressing cells was markedly shorter. Infection of
primary human foreskin keratinocytes with recombinant retroviruses
expressing HPV-16 E7 resulted in a decrease in pRB protein levels,
indicating this phenomenon is a consequence of E7 expression, not of
immortalization or transformation. These data strongly suggest E7
interferes with the stability of pRB and p107 protein. We propose that the
removal of these components of the p53-mediated G1 growth arrest pathway in
E7- expressing cells contributes to the ability of E7 to overcome a p53-
mediated G1 growth arrest.
Copyright © 1997, American Society for Microbiology
Analysis of the p53-mediated G1 growth arrest pathway in cells expressing the human papillomavirus type 16 E7 oncoprotein
Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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