DIFFERENTIATION-DEPENDENT UP-REGULATION OF THE HUMAN PAPILLOMAVIRUS E7 GENE REACTIVATES CELLULAR DNA-REPLICATION IN SUPRABASAL DIFFERENTIATED KERATINOCYTES
S. Cheng et al., DIFFERENTIATION-DEPENDENT UP-REGULATION OF THE HUMAN PAPILLOMAVIRUS E7 GENE REACTIVATES CELLULAR DNA-REPLICATION IN SUPRABASAL DIFFERENTIATED KERATINOCYTES, Genes & development, 9(19), 1995, pp. 2335-2349
mRNA transcription, DNA amplification, and progeny production of human
papillomaviruses (HPVs) are closely linked to squamous epithelial dif
ferentiation in patient papillomas. Because suprabasal, differentiated
keratinocytes have exited the cell cycle for days or weeks and becaus
e viral DNA synthesis requires the host DNA replication machinery, HPV
s must have a mechanism to reactivate the essential host genes. In thi
s study, we show via acute recombinant retrovirus infection that an in
tact E7 gene of either high-risk or of low-risk HPV genotypes, under t
he control of its respective native enhancer-promoter, induced prolife
rating cell nuclear antigen (PCNAs) expression in the suprabasal cells
of epithelial raft cultures of primary human foreskin keratinocytes (
PHK). The cellular differentiation program was unaltered by the viral
oncoprotein; it was essential for high HPV promoter activity. Furtherm
ore, extensive host chromosomal DNA replication took place in differen
tiated cells of HPV-18 E7-expressing raft cultures and of patient lary
ngeal papillomas caused by HPV-6. These results indicate that the main
function of the E7 protein is to reactivate host DNA replication mach
inery to support viral replication in differentiated, noncycling cells
.