The differentiation-specific factor CDP/Cut represses transcription and replication of human papillomaviruses through a conserved silencing element

Citation
Mj. O'Connor et al., The differentiation-specific factor CDP/Cut represses transcription and replication of human papillomaviruses through a conserved silencing element, J VIROLOGY, 74(1), 2000, pp. 401-410
Citations number
69
Categorie Soggetti
Microbiology
Journal title
JOURNAL OF VIROLOGY
ISSN journal
0022538X → ACNP
Volume
74
Issue
1
Year of publication
2000
Pages
401 - 410
Database
ISI
SICI code
0022-538X(200001)74:1<401:TDFCRT>2.0.ZU;2-9
Abstract
The life cycles of human papillomaviruses (HPVs) are intimately linked to t he differentiation program of infected stratified epithelia, with both vira l gene expression and replication being maintained at low levels in undiffe rentiated basal cells and increased upon host cell differentiation. We rece ntly identified, in HPV-16, a negative regulatory element between the epith elial-cell-specific enhancer and the E6 promoter that is capable of silenci ng E6 promoter activity, and we termed this element a papillomavirus silenc ing motif (PSM) and the unknown cellular factor that bound to it PSM bindin g protein (PSM-BP). Here we show that the homologous genomic segments of si x other distantly related genital HPV types contain a PSM that binds PSM-BP and is capable of repressing transcription. Conservation of the PSM sugges ts that it is indispensable for the HPV life cycle. Purification, electroph oretic mobility shift assay experiments, and the use of specific antibodies proved that the cellular factor PSM-BP is identical to a previously descri bed transcriptional repressor, the CCAAT displacement protein (CDP), also r eferred to as the human Cut protein (Cut). CDP/Cut repression of HPV-16 may stem from the modification of specifically positioned nucleosomes, as sugg ested by transcriptional stimulation under the influence of the histone dea cetylase inhibitor trichostatin A. CDP/Cut is an important developmental re gulator in several different tissues. It was recently shown that CDP/Cut is expressed in basal epithelial cells but not in differentiated primary kera tinocytes. This suggests the possibility that repression by PSM couples HPV transcription to the stratification of epithelia. In each of the studied H PV types, the two CDP/Cut binding sites of PSM overlap with the known or pr esumed binding sites of the replication initiator protein El. Transfection of CDP/Cut expression vectors into cells that support HPV-16 or HPV-31 repl ication leads to the elimination of viral episomes. Similarly, two PSM-like motifs overlapping the El binding site of bovine papillomavirus type 1 bin d CDP/Cut, and CDP/Cut overexpression reduces the copy number of episomally replicating BPV-1 genomes in mouse fibroblasts. CDP/Cut appears to be a ma ster regulator of HPV transcription and replication during epithelial diffe rentiation, and PSMs are important cis-responsive targets of this repressor .