The Differentiation-Specific Factor CDP/Cut Represses Transcription and Replication of Human Papillomaviruses through a Conserved Silencing Element

Abstract

The life cycles of human papillomaviruses (HPVs) are intimately linked to the differentiation program of infected stratified epithelia, with both viral gene expression and replication being maintained at low levels in undifferentiated basal cells and increased upon host cell differentiation. We recently identified, in HPV-16, a negative regulatory element between the epithelial-cell-specific enhancer and the E6 promoter that is capable of silencing E6 promoter activity, and we termed this element a papillomavirus silencing motif (PSM) and the unknown cellular factor that bound to it PSM binding protein (PSM-BP). Here we show that the homologous genomic segments of six other distantly related genital HPV types contain a PSM that binds PSM-BP and is capable of repressing transcription. Conservation of the PSM suggests that it is indispensable for the HPV life cycle. Purification, electrophoretic mobility shift assay experiments, and the use of specific antibodies proved that the cellular factor PSM-BP is identical to a previously described transcriptional repressor, the CCAAT displacement protein ( Human papillomaviruses (HPVs) infect mucosal and cutaneous epithelia and cause benign and malignant lesions, such as common warts, genital warts, and cervical cancer (29,67). Transcription of HPVs is regulated in a complex manner in response to the identity of the infected epithelial cell type, the differentiation state of the stratified epithelium, the physiological state of the host, and the episomal or chromosomally integrated state of the viral genome. Most of the cis-responsive elements that mediate the activity of cellular and viral factors on HPV gene regulation are located in the long control region (LCR), which lies between the 3Ј terminus of the L1 capsid gene and the start of the E6 oncogene. With a size of 850 bp in HPV-16 and a similar length in other genital HPVs, the LCR takes up about 11% of the 7.9-kb circular DNA genome. When one compares remotely related HPV types, one finds that their genes are clearly homologous but their LCRs have diverged so much that they cannot be unequivocally aligned and their nucleotide sequences lack long, similar segments. However, when one compares the LCRs of more closely related HPV types, such as the large group of genital HPVs, one finds many short similar cis-responsive elements, which are activated by a defined subset of the cellular transcription factors of the infected cell. This conservation of sequence and function suggests that these particular mechanisms are so appropriate for the biology of these HPV types that they could not undergo evolutionary changes (13, 44). Here we study such an element that is conserved among genital HPVs, and for the first time we describe an element that represses both transcription and replication, most probably in response to the differentiation of stratified epithelia.The central part of the LCR of genital HPVs functions as an epithelial-cell-specific transcriptional enhancer (14,23,50), and the 3Ј part contains the replication or...

Identification of CCAAT Displacement Protein (CDP/cut) as a Locus-specific Repressor of Major Histocompatibility Complex Gene Expression in Human Tumor Cells

“…Other evidence suggests that the C-terminal domain of CDP/ cut functions at a distance as a direct transcriptional repressor of some genes (71), possibly by association with histone deacetylase activity (49,53). However, our results indicate that neither DNA binding nor transcriptional repression of HLA-B7 gene expression by CDP/cut appear to require HDAC1.…”

“…to repress transcription of a number of genes, including myeloid cytochrome gp91-phox (59,60), lactoferrin (61), c-myc (62), p21 (63), histone H4 (64), tryptophan hydroxylase (65), the transforming growth factor-␤ receptor (57), the mouse mammary tumor virus long terminal repeat (66), several human papillomavirus genes (53,56), the cystic fibrosis transmembrane conductance regulator (49), the immunoglobulin heavy chain (67), and ␥-globin (68). CDP/cut expression is high in many undifferentiated cell types and decreases when the cells are induced to differentiate (60).…”

“…Results from recent studies suggest that CDP/cut may actively repress expression of some genes by associating with the histone deacetylase HDAC1 (49,53). To determine whether CDP/cut is associated with HDAC1 in the HLA-B7 repressor element binding complex, EMSA was carried out with HeLa nuclear extracts in which HDAC1 had been immunodepleted.…”

PDX1, a Cellular Homeoprotein, Binds to and Regulates the Activity of Human Cytomegalovirus Immediate Early Promoter

“…Interestingly, Lundquist et al (51) have identified a putative human papillomavirus (HPV) silencing motif at position Ϫ591 to Ϫ584 of the CMV IE promoter. It has been shown that the transcriptional repressor CDP binds to this silencing element and blocks transcription and replication of HPV (23). Future experiments will be carried out to examine the potential involvement of CDP in modulating the activity of the human CMV IE promoter.…”

“…Furthermore, a possible involvement of Brn-3a in the pathogenesis of HSV has also been suggested (21). The silencer CDP, the mammalian homolog of the Drosophila CUT protein and a homeoprotein, negatively regulates HPV-dependent transcription by binding to specific DNA elements located in the viral promoters and long control regions, thus repressing HPV replication (22)(23)(24). In addition, CDP has been shown to block the transcription of mouse mammary tumor viruses through binding to the negative regulatory regions located in the long terminal repeats of mouse mammary tumor virus (25-27).…”