Identification of DNA-protein interactions and enhancer activity at the 5' end of the upstream regulatory region in human papillomavirus type 11

Preclinical Models of Laryngeal Papillomavirus Infection: A Scoping Review

OBJECTIVE

Laryngeal human papillomavirus (HPV) infection causes recurrent respiratory papillomatosis (RRP) and accounts for up to 25% of laryngeal cancers. Lack of satisfactory preclinical models is one reason that treatments for these diseases are limited. We sought to assess the literature describing preclinical models of laryngeal papillomavirus infection.

DATA SOURCES

PubMed, Web of Science, and Scopus were searched from the inception of database through October 2022.

REVIEW METHODS

Studies searched were screened by two investigators. Eligible studies were peer-reviewed, published in English, presented original data, and described attempted models of laryngeal papillomavirus infection. Data examined included type of papillomavirus, infection model, and results including success rate, disease phenotype, and viral retention.

RESULTS

After screening 440 citations and 138 full-text studies, 77 studies published between 1923 and 2022 were included. Models used low-risk HPV or RRP (n = 51 studies), high-risk HPV or laryngeal cancer (n = 16), both low- and high-risk HPV (n = 1), and animal papillomaviruses (n = 9). For RRP, 2D and 3D cell culture models and xenografts retained disease phenotypes and HPV DNA in the short term. Two laryngeal cancer cell lines were consistently HPV-positive in multiple studies. Animal laryngeal infections with animal papillomaviruses resulted in disease and long-term retention of viral DNA.

CONCLUSIONS

Laryngeal papillomavirus infection models have been researched for 100 years and primarily involve low-risk HPV. Most models lose viral DNA after a short duration. Future work is needed to model persistent and recurrent diseases, consistent with RRP and HPV-positive laryngeal cancer.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:3256-3268, 2023.

SV40 T-Antigen Amino Acid Changes that Disrupt Cul-7 or Bub-1 Binding Do Not Globally Distort the T-Common Region

BACKGROUND

Amino acids 1-107 of the SV40 T antigen constitute a functionally important and complex region. Cellular proteins, Hsc70, Bub-1, Cul-7, and Rb, each of which is involved in cell growth control or genomic stability, bind within this portion of the T antigen. Mutational analysis has mapped the J domain/Hsc70, Bub-1, and the Rb binding motifs. Two regions of the T antigen have been implicated in Cul-7 binding. Mutation of F98A diminished Cul-7 binding, and deletion of amino acids 68-83 abolished it. The authors suggest, based on T-antigen structure, that F98 is inaccessible and that the F98A change altered the configuration of the upstream region, preventing Cul-7 binding. Our objective was to determine, by using monoclonal T-antigen antibodies, whether F98 is accessible and whether F98A substitution globally distorted the T-common region.

METHODS

Cell-expressing T antigens, immunoprecipitation, and immunoblot were used to determine the accessibility of amino acids.

CONCLUSION

Full-length T-antigen and N-terminal fragments containing F98A were immunoprecipitated by monoclonal antibody PAb902, which recognizes a conformation-dependent epitope within the first 82 amino acids. Therefore, this alteration does not globally distort the entire T-common region. Additionally, PAb416, which displaces Cul-7 from the T antigen and immunoprecipitates bound pRb peptides, depends on F98 for binding, implying that amino acid 98 is part of the epitope and accessible in the native T antigen.

Transcriptional activity of human papillomavirus type 16 variants having deletions in the long control region

Transcription of the E6 and E7 viral oncogenes of human papillomavirus (HPV) type 16 is regulated by the P97 major early promoter, and enhancer and silencer elements found in the long control region (LCR). In this study, we tested the transcriptional activity of natural HPV 16 variants having long deletions in the LCR. The HPV 16 LCR regions were amplified from invasive cervical cancer specimens, and cloned into the reporter vector pALuc. Transcriptional activity of the different clones was measured by luciferase test after transient transfection into HeLa cells. The deletions found in the LCR encompassed parts of the enhancer and either the YY1-specific silencer alone or together with the CDP-specific silencer. The transcriptional activity of these deletion variants were usually reduced compared with that of the corresponding full-length clones. However, a deletion variant lacking the whole enhancer and both silencer regions retained substantial enhancer activity on the P97 promoter. These results point to the existence of a novel context-dependent enhancer element in the 5' LCR of HPV 16.

The human papillomavirus type 11 upstream regulatory region triggers hair-follicle-specific gene expression in transgenic mice

We have generated transgenic mice carrying the URR of the human papillomavirus type 11 ligated in front of the Escherichia coli beta-galactosidase coding region sequence. Using X-Gal staining to demonstrate beta-galactosidase production, we observed a hair-specific transcription of the reporter gene. This transcription was limited to the epithelial cells of the hair bulge region. The transgene was developmentally regulated, as no LacZ staining was demonstrated during embryogenesis and specific staining was first observed after birth. Surprisingly, dexamethasone and ultraviolet B, but not phorbol myristate acetate or progesterone treatment of the animals resulted in an increase in number and intensity of hair follicles expressing the reporter gene.

Evidence for the separate regulation of the human papillomavirus type 11 E7 and E6 promoters by Viral cis sequences near the E6 promoter

The human papillomavirus type 11 (HPV-11) E7 protein can modulate host cell functions and is required for papilloma formation, but little is known concerning the regulation of its expression. This study was designed to determine whether the viral upstream regulatory region controlled expression from the E7 promoter and whether cis sequences differentially regulated E6 and E7 expression in laryngeal mucosal keratinocytes, the natural target cells for this virus. Reporter constructs were designed to study expression of the luciferase gene from the HPV-11 E7 promoter in its natural position downstream of a functional E6 promoter. E7 expression, like E6 expression, required upstream regulatory sequences. However, E7 expression was less sensitive to repression by viral E2 protein and to mutation of the Spl binding site adjacent to the E2 binding site. Moreover, there was differential sensitivity of the two promoters to mutation of the E6 TATA box, with E7 expression more affected than E6 expression. These findings show that, in the normal host cells for this virus, the E6 and E7 promoters can be independently regulated by the cis regulatory region adjacent to the E6 promoter.

CCAAT displacement protein, a regulator of differentiation-specific gene expression, binds a negative regulatory element within the 5' end of the human papillomavirus type 6 long control region

We have reported previously that a 636-bp fragment spanning the 5' two-thirds of the human papillomavirus type 6 (HPV6)-W50 long control region (LCR) functions as a transcriptional silencer (A. Farr, S. Pattison, B.-S. Youn, and A. Roman, J. Gen. Virol. 76:827-835, 1995). We have utilized nested deletion analyses to implicate a 66-bp sequence which appears to be critical for this activity. A comparison of the transcriptional regulatory activities of the LCRs of HPV6-W50 and HPV6b (which has a 94-bp deletion, resulting in the elimination of the 66-bp sequence) indicates that sequences within the 94-bp region negatively regulate the activity of the intact HPV6 LCR. Two sequence-specific DNA-protein interactions were visualized via electrophoretic mobility shift assays. One of the binding events is mediated by the transcriptional repressor CCAAT displacement protein (CDP), a factor which is active in undifferentiated cells but inactive in terminally differentiated cells. This conclusion is based on the following three lines of evidence: (i) a consensus CDP binding site oligonucleotide serves as a competitor in band shift assays, (ii) the band shift complex is not seen when a CDP-negative nuclear extract is used, and (iii) anti-CDP antiserum specifically inhibits the binding. These studies identify a DNA-protein interaction occurring within the 5' end of the LCR which may be important in maintaining the tight link between keratinocyte differentiation and HPV gene expression.

C/EBPbeta is a negative regulator of human papillomavirus type 11 in keratinocytes

We have evaluated the impact of the CCAAT enhancer-binding protein (C/EBP) transcription factors on human papillomavirus type 11 (HPV11). C/EBPbeta is in nuclei of cultured foreskin keratinocytes and binds its consensus sequence in HPV11 DNA. We have used the novel approach of depleting the availability of C/EBPs in vivo using nuclease-resistant oligomers containing C/EBP DNA binding sites. In cultured foreskin keratinocytes containing replicating HPV11 DNA, levels of both HPV11 transcripts and HPV DNA increase after treatment with oligomers; containing the C/EBPbeta DNA binding motif. These results indicate that C/EBPbeta is a repressor for HPV11 in keratinocytes.

A key DNA-protein interaction determines the function of the 5'URR enhancer in human papillomavirus type 11

The 5' end of the upstream regulatory region (URR) of human papillomavirus type 11 (HPV-11) has enhancer function and binds cellular proteins. We have determined that one particular motif, a CCNGTNAC pair, is both necessary and sufficient for enhancer activity. This enhancement of expression can be competed in vivo by concatenated double-stranded oligonucleotides, indicating that protein-DNA binding is a requisite for enhancer activity. A 41-kDa protein, present in all epithelial cells assayed, binds to this enhancer motif. The 5'URR fragment functions as an enhancer both in primary keratinocytes from a variety of body sites and in fibroblasts. We conclude that tissue specificity is not a feature of this enhancer, and that the 41-kDa binding protein is ubiquitous. These data provide evidence that the 5'URR enhancer activity is dependent on only a few sequences and perhaps only one protein.

Human papillomavirus type 6 long control region and human cellular DNA contain related sequences

We have identified a region of human papillomavirus type 6 (HPV-6) DNA that hybridizes with human cellular DNA containing no detectable HPV DNA sequences. The region of hybridization has been localized to a segment of the viral long control region between the end of the L1 open reading frame and the late polyadenylation signal and is likely contained within a 94-base-pair insertion at nucleotide 7350 which is present in the cloned HPV-6b DNA used for these studies. Restriction fragments of HPV-6 DNA from seven patients suggested that this insert was present in these naturally occurring viral genomes as well. The presence of this insert was confirmed by direct sequence analysis of polymerase chain reaction-amplified segments from four naturally occurring HPV-6 genomes. By analogy with other systems, this insert and surrounding sequences may function to destabilize the HPV-6 late mRNA.