Cell-type specific transcriptional activities among different papillomavirus long control regions and their regulation by E2

Ottinger, Matthias; Smith, Jennifer A.; Schweiger, Michal-Ruth; Robbins, Dana; Powell, M; You, Jianxin; Howley, Peter M.

doi:10.1016/j.virol.2009.09.027

Cited by 23 publications

(30 citation statements)

References 67 publications

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“…The initial screen used C33A cells, an HPV-negative human cervical carcinoma cell line engineered to stably express FLAG-HA-tagged bovine PV1 (BPV1) E2 from a bicistronic mRNA that also encodes the IL2 receptor α subunit (IL2Rα) (26,27). An E2-repressible reporter in which luciferase expression is controlled by the HPV18 LCR was introduced into these cells, and single cell clones were isolated and characterized (28). Transfection with siRNAs targeting BPV1 E2 resulted in a reduction of E2 protein below detection levels and a 7-to 11-fold increase in luciferase activity (Fig.…”

Section: Resultsmentioning

confidence: 99%

Genome-wide siRNA screen identifies SMCX, EP400, and Brd4 as E2-dependent regulators of human papillomavirus oncogene expression

Smith

White

Sowa

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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140

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An essential step in the pathogenesis of human papillomavirus (HPV)-associated cancers is the dysregulated expression of the viral oncogenes. The papillomavirus E2 protein can silence the long control region (LCR) promoter that controls viral E6 and E7 oncogene expression. The mechanisms by which E2 represses oncogene expression and the cellular factors through which E2 mediates this silencing are largely unknown. We conducted an unbiased, genome-wide siRNA screen and series of secondary screens that identified 96 cellular genes that contribute to the repression of the HPV LCR. In addition to confirming a role for the E2-binding bromodomain protein Brd4 in E2-mediated silencing, we identified a number of genes that have not previously been implicated in E2 repression, including the demethylase JARID1C/SMCX as well as EP400, a component of the NuA4/TIP60 histone acetyltransferase complex. Each of these genes contributes independently and additively to E2-mediated silencing, indicating that E2 functions through several distinct cellular complexes to repress E6 and E7 expression.P apillomaviruses infect squamous epithelial cells and cause a variety of epithelial lesions (1). A subset of the more than 140 human papillomavirus (HPV) types infect mucosal squamous epithelia, including that of the anogenital tract; these are classified as either low-risk or high-risk, depending on the lesions associated with infection. Infections with high-risk HPVs (i.e., HPV16 or HPV18) cause squamous intraepithelial lesions that can progress to cancer, most notably cervical cancer. HPV is considered the major cause of human cervical cancer, the second most common cancer in women worldwide (2).The viral proteins E6 and E7 account for the oncogenic potential of high-risk HPVs in part through their ability to target and degrade p53 and Rb, respectively (1). The long control region (LCR) is the upstream enhancer and promoter region that drives transcription of E6 and E7. An early step in cervical carcinogenesis frequently involves the integration of HPV DNA into cellular chromosomes in a manner that disrupts the E1 and/or E2 ORF (3-6). Because E2 is capable of repressing expression from the LCR, its loss leads to the increased, dysregulated expression of the HPV oncogenes E6 and E7 (7-9). Expression of E2 in HPVpositive cervical cancer cells causes a growth arrest and senescence (10, 11) due to E2-mediated repression of E6 and E7 expression (12, 13). The E2 protein consists of an N-terminal transactivation domain and a C-terminal DNA binding and dimerization domain (14, 15). The E2 proteins from different papillomavirus types are well conserved both functionally and at the amino acid level. The mucosal HPV LCRs contain four E2 binding sites (E2BS) and it has been hypothesized that E2 binding to the two promoter proximal binding sites within the LCRs competes with the binding of cellular transcription factors Sp1 and TBP at the promoter (16,17). Yet, this steric hindrance model cannot fully explain E2-mediated transcriptional silencing; f...

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Section: Resultsmentioning

confidence: 99%

Genome-wide siRNA screen identifies SMCX, EP400, and Brd4 as E2-dependent regulators of human papillomavirus oncogene expression

Smith

White

Sowa

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

140

149

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“…We chose to use the HPV-18 LCRcontrolled reporter in C33A cells because this cell line is known to support both E2-and E8 E2C-dependent repression of the HPV-18 LCR (Fig. 1B) (40). Single clones were isolated and characterized.…”

Section: Resultsmentioning

confidence: 99%

NCoR1 Mediates Papillomavirus E8^E2C Transcriptional Repression

Powell

Smith

Sowa

et al. 2010

J Virol

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The papillomavirus E2 open reading frame encodes the full-length E2 protein as well as an alternatively spliced product called E8 E2C. E8 E2C has been best studied for the high-risk human papillomaviruses, where it has been shown to regulate viral genome levels and, like the full-length E2 protein, to repress transcription from the viral promoter that directs the expression of the viral E6 and E7 oncogenes. The repression function of E8 E2C is dependent on the 12-amino-acid N-terminal sequence from the E8 open reading frame (ORF). In order to understand the mechanism by which E8 E2C mediates transcriptional repression, we performed an unbiased proteomic analysis from which we identified six high-confidence candidate interacting proteins (HCIPs) for E8 E2C; the top two are NCoR1 and TBLR1. We established an interaction of E8 E2C with an NCoR1/HDAC3 complex and demonstrated that this interaction requires the wild-type E8 open reading frame. Small interfering RNA (siRNA) knockdown studies demonstrated the involvement of NCoR1/HDAC3 in the E8 E2C-dependent repression of the viral long control region (LCR) promoter. Additional genetic work confirmed that the papillomavirus E2 and E8 E2C proteins repress transcription through distinct mechanisms.Papillomaviruses (PVs) infect the squamous epithelia, inducing proliferative lesions. The PV life cycle is tightly linked with the squamous cell differentiation program. In particular, late viral gene synthesis, genome amplification, and virion production occur with the progression of epithelial cell differentiation.The PVs are small DNA viruses that contain approximately 10 open reading frames (ORFs). Like those of many viruses, PV regulatory proteins are multifunctional. The E2 ORF encodes several viral products (21). The full-length E2 protein is the most studied; it is a prototypic transcription factor, with a C-terminal DNA binding and dimerization domain, an internal hinge region, and an N-terminal "transactivation" domain (34). Initially, E2 was characterized as a transcriptional activator, and subsequently, it was shown to be a potent repressor of the long control region (LCR), which is the viral promoter that controls E6 and E7 expression (21). In addition to its transcriptional activities, E2 functions in concert with the viral E1 helicase to initiate replication of the viral DNA (21). Also, the E2 protein is involved in tethering viral genomes to the host chromatin for maintenance during mitosis (23, 50). Both the C-terminal portion of E2 (E2C), which mediates dimerization and recognition of consensus E2-binding sequences (ACCN 6 GGT) within the viral LCR, and the N terminus of E2 are required for its various transcription, replication, and genome maintenance activities (9,13,21,33,35,38,45,64).In addition to full-length E2, PVs encode an alternatively spliced product of E2 called E8 E2C. This protein contains 12 amino acids from the E8 ORF fused to the C-terminal DNA binding/dimerization domain of E2 (E2C). To date, E8 E2C transcripts have been detected for bovine ...

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“…It is thought that the individual cell type characteristics determine the fate of any given HPV infection. The pattern of viral gene expression may vary depending on the cell type, which might ultimately result in different outcomes [161]. The currently existing model argues that productive viral life cycles are likely to be completed at the ectocervix, while a collapse of the viral life cycle or incomplete infection is more likely to occur at the endocervix [154].…”

Section: High Risk α-Hpv Infections At Different Anatomical Sitesmentioning

confidence: 99%

Functional Roles of E6 and E7 Oncoproteins in HPV-Induced Malignancies at Diverse Anatomical Sites

Tomaić

2016

Cancers

155

138

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Approximately 200 human papillomaviruses (HPVs) infect human epithelial cells, of which the alpha and beta types have been the most extensively studied. Alpha HPV types mainly infect mucosal epithelia and a small group of these causes over 600,000 cancers per year worldwide at various anatomical sites, especially anogenital and head-and-neck cancers. Of these the most important is cervical cancer, which is the leading cause of cancer-related death in women in many parts of the world. Beta HPV types infect cutaneous epithelia and may contribute towards the initiation of non-melanoma skin cancers. HPVs encode two oncoproteins, E6 and E7, which are directly responsible for the development of HPV-induced carcinogenesis. They do this cooperatively by targeting diverse cellular pathways involved in the regulation of cell cycle control, of apoptosis and of cell polarity control networks. In this review, the biological consequences of papillomavirus targeting of various cellular substrates at diverse anatomical sites in the development of HPV-induced malignancies are highlighted.

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Cell-type specific transcriptional activities among different papillomavirus long control regions and their regulation by E2

Cited by 23 publications

References 67 publications

Genome-wide siRNA screen identifies SMCX, EP400, and Brd4 as E2-dependent regulators of human papillomavirus oncogene expression

Genome-wide siRNA screen identifies SMCX, EP400, and Brd4 as E2-dependent regulators of human papillomavirus oncogene expression

NCoR1 Mediates Papillomavirus E8^E2C Transcriptional Repression

Functional Roles of E6 and E7 Oncoproteins in HPV-Induced Malignancies at Diverse Anatomical Sites

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