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...
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 ...
The histone acetyltransferase TIP60 regulates the DNA damage response following genotoxic stress by acetylating histone and remodeling chromatin. However, the molecular mechanisms underlying the TIP60-dependent response to UV-induced DNA damage remain poorly understood. To systematically analyse proteins that regulate TIP60 activity in response to UV irradiation, we performed a proteomic analysis of proteins selectively bound to TIP60 in response to UV irradiation using mass spectrometry and identified a novel regulatory mechanism by which TIP60 orchestrates transcriptional activation of p53-dependent checkpoint response in UV-irradiated cells. The initial step of this pathway involves UV-induced association of TIP60 with SUMO-conjugation enzymes and site-specific sumoylation of TIP60 at lysines 430 and 451 via Ubc9. This sumoylation initiates the relocation of TIP60 from nucleoplasm to the promyelocytic leukemia body, which is essential for the UV-irradiated DNA damage repair response via a p53-dependent pathway. Significantly, inhibition of TIP60 sumoylation by overexpression of non-sumoylatable mutant abrogates the p53-dependent DNA damage response, demonstrating the importance of TIP60 sumoylation in response to UV irradiation. Our biochemical characterization demonstrated that the sumoylation of TIP60 augments its acetyltransferase activity in vitro and in vivo. Thus, this study shed new light on the function and regulation of TIP60 activity in UV-irradiated DNA damage response.
This study systematically examined the viral long control region (LCR) activities and their responses to E2 for human papillomavirus (HPV) types 11. 16 and 18 as well as bovine papillomavirus 1 (BPV1) in a number of different cell types, including human cervical cancer cell lines, human oral keratinocytes, BJ fibroblasts, as well as CV1 cells. The study revealed cell- and virus-type specific differences among the individual LCRs and their regulation by E2. In addition, the integration of the LCR into the host genome was identified as a critical determinant for LCR activity and its response to E2. Collectively, these data indicate a more complex level of transcriptional regulation of the LCR by cellular and viral factors than previously appreciated, including a comparatively low LCR activity and poor E2 responsive for HPV16 in most human cells. This study should provide a valuable framework for future transcriptional studies in the papillomavirus field.
We describe and validate a new gene ratio based test for the diagnosis of prostate cancer, which was developed from the analysis of extensive gene profiling data for the diagnosis of prostate cancer. This test can be easily adapted to the clinical arena without the need for complex computer software or hardware. We anticipate that the gene ratio based diagnosis of prostate cancer using fine needle aspirations could serve as a useful adjunct to standard histopathological techniques.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.