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Romero-Masters JC, Lambert PF, Munger K. Molecular Mechanisms of MmuPV1 E6 and E7 and Implications for Human Disease. Viruses 2022; 14:2138. [PMID: 36298698 PMCID: PMC9611894 DOI: 10.3390/v14102138] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 11/16/2022] Open
Abstract
Human papillomaviruses (HPVs) cause a substantial amount of human disease from benign disease such as warts to malignant cancers including cervical carcinoma, head and neck cancer, and non-melanoma skin cancer. Our ability to model HPV-induced malignant disease has been impeded by species specific barriers and pre-clinical animal models have been challenging to develop. The recent discovery of a murine papillomavirus, MmuPV1, that infects laboratory mice and causes the same range of malignancies caused by HPVs provides the papillomavirus field the opportunity to test mechanistic hypotheses in a genetically manipulatable laboratory animal species in the context of natural infections. The E6 and E7 proteins encoded by high-risk HPVs, which are the HPV genotypes associated with human cancers, are multifunctional proteins that contribute to HPV-induced cancers in multiple ways. In this review, we describe the known activities of the MmuPV1-encoded E6 and E7 proteins and how those activities relate to the activities of HPV E6 and E7 oncoproteins encoded by mucosal and cutaneous high-risk HPV genotypes.
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Affiliation(s)
- James C. Romero-Masters
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705, USA
| | - Paul F. Lambert
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705, USA
| | - Karl Munger
- Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, MA 02111, USA
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Brimer N, Vande Pol S. Human papillomavirus type 16 E6 induces cell competition. PLoS Pathog 2022; 18:e1010431. [PMID: 35320322 PMCID: PMC8979454 DOI: 10.1371/journal.ppat.1010431] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Revised: 04/04/2022] [Accepted: 03/10/2022] [Indexed: 11/18/2022] Open
Abstract
High-risk human papillomavirus (HPV) infections induce squamous epithelial tumors in which the virus replicates. Initially, the virus-infected cells are untransformed, but expand in both number and area at the expense of uninfected squamous epithelial cells. We have developed an in vitro assay in which colonies of post-confluent HPV16 expressing cells outcompete and displace confluent surrounding uninfected keratinocytes. The enhanced colony competition induced by the complete HPV16 genome is conferred by E6 expression alone, not by individual expression of E5 or E7, and requires E6 interaction with p53. E6-expressing keratinocytes undermine and displace adjacent normal keratinocytes from contact with the attachment substrate, thereby expanding the area of the E6-expressing colony at the expense of normal keratinocytes. These new results separate classic oncogenicity that is primarily conferred by HPV16 E7 from cell competition that we show is primarily conferred by E6 and provides a new biological role for E6 oncoproteins from high-risk human papillomaviruses. Microbial infections can change the fate and behavior of normal vertebrate cells to resemble oncogenic cells. High-risk papillomaviruses induce infected squamous epithelial cells to form tumors, some of which evolve into malignancies. The present work shows that the enhanced competitiveness of HPV16-infected cells for the basal cell surface is primarily due to the expression of the E6 oncoprotein and not the E7 or E5 oncoproteins. Compared to normal keratinocytes, E6 induces a super-competitor phenotype while E5 and E7 do not. This work shows the importance of measuring oncoprotein traits not only as cell autonomous traits, but in the context of competition with uninfected cells and shows the potential of papillomavirus oncoproteins to be novel genetic probes for the analysis of cell competition.
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Affiliation(s)
- Nicole Brimer
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Scott Vande Pol
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
- * E-mail:
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3
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Drews CM, Brimer N, Vande Pol SB. Multiple regions of E6AP (UBE3A) contribute to interaction with papillomavirus E6 proteins and the activation of ubiquitin ligase activity. PLoS Pathog 2020; 16:e1008295. [PMID: 31971989 PMCID: PMC6999913 DOI: 10.1371/journal.ppat.1008295] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 02/04/2020] [Accepted: 12/25/2019] [Indexed: 12/23/2022] Open
Abstract
The HECT domain E3 ubiquitin ligase E6AP (UBE3A) is critical for the development of human papillomavirus (HPV) associated cancers, the neurodevelopment disorder Angelman Syndrome, and some cases of autism spectrum disorders. How E6AP recognizes its cellular targets and how its ubiquitin ligase activity is triggered remain poorly understood, and HPV E6 proteins are models for these processes. We examined diverse E6 proteins from human and non-human papillomaviruses and identified two different modes of interaction between E6 and E6AP. In Type I interactions, E6 can interact directly with the LXXLL peptide motif alone of E6AP (isolated from the rest of E6AP), and then recruit cellular substrates such as p53. In Type II interactions, E6 proteins require additional auxiliary regions of E6AP in either the amino terminus or in the carboxy-terminal HECT domain to interact with the LXXLL peptide motif of E6AP. A region of E6AP amino-terminal to the LXXLL peptide motif both augments association with E6 proteins and is required for E6 proteins to trigger ubiquitin ligase activity in the carboxy-terminal HECT ubiquitin ligase domain of E6AP. In Type I interactions, E6 can associate with E6AP and recruit p53, but a Type II interaction is required for the degradation of p53 or NHERF1. Interestingly, different E6 proteins varied in E6AP auxiliary regions that contributed to enhanced association, indicating evolutionary drift in the formation of Type II interactions. This classification of E6-E6AP interaction types and identification of a region in the E6AP amino terminus that is important for both E6 association and stimulation of ubiquitin ligase activity will inform future structural data of the E6-E6AP complex and future studies aiming to interfere with the activity of the E6-E6AP complex.
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Affiliation(s)
- Camille M. Drews
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Nicole Brimer
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Scott B. Vande Pol
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
- * E-mail:
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Brimer N, Drews CM, Vande Pol SB. Association of papillomavirus E6 proteins with either MAML1 or E6AP clusters E6 proteins by structure, function, and evolutionary relatedness. PLoS Pathog 2017; 13:e1006781. [PMID: 29281732 PMCID: PMC5760104 DOI: 10.1371/journal.ppat.1006781] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 01/09/2018] [Accepted: 11/29/2017] [Indexed: 01/11/2023] Open
Abstract
Papillomavirus E6 proteins bind to LXXLL peptide motifs displayed on targeted cellular proteins. Alpha genus HPV E6 proteins associate with the cellular ubiquitin ligase E6AP (UBE3A), by binding to an LXXLL peptide (ELTLQELLGEE) displayed by E6AP, thereby stimulating E6AP ubiquitin ligase activity. Beta, Gamma, and Delta genera E6 proteins bind a similar LXXLL peptide (WMSDLDDLLGS) on the cellular transcriptional co-activator MAML1 and thereby repress Notch signaling. We expressed 45 different animal and human E6 proteins from diverse papillomavirus genera to ascertain the overall preference of E6 proteins for E6AP or MAML1. E6 proteins from all HPV genera except Alpha preferentially interacted with MAML1 over E6AP. Among animal papillomaviruses, E6 proteins from certain ungulate (SsPV1 from pigs) and cetacean (porpoises and dolphins) hosts functionally resembled Alpha genus HPV by binding and targeting the degradation of E6AP. Beta genus HPV E6 proteins functionally clustered with Delta, Pi, Tau, Gamma, Chi, Mu, Lambda, Iota, Dyokappa, Rho, and Dyolambda E6 proteins to bind and repress MAML1. None of the tested E6 proteins physically and functionally interacted with both MAML1 and E6AP, indicating an evolutionary split. Further, interaction of an E6 protein was insufficient to activate degradation of E6AP, indicating that E6 proteins that target E6AP co-evolved to separately acquire both binding and triggering of ubiquitin ligase activation. E6 proteins with similar biological function clustered together in phylogenetic trees and shared structural features. This suggests that the divergence of E6 proteins from either MAML1 or E6AP binding preference is a major event in papillomavirus evolution.
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Affiliation(s)
- Nicole Brimer
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Camille M. Drews
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Scott B. Vande Pol
- Department of Pathology, University of Virginia, Charlottesville, Virginia, United States of America
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5
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Lace MJ, Ushikai M, Yamakawa Y, Anson JR, Ishiji T, Turek LP, Haugen TH. The truncated C-terminal E2 (E2-TR) protein of bovine papillomavirus (BPV) type-1 is a transactivator that modulates transcription in vivo and in vitro in a manner distinct from the E2-TA and E8^E2 gene products. Virology 2012; 429:99-111. [DOI: 10.1016/j.virol.2012.03.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 01/09/2012] [Accepted: 03/30/2012] [Indexed: 10/28/2022]
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6
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You J, Schweiger MR, Howley PM. Inhibition of E2 binding to Brd4 enhances viral genome loss and phenotypic reversion of bovine papillomavirus-transformed cells. J Virol 2006; 79:14956-61. [PMID: 16282494 PMCID: PMC1287565 DOI: 10.1128/jvi.79.23.14956-14961.2005] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The bovine papillomavirus E2 protein tethers the viral genomes to mitotic chromosomes in dividing cells through binding to the C-terminal domain (CTD) of Brd4. Expression of the Brd4-CTD competes the binding of E2 to endogenous Brd4 in cells. Here we extend our previous study that identified Brd4 as the E2 mitotic chromosome receptor to show that Brd4-CTD expression released the viral DNA from mitotic chromosomes in BPV-1 transformed cells. Furthermore, stable expression of Brd4-CTD enhanced the frequency of morphological reversion of BPV-1 transformed C127 cells resulting in the complete elimination of the viral DNA in the resulting flat revertants.
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Affiliation(s)
- Jianxin You
- Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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7
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Huh KW, DeMasi J, Ogawa H, Nakatani Y, Howley PM, Münger K. Association of the human papillomavirus type 16 E7 oncoprotein with the 600-kDa retinoblastoma protein-associated factor, p600. Proc Natl Acad Sci U S A 2005; 102:11492-7. [PMID: 16061792 PMCID: PMC1182135 DOI: 10.1073/pnas.0505337102] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The human papillomavirus type 16 (HPV-16) E7 gene encodes a multifunctional oncoprotein that can subvert multiple cellular regulatory pathways. The best-known cellular targets of the HPV-16 E7 oncoprotein are the retinoblastoma tumor suppressor protein pRB and the related pocket proteins p107 and p130. However, there is ample evidence that E7 has additional cellular targets that contribute to its transforming potential. We isolated HPV-16 E7 associated cellular protein complexes by tandem affinity purification and mass spectrometry and identified the 600-kDa retinoblastoma protein associated factor, p600, as a cellular target of E7. Association of E7 with p600 is independent of the pocket proteins and is mediated through the N terminal E7 domain, which is related to conserved region 1 of the adenovirus E1A protein and importantly contributes to cellular transformation independent of pRB binding. Depletion of p600 protein levels by RNA interference substantially decreased anchorage-independent growth in HPV-positive and -negative human cancer cells. Therefore, p600 is a cellular target of E7 that regulates cellular pathways that contribute to anchorage-independent growth and cellular transformation.
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Affiliation(s)
- Kyung-Won Huh
- The Channing Laboratory, Brigham and Women's Hospital and Department of Medicine, Harvard Medical School, Boston, MA 02115, USA
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8
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Princler GL, Julias JG, Hughes SH, Derse D. Roles of viral and cellular proteins in the expression of alternatively spliced HTLV-1 pX mRNAs11The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. Virology 2003; 317:136-45. [PMID: 14675632 DOI: 10.1016/j.virol.2003.09.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The human T cell leukemia virus type 1 (HTLV-1) genome contains a cluster of at least five open reading frames (ORFs) near the 3' terminus within the pX region. The pX ORFs are encoded by mono- or bicistronic mRNAs that are generated by alternative splicing. The various pX mRNAs result from skipping of the internal exon (2-exon versus 3-exon isofoms) or from the utilization of alternative splice acceptor sites in the terminal exon. The Rex and Tax proteins, encoded by ORFs X-III and X-IV, have been studied intensively and are encoded by the most abundant of the alternative 3-exon mRNAs. The protein products of the other pX ORFs have not been detected in HTLV-1-infected cell lines and the levels of the corresponding mRNAs have not been accurately established. We have used real-time RT-PCR with splice-site specific primers to accurately measure the levels of individual pX mRNA species in chronically infected T cell lines. We have asked whether virus regulatory proteins or ectopic expression of cellular factors influence pX mRNA splicing in cells that were transfected with HTLV-1 provirus clones. In chronically infected cell lines, the pX-tax/rex mRNA was present at 500- to 2500-fold higher levels than the pX-tax-orfII mRNA and at approximately 1000-fold higher levels than pX-rex-orfI mRNA. Chronically infected cell lines that contain numerous defective proviruses expressed 2-exon forms of pX mRNAs at significantly higher levels compared to cell lines that contain a single full-length provirus. Cells transfected with provirus expression plasmids expressed similar relative amounts of 3-exon pX mRNAs but lower levels of 2-exon mRNA forms compared to cells containing a single, full-length provirus. The pX mRNA expression patterns were nearly identical in cells transfected with wild-type, Tax-minus, or Rex-minus proviruses. Cotransfection of cells with HTLV-1 provirus in combination with SF2/ASF expression plasmid resulted in a relative increase in pX-tax/rex mRNA compared to pX-tax-orfII and pX-rex-orfI mRNAs, but did not affect exon skipping. Ectopic expression of hnRNP A1 did not affect pX splice site utilization, but increased exon skipping, as the level of pX-p21rex mRNA was increased by almost 10-fold.
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Affiliation(s)
- Gerald L Princler
- Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
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9
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Fan X, Liu Y, Chen JJ. Activation of c-Myc contributes to bovine papillomavirus type 1 E7-induced cell proliferation. J Biol Chem 2003; 278:43163-8. [PMID: 12937171 DOI: 10.1074/jbc.m306008200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inactivation of the tumor suppressor pRB by the human papillomavirus (HPV) oncoprotein E7 is a mechanism by which HPV promotes cell growth. The bovine papillomavirus type 1 (BPV-1) E7 does not bind pRB efficiently yet is required for full transformation of murine cells by BPV-1. In the present study, we investigated the mechanism of BPV-1 E7-induced cell proliferation. Our studies indicate that expression of BPV-1 E7 induces DNA synthesis and stimulates cells to enter S phase in quiescent cells. The induction of cell proliferation by BPV-1 E7 can occur in the retinoblastoma gene (Rb)-null cells, suggesting an Rb-independent mechanism. Consistent with this observation, BPV-1 E7 does not efficiently activate the transcription of the E2F family of transcription factors (E2F)-responsive promoters. Notably, c-Myc is able to induce cells to enter S phase in quiescent cells through an Rb/E2F-independent pathway. Significantly, c-Myc levels are increased in BPV-1 E7-expressing cells. Moreover, expression of a dominant negative c-Myc mutant inhibited BPV-1 E7-induced DNA synthesis. Consistent with the notion that c-Myc could down-regulate p27 and activate Cdk2, p27 level is decreased while both cyclin A and cyclin E-associated kinase activities are up-regulated in BPV-1 E7-expressing cells. These studies indicate an important role for c-Myc in BPV-1 E7-induced cell proliferation.
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Affiliation(s)
- Xueli Fan
- Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605-2324, USA
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10
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Hartley KA, Alexander KA. Human TATA binding protein inhibits human papillomavirus type 11 DNA replication by antagonizing E1-E2 protein complex formation on the viral origin of replication. J Virol 2002; 76:5014-23. [PMID: 11967317 PMCID: PMC136168 DOI: 10.1128/jvi.76.10.5014-5023.2002] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The human papillomavirus (HPV) protein E2 possesses dual roles in the viral life cycle. By interacting directly with host transcription factors in basal keratinocytes, E2 promotes viral transcription. As keratinocyte differentiation progresses, E2 associates with the viral helicase, E1, to activate vegetative viral DNA replication. How E2's major role switches from transcription to replication during keratinocyte differentiation is not understood, but the presence of a TATA site near the viral origin of replication led us to hypothesize that TATA-binding protein (TBP) could affect HPV replication. Here we show that the C-terminal domain of TBP (TBPc) is a potent inhibitor of E2-stimulated HPV DNA replication in vitro (50% inhibitory concentration = 0.56 nM). Increasing the E1 concentration could not overcome TBPc inhibition in replication assays, indicating that TBPc is a noncompetitive inhibitor of E1 binding. While direct E2-TBPc association could be demonstrated, this interaction could not fully account for the mechanism of TBPc-mediated inhibition of viral replication. Because E2 supports sequence-specific binding of E1 to the viral ori, we proposed that TBPc antagonizes E1-ori association indirectly through inhibition of E2-DNA binding. Indeed, TBPc potently antagonized E2 binding to DNA in the absence (K(i) = 0.5 +/- 0.1 nM) and presence (K(i) = 0.6 +/- 0.3 nM) of E1. Since E2 and TBPc cannot be coadjacent on viral sequences, direct DNA-binding competition between TBPc and E2 was responsible for replication inhibition. Given the ability of TBPc to inhibit HPV DNA replication in vitro and data indicating that TBPc antagonized E2-ori association, we propose that transcription factors regulate HPV DNA replication as well as viral transcription.
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Affiliation(s)
- Kelly A Hartley
- Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA
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11
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Bohl J, Hull B, Vande Pol SB. Cooperative transformation and coexpression of bovine papillomavirus type 1 E5 and E7 proteins. J Virol 2001; 75:513-21. [PMID: 11119620 PMCID: PMC113944 DOI: 10.1128/jvi.75.1.513-521.2001] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Productively infected bovine fibropapillomas were examined for bovine papillomavirus type 1 (BPV-1) E7 localization. BPV-1 E7 was observed in the cytoplasm of basal and lower spinous epithelial cells, coexpressed in the cytoplasm of basal cells with the E5 oncoprotein. E7 was also observed in nucleoli throughout the basal and spinous layers but not in the granular cell layer. Ectopic expression of E7 in cultured epithelial cells gave rise to localization similar to that seen in productive fibropapillomas, with cytoplasmic and nucleolar expression observed. Consistent with the coexpression of E7 and E5 in basal keratinocytes, BPV-1 E7 cooperated with E5 as well as E6 in an anchorage independence transformation assay. While E5 is expressed in both basal and superficial differentiating keratinocytes, BPV-1 E7 is only observed in basal and lower spinous epithelial cells. Therefore, BPV-1 E7 may serve to modulate the cellular response of basal epithelial cells to E5 expression.
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Affiliation(s)
- J Bohl
- Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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12
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Liu Y, Hong Y, Androphy EJ, Chen JJ. Rb-independent induction of apoptosis by bovine papillomavirus type 1 E7 in response to tumor necrosis factor alpha. J Biol Chem 2000; 275:30894-900. [PMID: 10887172 DOI: 10.1074/jbc.m000640200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bovine papillomavirus type 1 (BPV-1) is a small DNA virus that causes fibropapillomas of the host. BPV-1 has served as the prototype for studies of the molecular biology of the papillomaviruses. BPV-1 efficiently induces anchorage-independent growth and focus formation in murine C127 cells. The transforming properties of BPV-1 primarily reside in two genes, E5 and E6. Each of these genes is sufficient to transform cells. Although no independent transformation activity has been detected for E7, it was shown to be required for full transformation of C127 by BPV-1. We investigated the biological activities of BPV-1 E7 in several assays. Our results indicate that expression of BPV-1 E7 sensitizes cells to tumor necrosis factor alpha (TNF)-induced apoptosis. The TNF-induced apoptosis in E7-expressing cells was accompanied by increased release of arachidonic acid, indicating that phospholipase A(2) was activated. Unlike the E7 proteins from the cancer-related human papillomaviruses, the BPV-1 E7 protein does not associate efficiently with the retinoblastoma protein (pRB) in vitro, nor does it significantly affect the pRB levels in cultured cells. Furthermore, BPV-1 E7 sensitizes Rb-null cells to TNF-induced apoptosis. These studies indicate that BPV-1 E7 can sensitize cells to apoptosis through mechanisms that are independent of pRB.
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Affiliation(s)
- Y Liu
- Department of Dermatology, New England Medical Center and Tufts University School of Medicine and the Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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13
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Parker LM, Harris S, Gossen M, Botchan MR. The bovine papillomavirus E2 transactivator is stimulated by the E1 initiator through the E2 activation domain. Virology 2000; 270:430-43. [PMID: 10793002 DOI: 10.1006/viro.2000.0257] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bovine papillomavirus type 1 (BPV-1) encodes two regulatory proteins, E1 and E2, that are essential for viral replication and transcription. E1, an ATP-dependent helicase, binds to the viral ori and is essential for viral replication, while the viral transcriptional activator, E2, plays cis-dominant roles in both viral replication and transcription. At low reporter concentrations, E1 stimulates E2 enhancer function, while at high reporter concentrations, repression results. An analysis of cis requirements revealed that neither replication nor specific E1-binding sites are required for the initiators' effect on E2 transactivator function. Though no dependence on E1-binding sites was found, analysis of E1 DNA binding and ATPase mutants revealed that both domains are required for E1 modulation of E2. Through the use of E2 fusion-gene constructs we showed that a heterologous DNA-binding domain could be substituted for the E2 DNA-binding domain and this recombinant protein remained responsive to E1. Furthermore, E1 could rescue activation domain mutants of E2 defective for transactivation. These data suggest that E1 stimulation of E2 involves interactions between E1 and the E2 activation domain on DNA. We speculate that E1 may allosterically interact with the E2 activation domain, perhaps stabilizing a particular structure, which increases the enhancer function of E2.
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Affiliation(s)
- L M Parker
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-3204, USA
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14
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Das K, Bohl J, Vande Pol SB. Identification of a second transforming function in bovine papillomavirus type 1 E6 and the role of E6 interactions with paxillin, E6BP, and E6AP. J Virol 2000; 74:812-6. [PMID: 10623743 PMCID: PMC111601 DOI: 10.1128/jvi.74.2.812-816.2000] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Papillomavirus E6 oncoproteins transform mammalian cells through interaction with cellular proteins. Bovine papillomavirus type 1 E6 (BE6) interacts with three previously described cellular targets: the E6AP E3 ubiquitin ligase, the calcium-binding protein E6BP (also known as ERC-55), and paxillin, which is a focal adhesion adapter protein. BE6 interacts strongly with each of these proteins in vitro, binding to similar peptide sequences found in E6AP, E6BP, and paxillin. To determine which BE6 interactions are necessary for transformation by BE6, we used a novel selection strategy for temperature-sensitive BE6 mutants in yeast that could discriminate in their interaction between E6AP, E6BP, and paxillin. All BE6 mutants that retained transforming ability retained association with paxillin, while some mutants that were transformation positive failed to interact with E6AP or E6BP. This study demonstrates that oncogene mutants that are temperature sensitive for transformation can be selected in yeast and that the induction of anchorage-independent cell proliferation by BE6 does not require strong association of BE6 with either E6AP or E6BP. Of particular interest is the identification of a BE6 mutant that interacts strongly with the acidic charged leucine motifs of E6AP, E6BP, and paxillin but is devoid of transformation activity, thereby genetically identifying a second essential transformation function in BE6 that is independent of interaction with acidic charged leucine motifs.
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Affiliation(s)
- K Das
- Institute of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA
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15
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Abstract
Specific types of human papillomaviruses (HPV) are strongly associated with the development of cervical cancer. The E6 gene from cancer-related HPVs has exhibited functions in tumorigenesis, regulation of transcription, telomerase, and apoptosis. Cancer-related HPVs E6 proteins bind the tumor suppressor p53 and promotes its degradation through an ubiquitin-dependent pathway. Several additional cellular E6-binding proteins have recently been identified and implicated in playing roles in p53-independent functions of E6.
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Affiliation(s)
- L Rapp
- Department of Dermatology, New England Medical Center, Boston, MA, USA
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16
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Lepik D, Ilves I, Kristjuhan A, Maimets T, Ustav M. p53 protein is a suppressor of papillomavirus DNA amplificational replication. J Virol 1998; 72:6822-31. [PMID: 9658131 PMCID: PMC109891 DOI: 10.1128/jvi.72.8.6822-6831.1998] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/1998] [Accepted: 05/12/1998] [Indexed: 02/08/2023] Open
Abstract
p53 protein was able to block human and bovine papillomavirus DNA amplificational replication while not interfering with Epstein-Barr virus oriP once-per-cell cycle replication. Oligomerization, intact DNA-binding, replication protein A-binding, and proline-rich domains of the p53 protein were essential for efficient inhibition, while the N-terminal transcriptional activation and C-terminal regulatory domains were dispensable for the suppressor activity of the p53 protein. The inhibition of replication was caused neither by the downregulation of expression of the E1 and E2 proteins nor by cell cycle block or apoptosis. Our data suggest that the intrinsic activity of p53 to suppress amplificational replication of the papillomavirus origin may have an important role in the virus life cycle and in virus-cell interactions.
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Affiliation(s)
- D Lepik
- Department of Microbiology and Virology, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu EE2400, Estonia
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17
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Demeret C, Goyat S, Yaniv M, Thierry F. The human papillomavirus type 18 (HPV18) replication protein E1 is a transcriptional activator when interacting with HPV18 E2. Virology 1998; 242:378-86. [PMID: 9514974 DOI: 10.1006/viro.1997.9023] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human papillomavirus type 18 E1 and E2 proteins are both required for the initiation of viral DNA replication. Whereas E2 is the major viral transcription regulator, E1 is the replication initiator protein. They interact with each other and with the origin sequences to initiate viral DNA replication. We show that the HPV18 E1 and E2 proteins, when bound to an origin sequence cloned upstream of a heterologous promoter, synergistically activate transcription. This synergy required binding of E2 to at least two binding sites, but was partially independent of E1 binding to the origin of replication. Transcriptional activation was observed even in the absence of replication of the target DNA. Only homologous E1 and E2 proteins binding to homologous origin sequences from BPV1 or HPV18 viruses could synergistically activate transcription. We show that the HPV18 E1 protein can activate transcription when targeted to the DNA by fusion of the complete polypeptide with the BPV1 E2 C-terminus dimerization/DNA binding domain, implying that HPV18 E1 is an intrinsic transcriptional activator, though less potent than E2. The interaction between E1 and E2 may form a transcriptionally active complex during initiation of viral DNA replication.
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Affiliation(s)
- C Demeret
- Unité des Virus Oncogènes, U1644, Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
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18
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Ned R, Allen S, Vande Pol S. Transformation by bovine papillomavirus type 1 E6 is independent of transcriptional activation by E6. J Virol 1997; 71:4866-70. [PMID: 9151888 PMCID: PMC191716 DOI: 10.1128/jvi.71.6.4866-4870.1997] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We have generated mutants of bovine papillomavirus type 1 E6 (BE6) that are defective for transcriptional activation and have analyzed these mutants for transformation of contact-inhibited cells and association with the mammalian protein E6-AP. These BE6 mutants demonstrate that transformation by BE6 does not require transcriptional activation and that association of BE6 with E6-AP is a function separable from transcriptional activation by BE6. Association of BE6 with E6-AP appears to be necessary but not sufficient for transformation by BE6. In addition, the mutational analysis of BE6 demonstrates that transactivation, transformation, and association with E6-AP all require sequences throughout the BE6 gene, indicating that the papillomavirus E6 proteins do not have a simple domain structure.
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Affiliation(s)
- R Ned
- Institute of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA
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19
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Lehman CW, King DS, Botchan MR. A papillomavirus E2 phosphorylation mutant exhibits normal transient replication and transcription but is defective in transformation and plasmid retention. J Virol 1997; 71:3652-65. [PMID: 9094639 PMCID: PMC191514 DOI: 10.1128/jvi.71.5.3652-3665.1997] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Papillomavirus DNA persists in infected cells as a nuclear plasmid, causing epithelial lesions in many hosts, including humans. The viral protein E2 is required for both replication and transcription to facilitate this persistence. Bovine papillomavirus E2 protein is phosphorylated at two predominant sites. Phosphorylation of one of these sites (serine 301) inhibits replication of the genome. Using mass spectrometry and Edman sequencing, we have mapped additional phosphorylation sites in tryptic peptides to positions which lie primarily in the putatively unstructured hinge region of E2. Mutation of the major sites facilitates transformation in the absence of viral repressors and only has a minor effect on transformation when the repressors are present. Mutation of the major phosphorylation sites combined with one additional change at a newly discovered site (serine 235) blocks transformation. Transformation can be restored by mutating this residue to aspartic acid, mimicking a phosphorylated amino acid, suggesting that phosphorylation is key to the regulation. Transformation by the mutant genome can also be rescued by ectopic expression of the E2 enhancer protein, demonstrating a loss of function by the mutant protein and not a toxic defect. In transient assays, phosphorylation site mutants of E2 protein were normal for all viral functions tested, including replication, transcriptional activation and repression (by the overlapping mutant repressors), protein accumulation, and surprisingly, viral oncogene E5 promoter activation. While the mutant genome transiently replicated to high levels, stable replication was defective, suggesting that a function of E2 required for plasmid retention is regulated by phosphorylation.
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Affiliation(s)
- C W Lehman
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-3204, USA.
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20
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Tong X, Howley PM. The bovine papillomavirus E6 oncoprotein interacts with paxillin and disrupts the actin cytoskeleton. Proc Natl Acad Sci U S A 1997; 94:4412-7. [PMID: 9114003 PMCID: PMC20736 DOI: 10.1073/pnas.94.9.4412] [Citation(s) in RCA: 195] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/26/1997] [Indexed: 02/04/2023] Open
Abstract
The E6 oncoprotein of bovine papillomavirus type 1 (BPV-1) has been shown to transform cells through a p53-independent pathway, but its transforming mechanism is unknown. Here we demonstrate in vitro and in vivo interactions between BPV-1 E6 and the focal adhesion protein paxillin. The ability of BPV-1 E6 to complex with paxillin correlated with its ability to transform; E6 mutant proteins impaired in their transformation function also were impaired in their abilities to bind paxillin. E6 binding to paxillin also may contribute to the carcinogenic potential of the human papillomavirus (HPV); we were able to show in vitro binding of paxillin to the E6 proteins of the cancer-associated type HPV 16 but not of the nononcogenic types 6 and 11. The association of E6 with paxillin was affected by depolymerization of the actin fiber network, and overexpression of BPV-1 E6 led to disruption of actin fiber formation. Disruption of the actin cytoskeleton is a characteristic of many transformed cells, and, in BPV-1 transformed cells, may be mediated by BPV-1 E6 through its interaction with paxillin.
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Affiliation(s)
- X Tong
- Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
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21
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Zanardi TA, Stanley CM, Saville BM, Spacek SM, Lentz MR. Modulation of bovine papillomavirus DNA replication by phosphorylation of the viral E1 protein. Virology 1997; 228:1-10. [PMID: 9024804 DOI: 10.1006/viro.1996.8375] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
E1 is the DNA replication origin recognition protein for bovine papillomavirus (BPV), and it carries out enzymatic functions required for initiation of viral DNA replication. Cellular mechanisms likely play a role in regulating BPV DNA replication. We are investigating the role of phosphorylation of E1 on viral replication in vivo and on E1 activity in vitro. Serine 109 is a phosphoacceptor in vivo and is targeted by protein kinase A and protein kinase C in vitro. A viral genome carrying a serine 109 to alanine mutation replicates more efficiently than wild-type in vivo in a transient replication assay. Furthermore, purified mutant protein, while having wild-type levels of ATPase activity, is able to bind more origin-containing DNA than wild-type E1. Phosphorylation therefore appears to play a selective role in modulating a specific E1 function during viral DNA replication.
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Affiliation(s)
- T A Zanardi
- Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128, USA
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22
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Abstract
Many viral and non-viral vector systems have now been developed for gene therapy applications. In this article, the pros and cons of these vector systems are discussed in relation to the different cancer gene therapy strategies. The protocols used in cancer gene therapy can be broadly divided into six categories including gene transfer to explanted cells for use as cell-based cancer vaccines; gene transfer to a small number of tumour cells in situ to achieve a vaccine effect; gene transfer to vascular endothelial cells (VECs) lining the blood vessels of the tumour to interfere with tumour angiogenesis; gene transfer to T lymphocytes to enhance their antitumour effector capability; gene transfer to haemopoietic stem cells (HSCs) to enhance their resistance to cytotoxic drugs and gene transfer to a large number of tumour cells in situ to achieve nonimmune tumour reduction with or without bystander effect. Each of the six strategies makes unique demands on the vector system and these are discussed with reference to currently available vectors. Aspects of vector biology that are in need of further development are discussed in some detail. The final section points to the potential use of replicating viruses as delivery vehicles for efficient in vivo gene transfer to disseminated cancers.
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Affiliation(s)
- J Zhang
- Cambridge Centre for Protein Engineering, MRC Centre, UK
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23
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Sakai H, Yasugi T, Benson JD, Dowhanick JJ, Howley PM. Targeted mutagenesis of the human papillomavirus type 16 E2 transactivation domain reveals separable transcriptional activation and DNA replication functions. J Virol 1996; 70:1602-11. [PMID: 8627680 PMCID: PMC189983 DOI: 10.1128/jvi.70.3.1602-1611.1996] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The E2 gene products of papillomavirus play key roles in viral replication, both as regulators of viral transcription and as auxiliary factors that act with E1 in viral DNA replication. We have carried out a detailed structure-function analysis of conserved amino acids within the N-terminal domain of the human papillomavirus type 16 (HPV16) E2 protein. These mutants were tested for their transcriptional activation activities as well as transient DNA replication and E1 binding activities. Analysis of the stably expressed mutants revealed that the transcriptional activation and replication activities of HPV16 E2 could be dissociated. The 173A mutant was defective for the transcriptional activation function but retained wild-type DNA replication activity, whereas the E39A mutant wild-type transcriptional activation function but was defective in transient DNA replication assays. The E39A mutant was also defective for HPV16 E1 binding in vitro, suggesting that the ability of E2 protein to form a complex with E1 appears to be essential for its function as an auxiliary replication factor.
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Affiliation(s)
- H Sakai
- Department of Pathology, Harvard Medical School, Boston, Massachusetts, 02115, USA
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