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Basukala O, Banks L. The Not-So-Good, the Bad and the Ugly: HPV E5, E6 and E7 Oncoproteins in the Orchestration of Carcinogenesis. Viruses 2021; 13:1892. [PMID: 34696321 PMCID: PMC8541208 DOI: 10.3390/v13101892] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 09/13/2021] [Accepted: 09/14/2021] [Indexed: 12/15/2022] Open
Abstract
Infection with HPV starts with the access of the viral particles to basal cells in the epidermis, potentially via microtraumas to the skin. The basal cells are able to keep away these pathogens in normal circumstances through a robust immune response from the host, as HPV infections are, in general, cleared within 2 to 3 weeks. However, the rare instances of persistent infection and/or in cases where the host immune system is compromised are major risk factors for the development of lesions potentially leading to malignancy. Evolutionarily, obligatory pathogens such as HPVs would not be expected to risk exposing the host to lethal cancer, as this would entail challenging their own life cycle, but infection with these viruses is highly correlated with cancer and malignancy-as in cancer of the cervix, which is almost always associated with these viruses. Despite this key associative cause and the availability of very effective vaccines against these viruses, therapeutic interventions against HPV-induced cancers are still a challenge, indicating the need for focused translational research. In this review, we will consider the key roles that the viral proteins play in driving the host cells to carcinogenesis, mainly focusing on events orchestrated by early proteins E5, E6 and E7-the not-so-good, the bad and the ugly-and discuss and summarize the major events that lead to these viruses mechanistically corrupting cellular homeostasis, giving rise to cancer and malignancy.
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Affiliation(s)
| | - Lawrence Banks
- Tumour Virology Laboratory, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, I-34149 Trieste, Italy;
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2
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Scarth JA, Patterson MR, Morgan EL, Macdonald A. The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation. J Gen Virol 2021; 102:001540. [PMID: 33427604 PMCID: PMC8148304 DOI: 10.1099/jgv.0.001540] [Citation(s) in RCA: 90] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 11/25/2020] [Indexed: 12/24/2022] Open
Abstract
Persistent infection with high-risk human papillomaviruses (HR-HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell-cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR-HPV oncoproteins can lead to the acquisition of host genetic mutations, eventually culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis.
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Affiliation(s)
- James A. Scarth
- School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
| | - Molly R. Patterson
- School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
| | - Ethan L. Morgan
- School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
- Present address: Tumour Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institute of Health, Bethesda, MD 20892, USA
| | - Andrew Macdonald
- School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK
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3
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Lleonart ME, Artero-Castro A, Kondoh H. Senescence induction; a possible cancer therapy. Mol Cancer 2009; 8:3. [PMID: 19133111 PMCID: PMC2631463 DOI: 10.1186/1476-4598-8-3] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Accepted: 01/08/2009] [Indexed: 12/13/2022] Open
Abstract
Cellular immortalization is a crucial step during the development of human cancer. Primary mammalian cells reach replicative exhaustion after several passages in vitro, a process called replicative senescence. During such a state of permanent growth arrest, senescent cells are refractory to physiological proliferation stimuli: they have altered cell morphology and gene expression patterns, although they remain viable with preserved metabolic activity. Interestingly, senescent cells have also been detected in vivo in human tumors, particularly in benign lesions. Senescence is a mechanism that limits cellular lifespan and constitutes a barrier against cellular immortalization. During immortalization, cells acquire genetic alterations that override senescence. Tumor suppressor genes and oncogenes are closely involved in senescence, as their knockdown and ectopic expression confer immortality and senescence induction, respectively. By using high throughput genetic screening to search for genes involved in senescence, several candidate oncogenes and putative tumor suppressor genes have been recently isolated, including subtypes of micro-RNAs. These findings offer new perspectives in the modulation of senescence and open new approaches for cancer therapy.
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Affiliation(s)
- Matilde E Lleonart
- Pathology Department, Fundació Institut de Recerca Hospital Vall d'Hebron, Passeig Vall d'Hebron 119-129, 08035 Barcelona, Spain.
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HPV E7 contributes to the telomerase activity of immortalized and tumorigenic cells and augments E6-induced hTERT promoter function. Virology 2008; 375:611-23. [PMID: 18367227 DOI: 10.1016/j.virol.2008.02.025] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2008] [Revised: 02/01/2008] [Accepted: 02/14/2008] [Indexed: 01/31/2023]
Abstract
The E6 and E7 proteins of high-risk HPVs are both required for the immortalization of primary human keratinocytes and the maintenance of the malignant phenotype of HPV-positive cancer cell lines. Our previous studies have shown that E6 protein binds Myc protein and that both E6 and Myc associate with and cooperatively activate the hTERT promoter, thereby increasing cellular telomerase activity. In this study, we evaluated the role of E7 in the maintenance and activation of telomerase in immortalized and tumorigenic cells. siRNA knockdown of either E6 or E7 (or both) in HPV-immortalized cells or an HPV-positive cancer cell line reduced hTERT transcription and telomerase activity. Since telomerase was inhibited by E7 siRNA in cells that independently expressed the E6 and E7 genes, our results reveal an independent role for E7 in the maintenance of telomerase activity. However, E7 alone was insufficient to increase endogenous hTERT mRNA or telomerase activity, although it significantly augmented E6-induced hTERT transcription and telomerase activity. To further explore this apparent E7-induced promoter augmentation, we analyzed an exogenous hTERT core promoter in transduced keratinocytes. E7 alone induced the wt hTERT promoter and augmented E6-induced hTERT promoter activity. Mutation of the E2F site in the hTERT promoter abrogated the ability of E7 to induce the hTERT promoter or to enhance the ability of E6 to induce the promoter. Correspondingly, keratinocytes expressing E6 and a mutant E7 (defective for binding pRb pocket proteins) showed lower telomerase activity than cells expressing wt E6 and wt E7. Thus, HPV E7 plays a role in the maintenance of telomerase activity in stable cell lines and augments acute, E6-induced hTERT promoter activity.
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Hebner C, Beglin M, Laimins LA. Human papillomavirus E6 proteins mediate resistance to interferon-induced growth arrest through inhibition of p53 acetylation. J Virol 2007; 81:12740-7. [PMID: 17898049 PMCID: PMC2169108 DOI: 10.1128/jvi.00987-07] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The high-risk human papillomavirus (HPV) E6 and E7 proteins act cooperatively to mediate multiple activities in viral pathogenesis. For instance, E7 acts to increase p53 levels while E6 accelerates its rate of turnover through the binding of the cellular ubiquitin ligase E6AP. Interferons are important antiviral agents that modulate both the initial and persistent phases of viral infection. The expression of HPV type 16 E7 was found to sensitize keratinocytes to the growth-inhibitory effects of interferon, while coexpression of E6 abrogates this inhibition. Treatment of E7-expressing cells with interferon ultimately resulted in cellular senescence through a process that is dependent upon acetylation of p53 by p300/CBP at lysine 382. Cells expressing mutant forms of E6 that are unable to bind p300/CBP or bind p53 failed to block acetylation of p53 at lysine 382 and were sensitive to growth arrest by interferon. In contrast, mutant forms of E6 that are unable to bind E6AP remain resistant to the effects of interferon, demonstrating that the absolute levels of p53 are not the major determinants of this activity. Finally, p53 acetylation at lysine 382 was found not to be an essential determinant of other types of senescence such as that induced by overexpression of Ras in human fibroblasts. This study identifies an important physiological role for E6 binding to p300/CBP in blocking growth arrest of human keratinocytes in the presence of interferon and so contributes to the persistence of HPV-infected cells.
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Affiliation(s)
- Christy Hebner
- Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, 320 E. Superior St., Chicago, IL 60611, USA
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6
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Hoover AC, Spanos WC, Harris GF, Anderson ME, Klingelhutz AJ, Lee JH. The role of human papillomavirus 16 E6 in anchorage-independent and invasive growth of mouse tonsil epithelium. ACTA ACUST UNITED AC 2007; 133:495-502. [PMID: 17515506 PMCID: PMC2917346 DOI: 10.1001/archotol.133.5.495] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
OBJECTIVE To provide a manipulatable system to study the mechanism of human papillomavirus 16 (HPV16) E6-related transformation of an epithelial cell type affected by HPV16 in humans. DESIGN Biochemical and physiological studies of mouse tonsil epithelial cells (MTECs) transformed with HPV16 oncogenes plus H-ras in vitro and in vivo. SETTING Basic research laboratory. PARTICIPANTS C57BL/6 mice. INTERVENTIONS Transduction of the HPV16 oncogenes E6 and E7 in retroviral vectors into MTECs with isolation of multiple individual clones that expressed E6, E7, or both alone or in conjunction with H-ras. MAIN OUTCOME MEASURES Growth in culture, anchorage-independent growth, and growth in immune competent, syngeneic mice. RESULTS The MTECs that expressed E6 degraded p53 by a mechanism that is inhibited by proteasomal blockade. Although normal MTECs senesced after 20 population doublings, E6 alone or in combination with E7 was sufficient to immortalize MTECs beyond 25 population doublings, lower their population-doubling time, and permit anchorage-independent growth. However, only MTECs that express E6 plus H-ras or E6/E7 plus H-ras formed invasive tumors in immune competent, syngeneic mice at orthotopic intraoral and subdermal sites. CONCLUSIONS We found that HPV16 E6 and E7 alone are not sufficient for invasive growth. However, the synergistic activity of H-ras and E6 was sufficient to result in invasive growth.
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Affiliation(s)
- Andrew C. Hoover
- Department of Otolaryngology – Head and Neck Surgery, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
- Veterans Affairs Medical Center, Iowa City, Iowa
| | - William C. Spanos
- Department of Otolaryngology – Head and Neck Surgery, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
- Veterans Affairs Medical Center, Iowa City, Iowa
| | - George F. Harris
- Department of Otolaryngology – Head and Neck Surgery, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
- Veterans Affairs Medical Center, Iowa City, Iowa
| | - Mary E. Anderson
- Department of Otolaryngology – Head and Neck Surgery, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
- Veterans Affairs Medical Center, Iowa City, Iowa
| | - Aloysius J. Klingelhutz
- Department of Microbiology, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
| | - John H. Lee
- Department of Otolaryngology – Head and Neck Surgery, University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa
- Veterans Affairs Medical Center, Iowa City, Iowa
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7
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Abstract
Oncogenic stimuli are thought to induce senescence in normal cells in order to protect against transformation and to induce proliferation in cells with altered p53 and/or retinoblastoma (Rb) pathways. In human fibroblasts, RAS initiates senescence through upregulation of the cyclin-dependent kinase inhibitor p16INK4A. We show here that in contrast to cultured fibroblast strains, freshly isolated normal fibroblasts are resistant to RAS-induced senescence and instead show some characteristics of transformation. RAS did not induce growth arrest or expression of senescence-associated beta-galactosidase, and Rb remained hyperphosphorylated despite elevated levels of p16. Instead, RAS promoted anchorage-independent growth of normal fibroblasts, although expression of hTert with RAS increased colony formation and allowed normal fibroblasts to bypass contact inhibition. To test the hypothesis that p16 levels determine how cells respond to RAS, we expressed RAS in freshly isolated fibroblasts that expressed very low levels of p16, in hTert-immortalized fibroblasts that had accumulated intermediate levels of p16, and in IMR90 fibroblasts with high levels of p16. RAS induced growth arrest in cells with higher p16 levels, and this effect was reversed by p16 knockdown in the hTert-immortalized fibroblasts. These findings indicate that culture-imposed stress sensitizes cells to RAS-induced arrest, whereas early passage cells do not arrest in response to RAS.
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Affiliation(s)
- Jennifer A Benanti
- Program in Cancer Biology, Fred Hutchinson Cancer Research Center. Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, Washington 98109-1024, USA
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8
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Wei W, Jobling WA, Chen W, Hahn WC, Sedivy JM. Abolition of cyclin-dependent kinase inhibitor p16Ink4a and p21Cip1/Waf1 functions permits Ras-induced anchorage-independent growth in telomerase-immortalized human fibroblasts. Mol Cell Biol 2003; 23:2859-70. [PMID: 12665584 PMCID: PMC152557 DOI: 10.1128/mcb.23.8.2859-2870.2003] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2002] [Revised: 10/29/2002] [Accepted: 01/28/2003] [Indexed: 11/20/2022] Open
Abstract
Human cells are more resistant to both immortalization and malignant transformation than rodent cells. Recent studies have established the basic genetic requirements for the transformation of human cells, but much of this work relied on the expression of transforming proteins derived from DNA tumor viruses. We constructed an isogenic panel of human fibroblast cell lines using a combination of gene targeting and ectopic expression of dominantly acting mutants of cellular genes. Abolition of p21(Cip1/Waf1) and p16(Ink4a) functions prevented oncogenically activated Ras from inducing growth arrest and was sufficient for limited anchorage-independent growth but not tumorigenesis. Deletion of the tumor suppressor p53 combined with abolition of p16(Ink4a) function failed to mimic the introduction of simian virus 40 large T antigen, indicating that large T antigen may target additional cellular functions. Ha-Ras and Myc cooperated only to a limited extent, but in the absence of Ras, Myc cooperated strongly with the simian virus 40 small t antigen to elicit aggressive anchorage-independent growth. The experiments reported here further define specific components of human transformation pathways.
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Affiliation(s)
- Wenyi Wei
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island 02912, USA
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9
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Nguyen M, Song S, Liem A, Androphy E, Liu Y, Lambert PF. A mutant of human papillomavirus type 16 E6 deficient in binding alpha-helix partners displays reduced oncogenic potential in vivo. J Virol 2002; 76:13039-48. [PMID: 12438630 PMCID: PMC136691 DOI: 10.1128/jvi.76.24.13039-13048.2002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2002] [Accepted: 08/22/2002] [Indexed: 11/20/2022] Open
Abstract
Human papillomaviruses (HPVs) are small DNA tumor viruses that are the causative agent of warts and are associated with many anogenital cancers. The viral gene encoding the E6 protein has been found to be involved in HPV oncogenesis. E6 is known to inactivate the cellular tumor suppressor, p53. In addition, E6 has been shown to bind to a variety of other cellular proteins. The focus of this study was to determine what role the interactions of E6 with a subset of cellular proteins which contain a common alpha-helical domain in their E6 binding region (alpha-helix partners) play in E6-mediated phenotypes. We generated transgenic mice expressing a mutant of E6, E6(I128T), which is defective for binding at least a subset of the alpha-helix partners, including E6AP, the ubiquitin ligase that mediates E6-dependent degradation of the p53 protein, to determine whether binding of alpha-helix partners plays a role in E6-mediated activities in vivo. Unlike mice expressing the wild-type E6 (strain K14E6(WT)), the mice expressing E6(I128T) lacked the ability to alter the radiation-induced block to DNA synthesis and promote the formation of benign skin tumors in conjunction with chemical carcinogens. Additionally, they displayed reduced levels of skin hyperplasia, spontaneous skin tumors, and tumor progression activity compared to those of the K14E6(WT) mice. From these results, we conclude that a domain in E6 that mediates alpha-helix partner binding is critical for E6-induced phenotypes in transgenic mice.
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Affiliation(s)
- Marie Nguyen
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, 1400 University Avenue, Madison, WI 53706, USA
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10
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Mantovani F, Banks L. The human papillomavirus E6 protein and its contribution to malignant progression. Oncogene 2001; 20:7874-87. [PMID: 11753670 DOI: 10.1038/sj.onc.1204869] [Citation(s) in RCA: 350] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The human papillomavirus (HPV) E6 protein is one of three oncoproteins encoded by the virus. It has long been recognized as a potent oncogene and is intimately associated with the events that result in the malignant conversion of virally infected cells. In order to understand the mechanisms by which E6 contributes to the development of human malignancy many laboratories have focused their attention on identifying the cellular proteins with which E6 interacts. In this review we discuss these interactions in the light of their respective contributions to the malignant progression of HPV transformed cells.
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Affiliation(s)
- F Mantovani
- International Centre for Genetic Engineering and Biotechnology Padriciano 99, I-34012 Trieste, Italy
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11
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12
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Song S, Liem A, Miller JA, Lambert PF. Human papillomavirus types 16 E6 and E7 contribute differently to carcinogenesis. Virology 2000; 267:141-50. [PMID: 10662610 DOI: 10.1006/viro.1999.0106] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
High-risk human papillomaviruses (HPVs) are etiologically implicated in human cervical cancer. Two viral genes, E6 and E7, are commonly found expressed in these cancer cells. We have previously shown that mice transgenic for the HPV-16 E6 gene or E7 gene, in which the E6 or E7 was expressed in the basal layer of epithelia, developed skin tumors. The spectrum of tumors derived from E6 and E7 mice differed, however; although most tumors derived from the E7-transgenic mice were benign, the majority of the tumors from the E6-transgenic mice were malignant. These findings led us to hypothesize that E6 and E7 play different roles in carcinogenesis. To assess at what stages in carcinogenesis E6 and E7 act, we treated the skin of K14E6- and K14E7-transgenic mice with chemical carcinogens known to contribute to distinct stages in carcinogenesis. Both E6 and E7 were found to synergize with chemical carcinogens in causing tumor formation. E6 was found to act weakly at the promotion stage of carcinogenesis in the formation of benign tumors but strongly at the progression stage which involves the malignant conversion of benign tumors. In contrast, E7 primarily affected the promotion stage of carcinogenesis. These results provide direct evidence that E6 and E7 contribute differently to carcinogenesis; E7 promotes the formation of benign tumors, and E6 acts primarily to accelerate progression of these benign tumors to the malignant stage. Consistent with this model, we found E6 and E7 to cooperate in inducing tumor formation in mice expressing both oncogenes.
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Affiliation(s)
- S Song
- McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, 1400 University Avenue, Madison, Wisconsin 53706, USA
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13
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Park JS, Yang JM, Min MK. Hepatitis C virus nonstructural protein NS4B transforms NIH3T3 cells in cooperation with the Ha-ras oncogene. Biochem Biophys Res Commun 2000; 267:581-7. [PMID: 10631105 DOI: 10.1006/bbrc.1999.1999] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although the mechanism of carcinogenesis by hepatitis C virus (HCV) is not clearly known, core and NS3P protein have been shown to form tumors in specific cell lines. In this study, on the basis of the fact that the core and NS4B proteins of Kunjin virus translocate into the nucleus, we were prompted to investigate whether the HCV nonstructural protein NS4B has any function in tumor formation. First, we examined the location of the NS4B protein of HCV in transfected cells and then its oncogenic activity by transfection of NIH3T3 cells with the NS4B gene in the presence or absence of the Ha-ras gene. The NS4B protein was present only in the cytoplasm, particularly in the perinuclear region, different from the case of the Kunjun virus. The cells expressing HCV NS4B cooperatively with the Ha-ras gene showed loss of contact inhibition, morphological alterations, and anchorage-independent growth. These biological activities were confirmed by the transcription activation of the reporter gene from the AP1 promoter, by the NS4B protein in association with Ha-ras. Our results demonstrated that HCV NS4B protein in association with the Ha-ras gene played an important role in the malignant transformation of cells by HCV.
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Affiliation(s)
- J S Park
- Mogam Biotechnology Research Institute, 341 Pojung-Ri, Koosung-Myon, Yongin-City, Kyunggi-Do, 449-910, Korea
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14
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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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15
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Chen JJ, Hong Y, Rustamzadeh E, Baleja JD, Androphy EJ. Identification of an alpha helical motif sufficient for association with papillomavirus E6. J Biol Chem 1998; 273:13537-44. [PMID: 9593689 DOI: 10.1074/jbc.273.22.13537] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We recently identified a cellular protein named E6BP or ERC-55 that binds cancer-related papillomavirus E6 proteins (Chen, J. J., Reid, C. E., Band, V., and Androphy, E. J. (1995) Science 269, 529-531). By construction of a series of deletion mutants, the region of E6BP that is necessary and sufficient for complex formation with human papillomavirus type 16 E6 has been mapped to a 25-amino acid domain. The corresponding peptide was synthesized and found by nuclear magnetic resonance spectroscopy to bind calcium and fold into a classical helix-loop-helix EF-hand conformation. Additional deletion mutagenesis showed that 13 amino acids that form the second alpha helix mediated E6 association. Alanine replacement mutagenesis indicated that amino acids of this helix were most important for E6 binding. Alignment of this alpha helical E6 binding peptide with the 18-amino acid E6 binding region of E6AP (Huibregtse, J. M., Scheffner, M., and Howley, P. M. (1993) Mol. Cell. Biol. 13, 4918-4927) and the first LD repeat of another E6-binding protein, paxillin (Tong, X., and Howley, P. M. (1997) J. Biol. Chem. 272, 33373-33376), revealed substantial similarities among these E6 binding domains. The extent of homology and the mutational data define the peptide as an E6 binding motif.
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Affiliation(s)
- J J Chen
- Department of Dermatology, New England Medical Center and Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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16
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Stöppler MC, Ching K, Stöppler H, Clancy K, Schlegel R, Icenogle J. Natural variants of the human papillomavirus type 16 E6 protein differ in their abilities to alter keratinocyte differentiation and to induce p53 degradation. J Virol 1996; 70:6987-93. [PMID: 8794343 PMCID: PMC190749 DOI: 10.1128/jvi.70.10.6987-6993.1996] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Three naturally occurring variant human papillomavirus type 16 (HPV-16) E6 proteins, which contained amino acid substitutions predominantly near the N terminus, exhibited significant differences in their abilities to abrogate keratinocyte differentiation in response to serum and calcium and to induce the degradation of p53 in vitro. One variant surpassed the reference E6 protein in its ability to abrogate keratinocyte differentiation responses, whereas another showed a reduction in this activity. Interestingly, the biological activities of the HPV-16 E6 proteins and their abilities to induce p53 degradation in vitro were directly correlated. These results demonstrate that naturally occurring variants of HPV-16 differ in biological and biochemical properties which might result in differences in pathogenicity.
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Affiliation(s)
- M C Stöppler
- Department of Pathology, Georgetown University School of Medicine, Washington, DC 20007, USA
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17
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Ray RB, Lagging LM, Meyer K, Ray R. Hepatitis C virus core protein cooperates with ras and transforms primary rat embryo fibroblasts to tumorigenic phenotype. J Virol 1996; 70:4438-43. [PMID: 8676467 PMCID: PMC190377 DOI: 10.1128/jvi.70.7.4438-4443.1996] [Citation(s) in RCA: 302] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have previously demonstrated that hepatitis C virus (HCV) core protein regulates cellular protooncogenes at the transcriptional level; this observation implicates core protein in the alteration of normal hepatocyte growth. In the present study, the transforming potential of the HCV core gene was investigated by using primary rat embryo fibroblast (REF) cells which were transfected with or without cooperative oncogenes. Integration of the HCV core gene resulted in expression of the viral protein in REF stable transformants. REF cells cotransfected with HCV core and H-ras genes became transformed and exhibited rapid proliferation, anchor-independent growth, and tumor formation in athymic nude mice. Results from these studies suggest that the core protein plays an important role in the regulation of HCV-infected cell growth and in the transformation to tumorigenic phenotype. These observations suggest a possible mechanism for this viral protein in the pathogenesis of hepatocellular carcinoma in HCV-infected humans.
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Affiliation(s)
- R B Ray
- Division of Infectious Diseases and Immunology, Saint Louis University, St. Louis, Missouri 63110, USA
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18
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Sherman L, Schlegel R. Serum- and calcium-induced differentiation of human keratinocytes is inhibited by the E6 oncoprotein of human papillomavirus type 16. J Virol 1996; 70:3269-79. [PMID: 8627810 PMCID: PMC190193 DOI: 10.1128/jvi.70.5.3269-3279.1996] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Transfection of the E6 and E7 genes of the high-risk human papillomaviruses (HPVs) into primary genital keratinocytes generates colonies of proliferating cells which are resistant to calcium- and serum-induced terminal differentiation. To genetically map the HPV gene(s) responsible for this cellular phenotype, we cloned cDNAs for full-length E6, full-length E7, four truncated E6 splice variants (E6I to E6IV), and a series of E6 C-terminal truncation mutants into a simian virus 40 expression vector. The E6 proteins were tagged with the AU1 epitope at the C terminus to verify their expression in COS cells by immunoprecipitation and immunofluorescence. Transfection of the full-length E6 protein, either wild type or epitope tagged, induced calcium- and serum-resistant keratinocyte colonies, but the truncated E6 variants and full-length E7 protein did not. E6-induced colonies, while altered in response to serum and calcium, could not be established into cell lines without the combined presence of the E7 protein, further exemplifying the independent roles of E6 and E7 in cell differentiation and cell proliferation. The E6 C-terminal deletion mutants defined two distinct functional domains between amino acids 120 and 151. Amino acids 120 to 151 contained an apparent bipartite nuclear localization signal, whereas amino acids 132 to 141 were required for the induction of resistance to calcium- and serum-induced differentiation and for immortalization of human keratinocytes in conjunction with E7.
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Affiliation(s)
- L Sherman
- Department of Pathology, Georgetown University Medical School, Washington, DC 20007, USA
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Belaguli NS, Pater MM, Pater A. Splice sites of human papillomavirus type 16 E6 gene or heterologous gene required for transformation by E7 and accumulation of E7 RNA. J Med Virol 1995; 47:445-53. [PMID: 8636718 DOI: 10.1002/jmv.1890470426] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Transformation of primary baby rat kidney cells by the human papillomavirus type 16 (HPV 16) E7 gene and efficient accumulation of E7 RNA have been shown by this laboratory to depend on the integrity of the nucleotide position (nt) 880 splice donor site. Here, the splice sites within the HPV 16 E6 open reading frame (ORF) and the sites of the SV40 splicing unit were examined for an ability to provide this requirement. Constructs containing the HPV 16 E6 sites and the SV40 splice site sequences were used for transformation and RNase protection assays. E6 splice sites supported a low level of transformation, in assays for complete HPV 16 early region constructs containing loss-of-function mutations of the nt 880 site. Using constructs with wild-type E6 or SV40 splice sites showed that both splice sites could substitute similarly for the requirement in cis of the nt 880 site for transformation. HPV 16 E6 mutated splice site and SV40 splice site in reverse, nonfunctional orientation relative to the promoter, were not transformation competent. The HPV 16 E7 RNA levels for the E6 splice site constructs correlated closely with the transformation frequency. The SV40 splice sites were required for E7 transcript accumulation. The results showed E6 splice site function and evidence for enhanced exon skipping from E6 splice donor site to acceptor sites 3' of the E7 ORF. This was shown with constructs containing loss-of-function mutations of the nt 880 site. These results confirmed the function of the splice sites by the transformation competent constructs and suggested lower transformation frequency than for wild type was due to skipping of the E7 exon. These patterns of transcripts may have a role in the regulation of gene expression during progression to malignancy. The combined results revealed that the general presence of a functional splice donor site was absolutely required for transformation by HPV 16 E7 and accumulation of E7 RNA.
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Affiliation(s)
- N S Belaguli
- Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada
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Cerni C, Seelos C. Papillomaviruses as Promoting Agents in Human Epithelial Tumors. INFECTIOUS AGENTS AND PATHOGENESIS 1995. [DOI: 10.1007/978-1-4899-1100-1_8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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