The E6E7 oncoproteins of cutaneous human papillomavirus type 38 interfere with the interferon pathway

Non-melanoma skin cancer is the most frequent malignancy in Caucasian populations. Evidence suggests the involvement of cutaneous Human Papillomavirus (HPV) of the genus beta (beta) in this disease. The ability of E6 and E7 of mucosal HPV to promote cellular transformation and inhibit immune response-related pathways plays a key role in cervical carcinogenesis. beta HPV-38 E6 and E7 display transforming activities in in vitro and in vivo models, but their impact on immune surveillance is unknown. Here we show that HPV-38 E6 and E7 affect the IFN-induced up-regulation of MHC class I. Expression of the two viral proteins in HaCaT keratinocytes led to a decrease of MHC I levels. This down-regulation is associated with a reduction of expression of MHC I heavy chain, of the peptide chaperone TAP and of the STAT-1 downstream effector IRF-1. The down-regulation of these proteins is ultimately due to the inhibition of STAT-1 expression. Analysis of cells expressing either HPV-38 E6 or E7 suggests that these effects are primarily the result of E6 expression, although a contribution by E7 cannot be excluded. We conclude that HPV-38 encodes oncoproteins that potentially contribute to the evasion of host immune surveillance.     

Human papillomavirus type 16 E6 and E7 oncoproteins act synergistically to cause head and neck cancer in mice

High-risk human papillomaviruses (HPVs) contribute to cervical and other anogenital cancers, and they are also linked etiologically to a subset of head and neck squamous cell carcinomas (HNSCC). We previously established a model for HPV-associated HNSCC in which we treated transgenic mice expressing the papillomaviral oncoproteins with the chemical carcinogen 4-nitroquinoline-1-oxide (4-NQO). We found that the HPV-16 E7 oncoprotein was highly potent in causing HNSCC, and its dominance masked any potential oncogenic contribution of E6, a second papillomaviral oncoprotein commonly expressed in human cancers. In the current study, we shortened the duration of treatment with 4-NQO to reduce the incidence of cancers and discovered a striking synergy between E6 and E7 in causing HNSCC. Comparing the oncogenic properties of wild-type versus mutant E6 genes in this model for HNSCC uncovered a role for some but not other cellular targets of E6 previously shown to contribute to cervical cancer.     

Identification of novel E6-E7 sequence variants of human papillomavirus 16

The rate of evolution of the human papillomavirus 16 (HPV16) genome is low. However, the ability of the E6 oncoprotein to interact with distinct p53 variants causes selective pressure on the E6 gene. In addition, intratypic recombination events in the HPV16 E6 and E7 genes have been characterized as extraordinary phenomena during the evolutionary history of virus. In the present study, we identified two new sequence variants through nucleotide analysis of the E6-E7 region of the HPV16 genome. Maximum-likelihood and empirical Bayesian methods were used in order to identify positive selection at particular residues of the E6 and E7 genes. Using the single recombination breakpoint (SBP) method, we found evidence of recombination events in the E6 ORF. Nucleotide sequence analysis showed that the new sequence variants are phylogenetically distant from the other members of the population. Our results indicate that new evolutionary intermediates of HPV16 might be formed either though positive selective pressure or through recombination events by multiple infections with distinct HPV16 variants.     

Nucleotide and amino acid sequence variation in the L1 and E7 open reading frames of human papillomavirus type 6 and type 16.

Human papillomavirus (HPV) type 6 and type 16 DNA sequence variants were found by partially sequencing the L1 and E7 open reading frames, using templates generated with the polymerase chain reaction. Identical variants were found in patients from widely separated locations, such as the United States, the Philippines, and India. The same sequence variants of HPV 16 were found in women with invasive cervical carcinoma and in women with no evidence of disease. Variation in the predicted amino acid sequences of the HPV 16 L1 and E7 proteins was found. A single nucleotide change at position 6433 was found in about 50% of the HPV 16 DNAs, resulting in a change in predicted amino acid sequence from threonine to alanine at the equivalent position in the L1 protein. Predicted amino acid changes were found in the HPV 16 E7 proteins at amino acid positions 28, 29, and 47. Variation at these positions could affect known properties of the E7 protein, including binding to the retinoblastoma protein.     

人乳头瘤病毒E6、E7的表达对足叶乙甙作用下细胞凋亡的影响

目的探讨人乳头瘤毒(HPV)16早期基因E6和E7的表达对NIKS细胞凋亡表型的影响。方法用含有HPV16的E6、HPV16E7、HPV16E6E7病毒癌基因的逆转录病毒感染角质生成细胞株NIKS,puromycin筛选稳定表达细胞;基因组PCR和Western blot方法验证E6和E7的表达;转染后的NIKS细胞用不同浓度的足叶乙甙处理,流式细胞仪和Annexin V染色检测细胞凋亡情况。结果经逆转录病毒感染后,建立表达E6、E7及E6E7的NIKS细胞株,基因组PCR证明E6和E7整合入NIKS细胞基因组;Western blot证实表达的E6、E7具有生物学活性,能够分别降解p53和pRB;在足叶乙甙处理后,E6、E7以及E6E7表达细胞发生明显的细胞死亡,E6和E7具有叠加作用,且具有剂量依赖性,Annexin V染色证实细胞发生凋亡,凋亡率分别为(33.5±3.2)%、(38.3±2.4)%和(56.7±4.3)%。结论人乳头瘤病毒E6和E7的表达都可以促进细胞对DNA损伤药物的敏感性,提示乳头瘤病毒感染状态有可能影响肿瘤细胞对化疗的敏感性。     

T-helper epitopes identified within the E6 transforming protein of cervical cancer-associated human papillomavirus type 16

The E6 oncoprotein of human papillomavirus type 16 (HPV16 E6) produced by tumor cells of HPV16-associated cervical carcinoma is poorly immunogenic in patients, but nonetheless is a tumor-specific antigen to which therapeutic vaccine strategies may be directed. To investigate the subunit immunogenicity of E6 protein at the T-helper cell level, we immunized mice with overlapping peptides spanning the entire 158 amino acid sequence. Two peptides recalled a proliferative response in lymph node cells (LNC) from C57BL/6 (H-2b)-immunized mice. One of these peptides also recalled proliferative responses in the context of 5/5 other major histocompatibility complex (MHC) class II haplotypes, indicating a "promiscuous" T-epitope. Minimal consensus motif analysis identified the epitopes as 60VYRDGNPYA68 and 98GYNKPLCDLL107. LNC from mice immunized with T-epitope proliferated in response to challenge with whole E6 protein. Immunization with E6 T-epitopes linked to B-epitopes of HPV16 E7 protein elicited specific antibody indicating that T-cells recognizing the T-epitopes provided cognate "help" for B-cells. LNC from mice co-immunized with E6 T-epitope and the major T-helper epitope of HPV16 E7 (48DRAHYNI54) proliferated comparably when challenged with the peptides individually indicating co-dominance of the two T-epitopes. The findings have implications for incorporation of E6 into a therapeutic vaccine.     

Expression, purification and immunological characterization of the transforming protein E7, from cervical cancer-associated human papillomavirus type 16

E7 is the major oncogenic protein produced in cervical cancer-associated human papillomavirus type 16 (HPV16). This protein was expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. E7-enriched inclusion bodies were collected from bacterial lysates, were solubilized in 10 M urea, and the protein was purified using anion exchange column chromatography. After removal of endotoxin with serial Triton X-114 extractions, material of high purity (about 90%) was obtained, which is suitable for use in a human clinical trial. This material was immunogenic, and when used as a vaccine, protected mice against challenge with an HPV16 E7 DNA transfected tumour cell line. Based on this observation, the E7GST fusion protein is currently being used in a human clinical trial of a vaccine against HPV16-induced cervical cancer. This fusion protein could be cleaved with thrombin to remove the GST fusion part and further purified by preparative SDS gel electrophoresis to obtain free E7 with > 98% purity.     

The human papillomavirus type 16 E7 oncoprotein targets Myc-interacting zinc-finger protein-1

We demonstrate that HPV-16 E7 forms a complex with Miz-1. UV-induced expression of the CDK-inhibitor p21^Cip1 and subsequent cell cycle arrest depends upon endogenous Miz-1 in HPV-negative C33A cervical cancer cells containing mutated p53. Transient expression of E7 in C33A inhibits UV-induced expression of p21^Cip1 and overcomes Miz-1-induced G1-phase arrest. The C-terminal E7Δ79LEDLL83-mutant with reduced Miz-1-binding capacity was impaired in its capability to repress p21^Cip1 expression; whereas the pRB-binding-deficient E7C24G-mutant inhibited p21^Cip1 expression similar to wild-type E7. Using ChIP, we demonstrate that endogenous E7 is bound to the endogenous p21^Cip1 core-promoter in CaSki cells and RNAi-mediated knock down of Miz-1 abrogates E7-binding to the p21^Cip1 promoter. Co-expression of E7 with Miz-1 inhibited Miz-1-induced p21^Cip1 expression from the minimal-promoter via Miz-1 DNA-binding sites. Co-expression of E7Δ79LEDLL83 did not inhibit Miz-1-induced p21^Cip1 expression. E7C24G retained E7-wild-type capability to inhibit Miz-1-dependent transactivation. These findings suggest that HPV-16 E7 can repress Miz-1-induced p21^Cip1 gene expression.     

The biological properties of E6 and E7 oncoproteins from human papillomaviruses

More than 100 different human papillomavirus (HPV) types have been isolated so far, and they can be sub-grouped in cutaneous or mucosal according to their ability to infect the skin or the mucosa of the genital or upper-respiratory tracts. A sub-group of human mucosal HPVs, referred to as high-risk HPV types, is responsible for approximately 5% of all human cancers, which represents one-third of all the tumours induced by viruses. Epidemiological and biological studies have shown that HPV16 is the most oncogenic type within the high-risk group. Emerging lines of evidence suggest that, in addition to the high-risk mucosal HPV types, certain cutaneous HPVs are involved in skin cancer. HPV-associated cancers are intimately linked to HPV persistence and the accumulation of chromosomal rearrangements. The products of the early genes, E6 and E7, of the high-risk mucosal HPV types play a key role in both events. Indeed, these proteins have developed a number of strategies to evade host immuno-surveillance allowing viral persistence, and to alter cell cycle and apoptosis control, facilitating the accumulation of DNA damage/mutations. Often, the two oncoproteins target the same cellular pathways with different mechanisms, showing a strong synergism in promoting cellular transformation and neutralizing the immune response. Here, we review most of the findings on the biological properties and molecular mechanisms of the oncoproteins E6 and E7 from mucosal and cutaneous HPV types.     

Purification and characterisation of the E7 oncoproteins of the high-risk human papillomavirus types 16 and 18

E7 proteins are major oncoproteins of human papillomaviruses (HPVs) which play a key role in virus-associated cervical carcinogenesis. The E7 oncoprotein of HPV-16 has been shown to interact with a variety of cellular target proteins and these interactions are considered essential for the transforming properties of this oncoprotein. Several additional HPV types associated etiologically to cervical cancer have been described, the second most common being HPV-18. Less is known about the biochemical functions and interactions of HPV-18 E7. As a first step to determine biochemical properties common to the E7 proteins of the high-risk HPV types 16 and 18 these E7 proteins were expressed in bacteria and purified to homogeneity. Purified E7 proteins were used to investigate the in vitro interaction with the pocket protein p107 and insulin-like growth factor-binding protein-3 (IGFBP-3) that are known to interact with the amino-terminal and the carboxyl-terminal part of IGFBP-3, respectively. Both purified E7 proteins interacted strongly with p107 and, as demonstrated here for the first time, HPV-18 E7 was capable of binding to IGFBP-3, albeit to a lesser extent than HPV-16 E7. These findings suggest that the purified recombinant E7 proteins retain, at least in part, their biochemical activities.     

Different methods of identifying new antigenic epitopes of human papillomavirus type 16 E6 and E7 proteins

Human papillomavirus (HPV) infection is the most common cause of sexually transmitted viral infection and is the main cause of cervical cancer. Identification of HPV T-cell epitopes would be instrumental not only in our understanding of the protective immune response but also in the development of vaccines and immunotherapies. In contrast to viruses which cause systemic infection, identification of HPV epitopes is technically challenging because HPV causes a localized mucosal infection and the frequency of pathogen-specific T lymphocytes in peripheral blood is expected to be low. Here we describe three new antigenic epitopes (E7 7-15 [TLHEYMLDL], E6 52-61 [FAFRDLCIVY], and E7 79-87 [LEDLLMGTL]) of HPV 16 E6 and E7 proteins which have oncogenic activities. E7 7-15 was identified among peptides previously shown to bind to human leukocyte antigen (HLA)-A2.1 molecule, but it was found likely to be restricted by the HLA-B48 molecule. E6 52-61 (likely to be restricted by HLA-B57) and E7 79-87 (likely to be restricted by HLA-B60) were detected, based on the magnitude of the T-cell immune responses, in another individual. In particular, T-cell clones specific for the E6 52-61 epitope were isolated effectively by magnetically selecting them based on gamma interferon secretion. This is an efficient method of identifying new epitopes of antigens for which the number of specific T lymphocytes in the circulation is expected to be small, and it should be widely applicable in identifying new T-cell epitopes.     

Neuroepithelial carcinomas in mice transgenic with human papillomavirus type 16 E6/E7 ORFs.

The effect of the human papillomavirus (HPV) oncogenes E6 and E7 was examined in transgenic mice with a construct containing the human beta-actin promoter regulating HPV16 E6 and E7 open reading frames. In the sole line of mice that transmitted the transgene, neuroepithelial tumors appeared at 2.5 months of life, and by 10 months, 87 of 122 (71%) of the animals were dead from brain tumors. The most frequent type of tumor (74%) was an anaplastic neuroepithelial tumor associated with the ependyma of the third and fourth ventricles, which locally invaded adjacent brain tissue and spread for considerable distances along the ventricular surface. The other two types of tumor were well-differentiated choroid plexus carcinomas (26%) and rare pituitary carcinomas (8.7%). HPV16 E6 RNA and E7 oncoprotein expression were demonstrated in tumor tissue and primary cell lines derived from the tumors. Examination of two tumor suppressor gene products, the retinoblastoma protein and p53, known to bind to HPV16 E7 and E6 oncoproteins, respectively, showed both were expressed in the primary tumor cell lines. These data support a causative role for the HPV oncoproteins in epithelial carcinogenesis.     

Frequency of antibodies against E4 and E7 from human papillomavirus type 16 in Mexican soldiers

Summary. The high prevalence of HPV in men’s genitalia and the low frequency of virus-associated lesions gave rise to questions on the influence of infection-site on the HPV antibody profile. In a cross-sectional study, HPV infection in penis and urethra, and serum antibodies against HPV-16 E4 and E7 proteins were evaluated in 288 Mexican soldiers. The results showed that HPV prevalence was 31% (51% in penis, 11% in urethra and 38% in both sites), while 47% were multiple infections. Overall, seroprevalence was 13% for anti-E4 antibodies and 6% for anti-E7. However, the highest prevalence of anti-E4 antibodies was observed in men with HPV infection in urethra (30%), while for E7 antibodies, the highest prevalence (10%) was found in men who tested positive for HPV in penis. The prevalence of IgG and IgA anti-E4 was related to HPV-16 urethral infection, while detection of HPV-16 in penis was related to IgG anti-E7 prevalence. In conclusion, the high-risk sexual behavior observed in this population might be responsible for high HPV prevalence and multiple infections. However, the seroprevalence of E4 and E7 was similar to that observed in healthy Mexican women. These results suggest that the humoral immune response against HPV infection in men differs, depending on the site of infection.     

Insulin-like growth factor-binding protein 3 expression increases during immortalization of cervical keratinocytes by human papillomavirus type 16 E6 and E7 proteins

Human papillomaviruses (HPVs) infect cervical epithelial cells and induce both benign and precancerous lesions. High-risk HPVs promote the development of cervical cancer in vivo and can immortalize cervical epithelial cells in vitro, whereas low-risk HPVs cannot. We used cDNA microarrays and quantitative polymerase chain reaction to compare cellular gene expression in primary cervical epithelial cells during a time course after retroviral transduction with either low-risk or high-risk E6/E7 genes. At early passages, cervical cells transduced with high-risk E6/E7 genes demonstrated increased expression of the cell cycle-regulated genes CDC2 and ubiquitin carrier E2-C. At later passages, these same cells exhibited dramatic increases in insulin-like growth factor-binding protein-3 (IGFBP-3) mRNA and both secreted an intracellular protein, with mRNA levels increasing approximately 85-fold. Corroborating these in vitro studies, in situ hybridization of cervical biopsies with an IGFBP-3 riboprobe revealed high levels of expression in high-grade squamous intraepithelial neoplasia but not in normal cervical epithelium. Our in vitro results indicate that overexpression of IGFBP-3 is a late event after E6/E7 expression, and analysis of cervical lesions indicates that overexpression of this gene is also seen in vivo.     

人乳头瘤病毒16型修饰后E6E7基因免疫原性增强

利用突变修饰后消除转化活性并保留抗原性的中国山东地方株人乳头瘤病毒16型(human papillomavirus type 16,HPVl6)E6E7融合基因(fmE6E7)，研制治疗HPVl6相关疾病的DNA疫苗。用PCR扩增fmE6E7基因后，插人真核表达质粒获得pVRl012-fmE6E7，瞬时转染Cos-7细胞，免疫荧光法检测证实其表达后，在C57BL／6小鼠后腿肌肉进行裸DNA免疫，5lCr释放法体外分析免疫鼠的细胞毒性T淋巴细胞活性Cytotoxic T lymphocyte，CTL)，间接ELISA法检测免疫鼠血清中E7特异性抗体。研究表明修饰后的中国地方株E6E7融合基因可诱导机体产生特异的抗体反应和CTL反应，与单独野生型E7基因免疫相比，E6E7融和基因可更好的活化CTT反应。表明修饰后消除转化活性的中国地方株E6E7融合基因可作为HPVl6治疗性DNA疫苗的靶基因。     

Immunization against human papillomavirus type 16 tumor cells with recombinant vaccinia viruses expressing E6 and E7.

Papillomaviruses are etiological agents of epithelial proliferative disease. In man, neoplastic transformation of the uterine cervix has been linked to infection with specific subtypes of human papillomavirus, particularly types 16 and 18. We previously reported that live vaccinia virus recombinants expressing early transforming proteins of other tumor viruses can immunize against challenge with cognate tumor cells and we have extended this approach to HPV16. Neoplastic transformation by papillomaviruses involves expression of early open reading frames (ORFs) E5, E6, and E7, and we report the construction of vaccinia recombinants separately expressing ORFs E5-E7 of HPV16. Primary rat cell lines cotransformed with HPV16 and an activated ras oncogene were established in order to evaluate the potential of the recombinants to elicit antitumor immunity. We report that inoculation of rats with vaccinia recombinants expressing E6 or E7 retarded or prevented tumor development in a proportion of animals challenged by subcutaneous seeding of tumor cells whereas the recombinant expressing E5 was inactive.