Mechanism of HPV E6 proteins in cellular transformation

The E6 protein is a major transforming protein of many types of papillomaviruses. Mechanistically, the best characterized E6 proteins are those of the high-risk genital HPVs (e.g. HPV-16 and 18 E6), which function, at least in part, by inactivating the p53 tumor suppressor protein. Biochemical studies have shown that this occurs by targeted degradation of p53, dependent on the E6-AP ubiquitin-protein ligase. The model that has emerged from E6/E6-AP-dependent p53 degradation has provided insight into both HPV-associated carcinogenesis and the problem of substrate specificity of the ubiquitin system. Several observations suggest that the high-risk HPV E6 proteins may also have activities in addition to inactivation of p53.     

HPV E6 proteins interact with specific PML isoforms and allow distinctions to be made between different POD structures

Mucosal human papillomaviruses (HPVs) are the causative agents of a number of human pathologies, including benign condylomas, as well as of the majority of cervical cancers and their high-grade precursor lesions. Although the viral E6 protein is known to be essential for driving malignant progression of HPV-infected cells, there are still many uncertainties about its mode of action. In this study, we have analysed the intracellular distribution of the E6 oncoproteins from the high-risk HPV-18 and the low-risk HPV-11. We show that both E6 proteins localize within the nucleus in nuclear bodies that are confocal with the promyelocytic leukaemia (PML) protein. Using a panel of different PML isoforms, we demonstrate specific co-localization between the E6 proteins and PML isoforms I-IV, but not with PML isoforms V and VI. We also demonstrate the interaction between E6 and a subset of PML isoforms in vivo. As a consequence of this interaction, the insoluble form of PML IV is destabilized by HPV-18 E6 through a proteasome-dependent pathway. Interestingly, both HPV-11 E6 and HPV-18 E6 can readily overcome PML IV-induced cellular senescence in primary cells. These results show separable functions for different PML isoforms that are specifically targeted by the HPV E6 oncoproteins.     

HPV E6 specifically targets different cellular pools of its PDZ domain-containing tumour suppressor substrates for proteasome-mediated degradation

The high-risk HPV E6 proteins have been shown to direct the degradation of a variety of cellular proteins that contain PDZ domains. Although some of these proteins are involved in regulating processes of cell growth and polarity in Drosophila, little is known about their function in higher eukaryotic epithelial cells. In HPV-containing cells derived from cervical tumours, we find that the patterns of expression of the E6 targets hDlg (discs large), hScrib (Scribble), and MUPP1 are consistent with their being substrates for E6-induced degradation. It is also clear that, in the case of hDlg, E6 is specifically targeting nuclear pools of the protein rather than membrane-bound forms. We have also analysed the activity of a subset of E6 target proteins in the suppression of oncogene-induced cell transformation. Interestingly, Dlg, MAGI-1 and MUPP1 efficiently suppressed cell transformation, while MAGI-2 and MAGI-3 were ineffective in this assay. These results suggest that in the context of HPV-induced transformation Dlg, MAGI-1 and MUPP1 can function as tumour suppressors.     

Cisplatin and taxol activate different signal pathways regulating cellular injury-induced expression of GADD153.

Signal transduction pathways activated by injury play a central role in coordinating the cellular responses that determine whether a cell survives or dies. GADD153 expression increases markedly in response to some types of cellular injury and the product of this gene causes cell cycle arrest. Using induction of GADD153 as a model, we have investigated the activation of the cellular injury response after treatment with taxol and cisplatin (cDDP). Activation of the GADD153 promoter coupled to the luciferase gene and transfected into human ovarian carcinoma 2008 cells correlated well with the increase in endogenous GADD153 mRNA after treatment with taxol but not after treatment with cDDP. Following treatment with cDDP, the increase in endogenous GADD153 mRNA was 10-fold greater than the increase in GADD153 promoter activity. Likewise, at equitoxic levels of exposure (IC80), cDDP produced a 5-fold greater increase in endogenous GADD153 mRNA than taxol. The tyrosine kinase inhibitor tyrophostin B46 had no significant effect on the ability of taxol to activate the GADD153 promoter, but inhibited activation of the GADD153 promoter by cDDP in a concentration-dependent manner. Tyrphostin B46 synergistically enhanced the cytotoxicity of cisplatin; however, the same exposure had no significant effect on the cytotoxicity of taxol. We conclude that (1) taxol and cDDP activate GADD153 promoter activity through different mechanisms; (2) the signal transduction pathway mediating induction by cDDP involves a tyrosine kinase inhibitable by tyrphostin B46; and (3) that inhibition of this signal transduction pathway by tyrphostin synergistically enhances cDDP toxicity.     

Oncogenic human papillomavirus E6 proteins target the MAGI-2 and MAGI-3 proteins for degradation

The E6 proteins from the high-risk human papillomavirus (HPV) types have previously been shown to target a number of PDZ domain-containing proteins for proteasome-mediated degradation. These include the hDlg tumour suppressor and the MAGI-1 protein. In this study we show that high-risk HPV E6 proteins also target the related MAGI-2 and MAGI-3 proteins for degradation. Moreover, we show that the interaction is specific to one PDZ domain, and that co-expression of this domain can protect each of the full-length MAGI proteins from E6-mediated degradation. These data provide clear indicators for the potential design of compounds that could specifically inhibit the interaction of oncogenic HPV E6 proteins with an important class of target proteins.     

The PDZ protein Tip-1 is a gain of function target of the HPV16 E6 oncoprotein

Previous work has indicated that the PDZ domain Tax interacting protein 1 (Tip-1) is a target of the HTLV1 Tax protein and is a potential RhoA effector. We have used the yeast two-hybrid system to show that Tip-1 also interacts with the HPV16 E6 protein. This interaction was confirmed by co-immunoprecipitation from E6 expressing C33A cervical carcinoma cells (C33A-E6) which showed that Tip-1 was not degraded by interaction with the HPV16 E6 oncoprotein. During routine passage we observed that C33A-E6 had a less compact morphology and were less adherent than control vector transfected cells C33A-V cells - a known effect of GTP-RhoA. Comparison of C33A-E6 to C33A-V demonstrated that E6 expressing cells had higher levels of phosphorylated myosin light chains (MLC) and increased cell motility, which was inhibited by antisense silencing of Tip-1 expression and by the RhoA kinase (ROCK) inhibitor Y27632. Both C33A-E6 and C33A-V cells were shown to express GTP activated RhoA. Since ROCKs can be activated by GTP RhoA these data indicate that E6 may increase cell motility by augmenting GTP RhoA mediated activation of ROCKs and that this is dependent on the expression of the Tip-1 protein.     

乳腺浸润性导管癌组织中HPV16、18E6及MCM7蛋白的表达

目的:检测人乳腺浸润性导管癌及乳腺良性病变中HPV16、18E6和MCM7蛋白的表达,探讨高危型HPV感染和细胞周期复制调控异常与人乳腺癌发生、发展的关系.方法:采用免疫组织化学SP法检测30例正常乳腺、30例乳腺腺病,52例乳腺浸润性导管癌组织中HPV16、18E6和MCM7蛋白的表达.结果:癌组中HPV16、18E6和MCM7蛋白的阳性表达分别为57.69%和96.15%,均显著高于正常组和腺病组(P＜0.02、P＜0.05).HPV16、18E6与MCM7蛋白阳性表达呈正相关(r=0.5442;P＜0.001).MCM7蛋白阳性表达与IDC组织学分级、淋巴结转移和肿块大小有关(P＜0.01、P＜0.03、P＜0.01).结论:高危型HPV16、18感染和MCM7蛋白的高表达导致细胞周期复制调控异常涉及了HPV感染后乳腺癌的发生发展过程.MCM7高表达与乳腺癌细胞的增殖、侵袭和转移有关.二者联合检测可作为评价HPV感染乳腺上皮细胞的增殖状态和评价临床预后的生物学指标.     

乳腺浸润性导管癌组织中HPV16、18E6及MCM7蛋白的表达

目的：检测人乳腺浸润性导管癌及乳腺良性病变中HPV16、18E6和MCM7蛋白的表达,探讨高危型HPV感染和细胞周期复制调控异常与人乳腺癌发生、发展的关系。方法：采用免疫组织化学sP法检测30例正常乳腺、30例乳腺腺病,52例乳腺浸润性导管癌组织中HPV16、18E6和MCM7蛋白的表达。结果：癌组中HPV16、18E6和MCM7蛋白的阳性表达分别为57．69％和96．15％,均显著高于正常组和腺病组（P〈0．02、P〈0．05）。HPV16、18E6与MCM7蛋白阳性表达呈正相关（r=0．5442;P〈0．001）。MCM7蛋白阳性表达与IDC组织学分级、淋巴结转移和肿块大小有关（P〈0．01、P〈0．03、P〈0．01）。结论：高危型HPV16、18感染和MCM7蛋白的高表达导致细胞周期复制调控异常涉及了HPV感染后乳腺癌的发生发展过程。MCM7高表达与乳腺癌细胞的增殖、侵袭和转移有关。二者联合检测可作为评价HPV感染乳腺上皮细胞的增殖状态和评价临床预后的生物学指标。     

表达HPV16 E6和E7蛋白的非复制型重组痘苗病毒诱发的抗肿瘤免疫反应

目的　观察表达人乳头瘤病毒 (HPV) 16E6和E7蛋白的非复制型重组痘苗病毒的抗肿瘤免疫效果。方法　以重组痘苗病毒NTVJmE6E7免疫C5 7BL/ 6小鼠 ,检测特异性的细胞毒性T淋巴细胞 (CTL)活性 ;经免疫后的小鼠以TC 1肿瘤细胞攻击 ,观察免疫保护效果 ;荷瘤小鼠切除肿瘤后接种重组痘苗病毒 ,观察肿瘤复发情况。结果　以重组痘苗病毒NTVJmE6E7免疫小鼠 ,可诱导产生针对TC 1细胞的特异性的CTL反应 ;加强免疫后的小鼠能耐受 1× 10 4TC 1细胞的攻击 ;以重组痘苗病毒NTVJmE6E7免疫肿瘤术后小鼠 ,能有效地预防肿瘤复发。结论　非复制型重组痘苗病毒NTVJmE6E7可作为HPV16的相关肿瘤及其癌前病变免疫治疗的候选疫苗。     

E6 proteins from diverse cutaneous HPV types inhibit apoptosis in response to UV damage

In addition to their role in anogenital cancer, human papillomaviruses (HPVs) are also involved in the development of a range of cutaneous lesions. HPV types 5 and 8 are associated with the development of skin cancers in individuals with Epidermodysplasia verruciformis (EV). A broad spectrum of HPV types are also commonly found in non-melanoma skin cancers in immunocompromised individuals, such as organ transplant recipients. The skin cancers in EV and immunocompromised patients occur predominantly at body sites exposed to ultra violet (UV) radiation, pointing to a key role for UV in their development. Here we show that the E6 protein from a range of cutaneous HPV types effectively inhibits apoptosis in response to UV damage. This occurs in both p53 null and wild type cells and does not require p53 degradation.     

The DNA repair protein,O(6)-methylguanine-DNA methyltransferase is a proteolytic target for the E6 human papillomavirus oncoprotein

We have previously shown that O(6)-methylguanine-DNA methyltransferase (MGMT), a DNA repair protein that protects tissues against toxic and carcinogenic effects of alkylating agents, is degraded through ubiquitination-dependent proteolysis. Here, we investigated the role of the human papillomavirus (HPV) E6 protein in MGMT degradation. In three pairs of isogenic human tumor cell lines in which a member of each pair expressed the E6 protein through stable transfection (HCT116/HCT116-E6, MCF7/MCF7-E6, and RKO/RKO-E6), we found a consistent 40-55% reduction in the MGMT protein level and its activity in all E6-expressing cells compared with the parent cells (P=<0.05). E6 expression did not, however, alter the levels of MGMT mRNA. Addition of the recombinant MGMT (rMGMT) protein to extracts of HCT116/E6 cells resulted in the binding of E6 to MGMT. Further, the purified E6 protein promoted the degradation of rMGMT in rabbit reticulocyte lysates. Immunoprecipitation assays showed the presence of a ternary protein complex between MGMT, E6, and the cellular ubiquitin-ligase E6-associated protein (E6-AP). Transient transfection of the p53-null H1299 lung tumor cells with an E6 construct also down-regulated the MGMT. The MGMT protein also showed structural features that are compatible for interaction with the E6, and E6-AP components. Collectively, these data suggest that the oncogenic E6 proteins enhance the ubiquitin-dependent proteolysis of MGMT.     

Vaccination of full-length HPV16 E6 or E7 protein inhibits the growth of HPV16 associated tumors

Cervical cancer is the second most common cancer in women worldwide. Human papillomavirus (HPV) is the primary etiologic agent of cervical cancer. Two HPV16 proteins, E6 and E7, are consistently expressed in tumor cells. Most therapeutic vaccines target one or both of these proteins. Taking the advantages of safety and no human leukocyte antigen restriction, protein vaccine has become the most popular form of HPV therapeutic vaccines. Here we demonstrate that immunization with full-length HPV16 E6 or E7 protein elicited specific immunological effect and inhibition of TC-1 cell growth using TC-1 mouse model. HPV16 E6 and E7 genes were cloned into pET-28a(+) and introduced into E. coli Rosetta. Expression of the genes was induced by IPTG. Proteins were purified by Ni-NTA agarose and they were detected by SDS-PAGE and Western blotting. C57BL/6 mice were vaccinated with 1.5 nmol HPV16 E6 or E7 protein. Then they were implanted with 1x10(5) TC-1 cells. No tumor was detected in any mouse vaccinated with E7 protein. Forty days later, the tumor-free mice and control mice were challenged with 2x10(5) TC-1 cells. All control mice developed tumors 6 days later, but E7 immunized mice were tumor free until 90 days. Tumor growth was slow in the E6 immunized mice, but 83% of the mice developed tumors and the survival percentage was not significantly different from the control. An adoptive immune model was used to demonstrate the therapeutic effect. Results showed that the development of TC-1 cells was obviously reduced by transfusion of T-cells but not serum from mice immunized with E7 protein. T-cells from E7 immunized mice also induced the lysis of TC-1 cells in the cytotoxic T lymphocyte assay. These findings show that immunization with HPV16 E6 or E7 protein was able to elicit specific protective immunity against TC-1 tumor growth.     

HPV16 E6 E7 siRNA作用于人宫颈癌细胞株的实验研究

目的: 使用HPV16 E6、E7 siRNA处理表达HPV16阳性的人宫颈鳞癌细胞株CaSki和SiHa,观察其对HPV16 E6、E7原癌基因的特异性抑制作用,为探讨使用siRNA治疗宫颈癌的可行性提供实验基础. 方法: 分别设计并合成靶向于HPV16 E6、E7的siRNA各3条,经脂质体包裹后转染两株细胞,分别采用RT-PCR和Western Blot方法,通过对转染前后各时间段两基因mRNA及蛋白的表达情况的检测,验证RNAi作用的特异性及时效性. 结果: 同对照组相比,各E6、E7 siRNA均可引起靶基因表达水平的显著性下降(P<0.05);而空脂质体组及阴性对照siRNA组的靶基因表达水平则无明显变化.其中E6-1 siRNA和E7-2 siRNA对靶基因抑制作用较强.E6-1 siRNA和E7-2 siRNA转染两株细胞后24h、48h、72h及96h均可观察到靶基因表达的显著性降低(P<0.05),而对相应的非靶基因无明显抑制作用. 结论: 不同序列的E6、E7 siRNA,对靶基因的干扰效率不同;E6、E7 siRNA分别作用于宫颈鳞癌细胞株,均引起了靶基因的特异、高效性的抑制,而时非靶基因的表达无明显变化,且抑制作用至少维持到转染后96h.为进一步研究采用RAN干扰技术进行宫颈癌的生物治疗奠定了基础.     

Oncogenic human papillomavirus E6 proteins target the discs large tumour suppressor for proteasome-mediated degradation.

Previous studies have shown that the oncogenic HPV E6 proteins form a complex with the human homologue of the Drosophila tumour suppressor protein, discs large (Dlg). This is mediated by the carboxy terminus of the E6 proteins and involves recognition of at least one PDZ domain of Dlg. This region of E6 is not conserved amongst E6 proteins from the low risk papillomavirus types and, hence, binding of HPV E6 proteins to Dlg correlates with the oncogenic potential of these viruses. We have performed studies to investigate the consequences of the interaction between E6 and Dlg. Mutational analysis of both the HPV18 E6 and Dlg proteins has further defined the regions of E6 and Dlg necessary for complex formation. Strikingly, co-expression of wild type HPV18 E6 with Dlg in vitro or in vivo results in a dramatic decrease in the amount of Dlg protein, whereas mutants of E6 which fail to complex with Dlg have minimal effect on Dlg protein levels. The oncogenic HPV16 E6 also decreased the Dlg levels, but this was not observed with the low risk HPV11 E6 protein. Moreover, a region within the first 544 amino acids of Dlg containing the three PDZ domains confers susceptibility to E6 mediated degradation. Finally, treatment of cells with a proteasome inhibitor overrides the capacity of E6 to degrade Dlg. These results demonstrate that Dlg is targeted by high risk HPV E6 proteins for proteasome mediated degradation.     

RNA干扰在宫颈癌HPV16E6/E7中的研究进展

RNA干扰(RNAi)是一种有效的基因沉默过程,宫颈癌的重要基因型HPV16的关键致癌基因是E6和E7,目前RNAi在HPV16 E6/E7中的基因沉默作用已取得一些突破性进展.在体外研究方面,正在进一步确定稳定干扰目的 基因的载体形式和筛选更好的干扰序列,在体内研究方面,已建立相应的动物模型,为RNAi的临床研究打下...     

Enhanced specificity of HPV16 E6E7 siRNA by RNA-DNA chimera modification

Although efforts have been made to develop new drugs for infectious and neoplastic diseases utilizing synthetic small interfering RNA(siRNAs), those intrinsically have undesirable effects, including silencing of unintended genes (off-target effect) and nonspecific cytotoxicity. Off-target effects can be avoided by DNA substitution in the guide strand (GS) seed region of nucleotide positions 1-8 and its complementary part of the passenger strand plus the 3' overhang, which is designated as a double-strand RNA-DNA chimera (dsRDC). In this study, we found that the specificity of potent siRNAs targeting human papillomavirus 16 (HPV16) E6 and E7 oncogenes, which we previously reported, could be enhanced by short dsRDC modification (first six nucleotides from the 5' end of the GS and its complementary nucleotides of the passenger strand). Such dsRDC modification reduced nonspecific cytotoxicity in two of three siRNAs (497 and 752), although not in the other (573), which correlated with their off-target effects. In addition, silencing activity was marginally impaired in two dsRDCs (497 and 573) and moderately in one (752). Finally, dsRDC-497 induced E6E7-specific growth suppression of cervical cancer cells as well as E6E7-immortalized human keratinocytes. Our results show that dsRDC modification enhances the specificity of E6E7 siRNA, which is required for use in in vivo settings.     

HPV E6癌基因诱导宫颈癌发生机制研究进展

HPVE6和E7癌基因与宫颈癌密切相关，其中E6癌基因在宫颈癌的发生、发展过程中起重要作用。HPV-16 E6蛋白能诱导端粒酶的表达，增加角质形成细胞的端粒酶活性，提示端粒酶的活性在细胞永生化和恶变过程中起重要作用，端粒酶的激活是细胞转化的起始步骤。HPVE6癌基因增加细胞端粒酶活性的机制是激活了端粒酶催化亚基hTERT的转录活性。但HPV癌基因突变导致染色体改变、杂合子丢失、原癌基因的激活在宫颈致癌作用中同样起重要作用。针对E6癌基因诱导宫颈癌发生的分子生物学机制，综述近年来E6癌基因与宫颈癌关系方面的研究进展。