HPV-positive Cancer Cells Research Articles

Evaluation of HPV16 E7 expression in head and neck carcinoma cell lines and clinical specimens

Human papillomavirus (HPV) 16 infection in the oropharynx is one of the major risk factors for oropharyngeal carcinoma. Although the HPV E6 and E7 proteins are known to have a role in head and neck carcinogenesis, whether their expression is maintained once the tumour has developed still remains unclear. We evaluated the expression of these proteins in HPV16-positive cancer cell lines and clinical oropharyngeal specimens. Two out of the four commercially available antibodies directed against the E7 protein could detect the E7 protein overexpressed in the 293FT cells, human embryonic kidney cells, although none of the four commercially available anti-E6 antibodies could detect the overexpressed E6 protein. Whereas HPV16-positive head and neck or cervical carcinoma cell lines expressed the E7 mRNA, the antibodies with an ability to detect the E7 protein could not detect it in western blotting in these HPV16-positive cell lines. In clinical specimens, E7 protein was partially detected in p16-positive area in p16-positive and HPV16 DNA-positive samples, but not in p16-negative and HPV DNA-negative or p16-positive and HPV DNA-negative samples. Consistent with these findings, the E7 protein was poorly translated from the endogenous structure of the E7 mRNA, although significant E7 mRNA expression was detected in these samples. Our findings indicate that E7 protein is partially expressed in p16-positive area in p16-positive and HPV16 DNA-positive clinical specimens.

Tyrosine Kinase Inhibitors and Everolimus Reduce IGF1R Expression in HPV16-positive and -negative Squamous Cell Carcinoma.

The effects of tyrosine kinase inhibitors (TKI) in head and neck squamous cell cancer (HNSCC) are not fully understood. We investigated the effects of selective TKIs erlotinib, gefitinib, nilotinib, and dasatinib and the mTOR-inhibitor everolimus on the expression of insulin-like growth factor 1 receptor (IGF1R) in HPV-positive and HPV-negative squamous cancer cell lines. HPV-negative UMSCC-11A and UMSCC-14C cells and HPV-positive CERV196 cells were treated with TKIs or everolimus. Protein concentration of IGF1R was measured using ELISA. IGF1R expression was significantly reduced by all tested TKIs and everolimus in both HPV-negative cancer cell lines. In HPV-positive squamous cancer cells we observed significant protein inhibition. The crosstalk between epidermal growth factor receptors and IGF1R could be of central interest for the development of novel medical approaches for individualized therapy.

DNA demethylation agent 5azadC downregulates HPV16 E6 expression in cervical cancer cell lines independently of TBX2 expression.

HPV16 is the most carcinogenic human papillomavirus and causes >50% of cervical cancers, the majority of anal cancers and 30% of oropharyngeal squamous cell carcinomas. HPV carcinogenesis relies on the continuous expression of the two main viral oncoproteins E6 and E7 that target >150 cellular proteins. Among them, epigenetic modifiers, including DNA Methyl Transferases (DNMT), are dysregulated, promoting an aberrant methylation pattern in HPV-positive cancer cells. It has been previously reported that the treatment of HPV-positive cervical cancer cells with DNMT inhibitor 5-aza-2'-deoxycytidine (5azadC) caused the downregulation of E6 expression due to mRNA destabilization that was mediated by miR-375. Recently, the T-box transcription factor 2 (TBX2) has been demonstrated to repress HPV LCR activity. In the current study, the role of TBX2 in E6 repression was investigated in HPV16 cervical cancer cell lines following 5azadC treatment. A decrease of E6 expression was accompanied by p53 and p21 restoration. While TBX2 mRNA was upregulated in 5azadC-treated SiHa and Ca Ski cells, TBX2 protein was not detectable. Furthermore, the overexpression of TBX2 protein in cervical cancer cells did not allow the repression of E6 expression. The TBX2 transcription factor is therefore unlikely to be associated with the repression of E6 following 5azadC treatment of SiHa and Ca Ski cells.

A novel small-molecule inhibitor of the human papillomavirus E6-p53 interaction that reactivates p53 function and blocks cancer cells growth.

Despite prophylactic vaccination campaigns, human papillomavirus (HPV)-induced cancers still represent a major medical issue for global population, thus specific anti-HPV drugs are needed. Since the ability of HPV E6 oncoprotein to promote p53 degradation is linked to tumor progression, E6 has been proposed as an ideal target for cancer treatment. Using the crystal structure of the E6/E6AP/p53 complex, we performed an in silico screening of small-molecule libraries against a highly conserved alpha-helix in the N-terminal domain of E6 involved in the E6-p53 interaction. We discovered a compound able to inhibit the E6-mediated degradation of p53 through disruption of E6-p53 binding both in vitro and in cells. This compound could restore p53 intracellular levels and transcriptional activity, reduce the viability and proliferation of HPV-positive cancer cells, and block 3D cervospheres formation. Mechanistic studies revealed that the compound anti-tumor activity mainly relies on induction of cell cycle arrest and senescence. Our data demonstrate that the disruption of the direct E6-p53 interaction can be obtained with a small-molecule compound leading to specific antitumoral activity in HPV-positive cancer cells and thus represents a new approach for anti-HPV drug development.

Effects of the antifungal agent ciclopirox in HPV-positive cancer cells: Repression of viral E6/E7 oncogene expression and induction of senescence and apoptosis.

The malignant growth of human papillomavirus (HPV)-positive cancer cells is dependent on the continuous expression of the viral E6/E7 oncogenes. Here, we examined the effects of iron deprivation on the phenotype of HPV-positive cervical cancer cells. We found that iron chelators, such as the topical antifungal agent ciclopirox (CPX), strongly repress HPV E6/E7 oncogene expression, both at the transcript and protein level. CPX efficiently blocks the proliferation of HPV-positive cancer cells by inducing cellular senescence. Although active mTOR signaling is considered to be critical for the cellular senescence response towards a variety of prosenescent agents, CPX-induced senescence occurs under conditions of severely impaired mTOR signaling. Prolonged CPX treatment leads to p53-independent Caspase-3/7 activation and induction of apoptosis. CPX also eliminates HPV-positive cancer cells under hypoxic conditions through induction of apoptosis. Taken together, these results show that iron deprivation exerts profound antiviral and antiproliferative effects in HPV-positive cancer cells and suggest that iron chelators, such as CPX, possess therapeutic potential as HPV-inhibitory, prosenescent and proapoptotic agents in both normoxic and hypoxic environments.

Knockdown of METTL14 inhibits the growth and invasion of cervical cancer

Background: Increasing evidence has revealed that N6-methyladenosine (m6A) modification is implicated in multiple biological functions in mammals. Methyltransferase-like 14 (METTL14), an important component of m6A modification, has been reported to play important roles in the pathogenesis of acute myeloid leukaemia and hepatocellular carcinoma metastasis. However, its role in cervical cancer remains unclear. Methods: Expression of METTL14 was knocked down by shRNA-METTL14 interference in HPV-positive and HPV-negative cervical cancer cell lines SiHa and C33a. CCK8, colony formation, wound-healing, and Transwell assays were performed to evaluate the effects of METTL14 knockdown on the proliferation, migration and invasion abilities of SiHa and C33a cells. Flow cytometry analysis was utilized to detect cell cycle distribution, and the expression of related proteins was examined by western blot analysis. Results: Bioinformatics analysis demonstrated that up-regulation of METTL14 acted as an adverse prognostic factor for overall survival in cervical cancer patients. We demonstrated that down-regulation of METTL14 inhibited the proliferation, migration and invasion abilities of SiHa and C33a cells. Moreover, silencing METTL14 induced cell cycle arrest in cervical cancer cells. METTL14 knockdown suppressed the PI3K/Akt/mTOR signaling pathway by decreasing the phosphorylation of Akt and mTOR, and the expression of downstream apoptosis-related proteins was also impacted. Conclusions: In conclusion, these data suggest an important oncogenic role of METTL14 in the growth and invasion of both HPV-positive and HPV-negative cervical cancer cells.

Roles of E6 and E7 Human Papillomavirus Proteins in Molecular Pathogenesis of Cervical Cancer

Human papillomavirus (HPV) cancers are expected to be major global health concerns in the upcoming decades. The growth of HPV-positive cancer cells depends on the consistent expression of oncoprotein which has been poorly taken into account in the cellular communication. Among them, E6/E7 oncoproteins are attractive therapeutic targets as their inhibition rapidly leads to the onset of aging in HPV-positive cancer cells. This cellular response is associated with the regeneration of p53, pRb anti-proliferative proteins as well as the mTOR signaling pathway; hence, the identification of involved and application of E6/E7 inhibitors can lead to new therapeutic strategies. In the present review, we focused on the pathogenicity of E6/E7 Proteins of human papillomavirus and their roles associated with the cervical cancer.

Abstract 2124: Concurrent in vitro and in silico approach for the identification of surface proteome targets on HPV-associated cancer cells

Abstract Human papillomavirus (HPV)-associated Head and neck cancer (HNSCC) are among the fastest growing cancer types. In contrast to non-viral HNSCC caused by traditional risk factors, tobacco and alcohol, HPV-HNSCC displayed distinct molecular alterations and prognosis from HPV-negative HNSCC. Currently, there is no clinically-approved therapeutic vaccine, and no targeted therapy approach for HPV-driven cancer which exploits the unique biology of HPV infection. In order to identify novel targets suitable for therapeutic and diagnostic development, we developed two parallel approaches to identification of proteins/antigens expressed on the surface of the host cells, whose expression is altered by HPV infection. One is an “antigen-agnostic” approach by using immortalized HNSCC cell membrane fractions to generate monoclonal antibodies, which does not require advance knowledge of the identities of target antigens. The second approach is bioinformatics analyses of the TCGA database using the epigenomic deconvolution tool (EDec) to identify surface proteins that are differentially overexpressed in HPV- HNSCC. Five thousand hybridoma colonies were generated by the “antigen-agnostic” approach, and were then screened by flow cytometry to test the specificity of binding to HPV-positive cancer cell lines (2 HNSCC and 2 Cervical Cancer) and HPV-negative cancer cell lines (4 HNSCC and 1 CC). After primary screening, we narrowed down to forty-four clones with preliminarily favorable binding characteristics; among these hybridoma clones, we have identified seven which preferentially bind to HPV-positive cancer cells. We then identified the binding targets of three clones via immunoprecipitation and mass spectrometry. These targets are integrin alpha6 beta4 (ITGA6, ITGB4), tissue factor (F3) and keratin 8 (KRT8) respectively. The bioinformatics-based approach identified several surface proteins that are differentially overexpressed in HPV-positive HNSCC and at levels significantly higher than found in normal control tissue. Evaluation of gene and protein expression in cancer cell lines and/or patient tissue validated several genes identified by the deconvolution approach, including: ROR2, a non-canonical WNT member not previously associated with head and neck cancer; and LY6K, a cancer-testis antigen that overexpressed in both HPV-positive and negative HNSCC. We propose targeting membrane-expressed antigens on HPV-related cancer cells as a platform for further development of novel tumor imaging and therapeutic approaches for HNSCC and other HPV-associated cancers. Citation Format: Hsuan-Chen Liu, Ivenise Carrero, Falguni Parikh, Thomas Kraus, Thomas M. Moran, Mathew J. Ellis, Elizabeth Y. Chiao, Aleksandar Milosavljevic, Andrew G. Sikora. Concurrent in vitro and in silico approach for the identification of surface proteome targets on HPV-associated cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2124.

Abstract 3792: Restoring DREAM assembly in HPV-positive cancer cell lines promotes growth suppression

Abstract Human Papillomaviruses (HPV) 16 and 18 are recognized as causative factors in 4-5% of all human cancers, including the majority of cervical and oropharyngeal carcinomas. The HPV vaccine is expected to reduce the incidence of HPV-driven cancers in the future. However, millions of people in the US already infected with high-risk HPV are still at risk. Therefore, it remains a priority to improve our understanding of the mechanism of progression of the initial HPV infections to cancer. Furthermore, there are currently no therapies that specifically target HPV-positive cancers, despite evidence that viral genes continue to contribute to growth and survival of established cancer cell lines. In high risk HPV (those that cause cancer), viral protein E7 binds to pRb via a LxCxE motif to relieve repression of E2F1-mediated transcription of S-phase genes, whereas the E6 protein interacts with the tumor suppressor p53 protein and targets it for degradation. Therefore, the consequence of E6 and E7 expression in the host cell is an aberrant induction of cellular proliferation and suppression of apoptosis, which contribute to oncogenic transformation. Recently, it has also been demonstrated that E7 interaction with the pRb-like protein p130 disrupts the transcriptional repressor DREAM (dimerization partner, RB-like, E2F and MuvB) complex. In G0/G1, p130 serves as a scaffold to recruit E2F4/5-DP1/2 transcription factors, and the MuvB core complex of five proteins, to the promoters of approximately 800 cell-cycle regulated genes. In S-phase, DREAM dissociates and the MuvB core binds to B-Myb to promote expression of mitotic genes. The LIN52 subunit of the MuvB core serves as an adaptor that mediates the binding between p130 and MuvB core proteins. Our data show that LIN52 binds to the LxCxE-binding cleft in p130, and that the E7 protein can compete for p130 binding to LIN52 therefore disrupting the DREAM complex. Indeed, we found that the DREAM assembly was impaired in human cancer cell lines HeLa and SiHa containing integrated viral genomes of HPV18 and HPV16, respectively. Using our recently solved structure of the p130-LIN52 complex, we identified a LIN52 mutant (LIN52 S20C) that can compete for HPV E7 binding to p130. Stable expression of S20C-LIN52 in HeLa and SiHa cells resulted in significantly increased DREAM complex assembly as well as suppression of proliferation and colony formation in 2D and 3D cultures. Our findings identify the DREAM complex as an important tumor suppressor disrupted by high risk HPV, and support the rationale for targeting the interaction between the oncogenic HPV proteins and host cell factors as a therapeutic approach for treatment of HPV-positive cancers and pre-cancerous lesions. Citation Format: Fatmata Sesay, Siddharth Saini, Claire James, Jessica Felthousen, Iain Morgan, Larisa Litovchick. Restoring DREAM assembly in HPV-positive cancer cell lines promotes growth suppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3792.

PI3K/AKT/mTOR Signaling Regulates the Virus/Host Cell Crosstalk in HPV-Positive Cervical Cancer Cells.

Human papillomavirus (HPV)-induced cancers will remain a significant clinical challenge for decades. Thus, the development of novel treatment strategies is urgently required, which should benefit from improving our understanding of the mechanisms of HPV-induced cell transformation. This should also include analyses of hypoxic tumor cells, which represent a major problem for cancer therapy. Recent evidence indicates that the PI3K/AKT/mTOR network plays a key role for the virus/host cell crosstalk in both normoxic and hypoxic HPV-positive cancer cells. In normoxic cells, the efficacy of the senescence induction upon experimental E6/E7 repression depends on active mTORC1 signaling. Under hypoxia, however, HPV-positive cancer cells can evade senescence due to hypoxic impairment of mTORC1 signaling, albeit the cells strongly downregulate E6/E7. Hypoxic repression of E6/E7 is mediated by the AKT kinase, which is activated under hypoxia by its canonical upstream regulators mTORC2 and PI3K. This review highlights our current knowledge about the oxygen-dependent crosstalk of the PI3K/AKT/mTOR signaling circuit with the HPV oncogenes and the phenotypic state of the host cell. Moreover, since the PI3K/AKT/mTOR pathway is considered to be a promising target for anticancer therapy, we discuss clinical implications for the treatment of HPV-positive cervical and head and neck squamous cell carcinomas.

Repression of Human Papillomavirus Oncogene Expression under Hypoxia Is Mediated by PI3K/mTORC2/AKT Signaling.

Hypoxia is linked to therapeutic resistance and poor clinical prognosis for many tumor entities, including human papillomavirus (HPV)-positive cancers. Notably, HPV-positive cancer cells can induce a dormant state under hypoxia, characterized by a reversible growth arrest and strong repression of viral E6/E7 oncogene expression, which could contribute to therapy resistance, immune evasion and tumor recurrence. The present work aimed to gain mechanistic insights into the pathway(s) underlying HPV oncogene repression under hypoxia. We show that E6/E7 downregulation is mediated by hypoxia-induced stimulation of AKT signaling. Ablating AKT function in hypoxic HPV-positive cancer cells by using chemical inhibitors efficiently counteracts E6/E7 repression. Isoform-specific activation or downregulation of AKT1 and AKT2 reveals that both AKT isoforms contribute to hypoxic E6/E7 repression and act in a functionally redundant manner. Hypoxic AKT activation and consecutive E6/E7 repression is dependent on the activities of the canonical upstream AKT regulators phosphoinositide 3-kinase (PI3K) and mechanistic target of rapamycin (mTOR) complex 2 (mTORC2). Hypoxic downregulation of E6/E7 occurs, at least in part, at the transcriptional level. Modulation of E6/E7 expression by the PI3K/mTORC2/AKT cascade is hypoxia specific and not observed in normoxic HPV-positive cancer cells. Quantitative proteome analyses identify additional factors as candidates to be involved in hypoxia-induced activation of the PI3K/mTORC2/AKT signaling cascade and in the AKT-dependent repression of the E6/E7 oncogenes under hypoxia. Collectively, these data uncover a functional key role of the PI3K/mTORC2/AKT signaling cascade for viral oncogene repression in hypoxic HPV-positive cancer cells and provide new insights into the poorly understood cross talk between oncogenic HPVs and their host cells under hypoxia.IMPORTANCE Oncogenic HPV types are major human carcinogens. Under hypoxia, HPV-positive cancer cells can repress the viral E6/E7 oncogenes and induce a reversible growth arrest. This response could contribute to therapy resistance, immune evasion, and tumor recurrence upon reoxygenation. Here, we uncover evidence that HPV oncogene repression is mediated by hypoxia-induced activation of canonical PI3K/mTORC2/AKT signaling. AKT-dependent downregulation of E6/E7 is only observed under hypoxia and occurs, at least in part, at the transcriptional level. Quantitative proteome analyses identify additional factors as candidates to be involved in AKT-dependent E6/E7 repression and/or hypoxic PI3K/mTORC2/AKT activation. These results connect PI3K/mTORC2/AKT signaling with HPV oncogene regulation, providing new mechanistic insights into the cross talk between oncogenic HPVs and their host cells.

Long non-coding RNA-OIS1 inhibits HPV-positive, but not HPV-negative cervical squamous cell carcinoma by upregulating MTK-1.

Long non-coding RNA-oncogene-induced senescence 1 (lncRNA-OIS1) is a novel lncRNA that is involved in oncogene-induced senescence, while its functionality in cervical squamous cell carcinoma is unknown. In the present study, 68 human papillomavirus (HPV)-positive and 22 HPV-negative patients with cervical squamous cell carcinoma were recruited. Additionally, 40 healthy females were employed as healthy controls. Tumor tissues and adjacent healthy tissues were collected from all patients with cervical squamous cell carcinoma, and blood samples were obtained. Expression of OIS1 was detected by reverse transcription-quantitative polymerase chain reaction. Receiver operating characteristic curve analysis was used to evaluate the diagnostic value of OIS1 for cervical squamous cell carcinoma. HPV-positive and HPV-negative cervical squamous cell carcinoma and normal cervical cell lines were used, and the effects of OIS1 or mitogen-activated protein kinase kinase kinase 4, (MTK-1) expression vector transfection on the proliferation of cell lines and MTK-1 expression were detected by CCK-8 assay and western blotting, respectively. It was established that a reduction in OIS1 expression level in tumor tissues was apparent only in HPV-positive patients. Serum levels of OIS1 were lower in HPV-positive patients compared with that in HPV-negative patients and healthy controls, and no significant differences were observed between HPV-negative patients and healthy controls. Serum levels of OIS1 were significantly associated with tumor size, but not distant tumor metastasis. OIS1 expression level was lower in HPV-positive cancer cell lines compared with that in HPV-negative cancer cell lines, while no significant differences were observed between HPV-positive and HPV-negative normal cell lines. OIS1 overexpression inhibited and MTK-1 overexpression promoted the proliferation of HPV-positive, but not HPV-negative cancer or normal cell lines. OIS1 transfection also decreased the expression of MTK-1 in HPV-positive cancer cell lines, but not in any of the other cell lines. Therefore, it was concluded that OIS1 inhibited HPV-positive, but not HPV-negative cervical squamous cell carcinoma by upregulating MTK-1.

Isolation and Characterization of an HLA-DRB1*04-Restricted HPV16-E7 T Cell Receptor for Cancer Immunotherapy.

High-risk human papillomavirus (HPV) infection is a causal factor in oropharyngeal and gynecological malignancies, and development of HPV-targeted immunotherapy could be used to treat patients with these cancers. T cell-mediated adoptive immunotherapy targeting E6 and E7, two HPV16 proteins consistently expressed in tumor cells, appears to be both attractive and safe. However, isolation of HPV-specific T cells is difficult owing to the low frequency of these cell precursors in the peripheral blood. In addition, HPV-positive cancer cells often down-regulate major histocompatibility complex (MHC) class I expression ex vivo, limiting the efficacy of MHC class I-restricted approaches. Of particular interest is that both CD4 and CD8 T cells can mediate the responses. Given that CD4 T cells play a critical role in coordinating effective antitumor responses, the generation of a T helper response in patients with HPV16-associated malignancies would unleash the ultimate potential of immunotherapy. In this view, T-cell receptor (TCR) gene transfer could be a relevant strategy to generate HPV16-E7-specific and MHC class II-restricted T cells in sufficient numbers. An HPV16-E7/HLA-DRB1*04 TCR has been isolated from a cancer patient with complete response, and retroviral particles encoding this TCR have been produced. The transgenic TCR is highly expressed in transduced T cells, with a functional inducible caspase-9 suicide gene safety cassette. TCR transgenic T cells are HPV16-E770-89 specific and HLA-DRB1*04 restricted, as determined by interferon (IFN)-γ secretion. CD8 and CD4 T cells are equivalently transduced and secrete interleukin-2 and IFN-γ when cultured with appropriate targets. We also demonstrate that TCR transgenic T cells recognize the endogenously processed and presented HPV16-E770-89 peptide. In conclusion, our data indicate that the production of MHC class II-restricted HPV16-E7-specific T cells is feasible through TCR gene transfer and could be used for immunotherapy.

Abstract 721: Development of a therapeutic HPV vaccine based on mass spectrometry-verified target epitopes

Abstract For rational therapeutic vaccine design, detailed knowledge about target epitopes that are truly presented on cancer cells is essential. Many potential tumor-specific epitopes, such as viral epitopes or mutation-derived neoepitopes, are presented at low abundance. Thus, detection of these epitopes remains a challenge. We have developed a high-sensitivity targeted mass spectrometry (MS) approach for direct detection of low-abundant epitopes. We used human papillomavirus (HPV) as a model system, as high-risk HPVs cause over 600,000 cervical, anogenital and oropharyngeal cancer cases per year. Moreover, the HPV oncoproteins E6 and E7 are essential for the induction and maintenance of the malignant phenotype, and thus are ideal targets for immunotherapy. Potential HPV16 E6 and E7 target epitopes were predicted in silico and their HLA-binding verified in cellular binding assays. HLA-peptide complexes were immunoprecipitated from HPV16-positive cancer cells and the purified peptides were analyzed by MS. Identified HPV epitopes were assessed for immunogenicity in vitro with PBMC from healthy donors and in vivo in the MHC-humanized mouse model A2.DR1. The binding assays resulted in the identification of known and novel HPV16-derived HLA-binding peptides. Furthermore, we used this data to formulate rules on how to optimally use epitope prediction tools to increase the chances of predicting true HLA ligands. 14 HLA-A2-restricted HPV16 epitopes were detected on the surface of CaSki and 866 cervical cancer cells, 9 of which were novel. 13 out of the 14 MS-detected peptides were immunogenic in ELISpot assays. Vaccination of A2.DR1 mice with one selected epitope induced high numbers of specific cytotoxic T-cells, and caused anti-tumor effects in a newly developed HPV16 E6/E7-expressing A2.DR1-compatible tumor model. We conclude that our epitope detection and validation approach is suitable for validating even low-abundant candidate epitopes to be true immunotherapy targets. MS-detection of epitopes appears to be a good predictor of immunogenicity, which makes this approach an attractive platform for determining target epitopes for therapeutic cancer vaccines. Citation Format: Sebastian Kruse, Maria Bonsack, Sara Becker, Nitya Mohan, Alina Steinbach, Stephanie Hoppe, Renata Blatnik, Angelika B. Riemer. Development of a therapeutic HPV vaccine based on mass spectrometry-verified target epitopes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 721.

E6 Protein Expressed by High-Risk HPV Activates Super-Enhancers of the EGFR and c-MET Oncogenes by Destabilizing the Histone Demethylase KDM5C

The high-risk (HR) human papillomaviruses (HPV) are causative agents of anogenital tract dysplasia and cancers and a fraction of head and neck cancers. The HR HPV E6 oncoprotein possesses canonical oncogenic functions, such as p53 degradation and telomerase activation. It is also capable of stimulating expression of several oncogenes, but the molecular mechanism underlying these events is poorly understood. Here, we provide evidence that HPV16 E6 physically interacts with histone H3K4 demethylase KDM5C, resulting in its degradation in an E3 ligase E6AP- and proteasome-dependent manner. Moreover, we found that HPV16-positive cancer cell lines exhibited lower KDM5C protein levels than HPV-negative cancer cell lines. Restoration of KDM5C significantly suppressed the tumorigenicity of CaSki cells, an HPV16-positive cervical cancer cell line. Whole genome ChIP-seq and RNA-seq results revealed that CaSki cells contained super-enhancers in the proto-oncogenes EGFR and c-MET Ectopic KDM5C dampened these super-enhancers and reduced the expression of proto-oncogenes. This effect was likely mediated by modulating H3K4me3/H3K4me1 dynamics and decreasing bidirectional enhancer RNA transcription. Depletion of KDM5C or HPV16 E6 expression activated these two super-enhancers. These results illuminate a pivotal relationship between the oncogenic E6 proteins expressed by HR HPV isotypes and epigenetic activation of super-enhancers in the genome that drive expression of key oncogenes like EGFR and c-METSignificance: This study suggests a novel explanation for why infections with certain HPV isotypes are associated with elevated cancer risk by identifying an epigenetic mechanism through which E6 proteins expressed by those isotypes can drive expression of key oncogenes. Cancer Res; 78(6); 1418-30. ©2018 AACR.

Human Papillomavirus 16 E7 Stabilizes APOBEC3A Protein by Inhibiting Cullin 2-Dependent Protein Degradation.

ABSTRACTAPOBEC3 (A3) mutation signatures have been observed in a variety of human cancer genomes, including those of cervical and head and neck cancers caused by human papillomavirus (HPV) infection. However, the driving forces that promote off-target A3 activity remain mostly unclear. Here, we report a mechanism for the dramatic increase of A3A protein levels in HPV-positive keratinocytes. We show that expression of the viral protein E7 from high-risk HPVs, but not E7 from low-risk HPVs, significantly prolongs the cellular half-life of A3A protein in human keratinocytes and HPV-positive cancer cell lines. We have mapped several residues within the cullin 2 (CUL2) binding motif of HPV16 E7 as being important for mediating A3A protein stabilization. Furthermore, we provide direct evidence that both A3A and HPV16 E7 interact with CUL2, suggesting that the E7-CUL2 complex formed during HPV infection may regulate A3A protein levels in the cell. Using an in vitro cytidine deaminase assay, we show that E7-stabilized A3A remains catalytically active. Taken together, our findings suggest that the HPV oncoprotein E7 dysregulates endogenous A3A protein levels and thus provides novel mechanistic insight into cellular triggers of A3 mutations in HPV-positive cancers.IMPORTANCE Human papillomavirus (HPV) is causally associated with over 5% of all human malignancies. Several recent studies have shown that a subset of cancers, including HPV-positive head and neck and cervical cancers, have distinct mutational signatures potentially caused by members of the APOBEC3 cytidine deaminase family. However, the mechanism that induces APOBEC3 activity in cancer cells is poorly understood. Here, we report that the HPV oncoprotein E7 stabilizes the APOBEC3A (A3A) protein in human keratinocytes by inhibiting ubiquitin-dependent protein degradation in a cullin-dependent manner. Interestingly, the HPV E7-stabilized A3A protein maintains its deaminase activity. These findings provide a new insight into cancer mutagenesis enhanced by virus-induced A3A protein stabilization.

Viral E6/E7 oncogene and cellular hexokinase 2 expression in HPV-positive cancer cell lines.

Oncogenic types of human papillomaviruses (HPVs) are major human carcinogens. Cancer cells typically exhibit metabolic alterations which support their malignant growth. These include an enhanced rate of aerobic glycolysis (‘Warburg effect’) which in cancer cells is often linked to an increased expression of the rate-limiting glycolytic enzyme Hexokinase 2 (HK2). Intriguingly, recent studies indicate that the HPV E6/E7 oncogenes cause the metabolic reprogramming in HPV-positive cancer cells by directly upregulating HK2 expression. Notably, however, these results were obtained upon ectopic overexpression of E6/E7. Here, we investigated whether HK2 levels are affected by the endogenous E6/E7 amounts present in HPV-positive cancer cell lines. RNA interference analyses reveal that the sustained E6/E7 expression is critical to maintain HK2 expression levels in HeLa cells. Mechanistically, this effect is linked to the E6/E7-dependent upregulation of HK2-stimulatory MYC expression and the E6/E7-induced downregulation of the HK2-inhibitory micro(mi)RNA miR-143-3p. Importantly, however, a stimulatory effect of E6/E7 on HK2 expression was observed only in HeLa among a panel of 8 different HPV-positive cervical and head and neck cancer cell lines. Thus, whereas these results support the notion that E6/E7 can increase HK2 expression, they argue against the concept that the viral oncogenes, at endogenous expression levels, commonly induce the metabolic switch of HPV-positive cancer cells towards aerobic glycolysis by directly or indirectly stimulating HK2 expression.

Identification of E6/E7-Dependent MicroRNAs in HPV-Positive Cancer Cells.

Oncogenic types of human papillomaviruses (HPVs) are closely linked to the development of anogenital and head and neck cancers . The expression of the viral E6 and E7 genes is crucial for the transforming activities of HPVs. There is accumulating evidence that the HPV E6/E7 oncogenes can profoundly affect the cellular microRNA (miRNA) composition. Since alterations of miRNA expression levels can contribute to cancer development and maintenance, it will be important to understand in depth the crosstalk between the HPV oncogenes and the cellular miRNA network . Here, we describe a method to identify E6/E7-dependent intracellular miRNAs by small RNA deep sequencing , upon silencing of endogenous E6/E7 expression in HPV-positive cancer cells in vitro. In addition, we provide a protocol to identify E6/E7-dependent miRNA alterations in exosomes that are secreted by HPV-positive cancer cells in vitro.

Lack of differences in radiation-induced immunogenicity parameters between HPV-positive and HPV-negative human HNSCC cell lines

Background and purposeClinical studies indicate that patients with HPV/p16-associated head & neck squamous cell carcinoma (HNSCC) represent a subgroup with a better prognosis and improved response to conventional radiotherapy. Involvement of immune-based factors has been hypothesized. In the present study, we investigated radiation-induced differences in release of damage associated molecular patterns (DAMPs), cytokines and activation of dendritic cells (DCs) in HPV-positive and negative HNSCC cancer cell lines. Material and methodsCalreticulin (CRT) exposure was detected on cancer cell surface. ATP, HMGB1 and cytokines were measured in culture supernatants. Maturation marker CD83 surface exposure was determined on DCs after co-incubation with irradiated tumor cells. ResultsThere was no increase in DAMPs and cytokine profiles after radiation treatment and no difference between HPV+ and HPV− cell lines. The HPV/p16-positive SCC90 cells showed a trend for increased total CRT, HMGB1, and number of cytokines compared to all other cell lines. None of the irradiated cancer cell lines could affect DC maturation. ConclusionsRadiation treatment did not increase immunogenicity of HNSCC cell lines assessed by membrane CRT, ATP, HMGB1, cytokines production, and by activation of immature DCs. There was no difference between HPV-positive and HPV-negative cell lines.

Virus/Host Cell Crosstalk in Hypoxic HPV-Positive Cancer Cells.

Oncogenic types of human papillomaviruses (HPVs) are major human carcinogens. The expression of the viral E6/E7 oncogenes plays a key role for HPV-linked oncogenesis. It recently has been found that low oxygen concentrations (“hypoxia”), as present in sub-regions of HPV-positive cancers, strongly affect the interplay between the HPV oncogenes and their transformed host cell. As a result, a state of dormancy is induced in hypoxic HPV-positive cancer cells, which is characterized by a shutdown of viral oncogene expression and a proliferative arrest that can be reversed by reoxygenation. In this review, these findings are put into the context of the current concepts of both HPV-linked carcinogenesis and of the effects of hypoxia on tumor biology. Moreover, we discuss the consequences for the phenotype of HPV-positive cancer cells as well as for their clinical behavior and response towards established and prospective therapeutic strategies.