Targeting the human papillomavirus E6 and E7 oncogenes through expression of the bovine papillomavirus type 1 E2 protein stimulates cellular motility

The Role of the Hematopoietic Cell-Specific Protein 1-Associated Protein X-1 in Human Papillomavirus 16 E2-Induced Human Cervical Squamous Carcinoma Cell Apoptosis via a Mitochondria-Dependent Pathway

OBJECTIVES

Human papillomavirus 16 (HPV 16) E2 is a transcriptional regulator that plays a key role in regulating a variety of biological responses. Hematopoietic cell-specific protein 1-related protein X-1 (HAX-1) is a mitochondrial membrane protein, and the HAX-1 gene is involved in the occurrence, growth, invasion, and metastasis of various human malignant tumors. The purpose of this study was to investigate the relationships among HPV 16 E2, the role of HAX-1 gene, and the underlying intracellular apoptotic mechanism of human cervical squamous carcinoma cells (C33a and SiHa).

METHODS

In this study, HAX-1 expression was examined using real-time polymerase chain reaction, Western blot, and immunohistochemical staining analysis. Apoptosis of cells was assessed by flow cytometry. The mitochondrial function was assessed by the mitochondrial copy number, reactive oxygen species (ROS) generation, the mitochondrial membrane potential (ΔΨm), and mitochondrial morphology.

RESULTS

Our study demonstrated that the expression of the HAX-1 gene was significantly increased in human cervical carcinoma tissues relative to noncancerous cervix tissues. HPV 16 E2 inhibited HAX-1 protein expression. Overexpression of HAX-1 increased the mitochondrial copy number, decreased the production of ROS, and maintained the integrity of the mitochondrial membrane and morphology. So, enhanced expression of the HAX-1 gene could abrogate the HPV 16 E2-induced cell apoptosis.

CONCLUSION

Therefore, these data support a mechanism that HAX-1 plays a crucial role in HPV 16 E2-induced human cervical squamous carcinoma cell apoptosis in a mitochondrial-dependent manner.

Estrogen Attenuates the Growth of Human Papillomavirus-Positive Epithelial Cells

Human papillomaviruses cause around 5% of all human cancers, yet there are no specific antiviral therapeutic approaches available for combatting these cancers. These cancers are currently treated with standard chemoradiation therapy (CRT). Specific antiviral reagents are desperately required, particularly for HPV+HNSCC whose incidence is increasing and for which there are no diagnostic tools available for combatting this disease. Using data from The Cancer Genome Atlas (TCGA), we and others determined that the estrogen receptor alpha (ERα) is overexpressed in HPV+HNSCC and that elevated levels are associated with an improved disease outcome. This has led to the proposal that estrogen treatment could be a novel therapeutic approach for combatting HPV+cancers. Here, we demonstrate that estrogen attenuates the growth of HPV+epithelial cells using multiple mechanisms, supporting the idea that estrogen has potential as a therapeutic agent for the treatment of HPV+HNSCC.

Human papillomaviruses (HPVs) are small, double-stranded DNA viruses that are significant risk factors in the development of cancer, and HPV accounts for approximately 5% of all worldwide cancers. Recent studies using data from The Cancer Genome Atlas (TCGA) have demonstrated that elevated levels of estrogen receptor alpha (ERα) are associated with improved survival in oropharyngeal cancers, and these elevated receptor levels were linked with human papillomavirus-positive cancers (HPV+cancers). There has been a dramatic increase in HPV-related head and neck squamous cell carcinomas (HPV+HNSCCs) over the last 2 decades, and therapeutic options for this ongoing health crisis are a priority; currently, there are no antiviral therapeutics available for combatting HPV+cancers. During our TGCA studies on head and neck cancer, we had also discovered the overexpression of ERα in HPV+cancers. Here, we demonstrate that 17β-estradiol (estrogen) attenuates the growth/cell viability of HPV+cancers in vitro, but not HPV-negative cancer cells. In addition, N/Tert-1 cells (foreskin keratinocytes immortalized with human telomerase reverse transcriptase [hTERT]) containing human papillomavirus 16 (HPV16) have elevated levels of ERα and growth sensitivity after estrogen treatment compared with parental N/Tert-1 cells. Finally, we demonstrate that there are potentially two mechanisms contributing to the attenuation of HPV+ cell growth following estrogen treatment. First, estrogen represses the viral transcriptional long control region (LCR) downregulating early gene expression, including E6/E7. Second, expression of E6 and E7 by themselves sensitizes cells to estrogen. Overall, our results support the recent proposal that estrogen could be exploited therapeutically for the treatment of HPV-positive oral cancers.

IMPORTANCE Human papillomaviruses cause around 5% of all human cancers, yet there are no specific antiviral therapeutic approaches available for combatting these cancers. These cancers are currently treated with standard chemoradiation therapy (CRT). Specific antiviral reagents are desperately required, particularly for HPV+HNSCC whose incidence is increasing and for which there are no diagnostic tools available for combatting this disease. Using data from The Cancer Genome Atlas (TCGA), we and others determined that the estrogen receptor alpha (ERα) is overexpressed in HPV+HNSCC and that elevated levels are associated with an improved disease outcome. This has led to the proposal that estrogen treatment could be a novel therapeutic approach for combatting HPV+cancers. Here, we demonstrate that estrogen attenuates the growth of HPV+epithelial cells using multiple mechanisms, supporting the idea that estrogen has potential as a therapeutic agent for the treatment of HPV+HNSCC.

Transforming properties of ovine papillomaviruses E6 and E7 oncogenes

An increasing number of studies suggest that cutaneous papillomaviruses (PVs) might be involved in skin carcinogenesis. However, only a few animal PVs have been investigated regard to their transformation properties. Here, we investigate and compare the oncogenic potential of 2 ovine Delta and Dyokappa PVs, isolated from ovine skin lesions, in vitro and ex vivo. We demonstrate that both OaPV4 (Delta) and OaPV3 (Dyokappa) E6 and E7 immortalize primary sheep keratinocytes and efficiently deregulate pRb pathway, although they seem unable to alter p53 activity. Moreover, OaPV3 and OaPV4-E6E7 expressing cells show different shape, doubling time, and clonogenic activities, providing evidence for a stronger transforming potential of OaPV3 respect to OaPV4. Also, similarly to high-risk mucosal and cutaneous PVs, the OaPV3-E7 protein, constantly expressed in sheep squamous cell carcinomas, binds pRb with higher affinity compared to the E7 encoded by OaPV4, a virus associated to fibropapilloma. Finally, we found that OaPV3 and OaPV4-E6E7 determine upregulation of the pro-proliferative proteins cyclin A and cdk1 in both human and ovine primary keratinocytes. Collectively, results provide evidence for implication of ovine PVs in cutaneous proliferative lesions and skin cancer progression, and indicate sheep as a possible animal model for the study of cutaneous lesions and malignancies.

The role of eukaryotic translation initiation factor 5A-1 (eIF5A-1) gene in HPV 16 E6 induces cell growth in human cervical squamous carcinoma cells

Human Papillomavirus (HPV) is considered as the major risk factor for the development and progression of cervical cancer. The high expression of HPV 16 E6 may be the causative factor for induction and maintenance of the transformed phenotype. These oncoproteins would interact with several intracellular proteins, such as eukaryotic translation initiation factor 5A-1 (eIF5A-1) that is essential for proliferation of eukaryotic cells. Our study explored the expression level of HPV 16 E6 and eIF5A-1 in human cervical squamous carcinoma samples and the adjacent non-cancerous cervix samples. Both C33a cells and SiHa cells transfected with a vector encoding HPV 16 E6 resulted in increase of eIF5A-1 expression level and enhancement of viability, migration and proliferation of these cells, furthermore, these effects in both C33a cells and SiHa cells could be abrogated by treatment with eIF5A-1 small-interfering RNA (siRNA) or the specific inhibitors ciclopirox (CPX) that was used to inhibit the function of eIF5A-1 via blocking the main enzymes deoxyhypusine hydroxylase (DOHH). Our results support that the silencing the eIF5A-1 gene or blocking the DOHH could induce the apoptosis of HPV 16 E6-infected cervical carcinoma cells. Thus might provide a new approach to preventing and treating cervical cancer.

Retrospective analysis of HPV 16/18-related disease burden using archival clinical samples

PURPOSE

Estimation of HPV-related disease burden lies at the core of effective disease management. HPV testing is heavily reliant on its retrospective detection in archival clinical cancer samples, especially in parts of the world where HPV screening is not routinely practiced. During the last decade, valuable insights were gained through regional reports based on occasional screening of cervical smears or biopsy sections for the presence of high-risk HPV. HPV 16 and 18 were found to be predominant high-risk HPV subtypes with some regional differences and incidences of co-infections, detected mostly through PCR-based methods. In cases of multiple infections, the presence of viral DNA may not signify its etiologic involvement. The current study, therefore, combines PCR-based detection method with the immunohistochemical (IHC) detection of early viral protein E6 expression, in order to obtain a reliable read out for the disease causing viral subtype, especially in cases of co-infections with oncogenic subtypes other than HPV 16 and 18. Immunohistochemistry (IHC) and PCR-based methods are routinely used laboratory techniques in local hospitals. The concordance between IHC and PCR-based analyses may be useful for determining effective method for the retrospective testing of HPV 16 and 18 disease-related burden.

METHODS

A total of 49 paraffin-embedded cervical cancer biopsy sections representing patients from the northwest region of the country were collected from the tertiary care hospital for this study. Genotyping for HPV 16 and 18 was carried out through PCR. The HPV 16/18 E6 protein expression was evaluated by IHC and was compared with the clinicopathological features of cervical cancer.

RESULTS

Molecular analysis of 33 (67 %), E6-expressing paraffin-embedded cervical cancer biopsy sections revealed the presence of HPV 16 (n = 23; 47 %), HPV 18 (n = 6; 12 %) and co-infection (n = 4; 8 %) in 49 tumors through PCR. Despite the PCR-based detection of viral DNA in 37 cervical cancer samples, IHC analysis of E6 expression revealed the etiological involvement of HPV 16/18 in 33 out of 37 cervical cancer samples. Overall, there was 85 % concordance in the results of the two techniques.

CONCLUSION

IHC analysis provides more conclusive evidence regarding the etiological involvement of the viral subtypes, especially in the presence of multiple infections. About two-thirds (67 %) of cervical cancer samples were found to be caused due to HPV 16/18. Latent occurrence of HPV 16 and 18 is suggested in less than 10 % cervical cancer samples which were found to harbor viral DNA without E6 expression. Furthermore, E6 expression was found to be significantly correlated with the tumor grade.

Design of a PDZbody, a bivalent binder of the E6 protein from human papillomavirus

Chronic infection by high risk human papillomavirus (HPV) strains may lead to cancer. Expression of the two viral oncoproteins E6 and E7 is largely responsible for immortalization of infected cells. The HPV E6 is a small (approximately 150 residues) two domain protein that interacts with a number of cellular proteins including the ubiquitin ligase E6-associated protein (E6AP) and several PDZ-domain containing proteins. Our aim was to design a high-affinity binder for HPV E6 by linking two of its cellular targets. First, we improved the affinity of the second PDZ domain from SAP97 for the C-terminus of HPV E6 from the high-risk strain HPV18 using phage display. Second, we added a helix from E6AP to the N-terminus of the optimized PDZ variant, creating a chimeric bivalent binder, denoted PDZbody. Full-length HPV E6 proteins are difficult to express and purify. Nevertheless, we could measure the affinity of the PDZbody for E6 from another high-risk strain, HPV16 (Kd = 65 nM). Finally, the PDZbody was used to co-immunoprecipitate E6 protein from HPV18-immortalized HeLa cells, confirming the interaction between PDZbody and HPV18 E6 in a cellular context.

HPV16 E2 enhances the expression of NF-κB and STAT3 target genes and potentiates NF-κB activation by inflammatory mediators

HPV-transformed cells exhibit activation of NF-κB and STAT3 (mediators of inflammation), but very little is known about their regulation under inflammatory conditions before HPV integration. This study reports that cervical tissues with stromal inflammation and intact HPV16 E2 gene show increased expression of target genes of NF-κB and/or STAT3 which can regulate cell survival (cyclin D1, c-Myc, survivin and Bcl2) and inflammatory responses (TNF-α, IL-1β, IL-6, IL-8 and CCR2). Increased expression of RelA, p-IκBα, STAT3, p-STAT3 (Ser727), Pin1 (peptidyl-prolyl cis/trans isomerase) and MCM2 in the squamous epithelia of cervices with stromal inflammation supports early activation of NF-κB-STAT3. Furthermore, HPV16 E2 potentiated NF-κB activation induced by inflammatory mediators, IL-1β and SDF-1α, in HEK293 cells. These results reveal a novel role for E2 in regulating the activities of NF-κB and STAT3 that may have implications in carcinogenic progression of HPV16-infected cells under conditions of stromal inflammation.

SAHA inhibits the transcription initiation of HPV18 E6/E7 genes in HeLa cervical cancer cells

High risk human papillomavirus (HPV) is a well recognized causative agent of cervical cancer. Suberoylanilide hydroxamic acid (SAHA) is a potential anti-cervical cancer drug; however, its effect on the expression of HPV E6 and E7 genes remains unclear. Here, we show that, in SAHA treated HeLa cells, HPV18 E6 and E7 mRNA and protein levels were reduced, HPV18 promoter activity was decreased, and the association of RNP II with HPV18 promoter was diminished, suggesting that SAHA inhibited the transcription initiation of HPV18 E6 and E7 genes. In SAHA-treated HeLa, although the level of lysine 9-acetylated histone H3 in the whole cell extracts increased obviously, its enrichment on HPV18 promoter was significantly reduced which is correlated with the down-regulation of HPV E6 and E7.

The role of the globular heads of the C1q receptor in HPV-16 E2-induced human cervical squamous carcinoma cell apoptosis via a mitochondria-dependent pathway

Background

Human papillomavirus type-16 (HPV-16) E2 protein acts as a transcriptional modulator and plays a key role in regulating many biological responses. The purpose of this study was to investigate the relationship between HPV-16 E2, the receptor for the globular heads of human C1q (gC1qR) gene expression, mitochondrial dysfunction and apoptosis regulation in human cervical squamous carcinoma cells (C33a and SiHa).

Methods

HPV-16 E2 and gC1qR expression was examined using real-time PCR and western blot analysis. Apoptosis in C33a and SiHa cells was assessed by flow cytometry. Mitochondrial function was detected via ROS generation, the amount of cytosolic Ca²⁺, and changes in the mitochondrial membrane potential (Δψm).

Results

The expression of the HPV-16 E2 and gC1qR gene significantly decreased in human cervical squamous carcinoma samples relative to the non-cancerous cervix samples. C33a and SiHa cells that were transfected with a vector encoding HPV-16 E2 displayed significantly increased gC1qR gene expression and mitochondrial dysfunction as well as an up-regulation of cellular apoptosis, which was abrogated by the addition of gC1qR small-interfering RNA (siRNA).

Conclusions

These data support a mechanism whereby gC1qR plays an important role in HPV-16 E2-induced human cervical squamous carcinoma cell apoptosis via a mitochondria-dependent pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0286-y) contains supplementary material, which is available to authorized users.

Regulation of human genome expression and RNA splicing by human papillomavirus 16 E2 protein

Human papillomavirus 16 (HPV16) is causative in human cancer. The E2 protein regulates transcription from and replication of the viral genome; the role of E2 in regulating the host genome has been less well studied. We have expressed HPV16 E2 (E2) stably in U2OS cells; these cells tolerate E2 expression well and gene expression analysis identified 74 genes showing differential expression specific to E2. Analysis of published gene expression data sets during cervical cancer progression identified 20 of the genes as being altered in a similar direction as the E2 specific genes. In addition, E2 altered the splicing of many genes implicated in cancer and cell motility. The E2 expressing cells showed no alteration in cell growth but were altered in cell motility, consistent with the E2 induced altered splicing predicted to affect this cellular function. The results present a model system for investigating E2 regulation of the host genome.

HPV16 E2-mediated potentiation of NF-κB activation induced by TNF-α involves parallel activation of STAT3 with a reduction in E2-induced apoptosis

Human papilloma virus is associated with cervical and other tumors, and several cellular conditions also play an important role in carcinogenesis. Human papilloma virus (HPV)-infected cells exhibit activation of NF-κB and STAT3 (mediators of inflammation), but little is known about their regulation by HPV. This study attempts to understand the role of HPV16 E2, an important early protein of HPV16, in the regulation of NF-κB and STAT3 by reporter assays, quantitative reverse transcriptase-polymerase chain reaction, and immunoblotting. We demonstrate that E2 enhances NF-κB activation induced by TNF-α, a proinflammatory cytokine, in both non-tumor- and tumor-derived epithelial cell lines besides potentiating STAT3 transcriptional activity induced by TNF-α in HEK293 cells. E2 increases the expression of RelA and its transcriptional activation, and retention of E2 was observed in the nucleus with significant interaction with RelA (immunoprecipitation) upon TNF-α treatment. Transfection with shRNA-RelA or pretreatment with a STAT3 inhibitor had a negative effect on the ability of E2 to enhance TNF-α-induced NF-κB activation. Experiments with co-expression of a mutant of STAT3 with E2 also suggested that the activation of STAT3 is indispensible for TNF-α-induced NF-κB activation. Inhibition of STAT3 activation enhanced E2-induced apoptosis, whereas parallel activation of NF-κB and STAT3 by the combined action of E2 and TNF-α increased the expression of their common targets, cyclin-D1, c-Myc, survivin, and Bcl-2, leading to a decrease in E2-induced apoptosis (viability and cell cycle). Our results reveal novel mechanisms by which E2 may regulate NF-κB and STAT3 activation in the presence of TNF-α with implications on the survival of HPV-infected cells.

Photon-induced cell migration and integrin expression promoted by DNA integration of HPV16 genome

BACKGROUND

Persistent human papilloma virus 16 (HPV16) infections are a major cause of cervical cancer. The integration of the viral DNA into the host genome causes E2 gene disruption which prevents apoptosis and increases host cell motility. In cervical cancer patients, survival is limited by local infiltration and systemic dissemination. Surgical control rates are poor in cases of parametrial infiltration. In these patients, radiotherapy (RT) is administered to enhance local control. However, photon irradiation itself has been reported to increase cell motility. In cases of E2-disrupted cervical cancers, this phenomon would impose an additional risk of enhanced tumor cell motility. Here, we analyze mechanisms underlying photon-increased migration in keratinocytes with differential E2 gene status.

METHODS

Isogenic W12 (intact E2 gene status) and S12 (disrupted E2 gene status) keratinocytes were analyzed in fibronectin-based and serum-stimulated migration experiments following single photon doses of 0, 2, and 10 Gy. Quantitative FACS analyses of integrin expression were performed.

RESULTS

Migration and adhesion are increased in E2 gene-disrupted keratinocytes. E2 gene disruption promotes attractability by serum components, therefore, effectuating the risk of local infiltration and systemic dissemination. In S12 cells, migration is further increased by photon RT which leads to enhanced expression of fibronectin receptor integrins.

CONCLUSION

HPV16-associated E2 gene disruption is a main predictor of treatment-refractory cancer virulence. E2 gene disruption promotes cell motility. Following photon RT, E2-disrupted tumors bear the risk of integrin-related infiltration and dissemination.

Papillomavirus-associated squamous skin cancers following transplant immunosuppression: one Notch closer to control

The frequent occurrence of cutaneous squamous cell carcinomas (SCCs) containing weakly tumorigenic human papillomaviruses (HPVs) following iatrogenic immunosuppression for organ transplantation remains incompletely understood. Here we address this problem in the light of recent insights into (1) the association of low-risk β-HPVs with skin SCCs in the rare genetic syndromes of epidermodysplasia verruciformis and xeroderma pigmentosum, (2) the frequent recovery of post-transplant tumor control on substituting calcineurin-inhibitory with mTOR-inhibitory immunosuppression, (3) the unexpectedly favorable prognosis of node-positive SCCs containing high-risk α-HPVs originating in the activated immune niche of the oropharynx, (4) the rapid occurrence of HPV-negative SCCs in ultraviolet (UV)-damaged skin of melanoma patients receiving Raf-inhibitory drugs, and (5) the selective ability of β-HPV E6 oncoproteins to inhibit Notch tumor-suppressive signaling in cutaneous and mesenchymal tissues. The crosstalk so implied between oncogenic UV-induced mutations, defective host immunity, and β-HPV-dependent stromal-epithelial signaling suggests that immunosuppressants such as calcineurin inhibitors intensify mitogenic signalling in TP53-mutant keratinocytes while also abrogating immune-dependent Notch-mediated tumor repression. This emerging interplay between solar damage, viral homeostasis and immune control makes it timely to reappraise strategies for managing skin SCCs in transplant patients.