Nucleotide deficiency promotes genomic instability in early stages of cancer development.

Chromosomal instability in early cancer stages is caused by stress on DNA replication. The molecular basis for replication perturbation in this context is currently unknown. We studied the replication dynamics in cells in which a regulator of S phase entry and cell proliferation, the Rb-E2F pathway, is aberrantly activated. Aberrant activation of this pathway by HPV-16 E6/E7 or cyclin E oncogenes significantly decreased the cellular nucleotide levels in the newly transformed cells. Exogenously supplied nucleosides rescued the replication stress and DNA damage and dramatically decreased oncogene-induced transformation. Increased transcription of nucleotide biosynthesis genes, mediated by expressing the transcription factor c-myc, increased the nucleotide pool and also rescued the replication-induced DNA damage. Our results suggest a model for early oncogenesis in which uncoordinated activation of factors regulating cell proliferation leads to insufficient nucleotides that fail to support normal replication and genome stability.

HPV16 E6 induces chromosomal instability due to polar chromosomes caused by E6AP-dependent degradation of the mitotic kinesin CENP-E.

Chromosome segregation during mitosis is highly regulated to ensure production of genetically identical progeny. Recurrent mitotic errors cause chromosomal instability (CIN), a hallmark of tumors. The E6 and E7 oncoproteins of high-risk human papillomavirus (HPV), which causes cervical, anal, and head and neck cancers (HNC), cause mitotic defects consistent with CIN in models of anogenital cancers, but this has not been studied in the context of HNC. Here, we show that HPV16 induces a specific type of CIN in patient HNC tumors, patient-derived xenografts, and cell lines, which is due to defects in chromosome congression. These defects are specifically induced by the HPV16 oncogene E6 rather than E7. We show that HPV16 E6 expression causes degradation of the mitotic kinesin CENP-E, whose depletion produces chromosomes that are chronically misaligned near spindle poles (polar chromosomes) and fail to congress. Though the canonical oncogenic role of E6 is the degradation of the tumor suppressor p53, CENP-E degradation and polar chromosomes occur independently of p53. Instead, E6 directs CENP-E degradation in a proteasome-dependent manner via the E6-associated ubiquitin protein ligase E6AP/UBE3A. This study reveals a mechanism by which HPV induces CIN, which may impact HPV-mediated tumor initiation, progression, and therapeutic response.

Diverse tumorigenic consequences of human papillomavirus integration in primary oropharyngeal cancers.

Human papillomavirus (HPV) causes 5% of all cancers and frequently integrates into host chromosomes. The HPV oncoproteins E6 and E7 are necessary but insufficient for cancer formation, indicating that additional secondary genetic events are required. Here, we investigate potential oncogenic impacts of virus integration. Analysis of 105 HPV-positive oropharyngeal cancers by whole-genome sequencing detects virus integration in 77%, revealing five statistically significant sites of recurrent integration near genes that regulate epithelial stem cell maintenance (i.e., SOX2, TP63, FGFR, MYC) and immune evasion (i.e., CD274). Genomic copy number hyperamplification is enriched 16-fold near HPV integrants, and the extent of focal host genomic instability increases with their local density. The frequency of genes expressed at extreme outlier levels is increased 86-fold within ±150 kb of integrants. Across 95% of tumors with integration, host gene transcription is disrupted via intragenic integrants, chimeric transcription, outlier expression, gene breaking, and/or de novo expression of noncoding or imprinted genes. We conclude that virus integration can contribute to carcinogenesis in a large majority of HPV-positive oropharyngeal cancers by inducing extensive disruption of host genome structure and gene expression.

The role of HPV11 E7 in modulating STING-dependent interferon ß response in recurrent respiratory papillomatosis.

Recurrent respiratory papillomatosis (RRP) is a rare benign tumor caused mainly by the infection of the respiratory tract epithelial cells by the human papillomavirus (HPV) type 6/11. However, the specific mechanisms underlying the inhibition of the host's innate immune response by HPV remain unclear. For this purpose, we employed single-cell RNA sequencing to analyze the states of various immune cells in RRP samples post-HPV infection and utilized a cellular model of HPV infection to elucidate the mechanisms by which HPV evades the innate immune system in RRP. The results revealed distinct immune cell heterogeneity in RRP and demonstrated that HPV11 E7 can inhibit the phosphorylation of the stimulator of interferon genes protein, thereby circumventing the body's antiviral response. In vitro co-culture experiments demonstrated that stimulation of macrophages to produce interferon-beta induced the death of HPV-infected epithelial cells, also reducing HPV viral levels. In summary, our study preliminarily identifies the potential mechanisms by which HPV evades the host's antiviral immune response, as well as the latent antiviral functions exhibited by activated macrophages. This research serves as an initial exploration of antiviral immune evasion in RRP, laying a solid foundation for investigating immunotherapeutic approaches for the disease.IMPORTANCESurgical tumor reduction is the most common treatment for recurrent respiratory papillomatosis (RRP). One of the characteristics of RRP is its persistent recurrence, and multiple surgeries are usually required to control the symptoms. Recently, some adjuvant therapies have shown effectiveness, but none of them can completely clear human papillomavirus (HPV) infection, and thus, a localized antiviral immune response is significant for disease control; after all, HPV infection is limited to the epithelium. Inhibition of interferon-beta (IFN-ß) secretion by HPV11 E7 viral proteins in epithelial cells by affecting stimulator of interferon genes phosphorylation may account for the persistence of low-risk HPV replication in the RRP. Moreover, suppression of the IFN-I pathway in RRP cell types might provide clues regarding the hyporeactive function of local immune cells. However, activation of macrophage groups to produce IFN-ß can still destroy HPV-infected cells.

The membrane-associated ubiquitin ligase MARCHF8 stabilizes the human papillomavirus oncoprotein E7 by degrading CUL1 and UBE2L3 in head and neck cancer.

The human papillomavirus (HPV) oncoprotein E7 is a relatively short-lived protein required for HPV-driven cancer development and maintenance. E7 is degraded through ubiquitination mediated by cullin 1 (CUL1) and the ubiquitin-conjugating enzyme E2 L3 (UBE2L3). However, E7 proteins are maintained at high levels in most HPV-positive cancer cells. A previous proteomics study has shown that UBE2L3 and CUL1 protein levels are increased by the knockdown of the E3 ubiquitin ligase membrane-associated ring-CH-type finger 8 (MARCHF8). We have recently demonstrated that HPV16 upregulates MARCHF8 expression in HPV-positive keratinocytes and head and neck cancer (HPV+ HNC) cells. Here, we report that MARCHF8 stabilizes the HPV16 E7 protein by degrading the components of the S-phase kinase-associated protein 1-CUL1-F-box ubiquitin ligase complex in HPV+ HNC cells. We found that MARCHF8 knockdown in HPV+ HNC cells drastically decreases the HPV16 E7 protein level while increasing the CUL1 and UBE2L3 protein levels. We further revealed that the MARCHF8 protein binds to and ubiquitinates CUL1 and UBE2L3 proteins and that MARCHF8 knockdown enhances the ubiquitination of the HPV16 E7 protein. Conversely, the overexpression of CUL1 and UBE2L3 in HPV+ HNC cells decreases HPV16 E7 protein levels and suppresses tumor growth in vivo. Our findings suggest that HPV-induced MARCHF8 prevents the degradation of the HPV16 E7 protein in HPV+ HNC cells by ubiquitinating and degrading CUL1 and UBE2L3 proteins.IMPORTANCESince human papillomavirus (HPV) oncoprotein E7 is essential for virus replication; HPV has to maintain high levels of E7 expression in HPV-infected cells. However, HPV E7 can be efficiently ubiquitinated by a ubiquitin ligase and degraded by proteasomes in the host cell. Mechanistically, the E3 ubiquitin ligase complex cullin 1 (CUL1) and ubiquitin-conjugating enzyme E2 L3 (UBE2L3) components play an essential role in E7 ubiquitination and degradation. Here, we show that the membrane ubiquitin ligase membrane-associated ring-CH-type finger 8 (MARCHF8) induced by HPV16 E6 stabilizes the E7 protein by degrading CUL1 and UBE2L3 and blocking E7 degradation through proteasomes. MARCHF8 knockout restores CUL1 and UBE2L3 expression, decreasing E7 protein levels and inhibiting the proliferation of HPV-positive cancer cells. Additionally, overexpression of CUL1 or UBE2L3 decreases E7 protein levels and suppresses in vivo tumor growth. Our results suggest that HPV16 maintains high E7 protein levels in the host cell by inducing MARCHF8, which may be critical for cell proliferation and tumorigenesis.

MmuPV1 E7's interaction with PTPN14 delays Epithelial differentiation and contributes to virus-induced skin disease.

Human papillomaviruses (HPVs) contribute to approximately 5% of all human cancers. Species-specific barriers limit the ability to study HPV pathogenesis in animal models. Murine papillomavirus (MmuPV1) provides a powerful tool to study the roles of papillomavirus genes in pathogenesis arising from a natural infection. We previously identified Protein Tyrosine Phosphatase Non-Receptor Type 14 (PTPN14), a tumor suppressor targeted by HPV E7 proteins, as a putative cellular target of MmuPV1 E7. Here, we confirmed the MmuPV1 E7-PTPN14 interaction. Based on the published structure of the HPV18 E7/PTPN14 complex, we generated a MmuPV1 E7 mutant, E7K81S, that was defective for binding PTPN14. Wild-type (WT) and E7K81S mutant viral genomes replicated as extrachromosomal circular DNAs to comparable levels in mouse keratinocytes. E7K81S mutant virus (E7K81S MmuPV1) was generated and used to infect FoxN/Nude mice. E7K81S MmuPV1 caused neoplastic lesions at a frequency similar to that of WT MmuPV1, but the lesions arose later and were smaller than WT-induced lesions. The E7K81S MmuPV1-induced lesions also had a trend towards a less severe grade of neoplastic disease. In the lesions, E7K81S MmuPV1 supported the late (productive) stage of the viral life cycle and promoted E2F activity and cellular DNA synthesis in suprabasal epithelial cells to similar degrees as WT MmuPV1. There was a similar frequency of lateral spread of infections among mice infected with E7K81S or WT MmuPV1. Compared to WT MmuPV1-induced lesions, E7K81S MmuPV1-induced lesions had a significant expansion of cells expressing differentiation markers, Keratin 10 and Involucrin. We conclude that an intact PTPN14 binding site is necessary for MmuPV1 E7's ability to contribute to papillomavirus-induced pathogenesis and this correlates with MmuPV1 E7 causing a delay in epithelial differentiation, which is a hallmark of papillomavirus-induced neoplasia.

BRCA1 deficiency enhances the aggressiveness of breast cancer cells expressing HPV16 oncoproteins.

BACKGROUND INFORMATION: The precise etiology of breast cancer is not completely understood, although women with BRCA1 gene mutations have a significantly increased risk of developing the disease. In addition, sporadic breast cancer is frequently associated with decreased BRCA1 gene expression. Growing evidence of Human papillomaviruses (HPVs) infections in breast tumors has raised the possibility of the involvement of HPVs in the pathogenesis of breast cancer. We investigated whether the effects of HPV oncoproteins E6 and E7 were influenced by the expression levels of BRCA1. HPV16E6E7 (prototype or E6D25E/E7N29S Asian variant type) were stably expressed in MDA-MB231 breast cancer cells, wild type for BRCA1, or with BRCA1 knocked down. RESULTS: Expression of HPV16E6E7 oncogenes did not affect BRCA1 levels and the abundance of HPV16E6E7 was not altered by BRCA1 knockdown. BRCA1 levels did not alter HPV16E6E7-dependent degradation of G1-S cell cycle proteins p53 and pRb. However, we found that the expression of G2-M cell cycle protein cyclin B1 enhanced by HPV16E6E7 was impacted by BRCA1 levels. Especially, we found the correlation between BRCA1 and cyclin B1 expression and this was also confirmed in breast cancer samples from a Thai cohort. We further demonstrated that the combination of HPV oncoproteins and low levels of BRCA1 protein appears to enhance proliferation and invasion. Transactivation activities of HPV16E6E7 on genes regulating cell proliferation and invasion (TGF-ß and vimentin) were significantly increased in BRCA1-deficient cells. CONCLUSIONS: Our results indicate that a deficiency of BRCA1 promotes the transactivation activity of HPV16E6E7 leading to increase of cell proliferation and invasion. SIGNIFICANCE: HPV infection appears to have the potential to enhance the aggressiveness of breast cancers, especially those deficient in BRCA1.

Alterations of UHRF family Expression and was regulated by High Risk Type HPV16 in Uterine Cervical Cancer.

The altered protein expression of inverted CCAAT box-binding protein of 90 kDa/ubiquitin-like with PHD and RING finger domains 1 (ICBP90/UHRF1), and Np95-like ring finger protein (NIRF)/UHRF2, which belong to the ubiquitin-like with PHD and RING finger domains (UHRF) family, is linked to tumor malignancy and the progression of various cancers. In this study, we analyzed the UHRF family expression in cervical cancers, and it's regulation by human papillomavirus (HPV). Western blotting was performed to analyze protein expression in cervical cancer cell lines. Immunohistochemical analysis were used to investigate the expression of UHRF family and MIB-1 in cervical cancer tissues. Transfection were done for analyze the relationship between UHRF family and HPVs. We showed that NIRF expression was decreased and ICBP90 expression was increased in cervical cancers compared to normal counterparts. Western blotting also showed that NIRF expression was quite low levels, but ICBP90 was high in human cervical cancer cell lines. Interestingly, ICBP90 was up regulated by high risk type HPV16 E6 and E7, but not low-risk type HPV11. On the other hand, NIRF was down regulated by high risk type HPV16 E6 but not by E7. Low risk type HPV11 E6 did not affect the NIRF expression at all. We propose that ICBP90 overexpression, and reduced NIRF expression, found in cervical cancers, is an important event of a cervical carcinogenesis, and especially ICBP90 may offer a proliferating marker and therapeutic target for treating uterine cervical cancers.

Specific targeting of cancer vaccines to antigen-presenting cells via an endogenous TLR2/6 ligand derived from cysteinyl-tRNA synthetase 1.

Cancer vaccines have been developed as a promising way to boost cancer immunity. However, their clinical potency is often limited due to the imprecise delivery of tumor antigens. To overcome this problem, we conjugated an endogenous Toll-like receptor (TLR)2/6 ligand, UNE-C1, to human papilloma virus type 16 (HPV-16)-derived peptide antigen, E7, and found that the UNE-C1-conjugated cancer vaccine (UCV) showed significantly enhanced antitumor activity in vivo compared with the noncovalent combination of UNE-C1 and E7. The combination of UCV with PD-1 blockades further augmented its therapeutic efficacy. Specifically, the conjugation of UNE-C1 to E7 enhanced its retention in inguinal draining lymph nodes, the specific delivery to dendritic cells and E7 antigen-specific T cell responses, and antitumor efficacy in vivo compared with the noncovalent combination of the two peptides. These findings suggest the potential of UNE-C1 derived from human cysteinyl-tRNA synthetase 1 as a unique vehicle for the specific delivery of cancer antigens to antigen-presenting cells via TLR2/6 for the improvement of cancer vaccines.

Evidence for direct interaction between the oncogenic proteins E6 and E7 of high-risk human papillomavirus (HPV).

Human papillomaviruses (HPVs) are DNA tumor viruses that infect mucosal and cutaneous epithelial cells of more than 20 vertebrates. High-risk HPV causes about 5% of human cancers worldwide, and the viral proteins E6 and E7 promote carcinogenesis by interacting with tumor suppressors and interfering with many cellular pathways. As a consequence, they immortalize cells more efficiently in concert than individually. So far, the networks of E6 and E7 with their respective cellular targets have been studied extensively but independently. However, we hypothesized that E6 and E7 might also interact directly with each other in a novel interaction affecting HPV-related carcinogenesis. Here, we report a direct interaction between E6 and E7 proteins from carcinogenic HPV types 16 and 31. We demonstrated this interaction via cellular assays using two orthogonal methods: coimmunoprecipitation and flow cytometry-based FRET assays. Analytical ultracentrifugation of the recombinant proteins revealed that the stoichiometry of the E6/E7 complex involves two E7 molecules and two E6 molecules. In addition, fluorescence polarization showed that (I) E6 binds to E7 with a similar affinity for HPV16 and HPV31 (in the same micromolar range) and (II) that the binding interface involves the unstructured N-terminal region of E7. The direct interaction of these highly conserved papillomaviral oncoproteins may provide a new perspective for studying HPV-associated carcinogenesis and the overall viral life cycle.

An engineered Accum-E7 protein-based vaccine with dual anti-cervical cancer activity.

Worldwide prevalence of cervical cancer decreased significantly with the use of human papilloma virus (HPV)-targeted prophylactic vaccines. However, these multivalent antiviral vaccines are inert against established tumors, which leave patients with surgical ablative options possibly resulting in long-term reproductive complications and morbidity. In an attempt to bypass this unmet medical need, we designed a new E7 protein-based vaccine formulation using Accum™, a technology platform designed to promote endosome-to-cytosol escape as a means to enhance protein accumulation in target cells. Prophylactic vaccination of immunocompetent mice using the Accum-E7 vaccine (aE7) leads to complete protection from cervical cancer despite multiple challenges conducted with ascending C3.43 cellular doses (0.5-, 1.0-, and 2.0 × 106 cells). Moreover, the humoral response induced by aE7 was higher in magnitude compared with naked E7 protein vaccination and displayed potent inhibitory effects on C3.43 proliferation in vitro. When administered therapeutically to animals with pre-established C3.43 or Tal3 tumors, the vaccine-induced response synergized with multiple immune checkpoint blockers (anti-PD-1, anti-CTLA4, and anti-CD47) to effectively control tumor growth. Mechanistically, the observed therapeutic effect requires cross-presenting dendritic cells as well as CD8 T cells predominantly, with a non-negligible role played by both CD4+ and CD19+ lymphocytes. good laboratory practice (GLP) studies revealed that aE7 is immunogenic and well tolerated by immunocompetent mice with no observed adverse effects despite the use of a fourfold exceeding dose. In a nutshell, aE7 represents an ideal vaccine candidate for further clinical development as it uses a single engineered protein capable of exhibiting both prophylactic and therapeutic activity.

Human papillomavirus type 16 E6 induces cell competition.

High-risk human papillomavirus (HPV) infections induce squamous epithelial tumors in which the virus replicates. Initially, the virus-infected cells are untransformed, but expand in both number and area at the expense of uninfected squamous epithelial cells. We have developed an in vitro assay in which colonies of post-confluent HPV16 expressing cells outcompete and displace confluent surrounding uninfected keratinocytes. The enhanced colony competition induced by the complete HPV16 genome is conferred by E6 expression alone, not by individual expression of E5 or E7, and requires E6 interaction with p53. E6-expressing keratinocytes undermine and displace adjacent normal keratinocytes from contact with the attachment substrate, thereby expanding the area of the E6-expressing colony at the expense of normal keratinocytes. These new results separate classic oncogenicity that is primarily conferred by HPV16 E7 from cell competition that we show is primarily conferred by E6 and provides a new biological role for E6 oncoproteins from high-risk human papillomaviruses.

Manipulating host secreted protein gene expression: an indirect approach by HPV11/16 E6/E7 to suppress PBMC cytokine secretion.

Human papillomavirus (HPV) 11/16 E6/E7 proteins have been recognized to be pivotal in viral pathogenesis. This study sought to uncover the potential mechanisms of how HPV11/16 E6/E7-transfected keratinocytes inhibit cytokine secretion in peripheral blood mononuclear cells (PBMC). Upon co-culturing HPV11/16 E6/E7-transfected keratinocytes with PBMC in a non-contact manner, we observed a marked decrease in various cytokines secreted by PBMC. To determine if this suppression was mediated by specific common secreted factors, we conducted transcriptomic sequencing on these transfected cells. This analysis identified 53 common differentially secreted genes in all four HPV-transfected cells. Bioinformatics analysis demonstrated these genes were predominantly involved in immune regulation. Results from quantitative PCR (qPCR) and an extensive literature review suggested the downregulation of 12 genes (ACE2, BMP3, BPIFB1, CLU, CST6, CTF1, HMGB2, MMP12, PDGFA, RNASE7, SULF2, TGM2), and upregulation of 7 genes (CCL17, CCL22, FBLN1, PLAU, S100A7, S100A8, S100A9), may be crucial in modulating tumor immunity and combating pathogenic infections, with genes S100A8 and S100A9, and IL-17 signaling pathway being particularly noteworthy. Thus, HPV11/16 E6/E7 proteins may inhibit cytokine secretion of immune cells by altering the expression of host-secreted genes. Further exploration of these genes may yield new insights into the complex dynamics of HPV infection.

N6-methyladenosine methylation on FSCN1 mediated by METTL14/IGF2BP3 contributes to human papillomavirus type 16-infected cervical squamous cell carcinoma.

Human papillomavirus (HPV) infection has been reported to be associated with N6-methyladenosine (m6A) modification in cancers. However, the underlying mechanism by which m6A methylation participates in HPV-related cervical squamous cell carcinoma (CSCC) remains largely unclear. In this study, we observed that m6A regulators methyltransferase like protein (METTL14) and insulin like growth factor 2 mRNA binding protein 3 (IGF2BP3) were upregulated in HPV-positive CSCC tissues and cell lines, and their high expression predicted poor prognosis for HPV-infected CSCC patients. Cellular functional experiments verified that HPV16 oncogenes E6/E7 upregulated the expression of METTL14 and IGF2BP3 to promote cell proliferation and epithelial mesenchymal transition of CSCC cells. Next, we found that E6/E7 stabilized fascin actin-bundling protein 1 (FSCN1) mRNA and elevated FSCN1 expression in CSCC cells through upregulating METTL14/IGF2BP3-mediated m6A modification, and FSCN1 expression was also validated to be positively associated with worse outcomes of HPV-positive CSCC patients. Finally, HPV16-positive CSCC cell lines SiHa and CaSki were transfected with knockdown vector for E6/E7 or METTL14/IGF2BP3 and overexpressing vector for FSCN1, and functional verification experiments were performed through using MTT assay, flow cytometry, wound healing assay and tumour formation assay. Results indicated that knockdown of E6/E7 or METTL14/IGF2BP3 suppressed cell proliferation, migration and tumorigenesis, and accelerated cell apoptosis of HPV-positive CSCC cells. Their tumour-suppressive effects were abolished through overexpressing FSCN1. Overall, HPV E6/E7 advanced CSCC development through upregulating METTL14/IGF2BP3-mediated FSCN1 m6A modification.

Oncogenic HPV promotes the expression of the long noncoding RNA lnc-FANCI-2 through E7 and YY1.

Long noncoding RNAs (lncRNAs) play diverse roles in biological processes, but their expression profiles and functions in cervical carcinogenesis remain unknown. By RNA-sequencing (RNA-seq) analyses of 18 clinical specimens and selective validation by RT-qPCR analyses of 72 clinical samples, we provide evidence that, relative to normal cervical tissues, 194 lncRNAs are differentially regulated in high-risk (HR)-HPV infection along with cervical lesion progression. One such lncRNA, lnc-FANCI-2, is extensively characterized because it is expressed from a genomic locus adjacent to the FANCI gene encoding an important DNA repair factor. Both genes are up-regulated in HPV lesions and in in vitro model systems of HR-HPV18 infection. We observe a moderate reciprocal regulation of lnc-FANCI-2 and FANCI in cervical cancer CaSki cells. In these cells, lnc-FANCI-2 is transcribed from two alternative promoters, alternatively spliced, and polyadenylated at one of two alternative poly(A) sites. About 10 copies of lnc-FANCI-2 per cell are detected preferentially in the cytoplasm. Mechanistically, HR-HPVs, but not low-risk (LR)-HPV oncogenes induce lnc-FANCI-2 in primary and immortalized human keratinocytes. The induction is mediated primarily by E7, and to a lesser extent by E6, mostly independent of p53/E6AP and pRb/E2F. We show that YY1 interacts with an E7 CR3 core motif and transactivates the promoter of lnc-FANCI-2 by binding to two critical YY1-binding motifs. Moreover, HPV18 increases YY1 expression by reducing miR-29a, which targets the 3' untranslated region of YY1 mRNA. These data have provided insights into the mechanisms of how HR-HPV infections contribute to cervical carcinogenesis.

The role of RNA-binding proteins in the processing of mRNAs produced by carcinogenic papillomaviruses.

Human papillomaviruses (HPV) are epitheliotropic DNA tumor viruses that are prevalent in the human population. A subset of the HPVs termed high-risk HPVs (HR-HPVs) are causative agents of anogenital cancers and head-and-neck cancers. Cancer is the result of persistent high-risk HPV infections that have not been cleared by the immune system of the host. These infections are characterized by dysregulated HPV gene expression, in particular constitutive high expression of the HPV E6 and E7 oncogenes and absence of the highly immunogenic viral L1 and L2 capsid proteins. HPVs make extensive use of alternative mRNA splicing to express its genes and are therefore highly dependent on cellular RNA-binding proteins for proper gene expression. Levels of RNA-binding proteins are altered in HPV-containing premalignant cervical lesions and in cervical cancer. Here we review our current knowledge of RNA-binding proteins that control HPV gene expression. We focus on RNA-binding proteins that control expression of the E6 and E7 oncogenes since they initiate and drive development of cancer and on the immunogenic L1 and L2 proteins as there silencing may contribute to immune evasion during carcinogenesis. Furthermore, cellular RNA-binding proteins are essential for HPV gene expression and as such may be targets for therapy to HPV infections and HPV-driven cancers.

The HPV16 E6, E7/miR-23b-3p/ICAT signaling axis promotes proliferation, migration, invasion and EMT of cervical cancer cells.

Cervical cancer (CC) remains one of the most common female malignancies, with higher incidence and mortality rates. more than 99% of CCs are associated with persistent infection with high-risk human papillomavirus. In view of the growing evidence that HPV 16 E6 and E7, two key oncoproteins encoded by HPV 16, regulate the expression of many other multifunctional genes and downstream effectors that contribute to the development of CC. Herein, we undertook a comprehensive effort into how HPV16 E6, E7 oncogenes affect the progression of CC cells. Previous studies have shown that ICAT expression was significantly increased in CC and had a pro-cancer effect. We observed that knockdown of HPV16 E6, E7 expression in SiHa and CasKi cells resulted in significant inhibition of ICAT expression and upregulation of miR-23b-3p expression. Besides, dual luciferase assays confirmed that ICAT was a target gene of miR-23b-3p, and negatively modulated by miR-23b-3p. Functional experiments showed that the overexpression of miR-23b-3p suppressed malignant behaviors of CC cells, such as migration, invasion and EMT. The overexpression of ICAT counteracted the suppressive effect of miR-23b-3p on HPV16-positive CC cells. Furthermore, after the knockdown of HPV16 E6 and E7, the inhibition of miR-23b-3p could increase the ICAT expression and rescue the siRNA HPV16 E6, E7-mediated suppressive impact on the aggressiveness of SiHa and CaSki cells. Collectively, our findings uncover that HPV16 E6, E7/miR-23b-3p/ ICAT axis plays an important role in HPV16-positive CC pathogenesis, which may serve as a promising therapeutic target for HPV16-associated CC.

Overview of genetic and epigenetic regulation of human papillomavirus and apoptosis in cervical cancer.

Cervical cancer is the fourth most common cancer affecting women worldwide after breast, colorectal and lung cancers. Owing to a lack of awareness and resources, low- and middle-income countries bear most of the burden of cervical cancer. In developed countries, the incidence rate has been halved over the past three decades due to robust screening and implementation of vaccine programs. HPV is not the sole cause of cervical cancer but acts as a principal factor in the pathogenesis of cervical cancer. By integrating into the host genome, its oncogenic proteins (E6 and E7) alter and interfere with the standard signal transduction machinery of the host. Apoptosis is a key pathway affected by aberrant genetic mutations, polymorphisms and epigenetic mechanisms during cervical carcinogenesis. Along with DNA methylation and histone modifications, non-coding RNAs have also been implicated as epigenetic modulators in various malignancies and are being explored for reversing disease severity. This review emphasizes various genetic and epigenetic approaches regulating apoptotic pathways and HPV E6 and E7 genes that can be targeted to overcome the challenges in cervical cancer treatment. In addition, it also discusses the apoptosis targeting novel drug molecules in cervical cancer which are currently undergoing clinical and pre-clinical trials.

Mechanical profile of human keratinocytes expressing HPV-18 oncogenes.

During tumorigenesis, the mechanical properties of cancer cells change markedly, with decreased stiffness often accompanying a more invasive phenotype. Less is known about the changes in mechanical parameters at intermediate stages in the process of malignant transformation. We have recently developed a pre-tumoral cell model by stably transducing the immortalized but non-tumorigenic human keratinocyte cell line HaCaT with the E5, E6 and E7 oncogenes from HPV-18, one of the leading causes of cervical cancer and other types of cancer worldwide. We have used atomic force microscopy (AFM) to measure cell stiffness and to obtain mechanical maps of parental HaCaT and HaCaT E5/E6/E7-18 cell lines. We observed a significant decrease in Young's modulus in HaCaT E5/E6/E7-18 cells measured by nanoindentation in the central region, as well as decreased cell rigidity in regions of cell-cell contact measured by Peakforce Quantitative Nanomechanical Mapping (PF-QNM). As a morphological correlate, HaCaT E5/E6/E7-18 cells displayed a significantly rounder cell shape than parental HaCaT cells. Our results therefore show that decreased stiffness with concomitant perturbations in cell shape are early mechanical and morphological changes during the process of malignant transformation.

Systematic Analysis of IL-1 Cytokine Signaling Suppression by HPV16 Oncoproteins.

The human papillomavirus (HPV) E6 and E7 oncogenes are expressed at all stages of HPV-mediated carcinogenesis and are essential drivers of cancers caused by high-risk HPV. Some of the activities of HPV E6 and E7, such as their interactions with host cellular tumor suppressors, have been characterized extensively. There is less information about how high-risk HPV E6 and E7 alter cellular responses to cytokines that are present in HPV-infected tissues and are an important component of the tumor microenvironment. We used several models of HPV oncoprotein activity to assess how HPV16 E6 and E7 alter the cellular response to the proinflammatory cytokine IL-1ß. Models of early stage HPV infection and of established HPV-positive head and neck cancers exhibited similar dysregulation of IL-1 pathway genes and suppressed transcriptional responses to IL-1ß treatment. Such overlap in cell responses supports that changes induced by HPV16 E6 and E7 early in infection could persist and contribute to a dysregulated immune environment throughout carcinogenesis. HPV16 E6 and E7 also drove the upregulation of several suppressors of IL-1 cytokine signaling, including SIGIRR, both in primary keratinocytes and in cancer cells. SIGIRR knockout was insufficient to increase IL-1ß-dependent gene expression in the presence of HPV16 E6 and E7, suggesting that multiple suppressors of IL-1 signaling contribute to dampened IL-1 responses in HPV16-positive cells. IMPORTANCE Human papillomavirus (HPV) infection is responsible for nearly 5% of the worldwide cancer burden. HPV-positive tumors develop over years to decades in tissues that are subject to frequent stimulation by proinflammatory cytokines. However, the effects of HPV oncoproteins on the cellular response to cytokine stimulation are not well defined. We analyzed IL-1 cytokine signaling in several models of HPV biology and disease. We found that HPV16 E6 and E7 oncoproteins mediate a broad and potent suppression of cellular responses to IL-1ß in models of both early and late stages of carcinogenesis. Our data provide a resource for future investigation of IL-1 signaling in HPV-positive cells and cancers.