The HPV E6 oncoprotein targets histone methyltransferases for modulating specific gene transcription

The Hallmarks of Cervical Cancer: Molecular Mechanisms Induced by Human Papillomavirus

Human papillomaviruses (HPVs) and, specifically, high-risk HPVs (HR-HPVs) are identified as necessary factors in the development of cancer of the lower genital tract, with CaCU standing out as the most prevalent tumor. This review summarizes ten mechanisms activated by HR-HPVs during cervical carcinogenesis, which are broadly associated with at least seven of the fourteen distinctive physiological capacities of cancer in the newly established model by Hanahan in 2022. These mechanisms involve infection by human papillomavirus, cellular tropism, genetic predisposition to uterine cervical cancer (CaCU), viral load, viral physical state, regulation of epigenetic mechanisms, loss of function of the E2 protein, deregulated expression of E6/E7 oncogenes, regulation of host cell protein function, and acquisition of the mesenchymal phenotype.

Countenance and implication of Β-sitosterol, Β-amyrin and epiafzelechin in nickel exposed Rat: in-silico and in-vivo approach

The detrimental impact of reactive oxygen species on D.N.A. repair processes is one of the contributing factors to colon cancer. The idea that oxidative stress may be a significant etiological element for carcinogenesis is currently receiving more and more support. The goal of the current study is to evaluate the anti-inflammatory and anticancer activity of three powerful phytocompounds-sitosterol, amyrin, and epiafzelechin-alone and in various therapeutic combinations against colon cancer to identify the critical mechanisms that mitigate nickel's carcinogenic effect. To evaluate the ligand-protein interaction of four selected components against Vascular endothelial growth factor (VEGF), Matrix metalloproteinase-9 (MMP9) inhibitor and Interleukin-10 (IL-10) molecular docking approach was applied using PyRx bioinformatics tool. For in vivo analysis, hundred albino rats were included, divided into ten groups, each containing ten rats of weight 160-200 g. All the groups were injected with 1 ml/kg nickel intraperitoneally per week for three months, excluding the negative control group. Three of the ten groups were treated with β-sitosterol (100 mg/kg b wt), β-amyrin (100 mg/kg b wt), and epiafzelechin (200 mg/kg b wt), respectively, for one month. The later four groups were fed with combinatorial treatments of the three phyto compounds for one month. The last group was administered with commercial drug Nalgin (500 mg/kg b wt). The biochemical parameters Creatinine, Protein carbonyl, 8-hydroxydeoxyguanosine (8-OHdG), VEGF, MMP-9 Inhibitor, and IL-10 were estimated using ELISA kits and Glutathione (G.S.H.), Superoxide dismutase (S.O.D.), Catalase (C.A.T.) and Nitric Oxide (NO) were analyzed manually. The correlation was analyzed through Pearson's correlation matrix. All the parameters were significantly raised in the positive control group, indicating significant inflammation. At the same time, the levels of the foresaid biomarkers were decreased in the serum in all the other groups treated with the three phytocompounds in different dose patterns. However, the best recovery was observed in the group where the three active compounds were administered concomitantly. The correlation matrix indicated a significant positive correlation of IL-10 vs VEGF (r = 0.749**, p = 0.009), MMP-9 inhibitor vs SOD (r = 0.748**, p = 0.0 21). The study concluded that the three phytocompounds β-sitosterol, β-amyrin, and epiafzelechin are important anticancer agents which can target the cancerous biomarkers and might be used as a better therapeutic approach against colon cancer soon.

Protein arginine methylation in viral infection and antiviral immunity

Protein arginine methyltransferase (PRMT)-mediated arginine methylation is an important post-transcriptional modification that regulates various cellular processes including epigenetic gene regulation, genome stability maintenance, RNA metabolism, and stress-responsive signal transduction. The varying substrates and biological functions of arginine methylation in cancer and neurological diseases have been extensively discussed, providing a rationale for targeting PRMTs in clinical applications. An increasing number of studies have demonstrated an interplay between arginine methylation and viral infections. PRMTs have been found to methylate and regulate several host cell proteins and different functional types of viral proteins, such as viral capsids, mRNA exporters, transcription factors, and latency regulators. This modulation affects their activity, subcellular localization, protein-nucleic acid and protein-protein interactions, ultimately impacting their roles in various virus-associated processes. In this review, we discuss the classification, structure, and regulation of PRMTs and their pleiotropic biological functions through the methylation of histones and non-histones. Additionally, we summarize the broad spectrum of PRMT substrates and explore their intricate effects on various viral infection processes and antiviral innate immunity. Thus, comprehending the regulation of arginine methylation provides a critical foundation for understanding the pathogenesis of viral diseases and uncovering opportunities for antiviral therapy.

HPV E6 regulates therapy responses in oropharyngeal cancer by repressing the PGC-1α/ERRα axis

Therapy with radiation plus cisplatin kills HPV+ oropharyngeal squamous cell carcinomas (OPSCCs) by increasing reactive oxygen species beyond cellular antioxidant capacity. To explore why these standard treatments fail for some patients, we evaluated whether the variation in HPV oncoprotein levels among HPV+ OPSCCs affects mitochondrial metabolism, a source of antioxidant capacity. In cell line and patient-derived xenograft models, levels of HPV full-length E6 (fl-E6) inversely correlated with oxidative phosphorylation, antioxidant capacity, and therapy resistance, and fl-E6 was the only HPV oncoprotein to display such correlations. Ectopically expressing fl-E6 in models with low baseline levels reduced mitochondrial mass, depleted antioxidant capacity, and sensitized to therapy. In this setting, fl-E6 repressed the peroxisome proliferator-activated receptor gamma co-activator 1α/estrogen-related receptor α (PGC-1α/ERRα) pathway for mitochondrial biogenesis by reducing p53-dependent PGC-1α transcription. Concordant observations were made in 3 clinical cohorts, where expression of mitochondrial components was higher in tumors of patients with reduced survival. These tumors contained the lowest fl-E6 levels, the highest p53 target gene expression, and an activated PGC-1α/ERRα pathway. Our findings demonstrate that E6 can potentiate treatment responses by depleting mitochondrial antioxidant capacity and provide evidence for low E6 negatively affecting patient survival. E6's interaction with the PGC-1α/ERRα axis has implications for predicting and targeting treatment resistance in OPSCC.

AIB1 is a novel target of the high-risk HPV E6 protein and a biomarker of cervical cancer progression

The high-risk human papillomaviruses (HPV-16, -18) are critical etiologic agents in human malignancy, most importantly in cervical cancer. These oncogenic viruses encode the E6 and E7 proteins that are uniformly retained and expressed in cervical cancers and required for maintenance of the tumorigenic phenotype. The E6 and E7 proteins were first identified as targeting the p53 and pRB tumor suppressor pathways, respectively, in host cells, thereby leading to disruption of cell cycle controls. In addition to p53 degradation, a number of other functions and critical targets for E6 have been described, including telomerase, Myc, PDZ-containing proteins, Akt, Wnt, mTORC1, as well as others. In this study, we identified Amplified in Breast Cancer 1 (AIB1) as a new E6 target. We first found that E6 and hTERT altered similar profiling of gene expression in human foreskin keratinocytes (HFK), independent of telomerase activity. Importantly, AIB1 was a common transcriptional target of both E6 and hTERT. We then verified that high-risk E6 but not low-risk E6 expression led to increases in AIB1 transcript levels by real-time RT-PCR, suggesting that AIB1 upregulation may play an important role in cancer development. Western blots demonstrated that AIB1 expression increased in HPV-16 E6 and E7 expressing (E6E7) immortalized foreskin and cervical keratinocytes, and in three of four common cervical cancer cell lines as well. Then, we evaluated the expression of AIB1 in human cervical lesions and invasive carcinoma using immunohistochemical staining. Strikingly, AIB1 showed positivity in the nucleus of cells in the immediate suprabasal epithelium, while nuclei of the basal epithelium were negative, as evident in the Cervical Intraepithelial Neoplasia 1 (CIN1) samples. As the pathological grading of cervical lesions increased from CIN1, CIN2, CIN3 carcinoma in situ and invasive carcinoma, AIB1 staining increased progressively, suggesting that AIB1 may serve as a novel histological biomarker for cervical cancer development. For cases of invasive cervical carcinoma, AIB1 staining was specific to cancerous lesions. Increased expression of AIB1 was also observed in transgenic mouse cervical neoplasia and cancer models induced by E6E7 and estrogen. Knockdown of AIB1 expression in E6E7 immortalized human cervical cells significantly abolished cell proliferation. Taken together, these data support AIB1 as a novel target of HPV E6 and a biomarker of cervical cancer progression.

Gene Expression Profile Analysis of Human Epidermal Keratinocytes Expressing Human Papillomavirus Type 8 E7

Background: Human papillomavirus type 8 (HPV8) has been implicated in the progress of non-melanoma skin cancers and their precursor lesions. The HPV8 E7 oncoprotein plays a key role in the tumorigenesis of HPV-associated cutaneous tumors. However, the exact role of HPV8 E7 in human epidermal carcinogenesis has not been fully elucidated.

Methods: To investigate the potential carcinogenic effects of HPV8 E7 on epithelial cells, we used RNA-sequencing technology to analyze the gene expression profile of HPV8 E7-overexpressed normal human epidermal keratinocytes (NHEKs).

Results: RNA-sequencing revealed 831 differentially expressed genes (DEGs) between HPV8 E7-expressing NHEKs and control cells, among which, 631 genes were significantly upregulated, and 200 were downregulated. Gene ontology annotation enrichment analysis showed that HPV8 E7 mainly affected the expression of genes associated with protein heterodimerization activity, DNA binding, nucleosomes, and nucleosome assembly. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that overexpression of HPV8 E7 affected the expression of gene clusters associated with viral carcinogenesis and transcriptional misregulation in cancer and necroptosis signaling pathways that reportedly play crucial roles in HPV infection promotion and cancer progression. We also found the DEGs, such as HKDC1 and TNFAIP3, were associated with epigenetic modifications, immune regulation, and metabolic pathways.

Conclusion: Our results demonstrate that the pro-carcinogenic effect of HPV8 expression in epithelial cells may be attributed to the regulatory effect of oncogene E7 on gene expression associated with epigenetic modifications and immune and metabolic status-associated gene expression. Although our data are based on an in vitro experiment, it provides the theoretical evidence that the development of squamous cell carcinoma can be caused by HPV.

High Risk-Human Papillomavirus in HNSCC: Present and Future Challenges for Epigenetic Therapies

Head and Neck Squamous Cell Carcinoma (HNSCC) is a highly heterogeneous group of tumors characterized by an incidence of 650,000 new cases and 350,000 deaths per year worldwide and a male to female ratio of 3:1. The main risk factors are alcohol and tobacco consumption and Human Papillomavirus (HPV) infections. HNSCC cases are divided into two subgroups, the HPV-negative (HPV−) and the HPV-positive (HPV+) which have different clinicopathological and molecular profiles. However, patients are still treated with the same therapeutic regimens. It is thus of utmost importance to characterize the molecular mechanisms underlying these differences to find new biomarkers and novel therapeutic targets towards personalized therapies. Epigenetic alterations are a hallmark of cancer and can be exploited as both promising biomarkers and potential new targets. E6 and E7 HPV oncoviral proteins besides targeting p53 and pRb, impair the expression and the activity of several epigenetic regulators. While alterations in DNA methylation patterns have been well described in HPV+ and HPV− HNSCC, accurate histone post-translational modifications (hPTMs) characterization is still missing. Herein, we aim to provide an updated overview on the impact of HPV on the hPTMs landscape in HNSCC. Moreover, we will also discuss the sex and gender bias in HNSCC and how the epigenetic machinery could be involved in this process, and the importance of taking into account sex and/or gender also in this field.

Non-histone methylation of SET7/9 and its biological functions

BACKGROUND

(su(var)-3-9,enhancer-of-zeste,trithorax) domain-containing protein 7/9 (SET7/9) is a member of the protein lysine methyltransferases (PLMTs or PKMTs) family. It contains a SET domain. Recent studies demonstrate that SET7/9 methylates both lysine 4 of histone 3 (H3-K4) and lysine(s) of non-histone proteins, including transcription factors, tumor suppressors, and membrane-associated receptors.

OBJECTIVE

This article mainly reviews the non-histone methylation effects of SET7/9 and its functions in tumorigenesis and development.

METHODS

PubMed was screened for this information.

RESULTS

SET7/9 plays a key regulatory role in various biological processes such as cell proliferation, transcription regulation, cell cycle, protein stability, cardiac morphogenesis, and development. In addition, SET7/9 is involved in the pathogenesis of hair loss, breast cancer progression, human carotid plaque atherosclerosis, chronic kidney disease, diabetes, obesity, ovarian cancer, prostate cancer, hepatocellular carcinoma, and pulmonary fibrosis.

CONCLUSION

SET7/9 is an important methyltransferase, which can catalyze the methylation of a variety of proteins. Its substrates are closely related to the occurrence and development of tumors.

Epigenetic approaches for cervical neoplasia screening (Review)

Human papillomavirus (HPV) infection is the leading cause of cervical cancer. The Papanicolaou cytology test is the usually employed type of screening for this infection; however, its sensibility is limited. Only a small percentage of women infected with high-risk HPV develop cervical cancer with an array of genetic and epigenetic modifications. Thus, it is necessary to develop rapid, reproducible and minimally invasive technologies for screening. DNA methylation has gained attention as an alternative method for molecular diagnosis and prognosis in HPV infection. The aim of the present review was to highlight the potential of DNA methylation in cervical neoplasia screening for clinical applications. It was observed that the methylation human and viral genes was correlated with high-grade lesions and cancer. Methylation biomarkers have shown a good capacity to discriminate between high-grade lesions with a transformative potential and cervical cancer, being able to detect these modifications at an early stage. With further research, the epigenetic profiles and subtypes of the tumors could be elaborated, which would aid in therapy selection by opening avenues in personalized precision medicine. Response to therapy could also be evaluated through such methods and the accessibility of liquid biopsies would allow a constant monitoring of the patient's status without invasive sampling techniques.

Orthogonal ubiquitin transfer reveals human papillomavirus E6 downregulates nuclear transport to disarm interferon-γ dependent apoptosis of cervical cancer cells

The E6 protein of the human papillomavirus (HPV) underpins important protein interaction networks between the virus and host to promote viral infection. Through its interaction with E6AP, a host E3 ubiquitin (UB) ligase, E6 stirs the protein ubiquitination pathways toward the oncogenic transformation of the infected cells. For a systematic measurement of E6 reprogramming of the substrate pool of E6AP, we performed a proteomic screen based on "orthogonal UB transfer (OUT)" that allowed us to identify the ubiquitination targets of E6AP dependent on the E6 protein of HPV-16, a high-risk viral subtype for the development of cervical cancer. The OUT screen identified more than 200 potential substrates of the E6-E6AP pair based on the transfer of UB from E6AP to the substrate proteins. Among them, we verified that E6 would induce E6AP-catalyzed ubiquitination of importin proteins KPNA1-3, protein phosphatase PGAM5, and arginine methyltransferases CARM1 to trigger their degradation by the proteasome. We further found that E6 could significantly reduce the cellular level of KPNA1 that resulted in the suppression of nuclear transport of phosphorylated STAT1 and the inhibition of interferon-γ-induced apoptosis in cervical cancer cells. Overall, our work demonstrates OUT as a powerful proteomic platform to probe the interaction of E6 and host cells through protein ubiquitination and reveals a new role of E6 in down-regulating nuclear transport proteins to attenuate tumor-suppressive signaling.

Role of Virus-Induced Host Cell Epigenetic Changes in Cancer

The tumor viruses human T-lymphotropic virus 1 (HTLV-1), hepatitis C virus (HCV), Merkel cell polyomavirus (MCPyV), high-risk human papillomaviruses (HR-HPVs), Epstein-Barr virus (EBV), Kaposi’s sarcoma-associated herpes virus (KSHV) and hepatitis B virus (HBV) account for approximately 15% of all human cancers. Although the oncoproteins of these tumor viruses display no sequence similarity to one another, they use the same mechanisms to convey cancer hallmarks on the infected cell. Perturbed gene expression is one of the underlying mechanisms to induce cancer hallmarks. Epigenetic processes, including DNA methylation, histone modification and chromatin remodeling, microRNA, long noncoding RNA, and circular RNA affect gene expression without introducing changes in the DNA sequence. Increasing evidence demonstrates that oncoviruses cause epigenetic modifications, which play a pivotal role in carcinogenesis. In this review, recent advances in the role of host cell epigenetic changes in virus-induced cancers are summarized.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.

microRNA-21: a key modulator in oncogenic viral infections

Oncogenic viruses are associated with approximately 15% of human cancers. In viral infections, microRNAs play an important role in host-pathogen interactions. miR-21 is a highly conserved non-coding RNA that not only regulates the development of oncogenic viral diseases, but also responds to the regulation of intracellular signal pathways. Oncogenic viruses, including HBV, HCV, HPV, and EBV, co-evolve with their hosts and cause persistent infections. The upregulation of host miR-21 manipulates key cellular pathways to evade host immune responses and then promote viral replication. Thus, a better understanding of the role of miR-21 in viral infections may help us to develop effective genetically-engineered oncolytic virus-based therapies against cancer.

Regulation of the expression of proinflammatory cytokines induced by SARS-CoV-2

An outbreak of a novel coronavirus was reported in Wuhan, China, in late 2019. It has spread rapidly through China and many other countries, causing a global pandemic. Since February 2020, over 28 countries/regions have reported confirmed cases. Individuals with the infection known as coronavirus disease-19 (COVID-19) have similar clinical features as severe acute respiratory syndrome first encountered 17 years ago, with fever, cough, and upper airway congestion, along with high production of proinflammatory cytokines (PICs), which form a cytokine storm. PICs induced by COVID-19 include interleukin (IL)-6, IL-17, and monocyte chemoattractant protein-1. The production of cytokines is regulated by activated nuclear factor-kB and involves downstream pathways such as Janus kinase/signal transducers and activators transcription. Protein expression is also regulated by post-translational modification of chromosomal markers. Lysine residues in the peptide tails stretching out from the core of histones bind the sequence upstream of the coding portion of genomic DNA. Covalent modification, particularly methylation, activates or represses gene transcription. PICs have been reported to be induced by histone modification and stimulate exudation of hyaluronic acid, which is implicated in the occurrence of COVID-19. These findings indicate the impact of the expression of PICs on the pathogenesis and therapeutic targeting of COVID-19.

The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation

Persistent infection with high-risk human papillomaviruses (HR-HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell-cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR-HPV oncoproteins can lead to the acquisition of host genetic mutations, eventually culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis.

Structure of High-Risk Papillomavirus 31 E6 Oncogenic Protein and Characterization of E6/E6AP/p53 Complex Formation

The degradation of p53 is a hallmark of high-risk human papillomaviruses (HPVs) of the alpha genus and HPV-related carcinogenicity. The oncoprotein E6 forms a ternary complex with the E3 ubiquitin ligase E6-associated protein (E6AP) and tumor suppressor protein p53 targeting p53 for ubiquitination. The extent of p53 degradation by different E6 proteins varies greatly, even for the closely related HPV16 and HPV31. HPV16 E6 and HPV31 E6 display high sequence identity (∼67%). We report here, for the first time, the structure of HPV31 E6 bound to the LxxLL motif of E6AP. HPV16 E6 and HPV31 E6 are structurally very similar, in agreement with the high sequence conservation. Both E6 proteins bind E6AP and degrade p53. However, the binding affinities of 31 E6 to the LxxLL motif of E6AP and p53, respectively, are reduced 2-fold and 5.4-fold compared to 16 E6. The affinity of E6-E6AP-p53 ternary complex formation parallels the efficacy of the subsequent reaction, namely, degradation of p53. Therefore, closely related E6 proteins addressing the same cellular targets may still diverge in their binding efficiencies, possibly explaining their different phenotypic or pathological impacts.IMPORTANCE Variations of carcinogenicity of human papillomaviruses are related to variations of the E6 and E7 interactome. While different HPV species and genera are known to target distinct host proteins, the fine differences between E6 and E7 of closely related HPVs, supposed to target the same cellular protein pools, remain to be addressed. We compare the oncogenic E6 proteins of the closely related high-risk HPV31 and HPV16 with regard to their structure and their efficiency of ternary complex formation with their cellular targets p53 and E6AP, which results in p53 degradation. We solved the crystal structure of 31 E6 bound to the E6AP LxxLL motif. HPV16 E6 and 31 E6 structures are highly similar, but a few sequence variations lead to different protein contacts within the ternary complex and, as quantified here, an overall lower binding affinity of 31 E6 than 16 E6. These results align with the observed lower p53 degradation potential of 31 E6.

Epigallocatechin gallate inhibits HeLa cells by modulation of epigenetics and signaling pathways

This study examines the effect of epigallocatechin gallate (EGCG) on signaling pathways, epigenetic modulators and tumour suppressor genes in cervical cancer cells, HeLa. qRT-PCR, ELISA-based enzymatic assays and in silico studies were used to catalogue the modulation of these genes by EGCG treatment. qRT-PCR showed transcriptional modulation of several epigenetic modifiers including DNA methyltransferases and histone modifiers (DNMT1, DNMT3B, DNMT3A, AURKA, AURKC, AURKB, KDM4A, KDM5C, PRMT7, PRMT6, UBE2B, HDAC5, HDAC6, HDAC7 and HDAC11. Furthermore, ELISA-based assays showed that EGCG lowered the activity of DNA methyltransferases, histone deacetylases and histone methyltransferases (H3K9). Molecular docking results suggests that EGCG may competitively inhibit some epigenetic enzymes (DNMT1, DNMT3A, HDAC2, HDAC3, HDAC4, HDAC7 and EZH2). A functional outcome of these epigenetic alterations could be inferred from the reversal of promoter hypermethylation of tumour suppressor genes by quantitative methylation array and transcriptional re-expression of tumour suppressor genes including TP73, PTEN, SOCS1, CDH1, RARβ, and DAPK1 by qRT-PCR. Downregulation of key signaling moieties of PI3K, Wnt and MAPK pathways, cell cycle regulators, metastasis regulators and pro-inflammatory moieties including TERT, CCNB1, CCNB2, MMP2, MMP7. PIK3C2B, PIK3CA, MAPK8 and IL6 was also observed. In silico protein-protein interaction network analysis followed by KEGG analysis discerned the active participation of gene sets towards cancer pathways. This study comprehensively explains EGCG's anti-cancer mechanism via the synchronized transcriptional alteration of several molecular targets across different signaling pathways and reversal of tumour suppressor gene silencing through modulation of epigenetic enzymes.

Human papillomavirus type 16 E7 oncoprotein-induced upregulation of lysine-specific demethylase 5A promotes cervical cancer progression by regulating the microRNA-424-5p/suppressor of zeste 12 pathway

Human papillomavirus (HPV) infection and viral protein expression cause several epigenetic alterations that lead to cervical carcinogenesis. Our previous study identified that upregulated lysine-specific demethylase (KDM) 2 A promotes cervical cancer progression by inhibiting mircoRNA (miR)-132 function. However, the roles of histone methylation modifiers in HPV-related cervical cancer remain unclear. In the present study, changes in the expression of 48 histone methylation modifiers were assessed following knockdown of HPV16 E6/E7 in CaSki cells. The dysregulated expression of KDM5A was identified, and its function in cervical cancer was investigated in vitro and in vivo. E7 oncoprotein-induced upregulation of KDM5A promoted cervical cancer cell proliferation and invasiveness in vitro and in vivo, which was correlated with poor prognosis in patients with cervical cancer. KDM5A was found to physically interact with the promoter region of miR-424-5p, and to suppress its expression by removing the tri- and di-methyl groups from H3K4 at the miR-424-5p locus. Furthermore, miR-424-5p repressed cancer cell proliferation and invasiveness by targeting suppressor of zeste 12 (Suz12). KDM5A upregulation promoted cervical cancer progression by repressing miR-424-5p, which resulted in a decrease in Suz12. Therefore, KDM5A functions as a tumor activator in cervical cancer pathogenesis by binding to the miR-424-5p promoter and inhibiting its tumor-suppressive function. These results indicate a function for KDM5A in cervical cancer progression and suggest its candidacy as a novel prognostic biomarker and target for the clinical management of this malignancy.

A ubiquitin variant-based affinity approach selectively identifies substrates of the ubiquitin ligase E6AP in complex with HPV-11 E6 or HPV-16 E6

The E6 protein of both mucosal high-risk human papillomaviruses (HPVs) such as HPV-16, which have been causally associated with malignant tumors, and low-risk HPVs such as HPV-11, which cause the development of benign tumors, interacts with the cellular E3 ubiquitin ligase E6-associated protein (E6AP). This indicates that both HPV types employ E6AP to organize the cellular proteome to viral needs. However, whereas several substrate proteins of the high-risk E6-E6AP complex are known, e.g. the tumor suppressor p53, potential substrates of the low-risk E6-E6AP complex remain largely elusive. Here, we report on an affinity-based enrichment approach that enables the targeted identification of potential substrate proteins of the different E6-E6AP complexes by a combination of E3-selective ubiquitination in whole-cell extracts and high-resolution MS. The basis for the selectivity of this approach is the use of a ubiquitin variant that is efficiently used by the E6-E6AP complexes for ubiquitination but not by E6AP alone. By this approach, we identified ∼190 potential substrate proteins for low-risk HPV-11 E6 and high-risk HPV-16 E6. Moreover, subsequent validation experiments in vitro and within cells with selected substrate proteins demonstrate the potential of our approach. In conclusion, our data represent a reliable repository for potential substrates of the HPV-16 and HPV-11 E6 proteins in complex with E6AP.

Genistein Modulates Signaling Pathways and Targets Several Epigenetic Markers in HeLa Cells

BACKGROUND

Several epigenetic changes are responsible for transcriptional alterations of signaling pathways and tumour suppressor genes (TSGs) contributing to carcinogenesis. This study was aimed to examine the effect of the phytochemical, genistein on various molecular targets in HeLa cells.

METHODS

Quantitative PCR was used to analyze the expression of various molecular targets. Biochemical assays were employed to study the epigenetic enzymes. To correlate the transcriptional status of the selected TSGs and epigenetic modulation, their promoter 5'CpG methylation levels were evaluated by quantitative methylation array followed by methylation specific restriction digestion.

RESULTS

The expression of several genes involved in the cell cycle regulation, migration, inflammation, phosphatidylinositol 3-kinase (PI3K) and mitogen activated kinase-like protein (MAPK) pathway were found to be modulated including CCNB1, TWIST1, MMP14, TERT, AKT1, PTPRR, FOS and IL1A. Genistein modulated the expression of DNA methyltransferases (DNMTs), histone deacetylases (HDACs), histone methyltransferases (HMTs), demethylases, and histone phosphorylases. Furthermore, genistein decreased the activity of DNMTs, HDACs, and HMTs and reduced global DNA methylation levels. Promoter methylation of several TSGs, including FHIT, RUNX3, CDH1, PTEN, and SOC51, was lowered with corresponding transcriptional increase. Network analysis indicated similar effect of genistein.

CONCLUSION

This study presents a comprehensive mechanism of action of genistein showcasing effective epigenetic modulation and widespread transcriptional changes resulting in restoration of tumour suppressor gene expression. This study corroborates the development of genistein as a candidate for anti-cancer therapy.

Overview of biological mechanisms of human carcinogens

This review summarizes the carcinogenic mechanisms for 109 Group 1 human carcinogens identified as causes of human cancer through Volume 106 of the IARC Monographs. The International Agency for Research on Cancer (IARC) evaluates human, experimental and mechanistic evidence on agents suspected of inducing cancer in humans, using a well-established weight of evidence approach. The monographs provide detailed mechanistic information about all carcinogens. Carcinogens with closely similar mechanisms of action (e.g. agents emitting alpha particles) were combined into groups for the review. A narrative synopsis of the mechanistic profiles for the 86 carcinogens or carcinogen groups is presented, based primarily on information in the IARC monographs, supplemented with a non-systematic review. Most carcinogens included a genotoxic mechanism.

Epigenetic Dysregulation at the Crossroad of Women's Cancer

An increasingly number of women of all age groups are affected by cancer, despite substantial progress in our understanding of cancer pathobiology, the underlying genomic alterations and signaling cascades, and cellular-environmental interactions. Though our understanding of women’s cancer is far more complete than ever before, there is no comprehensive model to explain the reasons behind the increased incidents of certain reproductive cancer among older as well as younger women. It is generally suspected that environmental and life-style factors affecting hormonal and growth control pathways might help account for the rise of women’s cancers in younger age, as well, via epigenetic mechanisms. Epigenetic regulators play an important role in orchestrating an orderly coordination of cellular signals in gene activity in response to upstream signaling and/or epigenetic modifiers present in a dynamic extracellular milieu. Here we will discuss the broad principles of epigenetic regulation of DNA methylation and demethylation, histone acetylation and deacetylation, and RNA methylation in women’s cancers in the context of gene expression, hormonal action, and the EGFR family of cell surface receptor tyrosine kinases. We anticipate that a better understanding of the epigenetics of women’s cancers may provide new regulatory leads and further fuel the development of new epigenetic biomarkers and therapeutic approaches.

TRIM28 protects CARM1 from proteasome-mediated degradation to prevent colorectal cancer metastasis

TRIM28 (Tripartite motif-containing protein 28), a member of TRIM family, is aberrantly expressed and reportedly has different functions in many types of human cancer. However, the biological roles of TRIM28 and related mechanism in colorectal cancer (CRC) remain unclear. Here, we showed that TRIM28 was downregulated in colorectal cancer compared with normal mucosa, especially at advanced stages, and acted as an independent prognostic factor of favorable outcome. Functional studies demonstrated that TRIM28 restrained CRC migration and invasion in vitro and in vivo. Mechanistically, we reported that CARM1 (co-activator-associated arginine methyltransferase1) was a critical player downstream of TRIM28. TRIM28 interacted with CARM1, and protected CARM1 from proteasome-mediated degradation through physical protein-protein interaction to suppress CRC metastasis. Further, TRIM28 suppressed the migration and invasion of CRC cells through inhibiting WNT/β-catenin signaling in a CARM1-dependent manner, but independent of CARM1's methyltransferase activity. The protein expression of CARM1 was positively correlated with TRIM28 in CRC tissues. Patients with high levels of TRIM28 and CARM1 had improved prognosis, whereas patients with low TRIM28 and CARM1 expression had the poor outcomes. Thus, our study reveals an inhibitory role of TRIM28 in CRC metastasis, which was achieved through a TRIM28-CARM1-WNT/β-catenin axis. This work provides potential prognostic and therapeutic targets for CRC treatment.

Lysine-specific post-translational modifications of proteins in the life cycle of viruses

The process of protein post-translational modifications (PTM) is one of the critical mechanisms of regulation of many cellular processes, which makes it an attractive target for various viruses. Since viruses cannot replicate on their own, they have developed unique abilities to alter metabolic and signaling cell pathways, including protein PTMs, to ensure faithful replication of their genomes. This review describes several ways of how lysine-specific PTMs are used by various viruses to ensure its successful invasion and replication. Covalent modifications like acetylation, ubiquitination, and methylation form a complex system of reversible and often competing modifications, which adds an additional level of complexity to the system of regulation of the activity of host proteins involved in viral replication and propagation. In furthering these, we also describe the manner in which PTM pathways can also be accosted by various types of viruses to neutralize the host's cellular mechanisms for anti-viral protection and highlight key areas for future therapeutic targeting and design.

Quercetin modifies 5'CpG promoter methylation and reactivates various tumor suppressor genes by modulating epigenetic marks in human cervical cancer cells

The central role of epigenomic alterations in carcinogenesis has been widely acknowledged, particularly the impact of DNA methylation on gene expression across all stages of carcinogenesis is considered vital for both diagnostic and therapeutic strategies. Dietary phytochemicals hold great promise as safe anticancer agents and effective epigenetic modulators. This study was designed to investigate the potential of a phytochemical, quercetin as a modulator of the epigenetic pathways for anticancer strategies. Biochemical activity of DNA methyltransferases (DNMTs), histone deacetylases (HDACs), histone methyltransferases (HMTs), and global genomic DNA methylation was quantitated by an enzyme-linked immunosorbent assay based assay in quercetin-treated HeLa cells. Molecular docking studies were performed to predict the interaction of quercetin with DNMTs and HDACs. Quantitative methylation array was used to assess quercetin-mediated alterations in the promoter methylation of selected tumor suppressor genes (TSGs). Quercetin induced modulation of chromatin modifiers including DNMTs, HDACs, histone acetyltransferases (HAT) and HMTs, and TSGs were assessed by quantitative reverse transcription PCR (qRT-PCR). It was found that quercetin modulates the expression of various chromatin modifiers and decreases the activity of DNMTs, HDACs, and HMTs in a dose-dependent manner. Molecular docking results suggest that quercetin could function as a competitive inhibitor by interacting with residues in the catalytic cavity of several DNMTs and HDACs. Quercetin downregulated global DNA methylation levels in a dose- and time-dependent manner. The tested TSGs showed steep dose-dependent decline in promoter methylation with the restoration of their expression. Our study provides an understanding of the quercetin's mechanism of action and will aid in its development as a candidate for epigenetic-based anticancer therapy.

MiR-362-3p is downregulated by promoter methylation and independently predicts shorter OS of cervical squamous cell carcinoma

The current study was undertaken to investigate the potential influence of methylation on miR-362-5p/3p expression and further analyzed their independent prognostic value in cervical adenocarcinoma (ADC) and squamous cell carcinoma (SCC) respectively. SiHa and CaSki cells were used as the in vitro cell model. In silico bioinformatic analysis was conducted via the combined use of the Cancer Genome Atlas-Cervical Cancer (TCGA-CESC), Starbase 3.0 and String 10.5. Results revealed that the downregulation of miR-362-5p/3p was accompanied by the infection of high-risk human papillomavirus (HR-HPV) and their expression was further decreased in HR-HPV cancer tissues. Demethylation could restore their expression. By performing Methylation-specific PCR (MSP) based on methylated or unmethylated specific primers, we confirmed that the proximal promoter region was methylated in both cell lines. Higher miR-362-3p expression might independently predict favorable overall survival (OS) in SCC patients (HR: 0.561, 95%CI: 0.354-0.889, p = 0.014), after adjustment of clinical stages, lymphovascular invasion and miR-362-5p expression. However, no prognostic value of miR-362-5p or miR-362-3p expression was observed in terms of OS in patients with ADC. Via bioinformatic analysis, we found that miR-362-3p might have an entirely different regulatory network in cervical ADC and SCC, which might help to explain the distinct prognostic value of miR-362-3p in these two histological subtypes. In summary, we infer that the methylation level of the proximal promoter region of pre-miR-362 would influence the expression of miR-362-5p/3p in cervical cancer. MiR-362-3p expression might be a specific prognostic biomarker in cervical SCC, but not in ADC.

Molecular mechanisms in progression of HPV-associated cervical carcinogenesis

Cervical cancer is the fourth most frequent cancer in women worldwide and a major cause of mortality in developing countries. Persistent infection with high-risk human papillomavirus (HPV) is a necessary cause for the development of cervical cancer. In addition, genetic and epigenetic alterations in host cell genes are crucial for progression of cervical precancerous lesions to invasive cancer. Although much progress has been made in understanding the life cycle of HPV and it’s role in the development of cervical cancer, there is still a critical need for accurate surveillance strategies and targeted therapeutic options to eradicate these cancers in patients. Given the widespread nature of HPV infection and the type specificity of currently available HPV vaccines, it is crucial that molecular details of the natural history of HPV infection as well as the biological activities of viral oncoproteins be elucidated. A better understanding of the mechanisms involved in oncogenesis can provide novel insights and opportunities for designing effective therapeutic approaches against HPV-associated malignancies. In this review, we briefly summarize epigenetic alterations and events that cause alterations in host genomes inducing cell cycle deregulation, aberrant proliferation and genomic instability contributing to tumorigenesis.

Hallmarks of HPV carcinogenesis: The role of E6, E7 and E5 oncoproteins in cellular malignancy

Human papillomavirus (HPV) is the most common sexually transmitted infectious agent worldwide, being also responsible for 5% of all human cancers. The integration and hypermethylation mechanisms of the HPV viral genome promote the unbalanced expression of the E6, E7 and E5 oncoproteins, which are crucial factors for the carcinogenic cascade in HPV-induced cancers. This review highlights the action of E6, E7 and E5 over key regulatory targets, promoting all known hallmarks of cancer. Both well-characterized and novel targets of these HPV oncoproteins are described, detailing their mechanisms of action. Finally, this review approaches the possibility of targeting E6, E7 and E5 for therapeutic applications in the context of cancer.

Oncogenicitiy Comparison of Human Papillomavirus Type 52 E6 Variants

Human papillomavirus (HPV) infection contributes to virtually all cases of cervical cancer, the fourth most common cancer affecting women worldwide. The oncogenicity of HPV is mainly attributable to the E6 and E7 oncoproteins. HPV-52 is the seventh most common HPV type globally, but it has a remarkably high prevalence in East Asia. In previous studies it has been speculated that the oncogenicity might vary among different HPV-52 variants. In the present study, we compared the oncogenicity of E6 derived from the HPV-52 prototype and three commonly found variants, V1 (K93R), V2 (E14D/V92L) and V3 (K93R/N122K), through molecular and phenotypic approaches. We demonstrated that cells containing V1 achieved higher colony formation and showed greater cell migration ability when compared to other variants, but no difference in cell immortalization ability was observed. At the molecular level, the three variants formed complexes with E6-associated protein (E6AP) and p53 as efficiently as the prototype. They degraded p53 and PSD95/Dlg/ZO-1(PDZ) proteins, including MAGI-1c and Dlg, to a similar extent. They also exhibited a similar subcellular localization, and shared a half-life of approximately 45 min. Our findings provide a clearer picture of HPV-52 E6 variant oncogenicity, which is important for further studies aiming to understand the unusually high prevalence of HPV-52 among cervical cancers in East Asia.

HPV16 E7-induced upregulation of KDM2A promotes cervical cancer progression by regulating miR-132-radixin pathway

BACKGROUND

Human papillomavirus (HPV) infection and viral proteins expression cause a number of epigenetic alterations leading to cervical carcinogenesis. The recent discovery of a large amount of histone methylation modifiers reveals important roles of these enzymes in regulating tumor progression.

METHODS

The changes in expression of 48 histone methylation modifiers were assessed following knockdown of HPV16 E7 in CaSki cells. Lysine-specific demethylase 2A (KDM2A)-regulated microRNAs (miRNAs) in cervical cancer pathogenesis were disclosed using quantitative real-time polymerase chain reaction. The function of KDM2A-miRNAs on cervical cancer was investigated in vitro and in vivo.

RESULTS

Upregulation of KDM2A induced by HPV16 E7 promotes cervical cancer cell proliferation and invasion and is correlated with poor prognosis in patients with cervical cancer. KDM2A physically interacts with the promoter of miR-132 and suppresses its expression by removing the mono or dimethyl group from H3K36 at the miR-132 locus. Functionally, miR-132 represses cancer cell proliferation and invasion by inhibiting radixin (RDX). Upregulated KDM2A promotes cervical cancer progression by repressing miR-132, which results in a derepression of RDX. Therefore, KDM2A functions as a tumor activator in cervical cancer pathogenesis by binding miR-132 promoter and abrogating its tumor suppressive function.

CONCLUSION

Our results suggest a function for KDM2A in cervical cancer progression and suggest its candidacy as a new prognostic biomarker and target for clinical management of cervical cancer.

High-Risk Human Papillomaviral Oncogenes E6 and E7 Target Key Cellular Pathways to Achieve Oncogenesis

Infection with high-risk human papillomavirus (HPV) has been linked to several human cancers, the most prominent of which is cervical cancer. The integration of the viral genome into the host genome is one of the manners in which the viral oncogenes E6 and E7 achieve persistent expression. The most well-studied cellular targets of the viral oncogenes E6 and E7 are p53 and pRb, respectively. However, recent research has demonstrated the ability of these two viral factors to target many more cellular factors, including proteins which regulate epigenetic marks and splicing changes in the cell. These have the ability to exert a global change, which eventually culminates to uncontrolled proliferation and carcinogenesis.

5azadC treatment upregulates miR-375 level and represses HPV16 E6 expression

High-risk human papillomaviruses are the etiological agents of cervical cancer and HPV16 is the most oncogenic genotype. Immortalization and transformation of infected cells requires the overexpression of the two viral oncoproteins E6 and E7 following HPV DNA integration into the host cell genome. Integration often leads to the loss of the E2 open reading frame and the corresponding protein can no longer act as a transcriptional repressor on p97 promoter. Recently, it has been proposed that long control region methylation also contributes to the regulation of E6/E7 expression.

To determine which epigenetic mechanism is involved in HPV16 early gene regulation, 5-aza-2′-deoxycytidine was used to demethylate Ca Ski and SiHa cell DNA. Decreased expression of E6 mRNA and protein levels was observed in both cell lines in an E2-independent manner. E6 repression was accompanied by neither a modification of the main cellular transcription factor expression involved in long control region regulation, nor by a modification of the E6 mRNA splicing pattern. In contrast, a pronounced upregulation of miR-375, known to destabilize HPV16 early viral mRNA, was observed. Finally, the use of miR-375 inhibitor definitively proved the involvement of miR-375 in E6 repression. These results highlight that cellular DNA methylation modulates HPV16 early gene expression and support a role for epigenetic events in high-risk HPV associated-carcinogenesis.

Identification and Characterizations of Novel, Selective Histone Methyltransferase SET7 Inhibitors by Scaffold Hopping- and 2D-Molecular Fingerprint-Based Similarity Search

SET7, serving as the only histone methyltransferase that monomethylates 'Lys-4' of histone H3, has been proved to function as a key regulator in diverse biological processes, such as cell proliferation, transcriptional network regulation in embryonic stem cell, cell cycle control, protein stability, heart morphogenesis and development. What's more, SET7 is involved inthe pathogenesis of alopecia aerate, breast cancer, tumor and cancer progression, atherosclerosis in human carotid plaques, chronic renal diseases, diabetes, obesity, ovarian cancer, prostate cancer, hepatocellular carcinoma, and pulmonary fibrosis. Therefore, there is urgent need to develop novel SET7 inhibitors. In this paper, based on DC-S239 which has been previously reported in our group, we employed scaffold hopping- and 2D fingerprint-based similarity searches and identified DC-S285 as the new hit compound targeting SET7 (IC₅₀ = 9.3 μM). Both radioactive tracing and NMR experiments validated the interactions between DC-S285 and SET7 followed by the second-round similarity search leading to the identification ofDC-S303 with the IC₅₀ value of 1.1 μM. In cellular level, DC-S285 retarded tumor cell proliferation and showed selectivity against MCF7 (IC₅₀ = 21.4 μM), Jurkat (IC₅₀ = 2.2 μM), THP1 (IC₅₀ = 3.5 μM), U937 (IC₅₀ = 3.9 μM) cell lines. Docking calculations suggested that DC-S303 share similar binding mode with the parent compoundDC-S239. What's more, it presented good selectivity against other epigenetic targets, including SETD1B, SETD8, G9a, SMYD2 and EZH2. DC-S303 can serve as a drug-like scaffold which may need further optimization for drug development, and can be used as chemical probe to help the community to better understand the SET7 biology.

PRMT5: A novel regulator of Hepatitis B virus replication and an arginine methylase of HBV core

In mammals, protein arginine methyltransferase 5, PRMT5, is the main type II enzyme responsible for the majority of symmetric dimethylarginine formation in polypeptides. Recent study reported that PRMT5 restricts Hepatitis B virus (HBV) replication through epigenetic repression of HBV DNA transcription and interference with encapsidation of pregenomic RNA. Here we demonstrate that PRMT5 interacts with the HBV core (HBc) protein and dimethylates arginine residues within the arginine-rich domain (ARD) of the carboxyl-terminus. ARD consists of four arginine rich subdomains, ARDI, ARDII, ARDIII and ARDIV. Mutation analysis of ARDs revealed that arginine methylation of HBc required the wild-type status of both ARDI and ARDII. Mass spectrometry analysis of HBc identified multiple potential ubiquitination, methylation and phosphorylation sites, out of which lysine K7 and arginines R150 (within ARDI) and R156 (outside ARDs) were shown to be modified by ubiquitination and methylation, respectively. The HBc symmetric dimethylation appeared to be linked to serine phosphorylation and nuclear import of HBc protein. Conversely, the monomethylated HBc retained in the cytoplasm. Thus, overexpression of PRMT5 led to increased nuclear accumulation of HBc, and vice versa, down-regulation of PRMT5 resulted in reduced levels of HBc in nuclei of transfected cells. In summary, we identified PRMT5 as a potent controller of HBc cell trafficking and function and described two novel types of HBc post-translational modifications (PTMs), arginine methylation and ubiquitination.

Epigenetic Alterations in Human Papillomavirus-Associated Cancers

Approximately 15–20% of human cancers are caused by viruses, including human papillomaviruses (HPVs). Viruses are obligatory intracellular parasites and encode proteins that reprogram the regulatory networks governing host cellular signaling pathways that control recognition by the immune system, proliferation, differentiation, genomic integrity, and cell death. Given that key proteins in these regulatory networks are also subject to mutation in non-virally associated diseases and cancers, the study of oncogenic viruses has also been instrumental to the discovery and analysis of many fundamental cellular processes, including messenger RNA (mRNA) splicing, transcriptional enhancers, oncogenes and tumor suppressors, signal transduction, immune regulation, and cell cycle control. More recently, tumor viruses, in particular HPV, have proven themselves invaluable in the study of the cancer epigenome. Epigenetic silencing or de-silencing of genes can have cellular consequences that are akin to genetic mutations, i.e., the loss and gain of expression of genes that are not usually expressed in a certain cell type and/or genes that have tumor suppressive or oncogenic activities, respectively. Unlike genetic mutations, the reversible nature of epigenetic modifications affords an opportunity of epigenetic therapy for cancer. This review summarizes the current knowledge on epigenetic regulation in HPV-infected cells with a focus on those elements with relevance to carcinogenesis.

Human papillomaviruses in epigenetic regulations

Human Papillomaviruses (HPVs) are double-stranded DNA viruses, that infect epithelial cells and are etiologically involved in the development of human cancer. Today, over 200 types of human papillomaviruses are known. They are divided into low-risk and high-risk HPVs depending on their potential to induce carcinogenesis, driven by two major viral oncoproteins, E6 and E7. By interacting with cellular partners, these proteins are involved in interdependent viral and cell cycles in stratified differentiating epithelium, and concomitantly induce epigenetic changes in infected cells and those undergoing malignant transformation. E6 and E7 oncoproteins interact with and/or modulate expression of many proteins involved in epigenetic regulation, including DNA methyltransferases, histone-modifying enzymes and subunits of chromatin remodeling complexes, thereby influencing host cell transcription program. Furthermore, HPV oncoproteins modulate expression of cellular micro RNAs. Most of these epigenetic actions in a complex dynamic interplay participate in the maintenance of persistent infection, cell transformation, and development of invasive cancer by a considerable deregulation of tumor suppressor and oncogenes. In this study, we have undertaken to discuss a number of studies concerning epigenetic regulations in HPV-dependent cells and to focus on those that have biological relevance to cancer progression.

Epigenetic Pathways of Oncogenic Viruses: Therapeutic Promises

Cancerous transformation comprises different events that are both genetic and epigenetic. The ultimate goal for such events is to maintain cell survival and proliferation. This transformation occurs as a consequence of different features such as environmental and genetic factors, as well as some types of infection. Many viral infections are considered to be causative agents of a number of different malignancies. To convert normal cells into cancerous cells, oncogenic viruses must function at the epigenetic level to communicate with their host cells. Oncogenic viruses encode certain epigenetic factors that lead to the immortality and proliferation of infected cells. The epigenetic effectors produced by oncogenic viruses constitute appealing targets to prevent and treat malignant diseases caused by these viruses. In this review, we highlight the importance of epigenetic reprogramming for virus-induced oncogenesis, with special emphasis on viral epigenetic oncoproteins as therapeutic targets. The discovery of molecular components that target epigenetic pathways, especially viral factors, is also discussed.

Human papillomavirus type 16 E7 oncoprotein mediates CCNA1 promoter methylation

Human papillomavirus (HPV) oncoproteins drive distinctive promoter methylation patterns in cancer. However, the underlying mechanism remains to be elucidated. Cyclin A1 (CCNA1) promoter methylation is strongly associated with HPV-associated cancer. CCNA1 methylation is found in HPV-associated cervical cancers, as well as in head and neck squamous cell cancer. Numerous pieces of evidence suggest that E7 may drive CCNA1 methylation. First, the CCNA1 promoter is methylated in HPV-positive epithelial lesions after transformation. Second, the CCNA1 promoter is methylated at a high level when HPV is integrated into the human genome. Finally, E7 has been shown to interact with DNA methyltransferase 1 (Dnmt1). Here, we sought to determine the mechanism by which E7 increases methylation in cervical cancer by using CCNA1 as a gene model. We investigated whether E7 induces CCNA1 promoter methylation, resulting in the loss of expression. Using both E7 knockdown and overexpression approaches in SiHa and C33a cells, our data showed that CCNA1 promoter methylation decreases with a corresponding increase in expression in E7 siRNA-transfected cells. By contrast, CCNA1 promoter methylation was augmented with a corresponding reduction in expression in E7-overexpressing cells. To confirm whether the binding of the E7-Dnmt1 complex to the CCNA1 promoter induced methylation and loss of expression, ChIP assays were carried out in E7-, del CR3-E7 and vector control-overexpressing C33a cells. The data showed that E7 induced CCNA1 methylation by forming a complex with Dnmt1 at the CCNA1 promoter, resulting in the subsequent reduction of expression in cancers. It is interesting to further explore the genome-wide mechanism of E7 oncoprotein-mediated DNA methylation.

Novel Functions of the Human Papillomavirus E6 Oncoproteins

Human papillomaviruses (HPVs) infect the epidermis as well as mucous membranes of humans. They are the causative agents of anogenital tract and some oropharyngeal cancers. Infections begin in the basal epithelia, where the viral genome replicates slowly along with its host cell. As infected cells begin to differentiate and progress toward the periphery, the virus drives proliferation in cells that would otherwise be quiescent. To uncouple differentiation from continued cellular propagation, HPVs express two oncoproteins, HPV E6 and E7. This review focuses on high-risk α-HPV E6, which in addition to supporting viral replication has transforming properties. HPV E6 promotes p53 degradation and activates telomerase, but the multifaceted oncoprotein has numerous other functions that are highlighted here.

Set7 facilitates hepatitis C virus replication via enzymatic activity-dependent attenuation of the IFN-related pathway

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, usually resulting in persistent infection involving hepatic steatosis, cirrhosis, and hepatocellular carcinoma via escape of the host's immune response. Set7 is a lysine-specific methyltransferase that is involved in gene regulation and virus replication. However, the mechanism underlying the immune evasion between HCV and Set7 is not well understood. In this study, we observed that the expression of Set7 in Huh7.5.1 cells was upregulated by HCV infection, and high levels of Set7 expression were also found in the sera, PBMCs, and liver tissue of HCV patients relative to healthy individuals. Further investigation showed that Set7 enhanced HCV replication in an enzymatic activity-dependent manner. Moreover, our data showed that Set7 decreased the expression of virus-induced IFN and IFN-related effectors, such as dsRNA-activated protein kinase and 2',5'-oligoadenylate synthetase. Further investigation suggested that Set7 suppressed the endogenous IFN expression by reducing the nuclear translocation of IFN regulatory factor 3/7 and the p65 subunit of NF-κB and reduced IFN-induced dsRNA-activated protein kinase and 2',5'-oligoadenylate synthetase via attenuation of the phosphorylation of STAT1 and STAT2. Additionally, IFN receptors, including IFNAR1 and IFNAR2, which are located upstream of the JAK/STAT pathway, were reduced by Set7. Taken together, our results reveal that Set7 facilitates HCV replication through the attenuation of IFN signaling pathways and IFN-related effectors.

Methylation-mediated repression of PRDM14 contributes to apoptosis evasion in HPV-positive cancers

Promoter methylation of the transcription factor PRDM14 (PRDI-BF1 and RIZ domain containing 14) represents a highly frequent event in human papillomavirus (HPV)-induced cervical cancers and cancer precursor lesions. Here, we aimed to assess the functional consequences of PRDM14 promoter methylation in HPV-induced carcinogenesis. PRDM14 promoter methylation, expression and consequences of ectopic PRDM14 expression were studied in HPV16-positive cervical and oral cancer cell lines (SiHa, CaSki and 93VU147T), human embryonic kidney 293 (HEK293T) cells and primary human foreskin keratinocytes (HFK). PRDM14 mRNA expression was restricted to HEK293T and HFK cells, and could be upregulated in SiHa cells upon DNA methylation inhibition. Ectopic expression of PRDM14 in SiHa, CaSki and 93VU147T cells resulted in significantly more apoptotic cells, as measured by annexin V labelling, compared to HEK293T and HFK cells. MRNA profiling of 41 apoptosis regulators identified NOXA and PUMA as candidate target genes involved in PRDM14-mediated apoptosis induction. Full-length PRDM14 transactivated both NOXA and PUMA promoters. Transactivation was abolished upon deletion of the PRDM14 DNA binding domain. This suggests that NOXA and PUMA expression is directly regulated by PRDM14, which in case of NOXA was linked to a consensus PRDM14 binding motif in the promoter region. Taken together, these results suggest that PRDM14 acts as a regulator of NOXA and PUMA-mediated apoptosis induction, thereby providing evidence for a tumour suppressive role in HPV-induced carcinogenesis. The contribution of methylation-mediated gene silencing of PRDM14 to apoptosis evasion in HPV-positive cancer cells offers novel therapeutic options for HPV-induced cancers.

BAG3 down-modulation sensitizes HPV18(+) HeLa cells to PEITC-induced apoptosis and restores p53

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BAG3 down-modulation by siRNA technology restored p53.

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Reduced BAG3 expression sensitized HeLa but not C33A (HPV-negative) cells to PEITC.

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Reduced BAG3 expression was associated with a decrease of E6 viral protein levels.

BAG3 is a multi-functional component of tumor cell pro-survival machinery, and its biological functions have been largely associated to proteasome system. Here, we show that BAG3 down-modulation resulted in reduced cell viability and enhanced PEITC-induced apoptosis largely more extensively in HeLa (HPV18⁺) rather than in C33A (HPV⁻) cervical carcinoma cell lines. Moreover, we demonstrate that BAG3 suppression led to a decrease of viral E6 oncoprotein and a concomitant recovery of p53 tumor suppressor, the best recognized target of E6 for proteasome degradation. E6 and p53 expression were modulated at protein level, since their respective mRNAs were unaffected. Taken together our findings reveal a novel role for BAG3 as host protein contributing to HPV18 E6-activated pro-survival strategies, and suggest a possible relevance of its expression levels in drug/radiotherapy-resistance of HPV18-bearing cervical carcinomas.

Characterization of a new mouse p53 variant: loss-of-function and gain-of-function

Background

p53 is a major tumor suppressor that is inactivated in over 50% of human cancer types through either mutation or inactivating interactions with viral or cellular proteins. The uncertainties around the link between p53 status, therapeutic response, and outcome in cancer suggest that additional factors may be involved. p53 isoforms that are generated via the alternative splicing pathway may be promising candidates for further investigation.

Result

In this study, we report one new p53 protein with two internally deleted regions, resulting in one deleted amino acid fragment (from amino acid residues 42 to 89) and one reading frame-shift region (from amino acid residues 90-120) compared to wild-type p53. The functional status of the new p53 protein, which has a defect in its proline-rich and N-terminal DNA-binding domains, was characterized as possessing an intact conformation, exhibiting no transactivation activity, exerting a dominant-negative effect and an interacting with a coactivator with an arginine methyltransferase activity.

Conclusion

Taken together, our findings provide valuable information about the structure and function of p53 for the regulation of transactivation activity and cellular protein-protein interactions. Furthermore, natural p53 isoforms will help us understand the functional roles of the p53 family and potential therapeutics for p53-dependent cancers.

The functional diversity of protein lysine methylation

Large‐scale characterization of post‐translational modifications (PTMs), such as phosphorylation, acetylation and ubiquitination, has highlighted their importance in the regulation of a myriad of signaling events. While high‐throughput technologies have tremendously helped cataloguing the proteins modified by these PTMs, the identification of lysine‐methylated proteins, a PTM involving the transfer of one, two or three methyl groups to the ε‐amine of a lysine side chain, has lagged behind. While the initial findings were focused on the methylation of histone proteins, several studies have recently identified novel non‐histone lysine‐methylated proteins. This review provides a compilation of all lysine methylation sites reported to date. We also present key examples showing the impact of lysine methylation and discuss the circuitries wired by this important PTM.

Host-virus interactions: from the perspectives of epigenetics

Chromatin structure and histone modifications play key roles in gene regulation. Some virus genomes are organized into chromatin-like structure, which undergoes different histone modifications facilitating complex functions in virus life cycles including replication. Here, we present a comprehensive summary of recent research in this field regarding the interaction between viruses and host epigenetic factors with emphasis on how chromatin modifications affect viral gene expression and virus infection. We also describe the strategies employed by viruses to manipulate the host epigenetic program to facilitate virus replication as well as the underlying mechanisms. Together, knowledge from this field not only generates novel insights into virus life cycles but may also have important therapeutic implications.

Epigenetics of human papillomaviruses

Human papilllomaviruses (HPVs) are common human pathogens that infect cutaneous or mucosal epithelia in which they cause warts, self-contained benign lesions that commonly regress. The HPV life cycle is intricately tied to the differentiation of the host epithelium it infects. Mucosotropic HPVs are the most common sexually transmitted pathogen known to mankind. A subset of the mucosotropic HPVs, so-called high risk HPVs, is etiologically associated with numerous cancers of the anogenital tract, most notably the cervix, as well as a growing fraction of head and neck cancers. In these cancers, the HPV genome, which normally exists an a double stranded, circular, nuclear plasmid, is commonly found integrated into the host genome and expresses two viral oncogenes, E6 and E7, that are implicated in the development and maintainance of the cancers caused by these high risk HPVs. Numerous studies, primarily on the high risk HPV16, have documented that the methylation status of the viral genome changes not only in the context of the viral life cycle but also in the context of the progressive neoplastic disease that culminates in cancer. In this article, we summarize the knowledge gained from those studies. We also provide the first analysis of available ChIP-seq data on the occupancy of both epigentically modified histones as well as transcription factors on the high risk HPV18 genome in the context of HeLa cells, a cervical cancer-derived cell line that has been the subject of extensive analyses using this technique.

Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation

Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the 'normal' epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing.

Papillomavirus E6 oncoproteins

Papillomaviruses induce benign and malignant epithelial tumors, and the viral E6 oncoprotein is essential for full transformation. E6 contributes to transformation by associating with cellular proteins, docking on specific acidic LXXLL peptide motifs found on these proteins. This review examines insights from recent studies of human and animal E6 proteins that determine the three-dimensional structure of E6 when bound to acidic LXXLL peptides. The structure of E6 is related to recent advances in the purification and identification of E6 associated protein complexes. These E6 protein-complexes, together with other proteins that bind to E6, alter a broad array of biological outcomes including modulation of cell survival, cellular transcription, host cell differentiation, growth factor dependence, DNA damage responses, and cell cycle progression.