PDZ domains and viral infection: versatile potentials of HPV-PDZ interactions in relation to malignancy

Identification of HPV16 Lineages in South African and Mozambican Women with Normal and Abnormal Cervical Cytology

BACKGROUND

Human papillomavirus 16 (HPV16) is an oncogenic virus responsible for the majority of invasive cervical cancer cases worldwide. Due to genetic modifications, some variants are more oncogenic than others. We analysed the HPV16 phylogeny in HPV16-positive cervical Desoxyribonucleic Acid (DNA) samples collected from South African and Mozambican women to detect the circulating lineages.

METHODS

Polymerase chain reaction (PCR) amplification of the long control region (LCR) and 300 nucleotides of the E6 region was performed using HPV16-specific primers on HPV16-positive cervical samples collected in women from South Africa and Mozambique. HPV16 sequences were obtained through Next Generation Sequencing (NGS) methods. Geneious prime and MEGA 11 software were used to align the sequences to 16 HPV16 reference sequences, gathering the A, B, C, and D lineages and generating the phylogenetic tree. Single nucleotide polymorphisms (SNPs) in the LCR and E6 regions were analysed and the phylogenetic tree was generated using Geneious Prime software.

RESULTS

Fifty-eight sequences were analysed. Of these sequences, 79% (46/58) were from women who had abnormal cervical cytology. Fifteen SNPs in the LCR and eight in the E6 region were found to be the most common in all sequences. The phylogenetic analysis determined that 45% of the isolates belonged to the A1 sublineage (European variant), 34% belonged to the C1 sublineage (African 1 variant), 16% belonged to the B1 and B2 sublineage (African 2 variant), two isolates belonged to the D1-3 sublineages (Asian-American variant), and one to the North American variant.

CONCLUSIONS

The African and European HPV16 variants were the most common circulating lineages in South African and Mozambican women. A high-grade squamous intraepithelial lesion (HSIL) was the most common cervical abnormality observed and linked to European and African lineages. These findings may contribute to understanding molecular HPV16 epidemiology in South Africa and Mozambique.

Bioinformatics Analysis Reveals E6 and E7 of HPV 16 Regulate Metabolic Reprogramming in Cervical Cancer, Head and Neck Cancer, and Colorectal Cancer through the PHD2-VHL-CUL2-ELOC-HIF-1α Axis

Human papillomavirus 16 (HPV 16) infection is associated with several types of cancer, such as head and neck, cervical, anal, and penile cancer. Its oncogenic potential is due to the ability of the E6 and E7 oncoproteins to promote alterations associated with cell transformation. HPV 16 E6 and E7 oncoproteins increase metabolic reprogramming, one of the hallmarks of cancer, by increasing the stability of hypoxia-induced factor 1 α (HIF-1α) and consequently increasing the expression levels of their target genes. In this report, by bioinformatic analysis, we show the possible effect of HPV 16 oncoproteins E6 and E7 on metabolic reprogramming in cancer through the E6-E7-PHD2-VHL-CUL2-ELOC-HIF-1α axis. We proposed that E6 and E7 interact with VHL, CUL2, and ELOC in forming the E3 ubiquitin ligase complex that ubiquitinates HIF-1α for degradation via the proteasome. Based on the information found in the databases, it is proposed that E6 interacts with VHL by blocking its interaction with HIF-1α. On the other hand, E7 interacts with CUL2 and ELOC, preventing their binding to VHL and RBX1, respectively. Consequently, HIF-1α is stabilized and binds with HIF-1β to form the active HIF1 complex that binds to hypoxia response elements (HREs), allowing the expression of genes related to energy metabolism. In addition, we suggest an effect of E6 and E7 at the level of PHD2, VHL, CUL2, and ELOC gene expression. Here, we propose some miRNAs targeting PHD2, VHL, CUL2, and ELOC mRNAs. The effect of E6 and E7 may be the non-hydroxylation and non-ubiquitination of HIF-1α, which may regulate metabolic processes involved in metabolic reprogramming in cancer upon stabilization, non-degradation, and translocation to the nucleus.

Human Papilloma Virus Positive Oropharyngeal Squamous Cell Carcinoma and the Immune System: Pathogenesis, Immunotherapy and Future Perspectives

Oropharyngeal squamous cell carcinoma (OPSCC), a subset of head and neck squamous cell carcinoma (HNSCC), involves the palatine tonsils, soft palate, base of tongue, and uvula, with the ability to spread to adjacent subsites. Personalized treatment strategies for Human Papillomavirus-associated squamous cell carcinoma of the oropharynx (HPV+OPSCC) are yet to be established. In this article, we summarise our current understanding of the pathogenesis of HPV+OPSCC, the intrinsic role of the immune system, current ICI clinical trials, and the potential role of small molecule immunotherapy in HPV+OPSCC.

Viral Metagenomics Reveals a Putative Novel HPV Type in Anogenital Wart Tissues

Viral metagenomics is widely employed to identify novel viruses in biological samples. Recently, although numerous novel human papillomavirus (HPV) types have been identified in clinical samples including anogenital warts (AGWs), many novel HPV sequences remain to be discovered. In this study, a putative novel HPV type designated as HPV-JDFY01 was discovered from library GW05 with 63 sequence reads by the viral metagenomic technique. Its complete genomic sequence was determined by PCR to bridge the gaps between contigs combining Sanger sequencing. The complete genome of HPV-JDFY01 is a 7186 bp encoding 7 open reading frames (ORFs) (E6, E7, E1, E2, E4, L2 and L1) and contains a 487 bp long control region (LCR) between L1 and E6. Sequence and phylogeny analysis indicated that HPV-JDFY01 shared the highest sequence identity of 74.2% with HPV-mSK_244 (MH777383) and well clustered into the genus Gammapapillomavirus. It has the classical genomic organization of Gammapapillomaviruses. Epidemiological investigation showed that one out of the 413 AGW tissue samples was positive for HPV-JDFY01. Further research with large size and different type of samples should be performed to elucidate the epidemiologic status of HPV-JDFY01.

High-Risk Oncogenic Human Cytomegalovirus

Human cytomegalovirus (HCMV) is a herpesvirus that infects between 40% and 95% of the population worldwide, usually without symptoms. The host immune response keeps the virus in a latent stage, although HCMV can reactivate in an inflammatory context, which could result in sequential lytic/latent viral cycles during the lifetime and thereby participate in HCMV genomic diversity in humans. The high level of HCMV intra-host genomic variability could participate in the oncomodulatory role of HCMV where the virus will favor the development and spread of cancerous cells. Recently, an oncogenic role of HCMV has been highlighted in which the virus will directly transform primary cells; such HCMV strains are named high-risk (HR) HCMV strains. In light of these new findings, this review defines the criteria that characterize HR-HCMV strains and their molecular as well as the phenotypic impact on the infected cell and its tumor microenvironment.

Molecular Mechanisms of HIV Protease Inhibitors Against HPV-Associated Cervical Cancer: Restoration of TP53 Tumour Suppressor Activities

Cervical cancer is a Human Papilloma virus-related disease, which is on the rise in a number of countries, globally. Two essential oncogenes, E6 and E7, drive cell transformation and cancer development. These two oncoproteins target two of the most important tumour suppressors, p53 and pRB, for degradation through the ubiquitin ligase pathway, thus, blocking apoptosis activation and deregulation of cell cycle. This pathway can be exploited for anticancer therapeutic interventions, and Human Immunodeficiency Virus Protease Inhibitors (HIV-PIs) have attracted a lot of attention for this anticancer drug development. HIV-PIs have proven effective in treating HPV-positive cervical cancers and shown to restore impaired or deregulated p53 in HPV-associated cervical cancers by inhibiting the 26S proteasome. This review will evaluate the role players, such as HPV oncoproteins involved cervical cancer development and how they are targeted in HIV protease inhibitors-induced p53 restoration in cervical cancer. This review also covers the therapeutic potential of HIV protease inhibitors and molecular mechanisms behind the HIV protease inhibitors-induced p53-dependent anticancer activities against cervical cancer.

An internal class III PDZ binding motif in HPV16 E6* protein is required for Dlg degradation activity

BACKGROUND

A splice product of the E6 oncoprotein, E6*, is found in cells infected with HPV associated with a high-risk for cervical cancer. Both E6* and E6 promote Dlg degradation, considered a contributing factor for the tumorigenic potential of high-risk HPVs. The full-length E6 utilizes a conserved PDZ binding motif (PBM) at the extreme C-terminus to promote Dlg degradation. In contrast, this PBM is absent in E6*.

METHODS

We performed western blot analysis, site-directed mutagenesis and co-immunoprecipitation to identify the key elements required for Dlg degradation activity of high-risk HPVE6*, using HPV16E6* as a model.

RESULTS

Our data indicate that only one of the two internal putative class III PBMs, located between amino acids 24-27 (HDII) of HPV16E6*, was required to facilitate degradation of Dlg protein. Substitution of the two consensus residues in this region (D25 and I27) to glycine greatly diminished activity. Whereas substitution of the two conserved residues in the putative internal class I PBM (amino acids 16-19) or the second putative class III PBM (amino acids 28-31) was without effect. Interestingly, HPV66E6* which does not promote Dlg degradation can be converted into a form capable of facilitating Dlg degradation through the insertion of nine amino acids (20-28) containing the class III PBM from HPV16E6*. HPV16E6*-induced Dlg degradation appeared independent of E6AP.

CONCLUSIONS

The internal class III PBM of HPV16E6*I required for Dlg degradation is identified.

GENERAL SIGNIFICANCE

This study highlights that a novel class III PBM as the domain responsible for Dlg degradation activity in high-risk HPVE6*.

The Molecular and Pathophysiological Functions of Members of the LNX/PDZRN E3 Ubiquitin Ligase Family

The ligand of Numb protein-X (LNX) family, also known as the PDZRN family, is composed of four discrete RING-type E3 ubiquitin ligases (LNX1, LNX2, LNX3, and LNX4), and LNX5 which may not act as an E3 ubiquitin ligase owing to the lack of the RING domain. As the name implies, LNX1 and LNX2 were initially studied for exerting E3 ubiquitin ligase activity on their substrate Numb protein, whose stability was negatively regulated by LNX1 and LNX2 via the ubiquitin-proteasome pathway. LNX proteins may have versatile molecular, cellular, and developmental functions, considering the fact that besides these proteins, none of the E3 ubiquitin ligases have multiple PDZ (PSD95, DLGA, ZO-1) domains, which are regarded as important protein-interacting modules. Thus far, various proteins have been isolated as LNX-interacting proteins. Evidence from studies performed over the last two decades have suggested that members of the LNX family play various pathophysiological roles primarily by modulating the function of substrate proteins involved in several different intracellular or intercellular signaling cascades. As the binding partners of RING-type E3s, a large number of substrates of LNX proteins undergo degradation through ubiquitin-proteasome system (UPS) dependent or lysosomal pathways, potentially altering key signaling pathways. In this review, we highlight recent and relevant findings on the molecular and cellular functions of the members of the LNX family and discuss the role of the erroneous regulation of these proteins in disease progression.

Use of Cap Analysis Gene Expression to detect human papillomavirus promoter activity patterns at different disease stages

Transcription of human papillomavirus (HPV) genes proceeds unidirectionally from multiple promoters. Direct profiling of transcription start sites (TSSs) by Cap Analysis Gene Expression (CAGE) is a powerful strategy for examining individual HPV promoter activity. The objective of this study was to evaluate alterations of viral promoter activity during infection using CAGE technology. We used CAGE-based sequencing of 46 primary cervical samples, and quantitatively evaluated TSS patterns in the HPV transcriptome at a single-nucleotide resolution. TSS patterns were classified into two types: early promoter-dominant type (Type A) and late promoter-dominant type (Type B). The Type B pattern was more frequently found in CIN1 and CIN2 lesions than in CIN3 and cancer samples. We detected transcriptomes from multiple HPV types in five samples. Interestingly, in each sample, the TSS patterns of both HPV types were the same. The viral gene expression pattern was determined by the differentiation status of the epithelial cells, regardless of HPV type. We performed unbiased analyses of TSSs across the HPV genome in clinical samples. Visualising TSS pattern dynamics, including TSS shifts, provides new insights into how HPV infection status relates to disease state.

The differential role of HTRA1 in HPV-positive and HPV-negative cervical cell line proliferation

BACKGROUND

High-risk human papillomaviruses (HPVs) are strongly associated with the development of some malignancies. The E6 and E7 viral oncoproteins are the primary proteins responsible for cell homeostasis alteration and immortalization. Furthermore, the E6 protein from high-risk HPVs can interact with the PDZ (PSD-90/Dlg/ZO-1) domains of cellular proteins, triggering cell transformation. One protein that is associated with pathological conditions and has a PDZ domain is the protease HTRA1 (high temperature requirement 1). This protein is poorly expressed in some cancers, suggesting a tumor suppressor role. The aim of this study was to evaluate the effect of HTRA1 overexpression in HPV16-positive (CasKi) and HPV-negative (C33) cervical cell lines.

METHODS

The cells were transfected with a vector containing the HTRA1 ORF or an empty vector. HTRA1 overexpression was confirmed by qRT-PCR. The cells were subjected to cell proliferation, colony formation, apoptosis and cell cycle assays.

RESULTS

C33 cells expressing HTRA1 grew significantly fewer colonies and showed less proliferation than cells without HTRA1 expression. In contrast, in the CasKi cells overexpressing HTRA1, there was an increase in the cell growth rate and in the colonies density compared to cells expressing low levels of HTRA1. An apoptosis assay showed that HTRA1 does not interfere with the apoptosis rate in these cells. A cell cycle immunofluorescence assay revealed more CasKi cells overexpressing HTRA1 in the S phase and more C33 HTRA1-transfected cells in the G0/G1 phase, suggesting that HTRA1 plays different roles in the cell cycle progression of these cells.

CONCLUSIONS

HTRA1 overexpression prevents cell proliferation in the HPV-negative cell line and increases cell proliferation in the HPV-positive cell line. Although the E6/HTRA1 interaction has already been described in the literature, more studies are required to confirm whether the present functional findings are a result of this interaction.

Pharmacophore Modeling and Molecular Docking Studies of potential inhibitors to E6 PBM-PDZ from Human Papilloma Virus (HPV)

High-risk human papillomaviruses (HPVs) are known to cause cervical cancer. Vaccines are now available to prevent HPV infection. However, a clinically approved drug is yet not available to treat HPV. The PDZ(PSD−95/Dlg/ZO−1)−binding motif (PBM) in the E6 protein of HPVs targets the PDZ domain (known to be associated with oncogenesis) for degradation. Therefore, it is of interest to study PBM–PDZ interaction towards its possible inhibition with a potential inhibitor. Thus, four pharmocophore models of PBM−PDZ complex were developed. In order to obtain potent small molecules for its inhibition, a commercial compound database was screened using both these pharmacophore models and molecule docking method. These efforts identified four potential compounds (1−4) towards its inhibition with the docking scores range -18.2 to -15.0.

Human papillomavirus E6 triggers upregulation of the antiviral and cancer genomic DNA deaminase APOBEC3B

Several recent studies have converged upon the innate immune DNA cytosine deaminase APOBEC3B (A3B) as a significant source of genomic uracil lesions and mutagenesis in multiple human cancers, including those of the breast, head/neck, cervix, bladder, lung, ovary, and other tissues. A3B is upregulated in these tumor types relative to normal tissues, but the mechanism is unclear. Because A3B also has antiviral activity in multiple systems and is a member of the broader innate immune response, we tested the hypothesis that human papillomavirus (HPV) infection causes A3B upregulation. We found that A3B mRNA expression and enzymatic activity were upregulated following transfection of a high-risk HPV genome and that this effect was abrogated by inactivation of E6. Transduction experiments showed that the E6 oncoprotein alone was sufficient to cause A3B upregulation, and a panel of high-risk E6 proteins triggered higher A3B levels than did a panel of low-risk or noncancer E6 proteins. Knockdown experiments in HPV-positive cell lines showed that endogenous E6 is required for A3B upregulation. Analyses of publicly available head/neck cancer data further support this relationship, as A3B levels are higher in HPV-positive cancers than in HPV-negative cancers. Taken together with the established role for high-risk E6 in functional inactivation of TP53 and published positive correlations in breast cancer between A3B upregulation and genetic inactivation of TP53, our studies suggest a model in which high-risk HPV E6, possibly through functional inactivation of TP53, causes derepression of A3B gene transcription. This would lead to a mutator phenotype that explains the observed cytosine mutation biases in HPV-positive head/neck and cervical cancers.

The innate immune DNA cytosine deaminase APOBEC3B (A3B) accounts for a large proportion of somatic mutations in cervical and head/neck cancers, but nothing is known about the mechanism responsible for its upregulation in these tumor types. Almost all cervical carcinomas and large proportions of head/neck tumors are caused by human papillomavirus (HPV) infection. Here, we establish a mechanistic link between HPV infection and A3B upregulation. The E6 oncoprotein of high-risk, but not low-risk, HPV types triggers A3B upregulation, supporting a model in which TP53 inactivation causes a derepression of A3B gene transcription and elevated A3B enzyme levels. This virus-induced mutator phenotype provides a mechanistic explanation for A3B signature mutations observed in HPV-positive head/neck and cervical carcinomas and may also help to account for the preferential cancer predisposition caused by high-risk HPV isolates.