Gene expression profiles induced by E6 from non-European HPV18 variants reveals a differential activation on cellular processes driving to carcinogenesis

Epidemiology and Molecular Biology of HPV Variants in Cervical Cancer: The State of the Art in Mexico

Cervical cancer (CC) continues to be a major public health problem in Mexico, ranking second among cancers in women. A persistent infection with human papillomaviruses (HPV) is the main risk factor for CC development. In addition, a significant fraction of other cancers including those of the anus, oropharynx, and penis are also related to HPV infection. In CC, HPV-16 is the most prevalent high-risk HPV type, followed by HPV-18, both being responsible for 70% of cases. HPV intratype variant lineages differ in nucleotide sequences by 1–10%, while sublineages differ by 0.5–1%. Several studies have postulated that the nucleotide changes that occur between HPV intratype variants are reflected in functional differences and in pathogenicity. Moreover, it has been demonstrated that HPV-16 and -18 intratype variants differentially affect molecular processes in infected cells, changing their biological behavior that finally impacts in the clinical outcome of patients. Mexico has participated in providing knowledge on the geographical distribution of intratype variants of the most prevalent HPVs in premalignant lesions of the cervix and cervical cancer, as well as in other HPV-related tumors. In addition, functional studies have been carried out to assess the cellular effects of intratype variations in HPV proteins. This review addresses the state of the art on the epidemiology of HPV-16 and HPV-18 intratype variants in the Mexican population, as well as their association with persistence, precancer and cervical cancer, and functional aspects related to their biological behavior.

Reduced MAGI3 level by HPV18E6 contributes to Wnt/β-catenin signaling activation and cervical cancer progression

Human papillomavirus type 18 (HPV18) has high carcinogenic power in invasive cervical cancer (ICC) development. However, the underlying mechanism remains elusive. The carcinogenic properties of HPV18 require the PDZ‐binding motif of its E6 oncoprotein (HPV18 E6) to degrade its target PSD95/Dlg/ZO‐1 (PDZ) proteins. In this study, we demonstrated that the PDZ protein membrane‐associated guanylate kinase, WW and PDZ domain containing 3 (MAGI3) inhibited the Wnt/β‐catenin pathway, and subsequently cervical cancer (CC) cell migration and invasion, via decreasing β‐catenin levels. By reducing MAGI3 protein levels, HPV18 E6 promoted CC cell migration and invasion through activation of Wnt/β‐catenin signaling. Furthermore, HPV18 rather than HPV16 was preferentially associated with the downregulation of MAGI3 and activation of the Wnt/β‐catenin pathway in CC. These findings shed light on the mechanism that gives HPV18 its high carcinogenic potential in CC progression.

When Viruses Cross Developmental Pathways

Aberrant regulation of developmental pathways plays a key role in tumorigenesis. Tumor cells differ from normal cells in their sustained proliferation, replicative immortality, resistance to cell death and growth inhibition, angiogenesis, and metastatic behavior. Often they acquire these features as a consequence of dysregulated Hedgehog, Notch, or WNT signaling pathways. Human tumor viruses affect the cancer cell hallmarks by encoding oncogenic proteins, and/or by modifying the microenvironment, as well as by conveying genomic instability to accelerate cancer development. In addition, viral immune evasion mechanisms may compromise developmental pathways to accelerate tumor growth. Viruses achieve this by influencing both coding and non-coding gene regulatory pathways. Elucidating how oncogenic viruses intersect with and modulate developmental pathways is crucial to understanding viral tumorigenesis. Many currently available antiviral therapies target viral lytic cycle replication but with low efficacy and severe side effects. A greater understanding of the cross-signaling between oncogenic viruses and developmental pathways will improve the efficacy of next-generation inhibitors and pave the way to more targeted antiviral therapies.

E6/E7 Functional Differences among Two Natural Human Papillomavirus 18 Variants in Human Keratinocytes

It is suggested that HPV-18 variants from the A lineage have higher oncogenic potential compared to B variants. Some studies show uneven distribution of HPV-18 variants in cervical adenocarcinomas and squamous cell carcinomas. Regarding HPV-18 variants’ functions, the few studies reported focus on E6, and none were performed using natural host cells. Here, we immortalized primary human keratinocytes (PHKs) with E6/E7 of HPV-18 A1 and B1 sublineages and functionally characterized these cells. PHK18A1 reached immortalization significantly faster than PHK18B1 and formed a higher number of colonies in monolayer and 3D cultures. Moreover, PHK18A1 showed greater invasion ability and higher resistance to apoptosis induced by actinomycin-D. Nevertheless, no differences were observed regarding morphology, proliferation after immortalization, migration, or epithelial development in raft cultures. Noteworthy, our study highlights qualitative differences among HPV-18 A1 and B1 immortalized PHKs: in contrast to PHK18A1, which formed more compact colonies and spheroids of firmly grouped cells and tended to invade and migrate as clustered cells, morphologically, PHK18B1 colonies and spheroids were looser, and migration and invasion of single cells were observed. Although these observations may be relevant for the association of these variants with cervical cancer of different histological subtypes, further studies are warranted to elucidate the mechanisms behind these findings.

Lineage analysis of human papillomavirus types 31 and 45 in cervical samples of Iranian women

Knowing the regional lineages/sublineages of human papillomavirus 31 (HPV 31) and 45 would be of great importance for further evolutionary, epidemiological, and biological analysis. In this regard, to characterize more common lineages and sublineages of HPV 31 and 45, the sequence variations of E6 gene were investigated in normal, premalignant, and malignant samples collected from the cervix in Iran. In total, 54 HPV 31- and 24 HPV 45-positive samples were analyzed by hemi-nested polymerase chain reaction (PCR) and nested-PCR, respectively. All PCR products were subjected to direct sequencing analysis. The results indicated that all three lineages A, B, and C were detected in HPV 31-positive samples; among which HPV 31 lineage A was dominant as it was found in 66.7% of all samples. HPV 31 lineages B and C were identified in 5.5% and 27.8% of samples, respectively. In HPV 45-infected samples, lineage B comprised of 62.5% of all samples and the remaining 37.5%  belonged to lineage A. In conclusion, our findings showed that lineage A of HPV 31 was predominant in Iran. Lineage B of HPV 45 was also dominant among Iranian women. However, further studies with larger sample size should be addressed to estimate the pathogenicity risk of HPV 31 or HPV 45 lineages/sublineages in the development of cervical cancer among Iranian women.

Lineage analysis of human papillomavirus type 18 based on E6 region in cervical samples of Iranian women

Distinct human papillomavirus (HPV) 18 variants are thought to differ in oncogenic potential and geographic distribution. As such, understanding the regional variants of HPV 18 would be of great importance for evolutionary, epidemiological, and biological analysis. In this regard, the sequence variations of E6 gene were investigated to characterize more common variants of HPV 18 in normal cells, premalignant, and malignant samples collected from the cervix. In total, 99 samples of HPV 18 were analyzed by polymerase chain reaction and sequencing. In overall, lineages A was identified in all study subjects, among which sublineage A4 was dominant although the difference observed was not statistically significant with regard to different stages of disease. Sublineage A4 comprised 90.9% of samples and the remaining were belonged to sublineages A1, A2, A3, and A5 at the frequency of 6.1%, 1%, 1%, and 1%, respectively. In conclusion, our findings clearly highlight the sublineage A4 of HPV 18 as the most dominant variant in Iran.

New insights in Hippo signalling alteration in human papillomavirus-related cancers

The persistent infection with high-risk human papillomavirus (HPV) is an etiologic factor for the development of different types of cancers, mainly attributed to the continuous expression of E6 and E7 HPV oncoproteins, which regulate several cell signalling pathways including the Hippo pathway. It has been demonstrated that E6 proteins promote the increase of the Hippo elements YAP, TAZ and TEAD, at protein level, as well as their transcriptional targets. Also, E6 and E7 oncoproteins promote nuclear YAP localization and a decrease in YAP negative regulators such as MST1, PTPN14 or SOCS6. Interestingly, Hippo signalling components modulate HPV activity, such as TEAD1 and the transcriptional co-factor VGLL1, induce the activation of HPV early and late promoters, while hyperactivation of YAP in specific cells facilitates virus infection by increasing putative HPV receptors and by evading innate immunity. Additionally, alterations in Hippo signalling elements have been found in HPV-related cancers and particularly, the involvement of HPV oncoproteins on the regulation of some of these Hippo components has been also proposed, although the precise mechanisms remain unclear. The present review addresses the recent findings describing the interplay between HPV and Hippo signalling in HPV-related cancers, a fact that highlights the importance of developing more in-depth studies in this field to establish key therapeutic targets.

Functions of the WNT Signaling Network in Shaping Host Responses to Infection

It is well-established that aberrant WNT expression and signaling is associated with developmental defects, malignant transformation and carcinogenesis. More recently, WNT ligands have emerged as integral components of host responses to infection but their functions in the context of immune responses are incompletely understood. Roles in the modulation of inflammatory cytokine production, host cell intrinsic innate defense mechanisms, as well as the bridging of innate and adaptive immunity have been described. To what degree WNT responses are defined by the nature of the invading pathogen or are specific for subsets of host cells is currently not well-understood. Here we provide an overview of WNT responses during infection with phylogenetically diverse pathogens and highlight functions of WNT ligands in the host defense against infection. Detailed understanding of how the WNT network orchestrates immune cell functions will not only improve our understanding of the fundamental principles underlying complex immune response, but also help identify therapeutic opportunities or potential risks associated with the pharmacological targeting of the WNT network, as currently pursued for novel therapeutics in cancer and bone disorders.

E6-induced selective translation of WNT4 and JIP2 promotes the progression of cervical cancer via a noncanonical WNT signaling pathway

mRNA translation reprogramming occurs frequently in many pathologies, including cancer and viral infection. It remains largely unknown whether viral-induced alterations in mRNA translation contribute to carcinogenesis. Most cervical cancer is caused by high-risk human papillomavirus infection, resulting in the malignant transformation of normal epithelial cells mainly via viral E6 and E7 oncoproteins. Here, we utilized polysome profiling and deep RNA sequencing to systematically evaluate E6-regulated mRNA translation in HPV18-infected cervical cancer cells. We found that silencing E6 can cause over a two-fold change in the translation efficiency of ~653 mRNAs, most likely in an eIF4E- and eIF2α-independent manner. In addition, we identified that E6 can selectively upregulate the translation of WNT4, JIP1, and JIP2, resulting in the activation of the noncanonical WNT/PCP/JNK pathway to promote cell proliferation in vitro and tumor growth in vivo. Ectopic expression of WNT4/JIP2 can effectively rescue the decreased cell proliferation caused by E6 silencing, strongly suggesting that the WNT4/JIP2 pathway mediates the role of E6 in promoting cell proliferation. Thus, our results revealed a novel oncogenic mechanism of E6 via regulating the translation of mRNAs.

Genetic variations in human papillomavirus and cervical cancer outcomes

Cervical cancer is driven by persistent infection of human papillomavirus (HPV), which is influenced by HPV type and intratypic variants, yet the impact of HPV type and intratypic variants on patient outcomes is far less understood. Here, we examined the association of cervical cancer stage and survival with HPV type, clade, lineage, and intratypic variants within the HPV E6 locus. Of 1,028 HPV-positive cases recruited through the CerGE study, 301 were in-situ and 727 were invasive cervical cancer (ICC), with an average post-diagnosis follow-up of 4.8 years. HPV sequencing was performed using tumor-isolated DNA to assign HPV type, HPV 16 lineage, clade, and intratypic variants within the HPV 16 E6 locus, of which nonsynonomous variants were functionally annotated by molecular modeling. HPV 18-related types were more prevalent in ICC compared to in-situ disease and associated with significantly worse recurrence-free survival (RFS) compared to HPV 16-related types. The HPV 16 Asian American lineage D3 and Asian lineage A4 associated more frequently with ICC than with in situ disease and women with an intratypic HPV 16 lineage B exhibited a trend toward worse RFS than those with A, C, or D lineages. Participants with intratypic E6 variants predicted to stabilize the E6-E6AP-p53 complex had worse RFS. Variants within the highly immunogenic HPV 16 E6 region (E14-I34) were enriched in ICC compared to in-situ lesions but were not associated with survival. Collectively, our results suggest that cervical cancer outcome is associated with HPV variants that affect virus-host interactions.

Interaction of viral oncogenic proteins with the Wnt signaling pathway

It is estimated that up to 20% of all types of human cancers worldwide are attributed to viruses. The genome of oncogenic viruses carries genes that have protein products that act as oncoproteins in cell proliferation and transformation. The modulation of cell cycle control mechanisms, cellular regulatory and signaling pathways by oncogenic viruses, plays an important role in viral carcinogenesis. Different signaling pathways play a part in the carcinogenesis that occurs in a cell. Among these pathways, the Wnt signaling pathway plays a predominant role in carcinogenesis and is known as a central cellular pathway in the development of tumors. There are three Wnt signaling pathways that are well identified, including the canonical or Wnt/β-catenin dependent pathway, the noncanonical or β-catenin-independent planar cell polarity (PCP) pathway, and the noncanonical Wnt/Ca2+ pathway. Most of the oncogenic viruses modulate the canonical Wnt signaling pathway. This review discusses the interaction between proteins of several human oncogenic viruses with the Wnt signaling pathway.

The Wnt pathway: a key network in cell signalling dysregulated by viruses

Viruses are obligate parasites dependent on host cells for survival. Viral infection of a cell activates a panel of pattern recognition receptors that mediate antiviral host responses to inhibit viral replication and dissemination. Viruses have evolved mechanisms to evade and subvert this antiviral host response, including encoding proteins that hijack, mimic and/or manipulate cellular processes such as the cell cycle, DNA damage repair, cellular metabolism and the host immune response. Currently, there is an increasing interest whether viral modulation of these cellular processes, including the cell cycle, contributes to cancer development. One cellular pathway related to cell cycle signalling is the Wnt pathway. This review focuses on the modulation of this pathway by human viruses, known to cause (or associated with) cancer development. The main mechanisms where viruses interact with the Wnt pathway appear to be through (i) epigenetic modification of Wnt genes; (ii) cellular or viral miRNAs targeting Wnt genes; (iii) altering specific Wnt pathway members, often leading to (iv) nuclear translocation of β-catenin and activation of Wnt signalling. Given that diverse viruses affect this signalling pathway, modulating Wnt signalling could be a generalised critical process for the initiation or maintenance of viral pathogenesis, with resultant dysregulation contributing to virus-induced cancers. Further study of this virus-host interaction may identify options for targeted therapy against Wnt signalling molecules as a means to reduce virus-induced pathogenesis and the downstream consequences of infection. Copyright © 2016 John Wiley & Sons, Ltd.

The Asian-American variant of human papillomavirus type 16 exhibits higher activation of MAPK and PI3K/AKT signaling pathways, transformation, migration and invasion of primary human keratinocytes

Asian-American (AA) HPV-16 variants are associated with higher risk of cancer. Abnormal activation of intracellular signaling play a critical role in cancer development and progression. Our aim was to elucidate mechanisms underlying the higher oncogenic potential attributed to AA variant. We evaluated activation of MAPK and PI3K/AKT pathways in primary human keratinocytes (PHKs) transduced with E6/E7 of three HPV-16 variants: E-P, AA, E-350G. Phenotypes examined included migration, anchorage independent growth and invasion. AA PHKs presented the highest levels of active proteins involved in all cascades analyzed: MAPK-ERK, MAPK-p38 and PI3K-AKT. AA PHKs were more efficient in promoting anchorage independent growth, and in stimulating cell migration and invasion. MEK1 inhibition decreased migration. The mesenchymal phenotype marker vimentin was increased in AA PHKs. Our results suggest that MEK1, ERK2, AKT2 hyperactivation influence cellular behavior by means of GSK-3b inactivation and EMT induction prompting AA immortalized PHKs to more efficiently surpass carcinogenesis steps.

Regulation of the Wnt/β-Catenin Signaling Pathway by Human Papillomavirus E6 and E7 Oncoproteins

Cell signaling pathways are the mechanisms by which cells transduce external stimuli, which control the transcription of genes, to regulate diverse biological effects. In cancer, distinct signaling pathways, such as the Wnt/β-catenin pathway, have been implicated in the deregulation of critical molecular processes that affect cell proliferation and differentiation. For example, changes in β-catenin localization have been identified in Human Papillomavirus (HPV)-related cancers as the lesion progresses. Specifically, β-catenin relocates from the membrane/cytoplasm to the nucleus, suggesting that this transcription regulator participates in cervical carcinogenesis. The E6 and E7 oncoproteins are responsible for the transforming activity of HPV, and some studies have implicated these viral oncoproteins in the regulation of the Wnt/β-catenin pathway. Nevertheless, new interactions of HPV oncoproteins with cellular proteins are emerging, and the study of the biological effects of such interactions will help to understand HPV-related carcinogenesis. This review addresses the accumulated evidence of the involvement of the HPV E6 and E7 oncoproteins in the activation of the Wnt/β-catenin pathway.

The role of the PI3K/Akt/mTOR signalling pathway in human cancers induced by infection with human papillomaviruses

Infection with Human papillomaviruses (HPVs) leads to the development of a wide-range of cancers, accounting for 5% of all human cancers. A prominent example is cervical cancer, one of the leading causes of cancer death in women worldwide. It has been well established that tumor development and progression induced by HPV infection is driven by the sustained expression of two oncogenes E6 and E7. The expression of E6 and E7 not only inhibits the tumor suppressors p53 and Rb, but also alters additional signalling pathways that may be equally important for transformation. Among these pathways, the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signalling cascade plays a very important role in HPV-induced carcinogenesis by acting through multiple cellular and molecular events. In this review, we summarize the frequent amplification of PI3K/Akt/mTOR signals in HPV-induced cancers and discuss how HPV oncogenes E6/E7/E5 activate the PI3K/Akt/mTOR signalling pathway to modulate tumor initiation and progression and affect patient outcome. Improvement of our understanding of the mechanism by which the PI3K/Akt/mTOR signalling pathway contributes to the immortalization and carcinogenesis of HPV-transduced cells will assist in devising novel strategies for preventing and treating HPV-induced cancers.

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

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.

Sequence variation analysis of HPV-18 isolates in southwest China

Intratypic variations of HPV-18 are known to differ in the persistence of the infection, frequency of carcinogenesis and the progression of precursor lesions to advanced cervical cancer. This study was designed to analyze sequence variations of HPV-18 isolates in order to discover novel HPV-18 variants and to evaluate the variations among infected women in southwest China. Cervical biopsies from 56 HPV-18-positive women with cervical neoplasia were assayed by PCR amplification and sequencing of all eight genes (E1, E2, E4, E5, E6, E7, L1, L2) of the HPV-18 genome. The most frequently observed variation was a C to G transversion at nucleotide 287 of E6, which was found in 48.2% of samples. Analysis of E7 revealed only one specimen as having sequence variations. In addition, we have identified several novel variations: A551C in E6, G6906A in L1, and C4915T and C5147A in L2. The mutations in E6 and L2 are silent, while the E7 mutation results in a single amino acid change. This study complements and expands on previous descriptions of HPV-18 variants. The sequence variation data presented here provides a foundation for future research on HPV-induced oncogenesis and may prove valuable for developing diagnostic probes and in the design of HPV vaccines for targeted populations.