Establishment of human papillomavirus infection requires cell cycle progression

Suppression of Antitumor Immune Responses by Human Papillomavirus through Epigenetic Downregulation of CXCL14

High-risk human papillomaviruses (HPVs) are causally associated with multiple human cancers. Previous studies have shown that the HPV oncoprotein E7 induces immune suppression; however, the underlying mechanisms remain unknown. To understand the mechanisms by which HPV deregulates host immune responses in the tumor microenvironment, we analyzed gene expression changes of all known chemokines and their receptors using our global gene expression data sets from human HPV-positive and -negative head/neck cancer and cervical tissue specimens in different disease stages. We report that, while many proinflammatory chemokines increase expression throughout cancer progression, CXCL14 is dramatically downregulated in HPV-positive cancers. HPV suppression of CXCL14 is dependent on E7 and associated with DNA hypermethylation in the CXCL14 promoter. Using in vivo mouse models, we revealed that restoration of Cxcl14 expression in HPV-positive mouse oropharyngeal carcinoma cells clears tumors in immunocompetent syngeneic mice, but not in Rag1-deficient mice. Further, Cxcl14 reexpression significantly increases natural killer (NK), CD4⁺ T, and CD8⁺ T cell infiltration into the tumor-draining lymph nodes in vivo. In vitro transwell migration assays show that Cxcl14 reexpression induces chemotaxis of NK, CD4⁺ T, and CD8⁺ T cells. These results suggest that CXCL14 downregulation by HPV plays an important role in suppression of antitumor immune responses. Our findings provide a new mechanistic understanding of virus-induced immune evasion that contributes to cancer progression.

Human papillomaviruses (HPVs) are causally associated with more than 5% of all human cancers. During decades of cancer progression, HPV persists, evading host surveillance. However, little is known about the immune evasion mechanisms driven by HPV. Here we report that the chemokine CXCL14 is significantly downregulated in HPV-positive head/neck and cervical cancers. Using patient tissue specimens and cultured keratinocytes, we found that CXCL14 downregulation is linked to CXCL14 promoter hypermethylation induced by the HPV oncoprotein E7. Restoration of Cxcl14 expression in HPV-positive cancer cells clears tumors in immunocompetent syngeneic mice, but not in immunodeficient mice. Mice with Cxcl14 reexpression show dramatically increased natural killer and T cells in the tumor-draining lymph nodes. These results suggest that epigenetic downregulation of CXCL14 by HPV plays an important role in suppressing antitumor immune responses. Our findings may offer novel insights to develop preventive and therapeutic tools for restoring antitumor immune responses in HPV-infected individuals.

Characterization of serum antibodies from women immunized with Gardasil: A study of HPV-18 infection of primary human keratinocytes

The prevalent human papillomaviruses (HPVs) infect human epithelial tissues. Infections by the mucosotropic HPV genotypes cause hyperproliferative ano-genital lesions. Persistent infections by high-risk (HR) HPVs such as HPV-16, HPV-18 and related types can progress to high grade intraepithelial neoplasias and cancers. Prophylactic HPV vaccines are based on DNA-free virus-like particles (VLPs) composed of the major capsid protein L1 of HPV-16, -18, -6 and -11 (Gardasil) or HPV-16 and -18 (Cervarix). Sera from vaccinated animals effectively prevent HPV pseudovirions to infect cell lines and mouse cervical epithelia. Both vaccines have proven to be highly protective in people. HPV pseudovirions are assembled in HEK293TT cells from matched L1 and L2 capsid proteins to encapsidate a reporter gene. Pseudovirions and genuine virions have structural differences and they infect cell lines or primary human keratinocytes (PHKs) with different efficiencies. In this study, we show that sera and isolated IgG from women immunized with Gardasil prevent authentic HPV-18 virions from infecting PHKs, whereas non-immune sera and purified IgG thereof are uniformly ineffective. Using early passage PHKs, neutralization is achieved only if immune sera are added within 2-4h of infection. We attribute the timing effect to a conformational change in HPV virions, thought to occur upon initial binding to heparan sulfate proteoglycans (HSPG) on the cell surface. This interpretation is consistent with the inability of immune IgG bound to or taken up by PHKs to neutralize the virus. Interestingly, the window of neutralization increases to 12-16h in slow growing, late passage PHKs, suggestive of altered cell surface molecules. In vivo, this window might be further lengthened by the time required to activate the normally quiescent basal cells to become susceptible to infection. Our observations help explain the high efficacy of HPV vaccines.

Principles of Virus Uncoating: Cues and the Snooker Ball

Viruses are spherical or complex shaped carriers of proteins, nucleic acids and sometimes lipids and sugars. They are metastable and poised for structural changes. These features allow viruses to communicate with host cells during entry, and to release the viral genome, a process known as uncoating. Studies have shown that hundreds of host factors directly or indirectly support this process. The cell provides molecules that promote stepwise virus uncoating, and direct the virus to the site of replication. It acts akin to a snooker player who delivers accurate and timely shots (cues) to the ball (virus) to score. The viruses, on the other hand, trick (snooker) the host, hijack its homeostasis systems, and dampen innate immune responses directed against danger signals. In this review, we discuss how cellular cues, facilitators, and built‐in viral mechanisms promote uncoating. Cues come from receptors, enzymes and chemicals that act directly on the virus particle to alter its structure, trafficking and infectivity. Facilitators are defined as host factors that are involved in processes which indirectly enhance entry or uncoating. Unraveling the mechanisms of virus uncoating will continue to enhance understanding of cell functions, and help counteracting infections with chemicals and vaccines.

Viral Genome Tethering to Host Cell Chromatin: Cause and Consequences

Viruses are small infectious agents that replicate in cells of a host organism and that evolved to use cellular machineries for all stages of the viral life cycle. Here, we critically assess current knowledge on a particular mechanism of persisting viruses, namely, how they tether their genomes to host chromatin, and what consequences arise from this process. A group of persisting DNA viruses, i.e. gamma-herpesviruses and papillomaviruses (PV), uses this tethering strategy to maintain their genomes in the nuclei during cell division. Thus, these viruses face the challenge of viral genome loss during mitosis, as they are transported with the host chromosomes to the nascent daughter nuclei. Incidentally, another group of viruses, certain retroviruses and PV, have adopted this tethering strategy to deliver their genomes into the nuclei of dividing cells during cell entry. By exploiting a phase in the cell cycle when the nuclear envelope is disassembled, viruses bypass the need to engage with the nuclear import machinery. Recent reports suggest that tethering may induce severe cellular consequences that involve activation of mitotic checkpoints, causing missegregation of host chromosomes and genomic instability, which may contribute to cancer.

Viral Noncoding RNAs in Cancer Biology

Over 12 % of all human cancers are caused by oncoviruses, primarily including Epstein-Barr virus (EBV), high-risk human papillomaviruses (HPVs), hepatitis B and C viruses (HBV and HCV, respectively), and Kaposi's sarcoma herpesvirus (KSHV). In addition to viral oncoproteins, a variety of noncoding RNAs (ncRNAs) produced by oncoviruses have been recognized as important cofactors that contribute to the oncogenic events. In this chapter, we will focus on the recent understanding of the long and short noncoding RNAs, as well as microRNAs of the viruses, and discuss their roles in the biology of multistep oncogenesis mediated by established human oncoviruses.

TNF-α -308 G/A as a risk marker of cervical cancer progression in the Polish population

BACKGROUND AND OBJECTIVE

There are inconclusive data on the tumor necrosis factor-α (TNF-α) -308 G/A (rs1800629) polymorphism as a risk factor for cervical carcinogenesis.

METHODS

Using high-resolution melting curve analysis, we investigated the prevalence of the TNF-α -308 G/A transition (rs1800629) in patients with cervical cancer (n = 362) and control subjects (n = 399).

RESULTS

The p trend value calculated for the TNF-α -308 G/A transition was statistically significant (p trend = 0.026) for all patients. Logistic regression analysis with adjustment for age demonstrated that the A/A versus G/G genotype was significantly associated with cervical tumors. The adjusted odds ratio (OR) was 1.599 (95 % confidence interval [CI] 1.017-2.513; p = 0.042). Stratification of patients on the basis of the tumor stage revealed no contribution of the TNF-α -308 G/A transition to cervical cancer in stages I and II. However, we found a significant trend for the p value, as well as the contribution of TNF-α -308 G/A to cervical cancer, in stages III and IV. The p trend value was 0.003 in this group of patients. Moreover, logistic regression analysis with adjustment for age demonstrated that the adjusted OR for A/A versus G/G was 2.014 (95 % CI 1.122-3.613; p = 0.019) and the adjusted OR for A/A or A/G versus G/G was 1.583 (95 % CI 1.025-2.444; p = 0.038) for cervical cancer in stages III and IV.

CONCLUSION

Our results indicate that the TNF-α -308 G/A transition is a risk factor for cervical cancer, particularly in stages III and IV.

Human papillomavirus molecular biology and disease association

Human papillomaviruses (HPVs) have evolved over millions of years to propagate themselves in a range of different animal species including humans. Viruses that have co‐evolved slowly in this way typically cause chronic inapparent infections, with virion production in the absence of apparent disease. This is the case for many Beta and Gamma HPV types. The Alpha papillomavirus types have however evolved immunoevasion strategies that allow them to cause persistent visible papillomas. These viruses activate the cell cycle as the infected epithelial cell differentiates in order to create a replication competent environment that allows viral genome amplification and packaging into infectious particles. This is mediated by the viral E6, E7, and E5 proteins. High‐risk E6 and E7 proteins differ from their low‐risk counterparts however in being able to drive cell cycle entry in the upper epithelial layers and also to stimulate cell proliferation in the basal and parabasal layers. Deregulated expression of these cell cycle regulators underlies neoplasia and the eventual progression to cancer in individuals who cannot resolve high‐risk HPV infection. Most work to date has focused on the study of high‐risk HPV types such as HPV 16 and 18, which has led to an understanding of the molecular pathways subverted by these viruses. Such approaches will lead to the development of better strategies for disease treatment, including targeted antivirals and immunotherapeutics. Priorities are now focused toward understanding HPV neoplasias at sites other than the cervix (e.g. tonsils, other transformation zones) and toward understanding the mechanisms by which low‐risk HPV types can sometimes give rise to papillomatosis and under certain situations even cancers. Copyright © 2015 John Wiley & Sons, Ltd.

Topography of the Human Papillomavirus Minor Capsid Protein L2 during Vesicular Trafficking of Infectious Entry

The human papillomavirus (HPV) capsid is composed of the major capsid protein L1 and the minor capsid protein L2. During entry, the HPV capsid undergoes numerous conformational changes that result in endosomal uptake and subsequent trafficking of the L2 protein in complex with the viral DNA to the trans-Golgi network. To facilitate this transport, the L2 protein harbors a number of putative motifs that, if capable of direct interaction, would interact with cytosolic host cell factors. These data imply that a portion of L2 becomes cytosolic during infection. Using a low concentration of digitonin to selectively permeabilize the plasma membrane of infected cells, we mapped the topography of the L2 protein during infection. We observed that epitopes within amino acid residues 64 to 81 and 163 to 170 and a C-terminal tag of HPV16 L2 are exposed on the cytosolic side of intracellular membranes, whereas an epitope within residues 20 to 38, which are upstream of a putative transmembrane region, is luminal. Corroborating these findings, we also found that L2 protein is sensitive to trypsin digestion during infection. These data demonstrate that the majority of the L2 protein becomes accessible on the cytosolic side of intracellular membranes in order to interact with cytosolic factors to facilitate vesicular trafficking.

IMPORTANCE

In order to complete infectious entry, nonenveloped viruses have to pass cellular membranes. This is often achieved through the viral capsid protein associating with or integrating into intracellular membrane. Here, we determine the topography of HPV L2 protein in the endocytic vesicular compartment, suggesting that L2 becomes a transmembrane protein with a short luminal portion and with the majority facing the cytosolic side for interaction with host cell transport factors.

Papillomavirus Infectious Pathways: A Comparison of Systems

The HPV viral lifecycle is tightly linked to the host cell differentiation, causing difficulty in growing virions in culture. A system that bypasses the need for differentiating epithelium has allowed for generation of recombinant particles, such as virus-like particles (VLPs), pseudovirions (PsV), and quasivirions (QV). Much of the research looking at the HPV life cycle, infectivity, and structure has been generated utilizing recombinant particles. While recombinant particles have proven to be invaluable, allowing for a rapid progression of the HPV field, there are some significant differences between recombinant particles and native virions and very few comparative studies using native virions to confirm results are done. This review serves to address the conflicting data in the HPV field regarding native virions and recombinant particles.

Human Papillomaviruses; Epithelial Tropisms, and the Development of Neoplasia

Papillomaviruses have evolved over many millions of years to propagate themselves at specific epithelial niches in a range of different host species. This has led to the great diversity of papillomaviruses that now exist, and to the appearance of distinct strategies for epithelial persistence. Many papillomaviruses minimise the risk of immune clearance by causing chronic asymptomatic infections, accompanied by long-term virion-production with only limited viral gene expression. Such lesions are typical of those caused by Beta HPV types in the general population, with viral activity being suppressed by host immunity. A second strategy requires the evolution of sophisticated immune evasion mechanisms, and allows some HPV types to cause prominent and persistent papillomas, even in immune competent individuals. Some Alphapapillomavirus types have evolved this strategy, including those that cause genital warts in young adults or common warts in children. These strategies reflect broad differences in virus protein function as well as differences in patterns of viral gene expression, with genotype-specific associations underlying the recent introduction of DNA testing, and also the introduction of vaccines to protect against cervical cancer. Interestingly, it appears that cellular environment and the site of infection affect viral pathogenicity by modulating viral gene expression. With the high-risk HPV gene products, changes in E6 and E7 expression are thought to account for the development of neoplasias at the endocervix, the anal and cervical transformation zones, and the tonsilar crypts and other oropharyngeal sites. A detailed analysis of site-specific patterns of gene expression and gene function is now prompted.

Autophagy knocked down by high-risk HPV infection and uterine cervical carcinogenesis

Cervical cancer is a leading cause of cancer death among women in the world. The specific etiopathogenesis of cervical cancer is indeed complex. Even so, we should make arduous efforts to have a precise understanding of the complicate cellular/molecular mechanisms underlying initiation, progression and/or prevention of the cervical cancer. The high-risk human papillomavirus (hrHPV) is considered as the major causative agent of cervical cancer. But with the existence of hrHPV only is not sufficient, autophagy plays a vital character in the development of cervical cancer. Autophagy is the endogenous, tightly regulated cellular "housekeeping" process responsible for the degradation of damaged and dysfunctional cellular organelles and protein aggregates. Our aims in this review were (1) to provide a brief synopsis of process of autophagy (including an overview of the key molecular mediators of this catabolic process and its relationship with hrHPV infection) and (2) most importantly, summarize the current evidence for autophagy-mediated cervical carcinogenesis. One of the latest opinions about the etiopathogenesis is that hrHPV leads to the occurrence of cervical cancer via inhibiting the host's autophagy. The infection of hrHPV will cause the autophagy of cancerous cells, resulting in autophagic cell death, which will suppress the further infection of HPV in return. But the autophagy would be knocked down by the hrHPV, which means the protecting action would end with failure. What's worse, the negative denouement will enhance the infectivity of HPV ultimately, which leads to accelerate cervical carcinogenesis.

Human Papillomavirus Biology, Pathogenesis, and Potential for Drug Discovery: A Literature Review for HIV Nurse Clinical Scientists

Persistent oncogenic human papillomavirus (HPV) infection increases the probability that precancerous anal high-grade squamous intraepithelial lesions will progress to invasive anal cancer. Anal neoplasia associated with HPV disproportionately affects HIV-infected individuals, especially men who have sex with men. Prevention is limited to HPV vaccine recommendations, highlighting the need for new treatments. The purpose of this review is to provide HIV information to nurse clinical scientists about HPV-related cancer to highlight the connection between: (a) HPV biology and pathogenesis and (b) the development of drugs and novel therapeutic methods using high-throughput screening. PubMed and CINAHL were used to search the literature to determine HPV-related epidemiology, biology, and use of high-throughput screening for drug discovery. Several events in the HPV life cycle have the potential to be developed into biologic targets for drug discovery using the high-throughput screening technique, which has been successfully used to identify compounds to inhibit HPV infections.

Stratification of HPV-induced cervical pathology using the virally encoded molecular marker E4 in combination with p16 or MCM

High-risk human papillomavirus (HPV) types cause cervical lesions of varying severity, ranging from transient productive infections to high-grade neoplasia. Disease stratification requires the examination of lesional pathology, and possibly also the detection of biomarkers. P16(INK4a) and MCM are established surrogates of high-risk HPV E6/E7 activity, and can be extensively expressed in high-grade lesions. Here we have combined these two cellular biomarkers with detection of the abundant HPV-encoded E4 protein in order to identify both productive and transforming lesions. This approach has allowed us to distinguish true papillomavirus infections from similar pathologies, and has allowed us to divide the heterogeneous CIN2 category into those that are CIN1-like and express E4, and those that more closely resemble nonproductive CIN3. To achieve this, 530 lesional areas were evaluated according to standard pathology criteria and by using a multiple staining approach that allows us to superimpose biomarker patterns either singly or in combination onto an annotated hematoxylin and eosin (H&E) image. Conventional grading of neoplasia was established by review panel, and compared directly with the composite molecular pathology visualized on the same tissue section. The detection of E4 coincided with the onset of vacuolation, becoming abundant in koilocytes as the MCM marker declined and cells lost their defined nuclear margins as visualized by standard H&E staining. Of the dual marker approaches, p16(INK4a) and E4 appeared most promising, with E4 generally identifying areas of low-grade disease even when p16(INK4a) was present. Extensive p16(INK4a) expression usually coincided with an absence of E4 expression or its focal retention in sporadic cells within the lesion. Our results suggest that a straightforward molecular evaluation of HPV life-cycle deregulation in cervical neoplasia may help improve disease stratification, and that this can be achieved using complementary molecular biomarker pairs such as MCM/E4 or, more promisingly, p16(INK4a)/E4 as an adjunct to conventional pathology.

A Dual Role for the Nonreceptor Tyrosine Kinase Pyk2 during the Intracellular Trafficking of Human Papillomavirus 16

The infectious process of human papillomaviruses (HPVs) has been studied considerably, and many cellular components required for viral entry and trafficking continue to be revealed. In this study, we investigated the role of the nonreceptor tyrosine kinase Pyk2 during HPV16 pseudovirion infection of human keratinocytes. We found that Pyk2 is necessary for infection and appears to be involved in the intracellular trafficking of the virus. Small interfering RNA-mediated reduction of Pyk2 resulted in a significant decrease in infection but did not prevent viral entry at the plasma membrane. Pyk2 depletion resulted in altered endolysosomal trafficking of HPV16 and accelerated unfolding of the viral capsid. Furthermore, we observed retention of the HPV16 pseudogenome in the trans-Golgi network (TGN) in Pyk2-depleted cells, suggesting that the kinase could be required for the viral DNA to exit the TGN. While Pyk2 has previously been shown to function during the entry of enveloped viruses at the plasma membrane, the kinase has not yet been implicated in the intracellular trafficking of a nonenveloped virus such as HPV. Additionally, these data enrich the current literature on Pyk2's function in human keratinocytes.

IMPORTANCE

In this study, we investigated the role of the nonreceptor tyrosine kinase Pyk2 during human papillomavirus (HPV) infection of human skin cells. Infections with high-risk types of HPV such as HPV16 are the leading cause of cervical cancer and a major cause of genital and oropharyngeal cancer. As a nonenveloped virus, HPV enters cells by interacting with cellular receptors and established cellular trafficking routes to ensure that the viral DNA reaches the nucleus for productive infection. This study identified Pyk2 as a cellular component required for the intracellular trafficking of HPV16 during infection. Understanding the infectious pathways of HPVs is critical for developing additional preventive therapies. Furthermore, this study advances our knowledge of intracellular trafficking processes in keratinocytes.

Human Papillomavirus Infectious Entry and Trafficking Is a Rapid Process

Previous studies have indicated that human papillomavirus (HPV) infectious entry is slow, requiring many hours after initial infection for the virus to gain entry into the nucleus. However, intracellular transport pathways typically are very rapid, and in the context of a natural HPV infection in a wounded epithelium, such slow intracellular transport would seem to be at odds with a normal viral infection. Using synchronized cell populations, we show that HPV trafficking can be a rapid process. In cells that are infected in the late S-early G₂/M phase of the cell cycle, HPV16 pseudovirion (PsV) reporter DNA gene expression is detectable by 8 h postinfection. Likewise, reporter DNA can be visualized within the nucleus in conjunction with PML nuclear bodies 1 h to 2 h postinfection in cells that are infected with PsVs just prior to mitotic entry. This demonstrates that endosomal trafficking of HPV is rapid, with mitosis being the main restriction on nuclear entry.

IMPORTANCE

HPV infectious entry appears to be slow and requires mitosis to occur before the incoming viral DNA can access the nucleus. In this study, we show that HPV trafficking in the cell actually is very rapid. This demonstrates that in the context of a normal virus infection, the cell cycle state will have a major influence on the time it takes for an incoming virus to enter the nucleus and initiate viral gene expression.

Interaction of human tumor viruses with host cell surface receptors and cell entry

Currently, seven viruses, namely Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpes virus (KSHV), high-risk human papillomaviruses (HPVs), Merkel cell polyomavirus (MCPyV), hepatitis B virus (HBV), hepatitis C virus (HCV) and human T cell lymphotropic virus type 1 (HTLV-1), have been described to be consistently associated with different types of human cancer. These oncogenic viruses belong to distinct viral families, display diverse cell tropism and cause different malignancies. A key to their pathogenicity is attachment to the host cell and entry in order to replicate and complete their life cycle. Interaction with the host cell during viral entry is characterized by a sequence of events, involving viral envelope and/or capsid molecules as well as cellular entry factors that are critical in target cell recognition, thereby determining cell tropism. Most oncogenic viruses initially attach to cell surface heparan sulfate proteoglycans, followed by conformational change and transfer of the viral particle to secondary high-affinity cell- and virus-specific receptors. This review summarizes the current knowledge of the host cell surface factors and molecular mechanisms underlying oncogenic virus binding and uptake by their cognate host cell(s) with the aim to provide a concise overview of potential target molecules for prevention and/or treatment of oncogenic virus infection.

The Role of the DNA Damage Response throughout the Papillomavirus Life Cycle

The DNA damage response (DDR) maintains genomic integrity through an elaborate network of signaling pathways that sense DNA damage and recruit effector factors to repair damaged DNA. DDR signaling pathways are usurped and manipulated by the replication programs of many viruses. Here, we review the papillomavirus (PV) life cycle, highlighting current knowledge of how PVs recruit and engage the DDR to facilitate productive infection.

Serial type-specific human papillomavirus (HPV) load measurement allows differentiation between regressing cervical lesions and serial virion productive transient infections

Persistent high-risk human papillomavirus (HPV) infection is strongly associated with the development of high-grade cervical intraepithelial neoplasia (CIN) or cancer. Not all persistent infections lead to cancer. Viral load measured at a single time-point is a poor predictor of the natural history of HPV infections. However the profile of viral load evolution over time could distinguish nonprogressive from progressive (carcinogenic) infections. A retrospective natural history study was set up using a Belgian laboratory database including more than 800,000 liquid cytology specimens. All samples were submitted to qPCR identifying E6/E7 genes of 18 HPV types. Viral load changes over time were assessed by the linear regression slope. Database search identified 261 untreated women with persistent type-specific HPV DNA detected (270 infections) in at least three of the last smears for a average period of 3.2 years. Using the coefficient of determination (R²) infections could be subdivided in a latency group (n = 143; R² < 0.85) and a regressing group (n = 127; R² ≥ 0.85). In (≥ 3) serial viral load measurements, serial transient infections with latency is characterized by a nonlinear limited difference in decrease or increase of type-specific viral load (R² < 0.85 and slopes between 2 measurements 0.0010 and -0.0010 HPV copies/cell per day) over a longer period of time (1553 days), whereas regression of a clonal cell population is characterized by a linear (R² ≥ 0.85) decrease (-0.0033 HPV copies/cell per day) over a shorter period of time (708 days; P < 0.001). Using serial HPV type-specific viral load measurements we could for the first time identify regressing CIN2 and CIN3 lesions. Evolution of the viral load is an objective measurable indicator of the natural history of HPV infections and could be used for future triage in HPV-based cervical screening programs.

Nuclear entry of DNA viruses

DNA viruses undertake their replication within the cell nucleus, and therefore they must first deliver their genome into the nucleus of their host cells. Thus, trafficking across the nuclear envelope is at the basis of DNA virus infections. Nuclear transport of molecules with diameters up to 39 nm is a tightly regulated process that occurs through the nuclear pore complex (NPC). Due to the enormous diversity of virus size and structure, each virus has developed its own strategy for entering the nucleus of their host cells, with no two strategies alike. For example, baculoviruses target their DNA-containing capsid to the NPC and subsequently enter the nucleus intact, while the hepatitis B virus capsid crosses the NPC but disassembles at the nuclear side of the NPC. For other viruses such as herpes simplex virus and adenovirus, although both dock at the NPC, they have each developed a distinct mechanism for the subsequent delivery of their genome into the nucleus. Remarkably, other DNA viruses, such as parvoviruses and human papillomaviruses, access the nucleus through an NPC-independent mechanism. This review discusses our current understanding of the mechanisms used by DNA viruses to deliver their genome into the nucleus, and further presents the experimental evidence for such mechanisms.

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.

DNA virus uncoating

Virus genomes are condensed and packaged inside stable proteinaceous capsids that serve to protect them during transit from one cell or host organism, to the next. During virus entry, capsid shells are primed and disassembled in a complex, tightly-regulated, multi-step process termed uncoating. Here we compare the uncoating-programs of DNA viruses of the pox-, herpes-, adeno-, polyoma-, and papillomavirus families. Highlighting the chemical and mechanical cues virus capsids respond to, we review the conformational changes that occur during stepwise disassembly of virus capsids and how these culminate in the release of viral genomes at the right time and cellular location to assure successful replication.

Direct binding of retromer to human papillomavirus type 16 minor capsid protein L2 mediates endosome exit during viral infection

Trafficking of human papillomaviruses to the Golgi apparatus during virus entry requires retromer, an endosomal coat protein complex that mediates the vesicular transport of cellular transmembrane proteins from the endosome to the Golgi apparatus or the plasma membrane. Here we show that the HPV16 L2 minor capsid protein is a retromer cargo, even though L2 is not a transmembrane protein. We show that direct binding of retromer to a conserved sequence in the carboxy-terminus of L2 is required for exit of L2 from the early endosome and delivery to the trans-Golgi network during virus entry. This binding site is different from known retromer binding motifs and can be replaced by a sorting signal from a cellular retromer cargo. Thus, HPV16 is an unconventional particulate retromer cargo, and retromer binding initiates retrograde transport of viral components from the endosome to the trans-Golgi network during virus entry. We propose that the carboxy-terminal segment of L2 protein protrudes through the endosomal membrane and is accessed by retromer in the cytoplasm.

Pathogenesis of human papillomavirus-associated mucosal disease

Human papillomaviruses (HPVs) are a necessary cause of carcinoma of the cervix and other mucosal epithelia. Key events in high-risk HPV (HRHPV)-associated neoplastic progression include persistent infection, deregulated expression of virus early genes in basal epithelial cells and genomic instability causing secondary host genomic imbalances. There are multiple mechanisms by which deregulated virus early gene expression may be achieved. Integration of virus DNA into host chromosomes is observed in the majority of cervical squamous cell carcinomas (SCCs), although in ∼15% of cases the virus remains extrachromosomal (episomal). Interestingly, not all integration events provide a growth advantage to basal cervical epithelial cells or lead to increased levels of the virus oncogenes E6 and E7, when compared with episome-containing basal cells. The factors that provide a competitive advantage to some integrants, but not others, are complex and include virus and host contributions. Gene expression from integrated and episomal HRHPV is regulated through host epigenetic mechanisms affecting the virus long control region (LCR), which appear to be of functional importance. New approaches to treating HRHPV-associated mucosal neoplasia include knockout of integrated HRHPV DNA, depletion of virus transcripts and inhibition of virus early gene transcription through targeting or use of epigenetic modifiers. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Alpha-defensin HD5 inhibits furin cleavage of human papillomavirus 16 L2 to block infection

Human papillomavirus (HPV) is a significant oncogenic virus, but the innate immune response to HPV is poorly understood. Human α-defensin 5 (HD5) is an innate immune effector peptide secreted by epithelial cells in the genitourinary tract. HD5 is broadly antimicrobial, exhibiting potent antiviral activity against HPV at physiologic concentrations; however, the specific mechanism of HD5-mediated inhibition against HPV is unknown. During infection, the HPV capsid undergoes several critical cell-mediated viral protein processing steps, including unfolding and cleavage of the minor capsid protein L2 by host cyclophilin B and furin. Using HPV16 pseudovirus, we show that HD5 interacts directly with the virus and inhibits the furin-mediated cleavage of L2 at the cell surface during infection at a step downstream of the cyclophilin B-mediated unfolding of L2. Importantly, HD5 does not affect the enzymatic activity of furin directly. Thus, our data support a model in which HD5 prevents furin from accessing L2 by occluding the furin cleavage site via direct binding to the viral capsid.

IMPORTANCE

Our study elucidates a new antiviral action for α-defensins against nonenveloped viruses in which HD5 directly interferes with a critical host-mediated viral processing step, furin cleavage of L2, at the cell surface. Blocking this key event has deleterious effects on the intracellular steps of virus infection. Thus, in addition to informing the antiviral mechanisms of α-defensins, our studies highlight the critical role of furin cleavage in HPV entry. Innate immune control, mediated in part by α-defensins expressed in the genital mucosa, may influence susceptibility to HPV infections that lead to cervical cancer. Moreover, understanding the mechanism of these natural antivirals may inform the design of therapeutics to limit HPV infection.

Human papillomavirus species-specific interaction with the basement membrane-resident non-heparan sulfate receptor

Using a cell culture model where virus is bound to the extracellular matrix (ECM) prior to cell surface binding, we determined that human papillomavirus type 16 (HPV16) utilizes ECM resident laminin (LN) 332 as an attachment receptor for infectious entry. In presence of LN332, soluble heparin can function as ligand activator rather than competitive inhibitor of HPV16 infection. We also show that the ability to use LN332 binding as a productive attachment step for infectious entry is not conserved amongst HPV types. In the alpha genus, species 9 members (HPV16) attach to ECM via LN332, while members of species 7 (HPV18) are completely inhibited by heparin pre-incubation due to an inability to use LN332. Since HPV species 7 and 9 are preferentially associated with adenocarcinoma and squamous cell carcinoma of the cervix, respectively, our data provide first evidence that pre-entry events may contribute to the anatomical-site preference of HPV species.

APOBEC3A functions as a restriction factor of human papillomavirus

Human papillomaviruses (HPVs) are small DNA viruses causally associated with benign warts and multiple cancers, including cervical and head-and-neck cancers. While the vast majority of people are exposed to HPV, most instances of infection are cleared naturally. However, the intrinsic host defense mechanisms that block the early establishment of HPV infections remain mysterious. Several antiviral cytidine deaminases of the human APOBEC3 (hA3) family have been identified as potent viral DNA mutators. While editing of HPV genomes in benign and premalignant cervical lesions has been demonstrated, it remains unclear whether hA3 proteins can directly inhibit HPV infection. Interestingly, recent studies revealed that HPV-positive cervical and head-and-neck cancers exhibited higher rates of hA3 mutation signatures than most HPV-negative cancers. Here, we report that hA3A and hA3B expression levels are highly upregulated in HPV-positive keratinocytes and cervical tissues in early stages of cancer progression, potentially through a mechanism involving the HPV E7 oncoprotein. HPV16 virions assembled in the presence of hA3A, but not in the presence of hA3B or hA3C, have significantly decreased infectivity compared to HPV virions assembled without hA3A or with a catalytically inactive mutant, hA3A/E72Q. Importantly, hA3A knockdown in human keratinocytes results in a significant increase in HPV infectivity. Collectively, our findings suggest that hA3A acts as a restriction factor against HPV infection, but the induction of this restriction mechanism by HPV may come at a cost to the host by promoting cancer mutagenesis.

IMPORTANCE

Human papillomaviruses (HPVs) are highly prevalent and potent human pathogens that cause >5% of all human cancers, including cervical and head-and-neck cancers. While the majority of people become infected with HPV, only 10 to 20% of infections are established as persistent infections. This suggests the existence of intrinsic host defense mechanisms that inhibit viral persistence. Using a robust method to produce infectious HPV virions, we demonstrate that hA3A, but not hA3B or hA3C, can significantly inhibit HPV infectivity. Moreover, hA3A and hA3B were coordinately induced in HPV-positive clinical specimens during cancer progression, likely through an HPV E7 oncoprotein-dependent mechanism. Interestingly, HPV-positive cervical and head-and-neck cancer specimens were recently shown to harbor significant amounts of hA3 mutation signatures. Our findings raise the intriguing possibility that the induction of this host restriction mechanism by HPV may also trigger hA3A- and hA3B-induced cancer mutagenesis.

Human papillomavirus infection in oral fluids of HIV-1-positive men: prevalence and risk factors

Human papillomavirus is one of the most common sexually transmitted diseases worldwide. The natural history of oral HPV infection is unclear, and its risk factors have not been explored. Immunocompromised individuals, as exemplified by HIV patients, are at high risk for HPV-related diseases. The mean of this study is to determine the prevalence of HPV in the oral tract of HIV-1-positive male subjects and its association with risk factors. A total of 283 oral wash samples from HIV-1-positive men were tested. The oral fluid samples were used for DNA extraction and conventional PCR amplification; HPV genotyping was performed by hybridization. HPV genotyping revealed that nine samples (3.5%) were positive for HPV DNA; the major high-risk HPV types identified were 51 and 66. Worldwide studies have shown a variable prevalence of oral HPV. The diversity of genotypes and the high prevalence of multiple infections in HIV-infected subjects can be better explained by the effects of HIV-induced immunosuppression. The most important risk factors are unprotected sexual intercourse, but other factors for this infection have been described elsewhere including smoking, age and HIV-positive serostatus. In this study, smoking was the most important risk factor for acquiring oral HPV in HIV-1-infected subjects in Brazil.

Vesicular trafficking of incoming human papillomavirus 16 to the Golgi apparatus and endoplasmic reticulum requires γ-secretase activity

The route taken by papillomaviruses from the cell surface to the nucleus during infection is incompletely understood. Here, we developed a novel human papillomavirus 16 (HPV16) pseudovirus in which the carboxy terminus of the minor capsid protein L2 is exposed on the exterior of the intact capsid prior to cell binding. With this pseudovirus, we used the proximity ligation assay immune detection technique to demonstrate that during entry HPV16 L2 traffics into and out of the early endosome prior to Golgi localization, and we demonstrated that L2 enters the endoplasmic reticulum during entry. The cellular membrane-associated protease, γ-secretase, is required for infection by HPV16 pseudovirus and authentic HPV16. We also showed that inhibition of γ-secretase does not interfere substantively with virus internalization, initiation of capsid disassembly, entry into the early endosome, or exit from this compartment, but γ-secretase is required for localization of L2 and viral DNA to the Golgi apparatus and the endoplasmic reticulum. These results show that incoming HPV16 traffics sequentially from the cell surface to the endosome and then to the Golgi apparatus and the endoplasmic reticulum prior to nuclear entry.

The human papillomaviruses are small nonenveloped DNA viruses responsible for approximately 5% of all human cancer deaths, but little is known about the process by which these viruses transit from the cell surface to the nucleus. Here we show that incoming HPV16, the most common high-risk HPV, traffics though a series of vesicular compartments during infectious entry, including the endosome, Golgi apparatus, and endoplasmic reticulum. Furthermore, we show that γ-secretase, a cellular membrane-associated protease, is required for entry of the L2 minor capsid protein and viral DNA into the Golgi apparatus and endoplasmic reticulum. These studies reveal a new pathway of cell entry by DNA viruses and suggest that components of this pathway are candidate antiviral targets.

High incidence of female reproductive tract cancers in FA-deficient HPV16-transgenic mice correlates with E7's induction of DNA damage response, an activity mediated by E7's inactivation of pocket proteins

Fanconi anemia (FA) is a rare genetic disorder caused by defects in a DNA damage repair system, the FA pathway. FA patients frequently develop squamous cell carcinoma (SCC) at sites that are associated with human papillomavirus (HPV)-driven cancer including the female reproductive tract. To assess experimentally whether FA deficiency increases susceptibility to HPV-associated cervical/vaginal cancer, we monitored cancer incidence in the female lower reproductive tract of FA-deficient mice expressing HPV16 oncogenes, E6 and/or E7. FA deficiency specifically increased the incidence of cancers in mice expressing E7; but this effect was not observed in mice just expressing E6. We also observed that E7, but not E6, induced DNA damage as scored by induction of γ-H2AX and 53BP1 (p53 binding protein 1) nuclear foci, and this induction was heightened in FA-deficient tissue. Finally, we discovered that this induction of DNA damage responses was recapitulated in mice deficient in expression of 'pocket' proteins, pRb, p107 and p130, which are established targets of E7. Our findings support the hypothesis that E7 induces cancer by causing DNA damage at least in part through the inactivation of pocket proteins. This hypothesis explains why a deficiency in DNA damage repair would increase susceptibility to E7-driven cancer.

Human papillomavirus infection requires the TSG101 component of the ESCRT machinery

Infection with human papillomaviruses (HPV) requires the minor capsid component L2, which plays an essential role in directing appropriate endosomal trafficking. Previous studies have indicated an infection route involving multi-vesicular bodies (MVBs), and an essential element in their biogenesis is the ESCRT machinery. Here we show that the ESCRT component TSG101 is required for optimal infection with both HPV-16 and BPV-1, with loss of TSG101 resulting in a decrease in viral infection, whereas overexpressed TSG101 increases rates of infection. We find that L2 proteins from multiple PV types interact with TSG101 and show that this interaction contributes to an alteration in the subcellular distribution of L2. In addition, TSG101 can modulate the levels of L2 polyubiquitination. These results demonstrate that TSG101 plays an important part in infection with diverse PVs, and suggests that trafficking of HPV through the ESCRT machinery and MVBs is part of infectious virus entry.

Large scale RNAi reveals the requirement of nuclear envelope breakdown for nuclear import of human papillomaviruses

A two-step, high-throughput RNAi silencing screen was used to identify host cell factors required during human papillomavirus type 16 (HPV16) infection. Analysis of validated hits implicated a cluster of mitotic genes and revealed a previously undetermined mechanism for import of the viral DNA (vDNA) into the nucleus. In interphase cells, viruses were endocytosed, routed to the perinuclear area, and uncoated, but the vDNA failed to be imported into the nucleus. Upon nuclear envelope perforation in interphase cells HPV16 infection occured. During mitosis, the vDNA and L2 associated with host cell chromatin on the metaphase plate. Hence, we propose that HPV16 requires nuclear envelope breakdown during mitosis for access of the vDNA to the nucleoplasm. The results accentuate the value of genes found by RNAi screens for investigation of viral infections. The list of cell functions required during HPV16 infection will, moreover, provide a resource for future virus-host cell interaction studies.

Certain human papillomaviruses (HPV) are the etiological cause of cervical cancers and other epithelial tumors. Recent advances in the development of anti-HPV vaccines and their increasing deployment provide hope for a significant decrease of these cancers in the future. However, many details of the transmission of HPV between infected and uninfected individuals are still not well understood. In particular, the multistep process of entry into host cells is only partially characterized. Here, we used a systematic RNAi silencing approach to identify host cell proteins required during HPV16 infection, the most prevalent cancer-causing HPV. Our results indicated that HPV entry requires cells to divide. Cell division is important, since it removes the barrier between the nucleoplasm and the cytosol, so that the virus can access the nucleus for transcription and replication. Our study provides new mechanistic insights into the entry process of an important pathogen, and explains why it can only infect the stem cells or transiently amplifying cells of human skin or mucosa. This work also highlights a novel nuclear import strategy for DNA viruses, which typically use the nuclear import machinery to access the nucleoplasm for infection, Thus, HPV entry displays another unique aspect uncommon to most other viruses.

The antiviral restriction factors IFITM1, 2 and 3 do not inhibit infection of human papillomavirus, cytomegalovirus and adenovirus

Type I interferons (IFN-α and β) induce dynamic host defense mechanisms to inhibit viral infections. It has been recently recognized that the interferon-inducible transmembrane proteins (IFITM) 1, 2 and 3 can block entry of a broad spectrum of RNA viruses. However, no study to date has focused on the role of IFITM proteins in DNA virus restriction. Here, we demonstrate that IFN-α or -β treatment of keratinocytes substantially decreases human papillomavirus 16 (HPV16) infection while robustly inducing IFITM1, 2 and 3 expression. However, IFITM1, 2 and 3 overexpression did not inhibit HPV16 infection; rather, IFITM1 and IFITM3 modestly enhanced HPV16 infection in various cell types including primary keratinocytes. Moreover, IFITM1, 2 and 3 did not inhibit infection by two other DNA viruses, human cytomegalovirus (HCMV) and adenovirus type 5 (Ad5). Taken together, we reveal that the entry of several DNA viruses, including HPV, HCMV, and Ad5 is not affected by IFITM1, 2 and 3 expression. These results imply that HPV, and other DNA viruses, may bypass IFITM restriction during intracellular trafficking.

The nuclear retention signal of HPV16 L2 protein is essential for incoming viral genome to transverse the trans-Golgi network

The Human papillomavirus (HPV) capsid is composed of the major and minor capsid proteins, L1 and L2, respectively. Infectious entry requires a complex series of conformational changes in both proteins that lead to uptake and allow uncoating to occur. During entry, the capsid is disassembled and host cyclophilins dissociate L1 protein from the L2/DNA complex. Herein, we describe a mutant HPV16 L2 protein (HPV16 L2-R302/5A) that traffics pseudogenome to the trans-Golgi network (TGN) but fails to egress. Our data provide further evidence that HPV16 traffics through the TGN and demonstrates that L2 is essential for TGN egress. Furthermore, we show that cyclophilin activity is required for the L2/DNA complex to be transported to the TGN which is accompanied by a reduced L1 protein levels.

Concepts of papillomavirus entry into host cells

Papillomaviruses enter basal cells of stratified epithelia. Assembly of new virions occurs in infected cells during terminal differentiation. This unique biology is reflected in the mechanism of entry. Extracellularly, the interaction of nonenveloped capsids with several host cell proteins, after binding, results in discrete conformational changes. Asynchronous internalization occurs over several hours by an endocytic mechanism related to, but distinct from macropinocytosis. Intracellular trafficking leads virions through the endosomal system, and from late endosomes to the trans-Golgi-network, before nuclear delivery. Here, we discuss the existing data with the aim to synthesize an integrated model of the stepwise process of entry, thereby highlighting key open questions. Additionally, we relate data from experiments with cultured cells to in vivo results.

Human keratinocyte cultures in the investigation of early steps of human papillomavirus infection

Human papillomaviruses (HPVs) are non-enveloped DNA viruses that are highly tropic for mucosal and cutaneous epithelia. The HPV life cycle is tightly linked to epithelial cell differentiation, where HPVs only infect the basal proliferating keratinocytes, and progeny virus assembly and release only occurs in differentiated upper-layer keratinocytes. Therefore, human keratinocyte monolayer cultures provide a useful model to study the early stages of HPV infection. However, previous reports have shown some conflicting results of virus-host interactions during HPV entry, which may be partly attributable to the different cell culture models used to examine these steps of HPV infection. Thus, there is a need to have a standardized in vitro model system to study virus-host interactions during HPV entry. Here, we describe the three most widely accepted keratinocyte models for studying HPV infection: primary human foreskin keratinocytes, normal immortalized keratinocytes, and transformed HaCaT keratinocytes. We also describe methods to genetically manipulate these cells, enabling the study of candidate host genes that may be important during HPV infection. Lastly, we outline simple and robust methods to assay HPV infectivity, which can be used to determine whether knockdown or overexpression of a particular gene affects HPV entry.

Viral and cellular biomarkers in the diagnosis of cervical intraepithelial neoplasia and cancer

Cervical cancer arises from cells localized in the ectoendocervical squamocolumnar junction of the cervix persistently infected with one of about 13 human papillomavirus (HPV) genotypes. The majority of HPV infections induces low grade squamous epithelial lesions that in more than 90% of cases spontaneously regress and in about 10% eventually progress to high grade lesions and even less frequently evolve to invasive cancer. Tumor progression is characterized by (1) increased expression of E6 and E7 genes of high risk HPVs, known to bind to and inactivate p53 and pRb oncosuppressors, respectively; (2) integration of viral DNA into host genome, with disruption of E2 viral genes and host chromosomal loci; and (3) molecular alterations of key regulators of cell cycle. Molecular markers with high sensitivity and specificity in differentiating viral infections associated with cellular abnormalities with high risk of progression are strongly needed for cervical cancer screening and triage. This review will focus on the analysis of clinical validated or candidate biomarkers, such as HPV DNA, HPV E6/E7 mRNA, HPV proteins, p16(INK4a) and Ki67, TOP2A and MCM2 cellular factors, and DNA methylation profiles, which will likely improve the identification of premalignant lesions that have a high risk to evolve into invasive cervical cancer.

Sp100 provides intrinsic immunity against human papillomavirus infection

Most DNA viruses associate with, and reorganize, nuclear domain 10 (ND10) bodies upon entry into the host nucleus. In this study, we examine the roles of the ND10 components PML, Sp100, and Daxx in the establishment of human papillomavirus type 18 (HPV18) infection of primary human keratinocytes. HPV18 DNA or HPV18 quasivirus was introduced into primary human keratinocytes depleted of each ND10 protein by small interfering RNA technology, and genome establishment was determined by using a quantitative immortalization assay and measurements of viral transcription and DNA replication. Keratinocyte depletion of Sp100 resulted in a substantial increase in the number of HPV18-immortalized colonies and a corresponding increase in viral transcription and DNA replication. However, Sp100 repressed viral transcription and replication only during the initial stages of viral establishment, suggesting that Sp100 acts as a repressor of incoming HPV DNA.

IMPORTANCE

The intrinsic immune system provides a first-line defense against invading pathogens. Host cells contain nuclear bodies (ND10) that are important for antiviral defense, yet many DNA viruses localize here upon cell entry. However, viruses also disrupt, reorganize, and modify individual components of the bodies. In this study, we show that one of the ND10 components, Sp100, limits the infection of human skin cells by human papillomavirus (HPV). HPVs are important pathogens that cause many types of infection of the cutaneous and mucosal epithelium and are the causative agents of several human cancers. Understanding how host cells counteract HPV infection could provide insight into antimicrobial therapies that could limit initial infection.

Heparin increases the infectivity of Human Papillomavirus type 16 independent of cell surface proteoglycans and induces L1 epitope exposure

Human Papillomaviruses (HPVs) are the etiological agents of cervical cancer, and HPV-16 is the most prevalent type. Several HPVs require heparan sulfate proteoglycans (HSPGs) for cell binding. Here, we analyse the phenomenon that preincubation of HPV-16 with increasing concentrations of heparin results in partial restoration rather than more efficient inhibition of infection. While corroborating that the HSPGs are cell-binding receptors for HPV-16, heparin-preincubated virus bound to the extracellular matrix (ECM) via laminin-332. Furthermore, the interaction of virions with heparin, a representative of the highly sulfated S-domains of heparan sulfate (HS) chains of HSPGs, allowed HPV-16 infection in the absence of cell surface HSPGs. Therefore, we concluded that specific glycan moieties but not specific HSPG protein backbones are required for infection. The increased binding of an epitope-specific antibody to the viral capsid after heparin binding suggested that initial conformational changes in the HPV-16 virion occur during infection by interaction with'heparin-like' domains of cellular HSPGs. We propose that HS sequences with specific sulfation patterns are required to facilitate HPV-16 infection.

Inactivation of p53 rescues the maintenance of high risk HPV DNA genomes deficient in expression of E6

The human papillomavirus DNA genome undergoes three distinct stages of replication: establishment, maintenance and amplification. We show that the HPV16 E6 protein is required for the maintenance of the HPV16 DNA genome as an extrachromosomal, nuclear plasmid in its natural host cell, the human keratinocyte. Based upon mutational analyses, inactivation of p53 by E6, but not necessarily E6-mediated degradation of p53, was found to correlate with the ability of E6 to support maintenance of the HPV16 genome as a nuclear plasmid. Inactivation of p53 with dominant negative p53 rescued the ability of HPV16 E6STOP and E6SAT mutant genomes to replicate as extrachromosomal genomes, though not to the same degree as observed for the HPV16 E6 wild-type (WT) genome. Inactivation of p53 also rescued the ability of HPV18 and HPV31 E6-deficient genomes to be maintained at copy numbers comparable to that of HPV18 and HPV31 E6WT genomes at early passages, though upon further passaging copy numbers for the HPV18 and 31 E6-deficient genomes lessened compared to that of the WT genomes. We conclude that inactivation of p53 is necessary for maintenance of HPV16 and for HPV18 and 31 to replicate at WT copy number, but that additional functions of E6 independent of inactivating p53 must also contribute to the maintenance of these genomes. Together these results suggest that re-activation of p53 may be a possible means for eradicating extrachromosomal HPV16, 18 or 31 genomes in the context of persistent infections.

Human papillomaviruses (HPVs) infect epithelial tissues. HPVs that infect mucosal epithelia cause infectious lesions in the anogenital tract and oral cavity. HPV infections are normally cleared by the immune system; however, in rare cases, infections can persist for years. Persistent infections by certain HPVs place one at a high risk of developing carcinomas of the cervix, other anogenital tissues, and the head/neck region. These HPVs are responsible for over 5% of all human cancers. For an HPV infection to persist, the viral circular genome must be maintained, i.e. replicated and inherited during cell division. In this study we define the mechanism by which the viral gene E6 contributes to the maintenance of the HPV genome. We demonstrate that E6 must inactivate the cellular factor, p53, for the viral genome to be maintained. Significantly, p53, is inactivated in many types of human cancers and because much research has been done on p53, promising new drugs have been identified that can re-activate p53. If such drugs can re-activate the p53 that has been inactivated by E6, then we hypothesize that these drugs could be used to cure patients with persistent HPV infections and thereby reduce their risk of developing HPV associated cancers.

Cervical neoplasia-related factors and decreased prevalence of uterine fibroids among a cohort of African American women

OBJECTIVE

To investigate whether the previously reported inverse association between cervical neoplasia and uterine fibroids is corroborated.

DESIGN

Cross-sectional analysis of enrollment data from an ongoing prospective study of fibroid development.

SETTING

Not applicable.

PATIENT(S)

Self-reported data on abnormal Pap smear, colposcopy, and cervical treatment were obtained from 1,008 African American women ages 23-34 with no previous fibroid diagnosis and no reported history of human papillomavirus vaccination. Presence of fibroids was assessed at a standardized ultrasound examination.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The association between the three cervical neoplasia-related variables and the presence of fibroids was evaluated with logistic regression to estimate age-adjusted and multivariable-adjusted odds ratios (aORs).

RESULT(S)

Of the analysis sample, 46%, 29%, and 14% reported a prior abnormal Pap smear, colposcopy, and cervical treatment, respectively. Twenty-five percent had fibroids at ultrasound. Those reporting cervical treatment had a 39% (aOR, 0.61; 95% confidence interval [CI] [0.38-0.96]) reduction in fibroid risk. Weak nonsignificant associations were found for abnormal Pap smear and colposcopy.

CONCLUSION(S)

Although a protective-type association of cervical neoplasia with uterine fibroids seems counterintuitive, a causal pathway is possible, and the findings are consistent with two prior studies. Further investigation is needed on the relationship between fibroids and cervical neoplasia and human papillomavirus-related mechanisms.

HPV infection: immunological aspects and their utility in future therapy

High prevalence and mortality rates of cervical cancer create an imperative need to clarify the uniqueness of HPV (Human Papillomavirus) infection, which serves as the key causative factor in cervical malignancies. Understanding the immunological details and the microenvironment of the infection can be a useful tool for the development of novel therapeutic interventions. Chronic infection and progression to carcinogenesis are sustained by immortalization potential of HPV, evasion techniques, and alterations in the microenvironment of the lesion. Inside the lesion, Toll-like receptors expression becomes irregular; Langerhans cells fail to present the antigens efficiently, tumor-associated macrophages aggregate resulting in an unsuccessful immune response by the host. HPV products also downregulate the expression of microenvironment components which are necessary for natural-killer cells response and antigen presentation to cytotoxic cells. Additionally HPV promotes T-helper cell 2 (Th2) and T-regulatory cell phenotypes and reduces Th1 phenotype, leading to suppression of cellular immunity and lesion progression to cancer. Humoral response after natural infection is inefficient, and neutralizing antibodies are not adequate in many women. Utilizing this knowledge, new endeavors, such as therapeutic vaccination, aim to stimulate cellular immune response against the virus and alter the milieu of the lesion.

Identification and validation of human papillomavirus encoded microRNAs

We report here identification and validation of the first papillomavirus encoded microRNAs expressed in human cervical lesions and cell lines. We established small RNA libraries from ten human papillomavirus associated cervical lesions including cancer and two human papillomavirus harboring cell lines. These libraries were sequenced using SOLiD 4 technology. We used the sequencing data to predict putative viral microRNAs and discovered nine putative papillomavirus encoded microRNAs. Validation was performed for five candidates, four of which were successfully validated by qPCR from cervical tissue samples and cell lines: two were encoded by HPV 16, one by HPV 38 and one by HPV 68. The expression of HPV 16 microRNAs was further confirmed by in situ hybridization, and colocalization with p16INK4A was established. Prediction of cellular target genes of HPV 16 encoded microRNAs suggests that they may play a role in cell cycle, immune functions, cell adhesion and migration, development, and cancer. Two putative viral target sites for the two validated HPV 16 miRNAs were mapped to the E5 gene, one in the E1 gene, two in the L1 gene and one in the LCR region. This is the first report to show that papillomaviruses encode their own microRNA species. Importantly, microRNAs were found in libraries established from human cervical disease and carcinoma cell lines, and their expression was confirmed in additional tissue samples. To our knowledge, this is also the first paper to use in situ hybridization to show the expression of a viral microRNA in human tissue.

Virion factors that target Daxx to overcome intrinsic immunity

PML nuclear bodies and their associated functions are part of an intrinsic cellular mechanism aimed at maintaining transcriptional control over viral gene expression and preventing replication of invading viruses. To overcome these barriers, many viruses express early nonstructural, multifunctional proteins to support the viral replication cycle or modulate host immune responses. Virion proteins constituting the invading particle are traditionally investigated for their role in transport during entry or egress and in the assembly of new virions. The additional functions of virion proteins have largely been ignored, in contrast to those of their nonstructural counterparts. A number of recent reports suggest that several virion proteins may also play vital roles in gene activation processes, in particular by counteracting intrinsic immune mechanisms mediated by the PML nuclear body-associated cellular factors Daxx, ATRX, and Sp100. These virion proteins share several features with their more potent nonstructural counterparts, and they may serve to bridge the gap in the early phase of an infection until immediate early viral gene expression is established. In this review, we discuss how virion proteins are an integral part of gene regulation among several viral families and to what extent structural proteins of incoming virions may contribute to species barrier, latency, and oncogenesis.

Human papillomavirus infections: warts or cancer?

Human papillomaviruses (HPVs) are prevalent pathogens of mucosal and cutaneous epithelia. Productive infections of squamous epithelia lead to benign hyperproliferative warts, condylomata, or papillomas. Persistent infections of the anogenital mucosa by high-risk HPV genotypes 16 and 18 and closely related types can infrequently progress to high-grade intraepithelial neoplasias, carcinomas-in-situ, and invasive cancers in women and men. HPV-16 is also associated with a fraction of head and neck cancers. We discuss the interactions of the mucosotropic HPVs with the host regulatory proteins and pathways that lead to benign coexistence and enable HPV DNA amplification or, alternatively, to cancers that no longer support viral production.

Infection and transmission dynamics of rKSHV.219 in primary endothelial cells

Kaposi's sarcoma-associated herpesvirus (KSHV) is the aetiologic agent of Kaposi's sarcoma (KS), a tumour of endothelial cell origin. The study of KS development was aided by the generation of a recombinant GFP (latent)/RFP (lytic)-expressing KSHV (rKSHV.219) by Vieira and O'Hearn (2004). In this study the first data characterising primary endothelial cell infection and transmission with this virus is presented. Infection was predominantly latent and the percentage of GFP-positive cells increased over time. Neither horizontal transmission of infection, nor cellular proliferation, explained this increase. Analysis of latency-associated nuclear antigen (LANA-1) expression revealed that a threshold level of infection was required for GFP expression early post infection. At later time points GFP correlated more closely with LANA-1 expression, likely due to the accumulation of GFP over time. This study provides methodological guidance for the use of rKSHV.21. In addition, it highlights potential problems associated with the use of fluorescent proteins as markers of viral infection.

L2, the minor capsid protein of papillomavirus

The capsid protein L2 plays major roles in both papillomavirus assembly and the infectious process. While L1 forms the majority of the capsid and can self-assemble into empty virus-like particles (VLPs), L2 is a minor capsid component and lacks the capacity to form VLPs. However, L2 co-assembles with L1 into VLPs, enhancing their assembly. L2 also facilitates encapsidation of the ∼8 kbp circular and nucleosome-bound viral genome during assembly of the non-enveloped T=7d virions in the nucleus of terminally differentiated epithelial cells, although, like L1, L2 is not detectably expressed in infected basal cells. With respect to infection, L2 is not required for particles to bind to and enter cells. However L2 must be cleaved by furin for endosome escape. L2 then travels with the viral genome to the nucleus, wherein it accumulates at ND-10 domains. Here, we provide an overview of the biology of L2.

Annexin A2 and S100A10 regulate human papillomavirus type 16 entry and intracellular trafficking in human keratinocytes

Human papillomaviruses (HPVs) cause benign and malignant tumors of the mucosal and cutaneous epithelium. The initial events regulating HPV infection impact the establishment of viral persistence, which is requisite for malignant progression of HPV-infected lesions. However, the precise mechanisms involved in HPV entry into host cells, including the cellular factors regulating virus uptake, are not clearly defined. We show that HPV16 exposure to human keratinocytes initiates epidermal growth factor receptor (EGFR)-dependent Src protein kinase activation that results in phosphorylation and extracellular translocation of annexin A2 (AnxA2). HPV16 particles interact with AnxA2 in association with S100A10 as a heterotetramer at the cell surface in a Ca(2+)-dependent manner, and the interaction appears to involve heparan-sulfonated proteoglycans. We show multiple lines of evidence that this interaction promotes virus uptake into host cells. An antibody to AnxA2 prevents HPV16 internalization, whereas an antibody to S100A10 blocks infection at a late endosomal/lysosomal site. These results suggest that AnxA2 and S100A10 have separate roles during HPV16 binding, entry, and trafficking. Our data additionally imply that AnxA2 and S100A10 may be involved in regulating the intracellular trafficking of virus particles prior to nuclear delivery of the viral genome.

Impact of genetic targets on therapy in head and neck squamous cell carcinoma

Despite advances in surgical technique, radiation therapy and chemotherapy, the mortality from head and neck squamous cell carcinoma (HNSCC) has not improved significantly. Squamous cell carcinoma is caused by tobacco use, alcohol consumption and infection with high-risk types of human papillomavirus. It is the 6th most common cancer in the world, with upwards of 45,000 new cases reported yearly in the United States alone.In recent years, there has been a significant increase in the understanding of the molecular and genetic pathogenesis of head and neck cancer, shedding light on the unexpected heterogeneity of the disease. Genetic analysis has led to new classification schemes for HNSCC, with different subgroups exhibiting different prognoses. In addition, multiple targets in aberrant signaling pathways have been identified using increasingly sophisticated bio-informatics tools. Advances in technology have allowed for novel delivery mechanisms to introduce genetic material into cells to produce a therapeutic effect by targeting cancer cells via a number of different approaches.A pressing need to develop novel therapies to augment current treatment modalities has led to a number of translational studies involving gene therapy in the treatment of HNSCC. This article will focus on a review of the most recent developments in molecular biology of head and neck squamous cell carcinoma in regards to possible targets for gene therapy, as well as the array of novel therapeutic strategies directed at these targets.