Human papillomavirus type 6b virus-like particles are able to activate the Ras-MAP kinase pathway and induce cell proliferation

ErbB2/HER2 receptor tyrosine kinase regulates human papillomavirus promoter activity

Human papillomaviruses (HPVs) are a major cause of cancer. While surgical intervention remains effective for a majority of HPV-caused cancers, the urgent need for medical treatments targeting HPV-infected cells persists. The pivotal early genes E6 and E7, which are under the control of the viral genome's long control region (LCR), play a crucial role in infection and HPV-induced oncogenesis, as well as immune evasion. In this study, proteomic analysis of endosomes uncovered the co-internalization of ErbB2 receptor tyrosine kinase, also called HER2/neu, with HPV16 particles from the plasma membrane. Although ErbB2 overexpression has been associated with cervical cancer, its influence on HPV infection stages was previously unknown. Therefore, we investigated the role of ErbB2 in HPV infection, focusing on HPV16. Through siRNA-mediated knockdown and pharmacological inhibition studies, we found that HPV16 entry is independent of ErbB2. Instead, our signal transduction and promoter assays unveiled a concentration- and activation-dependent regulatory role of ErbB2 on the HPV16 LCR by supporting viral promoter activity. We also found that ErbB2's nuclear localization signal was not essential for LCR activity, but rather the cellular ErbB2 protein level and activation status that were inhibited by tucatinib and CP-724714. These ErbB2-specific tyrosine kinase inhibitors as well as ErbB2 depletion significantly influenced the downstream Akt and ERK signaling pathways and LCR activity. Experiments encompassing low-risk HPV11 and high-risk HPV18 LCRs uncovered, beyond HPV16, the importance of ErbB2 in the general regulation of the HPV early promoter. Expanding our investigation to directly assess the impact of ErbB2 on viral gene expression, quantitative analysis of E6 and E7 transcript levels in HPV16 and HPV18 transformed cell lines unveiled a noteworthy decrease in oncogene expression following ErbB2 depletion, concomitant with the downregulation of Akt and ERK signaling pathways. In light of these findings, we propose that ErbB2 holds promise as potential target for treating HPV infections and HPV-associated malignancies by silencing viral gene expression.

Adeno-associated virus vector system controlling capsid expression improves viral quantity and quality

Adeno-associated virus (AAV) vectors are promising tools for gene therapy. The current AAV vector system produces an abundance of empty capsids that are eliminated before clinical use, leading to increased costs for gene therapy. In the present study, we established an AAV production system that regulates the timing of capsid expression using a tetracycline-dependent promoter. Tetracycline-regulating capsid expression increased viral yield and reduced empty capsids in various serotypes without altering AAV vector infectivity in vitro and in vivo. The replicase expression pattern change observed in the developed AAV vector system improved viral quantity and quality, whereas timing control of capsid expression reduced empty capsids. These findings provide a new perspective on the development of AAV vector production systems in gene therapy.

HPV16 Entry into Epithelial Cells: Running a Gauntlet

During initial infection, human papillomaviruses (HPV) take an unusual trafficking pathway through their host cell. It begins with a long period on the cell surface, during which the capsid is primed and a virus entry platform is formed. A specific type of clathrin-independent endocytosis and subsequent retrograde trafficking to the trans-Golgi network follow this. Cellular reorganization processes, which take place during mitosis, enable further virus transport and the establishment of infection while evading intrinsic cellular immune defenses. First, the fragmentation of the Golgi allows the release of membrane-encased virions, which are partially protected from cytoplasmic restriction factors. Second, the nuclear envelope breakdown opens the gate for these virus–vesicles to the cell nucleus. Third, the dis- and re-assembly of the PML nuclear bodies leads to the formation of modified virus-associated PML subnuclear structures, enabling viral transcription and replication. While remnants of the major capsid protein L1 and the viral DNA remain in a transport vesicle, the viral capsid protein L2 plays a crucial role during virus entry, as it adopts a membrane-spanning conformation for interaction with various cellular proteins to establish a successful infection. In this review, we follow the oncogenic HPV type 16 during its long journey into the nucleus, and contrast pro- and antiviral processes.

Tetraspanin CD9 affects HPV16 infection by modulating ADAM17 activity and the ERK signalling pathway

Human papillomaviruses (HPV) are causative agents of various tumours such as cervical cancer. HPV binding to the cell surface of keratinocytes leads to virus endocytosis at tetraspanin enriched microdomains. Complex interactions of the capsid proteins with host proteins as well as ADAM17-dependent ERK1/2 signal transduction enable the entry platform assembly of the oncogenic HPV type 16. Here, we studied the importance of tetraspanin CD9, also known as TSPAN29, in HPV16 infection of different epithelial cells. We found that both overexpression and loss of the tetraspanin decreased infection rates in cells with low endogenous CD9 levels, while reduction of CD9 expression in keratinocytes that exhibit high-CD9 protein amounts, led to an increase of infection. Therefore, we concluded that low-CD9 supports infection. Moreover, we found that changes in CD9 amounts affect the shedding of the ADAM17 substrate transforming growth factor alpha (TGFα) and the downstream phosphorylation of ERK. These effects correlate with those on infection rates suggesting that a specific CD9 optimum promotes ADAM17 activity, ERK signalling and virus infection. Together, our findings implicate that CD9 regulates HPV16 infection through the modulation of ADAM17 sheddase activity.

Anatomy of a viral entry platform differentially functionalized by integrins α3 and α6

During cell invasion, human papillomaviruses use large CD151 patches on the cell surface. Here, we studied whether these patches are defined architectures with features for virus binding and/or internalization. Super-resolution microscopy reveals that the patches are assemblies of closely associated nanoclusters of CD151, integrin α3 and integrin α6. Integrin α6 is required for virus attachment and integrin α3 for endocytosis. We propose that CD151 organizes viral entry platforms with different types of integrin clusters for different functionalities. Since numerous viruses use tetraspanin patches, we speculate that this building principle is a blueprint for cell-surface architectures utilized by viral particles.

The tetraspanin CD151 in papillomavirus infection

Human papillomaviruses (HPV) are non-enveloped DNA tumor viruses that infect skin and mucosa. The most oncogenic subtype, HPV16, causes various types of cancer, including cervical, anal, and head and neck cancers. During the multistep process of infection, numerous host proteins are required for the delivery of virus genetic information into the nucleus of target cells. Over the last two decades, many host-cell proteins such as heparan sulfate proteoglycans, integrins, growth factor receptors, actin and the tetraspanin CD151 have been described to be involved in the process of infectious entry of HPV16. Tetraspanins have the ability to organize membrane microdomains and to directly influence the function of associated molecules, including binding of receptors to their ligands, receptor oligomerization and signal transduction. Here, we summarize the current knowledge on CD151, and CD151-associated partners during HPV infection and discuss the underlying mechanisms.

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.

Cellular entry of human papillomavirus type 16 involves activation of the phosphatidylinositol 3-kinase/Akt/mTOR pathway and inhibition of autophagy

The mammalian target of rapamycin (mTOR) downstream of phosphatidylinositol 3-kinase (PI3K) in the growth factor receptor (GFR) pathway is a crucial metabolic sensor that integrates growth factor signals in cells. We recently showed that human papillomavirus (HPV) type 16 exposure activates signaling from GFRs in human keratinocytes. Thus, we predicted that the virus would induce the PI3K/mTOR pathway upon interaction with host cells. We detected activation of Akt and mTOR several minutes following exposure of human keratinocytes to HPV type 16 (HPV16) pseudovirions. Activated mTOR induced phosphorylation of the mTOR complex 1 substrates 4E-BP1 and S6K, which led to induction of the functional protein translational machinery. Blockade of epidermal GFR (EGFR) signaling revealed that each of these events is at least partially dependent upon EGFR activation. Importantly, activation of PI3K/Akt/mTOR signaling inhibited autophagy in the early stages of virus-host cell interaction. Biochemical and genetic approaches revealed critical roles for mTOR activation and autophagy suppression in HPV16 early infection events. In summary, the HPV-host cell interaction stimulates the PI3K/Akt/mTOR pathway and inhibits autophagy, and in combination these events benefit virus infection.

Host-cell factors involved in papillomavirus entry

Papillomaviruses infect skin and mucosa where they induce warts and cancers. For entry to occur, they sequentially engage numerous host proteins, allowing them to deliver their genetic information into target cells. This multistep process starts with initial binding via its L1 major capsid protein, followed by structural changes of the capsid on the cell surface, engagement of different receptors, and endocytosis. The post-entry phase includes capsid disassembly, endosomal escape of a complex of the minor capsid protein L2 and the viral genome, its transport into the nucleus, and accumulation at nuclear substructures. This review summarizes the current knowledge of the papillomavirus entry pathway and the role of cellular proteins involved in this course of events.

Inhibition of integrin α6 expression by cell-free varicella-zoster virus

Varicella-zoster virus (VZV) causes chickenpox and shingles. VZV is released from infected cells during natural infection, but remains highly cell-associated during experimental infection, and so most studies have utilized cell-associated infection models. We examined the impact of cell-free VZV infection of primary human foreskin fibroblasts (HFFs) on the receptor integrin α6 (ITGA6). qPCR and flow cytometry demonstrated that both cell-free VZV and cell-free UV-inactivated VZV downregulated transcription and cell-surface protein expression of ITGA6. To establish whether ITGA6 altered VZV infection, VZV transcripts and nuclear DNA levels were measured in HFFs treated with ITGA6 blocking antibody before infection. ITGA6 blocking did not impair virus entry but did negatively impact VZV transcription, and this effect was virus specific as transcription of the related herpes simplex virus type 1 was not similarly inhibited. This study identifies modulation of ITGA6 during cell-free VZV infection, and provides the first evidence linking ITGA6 with post-entry productive VZV gene expression.

Essential roles for soluble virion-associated heparan sulfonated proteoglycans and growth factors in human papillomavirus infections

A subset of human papillomavirus (HPV) infections is causally related to the development of human epithelial tumors and cancers. Like a number of pathogens, HPV entry into target cells is initiated by first binding to heparan sulfonated proteoglycan (HSPG) cell surface attachment factors. The virus must then move to distinct secondary receptors, which are responsible for particle internalization. Despite intensive investigation, the mechanism of HPV movement to and the nature of the secondary receptors have been unclear. We report that HPV16 particles are not liberated from bound HSPG attachment factors by dissociation, but rather are released by a process previously unreported for pathogen-host cell interactions. Virus particles reside in infectious soluble high molecular weight complexes with HSPG, including syndecan-1 and bioactive compounds, like growth factors. Matrix mellatoproteinase inhibitors that block HSPG and virus release from cells interfere with virus infection. Employing a co-culture assay, we demonstrate HPV associated with soluble HSPG-growth factor complexes can infect cells lacking HSPG. Interaction of HPV-HSPG-growth factor complexes with growth factor receptors leads to rapid activation of signaling pathways important for infection, whereas a variety of growth factor receptor inhibitors impede virus-induced signaling and infection. Depletion of syndecan-1 or epidermal growth factor and removal of serum factors reduce infection, while replenishment of growth factors restores infection. Our findings support an infection model whereby HPV usurps normal host mechanisms for presenting growth factors to cells via soluble HSPG complexes as a novel method for interacting with entry receptors independent of direct virus-cell receptor interactions.

A subset of the >120 different types of human papillomaviruses (HPVs) are the most common cause of sexually transmitted infections. Certain HPVs are also associated with approximately 5% of all cancers worldwide. Like many pathogens, HPVs bind first to heparan sulfate proteoglycans (HSPGs) on cells before moving to more specific uptake receptors. However, relatively little is known about the mechanism(s) that triggers the translocation of HPV from HSPGs to the receptors that facilitate entry. As obligate parasites, viruses have evolved numerous means to hijack host cell functions to cause infection. We report two novel mechanisms of pathogen-host interactions. First, bound HPV particles are liberated from cells in an active complex with HSPGs and growth factors rather than dissociating from the sugars to engage secondary receptors. Second, HPV uses the specificity of the associated growth factors to bridge to their cognate receptors as opposed to direct binding to a cell internalization receptor. Signals transduced during these interactions are important for HPV infection. Our study provides new insights into the transmission of a significant viral pathogen and reveals novel means whereby microbes may repurpose normal cell functions during infection of their hosts. Likewise, this work uncovers new targets for HPV prophylaxis.

Modulation of vascular endothelial cell senescence by integrin β4

Increasing evidence has demonstrated that the senescence of vascular endothelial cells (VECs) has critical roles in the pathogenesis of vascular dysfunction. Finding important factors that regulate VEC senescence will help provide novel therapeutic strategies for vascular disorders. Previously, we found that integrin β4 was involved in VEC senescence. However, the mechanism underlying VEC senescence mediated by integrin β4 remains poorly understand. In this study, we used a mouse in vivo model and showed that the level of integrin β4 in the endothelium of mouse thoracic aorta was increased during natural aging and atherosclerosis. Furthermore, we found that H-ras, caveolin-1, and AP-1 were implicated in the senescent signal pathway mediated by integrin β4 in human umbilical vein ECs (HUVECs). Knockdown of integrin β4 could attenuate HUVEC senescent features, including increased interleukin-8 (IL-8) release and decreased endothelial nitric oxide synthase (eNOS) and NO levels and mitochondrial membrane potential in vitro. Our findings provide new clues illustrating the mechanism of VEC senescence. Integrin β4 might be a potential target for therapy in cardiovascular diseases.

Usage of heparan sulfate, integrins, and FAK in HPV16 infection

Human papillomavirus type 16 (HPV16) is the major causative agent of cervical cancer. Studies regarding the early binding and signaling molecules that play a significant role in infection are still lacking. The current study analyzes the role of heparan sulfate, integrins, and the signaling molecule FAK in HPV16 infection of human adult keratinocytes cell line (HaCaTs). Our data demonstrate that infection requires the binding of viral particles to heparan sulfate followed by activation of focal adhesion kinase through an integrin. Infections were reduced in the presence of the FAK inhibitor, TAE226. TAE226 was observed to inhibit viral entry to the early endosome a known infectious route. These findings suggest that FAK can serve as a novel target for antiviral therapy.

Establishment of human papillomavirus infection requires cell cycle progression

Human papillomaviruses (HPVs) are DNA viruses associated with major human cancers. As such there is a strong interest in developing new means, such as vaccines and microbicides, to prevent HPV infections. Developing the latter requires a better understanding of the infectious life cycle of HPVs. The HPV infectious life cycle is closely linked to the differentiation state of the stratified epithelium it infects, with progeny virus only made in the terminally differentiating suprabasal compartment. It has long been recognized that HPV must first establish its infection within the basal layer of stratified epithelium, but why this is the case has not been understood. In part this restriction might reflect specificity of expression of entry receptors. However, this hypothesis could not fully explain the differentiation restriction of HPV infection, since many cell types can be infected with HPVs in monolayer cell culture. Here, we used chemical biology approaches to reveal that cell cycle progression through mitosis is critical for HPV infection. Using infectious HPV16 particles containing the intact viral genome, G1-synchronized human keratinocytes as hosts, and early viral gene expression as a readout for infection, we learned that the recipient cell must enter M phase (mitosis) for HPV infection to take place. Late M phase inhibitors had no effect on infection, whereas G1, S, G2, and early M phase cell cycle inhibitors efficiently prevented infection. We conclude that host cells need to pass through early prophase for successful onset of transcription of the HPV encapsidated genes. These findings provide one reason why HPVs initially establish infections in the basal compartment of stratified epithelia. Only this compartment of the epithelium contains cells progressing through the cell cycle, and therefore it is only in these cells that HPVs can establish their infection. By defining a major condition for cell susceptibility to HPV infection, these results also have potentially important implications for HPV control.

Uptake of human papillomavirus virus-like particles by dendritic cells is mediated by Fcgamma receptors and contributes to acquisition of T cell immunity

Chimeric human papillomavirus virus-like particles (HPV cVLP) are immunogens able to elicit potent CTL responses in mice against HPV16-transformed tumors; however, the mechanism of T cell priming has remained elusive. HPV VLP bind to human MHC class II-positive APCs through interaction with FcgammaRIII, and immature dendritic cells (DC) become activated after incubation with HPV VLP; however, it is unclear whether FcgammaR on DC are involved. In mice, FcgammaRII and FcgammaRIII are homologous and bind similar ligands. In this study, we show that binding and uptake of VLP by DC from FcgammaRII, FcgammaRIII, and FcgammaRII/III-deficient mice are reduced by up to 50% compared with wild-type mice. Additionally, maturation of murine DC from FcgammaRII/III-deficient mice by VLP is also reduced, indicating that DC maturation, and thus Ag presentation, is diminished in the absence of expression of FcgammaR. To investigate the in vivo contribution of FcgammaR in the induction of cellular immunity, FcgammaR single- and double-knockout mice were immunized with HPV16 L1/L2-E7 cVLP, and the frequency of E7-specific T cells was analyzed by tetramer binding, IFN-gamma ELISPOT, and cytotoxicity assays. All readouts indicated that the frequency of E7-specific CD4(+) and CD8(+) T cells induced in all FcgammaR-deficient mice after immunization with cVLP was significantly diminished. Based on these results, we propose that the low-affinity FcgammaR contribute to the high immunogenicity of HPV VLP during T cell priming by targeting VLP to DC and inducing a maturation state of the DC that facilitates Ag presentation to and activation of naive T cells.

Human papillomavirus type 31 uses a caveolin 1- and dynamin 2-mediated entry pathway for infection of human keratinocytes

Papillomaviruses are species-specific and epitheliotropic DNA viruses that cause tumors in their natural hosts. Certain infections with genital human papillomavirus (HPV) types are causally related to cervical cancer development. Most papillomaviruses are thought to infect cells via a clathrin-dependent pathway, yet no studies have determined the entry route in permissive host epithelial cells. Employing fluorescently labeled and native virions, we tested the effects of dominant-negative and biochemical inhibitors of cellular endocytosis pathways. Infections of human keratinocytes, a natural host cell type for HPVs, were assessed visually and by infectious entry assays. We found that HPV type 31 (HPV31) entry and initiation of early infection events require both caveolin 1 and dynamin 2 and occur independently of clathrin-mediated endocytosis. Treatment with chlorpromazine and filipin had opposing effects on HPV31 and HPV16 infection. HPV31 entry was remarkably slow, with a half-time of approximately 14 h, whereas the entry half-time of HPV16 was 4 h. Consistent with a caveola-mediated entry pathway for HPV31, the virions associated with detergent-resistant lipid rafts. During a 16-h microscopic tracking of HPV31 and HPV16 virions, no colocalization of the two viral types was observed. These data suggest that HPV31 and HPV16 virions use distinct routes for host epithelial cell entry.

Mitogen-activated protein kinases activate the nuclear localization sequence of human papillomavirus type 11 E1 DNA helicase to promote efficient nuclear import

Human and animal papillomavirus DNA replicates as multicopy nuclear plasmids. Replication requires two viral proteins, the origin-recognition protein E2 and the replicative DNA helicase E1. Using genetic, biochemical, and immunofluorescence assays, we demonstrated that efficient nuclear import of the human papillomavirus (HPV) type 11 E1 protein depends on a codominant bipartite nuclear localization sequence (NLS) and on phosphorylation of the serine residues S89 and S93 by the mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase, and c-Jun N-terminal protein kinase. The NLS and the MAPK substrates are located within a 50-amino-acid-long peptide near the amino terminus, previously designated the localization regulatory region (LRR). The downstream NLS overlaps the cyclin-binding motif RRL, which is necessary for phosphorylation by the cyclin-dependent kinases to inactivate a dominant nuclear export sequence, also in the LRR. Alanine mutations of the MAPK substrates significantly impaired nuclear import, whereas phospho-mimetic mutations partially restored nuclear import. We further identified two MAPK docking motifs near the C terminus of E1 that are conserved among E1 proteins of many HPVs and bovine papillomavirus type 1. Mutations of these MAPK docking motifs or addition of specific MAPK inhibitors significantly reduced nuclear import. Interestingly, a fraction of the NLS-minus E1 protein was cotransported with the E2 protein into the nucleus and supported transient viral DNA replication. In contrast, E1 proteins mutated in the MAPK docking motifs were completely inactive in transient replication, an indication that additional properties were adversely affected by those changes.

Papillomavirus virus-like particles activate the PI3-kinase pathway via alpha-6 beta-4 integrin upon binding

We have previously shown that human papillomavirus virus-like particles (VLPs) are able to activate the Ras/MAP kinase pathway. Ras can also elicit an anti-apoptotic signal via PI3-kinase so we investigated this further. Here we show that binding of VLPs from HPV types 6b, 18, 31, 35 and BPV1 results in activation of PI3-kinase. Activation was achieved by either L1 or L1/L2 VLPs and was dependent on both VLP-cell interaction and correct conformation of the virus particle. VLP-induced PI3-kinase activity resulted in efficient downstream signaling to Akt and consequent phosphorylation of FKHR and GSK3beta. We also present evidence that PV signaling is activated via the alpha6beta4 integrin. These data suggest that papillomaviruses use a common receptor that is able to signal through to Ras. Combined activation of the Ras/MAP kinase and PI3-kinase pathways may be beneficial for the virus by increasing cell numbers and producing an environment more conducive to infection.

Digesting Oneself and Digesting Microbes

Although research in this area is still in a stage of infancy, it seems likely that the lysosomal degradation pathway of autophagy plays an evolutionarily conserved role in antiviral immunity. The interferon-inducible, antiviral PKR signaling pathway positively regulates autophagy, and both mammalian and plant autophagy genes restrict viral replication and protect against virus-induced cell death. Given this role of autophagy in innate immunity, it is not surprising that viruses have evolved numerous strategies to inhibit host autophagy. Different viral gene products can either modulate autophagy regulatory signals or directly interact with components of the autophagy execution machinery. Moreover, certain RNA viruses have managed to “co-apt” the autophagy pathway, selectively utilizing certain components of the dynamic membrane rearrangement system to promote their own replication inside the host cytoplasm.

In addition to this newly emerging role of autophagy in innate immunity, autophagy plays an important role in many other fundamental biological processes, including tissue homeostasis, differentiation and development, cell growth control, and the prevention of aging. Accordingly, the inhibition of host autophagy by viral gene products has important implications not only for understanding mechanisms of immune evasion, but also for understanding novel mechanisms of viral pathogenesis. It will be interesting to dissect the role of viral inhibition of autophagy in acute, persistent, and latent viral replication, as well as in the pathogenesis of cancer and other medical diseases.

Mineralocorticoid receptor antagonists do not block rapid ERK activation by aldosterone

Aldosterone can elicit rapid nongenomic effects both in vivo and in vitro, often mediated by signal transduction cascades. However, it is not understood how these rapid effects are initiated. In this study we show that aldosterone leads to rapid activation of mitogen activated protein kinases ERK1/2 in the cortical collecting duct cell line M-1. Inhibitors of transcription and translation could not block this activation, which suggests an extranuclear (nongenomic) mechanism. Although it is known that M-1 cells do not contain a transcriptionally functional MR, it is not known whether a closely related protein still could mediate the effects, or an unrelated nonclassic receptor. To test this hypothesis, the effects of four classical mineralocorticoid receptor antagonists were studied. None of the compounds could block the response to aldosterone. Altogether, the data suggest that rapid aldosterone effects in M-1 cells are initiated by a receptor different from the classical mineralocorticoid receptor.

Genogroup II noroviruses efficiently bind to heparan sulfate proteoglycan associated with the cellular membrane

Norovirus (NV), a member of the family Caliciviridae, is one of the important causative agents of acute gastroenteritis. In the present study, we found that virus-like particles (VLPs) derived from genogroup II (GII) NV were bound to cell surface heparan sulfate proteoglycan. Interestingly, the VLPs derived from GII were more than ten times likelier to bind to cells than were those derived from genogroup I (GI). Heparin, a sulfated glycosaminoglycan, and suramin, a highly sulfated derivative of urea, efficiently blocked VLP binding to mammalian cell surfaces. The reagents known to bind to cell surface heparan sulfate, as well as the enzymes that specifically digest heparan sulfate, markedly reduced VLP binding to the cells. Treatment of the cells with chlorate revealed that sulfation of heparan sulfate plays an important role in the NV-heparan sulfate interaction. The binding efficiency of NV to undifferentiated Caco-2 (U-Caco-2) cells differed largely between GI NV and GII NV, whereas the efficiency of binding to differentiated Caco-2 (D-Caco-2) cells did not differ significantly between the two genogroups, although slight differences between strains were observed. Digestion with heparinase I resulted in a reduction of up to 90% in U-Caco-2 cells and a reduction of up to only 50% in D-Caco-2 cells, indicating that heparan sulfate is the major binding molecule for U-Caco-2 cells, while it contributed to only half of the binding in the case of D-Caco-2 cells. The other half of those VLPs was likely to be associated with H-type blood antigen, suggesting that GII NV has two separate binding sites. The present study is the first to address the possible role of cell surface glycosaminoglycans in the binding of recombinant VLPs of NV.

Interplay between human papillomaviruses and dendritic cells

The design of the human papillomavirus (HPV) infection cycle is tightly fitted to the differentiation program of its natural host, the keratinocyte. This has important consequences for the role of antigen-presenting cells in the priming of antiviral immunity. The confinement of HPV infection to epithelia puts the epithelial dendritic cell, the Langerhans cell (LC), in charge of the induction of T cell-dependent immunity. Because HPV-infected keratinocytes cannot reach the regional lymphoid organs, and HPV-infection of LCs does not result in viral gene expression, priming of antiviral T cells exclusively depends on cross-presentation of viral antigens by the LC. Sensitization of the immune system in the regional lymphoid organs elicits systemic anti-HPV immunity as well as intraepithelial immune surveillance by memory-type intraepithelial T cells and locally produced antibodies. The high rate of spontaneous rejections of high-risk HPV-infections and HPV-positive premalignant lesions indicates that in general the LC-driven antigen presentation machinery is capable of raising an effective immune defense against HPV. Epidemiological studies also reveal that a decrease in the vigilance of the immune system is readily exploited by HPV to escape immune destruction, resulting in persistent infections and development of HPV-positive cancers. In view of the inherent antigenicity of HPV, immune intervention strategies constitute a promising approach for both the prevention and the therapeutic treatment of HPV-induced diseases. Importantly, the mechanisms that govern the induction and effector phases of the intraepithelial immune surveillance against HPV must be taken into account when designing such strategies.

Kaposi's sarcoma-associated herpesvirus induces the phosphatidylinositol 3-kinase-PKC-zeta-MEK-ERK signaling pathway in target cells early during infection: implications for infectivity

Human herpesvirus 8 (HHV-8) is implicated in the pathogenesis of Kaposi's sarcoma. HHV-8 envelope glycoprotein B (gB) possesses the RGD motif known to interact with integrin molecules, and HHV-8 infectivity was inhibited by RGD peptides, by antibodies against alpha3 and beta1 integrins, and by soluble alpha3beta1 integrin (S. M. Akula, N. P. Pramod, F.-Z. Wang, and B. Chandran, Cell 108:407-419, 2002). Anti-gB antibodies immunoprecipitated the virus alpha3 and beta1 complexes, and virus-binding studies suggest a role for alpha3beta1 in HHV-8 entry. HHV-8 infection induced the integrin-mediated activation of focal adhesion kinase (FAK), implicating a role for integrin and the associated signaling pathways in HHV-8 entry into the target cells. Immediately after infection, target cells exhibited morphological changes and cytoskeletal rearrangements, suggesting the induction of signal pathways. As early as 5 min postinfection, HHV-8 activated the MEK-ERK1/2 pathway. The focal adhesion components phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase C-zeta (PKC-zeta) were recruited as upstream mediators of the HHV-8-induced ERK pathway. Anti-HHV-8 gB-neutralizing antibodies and soluble alpha3beta1 integrin inhibited the virus-induced signaling pathways. Early kinetics of the cellular signaling pathway and its activation by UV-inactivated HHV-8 suggest a role for virus binding and/or entry but not viral gene expression in this induction. Studies with human alpha3 integrin-transfected Chinese hamster ovary cells and FAK-negative mouse DU3 cells suggest that the alpha3beta1 integrin and FAK play roles in the HHV-8 mediated signal induction. Inhibitors specific for PI 3-kinase, PKC-zeta, MEK, and ERK significantly reduced the virus infectivity without affecting virus binding to the target cells. Examination of viral DNA entry suggests a role for PI 3-kinase in HHV-8 entry into the target cells and a role for PKC-zeta, MEK, and ERK at a post-viral entry stage of infection. These findings implicate a critical role for integrin-associated mitogenic signaling in HHV-8's infection of target cells and suggest that, by orchestrating the signal cascade, HHV-8 may create an appropriate intracellular environment to facilitate the infection.

External genital warts: diagnosis, treatment, and prevention

External genital warts (EGWs) are visible warts that occur in the perigenital and perianal regions. They are due primarily to non-oncogenic human papillomavirus (HPV) types, usually types 6 and 11. Physical examination assisted by bright light and magnification is the recommended approach for primary diagnosis. Biopsy is indicated when EGWs are fixed to underlying structures or discolored or when standard therapies are not effective. Recurrences are common, and there is no single treatment that is superior to others. Among women with atypical squamous cells, molecular HPV testing may be useful in determining who should be referred for colposcopy. Condoms may provide some protection against HPV-related diseases and thus are recommended in new sexual relationships and when partnerships are not mutually monogamous. Because the efficacy of cesarean section in preventing vertical transmission of HPV infection from women with EGWs to their progeny has not been proved, it is not recommended.

Priming of human papillomavirus type 11-specific humoral and cellular immune responses in college-aged women with a virus-like particle vaccine

In this study, we evaluated the potency of a human papillomavirus (HPV) virus-like particle (VLP)-based vaccine at generating HPV type 11 (HPV-11)-specific cellular and humoral immune responses in seronegative women. The vaccine was administered by intramuscular immunizations at months 0, 2, and 6. A fourth immunization was administered to approximately half of the women at month 12. All vaccine recipients had positive HPV-11 VLP-specific lymphoproliferative responses at month 3 following the second immunization (geometric mean lymphoproliferative stimulation index [SI] = 28.4; 95% confidence interval [CI] = 16.9 to 48.0) and HPV-11 VLP-specific antibody titers following the first immunization at month 1 (geometric mean antibody titer = 53.9 milli-Merck units/ml, 95% CI, 34.8 to 83.7). In contrast, lymphoproliferative and antibody titer responses were never detected in the participants who received placebo. Relatively homogeneous lymphoproliferative responses were observed in all vaccinated women. The mean lymphoproliferative SI of the vaccinated group over the first 12 months of the study was 7.6-fold greater than that of the placebo group following the initial immunization. The cellular immune responses generated by VLP immunization were both Th1 and Th2, since peripheral blood mononuclear cells from vaccinees, but not placebo recipients, secreted interleukin 2 (IL-2), IL-5, and gamma interferon (IFN-gamma) in response to in vitro stimulation with HPV-11 VLP. The proliferation-based SI was moderately correlated with IFN-gamma production and significantly correlated with IL-2 production after the third immunization (P = 0.078 and 0.002, respectively). The robust lymphoproliferative responses were specific for HPV-11, since SIs generated against bovine papillomavirus and HPV-16 VLPs were not generally observed and when detected were similar pre- and postimmunization.