Merkel cell polyomavirus (MCV or MCPyV) is the first human polyomavirus to be definitively linked to cancer. The mechanisms of MCV-induced oncogenesis and much of MCV biology are largely unexplored. In this study, we demonstrate that bromodomain protein 4 (Brd4) interacts with MCV large T antigen (LT) and plays a critical role in viral DNA replication. Brd4 knockdown inhibits MCV replication, which can be rescued by recombinant Brd4. Brd4 colocalizes with the MCV LT/replication origin complex in the nucleus and recruits replication factor C (RFC) to the viral replication sites. A dominant negative inhibitor of the Brd4-MCV LT interaction can dissociate Brd4 and RFC from the viral replication complex and abrogate MCV replication. Furthermore, obstructing the physiologic interaction between Brd4 and host chromatin with the chemical compound JQ1(+) leads to enhanced MCV DNA replication, demonstrating that the role of Brd4 in MCV replication is distinct from its role in chromatin-associated transcriptional regulation. Our findings demonstrate mechanistic details of the MCV replication machinery; providing novel insight to elucidate the life cycle of this newly discovered oncogenic DNA virus.
MCV is a novel human polyomavirus that has recently been discovered in Merkel cell carcinoma (MCC), a rare but highly aggressive skin cancer. Several independent studies have confirmed that MCV is present in ∼80% of MCC tumors. However, very little is known about how the interaction between MCV and its human hosts contributes to the virus-induced cancers. Many aspects of the infectious life cycle of MCV are largely unexplored. In this study, we demonstrate that the MCV-encoded large T antigen can bind to host protein Brd4, which in turn serves as a scaffold that functionally recruits cellular DNA replication factors for replication of MCV viral DNA in host cells. This study is the first report to demonstrate mechanistic details of MCV's recruitment of the host cell DNA replication machinery; providing novel insight to elucidate the life cycle of this newly discovered oncogenic DNA virus. Importantly, our work demonstrates that blocking the Brd4 and MCV LT interaction can prevent MCV from replicating in host cells. This study identifies the Brd4-MCV LT interaction as an important target for potential development of effective therapeutic strategies to treat MCV infection.
Merkel cell polyomavirus (MCPyV) is prevalent in the general population, integrates into most Merkel cell carcinomas (MCCs) and encodes oncoproteins required for MCC tumor growth. We sought to characterize T-cell responses directed against viral proteins that drive this cancer as a step toward immunotherapy.
Intracellular cytokine cytometry, IFN-γ-ELISPOT, and a novel HLA-A*2402-restricted MCPyV tetramer were used to identify and characterize T-cell responses against MCPyV oncoproteins in tumors and blood of MCC patients and control subjects.
We isolated virus-reactive CD8 or CD4 T cells from MCPyV-positive MCC tumors (2 of 6), but not from virus-negative tumors (0 of 4). MCPyV-specific T-cell responses were also detected in the blood of MCC patients (14 of 27) and control subjects (5 of 13). These T cells recognized a broad range of peptides derived from capsid proteins (2 epitopes) and oncoproteins (24 epitopes). HLA-A*2402-restricted MCPyV oncoprotein processing and presentation by mammalian cells led to CD8-mediated cytotoxicity. Virus-specific CD8 T cells were markedly enriched among tumor-infiltrating lymphocytes as compared to blood, implying intact T-cell trafficking into the tumor. While tetramer-positive CD8 T cells were detected in the blood of 2 of 5 HLA-matched MCC patients, these cells failed to produce IFN-γ when challenged ex vivo with peptide.
Our findings suggest that MCC tumors often develop despite the presence of T cells specific for MCPyV T-Ag oncoproteins. The identified epitopes may be candidates for peptide-specific vaccines and tumor- or virus-specific adoptive immunotherapies to overcome immune evasion mechanisms in MCC patients.
While some studies have reported detection of oncogenic human papillomavirus (HPV) in colorectal tumors, others have not.
We examined the association between oncogenic HPV infection and colorectal polyps in a case-control study of individuals with colorectal adenomas (n=167), hyperplastic polyps (n=87), and polyp-free controls (n=250). We performed real-time PCR for HPV-16 /18 DNA, and SPF PCR covering 43 HPV types, on lesional and normal colorectal tissue samples. Plasma antibodies for oncogenic HPV types were assessed via a bead-based multiplex Luminex assay.
HPV DNA was not found in any of the 609 successfully assayed colorectal tissue samples from adenomas, hyperplastic polyps, normal biopsies adjacent to polyps, or normal biopsies of the rectum of disease-free controls. Also, there was no association between HPV seropositivity for all oncogenic HPV types combined, for either polyp type, and for men or women. When analyses were restricted to participants without a previous history of polyps, among men [adenomas (n=31), hyperplastic polyps (n=28), and controls (n=68)], there was an association between seropositivity and hyperplastic polyps when all oncogenic HPV types were combined (odds ratio=3.0; 95% confidence interval: 1.1–7.9).
Overall, our findings do not support an etiologic relationship between HPV and colorectal adenomas or hyperplastic polyps; however, our finding suggesting an association between HPV seropositivity and hyperplastic polyps in men may warrant further investigations.
After stringent controls for contamination and three methods to assess HPV infection, we report no evidence for HPV in the etiology of colorectal neoplasia for either men or women.
HPV; colorectal adenomas; hyperplastic polyps; DNA; antibodies
Cancer cells exhibit the ability to proliferate indefinitely, but paradoxically, overexpression of cellular oncogenes in primary cells can result in a rapid and irreversible cell cycle arrest known as oncogene-induced senescence (OIS). However, we have shown that constitutive overexpression of the oncogene c-MYC in primary human foreskin fibroblasts results in a population of cells with unlimited lifespan; these immortalized cells are henceforth referred to as iMYC. Here, in order to further elucidate the mechanisms underlying the immortalization process, a gene expression signature of three independently established iMYC cell lines compared with matched early passage c-MYC overexpressing cells was derived. Network analysis of this “iMYC signature” indicated that a large fraction of the downregulated genes were functionally connected and major nodes centered around the TGFβ, IL-6 and IGF-1 signaling pathways. Here, we focused on the functional validation of the alteration of TGFβ response during c-MYC-mediated immortalization. The results demonstrate loss of sensitivity of iMYC cells to activation of TGFβ signaling upon ligand addition. Furthermore, we show that aberrant regulation of the p27 tumor suppressor protein in iMYC cells is a key event that contributes to loss of response to TGFβ. These findings highlight the potential to reveal key pathways contributing to the self-renewal of cancer cells through functional mining of the unique gene expression signature of cells immortalized by c-MYC.
c-MYC; gene expression signature; immortalization; TGFβ; p27
Infection with genus beta human papillomaviruses (HPV) is implicated in the development of non-melanoma skin cancer. This was first evidenced for HPV5 and 8 in patients with epidermodysplasia verruciformis (EV), a genetic skin disease. So far, it has been unknown how these viruses overcome cutaneous immune control allowing their persistence in lesional epidermis of these patients. Here we demonstrate that Langerhans cells, essential for skin immunosurveillance, are strongly reduced in HPV8-positive lesional epidermis from EV patients. Interestingly, the same lesions were largely devoid of the important Langerhans cells chemoattractant protein CCL20. Applying bioinformatic tools, chromatin immunoprecipitation assays and functional studies we identified the differentiation-associated transcription factor CCAAT/enhancer binding protein β (C/EBPβ) as a critical regulator of CCL20 gene expression in normal human keratinocytes. The physiological relevance of this finding is supported by our in vivo studies showing that the expression patterns of CCL20 and nuclear C/EBPβ converge spatially in the most differentiated layers of human epidermis. Our analyses further identified C/EBPβ as a novel target of the HPV8 E7 oncoprotein, which co-localizes with C/EBPβ in the nucleus, co-precipitates with it and interferes with its binding to the CCL20 promoter in vivo. As a consequence, the HPV8 E7 but not E6 oncoprotein suppressed C/EBPβ-inducible and constitutive CCL20 gene expression as well as Langerhans cell migration. In conclusion, our study unraveled a novel molecular mechanism central to cutaneous host defense. Interference of the HPV8 E7 oncoprotein with this regulatory pathway allows the virus to disrupt the immune barrier, a major prerequisite for its epithelial persistence and procarcinogenic activity.
Human papillomaviruses (HPVs) infect squamous epithelial cells of skin or mucosa, giving rise to hyperproliferative lesions. A subgroup of “high-risk” genus alpha HPVs is associated with human anogenital malignancies, e.g. cervical cancer. The skin carcinogenic potential of genus beta HPV types, such as HPV8, is fully accepted in epidermodysplasia verruciformis (EV) patients and their contribution to the development of non-melanoma skin cancer in the general population is under investigation. This genetic disorder serves as a model disease for studying the immunobiology, viral persistence and molecular mechanisms of HPV-induced skin carcinogenesis. Here, we demonstrate that antigen-presenting Langerhans cells and the Langerhans cell attracting chemokine CCL20 are strongly reduced in lesional skin of EV patients. We show that the HPV8 encoded E7 oncoprotein substantially contributes to this disturbance of cutaneous innate immune control. Our data define a novel mechanism of C/EBPβ-dependent CCL20 gene regulation. HPV8 E7 directly interacts with this transcription factor, interferes with its binding to the CCL20 promoter and suppresses keratinocyte CCL20 expression as well as Langerhans cell migration. Our study unravels a molecular mechanism of virus-host interaction critical for evading host immune defense and providing a microenvironment that is conducive to persistent HPV infection and skin carcinogenesis.
Background. Although the prevalence of human papillomavirus (HPV) genital infection is similarly high in males and females, seroprevalence is lower in males. This study assessed rates and determinants of seroconversion after detection of genital HPV infection in young men.
Methods. We investigated HPV type-specific seroconversion in a cohort of heterosexual male university students who had an α9 HPV type (HPV-16, -31, -33, -35, -52, -58, or -67) detected in the genital tract (n = 156). HPV DNA and antibodies were detected and typed using liquid bead-based multiplex assays. We calculated seroconversion using Kaplan–Meier survival analysis. Cox proportional hazards models with generalized estimating equations were used to examine associations with seroconversion.
Results. Within 24 months of detecting genital HPV infection, type-specific seroconversion ranged from 4% for HPV–52 to 36% for HPV-31. HPV-16 seroconversion at 24 months was 13% (95% confidence interval [CI], 7%–25%). Among incident HPV infections, ever cigarette smoking and infection site(s) (shaft/scrotum and glans/urine vs shaft/scrotum or glans/urine only) were positively associated with type-specific seroconversion.
Conclusions. For each of the α9 HPV types, type-specific seroconversion within 24 months was observed in 36% or less of infected men. Seroconversion might be related to cigarette smoking and genital site(s) infected.
The role of the E6 oncoprotein from high-risk members of the α human papillomavirus genus in anogenital cancer has been well established. However, far less is known about the E6 protein from the β human papillomavirus genus (β-HPVs). Some β-HPVs potentially play a role in non-melanoma skin cancer development, although they are not required for tumor maintenance. Instead, they may act as a co-factor that enhances the carcinogenic potential of UV damage. Indeed, the E6 protein from certain β-HPVs (HPV 5 and 8) promotes the degradation of p300, a histone acetyl transferase involved in UV damage repair. Here, we show that the expression of HPV 5 and 8 E6 increases thymine dimer persistence as well as the likelihood of a UVB induced double strand break (DSB). Importantly, we provide a mechanism for the increased DNA damage by showing that both extended thymine dimer persistence as well as elevated DSB levels are dependent on the ability of HPV 8 E6 to promote p300 degradation. We further demonstrate that HPV 5 and 8 E6 expression reduces the mRNA and protein levels of ATR, a PI3 kinase family member that plays a key role in UV damage signaling, but that these levels remain unperturbed in cells expressing a mutated HPV 8 E6 incapable of promoting p300 degradation. We confirm that the degradation of p300 leads to a reduction in ATR protein levels, by showing that ATR levels rebound when a p300 mutant resistant to HPV 8 mediated degradation and HPV 8 E6 are co-transfected. Conversely, we show that ATR protein levels are reduced when p300 is targeted for degradation by siRNA. Moreover, we show the reduced ATR levels in HPV 5 and 8 E6 expressing cells results in delayed ATR activation and an attenuated ability of cells to phosphorylate, and as a result accumulate, p53 in response to UVB exposure, leading to significantly reduced cell cycle arrest. In conclusion, these data demonstrate that β-HPV E6 expression can enhance the carcinogenic potential of UVB exposure by promoting p300 degradation, resulting in a reduction in ATR levels, which leads to increased thymine dimer persistence and increased UVB induced DSBs.
Human papillomaviruses are a large family of viruses that can cause ailments ranging from benign warts to anogenital cancer. Recently, interest has increased for a subgroup of these viruses, the β-HPVs, because of their potential involvement in squamous cell skin cancer. In this work, we show that the E6 protein from two of these viruses (HPV 5 and 8) is able to increase the damage that UV exposure causes to the host cell's DNA. The E6 protein from these viruses promotes the degradation of p300, a cellular protein involved in DNA damage repair. This in turn reduces amounts of another cellular protein, ATR, which facilitates the process of signaling the cell to repair its damaged DNA. The decrease in ATR levels delays the cell's recognition of the damaged DNA, allowing thymine dimers to remain unrepaired longer and more often leading to a double strand break in the DNA. Together, our data show that the β HPVs can cause UV exposures to be more deleterious to host cell DNA, potentially increasing the likelihood that these cells become cancerous.
We sought to determine whether oral fluid can be used to assess serum human papillomavirus (HPV) antibody status by enrolling women who had received a prophylactic HPV-16 vaccine in a new follow-up study. After the prophylactic HPV-6/11/16/18 vaccine was licensed in the United States, we administered it to consenting participants. The sensitivity of oral fluid, treating serology as the gold standard, before and after administration of the quadrivalent vaccine was 49.6% (95% confidence interval [CI]: 42.0%–57.3%) and 100% (95% CI: 92.0%–100%), respectively. Oral fluid may have the potential to be used for monitoring of prophylactic HPV vaccines in the future.
Human papillomavirus; Prophylactic vaccines; Antibodies; Oral fluid
Background. Viral load may influence the course of human papillomavirus type 16 (HPV-16) infection.
Methods. This case-control study was nested within the 2-year Atypical Squamous Cells of Undetermined Significance and Low-Grade Squamous Intraepithelial Lesion Triage Study, in which women were followed semiannually for HPV and cervical intraepithelial neoplasia (CIN). Case patients (n = 62) were women diagnosed with CIN3 following HPV-16–positive detection at a follow-up visit. HPV-16–positive controls (n = 152) without CIN2 or CIN3 were matched to cases based on the follow-up visit in which viral load was measured. Real-time polymerase chain reaction was used for HPV-16 DNA quantification.
Results. The risk of CIN3 increased with increasing HPV-16 DNA load at the follow-up visit (odds ratio, 1.63; 95% confidence interval, 1.33–1.99 per 1 log10 unit increase); the association was not affected by whether HPV-16 was present at enrollment. When HPV-16 was present at both enrollment and follow-up, viral load remained high among cases (P = .77) but decreased substantially among controls (P = .004). Among women with HPV-16 found initially during follow-up, viral load in the first HPV-16–positive sample was associated with short-term persistence; load was higher in those with infection, compared with those without infection, 1 visit after the initial positivity (P = .001).
Conclusions. Viral load of newly detected infections and changes in viral load predict persistence and progression of HPV-16 infections.
Merkel cell carcinoma (MCC) is a polyomavirus-associated skin cancer that is frequently lethal and lacks established prognostic biomarkers. This study sought to identify biomarkers that improve prognostic accuracy and provide insight into MCC biology.
Patients and Methods
Gene expression profiles of 35 MCC tumors were clustered based on prognosis. The cluster of genes overexpressed in good-prognosis tumors was tested for biologic process enrichment. Relevant mRNA expression differences were confirmed by quantitative polymerase chain reaction and immunohistochemistry. An independent set of 146 nonoverlapping MCC tumors (median follow-up, 25 months among 116 living patients) was employed for biomarker validation. Univariate and multivariate Cox regression analyses were performed.
Immune response gene signatures were prominent in patients with good prognoses. In particular, genes associated with cytotoxic CD8+ lymphocytes were overexpressed in tumors from patients with favorable prognoses. In the independent validation set, cases with robust intratumoral CD8+ lymphocyte infiltration had improved outcomes (100% MCC-specific survival, n = 26) compared with instances characterized by sparse infiltration (60% survival, n = 120). Only stage and intratumoral CD8 infiltration (but not age, sex, or CD8+ lymphocytes localized to the tumor-stroma interface) were significant in both univariate and multivariate Cox regression analyses. Notably, traditional histologic identification of tumor-infiltrating lymphocytes was not a significant independent predictor of survival.
Intratumoral CD8+ lymphocyte infiltration can be readily assessed on paraffin-embedded tissue, is independently associated with improved MCC-specific survival, and therefore, may provide prognostic information that enhances established MCC staging protocols.
Human papillomavirus is the acknowledged cause of cervical cancer. We hypothesized that allergies, characterized by hyperimmune reaction to common allergens andwhich have been associated with various cancers, may be related to cervical cancer, and that genetic variation in cytokine genes related to allergies might impact cervical cancer risk.
We investigated the risk of invasive squamous cell cervical cancer (SCC) associated with self-reported allergies and with variation in allergy-related cytokine genes using data from a case-control study (561 cases, 1258 controls) conducted in Washington State. Logistic regression models yielded odds ratios (OR) and 95% confidence intervals (CI).
Pollen allergy, the most commonly reported allergy, was associated with reduced SCC risk (OR 0.6, 95% CI 0.5–0.8). Of 60 tagging single nucleotide polymorphisms covering eight genes (CSF2, IL3, IL4, IL13, CSF2RB, IL4R, IL13RA1, IL13RA2), several were related to pollen allergies among controls: IL4R rs3024647 (dominant OR 1.5 95% CI 1.0–2.3, p=0.04), CSF2RB rs16997517 (dominant OR 2.2 95% CI 1.0–4.7, p=0.04), and IL13 rs1800925 (per-allele OR 1.7, 95% CI 1.3–2.4, p=0.0007). Two variants were inversely associated with SCC risk: IL4R rs3024656 (per-allele OR 0.8, 95% CI 0.6–1.0, p=0.03) and CSF2RB rs16997517 (dominant OR 0.4, 95% CI 0.2–0.9, p=0.04).
Pollen allergies were related to reduced SCC risk. CSF2RB rs16997517 was directly related to pollen allergies in controls and to reduced SCC risk.
If other studies confirm these results, the mechanism behind allergy-associated immune response associated with SCC risk may be worth exploring in the context of therapeutic or prophylactic vaccines.
Cervical cancer; HPV; allergy; cytokines
Merkel cell polyomavirus (MCPyV) is a common infectious agent that is likely involved in the etiology of most Merkel cell carcinomas (MCCs). Serum antibodies recognizing the MCPyV capsid protein, VP1, are detectable at high titer in nearly all MCC patients, and remain stable over time. Although antibodies to the viral capsid indicate prior MCPyV infection, they provide limited clinical insight into MCC because they are also detected in more than half of the general population. We investigated whether antibodies recognizing MCPyV large and small tumor-associated antigens (T-Ags) would be more specifically associated with MCC. Among 530 population control subjects, these antibodies were present in only 0.9% and were of low titer. In contrast, among 205 MCC cases, 40.5% had serum IgG antibodies that recognize a portion of T-Ag shared between small and large T-Ags. Among cases, titers of T-Ag antibodies fell rapidly (approximately 8 fold/year) in patients whose cancer did not recur, while they rose rapidly in those with progressive disease. Importantly, in several patients who developed metastases, the rise in T-Ag titer preceded clinical detection of disease spread. These results suggest that antibodies recognizing T-Ag are relatively specifically associated with MCC, do not effectively protect against disease progression, and may serve as a clinically useful indicator of disease status.
Merkel cell carcinoma; Merkel cell polyomavirus; MCPyV; antibody; biomarker
The E6 oncoprotein from high-risk genus alpha human papillomaviruses (α-HPVs), such as HPV 16, has been well characterized with respect to the host-cell proteins it interacts with and corresponding signaling pathways that are disrupted due to these interactions. Less is known regarding the interacting partners of E6 from the genus beta papillomaviruses (β-HPVs); however, it is generally thought that β-HPV E6 proteins do not interact with many of the proteins known to bind to α-HPV E6. Here we identify p300 as a protein that interacts directly with E6 from both α- and β-HPV types. Importantly, this association appears much stronger with β-HPV types 5 and 8-E6 than with α-HPV type 16-E6 or β-HPV type 38-E6. We demonstrate that the enhanced association between 5/8-E6 and p300 leads to p300 degradation in a proteasomal-dependent but E6AP-independent manner. Rather, 5/8-E6 inhibit the association of AKT with p300, an event necessary to ensure p300 stability within the cell. Finally, we demonstrate that the decreased p300 protein levels concomitantly affect downstream signaling events, such as the expression of differentiation markers K1, K10 and Involucrin. Together, these results demonstrate a unique way in which β-HPV E6 proteins are able to affect host-cell signaling in a manner distinct from that of the α-HPVs.
Human papillomaviruses (HPVs) are a family of more than 100 different viruses that cause a wide range of pathologies, from benign warts to cervical cancer. One subgroup of HPVs, the beta-HPVs, have recently become a topic of interest due to their potential involvement in squamous cell skin cancer. However, unlike the HPVs involved in cervical cancer, little is known with regards to how the beta-HPVs may facilitate cellular changes that would allow cancerous lesions to develop. Here we have identified a host-cell protein, p300, which interacts strongly with the E6 oncoprotein from two beta-HPVs, HPV 5 and HPV 8. We show that this interaction subsequently blocks another cellular protein, AKT, from binding to and stabilizing p300. By blocking this association, p300 is targeted for degradation, and thus is present in lower amounts than in normal cells. Importantly, because p300 is involved in numerous cell processes such as DNA repair, cell growth, and differentiation, the potential for E6 disrupting a number of cellular signaling pathways is vast. Taken together, our findings shed new light on how the beta-HPVs may facilitate carcinogenesis.
The high-risk human papillomavirus (HPV) E6 and E7 oncoproteins are critical to the immortalization of keratinocytes. HPV type 16 (HPV16) E6 interacts with endogenous proteins to activate hTERT, the catalytic subunit of telomerase, thus avoiding cellular senescence signals. NFX1-123, the longer splice variant of NFX1, interacts with HPV16 E6, as well as cytoplasmic poly(A) binding proteins 1 and 4 (PABPC1 and PABPC4). HPV16 E6 affects hTERT expression posttranscriptionally through NFX1-123, as NFX1-123 interacts with hTERT mRNA and stabilizes it, leading to greater telomerase activity. The PAM2 motif of NFX1-123, with which it binds PABPCs, is required for the posttranscriptional regulation of hTERT by HPV16 E6 and NFX1-123. There is increasing evidence that RNA and DNA viruses utilize RNA-processing proteins, and specifically PABPCs, in the normal virus life cycle, and there is also evidence that RNA-processing proteins are perturbed in cancers. Here, we show that PABPCs are critical in hTERT regulation by HPV16 E6. Although the amount and cellular localization of PABPCs were largely unchanged in cervical cancer cell lines with or without HPV16 and in human foreskin keratinocytes (HFKs) with or without HPV16 E6, knockdown of PABPCs decreased hTERT mRNA and telomerase activity and overexpression of PABPC4 increased these in HPV16 E6-expressing HFKs. In contrast, knockdown of PABPCs in C33A cells had no effect on hTERT mRNA or telomerase activity. Additionally, overexpression of PABPC4 and hTERT led to greater growth of cultured HPV16 E6-expressing HFKs. This is the first evidence that PABPCs have a targeted role in hTERT regulation leading to a growth advantage in cells expressing HPV16 E6.
Non-enveloped viruses penetrate host membranes to infect cells. A cell-based assay was used to probe the endoplasmic reticulum (ER)-to-cytosol membrane transport of the non-enveloped SV40. We found that, upon ER arrival, SV40 is released into the lumen and undergoes sequential disulfide bond disruptions to reach the cytosol. However, despite these ER-dependent conformational changes, SV40 crosses the ER membrane as a large and intact particle consisting of the VP1 coat, the internal components VP2, VP3, and the genome. This large particle subsequently disassembles in the cytosol. Mutant virus and inhibitor studies demonstrate VP3 and likely the viral genome, as well as cellular proteasome, control ER-to-cytosol transport. Our results identify the sequence of events, as well as virus and host components, that regulate ER membrane penetration. They also suggest that the ER membrane supports passage of a large particle, potentially through either a sizeable protein-conducting channel or the lipid bilayer.
Biological membranes represent a major barrier during viral infection. While the mechanism by which an enveloped virus breaches the limiting membrane of a host cell is well-characterized, this membrane penetration process is poorly understood for non-enveloped viruses. Indeed, most available insights on membrane transport of non-enveloped viruses are built upon in vitro studies. Here we established a cell-based assay to elucidate the molecular mechanism by which the non-enveloped SV40 penetrates the endoplasmic reticulum (ER) membrane to access the cytosol, a critical step in infection. Strikingly, we uncovered SV40 breaches the ER membrane as a large and intact viral particle, despite the conformational changes it experiences in the ER lumen. This result suggests that the ER membrane can accommodate translocation of a large protein complex, possibly through either a sizeable protein channel or the ER membrane bilayer. In addition to this finding, we also pinpoint viral and host components that control the ER-to-cytosol membrane transport event. Together, our data illuminate the cellular mechanism by which a non-enveloped virus penetrates the limiting membrane of a target cell during infection.
High-risk human papillomavirus (HR HPV) requires differentiating epithelial cells to continue to divide in order to replicate the viral DNA. To achieve this, HPV perturbs several regulatory pathways, including cellular apoptosis and senescence signals. HPV E6 has been identified as a regulator of the NFκB signaling pathway, a pathway important in many cellular processes, as well as regulation of virus-host cell interactions. We report here that NFX1-91, an endogenously expressed transcriptional regulator of human telomerase reverse transcriptase (hTERT) that is targeted by HPV type 16 (HPV16) E6/E6-associated protein (E6AP) for degradation, is also critical for regulation of the NFκB pathway by HPV16 E6. Microarray analysis revealed induction of NFκB-responsive genes and reduction of NFκB inhibitors with knockdown of NFX1-91. Knockdown of NFX1-91 induced downregulation of p105, an NFκB inhibitor in both primary human foreskin keratinocytes (HFKs) and HCT116 cells. Chromatin immunoprecipitation assays further confirmed that NFX1-91 bound to the p105 promoter and upregulated its expression. Similarly, in HPV16 E6-positive cells, reduction of p105 expression was observed, paralleling knockdown of NFX1-91 expression. Overall, our data suggest a mechanism for HPV16 E6 activation of the NFκB pathway through NFX1-91. Also, it provides evidence that NFX1-91 can function as a dual regulator, not only a transcriptional repressor, but also a transcriptional activator, when bound to DNA.
The human antibody response to polyomavirus capsid proteins is not well characterized. Recombinant BK virus (BKV), JC virus (JCV) and simian virus 40 (SV40) virus-like particles (VLP) were produced in a baculovirus system, and mouse monoclonal antibodies (mAbs) to these proteins were generated using standard methods. Nine of 12 BKV mAbs showed neutralizing activity. The non-neutralizing antibodies also bound BKV pseudocapsids in an ELISA binding assay. Most antibodies recognized conformational species-specific epitopes, but several exceptions were found: (i) BKV mAb BK-F11 cross-reacted with a linear buried epitope common to both JCV and SV40 pseudocapsids, (ii) two of six JCV antibodies (JC-6.7 and JC-7.9) and two of 13 SV40 antibodies (VP1-H2 and VP1-I2) recognized linear buried epitopes common to all three viruses and (iii) SV40 antibody VP1-E5 recognized a linear surface epitope on JCV pseudocapsids.
Intratypic diversity of human papillomavirus (HPV) genome is generally characterized by point mutation, insertion, and/or deletion. Using PCR-based cloning and sequencing, we detected concurrent infection with 8 HPV16 variants in a woman enrolled in the ASCUS-LSIL Triage Study. The European variant was the major variant; each of the seven minor variants had partial DNA sequences identical to the European variant and another part identical to the African-2 variant. At a follow-up visit, only an HPV16 African-2 variant was detected. Results from the present study suggest presence of intratypic recombination of HPV genome in natural infection.
human papillomavirus; recombination; variant
Merkel Cell Polyomavirus (MCPyV) is associated with Merkel Cell carcinoma (MCC), a rare, aggressive skin cancer with neuroendocrine features. The causal role of MCPyV is highly suggested by monoclonal integration of its genome and expression of the viral large T (LT) antigen in MCC cells. We investigated and characterized MCPyV molecular features in MCC, respiratory, urine and blood samples from 33 patients by quantitative PCR, sequencing and detection of integrated viral DNA. We examined associations between either MCPyV viral load in primary MCC or MCPyV DNAemia and survival. Results were interpreted with respect to the viral molecular signature in each compartment. Patients with MCC containing more than 1 viral genome copy per cell had a longer period in complete remission than patients with less than 1 copy per cell (34 vs 10 months, P = 0.037). Peripheral blood mononuclear cells (PBMC) contained MCPyV more frequently in patients sampled with disease than in patients in complete remission (60% vs 11%, P = 0.00083). Moreover, the detection of MCPyV in at least one PBMC sample during follow-up was associated with a shorter overall survival (P = 0.003). Sequencing of viral DNA from MCC and non MCC samples characterized common single nucleotide polymorphisms defining 8 patient specific strains. However, specific molecular signatures truncating MCPyV LT were observed in 8/12 MCC cases but not in respiratory and urinary samples from 15 patients. New integration sites were identified in 4 MCC cases. Finally, mutated-integrated forms of MCPyV were detected in PBMC of two patients with disseminated MCC disease, indicating circulation of metastatic cells. We conclude that MCPyV molecular features in primary MCC tumour and PBMC may help to predict the course of the disease.
Merkel cell polyomavirus (MCPyV) is a recently discovered virus highly associated with a rare skin cancer, Merkel cell carcinoma (MCC). The causal role of MCPyV in cancer is suggested by integration of viral sequences into the cell genome and by a specific molecular signature. We looked for and compared molecular species of MCPyV in tumour and non tumour samples of 33 MCC patients. We showed that a tumour viral load greater than 1 copy per cell was associated with a better outcome, and that detection of the virus in blood but not in urine correlated with a shorter overall survival. A tumour–specific molecular signature was found in the blood of two patients with metastatic disease, but did not occur in their respiratory nor urine samples. We propose that molecular analysis of MCPyV in tumour and blood be used as a biomarker of infection and cancer progression in MCC patients.
Given the established links between young age at first intercourse (AFI), number of sex partners, high-risk human papillomavirus infection, and squamous cell cervical cancer (SCC), we hypothesized that women diagnosed with SCC at younger ages would be more likely to report young AFI than women diagnosed later in life.
We performed a population-based investigation among invasive SCC cases who were diagnosed between 1986 and 2004, were 22 to 53 years old, and lived in the metropolitan Seattle-Puget Sound region (n=333). Using multivariate linear regression, we estimated coefficients and 95% confidence intervals (CI) to assess the association between age at SCC diagnosis and AFI (<15, 15–18, ≥19) and number of sex partners before age 20 (0, 1, 2–4, 5–14, 15+), accounting for birth year and other factors. Interactions were assessed using the likelihood ratio test.
The interval between AFI and SCC diagnosis ranged from 4 to 35 years. In a multivariate model, compared to SCC cases reporting AFI≥19, the mean age of diagnosis was 3.1 years younger for SCC cases reporting AFI<15 (CI: −5.8, −0.5) and 2.6 years younger for SCC cases reporting AFI 15–18 years (CI: −4.6, −0.6). Although number of sex partners before age 20 was associated with age at SCC diagnosis in a crude analysis, the association was not independent of AFI. However, in the AFI≥19 and AFI<15 groups, differences in effect were seen by number of sex partners before age 20 (p for interaction=0.08), with the association remaining strong and significant only in the AFI<15 group that had 2 or more partners before age 20 (coefficient: −4.2, CI: −6.3, −2.1).
Among younger and middle-aged women with SCC, early age of diagnosis was associated with early AFI, though the effect appeared to be modified by number of sex partners before age 20.
Cervical Carcinoma; Sexual Initiation; Age
The papillomaviruses are small DNA viruses that encode approximately eight genes, and require the host cell DNA replication machinery for their viral DNA replication. Thus papillomaviruses have evolved strategies to induce host cell DNA synthesis balanced with strategies to protect the cell from unscheduled replication. While the papillomavirus E1 and E2 genes are directly involved in viral replication by binding to and unwinding the origin of replication, the E6 and E7 proteins have auxillary functions that promote proliferation. As a consequence of disrupting the normal checkpoints that regulate cell cycle entry and progression, the E6 and E7 proteins play a key role in the oncogenic properties of human papillomaviruses with a high risk of causing anogenital cancers (HR HPVs). As a consequence, E6 and E7 of HR HPVs are invariably expressed in cervical cancers. This article will focus on the E6 protein and its numerous activities including inactivating p53, blocking apoptosis, activating telomerase, disrupting cell adhesion, polarity and epithelial differentiation, altering transcription and reducing immune recognition.
The clinical relevance of the amount of human papillomavirus type 18 (HPV18) DNA in cervical tissue (ie, HPV18 DNA load) is unknown.
Study subjects were 303 women who were HPV18 positive at enrollment into the Atypical Squamous Cells of Undetermined Significance (ASC-US) and Low-Grade Squamous Intraepithelial Lesion (LSIL) Triage Study. HPV18 DNA load, expressed as copies of HPV18 per nanogram of cellular DNA, at enrollment was quantitatively measured. Subjects were followed up semiannually for a period of 2 years for detection of cervical intraepithelial neoplasia 2–3 (CIN2–3). A linear regression model was used to examine associations of CIN2–3 with HPV18 DNA load. All statistical tests were two-sided.
CIN2–3 was confirmed in 92 of 303 (30.4%) HPV18-positive women. Among women without CIN2–3, HPV18 DNA load was positively associated with increasing severity of cervical cytology at enrollment (Ptrend < .001). However, among those with CIN2–3, HPV18 DNA load was not associated with severity of cervical cytology at enrollment (Ptrend = .33). The ratios of geometric means of HPV18 DNA load at enrollment among women with CIN2–3, relative to those without, were 6.06 (95% confidence interval [CI] = 0.31 to 117.92) for those with normal cytology at enrollment, 0.50 (95% CI = 0.10 to 2.44) for those with ASC-US, 0.11 (95% CI = 0.03 to 0.46) for those with LSIL, and 0.07 (95% CI = 0.01 to 0.80) for those with high-grade squamous intraepithelial lesion (HSIL). After adjusting for age and coinfection with other high-risk HPVs, a statistically significant association of lower HPV18 DNA load with CIN2–3 was observed among women with LSIL or HSIL at enrollment (P = .02). Within the 2-year period, HPV18 DNA load was unrelated to the timing of CIN2–3 diagnosis. Overall results were similar when the outcome was CIN3.
HPV18 DNA load was higher for women with LSIL or HSIL at enrollment with no evidence of CIN2–3 during the 2-year follow-up period than it was for women with CIN2–3. Thus, testing for high levels of HPV18 DNA does not appear to be clinically useful.
High-risk human papillomavirus (HPV) E6 protein induces telomerase activity through transcriptional activation of hTERT, the catalytic subunit of telomerase. HPV type 16 (HPV16) E6 interacts with two splice variants of NFX1 to increase hTERT expression. NFX1-91 is a transcriptional repressor of hTERT that is polyubiquitinated and targeted for degradation by HPV16 E6 in concert with E6-associated protein. We previously showed that NFX1-123 augments hTERT expression through binding to cytoplasmic poly(A) binding proteins (PABPCs). In this study, we determined that unlike NFX1-91, NFX1-123 is a cytoplasmic protein that colocalized with PABPCs but does not shuttle with PABPCs between the nucleus and cytoplasm. NFX1-123 requires both its PAM2 motif, with which it binds PABPCs, and its R3H domain, which has putative nucleic acid binding capabilities, to increase hTERT mRNA levels and telomerase activity in keratinocytes expressing HPV16 E6. In keratinocytes expressing HPV16 E6 and overexpressing NFX1-123, there was increased protein expression from in vitro-transcribed RNA fused with the 5′ untranslated region (5′ UTR) of hTERT. This posttranscriptional increase in expression required the PAM2 motif and R3H domain of NFX1-123 as well as the coexpression of HPV16 E6. NFX1-123 bound endogenous hTERT mRNA and increased its stability in HPV16 E6-expressing human foreskin keratinocytes, and NFX1-123 increased the stability of in vitro-transcribed RNA fused with the 5′ UTR of hTERT. Together, these studies describe the first evidence of posttranscriptional regulation of hTERT, through the direct interaction of the cytoplasmic protein NFX1-123 with hTERT mRNA, in HPV16 E6-expressing keratinocytes.
Although correlations of cervical cytology to human papillomavirus (HPV) load and histopathology are recognized, it is largely undetermined whether viral load-related risks of cervical intraepithelial neoplasia III (CIN3) differ by cytology.
Study subjects were 821 women enrolled in the ASCUS-LSIL Triage Study who were positive for HPV16 at entry. Women were followed semi-annually over 2 years. Baseline HPV16 load was measured by real-time PCR; expressed as log10 [HPV16 copies per-nanogram of cellular DNA].
CIN3 was confirmed in 34.8% of 821 women during 2-year follow-up. The adjusted odds ratio (OR) associating 2-year cumulative risk of CIN3 with per log10–unit increase in HPV16 load was 1.46 (95%CI, 1.29-1.64). The ORs varied from 1.66 (95%CI, 1.16-2.37) for women with normal cytology at enrollment to 0.86 (95%CI, 0.61-1.20) for those with HSIL. Among women with normal cytology at enrollment, the area under the receiver operating characteristic curve for detecting CIN3 by viral load was 0.70 (95%CI, 0.61-0.78).
HPV16 DNA load was associated with CIN3 risk but the associations varied with cytology detected at the time when the viral load was measured. Clinical utility of testing for HPV16 load for CIN3 detection was minimal even in women with normal cytology.
Human Papillomavirus; Viral load; Cervical Intraepithelial Neoplasia