Merkel cell polyomavirus protein ALTO modulates TBK1 activity to support persistent infection.

While Merkel cell polyomavirus (MCPyV or MCV) is an abundant virus frequently shed from healthy skin, it is one of the most lethal tumor viruses in immunocompromised individuals, highlighting the crucial role of host immunity in controlling MCPyV oncogenic potential. Despite its prevalence, very little is known about how MCPyV interfaces with the host immune response to maintain asymptomatic persistent infection and how inadequate control of MCPyV infection triggers MCC tumorigenesis. In this study, we discovered that the MCPyV protein, known as the Alternative Large Tumor Open Reading Frame (ALTO), also referred to as middle T, effectively primes and activates the STING signaling pathway. It recruits Src kinase into the complex of STING downstream kinase TBK1 to trigger its autophosphorylation, which ultimately activates the subsequent antiviral immune response. Combining single-cell analysis with both loss- and gain-of-function studies of MCPyV infection, we demonstrated that the activity of ALTO leads to a decrease in MCPyV replication. Thus, we have identified ALTO as a crucial viral factor that modulates the STING-TBK1 pathway, creating a negative feedback loop that limits viral infection and maintains a delicate balance with the host immune system. Our study reveals a novel mechanism by which a tumorigenic virus-encoded protein can link Src function in cell proliferation to the activation of innate immune signaling, thereby controlling viral spread, and sustaining persistent infection. Our previous findings suggest that STING also functions as a tumor suppressor in MCPyV-driven oncogenesis. This research provides a foundation for investigating how disruptions in the finely tuned virus-host balance, maintained by STING, could alter the fate of MCPyV infection, potentially encouraging malignancy.

Virology-the path forward.

In the United States (US), biosafety and biosecurity oversight of research on viruses is being reappraised. Safety in virology research is paramount and oversight frameworks should be reviewed periodically. Changes should be made with care, however, to avoid impeding science that is essential for rapidly reducing and responding to pandemic threats as well as addressing more common challenges caused by infectious diseases. Decades of research uniquely positioned the US to be able to respond to the COVID-19 crisis with astounding speed, delivering life-saving vaccines within a year of identifying the virus. We should embolden and empower this strength, which is a vital part of protecting the health, economy, and security of US citizens. Herein, we offer our perspectives on priorities for revised rules governing virology research in the US.

Virology under the Microscope-a Call for Rational Discourse.

Viruses have brought humanity many challenges: respiratory infection, cancer, neurological impairment and immunosuppression to name a few. Virology research over the last 60+ years has responded to reduce this disease burden with vaccines and antivirals. Despite this long history, the COVID-19 pandemic has brought unprecedented attention to the field of virology. Some of this attention is focused on concern about the safe conduct of research with human pathogens. A small but vocal group of individuals has seized upon these concerns - conflating legitimate questions about safely conducting virus-related research with uncertainties over the origins of SARS-CoV-2. The result has fueled public confusion and, in many instances, ill-informed condemnation of virology. With this article, we seek to promote a return to rational discourse. We explain the use of gain-of-function approaches in science, discuss the possible origins of SARS-CoV-2 and outline current regulatory structures that provide oversight for virological research in the United States. By offering our expertise, we - a broad group of working virologists - seek to aid policy makers in navigating these controversial issues. Balanced, evidence-based discourse is essential to addressing public concern while maintaining and expanding much-needed research in virology.

Characterization of ALTO-encoding circular RNAs expressed by Merkel cell polyomavirus and trichodysplasia spinulosa polyomavirus.

Circular RNAs (circRNAs) are a conserved class of RNAs with diverse functions, including serving as messenger RNAs that are translated into peptides. Here we describe circular RNAs generated by human polyomaviruses (HPyVs), some of which encode variants of the previously described alternative large T antigen open reading frame (ALTO) protein. Circular ALTO RNAs (circALTOs) can be detected in virus positive Merkel cell carcinoma (VP-MCC) cell lines and tumor samples. CircALTOs are stable, predominantly located in the cytoplasm, and N6-methyladenosine (m6A) modified. The translation of MCPyV circALTOs into ALTO protein is negatively regulated by MCPyV-generated miRNAs in cultured cells. MCPyV ALTO expression increases transcription from some recombinant promoters in vitro and upregulates the expression of multiple genes previously implicated in MCPyV pathogenesis. MCPyV circALTOs are enriched in exosomes derived from VP-MCC lines and circALTO-transfected 293T cells, and purified exosomes can mediate ALTO expression and transcriptional activation in MCPyV-negative cells. The related trichodysplasia spinulosa polyomavirus (TSPyV) also expresses a circALTO that can be detected in infected tissues and produces ALTO protein in cultured cells. Thus, human polyomavirus circRNAs are expressed in human tumors and infected tissues and express proteins that have the potential to modulate the infectious and tumorigenic properties of these viruses.

FOXM1 drives HPV+ HNSCC sensitivity to WEE1 inhibition.

Head and neck squamous cell carcinoma (HNSCC) associated with high-risk human papilloma virus (HPV) infection is a growing clinical problem. The WEE1 kinase inhibitor AZD1775 (WEE1i) overrides cell cycle checkpoints and is being studied in HNSCC regimens. We show that the HPV16 E6/E7 oncoproteins sensitize HNSCC cells to single-agent WEE1i treatment through activation of a FOXM1-CDK1 circuit that drives mitotic gene expression and DNA damage. An isogenic cell system indicated that E6 largely accounts for these phenotypes in ways that extend beyond p53 inactivation. A targeted genomic analysis implicated FOXM1 signaling downstream of E6/E7 expression and analyses of primary tumors and The Cancer Genome Atlas (TCGA) data revealed an activated FOXM1-directed promitotic transcriptional signature in HPV+ versus HPV- HNSCCs. Finally, we demonstrate the causality of FOXM1 in driving WEE1i sensitivity. These data suggest that elevated basal FOXM1 activity predisposes HPV+ HNSCC to WEE1i-induced toxicity and provide mechanistic insights into WEE1i and HPV+ HNSCC therapies.

High-risk human papillomavirus oncogenes disrupt the Fanconi anemia DNA repair pathway by impairing localization and de-ubiquitination of FancD2.

Persistent expression of high-risk HPV oncogenes is necessary for the development of anogenital and oropharyngeal cancers. Here, we show that E6/E7 expressing cells are hypersensitive to DNA crosslinking agent cisplatin and have defects in repairing DNA interstrand crosslinks (ICL). Importantly, we elucidate how E6/E7 attenuate the Fanconi anemia (FA) DNA crosslink repair pathway. Though E6/E7 activated the pathway by increasing FancD2 monoubiquitination and foci formation, they inhibited the completion of the repair by multiple mechanisms. E6/E7 impaired FancD2 colocalization with double-strand breaks (DSB), which subsequently hindered the recruitment of the downstream protein Rad51 to DSB in E6 cells. Further, E6 expression caused delayed FancD2 de-ubiquitination, an important process for effective ICL repair. Delayed FancD2 de-ubiquitination was associated with the increased chromatin retention of FancD2 hindering USP1 de-ubiquitinating activity, and persistently activated ATR/CHK-1/pS565 FancI signaling. E6 mediated p53 degradation did not hamper the cell cycle specific process of FancD2 modifications but abrogated repair by disrupting FancD2 de-ubiquitination. Further, E6 reduced the expression and foci formation of Palb2, which is a repair protein downstream of FancD2. These findings uncover unique mechanisms by which HPV oncogenes contribute to genomic instability and the response to cisplatin therapies.

Merkel cell polyomavirus Tumor antigens expressed in Merkel cell carcinoma function independently of the ubiquitin ligases Fbw7 and ß-TrCP.

Merkel cell polyomavirus (MCPyV) accounts for 80% of all Merkel cell carcinoma (MCC) cases through expression of two viral oncoproteins: the truncated large T antigen (LT-t) and small T antigen (ST). MCPyV ST is thought to be the main driver of cellular transformation and has also been shown to increase LT protein levels through the activity of its Large-T Stabilization Domain (LSD). The ST LSD was reported to bind and sequester several ubiquitin ligases, including Fbw7 and ß-TrCP, and thereby stabilize LT-t and several other Fbw7 targets including c-Myc and cyclin E. Therefore, the ST LSD is thought to contribute to transformation by promoting the accumulation of these oncoproteins. Targets of Fbw7 and ß-TrCP contain well-defined, conserved, phospho-degrons. However, as neither MCPyV LT, LT-t nor ST contain the canonical Fbw7 phospho-degron, we sought to further investigate the proposed model of ST stabilization of LT-t and transformation. In this study, we provide several lines of evidence that fail to support a specific interaction between MCPyV T antigens and Fbw7 or ß-TrCP by co-immunoprecipitation or functional consequence. Although MCPyV ST does indeed increase LT protein levels through its Large-T Stabilization domain (LSD), this is accomplished independently of Fbw7. Therefore, our study indicates a need for further investigation into the role and mechanism(s) of MCPyV T antigens in viral replication, latency, transformation, and tumorigenesis.

Analysis of Memory B-Cell Responses Reveals Suboptimal Dosing Schedule of a Licensed Vaccine.

Current guidance recommends that adolescents receive a 2-dose human papillomavirus (HPV) vaccine, whereas young adults and immunocompromised persons receive 3 doses. We examined secondary responses of vaccine-elicited memory B cells (Bmem) in naive women receiving 3 doses of the quadrivalent HPV vaccine to understand the quality of B-cell memory generated by this highly effective vaccine. Unexpectedly, we observed a lower Bmem response rate and magnitude of Bmem responses to the third dose than to a booster dose administered at month 24. Moreover, high titers of antigen-specific serum antibody at vaccination inversely correlated with Bmem responses. As the purpose of additional doses/boosters is to stimulate Bmem to rapidly boost antibody levels, these results indicate the timing of the third dose is suboptimal and lend support to a 2-dose HPV vaccine for young adults. Our findings also indicate more broadly that multidose vaccine schedules should be rationally determined on the basis of Bmem responses.

High-Risk Alphapapillomavirus Oncogenes Impair the Homologous Recombination Pathway.

Persistent high-risk genus human Alphapapillomavirus (HPV) infections cause nearly every cervical carcinoma and a subset of tumors in the oropharyngeal tract. During the decades required for HPV-associated tumorigenesis, the cellular genome becomes significantly destabilized. Our analysis of cervical tumors from four separate data sets found a significant upregulation of the homologous-recombination (HR) pathway genes. The increased abundance of HR proteins can be replicated in primary cells by expression of the two HPV oncogenes (E6 and E7) required for HPV-associated transformation. HPV E6 and E7 also enhanced the ability of HR proteins to form repair foci, and yet both E6 and E7 reduce the ability of the HR pathway to complete double-strand break (DSB) repair by about 50%. The HPV oncogenes hinder HR by allowing the process to begin at points in the cell cycle when the lack of a sister chromatid to serve as a homologous template prevents completion of the repair. Further, HPV E6 attenuates repair by causing RAD51 to be mislocalized away from both transient and persistent DSBs, whereas HPV E7 is only capable of impairing RAD51 localization to transient lesions. Finally, we show that the inability to robustly repair DSBs causes some of these lesions to be more persistent, a phenotype that correlates with increased integration of episomal DNA. Together, these data support our hypothesis that HPV oncogenes contribute to the genomic instability observed in HPV-associated malignancies by attenuating the repair of damaged DNA.IMPORTANCE This study expands the understanding of HPV biology, establishing a direct role for both HPV E6 and E7 in the destabilization of the host genome by blocking the homologous repair of DSBs. To our knowledge, this is the first time that both viral oncogenes were shown to disrupt this DSB repair pathway. We show that HPV E6 and E7 allow HR to initiate at an inappropriate part of the cell cycle. The mislocalization of RAD51 away from DSBs in cells expressing HPV E6 and E7 hinders HR through a distinct mechanism. These observations have broad implications. The impairment of HR by HPV oncogenes may be targeted for treatment of HPV+ malignancies. Further, this attenuation of repair suggests HPV oncogenes may contribute to tumorigenesis by promoting the integration of the HPV genome, a common feature of HPV-transformed cells. Our data support this idea since HPV E6 stimulates the integration of episomes.

Minimally Mutated HIV-1 Broadly Neutralizing Antibodies to Guide Reductionist Vaccine Design.

An optimal HIV vaccine should induce broadly neutralizing antibodies (bnAbs) that neutralize diverse viral strains and subtypes. However, potent bnAbs develop in only a small fraction of HIV-infected individuals, all contain rare features such as extensive mutation, insertions, deletions, and/or long complementarity-determining regions, and some are polyreactive, casting doubt on whether bnAbs to HIV can be reliably induced by vaccination. We engineered two potent VRC01-class bnAbs that minimized rare features. According to a quantitative features frequency analysis, the set of features for one of these minimally mutated bnAbs compared favorably with all 68 HIV bnAbs analyzed and was similar to antibodies elicited by common vaccines. This same minimally mutated bnAb lacked polyreactivity in four different assays. We then divided the minimal mutations into spatial clusters and dissected the epitope components interacting with those clusters, by mutational and crystallographic analyses coupled with neutralization assays. Finally, by synthesizing available data, we developed a working-concept boosting strategy to select the mutation clusters in a logical order following a germline-targeting prime. We have thus developed potent HIV bnAbs that may be more tractable vaccine goals compared to existing bnAbs, and we have proposed a strategy to elicit them. This reductionist approach to vaccine design, guided by antibody and antigen structure, could be applied to design candidate vaccines for other HIV bnAbs or protective Abs against other pathogens.

Correction: Minimally Mutated HIV-1 Broadly Neutralizing Antibodies to Guide Reductionist Vaccine Design.

[This corrects the article DOI: 10.1371/journal.ppat.1005815.].

Type-dependent association between risk of cervical intraepithelial neoplasia and viral load of oncogenic human papillomavirus types other than types 16 and 18.

Studies of the clinical relevance of human papillomavirus (HPV) DNA load have focused mainly on HPV16 and HPV18. Data on other oncogenic types are rare. Study subjects were women enrolled in the atypical squamous cells of undetermined significance (ASC-US) and low-grade squamous intraepithelial lesion (LSIL) triage study who had ≥1 of 11 non-HPV16/18 oncogenic types detected during a 2-year follow-up at 6-month intervals. Viral load measurements were performed on the first type-specific HPV-positive specimens. The association of cervical intraepithelial neoplasia grades 2-3 (CIN2/3) with type-specific HPV DNA load was assessed with discrete-time Cox regression. Overall, the increase in the cumulative risk of CIN2/3 per 1 unit increase in log10 -transformed viral load was statistically significant for four types within species 9 including HPV31 (adjusted hazard ratio [HR adjusted ] = 1.32: 95% confidence interval [CI], 1.14-1.52), HPV35 (HR adjusted = 1.47; 95% CI, 1.23-1.76), HPV52 (HR adjusted = 1.14; 95% CI, 1.01-1.30) and HPV58 (HR adjusted = 1.49; 95% CI, 1.23-1.82). The association was marginally significant for HPV33 (species 9) and HPV45 (species 7) and was not appreciable for other types. The per 1 log10 -unit increase in viral load of a group of species 9 non-HPV16 oncogenic types was statistically significantly associated with risk of CIN2/3 for women with a cytologic diagnosis of within normal limits, ASC-US, or LSIL at the first HPV-positive visit but not for those with high-grade SIL. Findings suggest that the viral load-associated risk of CIN2/3 is type-dependent, and mainly restricted to the species of HPV types related to HPV16, which shares this association.

Viral oncoprotein antibodies as a marker for recurrence of Merkel cell carcinoma: A prospective validation study.

BACKGROUND: Merkel cell carcinoma (MCC) is an aggressive skin cancer with a recurrence rate of >40%. Of the 2000 MCC cases per year in the United States, most are caused by the Merkel cell polyomavirus (MCPyV). Antibodies to MCPyV oncoprotein (T-antigens) have been correlated with MCC tumor burden. The present study assesses the clinical utility of MCPyV-oncoprotein antibody titers for MCC prognostication and surveillance. METHODS: MCPyV-oncoprotein antibody detection was optimized in a clinical laboratory. A cohort of 219 patients with newly diagnosed MCC were followed prospectively (median follow-up, 1.9 years). Among the seropositive patients, antibody titer and disease status were serially tracked. RESULTS: Antibodies to MCPyV oncoproteins were rare among healthy individuals (1%) but were present in most patients with MCC (114 of 219 patients [52%]; P < .01). Seropositivity at diagnosis independently predicted decreased recurrence risk (hazard ratio, 0.58; P = .04) in multivariate analyses adjusted for age, sex, stage, and immunosuppression. After initial treatment, seropositive patients whose disease did not recur had rapidly falling titers that became negative by a median of 8.4 months. Among seropositive patients who underwent serial evaluation (71 patients; 282 time points), an increasing oncoprotein titer had a positive predictive value of 66% for clinically evident recurrence, whereas a decreasing titer had a negative predictive value of 97%. CONCLUSIONS: Determination of oncoprotein antibody titer assists in the clinical management of patients with newly diagnosed MCC by stratifying them into a higher risk seronegative cohort, in which radiologic imaging may play a more prominent role, and into a lower risk seropositive cohort, in which disease status can be tracked in part by oncoprotein antibody titer. Cancer 2017;123:1464-1474. © 2016 American Cancer Society.

ß-HPV 5 and 8 E6 disrupt homology dependent double strand break repair by attenuating BRCA1 and BRCA2 expression and foci formation.

Recent work has explored a putative role for the E6 protein from some ß-human papillomavirus genus (ß-HPVs) in the development of non-melanoma skin cancers, specifically ß-HPV 5 and 8 E6. Because these viruses are not required for tumor maintenance, they are hypothesized to act as co-factors that enhance the mutagenic capacity of UV-exposure by disrupting the repair of the resulting DNA damage. Supporting this proposal, we have previously demonstrated that UV damage signaling is hindered by ß-HPV 5 and 8 E6 resulting in an increase in both thymine dimers and UV-induced double strand breaks (DSBs). Here we show that ß-HPV 5 and 8 E6 further disrupt the repair of these DSBs and provide a mechanism for this attenuation. By binding and destabilizing a histone acetyltransferase, p300, ß-HPV 5 and 8 E6 reduce the enrichment of the transcription factor at the promoter of two genes critical to the homology dependent repair of DSBs (BRCA1 and BRCA2). The resulting diminished BRCA1/2 transcription not only leads to lower protein levels but also curtails the ability of these proteins to form repair foci at DSBs. Using a GFP-based reporter, we confirm that this reduced foci formation leads to significantly diminished homology dependent repair of DSBs. By deleting the p300 binding domain of ß-HPV 8 E6, we demonstrate that the loss of robust repair is dependent on viral-mediated degradation of p300 and confirm this observation using a combination of p300 mutants that are ß-HPV 8 E6 destabilization resistant and p300 knock-out cells. In conclusion, this work establishes an expanded ability of ß-HPV 5 and 8 E6 to attenuate UV damage repair, thus adding further support to the hypothesis that ß-HPV infections play a role in skin cancer development by increasing the oncogenic potential of UV exposure.

Human papillomaviruses: a growing field.

A combination of functional studies on human papillomavirus (HPV) oncoproteins and epidemiological studies on persistence of HPV infection firmly established a role for HPV in the etiology of cervical cancers. Understanding the viral life cycle of HPVs has been more difficult. In this issue of Genes & Development, Wang et al. (pp. 181 - 194) describe an efficient method to propagate infectious HPV in differentiating epithelium, providing clear evidence for temporal separation of viral and cellular replication.

Variant-specific persistence of infections with human papillomavirus Types 31, 33, 45, 56 and 58 and risk of cervical intraepithelial neoplasia.

In our previous study of the etiologic role of oncogenic human papillomavirus (HPV) types other than HPV16 and 18, we observed a significantly higher risk of cervical intraepithelial neoplasia Grades 2-3 (CIN2/3) associated with certain lineages of HPV types 31/33/45/56/58 [called high-risk (HR) variants] compared with non-HR variants. This study was to examine whether these intra-type variants differ in persistence of the infection and persistence-associated risk of CIN2/3. Study subjects were women who had any of HPV types 31/33/45/56/58 newly detected during a 2-year follow-up with 6-month intervals. For each type, the first positive sample was used for variant characterization. The association of reverting-to-negativity with group of the variants and CIN2/3 with length of positivity was assessed using discrete Cox regression and logistic regression, respectively. Of the 598 newly detected, type-specific HPV infections, 312 became undetectable during follow-up. Infections with HR, compared with non-HR, variants were marginally more likely to become negative [adjusted hazard ratio = 1.3; 95% confidence interval (CI), 0.9-1.8]. The adjusted odds ratio associating with the development of CIN2/3 was 3.0 (95% CI, 1.2-7.4) for persistent infections with HR variants for 6 months and 10.0 (95% CI, 3.8-38.0) for persistent infections with HR variants for 12-18 months as compared with the first positive detection of HR variants. Among women with non-HR variants, there were no appreciable differences in risk of CIN2/3 by length of positivity. Findings suggest that the lineage-associated risk of CIN2/3 was not mediated through a prolonged persistent infection, but oncogenic heterogeneity of the variants.

Re-detection vs. new acquisition of high-risk human papillomavirus in mid-adult women.

To understand high-risk (hr) human papillomavirus (HPV) epidemiology in mid-adulthood, we assessed whether associations between incident detection of hrHPV DNA and recent sexual behavior differed according to whether or not there was serologic evidence of prior infection. From 2011 to 2012, we enrolled 409 women aged 30-50 years into a 6-month longitudinal study. We collected health and sexual behavior histories, enrollment sera for HPV antibody testing, and monthly self-collected vaginal swabs for HPV DNA genotyping. Generalized estimating equations logistic regression identified risk factors for type-specific incident hrHPV DNA, stratified by type-specific hrHPV serostatus at enrollment. Population attributable risks of hrHPV due to prior and recent exposure were estimated. When type-specific hrHPV serology was negative, recent sexual risk behavior was positively associated with incident hrHPV DNA (odds ratio in women reporting ≥3 recent sexual risk behaviors [e.g., new or multiple partners] vs. no recent sexual activity = 9.8, 95% CI: 2.4-40.6). No associations with recent sexual behavior were observed with positive type-specific hrHPV serology. Thirty percent of incident hrHPV DNA detection was attributable to prior infection (with positive serology) and 40% was attributable to recent sexual risk behavior (with negative serology). The proportion of incident hrHPV DNA detection attributable to recent sexual risk behavior decreased with increasing age. Among women with serologic evidence of prior infection, re-detection of the same hrHPV type is likely due to reactivation or intermittent detection of persistent infection. Without serologic evidence of prior infection, new detection is likely due to new acquisition or to intermittent detection of persisting infection.

Characteristics of memory B cells elicited by a highly efficacious HPV vaccine in subjects with no pre-existing immunity.

Licensed human papillomavirus (HPV) vaccines provide near complete protection against the types of HPV that most commonly cause anogenital and oropharyngeal cancers (HPV 16 and 18) when administered to individuals naive to these types. These vaccines, like most other prophylactic vaccines, appear to protect by generating antibodies. However, almost nothing is known about the immunological memory that forms following HPV vaccination, which is required for long-term immunity. Here, we have identified and isolated HPV 16-specific memory B cells from female adolescents and young women who received the quadrivalent HPV vaccine in the absence of pre-existing immunity, using fluorescently conjugated HPV 16 pseudoviruses to label antigen receptors on the surface of memory B cells. Antibodies cloned and expressed from these singly sorted HPV 16-pseudovirus labeled memory B cells were predominantly IgG (>IgA>IgM), utilized diverse variable genes, and potently neutralized HPV 16 pseudoviruses in vitro despite possessing only average levels of somatic mutation. These findings suggest that the quadrivalent HPV vaccine provides an excellent model for studying the development of B cell memory; and, in the context of what is known about memory B cells elicited by influenza vaccination/infection, HIV-1 infection, or tetanus toxoid vaccination, indicates that extensive somatic hypermutation is not required to achieve potent vaccine-specific neutralizing antibody responses.