Sirolimus and Other Mechanistic Target of Rapamycin Inhibitors Directly Activate Latent Pathogenic Human Polyomavirus Replication

The impact of DNA tumor viruses in low-to-middle income countries (LMICS): A literature review

DNA viruses are common in the human population and act as aetiological agents of cancer on a large scale globally. They include the human papillomaviruses (HPV), Epstein-Barr virus (EBV), Kaposi sarcoma-associated herpesvirus (KSHV), hepatitis viruses, and human polyomaviruses. Oncogenic viruses employ different mechanisms to induce cancer. Notably, cancer only develops in a minority of individuals who are infected, usually following protracted years of chronic infection. The human papillomaviruses (HPVs) are associated with the highest number of cancer cases, including cervical cancer and other epithelial malignancies. Hepatitis B virus (HBV) and the RNA virus hepatitis C (HCV) are significant contributors to hepatocellular cancer (HCC). Other oncoviruses include Epstein-Barr virus (EBV), Kaposi sarcoma-associated herpes virus (KSHV), human T-cell leukemia virus (HTLV-I), and Merkel cell polyomavirus (MCPyV). The identification of these infectious agents as aetiological agents for cancer has led to reductions in cancer incidence through preventive interventions such as HBV and HPV vaccination, HPV-DNA based cervical cancer screening, antiviral treatments for chronic HBV and HCV infections, and screening of blood for transfusion for HBV and HCV. Successful efforts to identify additional oncogenic viruses in human cancer may provide further understanding of the aetiology and development of cancer, and novel approaches for prevention and treatment. Cervical cancer, caused by HPV, is the leading gynaecological malignancy in LMICs, with high age-standardised incidence and mortality rates, HCC due to HBV is an important cause of cancer deaths, and the burden of other cancer attributable to infections continues to rise globally. Hence, cancers attributable to DNA viruses have become a significant global health challenge. These viruses hence warrant continued attention and interrogation as efforts to understand them further and device further preventive interventions are critical.

Casein kinase 1α mediates phosphorylation of the Merkel cell polyomavirus large T antigen for β-TrCP destruction complex interaction and subsequent degradation

Merkel cell polyomavirus (MCPyV) is a double-stranded tumor virus that is the main causative agent of Merkel cell carcinoma (MCC). The MCPyV large T antigen (LT), an essential viral DNA replication protein, maintains viral persistence by interacting with host Skp1-Cullin 1-F-box (SCF) E3 ubiquitin ligase complexes, which subsequently induces LT's proteasomal degradation, restricting MCPyV DNA replication. SCF E3 ubiquitin ligases require their substrates to be phosphorylated to bind them, utilizing phosphorylated serine residues as docking sites. The MCPyV LT unique region (MUR) is highly phosphorylated and plays a role in multiple host protein interactions, including SCF E3 ubiquitin ligases. Therefore, this domain highly governs LT stability. Though much work has been conducted to identify host factors that restrict MCPyV LT protein expression, the kinase(s) that cooperates with the SCF E3 ligase remains unknown. Here, we demonstrate that casein kinase 1 alpha (CK1α) negatively regulates MCPyV LT stability and LT-mediated replication by modulating interactions with the SCF β-TrCP. Specifically, we show that numerous CK1 isoforms (α, δ, ε) localize in close proximity to MCPyV LT through in situ proximity ligation assays (PLA) and CK1α overexpression mainly resulted in decreased MCPyV LT protein expression. Inhibition of CK1α using short hairpin RNA (shRNA) and treatment of a CK1α inhibitor or an mTOR inhibitor, TORKinib, resulted in decreased β-TrCP interaction with LT, increased LT expression, and enhanced MCPyV replication. The expression level of the CSNK1A1 gene transcripts is higher in MCPyV-positive MCC, suggesting a vital role of CK1α in limiting MCPyV replication required for establishing persistent infection.

IMPORTANCE

Merkel cell polyomavirus (MCPyV) large tumor antigen is a polyphosphoprotein and the phosphorylation event is required to modulate various functions of LT, including viral replication. Therefore, cellular kinase pathways are indispensable for governing MCPyV polyomavirus infection and life cycle in coordinating with the immunosuppression environment at disease onset. Understanding the regulation mechanisms of MCPyV replication by viral and cellular factors will guide proper prevention strategies with targeted inhibitors for MCPyV-associated Merkel cell carcinoma (MCC) patients, who currently lack therapies.

Mapping of Human Polyomavirus in Renal Cell Carcinoma Tissues

Worldwide, the incidence of renal cell carcinoma (RCC) is rising, accounting for approximately 2% of all cancer diagnoses and deaths. The etiology of RCC is still obscure. Here, we assessed the presence of HPyVs in paraffin-embedded tissue (FFPE) resected tissue from patients with RCC by using different molecular techniques. Fifty-five FFPE tissues from 11 RCC patients were included in this study. Consensus and HPyV-specific primers were used to screen for HPyVs. Both PCR approaches revealed that HPyV is frequently detected in the tissues of RCC kidney resections. A total of 78% (43/55) of the tissues tested were positive for at least one HPyV (i.e., MCPyV, HPyV6, HPyV7, BKPyV, JCPyV, or WUyV). Additionally, 25 tissues (45%) were positive for only one HPyV, 14 (25%) for two HPyVs, 3 (5%) for three HPyVs, and 1 one (1%) tissue specimen was positive for four HPyVs. Eleven (20%) RCC specimens were completely devoid of HPyV sequences. MCPyV was found in 24/55 RCC tissues, HPyV7 in 19, and HPyV6 in 8. The presence of MCPyV and HPyV6 was confirmed by specific FISH or RNA-ISH. In addition, we aimed to confirm HPyV gene expression by IHC. Our results strongly indicate that these HPyVs infect RCC and nontumor tissues, possibly indicating that kidney tissues serve as a reservoir for HPyV latency. Whether HPyVs possibly contribute to the etiopathogenesis of RCC remains to be elucidated.

mTOR inhibitors a potential predisposing factor for chronic hepatitis E: Results from the prospective collaborative CHES study (Chronic Hepatitis EScreening in patients with immune impairment and increased transaminases levels)

BACKGROUND

Chronic hepatitis E virus (HEV) in persons with immune impairment has a progressive course leading to a rapid progression to liver cirrhosis. However, prospective data on chronic HEV is scarce. The aim of this study was to determine the prevalence and risk factors for chronic HEV infection in subjects with immune dysfunction and elevated liver enzymes.

PATIENTS AND METHODS

CHES is a multicenter prospective study that included adults with elevated transaminases values for at least 6 months and any of these conditions: transplant recipients, HIV infection, haemodialysis, liver cirrhosis, and immunosuppressant therapy. Anti-HEV IgG/IgM (Wantai ELISA) and HEV-RNA by an automated highly sensitive assay (Roche diagnostics) were performed in all subjects. In addition, all participants answered an epidemiological survey.

RESULTS

Three hundred and eighty-one patients were included: 131 transplant recipients, 115 cirrhosis, 51 HIV-infected subjects, 87 on immunosuppressants, 4 hemodialysis. Overall, 210 subjects were on immunosuppressants. Anti-HEV IgG was found in 94 (25.6%) subjects with similar rates regardless of the cause for immune impairment. HEV-RNA was positive in 6 (1.6%), all of them transplant recipients, yielding a rate of chronic HEV of 5.8% among solid-organ recipients. In the transplant population, only therapy with mTOR inhibitors was independently associated with risk of chronic HEV, whereas also ALT values impacted in the general model.

CONCLUSIONS

Despite previous abnormal transaminases values, chronic HEV was only observed among solid-organ recipients. In this population, the rate of chronic HEV was 5.8% and only therapy with mTOR inhibitors was independently associated with chronic hepatitis E.

Phosphorylation of Human Polyomavirus Large and Small T Antigens: An Ignored Research Field

Protein phosphorylation and dephosphorylation are the most common post-translational modifications mediated by protein kinases and protein phosphatases, respectively. These reversible processes can modulate the function of the target protein, such as its activity, subcellular localization, stability, and interaction with other proteins. Phosphorylation of viral proteins plays an important role in the life cycle of a virus. In this review, we highlight biological implications of the phosphorylation of the monkey polyomavirus SV40 large T and small t antigens, summarize our current knowledge of the phosphorylation of these proteins of human polyomaviruses, and conclude with gaps in the knowledge and a proposal for future research directions.

Regulation of Transcriptional Activity of Merkel Cell Polyomavirus Large T-Antigen by PKA-Mediated Phosphorylation

Merkel cell polyomavirus (MCPyV) is the major cause of Merkel cell carcinoma (MCC), an aggressive skin cancer. MCPyV large T-antigen (LTag) and small T-antigen (sTag) are the main oncoproteins involved in MCPyV-induced MCC. A hallmark of MCPyV-positive MCC cells is the expression of a C-terminal truncated LTag. Protein kinase A (PKA) plays a fundamental role in a variety of biological processes, including transcription by phosphorylating and thereby regulating the activity of transcription factors. As MCPyV LTag has been shown to be phosphorylated and acts as a transcription factor for the viral early and late promoter, we investigated whether LTag can be phosphorylayted by PKA, and whether this affects the transcript activity of LTag. Using a phosphorylation prediction algorithm, serine 191, 203, and 265 were identified as putative phosphorylation sites for PKA. Mass spectrometry of in vitro PKA-phosphorylated peptides confirmed phosphorylation of S203 and S265, but not S191. Full-length LTag inhibited early and late promoter activity of MCPyV, whereas the truncated MKL2 LTag variant stimulated both promoters. Single non-phosphorylable, as well as phosphomimicking mutations did not alter the inhibitory effect of full-length LTag. However, the non-phosphorylable mutations abrogated transactivation of the MCPyV promoters by MKL2 LTag, whereas phosphomimicking substitutions restored the ability of MKL2 LTag to activate the promoters. Triple LTag and MKL2 LTag mutants had the same effect as the single mutants. Activation of the PKA signaling pathway did not enhance MCPyV promoter activity, nor did it affect LTag expression levels in MCPyV-positive Merkel cell carcinoma (MCC) cells. Our results show that phosphorylation of truncated LTag stimulates viral promoter activity, which may contribute to higher levels of the viral oncoproteins LTag and sTag. Interfering with PKA-induced LTag phosphorylation/activity may be a therapeutic strategy to treat MCPyV-positive MCC patients.

Merkel cell polyomavirus small T antigen is a viral transcription activator that is essential for viral genome maintenance

Merkel cell polyomavirus (MCV) is a small DNA tumor virus that persists in human skin and causes Merkel cell carcinoma (MCC) in immunocompromised individuals. The multi-functional protein MCV small T (sT) activates viral DNA replication by stabilizing large T (LT) and promotes cell transformation through the LT stabilization domain (LTSD). Using MCVΔsT, a mutant MCV clone that ablates sT, we investigated the role of sT in MCV genome maintenance. sT was dispensable for initiation of viral DNA replication, but essential for maintenance of the MCV genome and activation of viral early and late gene expression for progression of the viral lifecycle. Furthermore, in phenotype rescue studies, exogenous sT activated viral DNA replication and mRNA expression in MCVΔsT through the LTSD. While exogenous LT expression, which mimics LT stabilization, increased viral DNA replication, it did not activate viral mRNA expression. After cataloging transcriptional regulator proteins by proximity-based MCV sT-host protein interaction analysis, we validated LTSD-dependent sT interaction with four transcriptional regulators: Cux1, c-Jun, BRD9, and CBP. Functional studies revealed Cux1 and c-Jun as negative regulators, and CBP and BRD9 as positive regulators of MCV transcription. CBP inhibitor A-485 suppressed sT-induced viral gene activation in replicating MCVΔsT and inhibited early gene expression in MCV-integrated MCC cells. These results suggest that sT promotes viral lifecycle progression by activating mRNA expression and capsid protein production through interaction with the transcriptional regulators. This activity is essential for MCV genome maintenance, suggesting a critical role of sT in MCV persistence and MCC carcinogenesis.

Clinicopathological features, MCPyV status and outcomes of Merkel cell carcinoma in solid-organ transplant recipients: a retrospective, multicentre cohort study

BACKGROUND

The proportion of Merkel cell carcinomas (MCCs) in solid-organ transplant recipients (SOTR) harbouring Merkel cell polyomavirus (MCPyV) is unknown, as are factors affecting their outcomes.

OBJECTIVE

To describe clinicopathological features of MCC in SOTR, investigate the tumoral MCPyV-status and identify factors associated with tumour outcomes.

METHODS

Retrospective, international, cohort-study. MCPyV-status was investigated by immunohistochemistry and polymerase chain reaction.

RESULTS

A total of 30 SOTR and 44 consecutive immunocompetent patients with MCC were enrolled. SOTR were younger at diagnosis (69 vs. 78 years, P < 0.001). Thirty-three percent of SOTR MCCs were MCPyV-positive vs. 91% of immunocompetent MCCs (P = 0.001). Solid-organ transplantation was associated with an increased cumulative incidence of progression (SHR: 3.35 [1.57-7.14], P = 0.002), MCC-specific mortality (SHR: 2.55 [1.07-6.06], P = 0.034) and overall mortality (HR: 3.26 [1.54-6.9], P = 0.002). MCPyV-positivity and switching to an mTOR inhibitor (mTORi) after MCC diagnosis were associated with an increased incidence of progression (SHR: 4.3 [1.5-13], P = 0.008 and SHR: 3.6 [1.1-12], P = 0.032 respectively) in SOTR.

LIMITATIONS

Retrospective design and heterogeneity of SOTR cohort.

CONCLUSIONS

MCPyV appears to play a less prominent role in the aetiopathogenesis of MCC in SOTR. SOTR have a worse prognosis than their immunocompetent counterparts and switching to an mTORi after the diagnosis of MCC does not improve progression.

Ischemia-Reperfusion Injury and Immunosuppressants Promote Polyomavirus Replication Through Common Molecular Mechanisms

Background

BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) causes renal allograft dysfunction and graft loss. However, the mechanism of BKPyV replication after kidney transplantation is unclear. Clinical studies have demonstrated that immunosuppressants and renal ischemia–reperfusion injury (IRI) are risk factors for BKPyV infection. Studying the pathogenic mechanism of BKPyV is limited by the inability of BKPyV to infect the animal. Mouse polyomavirus (MPyV) is a close homolog of BKPyV. We used a model of MPyV infection to investigate the core genes and underlying mechanism of IRI and immunosuppressants to promote polyomavirus replication.

Materials and Methods

One-day-old male C57BL/6 mice were intraperitoneally injected with MPyV. At week 9 post-infection, all mice were randomly divided into IRI, immunosuppressant, and control groups and treated accordingly. IRI was established by clamping the left renal pedicle. Subsequently, kidney specimens were collected for detecting MPyV DNA, histopathological observation, and high-throughput RNA sequencing. Weighted gene correlation network analysis (WGCNA), protein–protein interaction network analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to screen for core genes and common signaling pathways involved in promoting MPyV replication by IRI and immunosuppressants.

Results

After primary infection, MPyV established persistent infection in kidneys and subsequently was significantly increased by IRI or immunosuppressant treatment individually. In the IRI group, viral loads peaked on day 3 in the left kidney, which were significantly higher than those in the right kidney and the control group. In the immunosuppressant group, viral loads in the left kidney were significantly increased on day 3, which were significantly higher than those in the control group. Protein–protein interaction network analysis and WGCNA screened complement C3, epidermal growth factor receptor (EGFR), and FN1 as core genes. Pathway enrichment analysis based on the IRI- or immunosuppressant-related genes selected by WGCNA indicated that the NF-κB signaling pathway was the main pathway involved in promoting MPyV replication. The core genes were further confirmed using published datasets GSE47199 and GSE75693 in human polyomavirus-associated nephropathy.

Conclusions

Our study demonstrated that IRI and immunosuppressants promote polyomavirus replication through common molecular mechanisms. In future studies, knockdown or specific inhibition of C3, EGFR, FN1, and NF-κB signaling pathway will further validate their critical roles in promoting polyomavirus replication.

Spectrum of Nonkeratinocyte Skin Cancer Risk Among Solid Organ Transplant Recipients in the US

Importance

Nonkeratinocyte skin cancers are an important cause of morbidity and mortality for immunosuppressed solid organ transplant recipients (SOTRs), but the spectrum of disease and risk factor characteristics are unknown.

Objective

To characterize the spectrum of disease and risk factors for common and rare nonkeratinocyte skin cancers in SOTRs.

Design, Setting, and Participants

This population-based cohort study included 444 497 SOTRs who underwent a transplant in the US between January 1, 1987, and December 31, 2017, using linked data from the national transplant registry and 32 cancer registries. Data analysis was conducted from April 1, 2021, to September 30, 2021.

Main Outcomes and Measures

Standardized incidence ratios (SIRs) were used to assess risk relative to the general population, and Poisson regression was used to evaluate risk factors.

Results

A total of 2380 nonkeratinocyte skin cancers were identified among 444 497 SOTRs (median age at transplant, 50 years; range, 0-96 years; 274 276 [61.7%] male; 272 241 [61.2%] non-Hispanic White). Melanoma was the most common cancer (1471 [61.8%]), followed by Merkel cell carcinoma (334 [14.0%]), Kaposi sarcoma (186 [7.8%]), sebaceous carcinoma (170 [7.1%]), and cutaneous lymphomas (108 [4.5%]). Risks were most strongly elevated for cancers associated with viruses, including Kaposi sarcoma (SIR, 20.5; 95% CI, 17.7-23.7), Merkel cell carcinoma (SIR, 16.2; 95% CI, 14.5-18.1), and extranodal natural killer/T-cell lymphoma (SIR, 44.3; 95% CI, 5.37-160). Risks were also significantly elevated for sebaceous carcinoma (SIR, 15.2; 95% CI, 13.0-17.7), anaplastic large cell lymphoma (SIR, 6.82; 95% CI, 4.53-9.85), and diffuse large B-cell lymphoma (SIR, 5.17; 95% CI, 3.28-7.76). Several characteristics were independently associated with greater risk for multiple skin cancer types, including male sex, older age at transplant, factors associated with UV radiation exposure (non-Hispanic White race and ethnicity, living in an area with higher UV radiation exposure, and posttransplant diagnosis of keratinocyte carcinoma), and increasing time since transplantation. Treatment with mammalian target of rapamycin inhibitors was associated with reduced melanoma incidence (incidence rate ratio, 0.75; 95% CI, 0.57-0.98). A total of 847 skin cancers (39.4%) occurred on the head and neck.

Conclusions and Relevance

The findings of this cohort study suggest that viruses, UV radiation exposure, and immunosuppression are associated with the development of skin cancer in SOTRs. Certain high-risk subgroups may benefit from increased skin surveillance, and treatment with mammalian target of rapamycin inhibitors could be effective for melanoma chemoprevention in the transplant population.

Replication Kinetics for a Reporter Merkel Cell Polyomavirus

Merkel cell polyomavirus (MCV) causes one of the most aggressive human skin cancers, but laboratory studies on MCV replication have proven technically difficult. We report the first recombinase-mediated MCV minicircle (MCVmc) system that generates high levels of circularized virus, allowing facile MCV genetic manipulation and characterization of viral gene expression kinetics during replication. Mutations to Fbw7, Skp2, β-TrCP and hVam6p interaction sites, or to the stem loop sequence for the MCV-encoded miRNA precursor, markedly increase viral replication, whereas point mutation to an origin-binding site eliminates active virus replication. To further increase the utility of this system, an mScarlet fusion protein was inserted into the VP1 c-terminus to generate a non-infectious reporter virus for studies on virus kinetics. When this reporter virus genome is heterologously expressed together with MCV VP1 and VP2, virus-like particles are generated. The reporter virus genome is encapsidated and can be used at lower biosafety levels for one-round infection studies. Our findings reveal that MCV has multiple, self-encoded viral restriction mechanisms to promote viral latency over lytic replication, and these mechanisms are now amenable to examination using a recombinase technology.

Functional Domains of the Early Proteins and Experimental and Epidemiological Studies Suggest a Role for the Novel Human Polyomaviruses in Cancer

As their name indicates, polyomaviruses (PyVs) can induce tumors. Mouse PyV, hamster PyV and raccoon PyV have been shown to cause tumors in their natural host. During the last 30 years, 15 PyVs have been isolated from humans. From these, Merkel cell PyV is classified as a Group 2A carcinogenic pathogen (probably carcinogenic to humans), whereas BKPyV and JCPyV are class 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer. Although the other PyVs recently detected in humans (referred to here as novel HPyV; nHPyV) share many common features with PyVs, including the viral oncoproteins large tumor antigen and small tumor antigen, as their role in cancer is questioned. This review discusses whether the nHPyVs may play a role in cancer based on predicted and experimentally proven functions of their early proteins in oncogenic processes. The functional domains that mediate the oncogenic properties of early proteins of known PyVs, that can cause cancer in their natural host or animal models, have been well characterized and we examined whether these functional domains are conserved in the early proteins of the nHPyVs and presented experimental evidence that these conserved domains are functional. Furthermore, we reviewed the literature describing the detection of nHPyV in human tumors.

PI3K/AKT/mTOR Signaling Pathway Is Required for JCPyV Infection in Primary Astrocytes

Astrocytes are a main target of JC polyomavirus (JCPyV) in the central nervous system (CNS), where the destruction of these cells, along with oligodendrocytes, leads to the fatal disease progressive multifocal leukoencephalopathy (PML). There is no cure currently available for PML, so it is essential to discover antivirals for this aggressive disease. Additionally, the lack of a tractable in vivo models for studying JCPyV infection makes primary cells an accurate alternative for elucidating mechanisms of viral infection in the CNS. This research to better understand the signaling pathways activated in response to JCPyV infection reveals and establishes the importance of the PI3K/AKT/mTOR signaling pathway in JCPyV infection in primary human astrocytes compared to transformed cell lines. Using RNA sequencing and chemical inhibitors to target PI3K, AKT, and mTOR, we have demonstrated the importance of this signaling pathway in JCPyV infection of primary astrocytes not observed in transformed cells. Collectively, these findings illuminate the potential for repurposing drugs that are involved with inhibition of the PI3K/AKT/mTOR signaling pathway and cancer treatment as potential therapeutics for PML, caused by this neuroinvasive virus.

Chk1 and the Host Cell DNA Damage Response as a Potential Antiviral Target in BK Polyomavirus Infection

The human BK polyomavirus (BKPyV) is latent in the kidneys of most adults, but can be reactivated in immunosuppressed states, such as following renal transplantation. If left unchecked, BK polyomavirus nephropathy (PyVAN) and possible graft loss may result from viral destruction of tubular epithelial cells and interstitial fibrosis. When coupled with regular post-transplant screening, immunosuppression reduction has been effective in limiting BKPyV viremia and the development of PyVAN. Antiviral drugs that are safe and effective in combating BKPyV have not been identified but would be a benefit in complementing or replacing immunosuppression reduction. The present study explores inhibition of the host DNA damage response (DDR) as an antiviral strategy. Immunohistochemical and immunofluorescent analyses of PyVAN biopsies provide evidence for stimulation of a DDR in vivo. DDR pathways were also stimulated in vitro following BKPyV infection of low-passage human renal proximal tubule epithelial cells. The role of Chk1, a protein kinase known to be involved in the replication stress-induced DDR, was examined by inhibition with the small molecule LY2603618 and by siRNA-mediated knockdown. Inhibition of Chk1 resulted in decreased replication of BKPyV DNA and viral spread. Activation of mitotic pathways was associated with the reduction in BKPyV replication. Chk1 inhibitors that are found to be safe and effective in clinical trials for cancer should also be evaluated for antiviral activity against BKPyV.

Targeting nucleotide metabolism as the nexus of viral infections, cancer, and the immune response

Virus-infected cells and cancers share metabolic commonalities that stem from their insatiable need to replicate while evading the host immune system. These similarities include hijacking signaling mechanisms that induce metabolic rewiring in the host to up-regulate nucleotide metabolism and, in parallel, suppress the immune response. In both cancer and viral infections, the host immune cells and, specifically, lymphocytes augment nucleotide synthesis to support their own proliferation and effector functions. Consequently, established treatment modalities targeting nucleotide metabolism against cancers and virally infected cells may result in restricted immune response. Encouragingly, following the introduction of immunotherapy against cancers, multiple studies improved our understanding for improving antigen presentation to the immune system. We propose here that understanding the immune consequences of targeting nucleotide metabolism against cancers may be harnessed to optimize therapy against viral infections.

Pediatric trichodysplasia spinulosa: A report of 2 cases and review of the literature

Trichodysplasia spinulosa is a rare disorder caused by the ubiquitous trichodysplasia spinulosa-associated polyomavirus (TSPyV) and characterized clinically by predominately centrofacial, but often generalized, folliculocentric papules with protuberant keratinaceous spines. Although seroprevalence reaches up to 70% in adult populations, TSPyV causes clinical manifestations in a small percentage of patients who are immunosuppressed. Diagnosis can be made using typical clinical and histologic features, SV40T antibody immunostaining, and PCR of various tissues including the keratinaceous spine, skin, serum, urine, and CSF. Various topical and systemic medications have demonstrated variable success. Decreasing or discontinuing immunosuppression has also been shown to improve or alleviate clinical manifestations.

JCPyV VP1 Mutations in Progressive MultifocalLeukoencephalopathy: Altering Tropismor Mediating Immune Evasion?

Polyomaviruses are ubiquitous human pathogens that cause lifelong, asymptomatic infections in healthy individuals. Although these viruses are restrained by an intact immune system, immunocompromised individuals are at risk for developing severe diseases driven by resurgent viral replication. In particular, loss of immune control over JC polyomavirus can lead to the development of the demyelinating brain disease progressive multifocal leukoencephalopathy (PML). Viral isolates from PML patients frequently carry point mutations in the major capsid protein, VP1, which mediates virion binding to cellular glycan receptors. Because polyomaviruses are non-enveloped, VP1 is also the target of the host's neutralizing antibody response. Thus, VP1 mutations could affect tropism and/or recognition by polyomavirus-specific antibodies. How these mutations predispose susceptible individuals to PML and other JCPyV-associated CNS diseases remains to be fully elucidated. Here, we review the current understanding of polyomavirus capsid mutations and their effects on viral tropism, immune evasion, and virulence.

Merkel Cell Polyomavirus Large T Antigen Unique Domain Regulates Its Own Protein Stability and Cell Growth

Merkel cell polyomavirus (MCV) is the only known human oncogenic virus in the polyomaviridae family and the etiological agent of most Merkel cell carcinomas (MCC). MCC is an aggressive and highly metastatic skin cancer with a propensity for recurrence and poor prognosis. Large tumor antigen (LT), is an essential oncoprotein for MCV transcription, viral replication, and cancer cell proliferation. MCV LT is a short-lived protein that encodes a unique domain: MCV LT unique regions (MURs). These domains consist of phosphorylation sites that interact with multiple E3 ligases, thus limiting LT expression and consequently, viral replication. In this study, we show that MURs are necessary for regulating LT stability via multiple E3 ligase interactions, resulting in cell growth arrest. While expression of wild-type MCV LT induced a decrease in cellular proliferation, deletion of the MUR domains resulted in increased LT stability and cell proliferation. Conversely, addition of MURs to SV40 LT propagated E3 ligase interactions, which in turn, reduced SV40 LT stability and decreased cell growth activity. Our results demonstrate that compared to other human polyomaviruses (HPyVs), MCV LT has evolved to acquire the MUR domains that are essential for MCV LT autoregulation, potentially leading to viral latency and MCC.