Polyomavirus-associated Trichodysplasia spinulosa involves hyperproliferation, pRB phosphorylation and upregulation of p16 and p21

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.

Trichodysplasia spinulosa polyomavirus small T antigen synergistically modulates S6 protein translation and DNA damage response pathways to shape host cell environment

TSPyV is a viral agent linked to Trichodysplasia spinulosa, a disfiguring human skin disease which presents with hyperkeratotic spicule eruption in immunocompromised hosts. This proliferative disease state requires extensive modulation of the host cell environment. While the small T (sT) antigen of TSPyV has been postulated to cause widespread cellular perturbation, its specific substrates and their mechanistic connection are unclear. To identify the cellular substrates and pathways perturbed by TSPyV sT and propose a nuanced model that reconciles the multiple arms of TSPyV pathogenesis, changes in expression of several proteins and phospho-proteins in TSPyV sT expressing and TSPyV sT deletion mutant-expressing cell lysates were interrogated using Western blot assays. TSPyV sT expression exploits the DNA damage response pathway, by inducing hyperphosphorylation of ATM and 53BP1 and upregulation of BMI-1. Concurrently, sT dysregulates the S6 protein translation pathway via hyperphosphorylation of CDC2, p70 S6 kinase, S6, and PP1α. The S6^S244/247 and p-PP1α^T320 phospho-forms are points of overlap between the DDR and S6 networks. We propose a mechanistic rationale for previous reports positioning sT antigen as the key driver of TSPyV pathogenesis. We illuminate novel targets in the S6 and DDR pathways and recognize a potential synergy between these pathways. TSPyV may sensitize the cell to both unrestricted translation and genomic instability. This multi-pronged infection model may inform future therapeutic modalities against TSPyV and possibly other viruses with overlapping host substrates.

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.

Trichodysplasia spinulosa: a comprehensive review of the disease and its treatment

Trichodysplasia spinulosa (TS) is a rare dermatological disease caused by TS‐associated polyomavirus (TSPyV) in immunosuppressed patients. The seroprevalence of TSPyV in immunocompetent adults is high and the number of immunosuppressed patients developing TS remains low, suggesting that TS is underdiagnosed and/or that additional unknown factors are needed in order to develop TS. There is no well‐established treatment for TS, and to date a majority of reported cases have consequently received ineffective therapies, likely due to the unavailability of reviews and recommendations of treatments for TS. The few treatments reported in case reports to be effective include topical cidofovir 3%, reduction of immunosuppression and oral valganciclovir. In this comprehensive review, we present all published cases to date, together with a summary of all treatments for TS categorized by overall clinical efficacy, thus addressing this rare disease and what appears to be its clinically efficacious treatment.

Functional Analysis of Trichodysplasia Spinulosa-Associated Polyomavirus-Encoded Large T Antigen

Trichodysplasia spinulosa-associated polyomavirus (TSPyV or human polyomavirus 8) was identified from patients with trichodysplasia spinulosa, a rare skin disease affecting the faces of immunocompromised patients. Like other polyomaviruses, the TSPyV genome encodes a large T antigen (LT). However, the expression and functions of TSPyV LT in infected cells remain largely unknown. In the present study, we cloned a full-length TSPyV LT cDNA from cells transfected with the full-length of TSPyV LT DNA. Transfection study using green fluorescence protein-tagged LT expression plasmids showed that TSPyV LT was expressed in the nucleus of transfected cells. Analysis of deletion mutants identified a nuclear localization signal in TSPyV LT. Recombinant TSPyV LT exhibited an ATPase activity. TSPyV LT has a chitinase-like domain; however, no chitinase activity was detected. Immunoprecipitation assays revealed that TSPyV LT bound to retinoblastoma 1, but not to p53 in transfected cells. Expression of TSPyV LT in NIH3T3 cells induced colony formation in soft agar, suggesting its transformation activity. These data indicate that TSPyV LT may be associated with the pathogenesis of trichodysplasia spinulosa, which is a hyperplasia of keratinocytes in inner hair follicles.

Effect of the Large and Small T-Antigens of Human Polyomaviruses on Signaling Pathways

Viruses are intracellular parasites that require a permissive host cell to express the viral genome and to produce new progeny virus particles. However, not all viral infections are productive and some viruses can induce carcinogenesis. Irrespective of the type of infection (productive or neoplastic), viruses hijack the host cell machinery to permit optimal viral replication or to transform the infected cell into a tumor cell. One mechanism viruses employ to reprogram the host cell is through interference with signaling pathways. Polyomaviruses are naked, double-stranded DNA viruses whose genome encodes the regulatory proteins large T-antigen and small t-antigen, and structural proteins that form the capsid. The large T-antigens and small t-antigens can interfere with several host signaling pathways. In this case, we review the interplay between the large T-antigens and small t-antigens with host signaling pathways and the biological consequences of these interactions.

Primary trichodysplasia spinulosa polyomavirus infection in a kidney transplant child displaying virus-infected decoy cells in the urine

We report a case of primary trichodysplasia spinulosa (TS) infection in a kidney transplant child and describe for the first time the presence of degenerated TS-associated polyomavirus (TSPyV)-infected cells in a TS patient's urine that are morphologically different from BK or JC polyomavirus-infected decoy cells.

Polyomaviruses of the skin: integrating molecular and clinical advances in an emerging class of viruses

BACKGROUND

Human polyomaviruses (HPyVs) are small, nonenveloped, double-stranded DNA viruses that express tumour antigen proteins. Fourteen species of polyomaviruses have been discovered in humans, and since the 2008 discovery of the first cutaneous polyomavirus - Merkel cell polyomavirus (MCPyV) - six more species have been detected in the skin: trichodysplasia spinulosa-associated polyomavirus (TSPyV), HPyV6, HPyV7, HPyV9, HPyV10 and HPyV13. Of these cutaneous species, only MCPyV, TSPyV, HPyV6 and HPyV7 have been definitively associated with diseases of the skin, most commonly in immunocompromised individuals. MCPyV is a predominant aetiology in Merkel cell carcinomas. TSPyV is one of the aetiological factors of trichodysplasia spinulosa. HPyV6 and HPyV7 have been recently linked to pruritic skin eruptions. The roles of HPyV9, HPyV10 and HPyV13 in pathogenesis, if any, are still unknown, but their molecular features have provided some insight into their functional biology.

RESULTS

In this review, we summarize the known molecular mechanisms, clinical presentation and targeted therapies of each of the eight cutaneous HPyVs.

CONCLUSIONS

We hope that heightened awareness and clinical recognition of HPyVs will lead to increased reports of HPyV-associated diseases and, consequently, a more robust understanding of how to diagnose and treat these conditions.

The Biology and Clinical Features of Cutaneous Polyomaviruses

Human polyomaviruses are double-stand DNA viruses with a conserved genomic structure, yet they present with diverse tissue tropisms and disease presentations. Merkel cell polyomavirus, trichodysplasia spinulosa polyomavirus, human polyomavirus 6 and 7, and Malawi polyomavirus are shed from the skin, and Merkel cell polyomavirus, trichodysplasia spinulosa polyomavirus, human polyomavirus 6 and 7 have been linked to specific skin diseases. We present an update on the genomic and clinical features of these cutaneous polyomaviruses.

Human polyomaviruses and cancer: an overview

The name of the family Polyomaviridae, derives from the early observation that cells infected with murine polyomavirus induced multiple (poly) tumors (omas) in immunocompromised mice. Subsequent studies showed that many members of this family exhibit the capacity of mediating cell transformation and tumorigenesis in different experimental models. The transformation process mediated by these viruses is driven by viral pleiotropic regulatory proteins called T (tumor) antigens. Similar to other viral oncoproteins T antigens target cellular regulatory factors to favor cell proliferation, immune evasion and downregulation of apoptosis. The first two human polyomaviruses were isolated over 45 years ago. However, recent advances in the DNA sequencing technologies led to the rapid identification of additional twelve new polyomaviruses in different human samples. Many of these viruses establish chronic infections and have been associated with conditions in immunosuppressed individuals, particularly in organ transplant recipients. This has been associated to viral reactivation due to the immunosuppressant therapy applied to these patients. Four polyomaviruses namely, Merkel cell polyomavirus (MCPyV), Trichodysplasia spinulosa polyomavirus (TSPyV), John Cunningham Polyomavirus (JCPyV) and BK polyomavirus (BKPyV) have been associated with the development of specific malignant tumors. However, present evidence only supports the role of MCPyV as a carcinogen to humans. In the present review we present a summarized discussion on the current knowledge concerning the role of MCPyV, TSPyV, JCPyV and BKPyV in human cancers.

Human Polyomaviruses: The Battle of Large and Small Tumor Antigens

About 40 years ago, the large and small tumor antigens (LT-Ag and sT-Ag) of the polyomavirus (PyVs) simian vacuolating virus 40 have been identified and characterized. To date, it is well known that all the discovered human PyVs (HPyVs) encode these 2 multifunctional and tumorigenic proteins, expressed at viral replication early stage. The 2 T-Ags are able to transform cells both in vitro and in vivo and seem to play a distinct role in the pathogenesis of some tumors in humans. In addition, they are involved in viral DNA replication, transcription, and virion assembly. This short review focuses on the structural and functional features of the HPyVs’ LT-Ag and sT-Ag, with special attention to their transforming properties.

Trichodysplasia spinulosa: a polyomavirus infection specifically targeting follicular keratinocytes in immunocompromised patients

Trichodysplasia spinulosa (TS) is a rare skin disease, caused by a specific polyomavirus, occurring in immunocompromised patients. The pathophysiological mechanisms of TS are not yet fully understood. By using polymerase chain reaction and skin biopsy immunostaining we report evidence, in a paediatric case, of follicular keratinocytes being the primary target of trichodysplasia spinulosa-associated polyomavirus.

Molecular insight into the viral biology and clinical features of trichodysplasia spinulosa

Trichodysplasia spinulosa (TS) is a disfiguring skin disease that occurs most frequently in patients receiving immunosuppressive therapies, and is thus frequently associated with organ transplantation. TS is characterized clinically by folliculocentric papular eruption, keratin spine formation and development of leonine face; and histologically by expansion of the inner root sheath epithelium and high expression of the proliferative marker Ki-67. Recent discovery of the TS-associated polyomavirus (TSPyV) and emerging studies demonstrating the role of TSPyV tumour antigens in cell proliferation pathways have opened a new corridor for research on TS. In this brief review, we summarize the clinical and histological features of TS and evaluate the current options for therapy. Furthermore, we address the viral aetiology of the disease and explore the mechanisms by which TSPyV may influence TS development and progression. As reports of TS continue to rise, clinician recognition of TS, as well as accompanying research on its underlying pathogenesis and therapeutic options, is becoming increasingly important. It is our hope that heightened clinical suspicion for TS will increase rates of diagnosis and will galvanize both molecular and clinical interest in this disease.

Spiny Papules in an Immunosuppressed Child

Trichodysplasia spinulosa is a rare folliculocentric polyomavirus infection observed in the setting of immunosuppression. We report a 7-year-old boy with pre-B-cell lymphoblastic leukemia who presented with folliculocentric spiny papules on the face. Histologic evaluation revealed hypertrophic bulbs, an expanded inner root sheath, and numerous brightly eosinophilic trichohyalin granules. We present this case to raise awareness of this rare but recognizable entity and to highlight the availability of appropriate diagnostic and therapeutic modalities.

Trichodysplasia spinulosa-Associated Polyomavirus Uses a Displaced Binding Site on VP1 to Engage Sialylated Glycolipids

Trichodysplasia spinulosa-associated Polyomavirus (TSPyV) was isolated from a patient suffering from trichodysplasia spinulosa, a skin disease that can appear in severely immunocompromised patients. While TSPyV is one of the five members of the polyomavirus family that are directly linked to a human disease, details about molecular recognition events, the viral entry pathway, and intracellular trafficking events during TSPyV infection remain unknown. Here we have used a structure-function approach to shed light on the first steps of TSPyV infection. We established by cell binding and pseudovirus infection studies that TSPyV interacts with sialic acids during attachment and/or entry. Subsequently, we solved high-resolution X-ray structures of the major capsid protein VP1 of TSPyV in complex with three different glycans, the branched GM1 glycan, and the linear trisaccharides α2,3- and α2,6-sialyllactose. The terminal sialic acid of all three glycans is engaged in a unique binding site on TSPyV VP1, which is positioned about 18 Å from established sialic acid binding sites of other polyomaviruses. Structure-based mutagenesis of sialic acid-binding residues leads to reduction in cell attachment and pseudovirus infection, demonstrating the physiological relevance of the TSPyV VP1-glycan interaction. Furthermore, treatments of cells with inhibitors of N-, O-linked glycosylation, and glycosphingolipid synthesis suggest that glycolipids play an important role during TSPyV infection. Our findings elucidate the first molecular recognition events of cellular infection with TSPyV and demonstrate that receptor recognition by polyomaviruses is highly variable not only in interactions with sialic acid itself, but also in the location of the binding site.

Viruses engage receptors on their host cell to initiate entry and infection. Members within a virus family are known to target different tissues and hosts and exploit different pathogenic mechanisms due to critical changes in receptor specificity. The human Trichodysplasia spinulosa-associated Polyomavirus (TSPyV) is known to cause a rare skin disease in immunocompromised individuals. The pathogenic mechanism includes hyperproliferation of inner root sheath cells, but molecular determinants underlying the infection and the associated disease remain unknown. Here we applied a structural and functional approach to investigate the recognition events during early infection steps of the virus. We found that TSPyV engages sialic acid receptors but employs a novel binding site on the capsid that is shifted in comparison to other structurally characterized polyomaviruses. Cell-based studies demonstrate the relevance of the observed interaction for attachment and infection and suggest that glycolipids, rather than N- and O-linked glycoproteins, are important for infection. Our findings demonstrate exemplarily that receptor recognition by (polyoma-) viruses is highly variable not only in interactions with sialic acids, but also in the location of the binding site on the capsid, providing insights about structural determinants of receptor and host specificity and evolution of these viruses.

Characterization of T Antigens, Including Middle T and Alternative T, Expressed by the Human Polyomavirus Associated with Trichodysplasia Spinulosa

The polyomavirus tumor (T) antigens play crucial roles in viral replication, transcription, and cellular transformation. They are encoded by partially overlapping open reading frames (ORFs) located in the early region through alternative mRNA splicing. The T expression pattern of the trichodysplasia spinulosa-associated polyomavirus (TSPyV) has not been established yet, hampering further study of its pathogenic mechanisms and taxonomic relationship. Here, we characterized TSPyV T antigen expression in human cell lines transfected with the TSPyV early region. Sequencing of T antigen-encoded reverse transcription-PCR (RT-PCR) products revealed three splice donor and acceptor sites creating six mRNA splice products that potentially encode the antigens small T (ST), middle T (MT), large T (LT), tiny T, 21kT, and alternative T (ALTO). Except for 21kT, these splice products were also detected in skin of TSPyV-infected patients. At least three splice products were confirmed by Northern blotting, likely encoding LT, MT, ST, 21kT, and ALTO. Protein expression was demonstrated for LT, ALTO, and possibly MT, with LT detected in the nucleus and ALTO in the cytoplasm of transfected cells. Splice site and start codon mutations indicated that ALTO is encoded by the same splice product that encodes LT and uses internal start codons for initiation. The genuineness of ALTO was indicated by the identification of acetylated N-terminal ALTO peptides by mass spectrometry. Summarizing, TSPyV exhibits an expression pattern characterized by both MT and ALTO expression, combining features of rodent and human polyomaviruses. This unique expression pattern provides important leads for further study of polyomavirus-related disease and for an understanding of polyomavirus evolution.

IMPORTANCE

The human trichodysplasia spinulosa-associated polyomavirus (TSPyV) is distinguished among polyomaviruses for combining productive infection with cell-transforming properties. In the research presented here, we further substantiate this unique position by indicating expression of both middle T antigen (MT) and alternative T antigen (ALTO) in TSPyV. So far, none of the human polyomaviruses was shown to express MT, which is considered the most important viral oncoprotein of rodent polyomaviruses. Coexpression of ALTO and MT, which involves a conserved, recently recognized overlapping ORF subject to positive selection, has not been observed before for any polyomavirus. As a result of our findings, this study provides valuable new insights into polyomavirus T gene use and expression. Obviously, these insights will be instrumental in further study and gaining an understanding of TSPyV pathogenicity. More importantly, however, they provide important leads with regard to the interrelationship, functionality, and evolution of polyomaviruses as a whole, indicating that TSPyV is a suitable model virus to study these entities further.

Interspecific adaptation by binary choice at de novo polyomavirus T antigen site through accelerated codon-constrained Val-Ala toggling within an intrinsically disordered region

It is common knowledge that conserved residues evolve slowly. We challenge generality of this central tenet of molecular biology by describing the fast evolution of a conserved nucleotide position that is located in the overlap of two open reading frames (ORFs) of polyomaviruses. The de novo ORF is expressed through either the ALTO protein or the Middle T antigen (MT/ALTO), while the ancestral ORF encodes the N-terminal domain of helicase-containing Large T (LT) antigen. In the latter domain the conserved Cys codon of the LXCXE pRB-binding motif constrains codon evolution in the overlapping MT/ALTO ORF to a binary choice between Val and Ala codons, termed here as codon-constrained Val-Ala (COCO-VA) toggling. We found the rate of COCO-VA toggling to approach the speciation rate and to be significantly accelerated compared to the baseline rate of chance substitution in a large monophyletic lineage including all viruses encoding MT/ALTO and three others. Importantly, the COCO-VA site is located in a short linear motif (SLiM) of an intrinsically disordered region, a typical characteristic of adaptive responders. These findings provide evidence that the COCO-VA toggling is under positive selection in many polyomaviruses, implying its critical role in interspecific adaptation, which is unprecedented for conserved residues.