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Project description:Merkel cell polyomavirus (MCV) is clonally integrated in over 80% of Merkel cell carcinomas and mediates tumor development through the expression of viral oncoproteins large T (LT) and small T antigens (sT). Viral integration is associated with signature mutations in the T antigen locus that result in deletions of carboxy-terminal replicative functions of the LT antigen. Despite these truncations, the LT LxCxE retinoblastoma (Rb) pocket protein family-binding domain is retained, and the entire sT isoform is maintained intact. To investigate the ability of MCV oncoproteins to regulate host gene expression, we performed microarray analysis on cells stably expressing tumor-derived LT, tumor-derived LT along with sT, and tumor-derived LT with a mutated Rb interaction motif. Gene expression alterations in the presence of tumor-derived LT could be classified into three main groups: genes that are involved in the cell cycle (specifically the G1/S transition), genes involved in DNA replication, and genes involved in cellular movement. The LxCxE mutant LT largely reversed gene expression alterations detected with the wild type LT, while co-expression of sT did not significantly affect these patterns of gene expression. LxCxE-dependent upregulation of cyclin E and CDK2 correlates with increased proliferation in tumor-derived LT expressing cells. We conclude that in hTERT-immortalized human fibroblasts the LXCXE motif of tumor-derived LT enhances cellular proliferation and upregulates cell cycle and immune signaling gene transcription. RNA was isolated from BJ-hTERT cell lines and hybridized to an Illumina chip for global gene expression analysis
2015-09-21 | E-GEOD-68503 | biostudies-arrayexpress
Project description:Merkel cell polyomavirus (MCV) is clonally integrated in over 80% of Merkel cell carcinomas and mediates tumor development through the expression of viral oncoproteins large T (LT) and small T antigens (sT). Viral integration is associated with signature mutations in the T antigen locus that result in deletions of carboxy-terminal replicative functions of the LT antigen. Despite these truncations, the LT LxCxE retinoblastoma (Rb) pocket protein family-binding domain is retained, and the entire sT isoform is maintained intact. To investigate the ability of MCV oncoproteins to regulate host gene expression, we performed microarray analysis on cells stably expressing tumor-derived LT, tumor-derived LT along with sT, and tumor-derived LT with a mutated Rb interaction motif. Gene expression alterations in the presence of tumor-derived LT could be classified into three main groups: genes that are involved in the cell cycle (specifically the G1/S transition), genes involved in DNA replication, and genes involved in cellular movement. The LxCxE mutant LT largely reversed gene expression alterations detected with the wild type LT, while co-expression of sT did not significantly affect these patterns of gene expression. LxCxE-dependent upregulation of cyclin E and CDK2 correlates with increased proliferation in tumor-derived LT expressing cells. We conclude that in hTERT-immortalized human fibroblasts the LXCXE motif of tumor-derived LT enhances cellular proliferation and upregulates cell cycle and immune signaling gene transcription.
2015-09-21 | GSE68503 | GEO
Project description:Investigation of Gene Regulation Induced by Merkel Cell Polyomavirus (MCV) Large T Antigen
| PRJNA782359 | ENA
Project description:Viral noncoding RNAs have acquired increasing prominence as important regulators of infection and mediators of pathogenesis. Circular RNAs (circRNAs) generated by backsplicing events have been identified in several oncogenic human DNA viruses. Here, we show that Merkel cell polyomavirus (MCV), the etiologic cause of ~80% of Merkel cell carcinomas (MCCs), also expresses circular RNAs. By RNase R-resistant RNA sequencing, four putative circRNA backsplice junctions (BSJs) were identified from the MCV early region (ER). The most abundantly expressed MCV circRNA, designated circMCVT, is generated through backsplicing of all of ER exon II to form a 762-nucleotide (nt) circular RNA molecule. Curiously, circMCV-T, as well as two other less abundantly expressed putative MCV circRNAs, overlaps in a complementary fashion the MCV microRNA (miRNA) locus that encodes MCV-miR-M1. circMCV-T is consistently detected in concert with linear T antigen transcripts throughout infection, suggesting a crucial role for this RNA molecule in the regulatory functions of the early region, known to be vital for viral replication. Knocking out the hairpin structure of MCV-miR-M1 in genomic early region expression constructs and using a new high-efficiency, recombinase-mediated, recircularized MCV molecular clone demonstrates that circMCV-T levels decrease in the presence of MCV-miR-M1, underscoring the interplay between MCV circRNA and miRNA. Furthermore, circMCV-T partially reverses the known inhibitory effect of MCV-miR-M1 on early gene expression. RNase R-resistant RNA sequencing of lytic rat polyomavirus 2 (RatPyV2) identified an analogously located circRNA, stipulating a crucial, conserved regulatory function of this class of RNA molecules in the family of polyomaviruses.
2020-12-07 | GSE162627 | GEO
Project description: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.
| S-EPMC9820997 | biostudies-literature
Project description:Merkel Cell Polyomavirus (MCPyV) was recently discovered as a novel human polyomavirus that is associated with ~80% of Merkel Cell Carcinomas. The Large Tumor antigen (LT) is an early viral protein which has a variety of functions, including manipulation of the cell cycle and initiating viral DNA replication. Phosphorylation plays a critical regulatory role for polyomavirus LT proteins, but no investigation of MCPyV LT phosphorylation has been performed to date. In this report mass spectrometry analysis reveals three unique phosphorylation sites: T271, T297 and T299. In vivo replication assays confirm that phosphorylation of T271 does not play a role in viral replication, while modification at T297 and T299 have dramatic and opposing effects on LT's ability to initiate replication from the viral origin. We test these mutants for their ability to bind, unwind, and act as a functional helicase at the viral origin. These studies provide a framework for understanding how phosphorylation of LT may dynamically regulate viral replication. Although the natural host cell of MCPyV has not yet been established, this work provides a foundation for understanding how LT activity is regulated and provides tools for better exploring this regulation in both natural host cells and Merkel cells.
| S-EPMC4190550 | biostudies-literature
Project description:Merkel cell carcinoma (MCC) is a rare and aggressive form of skin cancer. In at least 80% of all MCC, Merkel cell polyomavirus (MCPyV) DNA has undergone clonal integration into the host cell genome, and most tumors express the MCPyV large and small T antigens. In all cases of MCC reported to date, the integrated MCPyV genome has undergone mutations in the large T antigen. These mutations result in expression of a truncated large T antigen that retains the Rb binding or LXCXE motif but deletes the DNA binding and helicase domains. However, the transforming functions of full-length and truncated MCPyV large T antigen are unknown. We compared the transforming activities of full-length, truncated, and alternatively spliced 57kT forms of MCPyV large T antigen. MCPyV large T antigen could bind to Rb but was unable to bind to p53. Furthermore, MCPyV-truncated large T antigen was more effective than full-length and 57kT large T antigen in promoting the growth of human and mouse fibroblasts. In contrast, expression of the MCPyV large T antigen C-terminal 100 residues could inhibit the growth of several different cell types. These data imply that the deletion of the C terminus of MCPyV large T antigen found in MCC serves not only to disrupt viral replication but also results in the loss of a distinct growth-inhibitory function intrinsic to this region.
| S-EPMC3648111 | biostudies-literature
Project description:Merkel cell polyomavirus (MCPyV) large tumor (LT) antigen is a DNA binding protein essential for viral gene transcription and genome replication. MCPyV LT interacts with multiple E3 ligases in a phosphorylation-dependent manner, limiting its own viral replication by enhancing LT protein degradation, which is a unique mechanism for MCPyV latency. Thus, identifying LT ubiquitination sites is an important step toward understanding the biological role of these virus-host interactions that can potentially result in viral oncogenesis. The ubiquitin (Ub) attachment sites in LT were predicted by using Rapid UBIquitination (RUBI), a sequence-based ubiquitination web server. Using an immunoprecipitation approach, the lysine (Lys, K) 585 residue in LT is identified as the ubiquitin conjugation site. Lysine 585 is deleted from tumor-derived truncated LTs (tLTs), resulting in stable expression of tLTs present in cancers. Substitution of lysine 585 to arginine (Arg, R) increased LT protein stability, but impaired MCPyV origin replication, due to a loss of ATP hydrolysis activity. These findings uncover a never-before-identified ubiquitination site of LT and its importance not only in the regulation of protein turnover, but also in MCPyV genome replication.
| S-EPMC8267701 | biostudies-literature
Project description:Merkel cell carcinoma is supposed to be derived from Merkel cells after infection by Merkel cell polyomavirus (MCV) and other poorly known events. A transcriptional profiling with cDNA microarrays was performed on cells from MCV+ Merkel cell carcinomas and isolated normal Merkel cells. This microarray revealed numerous significantly upregulated genes and down-regulated genes. The extensive list of genes identified in these experiments provides a large body of potentially valuable information of Merkel cell carcinoma carcinogenesis and could represent a source of potential targets for cancer therapy. Two-conditions experiment, MCV vs Normal Merkel Cell. Biological replicates : 4 MCV (Cy5), 1 control = pool of Normal Merkel cells from 3 liftings
2014-01-01 | E-GEOD-50434 | biostudies-arrayexpress
Project description:The pocket protein (PP) family consists of the three members RB1, p107 and p130 all possessing tumor suppressive properties. Indeed, the PPs jointly control the G1/S transition mainly by inhibiting E2F transcription factors. Notably, several viral oncoproteins are capable of binding and inhibiting PPs. Merkel cell polyomavirus (MCPyV) is considered as etiological factor for Merkel cell carcinoma (MCC) with expression of the viral Large T antigen (LT) harboring an intact PP binding domain being required for proliferation of most MCC cells. Therefore, we analyzed the interaction of MCPyV-LT with the PPs. Co-IP experiments indicate that MCPyV-LT binds potently only to RB1. Moreover, MCPyV-LT knockdown-induced growth arrest in MCC cells can be rescued by knockdown of RB1, but not by p107 or p130 knockdown. Accordingly, cell cycle arrest and E2F target gene repression mediated by the single PPs can only in the case of RB1 be significantly reverted by MCPyV-LT expression. Moreover, data from an MCC patient indicate that loss of RB1 rendered the MCPyV-positive MCC cells LT independent. Thus, our results suggest that RB1 is the dominant tumor suppressor PP in MCC, and that inactivation of RB1 by MCPyV-LT is largely sufficient for its growth supporting function in established MCPyV-positive MCC cells.
| S-EPMC5078066 | biostudies-literature