Homodimerization of the Meq Viral Oncoprotein Is Necessary for Induction of T-Cell Lymphoma by Marek's Disease Virus

cGallid herpesvirus 2 (GaHV-2) is an oncogenic herpesvirus that causes T lymphoma in chicken. GaHV-2 encodes a basic leucine zipper (bZIP) protein of the AP-1 family, Meq. Upon formation of homo-or heterodimers with c-Jun, Meq may modulate the expression of viral and cellular genes involved in lymphomagenesis. GaHV-2 also encodes viral microRNAs (miRNAs) involved in latency and apoptosis escape. However, little is known about cellular miRNA deregulation during the development of GaHV-2-associated lymphoma. We determined the cellular miRNA expression profiles of chickens infected with a very virulent strain (RB-1B) or a vaccine strain (CVI988) or noninfected. Among the most deregulated cellular miRNAs, we focused our efforts on gga-miR-21, which is upregulated during GaHV-2 infection. We mapped the gga-miR-21 promoter to the 10th intron of the TMEM49 gene and found it to be driven by AP-1-and Ets-responsive elements. We show here that the viral oncoprotein Meq binds to this promoter, thereby transactivating gga-miR-21 expression. We confirmed that this miRNA targets chicken programmed death cell 4 (PDCD4) and promotes tumor cell growth and apoptosis escape. Finally, gga-miR-21 was overexpressed only during infection with a very virulent strain (RB-1B) and not during infection with a nononcogenic strain (CVI988), providing further evidence for its role in GaHV-2 lymphomagenesis. Our data therefore suggest an additional role for Meq in GaHV-2-mediated lymphomagenesis through the induction of miR-21 expression.

Section: Discussionmentioning

confidence: 99%

The Oncogenic MicroRNA OncomiR-21 Overexpressed during Marek's Disease Lymphomagenesis Is Transactivated by the Viral Oncoprotein Meq

Stik

Dambrine

Pfeffer

et al. 2013

“…The best candidate for an MDV protein involved in histone modification is Meq, since it is one of the few proteins expressed during latency, has a nuclear distribution, binds DNA, and regulates transcription (9,49,50). The ability to repress transcription as a homodimer probably relates to its ability to interact with the cellular corepressor CtBP (8), and this provides a potential link to the polycomb complexes responsible for H3K27me3 (46).…”

Section: Discussionmentioning

confidence: 99%

“…The only homodimer binding site that has been identified in the MDV genome is at OriLyt, but several MERE-1 (AP-1) sites are found in the latencyassociated region (27,34). Meq homo-and heterodimerization and Meq binding to the cellular corepressor CtBP are all required for its oncogenic activity (8,9,30,49,50).…”

mentioning

confidence: 99%

Epigenetic Regulation of the Latency-Associated Region of Marek's Disease Virus in Tumor-Derived T-Cell Lines and Primary Lymphoma

Brown

Nair

Allday

2012

Self Cite

Meq is the major Marek's disease virus (MDV)-encoded oncoprotein and is essential for T-cell lymphomagenesis. Meq and several noncoding RNAs, including three microRNA (MiR) clusters, are expressed from the repeats of the MDV genome during latent infection of T cells. To investigate the state of the chromatin in this and flanking regions, we carried out chromatin immunoprecipitation (ChIP) analysis of covalent histone modifications and associated bound proteins. T-cell lines and a lymphoma were compared. The chromatin around the promoters for Meq and the noncoding RNAs in both cell lines and the lymphoma were associated with H3K9 acetylation and H3K4 trimethylation, which are marks of transcriptionally active chromatin. These correlated with bound Meq-c-Jun heterodimers. The only binding site for Meq homodimers is located at the lytic origin of replication (OriLyt), next to the lytic gene pp38. This region lacked active marks and was associated with repressive histone modifications (H3K27 and H3K9 trimethylation). DNA CpG methylation was investigated using methylated DNA precipitation (MeDP). In cell lines, DNA methylation was abundant across the repeats but noticeably reduced or absent around the active promoters. In primary tumors, CpG methylation occurred less than 2 months after infection, focused within the ICP4 gene. These data suggest that nonrandom de novo DNA methylation occurs early in lymphomagenesis. In addition, the histone data indicate a role for Meq in the epigenetic regulation of the MDV genome repeats in transformed T cells and suggest that the OriLyt region and the Meq/MiR region might be separated by chromatin boundary elements, and preliminary data on CTCF binding are consistent with this.

“…Briefly, BAC DNA was digested with various restriction enzymes, resolved on an agarose gel, and transferred onto a positively charged nylon membrane (NytranSPC membrane; Whatman). TMR or mutant repeats were detected using digoxigenin (DIG)-labeled oligonucleotide probes specific for the telomeric repeats (TTAGGG) 6 or the scrambled repeat sequence (ACGACA) 6 (Eurofins MWG) (16).…”

Section: Cells and Virusesmentioning

confidence: 99%

“…The major oncogene is meq, which encodes the Marek's EcoRI-Q-encoded protein, a basic leucine zipper protein that functions as a transcriptional regulator for viral and cellular genes (1,4). In addition, Meq contributes to T-cell transformation via interaction with cellular factors, including the tumor suppressor proteins p53 and retinoblastoma (Rb) as well as the transcriptional corepressor C-terminal binding protein (CtBP) (1,3,(5)(6)(7). Another factor involved in MDV-induced tumorigenesis is the viral telomerase RNA (vTR), a homologue of cellular telomerase RNA (8)(9)(10).…”

mentioning

confidence: 99%

Role of the Short Telomeric Repeat Region in Marek's Disease Virus Replication, Genomic Integration, and Lymphomagenesis

Greco

Fester

Engel

et al. 2014

Marek's disease virus (MDV) is a cell-associated alphaherpesvirus that causes generalized polyneuritis and T-cell lymphomas in chickens. MDV is able to integrate its genome into host telomeres, but the mechanism of integration is poorly understood. The MDV genome harbors two arrays of telomeric repeats (TMR) at the ends of its linear genome: multiple telomeric repeats (mTMR), with a variable number of up to 100 repeats, and short telomeric repeats (sTMR), with a fixed number of 6 repeats. The mTMR have recently been shown to play an important role in MDV integration and tumor formation; however, the functions of the sTMR have remained unknown. In this study, we demonstrate that deletion of the sTMR in the MDV genome abrogates virus replication, while extensive mutation of the sTMR does not, indicating that the presence of the sTMR but not the sTMR sequence itself is important. Furthermore, we generated a panel of truncation mutants to determine the minimal length of the sTMR and observed a direct correlation between sTMR length and MDV replication. To address the role of sTMR in MDV replication, integration, and tumorigenesis, sTMR sequences were replaced by a scrambled repeated sequence (vsTMR_mut). vsTMR_mut replicated comparably to parental and revertant viruses in vitro. In vivo, however, a significant reduction in disease and tumor incidence was observed in chickens infected with vsTMR_mut that also correlated with a reduced number of viral integration sites in tumor cells. Taken together, our data demonstrate that the sTMR play a central role in MDV genome replication, pathogenesis, and MDV-induced tumor formation. IMPORTANCE Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus that infects chickens and causes high economic losses in the poultry industry. MDV integrates its genetic material into host telomeres, a process that is crucial for efficient tumor formation.The MDV genome harbors two arrays of telomeric repeats (TMR) at the ends of its linear genome that are identical to host telomeres and that are termed mTMR and sTMR. mTMR have been recently shown to be involved in MDV integration, while the functions of sTMR remain unknown. Here, we demonstrate that the presence and length of sTMR sequence, but not the exact nucleotide sequence, are crucial for MDV replication. Furthermore, the sTMR contribute to the high integration frequency of MDV and are important for MDV pathogenesis and tumor formation. As a number of herpesviruses harbor arrays of telomeric repeats (TMR), MDV serves as a model to determine the role of the herpesvirus TMR in replication, integration, and pathogenesis.