Characterization of integrated Marek's disease virus genomes supports a model of integration by homology-directed recombination and telomere-loop-driven excision.

IMPORTANCE: Marek's disease virus (MDV) is a ubiquitous chicken pathogen that inflicts a large economic burden on the poultry industry, despite worldwide vaccination programs. MDV is only partially controlled by available vaccines, and the virus retains the ability to replicate and spread between vaccinated birds. Following an initial infection, MDV enters a latent state and integrates into host telomeres and this may be a prerequisite for malignant transformation, which is usually fatal. To understand the mechanism that underlies the dynamic relationship between integrated-latent and reactivated MDV, we have characterized integrated MDV (iMDV) genomes and their associated telomeres. This revealed a single orientation among iMDV genomes and the loss of some terminal sequences that is consistent with integration by homology-directed recombination and excision via a telomere-loop-mediated process.

CRISPR-Mediated Gene Activation (CRISPRa) of pp38/pp24 Orchestrates Events Triggering Lytic Infection in Marek's Disease Virus-Transformed Cell Lines.

Marek's disease (MD) is an immunosuppressive and highly contagious lymphoproliferative disease caused by Marek's disease virus (MDV) in poultry. Lymphoblastoid cell lines (LCLs) generated ex vivo from MD lymphomas are considered excellent models to study virus-host molecular interactions. LCLs mostly have latently infected MDV genome, but many of them also have varying populations of lytically-infected cells, thus making them very suitable to examine the molecular events associated with the switch from latent to lytic infection. MDV-encoded phosphoprotein 38 (pp38) is readily detectable in lytically-infected LCLs and hence considered as a biomarker for lytic infection. Whilst previous studies have suggested that pp38 is essential for the early cytolytic infection of B-cells, its role in the switch from latent to lytic infection of LCLs is still unclear. pp24, another phosphorylated protein in the same protein complex, shares the same promoter and N-terminal 65 amino acids as pp38. In this study we employed CRISPR activation (CRISPRa) technology for targeted activation of pp38/pp24 in LCLs to investigate their role in inducing lytic infection. Our results show that enforced expression of pp38/pp24 through CRISPRa induces orchestrated upregulation of other MDV genes including ICP4, gB, Meq and pp14 as well as differential expression of host genes thereby facilitating lytic infection. Our results also show that pp38/pp24 expression induces the lytic switch through inhibiting apoptosis.

Adhesion G-protein coupled receptor 56 is required for 3T3-L1 adipogenesis.

Obesity-associated conditions represent major global health and financial burdens and understanding processes regulating adipogenesis could lead to novel intervention strategies. This study shows that adhesion G-protein coupled receptor 56 (GPR56) gene transcripts are reduced in abdominal visceral white adipose tissue derived from obese Zucker rats versus lean controls. Immunostaining in 3T3-L1 preadipocytes reveals both mitotic cell restricted surface and low level general expression patterns of Gpr56. Gpr56 transcripts are differentially expressed in 3T3-L1 cells during adipogenesis. Transient knockdown (KD) of Gpr56 in 3T3-L1 cells dramatically inhibits differentiation through reducing the accumulation of both neutral cellular lipids (56%) and production of established adipogenesis Pparγ 2 (60-80%), C/ebpα (40-78%) mediator, and Ap2 (56-80%) marker proteins. Furthermore, genome editing of Gpr56 in 3T3-L1 cells created CW2.2.4 and RM4.2.5.5 clones (Gpr56 -/- cells) with compound heterozygous deletion frameshift mutations which abolish adipogenesis. Genome edited cells have sustained levels of the adipogenesis inhibitor ß-catenin, reduced proliferation, reduced adhesion, altered profiles, and or abundance of extracellular matrix component gene transcripts for fibronectin, types I, III, and IV collagens and loss of actin stress fibers. ß-catenin KD alone is insufficient to restore adipogenesis in Gpr56 -/- cells. Together these data show that Gpr56 is required for adipogenesis in 3T3-L1 cells. This report is the first demonstration that Gpr56 participates in regulation of the adipogenesis developmental program. Modulation of the levels of this protein and/or its biological activity may represent a novel target for development of therapeutic agents for the treatment of obesity.

BCR-ABL1 tyrosine kinase sustained MECOM expression in chronic myeloid leukaemia.

MECOM oncogene expression correlates with chronic myeloid leukaemia (CML) progression. Here we show that the knockdown of MECOM (E) and MECOM (ME) isoforms reduces cell division at low cell density, inhibits colony-forming cells by 34% and moderately reduces BCR-ABL1 mRNA and protein expression but not tyrosine kinase catalytic activity in K562 cells. We also show that both E and ME are expressed in CD34(+) selected cells of both CML chronic phase (CML-CP), and non-CML (normal) origin. Furthermore, MECOM mRNA and protein expression were repressed by imatinib mesylate treatment of CML-CP CD34(+) cells, K562 and KY01 cell lines whereas imatinib had no effect in non-CML BCR-ABL1 -ve CD34(+) cells. Together these results suggest that BCR-ABL1 tyrosine kinase catalytic activity regulates MECOM gene expression in CML-CP progenitor cells and that the BCR-ABL1 oncoprotein partially mediates its biological activity through MECOM. MECOM gene expression in CML-CP progenitor cells would provide an in vivo selective advantage, contributing to CML pathogenesis.