Repression of the proapoptotic cellular BIK/NBK gene by Epstein-Barr virus antagonizes transforming growth factor ß1-induced B-cell apoptosis.

UNLABELLED: The Epstein-Barr virus (EBV) establishes a lifelong latent infection in humans. EBV infection of primary B cells causes cell activation and proliferation, a process driven by the viral latency III gene expression program, which includes EBV nuclear proteins (EBNAs), latent membrane proteins, and untranslated RNAs, including microRNAs. Some latently infected cells enter the long-lived memory B-cell compartment and express only EBNA1 transiently (Lat I) or no EBV protein at all (Lat 0). Targeting the molecular machinery that controls B-cell fate decisions, including the Bcl-2 family of apoptosis-regulating proteins, is crucial to the EBV cycle of infection. Here, we show that BIK (also known as NBK), which encodes a proapoptotic "sensitizer" protein, is repressed by the EBNA2-driven Lat III program but not the Lat I program. BIK repression occurred soon after infection of primary B cells by EBV but not by a recombinant EBV in which the EBNA2 gene had been knocked out. Ectopic BIK induced apoptosis in Lat III cells by a mechanism dependent on its BH3 domain and the activation of caspases. We show that EBNA2 represses BIK in EBV-negative B-cell lymphoma-derived cell lines and that this host-virus interaction can inhibit the proapoptotic effect of transforming growth factor ß1 (TGF-ß1), a key physiological mediator of B-cell homeostasis. Reduced levels of TGF-ß1-associated regulatory SMAD proteins were bound to the BIK promoter in response to EBV Lat III or ectopic EBNA2. These data are evidence of an additional mechanism used by EBV to promote B-cell survival, namely, the transcriptional repression of the BH3-only sensitizer BIK. IMPORTANCE: Over 90% of adult humans are infected with the Epstein-Barr virus (EBV). EBV establishes a lifelong silent infection, with its DNA residing in small numbers of blood B cells that are a reservoir from which low-level virus reactivation and shedding in saliva intermittently occur. Importantly, EBV DNA is found in some B-cell-derived tumors in which viral genes play a key role in tumor cell emergence and progression. Here, we report for the first time that EBV can shut off a B-cell gene called BIK. When activated by a molecular signal called transforming growth factor ß1 (TGF-ß1), BIK plays an important role in killing unwanted B cells, including those infected by viruses. We describe the key EBV-B-cell molecular interactions that lead to BIK shutoff. These findings further our knowledge of how EBV prevents the death of its host cell during infection. They are also relevant to certain posttransplant lymphomas where unregulated cell growth is caused by EBV genes.

Identification of an MLL4-GPS2 fusion as an oncogenic driver of undifferentiated spindle cell sarcoma in a child.

Undifferentiated spindle cell sarcoma (UDS) is a poorly defined or understood entity, essentially a waste-basket for cases failing to fulfill criteria for better-established diagnoses based on combined histology, immunohistochemistry, and tumor genetic assays. We identified a novel chromosomal translocation t(17;19)(p13;q13) in a pediatric UDS and have characterized this alteration to show rearrangement of the MLL4 and GPS2 genes, resulting in an in-frame fusion gene MLL4-GPS2, the expression of which promotes anchorage-independent growth. MLL4 was previously reported to be similarly rearranged in hepatocellular carcinomas, notably those positive for hepatitis B virus. Isolated reports of individual rearrangements of GPS2 in a prostate carcinoma cell line and in glioblastoma multiforme, each with different partner genes, recently emerged from high-throughput sequencing studies but have not been further evaluated for biological effect.

Shear stress is a positive regulator of thimet oligopeptidase (EC3.4.24.15) in vascular endothelial cells: consequences for MHC1 levels.

AIMS: Thimet oligopeptidase (TOP, endopeptidase EC3.4.24.15) is a soluble metallopeptidase known to be expressed within the mammalian vasculature. We examine for the first time the relationship between TOP expression and laminar shear stress, a haemodynamic force associated with endothelium-mediated vascular homeostasis. METHODS AND RESULTS: Human and bovine aortic endothelial cells were exposed to physiological levels of laminar shear (0-10 dynes/cm², 24-48 h) and monitored for TOP expression using promoter activity assay, qRT-PCR, western blotting, and immunocytochemistry. Using a luciferase reporter encoding the full-length rat TOP promoter, initial studies demonstrated shear-dependent promoter activation (~five-fold). TOP mRNA and protein were also consistently up-regulated by shear, events which could be completely prevented by pre-treatment of cells with either N-acetylcysteine, superoxide dismutase, or catalase, confirming ROS involvement. Consistent with this, targeted inhibition of NADPH oxidase (apocynin, NSC23766, NOX4 siRNA) had a similar blocking effect. Finally, in view of its pivotal role in cellular antigen presentation and major histocompatibility complex (MHC) class-1 regulation, we hypothesized that the shear-dependent induction of TOP may lower MHC1 expression. In this respect, we observed that recombinant TOP over-expression in static HAECs dose-dependently depleted MHC1 (>60%), while siRNA-mediated blockade of TOP induction in sheared HAECs led to substantially elevated MHC1 (~66%). CONCLUSION: Our findings demonstrate that laminar shear positively regulates endothelial TOP expression. Moreover, a role for ROS production by NADPH oxidase is indicated. Finally, our studies suggest that shear-dependent TOP induction down-regulates MHC1 levels, pointing to a role for TOP in the flow-mediated regulation of endothelial immunogenicity.