During viral infection, cells initiate antiviral responses to contain replication and inhibit virus spread. One protective mechanism involves activation of transcription factors interferon regulatory factor-3 (IRF-3) and NF-B, resulting in secretion of the antiviral cytokine, interferon-␤. Another is induction of apoptosis, killing the host cell before virus disseminates. Mammalian reovirus induces both interferon-␤ and apoptosis, raising the possibility that both pathways are initiated by a common cellular sensor. We show here that reovirus activates IRF-3 with kinetics that parallel the activation of NF-B, a known mediator of reovirus-induced apoptosis. Activation of IRF-3 requires functional retinoic acid inducible gene-I and interferon-␤ promoter stimulator-1, but these intracellular sensors are dispensable for activation of NF-B. Interferon-␤ promoter stimulator-1 and IRF-3 are required for efficient apoptosis following reovirus infection, suggesting a common mechanism of antiviral cytokine induction and activation of the cell death response.A primary function of the innate immune system is to detect nascent viral infections and direct subsequent cellular responses. The innate immune system responds to infection by producing a range of soluble cytokines, such as interferon-␤ (IFN-␤), 5 that create an antiviral state in surrounding tissue. In response to these immune pressures, viruses have evolved multiple strategies for subverting innate immunity, which frequently center on manipulating cell death pathways. The interface between the innate immune response, viral infection, and the cellular apoptotic machinery is therefore a critical nexus of disease pathogenesis.Cells possess a variety of sensors to detect invading pathogens. Toll-like receptors (TLRs) and other pattern recognition receptors, including the nucleotide-binding oligomerization domain proteins and RNA helicases such as retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated protein-5 (Mda-5), recognize viral pathogen-associated molecular patterns (1). TLRs are expressed on the cell surface and recognize extracellular pathogen-associated molecular patterns, whereas RIG-I and Mda-5 detect intracellular viral RNA products (2-4). RIG-I recognizes viral RNAs from the Flaviviridae, Orthomyxoviridae, Paramyxoviridae, and Rhabdoviridae families, whereas Mda-5 is involved in the response to Picornaviridae (4). The ligand for RIG-I has been identified as a 5Ј triphosphate moiety on single-or double-stranded RNA (5, 6); the molecular ligand for Mda-5 is unknown. Following ligand engagement, these intracellular sensors signal through caspase activation and recruitment domains to activate the adaptor, interferon-␤ promoter stimulator-1 (IPS-1/MAVS/ VISA/Cardif) (7-10). IPS-1 activates inhibitor of B kinase (IKK)-␣, IKK-␤, IKK-⑀, and Tank-binding kinase 1 to phosphorylate transcription factors, including activating transcription factor-2/c-Jun, NF-B, and interferon regulatory factor-3 (IRF-3), which direct transcription of antiviral g...

Chronic lymphocytic leukemia (CLL) is characterized by clonal accumulation of CD5؉ CD19 ؉ B lymphocytes that are arrested in the G 0 /G 1 phase of the cell cycle and fail to undergo apoptosis because of overexpression of the antiapoptotic B-cell CLL/lymphoma 2 (BCL-2) protein. Oncolytic viruses, such as vesicular stomatitis virus (VSV), have emerged as potential anticancer agents that selectively target and kill malignant cells via the intrinsic mitochondrial pathway. Although primary CLL cells are largely resistant to VSV oncolysis, we postulated that targeting the apoptotic pathway via inhibition of BCL-2 may sensitize CLL cells to VSV oncolysis. In the present study, we examined the capacity of EM20-25-a small-molecule antagonist of the BCL-2 protein-to overcome CLL resistance to VSV oncolysis. We demonstrate a synergistic effect of the two agents in primary ex vivo CLL cells (combination index of 0.5; P < 0.0001). In a direct comparison of peripheral blood mononuclear cells from healthy volunteers with primary CLL, the two agents combined showed a therapeutic index of 19-fold; furthermore, the combination of VSV and EM20-25 increased apoptotic cell death in Karpas-422 and Granta-519 B-lymphoma cell lines (P < 0.005) via the intrinsic mitochondrial pathway. Mechanistically, EM20-25 blocked the ability of the BCL-2 protein to dimerize with proapoptotic BAX protein, thus sensitizing CLL to VSV oncolytic stress. Together, these data indicate that the use of BCL-2 inhibitors may improve VSV oncolysis in treatment-resistant hematological malignancies, such as CLL, with characterized defects in the apoptotic response.