MDA5

Abstract: Toll-like receptors (TLRs) are a group of transmembrane receptors that recognize molecular motifs of pathogen origin and activate immune response. Although TLRs were first identified in immune system cells, recent studies show they can also be expressed in tumor cells. TLR3 recognizes dsRNA or its synthetic ligand poly (I: C) and is responsible primarily for the defense against viral infections. Recent studies showed that TLR3 can trigger apoptosis in cancer cell. Furthermore, other dsRNA binding receptors (MDA5 and RIG-I), localized in cytoplasm, can also bind poly (I: C) and therefore contribute to this effect. With TLR3's capacity to induce apoptosis and activate the immune system at the same time, TLR3 ligands are an attractive therapeutic option for treatment of cancer. Novel therapies include combining poly (I: C) with other components such as chemotherapeutics, apoptosis enhancers, other TLR ligands and peptides activating the immune system. Slightly modified TLR3 agonists (Ampligen®, Hiltonol®, poly IC-LC) are already being used in clinical studies for cancer therapy as single agents or in combination with other drugs. On the other hand, latest studies forewarn that TLR3 activation can also have tumor promoting role so it is crucial to identify the terms by which TLR3 has pro-tumor/anti-tumor effect in order to safely implement TLR3 ligand based therapy into clinical trials.

Abstract: The V proteins of paramyxoviruses control the innate immune response. In particular, the V protein of the genus Morbillivirus interferes with the signal transducer and activator of transcription 1 (STAT1), STAT2, and melanoma differentiation-associated protein 5 (mda5) signaling pathways. To characterize the contributions of these pathways to canine distemper virus (CDV) pathogenesis, we took advantage of the knowledge about the mechanisms of interaction between the measles virus V protein with these key regulators of innate immunity. We generated recombinant CDVs with V proteins unable to properly interact with STAT1, STAT2, or mda5. A virus with combined STAT2 and mda5 deficiencies was also generated, and available wild-type and V-protein-knockout viruses were used as controls. Ferrets infected with wild-type and STAT1-blind viruses developed severe leukopenia and loss of lymphocyte proliferation activity and succumbed to the disease within 14 days. In contrast, animals infected with viruses with STAT2 or mda5 defect or both STAT2 and mda5 defects developed a mild self-limiting disease similar to that associated with the V-knockout virus. This study demonstrates the importance of interference with STAT2 and mda5 signaling for CDV immune evasion and provides a starting point for the development of morbillivirus vectors with reduced immunosuppressive properties. IMPORTANCE The V proteins of paramyxoviruses interfere with the recognition of the virus by the immune system of the host. For morbilliviruses, the V protein is known to interact with the signal transducer and activator of transcription 1 (STAT1) and STAT2 and the melanoma differentiation-associated protein 5 (mda5), which are involved in interferon signaling. Here, we examined the contribution of each of these signaling pathways to the pathogenesis of the carnivore morbillivirus canine distemper virus. Using viruses selectively unable to interfere with the respective signaling pathway to infect ferrets, we found that inhibition of STAT2 and mda5 signaling was critical for lethal disease. Our findings provide new insights in the mechanisms of morbillivirus immune evasion and may lead to the development of new vaccines and oncolytic vectors.