Induction of
type-I interferons (IFNs), IFN-α/β, is crucial to innate immunity against
RNA virus infection. Cytoplasmic
retinoic acid-inducible gene I (RIG-I)-like receptors, including RIG-I and
melanoma differentiation-associated gene 5 (MDA5), are critical pathogen sensors for activation of type-I IFN expression in response to
RNA virus infection. MDA5 is required for type-I IFN expression in mouse models in response to
infection by picornaviruses, such as encephalomyocarditis virus (EMCV) and coxsackievirus B3. Enterovirus 71 (EV71) belongs to picornaviridae and contains positive-stranded
RNA genome that is linked with VPg
protein at the 5' end. Although a recent study showed that EV71 3C
protease could suppress RIG-I-mediated IFN-β response, the cytoplasmic RIG-I-like receptor that is directly involved in the recognition of EV71
RNA remains unclear. Using EV71-derived
RNA as an agonist, we demonstrate that MDA5 is involved in EV71
RNA-mediated IRF3 activation and IFN-β transcription. Our data also show that overexpression of the MDA5
protein reverses the suppression of IRF3 activation caused by EV71
infection. These results indicate that MDA5 is an important factor for EV71
RNA-activated type-I IFN expression. Furthermore, we also show that EV71
infection enhances MDA5 degradation and that the degradation could be inhibited by a broad spectrum
caspase inhibitor.