The larger MAVS isoform is selectively degraded concomitantly with downstream signaling following RLR activation. (A) HEK293T or HeLa cells were infected with SeV WT or H4, and at various times after infection RIG-I, MAVS, p-IRF3, IRF3, p-IκBα and IκBα were analyzed in cell extracts by immunoblotting. Actin was used as a protein loading control. (B) HEK293T cells were transfected with either an IFN-β promoter reporter or with NF-κB reporter as well as with renilla luciferase as an internal control. Twenty hours after transfection, cells were infected with SeV WT or SeV H4 or else left non-infected (-). Luciferase assay was performed 8 hr after infection and was normalized using renilla luciferase activity. Data represent means ± SD (n = 3). (C) HeLa cells were transfected with HMW Poly(I:C) (1 μg/ml) for 9 hr and then, cell extracts were analyzed by immunoblotting. * Probable non-specific protein bands. Values represent the ratio of the larger MAVS isoform band normalized with respect to the loading control, analyzed with ImageJ software. (D) Control or MAVS siRNAs were transfected into HEK293T or HeLa cells. Knockdown of MAVS was confirmed by immunoblotting 72 hr later.