RNF26 regulates IRF3 stability.

<p>(A) Effects of RNF26 knockdown on IRF3 level. In the left panel, whole cell lysates of THP-1-RNF26-RNAi or control cells (1×10⁶) were analyzed by immunoblots with the indicated antibodies. In the right panel, cells (1×10⁶) were subjected to quantitative real-time PCR analysis. (B) Effects of RNF26 on IRF3 stability. The 293 cells (1×10⁶) were transfected with HA-IRF3 (0.5 µg) and HA-β-actin (0.1 µg) together with RNF26 or its mutant (0.3 µg each). Twenty-four hours later, whole cell lysates were analyzed by immunoblots with anti-HA or anti-RNF26. (C) Effects of RNF26 and its mutant on SeV-triggered activation of the IFN-β promoter. The 293 cells (2×10⁵) were transfected with the IFN-β promoter reporter (0.1 µg) and RNF26 or its mutant (0.1 µg each). Twenty hours after transfection, cells were infected with SeV for 12 hours or left uninfected before reporter assays were performed. (D) Effects of RNF26 on IRF3 ubiquitination. The 293 cells (5×10⁶) were transfected with Flag-IRF3 (5 µg) and RNF26 (1 µg) together with HA-Ub or its mutants (1 µg each). Eighteen hours after transfection, 3-MA (500 ng/mL) was added into culture medium for 4 hours to protect IRF3 from autophagosomal degradation during the experiment. The cell lysates were subjected to IP under denatured conditions with anti-Flag and the immunoprecipitates were analyzed by immunoblots with anti-HA (upper panels) or anti-Flag (lower panels). The whole cell lysates were analyzed by immunoblots with anti-Flag or anti-RNF26 as indicated. (E) Effects of inhibitors on RNF26-mediated destabilization of IRF3. The 293 cells (1×10⁶) were transfected with the indicated plasmids as described in (B). Eighteen hours after transfection, 3-MA (500 ng/mL), NH₄Cl (25 mM) or MG132 (100 µM) was added into culture medium for four hours. Whole cell lysates were analyzed by immunoblots with anti-HA or anti-RNF26. (F) Effects of ATG12 knockdown on RNF26-mediated destabilization of IRF3. The 293-ATG12-RNAi or control cells (1×10⁶) were transfected with the indicated plasmids. Twenty-four hours later, whole cell lysates were analyzed by immunoblots with anti-HA, anti-RNF26 or anti-ATG12 as indicated. All experiments were repeated for at least three times with similar results. The bar graphs show mean ± S.D. (<i>n</i> = 3) of a representative experiment performed in triplicate.