RNF26 catalyzes K11-linked polyubiquitination of MITA.

<p>(A and B) RNF26 targeted MITA for K11-linked polyubiquitination. The 293 cells (5×10⁶) were transfected with Flag-MITA (5 µg) and RNF26 (1 µg) together with HA-Ub or its mutants (1 µg each). Twenty-four hours after transfection, cells were subjected for IP under denatured conditions with limited amount of anti-Flag (0.5 µg) so that equal amount of Flag-MITA is pulled down. The immunoprecipitates were analyzed by immunoblots with anti-HA (upper panel) or anti-Flag (lower panel). The whole cell lysates were analyzed by immunoblots with anti-Flag or anti-RNF26 as indicated. Ub-AKR, all lysine residues of ubiquitin were mutated to arginine. (C) Effects of RNF26-RNAi plasmids on the expression of RNF26. In the upper panels, the 293 cells (1×10⁶) were transfected with the expression plasmids for RNF26-Flag (0.5 µg) and HA-β-actin (0.1 µg) together with the indicated RNAi plasmids (1 µg each). Twenty-four hours after transfection, whole cell lysates were analyzed by immunoblots with anti-Flag or anti-HA. In the lower panels, 293 cells were transduced with a control or RNF26-RNAi by retrovirus mediated gene transfer. Cells (1×10⁶) were lysed and whole cell lysates were analyzed by immunoblots with anti-RNF26 or anti-β-actin. (D) Immunoblot analysis of Flag-tagged ubiquitin expression in THP-1 cells stably transfected with Flag-Ub-K11O plasmid. Whole cell lysates of THP-1-Flag-Ub-K11O-RNF26-RNAi and control cells (1×10⁶) were analyzed by immunoblots with antibodies against the indicated proteins. RNF26-RNAi #1 was used here and in the following experiments if not noted. (E and F) Effects of RNF26 knockdown on virus-induced K11-linked polyubiquitination of endogenous MITA. In (E), THP-1-Flag-Ub-K11O-RNF26-RNAi or control cells (2×10⁷) were infected with SeV or HSV-1 for the indicated time points or left uninfected followed by IP under denatured conditions with anti-MITA. The immunoprecipitates were analyzed by immunoblots with anti-Flag (upper panels) or anti-MITA (lower panels). The whole cell lysates were analyzed by immunoblots with antibodies against the indicated cellular or viral proteins. In (F), 293-HA-Ub-K11O cells (2×10⁷) were transfected with a control or RNF26-RNAi plasmid (10 µg each). Twelve hours after transfection, puromycin (1 µg/mL) was added into the culture medium. The cells were selected for twenty-four hours and infected with SeV or left uninfected for the indicated time points followed by IP under denatured conditions and immunoblot analysis as in (E). All experiments were repeated for at least three times with similar results.