TRAF3 negatively regulates IL-17–mediated signaling. (A and B) HeLa cells transfected with plasmids for empty vector (EV) or M2 (Flag)-tagged TRAF3 (A) or infected with lentivirus encoding scrambled siRNA (siNC) or TRAF3 siRNA (siTRAF3; B) were left untreated or treated with IL-17 for 7.5, 15, or 30 min. Whole cell lysates were immunoblotted with anti–p-IκBα, anti-IκBα, anti–p-p65, anti–p-p38, anti-p38, anti–p-ERK, anti-ERK, anti-M2, anti-TRAF3, or anti–β-actin. (C) Traf3^−/− MEFs transduced with control retrovirus or retrovirus encoding mouse TRAF3 (M2-TRAF3) were left untreated or treated with IL-17 for 7.5, 15, or 30 min. Whole cell lysates were immunoblotted with the indicated antibodies. (D–F) Mouse primary astrocytes (D), U87-MG astrocyte cell line (E), or human primary synoviocytes (FLS; F) infected with lentivirus encoding scrambled siRNA, TRAF3 siRNA, or Act1 siRNA (siAct1) were left untreated or treated with IL-17 for 7.5, 15, or 30 min. Whole cell lysates were immunoblotted with the indicated antibodies. Data are representative of three (A–C) or two (D–F) independent experiments.