TAB2 activates TAK1 in the endothelium. (A) TAK1 control (Tak1^flox/flox; TAK1 CT) and Rosa26-Cre Tak1^flox/flox (TAK1^iko) mice were treated with tamoxifen and lung endothelial cells were purified by magnetic beads coated with PECAM-1 Ab. The purified endothelial cells were analyzed by immunoblotting. (B) Lung endothelial cells from TAB2 control (Tab2^flox/flox; TAB2 CT) and Rosa26-Cre Tab2^flox/flox (TAB2^iko) mice were analyzed by immunoblotting. (C) Cell lysates from control TNFR1^−/− (Tak1^flox/flox Tnfr1^−/−) and TAK1^ecko TNFR1^−/− (Tie2-Cre Tak1^flox/flox Tnfr1^−/−) yolk sacs at E10.5 were analyzed by immunoblotting. (D) Cell lysates from TNFR1^−/− (Tab2^flox/flox Tnfr1^−/−) and TAB2^ecko TNFR1^−/− (Tie2-Cre Tab2^flox/flox Tnfr1^−/−) yolk sacs at E11.5 and E12.5, respectively, were analyzed by immunoblotting. One control and 2 TAB2^ecko TNFR1^−/− embryos from the same litter were analyzed. Molecular weight markers are shown (kDa). Asterisks indicate nonspecific bands.