Effect of Dex on TLR-induced TAK1 activation. Macrophages were treated with Dex followed by (A) Poly (I:C), (B) CpG, and (C) LPS treatment for the indicated periods of time. Cell lysates were analyzed by Western blot using anti-TAK1 and total TAK1 antibodies. Representative of 2 to 3 independent experiments. (D) Effect of Dex on LPS-induced TAK1 phosphorylation in Lps2 mutant and Trif^−/− macrophages. Peritoneal macrophages isolated from Lps2 mutant and Trif^−/− mice treated with LPS for 30 minutes in the presence or absence of Dex. Cell lysates were analyzed by Western blot using anti-TAK1 and total TAK1 antibodies. Representative of 2 independent experiments. (E) Differential regulation of TLR-induced MAPK and NKκB activation by glucocorticoids. TAK1 induces activation of MAP kinases and NFκB irrespective of the nature of TLR ligation. However, activation of GR by Dex suppresses TAK1-induced MAPK and NFκB activation in a stimulus-specific manner. TLR4-MyD88-Trif–induced TAK1 activity is Dex resistant, and Dex attenuates p38 MAPK activity only via induction of MKP-1. TLR9-MyD88–induced TAK1 activity is Dex sensitive, and as such, NFκB, p38 MAPK, and JNK activity is as well. TLR3-Trif–induced TAK1 activity is also Dex sensitive, and Dex inhibits p38 MAPK, ERK, and JNK activity (NFκB is not significantly induced). Dex-sensitive TAK1 targets are designated in red font; Dex-resistant targets are in black font.