RESUMO
Transforming growth factor (TGF)-ß1 plays several roles in a variety of cellular functions. TGF-ß1 transmits its signal through Smad transcription factor-dependent and -independent pathways. It was reported that TGF-ß1 activates NF-κB and RhoA, and RhoA activates NF-κB in several kinds of cells in a Smad-independent pathway. However, the activation molecular mechanism of NF-κB by RhoA upon TGF-ß1 has not been clearly elucidated. We observed that RhoA-GTP level was increased by TGF-ß1 in RAW264.7 cells. RhoA-GDP and RhoGDI were bound to N- and C-terminal domains of IKKγ, respectively. Purified IKKγ facilitated GTP binding to RhoA complexed with RhoGDI. Furthermore, Dbs, a guanine nucletotide exchange factor of RhoA much more enhanced GTP binding to RhoA complexed with RhoGDI in the presence of IKKγ. Indeed, si-IKKγ abolished RhoA activation in response to TGF-ß1 in cells. However, TGF-ß1 stimulated the release of RhoA-GTP from IKKγ and Rho-associated kinase (ROCK), an active RhoA effector protein, directly phosphorylated IKKß in vitro, whereas TGF-ß1-activated kinase 1 activated RhoA upon TGF-ß1 stimulation. Taken together, our data indicate that IKKγ facilitates RhoA activation via a guanine nucletotide exchange factor, which in turn activates ROCK to phosphorylate IKKß, leading to NF-κB activation that induced the chemokine expression and cell migration upon TGF-ß1.