Activation of NF-κB by Bradykinin through a Gαq- and Gβγ-dependent Pathway That Involves Phosphoinositide 3-Kinase and Akt*

Recent work has suggested a role for the serine/threonine kinase Akt and IκB kinases (IKKs) in nuclear factor (NF)-κB activation. In this study, the involvement of these components in NF-κB activation through a G protein-coupled pathway was examined using transfected HeLa cells that express the B2-type bradykinin (BK) receptor. The function of IKK2, and to a lesser extent, IKK1, was suggested by BK-induced activation of their kinase activities and by the ability of their dominant negative mutants to inhibit BK-induced NF-κB activation. BK-induced NF-κB activation and IKK2 activity were markedly inhibited by RGS3T, a regulator of G protein signaling that inhibits Gαq, and by two Gβγ scavengers. Co-expression of Gαq potentiated BK-induced NF-κB activation, whereas co-expression of either an activated Gαq(Q209L) or Gβ1γ2 induced IKK2 activity and NF-κB activation without BK stimulation. BK-induced NF-κB activation was partially blocked by LY294002 and by a dominant negative mutant of phosphoinositide 3-kinase (PI3K), suggesting that PI3K is a downstream effector of Gαq and Gβ1γ2 for NF-κB activation. Furthermore, BK could activate the PI3K downstream kinase Akt, whereas a catalytically inactive mutant of Akt inhibited BK-induced NF-κB activation. Taken together, these findings suggest that BK utilizes a signaling pathway that involves Gαq, Gβ1γ2, PI3K, Akt, and IKK for NF-κB activation.