G alpha(16) couples chemoattractant receptors to NF-kappa B activation

The guanine nucleotide-binding regulatory protein alpha -subunit, G alpha ( 16), is primarily expressed in hemopoietic cells, and interacts with a larg e number of seven-membrane span receptors including chemoattractant recepto rs. We investigated the biological functions resulting from G alpha (16), c oupling of chemoattractant receptors in a transfected cell model system. He La cells expressing a kappaB-driven luciferase reporter, G alpha (16), and the formyl peptide receptor responded to fMLP with a similar to7- to 10-fol d increase in luciferase activity. This response was accompanied by phospho rylation of I kappaB alpha and elevation of nuclear kappaB-DNA binding acti vity, indicating activation of NF-kappaB. In contrast to G alpha (16), expr ession of G alpha (q), G alpha (13), and G alpha (12) resulted in a margina l increase in kappaB luciferase activity. A GTPase-deficient, constitutivel y active G alpha (16), mutant (Q212L) could replace agonist stimulation for activation of NF-kappaB. Furthermore, expression of G alpha (16) (Q212L) m arkedly enhanced TNF-alpha -induced kappaB reporter activity. The G alpha ( 16)-mediated NF-kappaB activation was paralleled by an increase in phosphol ipase C-beta activity, and was blocked by pharmacological inhibitors of pro tein kinase C (PKC) and by buffering of intracellular Ca2+. The involvement of a conventional PKC isoform was confirmed by the finding that expression of PKC alpha enhanced the effect of G alpha (16), and a dominant negative PKC alpha partially blocked G alpha (16),-mediated NF-kappaB activation. In addition to formyl peptide receptor, G alpha (16) also enhanced NF-kappaB activation by the C5a and C3a receptors, and by CXC chemokine receptor 2 an d CCR8. These results suggest a potential role of G alpha (16), in transcri ptional regulation downstream of chemoattractant receptors.