Gαq and Gβγ regulate PAR-1 signaling of thrombin-induced NF-κB activation and ICAM-1 transcription in endothelial cells

Abstract

As thrombin binding to the G protein-coupled proteinase activated receptor-1 (PAR-1) induces endothelial adhesivity to leukocytes through NF-κB activation and intercellular adhesion molecule-1 (ICAM-1) expression, we determined the signaling pathways mediating the response. Studies showed that the heterotrimeric G proteins, Gαq, and the GΒγ dimer were key determinants of the PAR-1 agonist peptide (TFLLRNPNDK)-induced NF-κB activation and ICAM-1 expression in endothelial cells. Cotransfection of RGS3T, a regulator of G-protein signaling that inhibits Gαq or α-transducin (Gαt), a scavenger of the GΒγ, markedly decreased NF-κB activity induced by PAR-1 activation. We determined the downstream signaling targets activated by Gαq and GΒγ that mediate NF-κB activation. Expression of the kinase-defective protein kinase C (PKC)-δ mutant inhibited NF-κB activation induced by the constitutively active Gαq mutant, but had no effect on NF-κB activity induced by GΒ1γ2. In related experiments, NF-κB as well as ICAM-1 promoter activation induced by GΒ1γ2 were inhibited by the expression of the dominant-negative mutant of 85-kDa regulatory subunit of PI 3-kinase; however, the expression of this mutant had no effect on the response induced by activated Gαq. Cotransfection of the catalytically inactive Akt mutant inhibited the NF-κB activation induced by the constitutively active PI 3-kinase mutant as well as that by the activated forms of Gαq and PKC-δ. These results support a model in which ligation of PAR-1 induces NF-κB activation and ICAM-1 transcription by the engagement of parallel Gαq/PKC-δ and GΒγ/PI3-kinase pathways that converge at Akt.