Angiotensin II (AngII) functions as a stress hormone under conditions of stretch, pressure and injury to stimulate smooth muscle cell migration and proliferation. Since the cellular response to stress is mediated in part by the transcription factor NF-kappaB, the relationship between AngII and NF-kappaB was investigated. Our study revealed that AngII promoted a dose-dependent and transient phosphorylation of the regulatory IkappaBalpha protein in smooth muscle cells from porcine coronary artery, with concomitant nuclear translocation of NF-kappaB and increased binding to a kappaB promoter element. Both nuclear translocation and kappaB-element binding were prevented by the AT(1) receptor antagonist losartan. The role of NF-kappaB in AngII-dependent smooth muscle cell migration and proliferation was then assessed. Inhibitors of NF-kappaB nuclear translocation (phenethyl caffeiate) and IkappaB phosphorylation (Bay 11-7085) effectively arrested both AngII-dependent DNA synthesis and migration. These results were confirmed with SN50, a highly selective peptide inhibitor of NF-kappaB activation. Phenethyl caffeiate also prevented the phosphorylation of cdk2 and Rb, indicating NF-kappaB was required for G1/S transition. The target of NF-kappaB inhibition was identified as cyclin E, since induction of this gene, but not cyclin D1, was suppressed by phenethyl caffeiate. We subsequently examined the relationship between NF-kappaB and neointimal formation in response to angioplasty-induced injury, a process susceptible to inhibition by losartan. Both phenethyl caffeiate and Bay 11-7085 blocked neointimal hyperplasia in organ culture following balloon angioplasty. These data indicate NF-kappaB is an important mediator of intracellular signalling by AngII under normal physiological conditions, and following vascular injury.