Regulation of vascular smooth muscle cell proliferation by nuclear factor-κB and its inhibitor, I-κB

Proliferation of vascular smooth muscle cells (SMC) is a crucial event in the formation of atherosclerotic tissues and is regulated by nuclear transcriptional factors including nuclear factor-kappa B (NF-kappa B). We constructed a reporter gene assay to measure NF-kappa B-dependent transcriptional activity in SMC. Thrombin receptor-activating peptide (TRAP) and basic fibroblast growth factor (bFGF) stimulated SMC proliferation and rapidly enhanced the NF-kappa B transcriptional activity in a dose-dependent manner. 4-Cyano-5,5-bis-(methoxyphenyl)4-pentenoic acid (E5510) significantly inhibited SMC proliferation and also suppressed NF-kappa B transcription stimulated by TRAP and bFGF. In contrast, although tumor necrosis factor (TNF)-alpha activated NF-kappa B transcription, E5510 had no effect on TNF-alpha-induced activation. NF-kappa B was activated after the stimulation of TRAP, bFGF, and TNF-alpha in electrophoretic mobility shift assay, and E5510 suppressed the NF-kappa B activation induced by TRAP and bFGF but not the activation by TNF-alpha. Western blot analysis of I-kappa B alpha and I-kappa B beta, inhibitors of NF-kappa B, indicated that I-kappa B alpha degradation, rather than I-kappa B beta degradation, was important in NF-kappa B activation after the stimulation of TRAP and bFGF. PD98059, an inhibitor of extracellular signal-regulated kinase (ERK) kinase, suppressed NF-kappa B transcriptional activity and SMC proliferation. The phosphorylation of ERK1/2 was rapidly induced by TRAP and bFGF but not by TNF-alpha. These results indicate that TRAP and bFGF induced I-kappa B degradation and NF-kappa B activation through a distinct pathway from TNF-alpha and that ERK1/2 may play an important role in NF-kappa B activation induced by TRAP and bFGF.