The nuclear factor kappa-B signaling pathway participates in dysregulation of vascular smooth muscle cells in vitro and in human atherosclerosis

In the lesions of atherosclerosis, vascular smooth muscle cells (SMC) display many functions characteristic of cytokine activation that likely contribute importantly to ongoing inflammation during human atherogenesis. The transcription factor nuclear factor kappa-B (NF kappa B) often mediates the effects of cytokines on target cells, but the identity of Rel family members important in human SMC activation remains uncertain. In vitro, human SMC express multiple Rel family members. Of these, dimers of p65 and p50, but not a putative SMC-Rel, comprise basal and inducible NF kappa B binding activities. SMC express two inhibitor proteins I kappa B beta and I kappa B alpha. Interleukin-lp stimulation caused transient loss of I kappa B alpha and a sustained decrease of I kappa B beta that correlated with increased and persistent levels of p65/p50 protein and binding activity in the nucleus. SMC cultured under serum-free conditions displayed little NF kappa B activity, but addition of serum or platelet-derived growth factor did activate NF kappa B. In situ analyses showed no evidence for basal NF kappa B activity in SMC in vivo as nonatherosclerotic arteries did not contain nuclear p65 or p50 protein. However, the nuclei of intimal SMC within human atheroma did contain both Rel proteins. We conclude that (i) dimers of p65 and p50, but not SMC-Rel, comprise NF kappa B complexes in human SMC; (ii) stimulatory compo nents in serum, activate NF kappa B and likely account for previously reported ''constitutive'' NF kappa B activity in cultured SMC; and (iii) exposure to inflammatory cytokines may produce prolonged NF kappa B activation in SMC because of sustained decreases in the inhibitory subunit I kappa B-beta.