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

Peter Libby,Galina Sukhova,Todd Bourcier

doi:10.1074/jbc.272.25.15817

Abstract

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 (NFkappaB) 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 NFkappaB binding activities. SMC express two inhibitor proteins IkappaBbeta and IkappaBalpha. Interleukin-1beta stimulation caused transient loss of IkappaBalpha and a sustained decrease of IkappaBbeta 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 NFkappaB activity, but addition of serum or platelet-derived growth factor did activate NFkappaB. In situ analyses showed no evidence for basal NFkappaB 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 NFkappaB complexes in human SMC; (ii) stimulatory components in serum activate NFkappaB and likely account for previously reported "constitutive" NFkappaB activity in cultured SMC; and (iii) exposure to inflammatory cytokines may produce prolonged NFkappaB activation in SMC because of sustained decreases in the inhibitory subunit IkappaB-beta.

Highlights

Vascular smooth muscle cells (SMC)1 at sites of atherosclerotic lesions express features of an inflammatory process, such as increased expression of genes encoding growth factors, inducible surface proteins, and molecules involved in extracellular matrix remodeling [1,2,3]
Human SMC Cultured in Serum-containing Medium Exhibit Two Complexes of Constitutive and Inducible nuclear factor ␬-B (NF␬B) Binding Activity—Previous studies reported that cultured bovine SMC exhibit constitutive NF␬B binding activity composed of p50 complexed with a putative Rel protein termed SMC-Rel [16]
To identify the Rel proteins in human SMC that participate in binding DNA under basal and cytokinestimulated conditions, nuclear extracts were prepared from saphenous vein or aortic SMC following 2 h of incubation with or without IL-1␤, a potent stimulus of NF␬B activation

Summary

Introduction

Vascular smooth muscle cells (SMC) at sites of atherosclerotic lesions express features of an inflammatory process, such as increased expression of genes encoding growth factors, inducible surface proteins, and molecules involved in extracellular matrix remodeling [1,2,3]. Phosphorylated I␬B or p105 is enzymatically degraded or processed to p50, respectively, by the multicatalytic proteasome complex [10], and liberated NF␬B dimers translocate to the nucleus and promote transactivation of target genes. One of these target genes encodes the inhibitor I␬B␣ that binds to and limits further NF␬B activity and gene expression [11, 12]. NF␬B Signaling in Human Smooth Muscle Cells have addressed the identity of Rel family members and the issue of their constitutive expression in vitro and in vivo in human SMC cultures and in normal and diseased arterial specimens. As the inhibitory limb of control of NF␬B activity appears critical, we tested the hypothesis that I␬B␣ and I␬B␤ may play distinct roles in the control of cytokine activation of this cell type central to the pathogenesis of atherosclerosis

Methods

Results

Conclusion