Fluid Shear Stress Activation of IκB Kinase Is Integrin-dependent

Abstract

Vascular endothelial cells (ECs),1 serving as a barrier between the circulating blood and the vessel wall, are constantly exposed to fluid shear stress. The focal nature of atherosclerotic lesions in the arterial tree demonstrates the critical role of flow conditions in atherogenesis. In vitro experiments using flow channels with cultured ECs have shown that shear stress activates the platelet derived-growth factor gene (1), a potent mitogen for vascular smooth muscle cells. The shear stress activation of the platelet derived-growth factor gene is through the action of the transcription factor NF-B on the shear stressresponsive element GAGACC (2, 3). In addition, electrophoresis mobility shift assay showed that nuclear extracts isolated from ECs exposed to shear stress increase their binding to oligonucleotides containing the B enhancer element (4), and a luciferase reporter driven by the B enhancer element was shown to be shear-inducible (5). However, the signal transduction pathway leading to the activation of NF-B in ECs in response to shear stress is still unclear.The transcription factor NF-B was first identified as a protein that binds to a specific DNA site in the intronic enhancer of the immunoglobulin light chain gene (6). It is composed of homo-or heterodimers of members of the Rel family of transcription factors that control the expression of numerous genes involved in the immune and inflammatory responses, cell adhesion, and growth control (see Refs. 7 and 8 for review). NF-B can be activated by many types of extracellular stimuli, including tumor necrosis factor (TNF), interleukin-1, bacterial endotoxin lipopolysaccharide, viral infection, viral proteins, antigen receptor cross-linking of T and B cells, calcium ionophores, phorbol esters, UV radiation, free radicals, hypoxia, etc. (see Ref. 9 for review). In almost all cell types, NF-B is sequestered in the cytoplasm through tight association with the inhibitory IB proteins, including IB-␣ and IB-␤. Activation of NF-B by a variety of stimuli is dependent upon the phosphorylation and subsequent degradation of the IB proteins; this allows the translocation of NF-B into the nucleus to activate various target genes. Phosphorylation of IB proteins occurs at specific residues, Ser-32 and Ser-36 of IB-␣ and Ser-19 and Ser-23 of IB-␤ (10 -13). Following phosphorylation, IB proteins are ubiquitinated and then degraded by a proteasome-dependent pathway (10 -17). The IB kinase (IKK) complex was recently purified and is composed of several subunits (18 -21). Two of the subunits, 85 and 87 kDa in size, were termed IKK␣ and IKK␤, respectively. These two proteins (with 52% homology) contain an N-terminal catalytic kinase domain and several putative protein interaction motifs, including a leucine zipper and a helix-loop-helix domain at their C termini (18,19).Integrins are a family of Ͼ20 different transmembrane heterodimers composed of ␣-and ␤-subunits that are associated noncovalently. All integrins consist of a large extracellular domain, a transmembrane region,...

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MicroRNA-10a regulation of proinflammatory phenotype in athero-susceptible endothelium in vivo and in vitro

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Laminar Shear Stress Up-Regulates Inducible Nitric Oxide Synthase in the Endothelium

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