Phosphatidylinositol 3-Kinase Is Involved in the Induction of Macrophage Growth by Oxidized Low Density Lipoprotein

Jason S Martens,Neil E Reiner,Patricia Herrera-Velit,Urs P Steinbrecher

doi:10.1074/jbc.273.9.4915

Phosphatidylinositol 3-Kinase Is Involved in the Induction of Macrophage Growth by Oxidized Low Density Lipoprotein

Jason S Martens, Neil E Reiner + Show 2 more

Open Access

https://doi.org/10.1074/jbc.273.9.4915

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Abstract

Early atherosclerotic lesions are characterized by the presence of cholesterol-rich, macrophage-derived foam cells. It has recently been shown that macrophage proliferation occurs during the development of early lesions and that oxidized low density lipoprotein (LDL) stimulates macrophage growth. Possible mechanisms for this induction of macrophage growth include potentiation of mitogenic signal transduction by a component of oxidized LDL following internalization and degradation, interaction with integral plasma membrane proteins coupled to signaling pathways, or direct or indirect activation of growth factor receptors on the cell surface (e.g. GM-CSF receptor) through an autocrine/paracrine mechanism. The present study was undertaken to characterize some of the early intracellular signaling events by which oxidized LDL mediates macrophage cell growth. Extensively oxidized LDL increased protein-tyrosine phosphorylation and caused a 2-fold increase in phosphatidylinositol (PI) 3-kinase activity in phorbol ester-pretreated THP-1 cells (a human monocyte-like cell line). Similar concentrations of native LDL had no effect. Oxidized LDL also stimulated growth of resident mouse peritoneal macrophages, and this effect was reduced by 40-50% in cells treated with PI 3-kinase inhibitors (100 nM wortmannin or 20 microM LY294002). These results suggest that PI 3-kinase mediates part of the mitogenic effect of oxidized LDL, but parallel pathways involving other receptors and signal transduction pathways are likely also involved.

Highlights

Several lines of evidence have implicated oxidized low density lipoprotein (LDL)1 in the pathogenesis of atherosclerosis, including the demonstration that oxidatively modified LDL exists in the arterial intima in vivo [1, 2] and that antioxidant drugs can retard atherogenesis in some animal models [3,4,5,6,7]
Protein-tyrosine Phosphorylation in Macrophages Treated with Oxidized LDL—Differentiated THP-1 cells were exposed to 40 ␮g/ml oxidized LDL, and cell lysates were assayed for total tyrosine-directed protein phosphorylation by immunoblotting with 4G10 anti-phosphotyrosine antibody
Phosphatidylinositol 3-Kinase Activity in Macrophages Treated with Oxidized LDL—Differentiated THP-1 cells were incubated with 40 ␮g/ml oxidized LDL, and whole cell lysates were examined for PI 3-kinase activity

Summary

Introduction

Several lines of evidence have implicated oxidized low density lipoprotein (LDL) in the pathogenesis of atherosclerosis, including the demonstration that oxidatively modified LDL exists in the arterial intima in vivo [1, 2] and that antioxidant drugs can retard atherogenesis in some animal models [3,4,5,6,7]. Foam cells are lipid-laden macrophages and are derived from blood-borne monocytes that have been recruited to sites of predilection of atherosclerosis by overexpression of endothelial adhesion molecules and by local release of chemotactic factors [13, 14]. Both of these effects have been associated with oxidized LDL [15,16,17,18,19,20,21]. The objective of the present study was to determine if oxidized LDL leads to increased protein-tyrosine phosphorylation and PI 3-kinase activation in macrophages and to define the role of PI 3-kinase in the mitogenic activity of oxidized LDL

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