Abstract

A unique property of the extracellular matrix of J774 and THP-1 cells has been identified, which contributes to the ability of these cells to promote cholesterol efflux. We demonstrate high level apolipoprotein (apo) A-I binding to macrophage cells (THP-1 and J774) and to their extracellular matrix (ECM). However, high level apoA-I binding is not observed on fibroblasts, HepG2 cells, or U937 cells (a macrophage cell line that does not efflux cholesterol to apoA-I or bind apoA-I on their respective ECM). Binding to the ECM of THP-1 or J774 macrophages depends on the presence of apoA-I C-terminal helices and is markedly reduced with a mutant lacking residues 187-243 (apoA-I Delta(187-243)), suggesting that the hydrophobic C terminus forms a hydrophobic interaction with the ECM. ApoA-I binding is lost upon trypsin treatment or with Triton X-100, a preparation method that de-lipidates the ECM. However, binding is recovered with re-lipidation, and is preserved with ECM prepared using cytochalasin B, which conserves the endogenous phospholipid levels of the ECM. We also demonstrate that specific cholesterol efflux to apoA-I is much reduced in cells released from their native ECM, but fully restored when ECM-depleted cells are added back to ECM in the presence of apoA-I. The apoA-I-mediated efflux is deficient in plated or suspension U937 macrophages, but is restored to high levels when the suspension U937 cells are reconstituted with the ECM of J774 cells. The ECM-dependent activity was much reduced in the presence of glyburide, indicating participation of ABCA1 (ATP-binding cassette transporter 1) in the efflux mechanism. These studies establish a novel binding site for apoA-I on the macrophage ECM that may function together with ABCA1 in promoting cholesterol efflux.

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Publisher Full Text

Authors

Burgess JW, Kiss RS, Zheng H, Zachariah S, Marcel YL

Institution

Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ontario K1Y 4W7, Canada.

Source

The Journal of biological chemistry 277:35 2002 Aug 30 pg 31318-26

MeSH

ATP-Binding Cassette Transporters
Animals
Apolipoprotein A-I
Binding Sites
Cell Line
Cells, Cultured
Cholesterol
Extracellular Matrix
Extracellular Matrix Proteins
Fibroblasts
Fibronectins
Humans
Laminin
Macrophages
Mice
Organ Specificity
Phospholipids
Skin
Tetradecanoylphorbol Acetate
Trypsin

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

12050168