Submitted on September 26, 2005
Revised on October 25, 2005
Accepted on October 26, 2005
Cell-surface expressed Moesin-like HDL/Apo A-I binding protein is involved in cholesterol efflux from human monocyte-derived macrophages
Akifumi Matsuyama, Naohiko Sakai, Hisatoyo Hiraoka, Ken-ichi Hirano, and Shizuya Yamashita
Department of Internal Medicine and Molecular Science, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871
Corresponding Author: shizu{at}imed2.med.osaka-u.ac.jp
Background: High-density lipoprotein (HDL) and its major component, apolipoprotein (apo) A-I, play a central role in reverse cholesterol transport. We recently reported the involvement of glycosylphosphatidylinositol-anchor (GPI-anchor) in the binding of HDL and apo A-I on human macrophages and purified an 80 kDa HDL/apo A-I binding protein. In the present study, we characterized the GPI-anchored HDL/apo A-I binding protein from macrophages. Methods:, The HDL/apo A-I binding protein was purified from macrophages and digested with endopeptidase and the resultant fragments were sequenced. Cholesterol efflux, flow cytometry, immunoblotting and immunohistochemical analyses were performed to characterize the HDL/apo A-I binding protein. Results: Two parts of 7 amino acid sequences completely matched those of moesin. Flow cytometry, immunoblotting and immunohistochemistry using anti-moesin antibody, showed that the HDL/apo A-I-binding protein was N-glycosylated and expressed on cell-surface. It was termed moesin-like protein. Treatment of macrophages with anti-moesin antibody blocked the binding of HDL/apo A-I and suppressed cholesterol efflux. The moesin-like protein was exclusively expressed on macrophages and upregulated by cholesterol loading and cell differentiation. Conclusion: Our results indicate that the moesin-like HDL/apo A-I binding protein is specifically expressed on the surface of human macrophages and promotes cholesterol efflux from macrophages.
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