Submitted on March 29, 2006
Accepted on April 9, 2006
Serum amyloid A generates high density lipoprotein with cellular lipid in an ABCA1- or ABCA7-dependent manner
Sumiko Abe-Dohmae, Koichi H. Kato, Yoshitaka Kumon, Wei Hu, Hideaki Ishigami, Noriyuki Iwamoto, Mitsuyo Okazaki, Chen-Ai Wu, Maki Tsujita, Kazumitsu Ueda, and Shinji Yokoyama
Biochemistry, Cell Biology and Metabolism, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi 467-8601
Corresponding Author: syokoyam{at}med.nagoya-cu.ac.jp
Serum amyloid A (SAA) is an amphiphilic helical protein and is found associated with plasma high-density lipoprotein (HDL) in various pathological conditions such as acute or chronic inflammation. Cellular lipid release and generation of HDL by this protein were investigated, comparing to the reactions by apolipoprotein A-I (apoA-I) with several types of cells that appear with various specific profiles of cholesterol and phospholipid release. SAA mediated cellular lipid release from these cells with the same profile as apoA-I. Upregulation of cellular ATP binding cassette transporter (ABC) A1 protein by liver X receptor/retinoid X receptor agonists resulted in the increase of cellular lipid release by apoA-I and SAA. SAA reacted with the HEK293-derived clones that stably express human ABCA1 (293/2c) or ABCA7 (293/6c) to generate cholesterol-containing HDL in a similar manner to apoA-I. Dibutyryl cyclic AMP and phorbol 12-myristate-13-acetate that differentiate apoA-I-mediated cellular lipid release between 293/2c and 293/6c, also exhibited the same differential effects on the SAA-mediated reactions. No evidence was demonstrated for the ABCA1/ABCA7-independent lipid release by SAA. Characterization of physicochemical properties of the HDL revealed that SAA-generated HDL particles appeared with higher density, larger diameters and slower electrophoretic mobility, than those generated by apoA-I. The results demonstrated that SAA generates cholesterol-containing HDL directly with cellular lipid, and the reaction is mediated by ABCA1 and ABCA7.