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Phillips MC. Is ABCA1 a lipid transfer protein? J Lipid Res 2018; 59:749-763. [PMID: 29305383 DOI: 10.1194/jlr.r082313] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Revised: 01/02/2018] [Indexed: 12/16/2022] Open
Abstract
ABCA1 functions as a lipid transporter because it mediates the transfer of cellular phospholipid (PL) and free (unesterified) cholesterol (FC) to apoA-I and related proteins present in the extracellular medium. ABCA1 is a membrane PL translocase and its enzymatic activity leads to transfer of PL molecules from the cytoplasmic leaflet to the exofacial leaflet of a cell plasma membrane (PM). The presence of active ABCA1 in the PM promotes binding of apoA-I to the cell surface. About 10% of this bound apoA-I interacts directly with ABCA1 and stabilizes the transporter. Most of the pool of cell surface-associated apoA-I is bound to lipid domains in the PM that are created by the activity of ABCA1. The amphipathic α-helices in apoA-I confer detergent-like properties on the protein enabling it to solubilize PL and FC in these membrane domains to create a heterogeneous population of discoidal nascent HDL particles. This review focuses on current understanding of the structure-function relationships of human ABCA1 and the molecular mechanisms underlying HDL particle production.
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Affiliation(s)
- Michael C Phillips
- Division of Translational Medicine and Human Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-5158
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Tomioka M, Toda Y, Mañucat NB, Akatsu H, Fukumoto M, Kono N, Arai H, Kioka N, Ueda K. Lysophosphatidylcholine export by human ABCA7. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:658-665. [PMID: 28373057 DOI: 10.1016/j.bbalip.2017.03.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2016] [Revised: 03/27/2017] [Accepted: 03/29/2017] [Indexed: 10/19/2022]
Abstract
The ATP-binding cassette transporter A7 (ABCA7), which is highly expressed in the brain, is associated with the pathogenesis of Alzheimer's disease (AD). However, the physiological function of ABCA7 and its transport substrates remain unclear. Immunohistochemical analyses of human brain sections from AD and non-AD subjects revealed that ABCA7 is expressed in neuron and microglia cells in the cerebral cortex. The transport substrates and acceptors were identified in BHK/ABCA7 cells and compared with those of ABCA1. Like ABCA1, ABCA7 exported choline phospholipids in the presence of apoA-I and apoE; however, unlike ABCA1, cholesterol efflux was marginal. Lipid efflux by ABCA7 was saturated by 5μg/ml apoA-I and was not dependent on apoE isoforms, whereas efflux by ABCA1 was dependent on apoA-I up to 20μg/ml and apoE isoforms. Liquid chromatography-tandem mass spectrometry analyses revealed that the two proteins had different preferences for phospholipid export: ABCA7 preferred phosphatidylcholine (PC)≥lysoPC>sphingomyelin (SM)=phosphatidylethanolamine (PE), whereas ABCA1 preferred PC>>SM>PE=lysoPC. The major difference in the pattern of lipid peaks between ABCA7 and ABCA1 was the high lysoPC/PC ratio of ABCA7. These results suggest that lysoPC is one of the major transport substrates for ABCA7 and that lysoPC export may be a physiologically important function of ABCA7 in the brain.
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Affiliation(s)
- Maiko Tomioka
- Institute for integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Kyoto 606-8502, Japan
| | - Yoshinobu Toda
- Faculty of Health Care, Tenri Health Care University, Tenri, Nara 632-0018, Japan.
| | - Noralyn B Mañucat
- Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
| | - Hiroyasu Akatsu
- Graduate School of Medical Sciences and Medical School, Nagoya City University, Nagoya 467-8601, Japan
| | - Manabu Fukumoto
- Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi 980-8575, Japan
| | - Nozomu Kono
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan
| | - Hiroyuki Arai
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan
| | - Noriyuki Kioka
- Institute for integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Kyoto 606-8502, Japan; Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
| | - Kazumitsu Ueda
- Institute for integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Kyoto 606-8502, Japan; Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
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