Cholesterol Research Today is a free monthly online journal that collates and summarizes the latest research about Cholesterol, including details on high cholesterol, hdl, ldl, diet, risks. | ||||||||
|
Enhanced apoA-I-dependent cholesterol efflux by ABCA1 from sphingomyelin-deficient Chinese hamster ovary cells.Nagao K, Takahashi K, Hanada K, Kioka N, Matsuo M, Ueda K Laboratory of Cellular Biochemistry, Division of Applied Life Sciences, Kyoto University Graduate School of Agriculture, Kyoto 606-8502, Japan. ATP binding cassette protein A1 (ABCA1) plays a major role in cholesterol homeostasis and high density lipoprotein (HDL) metabolism. It is proposed that ABCA1 reorganizes the plasma membrane and generates more loosely packed domains that facilitate apoA-I-dependent cholesterol efflux. In this study, we examined the effects of the cellular sphingomyelin level on HDL formation by ABCA1 by using a Chinese hamster ovary-K1 mutant cell line, LY-A, which has a missense mutation in the ceramide transfer protein CERT. When LY-A cells were cultured in Nutridoma-BO medium and sphingomyelin content was reduced, apoA-I-dependent cholesterol efflux by ABCA1 from LY-A cells increased 1.65-fold compared with that from LY-A/CERT cells stably transfected with human CERT cDNA. Exogenously added sphingomyelin significantly reduced the apoA-I-dependent efflux of cholesterol from LY-A cells, confirming that the decrease in sphingomyelin content in the plasma membrane stimulates cholesterol efflux by ABCA1. The amount of cholesterol available to cold methyl-beta-cyclodextrin (MbetaCD) extraction from LY-A cells was increased by 40% by the expression of ABCA1 and was 1.6-fold higher than that from LY-A/CERT cells. This step in ABCA1 function, making cholesterol available to cold MbetaCD, was independent of apoA-I. These results suggest that the function of ABCA1 could be divided into two steps: (i) a flopping step to move phosphatidylcholine and cholesterol from the inner to outer leaflet of the plasma membrane, where cholesterol becomes available to cold MbetaCD extraction, and (ii) a loading step to load phosphatidylcholine and cholesterol onto apoA-I to generate HDL. Published 14 May 2007 in J Biol Chem, 282(20): 14868-74.
© 2004-2008 Cholesterol Research Today. All Rights Reserved. |
| ||||||
