ATP-binding Cassette Transporter A1 Expression Disrupts Raft Membrane Microdomains through Its ATPase-related Functions

Abstract

ATP-binding cassette transporter A1 (ABCA1) is known to mediate cholesterol efflux to lipid-poor apolipoprotein A-I. In addition, ABCA1 has been shown to influence functions of the plasma membrane, such as endocytosis and phagocytosis. Here, we report that ABCA1 expression results in a significant redistribution of cholesterol and sphingomyelin from rafts to non-rafts. Caveolin, a raft/caveolae marker also redistributes from punctate caveolae-like structures to the general area of the plasma membrane upon ABCA1 expression. Furthermore, we observed significant reduction of Akt activation in ABCA1-expressing cells, consistent with raft disruption. Cholesterol content in the plasma membrane is, however, not altered. Moreover, we provide evidence that a non-functional ABCA1 with mutation in an ATP-binding domain, A937V, fails to redistribute cholesterol, sphingomyelin, or caveolin. A937V also fails to influence Akt activation. Finally, we show that apolipoprotein A-I preferentially associates with nonraft membranes in ABCA1-expressing cells. Our results thus demonstrate that ABCA1 causes a change in overall lipid packing of the plasma membrane, likely through its ATPase-related functions. Such reorganization by ABCA1 effectively expands the non-raft membrane fractions and, consequentially, pre-conditions cells for cholesterol efflux.

Sphingomyelin Depletion Impairs Anionic Phospholipid Inward Translocation and Induces Cholesterol Efflux

“…Most researchers agree that ABCA1 is not located in lipid rafts and that it mediates cholesterol efflux primarily from non-raft domains (52)(53)(54). ABCA1 activity seems to destabilize lipid rafts and has been shown to promote the transfer of FC from the raft to the non-raft domain in BHK cells (55), and Abca1-deficient macrophages are reported to have more lipid rafts (56).…”

Bile salt–dependent efflux of cellular phospholipids mediated by ATP binding cassette protein B4

“…Even in the case of ABCA1, which mediates apoA-I-dependent PC and cholesterol efflux, the direct involvement of ABCA1 in cholesterol movement is still controversial. 37,38 Cholesterol excretion into the bile is almost completely impaired in the Abcb4 knockout mice. [8][9][10]18 In the absence of either ABCG5 or ABCG8 (or both), cholesterol excretion in mice is strongly reduced.…”

Enhanced ApoA-I-dependent Cholesterol Efflux by ABCA1 from Sphingomyelin-deficient Chinese Hamster Ovary Cells

“…Triton X-100 Extraction-Cellular content of Triton X-100 (TX)-soluble cholesterol was analyzed as described previously (8). Briefly, cell monolayers were washed twice with ice-cold PBS and chilled on ice for 30 min in F-12 containing 10 mM HEPES, pH 7.4.…”

“…It was also reported that macrophages from ABCA1-deficient mice exhibited increased lipid rafts on the cell surface (9) and induction of ABCA1 by 8Br-cAMP made RAW264.7 cells more sensitive to M␤CD treatment (5). ABCA1 expression increased the Triton X-100 solubility of SM, but not that of PC (8). As SM has high affinity to cholesterol and tends to form raft domains in the plasma membrane, a change in SM content likely affects membrane dynamics.…”

“…Recently, Landry et al (8) reported that ABCA1 reorganizes the plasma membrane and generates more loosely packed domains and suggested that the loosely packed domains facilitate apoA-I association with cells and, consequently, lipid acquisition by apoA-I to form nascent HDL particles. It was also reported that macrophages from ABCA1-deficient mice exhibited increased lipid rafts on the cell surface (9) and induction of ABCA1 by 8Br-cAMP made RAW264.7 cells more sensitive to M␤CD treatment (5).…”