Formation of cholesterol-enriched structures by aberrant intracellular accumulation of ATP-binding cassette transporter A1

• Published in: Genes to cells : devoted to molecular & cellular mechanisms Vol. 13; no. 8; pp. 889 - 904
• Main Authors: Tanaka, Arowu R, Kano, Fumi, Yamamoto, Akitsugu, Ueda, Kazumitsu, Murata, Masayuki
• Format: Journal Article
• Language: English
• Published: Malden, USA Malden, USA : Blackwell Publishing Inc 01.08.2008; Blackwell Publishing Inc
• Subjects: ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters - analysis; ATP-Binding Cassette Transporters - metabolism; Cell Line; Cholesterol; Humans; Macrophages, Peritoneal - metabolism; Oligonucleotide Array Sequence Analysis; Proteasome Inhibitors; Protein Transport; rab4 GTP-Binding Proteins - metabolism; Receptors, Scavenger - metabolism; Transport Vesicles - metabolism
• ISSN: 1356-9597; 1365-2443
• DOI: 10.1111/j.1365-2443.2008.01213.x

ATP-binding cassette transporter A1 (ABCA1) is a key transporter associated with excess cellular lipid efflux. Here, we report that in HEK293 cells ABCA1 functions in intracellular compartments along the endocytic pathway. Inhibition of ABCA1-GFP degradation with proteasome inhibitors induced the internalization of ABCA1 and the formation of intracellular round-shaped structures, designated "A1 bodies". Importantly, cholesterol was selectively accumulated in A1 bodies, and this depended on the cholesterol efflux activity of ABCA1. Treatment with either lactacystin or acetylated LDL, which reduces proteasome activity, resulted in internalization of ABCA1 in mouse peritoneal macrophages. By performing array analysis on macrophages treated with these reagents, we identified Rab4 as a key protein involved in the internalization and aberrant accumulation of ABCA1 in HEK cells. Treatment of the cells with proteasome inhibitors inhibited the degradation of Rab4, and Rab4 over-expression induced the formation of small A1 bodies. Furthermore, A1 bodies formation was substantially inhibited by silencing of the endogenous Rab4 gene. Taken together, our findings suggest that the endocytic ABCA1 possesses cholesterol efflux activity, and thus the cellular control of post-endocytic sorting, retention or recycling of functional ABCA1 in the endocytic vesicles, which is in part regulated by Rab4, is important for cholesterol metabolism in living cells.