Lipidation of apolipoprotein A-I by ATP-binding cassette transporter (ABC) A1 generates an interaction partner for ABCG1 but not for scavenger receptor BI

• Published in: Biochimica et biophysica acta Vol. 1781; no. 6; pp. 306 - 313
• Main Authors: Lorenzi, Iris, von Eckardstein, Arnold, Radosavljevic, Silvija, Rohrer, Lucia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2008
• Subjects: ABC1; ABCG1; Animals; Apolipoprotein A-I; Apolipoprotein A-I - metabolism; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters - metabolism; Base Sequence; Cell Line; Cholesterol efflux; DNA Primers; Electrophoresis, Agar Gel; High density lipoproteins; Humans; Macrophages; Mice; Protein Binding; Scavenger Receptors, Class B - metabolism; SR-BI; ABCA1; SR-BI; rHDL; siRNA; cAMP; Macrophages; CsA; HDL; BSA; ABC1; High density lipoproteins; LDL; shRNA; acLDL; Apolipoprotein A-I; apoA-I; ABCG1; Cholesterol efflux
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2008.04.006

The ATP-binding cassette transporters ABCA1 and ABCG1 as well as scavenger receptor BI (SR-BI) mediate the efflux of lipids from macrophages to apolipoprotein A-I (apoA-I) and high density lipoproteins (HDL). We used RNA interference in RAW264.7 macrophages to study the interactions of ABCA1, ABCG1, and SR-BI with lipid-free apoA-I, native and reconstituted HDL with apoA-I:phosphatidylcholine ratios of either 1:40 (rHDL 1:40) or 1:100 (rHDL 1:100). Knock-down of ABCA1 inhibits the cellular binding at 4 °C of lipid-free apoA-I but not of HDL whereas suppression of ABCG1 or SR-BI reduces the binding of HDL but not lipid-free apoA-I. The degree of lipidation influences the interactions of rHDL with ABCG1 and SR-BI. Knock-down of ABCG1 inhibits more effectively the binding and cholesterol efflux capacities of lipid-poorer rHDL 1:40 whereas knock-down of SR-BI has a more profound effect on the binding and cholesterol efflux capacities of lipid-richer rHDL 1:100. Moreover, knock-down of ABCG1 but not SR-BI interferes with the association of lipid-free apoA-I during prolonged incubation at 37 °C. Finally, knock-down of ABCG1 inhibits the binding of initially lipid-free apoA-I which has been preconditioned by cells with high ABCA1 activity. The gained ability of initially lipid-free apoA-I to interact with ABCG1 is accompanied by its shift from electrophoretic pre-β- to α-mobility. Taken together, these data suggest that the interaction of lipid-free apoA-I with ABCA1 generates a particle that immediately interacts with ABCG1 but not with SR-BI. Furthermore, the degree of lipidation influences the interaction of HDL with ABCG1 or SR-BI.