Lipidation of apolipoprotein A-I by ATP-binding cassette transporter (ABC) A1 generates an interaction partner for ABCG1 but not for scavenger receptor BI.
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 degrees 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 degrees 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-beta- to alpha-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.
Lorenzi
Iris
I
Institute of Clinical Chemistry and Center for Integrative Human Biology, University of Zurich, University Hospital Zurich, Rämistrasse 100, Zurich, Switzerland.
von Eckardstein
Arnold
A
Radosavljevic
Silvija
S
Rohrer
Lucia
L
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004587:Electrophoresis, Agar Gel; D006801:Humans; D051379:Mice; D011485:Protein Binding; D051122:Scavenger Receptors, Class B / Q000378:metabolism*
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D017931:DNA Primers; D051122:Scavenger Receptors, Class B