Functional expression and characterization of the human ABCG1 and ABCG4 proteins: indications for heterodimerization

• Published in: Biochemical and biophysical research communications Vol. 320; no. 3; pp. 860 - 867
• Main Authors: Cserepes, Judit, Szentpétery, Zsófia, Seres, László, Özvegy-Laczka, Csilla, Langmann, Thomas, Schmitz, Gerd, Glavinas, Hristos, Klein, Izabella, Homolya, László, Váradi, András, Sarkadi, Balázs, Elkind, N.Barry
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 30.07.2004
• Subjects: ABC half-transporter; ABCG1; ABCG4; Adenosine Triphosphatases - metabolism; Animals; ATP Binding Cassette Transporter, Sub-Family G; ATP Binding Cassette Transporter, Sub-Family G, Member 1; ATP-Binding Cassette Transporters - metabolism; Cell Line; Cell Membrane - drug effects; Cell Membrane - metabolism; Dimerization; Dominant negative; Drosophila - drug effects; Drosophila - metabolism; Drug-stimulated ATPase activity; Heterodimer; Humans; Protein Binding; Recombinant Proteins - metabolism; Sf9 cells; Vanadates - pharmacology; Dominant negative; ABCG4; Heterodimer; ABCG1; Drug-stimulated ATPase activity; ABC half-transporter; Sf9 cells
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2004.06.037

The closely related human ABC half-transporters, ABCG1 and ABCG4, have been suggested to play an important role in cellular lipid/sterol regulation but no experimental data for their expression or function are available. We expressed ABCG1 and ABCG4 and their catalytic site mutant variants in insect cells, generated specific antibodies, and analyzed their function in isolated membrane preparations. ABCG1 had a high basal ATPase activity, further stimulated by lipophilic cations and significantly inhibited by cyclosporin A, thyroxine or benzamil. ABCG4 had a lower basal ATPase activity which was not modulated by any of the tested compounds. The catalytic site (K–M) mutants had no ATPase activity. Since dimerization is a requirement for half-transporters, we suggest that both ABCG1 and ABCG4 function as homodimers. Importantly, we also found that co-expression of the ABCG4-KM mutant selectively abolished the ATPase activity of the ABCG1 and therefore they most probably also heterodimerize. The heterologous expression, specific recognition, and functional characterization of these transporters should help to delineate their physiological role and mechanism of action.