Functional analysis of candidate ABC transporter proteins for sitosterol transport

• Published in: Biochimica et biophysica acta 2002-12, Vol.1567 (1-2), p.133-142
• Main Authors: Albrecht, C, Elliott, J.I, Sardini, A, Litman, T, Stieger, B, Meier, P.J, Higgins, C.F
• Format: Article
• Language: English
• Subjects: 3T3 Cells; ABC transporter; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1 - metabolism; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters - metabolism; Biological Transport; Cholesterol; Confocal microscopy; Flow Cytometry; Mice; Mice, Knockout; Microscopy, Confocal; Multidrug Resistance-Associated Proteins - metabolism; Neoplasm Proteins; Sitosterol; Sitosterols - metabolism; Spodoptera
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/S0005-2736(02)00608-9

Two ATP-binding cassette (ABC) proteins, ABCG5 and ABCG8, have recently been associated with the accumulation of dietary cholesterol in the sterol storage disease sitosterolemia. These two ‘half-transporters’ are assumed to dimerize to form the complete sitosterol transporter which reduces the absorption of sitosterol and related molecules in the intestine by pumping them back into the lumen. Although mutations altering ABCG5 and ABCG8 are found in affected patients, no functional demonstration of sitosterol transport has been achieved. In this study, we investigated whether other ABC transporters implicated in lipid movement and expressed in tissues with a role in sterol synthesis and absorption, might also be involved in sitosterol transport. Transport by the multidrug resistance P-glycoprotein (P-gp; Abcb1), the multidrug resistance-associated protein (Mrp1; Abcc1), the breast cancer resistance protein (Bcrp; Abcg2) and the bile salt export pump (Bsep; Abcb11) was assessed using several assays. Unexpectedly, none of the candidate proteins mediated significant sitosterol transport. This has implications for the pathology of sitosterolemia. In addition, the data suggest that otherwise broad-specific ABC transporters have acquired specificity to exclude sitosterol and related sterols like cholesterol presumably because the abundance of cholesterol in the membrane would interfere with their action; in consequence, specific transporters have evolved to handle these sterols.