Institute for Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany. gerd.schmitz@klinik.uni-regensburg.de
The molecular cloning and identification of mutations in ATP-binding cassette transporters in hereditary diseases have greatly expanded our knowledge of the normal physiology of intracellular lipid transport processes. In addition to the well-known ATP-binding cassette transporter A1 (ABCA1) molecule, ABC transporters belonging to the ABCG (White) subfamily (ABCG1, ABCG5, and ABCG8) have been shown to be critically involved in the regulation of lipid-trafficking mechanisms in macrophages, hepatocytes, and intestinal mucosa cells. ABCG1, the product of a sterol-induced gene, participates in cholesterol and phospholipid efflux. The ABCG5 and ABCG8 transporters, defective in beta-sitosterolemia, are also now considered interesting targets in the control and influence of total body sterol homeostasis. In this review, advances referring to the regulation and function of ABCG half-size transporters are summarized and discussed. In addition, new implications for the transcriptional control, as well as the intracellular routing and localization, of these proteins are presented.