Biology of a novel organic solute and steroid transporter, OSTalpha-OSTbeta.
Using a comparative approach, recent studies have identified and functionally characterized a new type of organic solute and steroid transporter (OST) from skate, mouse, rat, and human genomes. In contrast to all other organic anion transporters identified to date, transport activity requires the coexpression of two distinct gene products, a predicted 340-amino acid, seven-transmembrane (TM) domain protein (OSTalpha) and a putative 128-amino acid, single-TM domain ancillary polypeptide (OSTbeta). When OSTalpha and OSTbeta are coexpressed in Xenopus oocytes, they are able to mediate transport of estrone 3-sulfate, dehydroepiandrosterone 3- sulfate, taurocholate, digoxin, and prostaglandin E2, indicating a role in the disposition of key cellular metabolites or signaling molecules. OSTalpha and OSTbeta are expressed at relatively high levels in intestine, kidney, and liver, but they are also expressed at lower levels in many human tissues. Indirect immunofluorescence microscopy revealed that intestinal OSTalpha and OSTbeta proteins are localized to the baso-lateral membrane of mouse enterocytes. In MDCK cells, mouse Ostalpha-Ostbeta mediated the vectorial movement of taurocholate from the apical to the basolateral membrane, but not in the opposite direction, indicating basolateral efflux of bile acids. Overall, these findings indicate that OSTalpha-OSTbeta is a heteromeric transporter that is localized to the basolateral membrane of specific epithelial tissues and serves to regulate the export and disposition of bile acids and structurally related compounds from the cell. If confirmed, this model would have important implications for the body's handling of various steroid-derived molecules and may provide a new pharmacologic target for altering sterol homeostasis.
Ballatori
Nazzareno
N
Department of Environmental Medicine, Box EHSC, University of Rochester School of Medicine, 575 Elmwood Avenue, Rochester, NY 14642, USA. Ned_Ballatori@urmc.rochester.edu
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013256:Steroids / Q000378:metabolism*; D014018:Tissue Distribution
D027361:Organic Anion Transporters; D013256:Steroids