The SLC51 organic solute transporter family of transporters is a pair of heterodimeric proteins which regulate bile salt movements in the small intestine, bile duct, and liver, as part of the enterohepatic circulation [1-2,4]. OSTα/OSTβ is also expressed in steroidogenic cells of the brain and adrenal gland, where it may contribute to steroid sulphate movement [5]. Bile acid and steroid sulphate transport is suggested to be facilitative and independent of sodium, potassium, chloride ions or protons [2,4]. OSTα/OSTβ heterodimers have been shown to transport [³H]taurocholic acid, [³H]dehydroepiandrosterone sulphate, [³H]estrone-3-sulphate, [³H]pregnenolone sulphate and [³H]dehydroepiandrosterone sulphate[2,4-5]. OSTα/OSTβ-mediated transport is inhibited by clofazimine and fidaxomicin [8,10]. OSTα is suggested to be a seven TM protein, while OSTβ is a single TM 'ancillary' protein, both of which are thought to have intracellular C-termini [7]. Both proteins function in solute transport [3,7]. Inherited mutations in OSTα and OSTβ are associated with liver disease and congenital diarrhea in children [6,9].

* Key recommended reading is highlighted with an asterisk

* Ballatori N. (2011) Pleiotropic functions of the organic solute transporter Ostα-Ostβ. Dig Dis, 29 (1): 13-7. [PMID:21691099]

* Ballatori N, Christian WV, Wheeler SG, Hammond CL. (2013) The heteromeric organic solute transporter, OSTα-OSTβ/SLC51: a transporter for steroid-derived molecules. Mol Aspects Med, 34 (2-3): 683-92. [PMID:23506901]

* Beaudoin JJ, Bezençon J, Sjöstedt N, Fallon JK, Brouwer KLR. (2020) Role of Organic Solute Transporter Alpha/Beta in Hepatotoxic Bile Acid Transport and Drug Interactions. Toxicol Sci, 176 (1): 34-35. [PMID:32294204]

* Dawson PA. (2011) Role of the intestinal bile acid transporters in bile acid and drug disposition. Handb Exp Pharmacol, (201): 169-203. [PMID:21103970]

* Malinen MM, Ali I, Bezençon J, Beaudoin JJ, Brouwer KLR. (2018) Organic solute transporter OSTα/β is overexpressed in nonalcoholic steatohepatitis and modulated by drugs associated with liver injury. Am J Physiol Gastrointest Liver Physiol, 314 (5): G597-G609. [PMID:29420067]

1. Alexander SPH, Kelly E, Mathie A, Peters JA, Veale EL, Armstrong JF, Faccenda E, Harding SD, Pawson AJ, Sharman JL et al.. (2019) THE CONCISE GUIDE TO PHARMACOLOGY 2019/20: Transporters. Br J Pharmacol, 176 Suppl 1: S397-S493. [PMID:31710713]

2. Ballatori N, Christian WV, Lee JY, Dawson PA, Soroka CJ, Boyer JL, Madejczyk MS, Li N. (2005) OSTalpha-OSTbeta: a major basolateral bile acid and steroid transporter in human intestinal, renal, and biliary epithelia. Hepatology, 42 (6): 1270-9. [PMID:16317684]

3. Christian WV, Li N, Hinkle PM, Ballatori N. (2012) β-Subunit of the Ostα-Ostβ organic solute transporter is required not only for heterodimerization and trafficking but also for function. J Biol Chem, 287 (25): 21233-43. [PMID:22535958]

4. Dawson PA, Hubbert M, Haywood J, Craddock AL, Zerangue N, Christian WV, Ballatori N. (2005) The heteromeric organic solute transporter alpha-beta, Ostalpha-Ostbeta, is an ileal basolateral bile acid transporter. J Biol Chem, 280 (8): 6960-8. [PMID:15563450]

5. Fang F, Christian WV, Gorman SG, Cui M, Huang J, Tieu K, Ballatori N. (2010) Neurosteroid transport by the organic solute transporter OSTα-OSTβ. J Neurochem, 115 (1): 220-33. [PMID:20649839]

6. Gao E, Cheema H, Waheed N, Mushtaq I, Erden N, Nelson-Williams C, Jain D, Soroka CJ, Boyer JL, Khalil Y et al.. (2020) Organic Solute Transporter Alpha Deficiency: A Disorder With Cholestasis, Liver Fibrosis, and Congenital Diarrhea. Hepatology, 71 (5): 1879-1882. [PMID:31863603]

7. Li N, Cui Z, Fang F, Lee JY, Ballatori N. (2007) Heterodimerization, trafficking and membrane topology of the two proteins, Ost alpha and Ost beta, that constitute the organic solute and steroid transporter. Biochem J, 407 (3): 363-72. [PMID:17650074]

8. Malinen MM, Kauttonen A, Beaudoin JJ, Sjöstedt N, Honkakoski P, Brouwer KLR. (2019) Novel in Vitro Method Reveals Drugs That Inhibit Organic Solute Transporter Alpha/Beta (OSTα/β). Mol Pharm, 16 (1): 238-246. [PMID:30481467]

9. Sultan M, Rao A, Elpeleg O, Vaz FM, Abu-Libdeh B, Karpen SJ, Dawson PA. (2018) Organic solute transporter-β (SLC51B) deficiency in two brothers with congenital diarrhea and features of cholestasis. Hepatology, 68 (2): 590-598. [PMID:28898457]

10. van de Wiel SMW, de Waart DR, Oude Elferink RPJ, van de Graaf SFJ. (2018) Intestinal Farnesoid X Receptor Activation by Pharmacologic Inhibition of the Organic Solute Transporter α-β. Cell Mol Gastroenterol Hepatol, 5 (3): 223-237. [PMID:29675448]

Paul A. Dawson Division of Pediatric Gastroenterology, Hepatology & Nutrition Emory University School of Medicine Health Sciences Research Building (HSRB) 1760 Haygood Drive Suite E200; Office E206 Atlanta, GA 30322 USA