title: Na+-taurocholate cotransporting polypeptide (NTCP/SLC10A1) ortholog in the marine skateLeucoraja erinaceais not a physiological bile salt transporter.
abstract: The Na+-dependent taurocholate cotransporting polypeptide (NTCP/SLC10A1) is a hepatocyte-specific solute carrier, which plays an important role in maintaining bile salt homeostasis in mammals. The absence of a hepatic Na+-dependent bile salt transport system in marine skate and rainbow trout raises a question regarding the function of the Slc10a1 gene in these species. Here, we have characterized the Slc10a1 gene in the marine skate,Leucoraja erinaceaThe transcript of skate Slc10a1 (skSlc10a1) encodes 319 amino acids and shares 46% identity to human NTCP (hNTCP) with similar topology to mammalian NTCP. SkSlc10a1 mRNA was mostly confined to the brain and testes with minimal expression in the liver. An FXR-bile salt reporter assay indicated that skSlc10a1 transported taurocholic acid (TCA) and scymnol sulfate, but not as effectively as hNTCP. An [3H]TCA uptake assay revealed that skSlc10a1 functioned as a Na+-dependent transporter, but with low affinity for TCA (Km= 92.4 µM) and scymnol sulfate (Ki= 31 µM), compared with hNTCP (TCA,Km= 5.4 µM; Scymnol sulfate,Ki= 3.5 µM). In contrast, the bile salt concentration in skate plasma was 2 µM, similar to levels seen in mammals. Interestingly, skSlc10a1 demonstrated transport activity for the neurosteroids dehydroepiandrosterone sulfate and estrone-3-sulfate at physiological concentration, similar to hNTCP. Together, our findings indicate that skSlc10a1 is not a physiological bile salt transporter, providing a molecular explanation for the absence of a hepatic Na+-dependent bile salt uptake system in skate. We speculate that Slc10a1 is a neurosteroid transporter in skate that gained its substrate specificity for bile salts later in vertebrate evolution.
authors.affiliation: Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut; and.
authors.forename: Dongke
authors.initials: D
authors.lastname: Yu
authors.affiliation: Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut; and.
authors.forename: Han
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut; and.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lionarons
authors.affiliation: Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut; and.|Mount Desert Island Biological Laboratory, Salisbury Cove, Maine.
authors.forename: James L
authors.initials: JL
authors.lastname: Boyer
authors.affiliation: Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut; and shi-ying.cai@yale.edu.
authors.forename: Shi-Ying
authors.initials: SY
authors.lastname: Cai
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D006801:Humans; D008099:Liver / Q000378:metabolism; D009928:Organ Specificity; D029363:Organic Anion Transporters, Sodium-Dependent / Q000097:blood / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017385:Sequence Homology; D012860:Skates, Fish / Q000145:classification / Q000378:metabolism*; D012964:Sodium / Q000737:chemistry / Q000378:metabolism*; D013045:Species Specificity; D013329:Structure-Activity Relationship; D027981:Symporters / Q000097:blood / Q000737:chemistry* / Q000378:metabolism*; D013656:Taurocholic Acid / Q000737:chemistry / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: D001647:Bile Acids and Salts; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid; D012964:Sodium
keywords: evolution; neuroactive steroid; sodium-dependent transporter; solute carrier