title: Expression and localization of hepatobiliary transport proteins in progressive familial intrahepatic cholestasis.
abstract: Mutations of the bile salt export pump (BSEP) or the multidrug resistance P-glycoprotein 3 (MDR3) are linked to impaired bile salt homeostasis and lead to progressive familial intrahepatic cholestasis (PFIC)-2 and -3, respectively. The regulation of bile salt transporters in PFIC is not known. Expression of hepatobiliary transporters in livers of ten patients with a PFIC phenotype was studied by quantitative reverse transcription polymerase chain reaction, Western blotting, and immunofluorescence microscopy. PFIC was diagnosed by clinical and laboratory findings. All patients could be assigned to PFIC-2 or PFIC-3 by the use of BSEP- and MDR3-specific antibodies and by MDR3 gene-sequencing. Whereas in all PFIC-2 patients, BSEP immunoreactivity was absent from the canalicular membrane, in three PFIC-3 livers, canalicular MDR3 immunoreactivity was detectable. Serum bile salts were elevated to 276 +/- 233 and to 221 +/- 109 micromol/L in PFIC-2 and PFIC-3, respectively. Organic anion transporting polypeptide OATP1B1, OATP1B3, and MRP2 mRNA and protein levels were reduced, whereas sodium taurocholate cotransporting polypeptide (NTCP) was only reduced at the protein level, suggesting a posttranscriptional NTCP regulation. Whereas MRP3 mRNA and protein were not significantly altered, MRP4 messenger RNA and protein were significantly increased in PFIC. In conclusion, PFIC-2 may be reliably diagnosed by immunofluorescence, whereas the diagnosis of PFIC-3 requires gene-sequencing. Several mechanisms may contribute to elevated plasma bile salts in PFIC: reduced bile salt uptake via NTCP, OATP1B1, and OATP1B3, decreased BSEP-dependent secretion into bile, and increased transport back into plasma by MRP4. Upregulation of MRP4, but not of MRP3, might represent an important escape mechanism for bile salt extrusion in PFIC.
authors.affiliation: Klinik für Gastroenterologie, Hepatologie und Infektiologie, Heinrich Heine Universität, Düsseldorf, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Keitel
authors.forename: Martin
authors.initials: M
authors.lastname: Burdelski
authors.forename: Ulrich
authors.initials: U
authors.lastname: Warskulat
authors.forename: Thomas
authors.initials: T
authors.lastname: Kühlkamp
authors.forename: Dietrich
authors.initials: D
authors.lastname: Keppler
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
authors.forename: Ralf
authors.initials: R
authors.lastname: Kubitz
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D001647:Bile Acids and Salts / Q000378:metabolism; D002780:Cholestasis, Intrahepatic / Q000378:metabolism* / Q000503:physiopathology*; D005260:Female; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D008099:Liver / Q000502:physiology*; D027381:Liver-Specific Organic Anion Transporter 1 / Q000235:genetics / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008875:Middle Aged; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D029362:Organic Anion Transporters, Sodium-Independent / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D027981:Symporters; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D027381:Liver-Specific Organic Anion Transporter 1; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D029362:Organic Anion Transporters, Sodium-Independent; D012333:RNA, Messenger; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D027981:Symporters; D005723:gamma-Glutamyltransferase; C000715087:ABCC2 protein, human; C421209:SLCO1B3 protein, human; C071908:sodium-bile acid cotransporter; C095122:multidrug resistance protein 3