Trafficking of the bile salt export pump from the Golgi to the canalicular membrane is regulated by the p38 MAP kinase.
OBJECTIVE
Bile secretion depends on the delivery and removal of transporter proteins to and from the canalicular membrane. Trafficking of the bile salt export pump (BSEP) to the canalicular membrane was investigated in HepG2 cells and rat hepatocytes.


METHODS
Subcellular localization of BSEP was determined by confocal laser scanning microscopy using different BSEP antibodies.


RESULTS
Ten percent of untreated HepG2 cells developed pseudocanaliculi, but only 15% of these pseudocanaliculi contained BSEP, which largely colocalized with the Golgi marker GM130. Cycloheximide, an inhibitor of protein translation, induced a microtubule- and p38(MAP) kinase-dependent decrease of Golgi-associated BSEP, accompanied by a more than 2-fold increase in BSEP-positive pseudocanaliculi. Also, tauroursodeoxycholate (TUDC), which activates p38(MAP) kinase (p38(MAPK), increased BSEP-positive pseudocanaliculi by more than 50% in rat sodium taurocholate cotransporting peptide (Ntcp)-transfected but not in untransfected HepG2 cells. The TUDC-dependent increase was sensitive to inhibitors of p38(MAPK) and microtubules and involved Ca(2+)-independent protein kinase C isoforms as suggested by its sensitivity to Gö6850 but insensitivity to Gö6976. In isolated rat hepatocytes with intact bile secretion, no colocalization of rat isoforms of the bile salt export pump (Bsep) and Golgi was found, but colocalization occurred after inhibition of p38(MAPK) and PKC, suggesting that Bsep trafficking to the canalicular membrane depends on the basal activity of these kinases in polarized cells.


CONCLUSIONS
p38(MAPK) regulates BSEP trafficking from the Golgi to the canalicular membrane, and the Golgi may serve as a BSEP pool in certain forms of cholestasis or when p38(MAPK) activity is inhibited. Activation of p38(MAPK) by TUDC can recruit Golgi-associated BSEP in line with its choleretic action.
Kubitz
Ralf
R
Department of Gastroenterology, Hepatology, and Infectiology, Heinrch Heine University, Duesseldorf, Germany. kubitz@med.uni-duesseldorf.de
Sütfels
Gerrit
G
Kühlkamp
Thomas
T
Kölling
Ralf
R
Häussinger
Dieter
D
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D001648:Bile Canaliculi / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D008566:Membranes / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D013657:Taurodeoxycholic Acid / Q000494:pharmacology; D014018:Tissue Distribution; D048051:p38 Mitogen-Activated Protein Kinases
C093491:ABCB11 protein, human; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D011500:Protein Synthesis Inhibitors; D013657:Taurodeoxycholic Acid; D003513:Cycloheximide; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases