The hepatocellular bile acid transporter Ntcp facilitates uptake of the lethal mushroom toxin alpha-amanitin.
Hepatotoxicity caused by the mushroom poison alpha-amanitin is an unusual but serious cause of death and liver transplantation. Understanding the mechanisms of alpha-amanitin uptake may lead to rational therapeutic approaches. Because older data suggested that a sodium-dependent bile acid transporter is responsible for alpha-amanitin uptake, we tested the hypothesis that Na(+)-taurocholate cotransporter polypeptide (Ntcp) facilitates hepatocellular alpha-amanitin uptake. Human hepatoblastoma cells (HepG2), cells that have lost native Ntcp expression, were stably transfected with the rat Ntcp gene. Taurocholate uptake by the transfected cells exhibited a physiologically normal K(m) and V(max). A toxicologically relevant functional assay for alpha-amanitin uptake was developed by measuring its ability to block cytokine-induced synthesis of interleukin-1 receptor antagonist (IL-1Ra) mRNA. Treatment with interleukin-1beta (10 ng/ml) and interleukin-6 (100 ng/ml) increased IL-1Ra mRNA abundance 8.6-fold and 15.6-fold in HepG2 cells and Ntcp-transfected cells, respectively. Pretreatment of transfected cells with 1 micro M alpha-amanitin for 6-10 h almost completely blocked induction of IL-1Ra mRNA (1.9-fold induction) whereas pretreatment of non-transfected cells did not block induction of IL-1Ra mRNA (21.6-fold induction, P<0.02 compared with stimulated transfected cells without alpha-amanitin). These findings demonstrate that Ntcp may be an important mediator of alpha-amanitin uptake by the liver.
Gundala
Sri
S
Division of Gastroenterology and Hepatology, Department of Internal Medicine, Saint Louis University School of Medicine, 3635 Vista Ave., St. Louis, MO 63110, USA.
Wells
Lisa D
LD
Milliano
Michael T
MT
Talkad
Vanita
V
Luxon
Bruce A
BA
Neuschwander-Tetri
Brent A
BA
D000546:Amanitins / Q000493:pharmacokinetics* / Q000494:pharmacology; D000818:Animals; D004338:Drug Combinations; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D018197:Hepatoblastoma / Q000188:drug therapy / Q000473:pathology; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000493:pharmacokinetics*; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism* / Q000494:pharmacology; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000187:drug effects; D051381:Rats; D012795:Sialoglycoproteins / Q000096:biosynthesis / Q000235:genetics; D027981:Symporters / Q000378:metabolism* / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D000546:Amanitins; D004338:Drug Combinations; D004791:Enzyme Inhibitors; C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D015850:Interleukin-6; D019384:Nucleic Acid Synthesis Inhibitors; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; D012795:Sialoglycoproteins; D027981:Symporters; C071908:sodium-bile acid cotransporter