Short-term feedback regulation of bile salt uptake by bile salts in rodent liver

Abstract

The sodium taurocholate cotransporting polypeptide (Ntcp) is the major bile salt uptake transporter at the sinusoidal membrane of hepatocytes. Short-term feedback regulation of Ntcp by primary bile salts has not yet been investigated in vivo. Subcellular localization of Ntcp was analyzed in Ntcp-transfected HepG2-cells by flow cytometry and in immunofluorescence images from tissue sections by a new automated image analysis method. Net bile salt uptake was investigated in perfused rat liver by a pulse chase technique. In Flag-Ntcp-EGFP (enhanced green fluorescent protein) expressing HepG2-cells, taurochenodeoxycholate (TCDC), but not taurocholate (TC), induced endocytosis of Ntcp. TCDC, but not TC, caused significant internalization of Ntcp in perfused rat livers, as shown by an increase in intracellular Ntcp immunoreactivity, whereas Bsep distribution remained unchanged. These results correlate with functional studies. Rat livers were continuously perfused with 100 mu mol/L of TC. 25 mu mol/L of TCDC, taurodeoxycholate (TDC), tauroursodeoxycholate (TUDC), or TC were added for 30 minutes, washed out, followed by a pulse of (3)[H]-TC. TCDC, but not TDC, TUDC, or TC significantly increased the amount of (3)[H]-TC in the effluent, indicating a reduced sinusoidal net TC uptake. This effect was sensitive to chelerythrine (protein kinase C inhibitor) and cypermethrin (protein phosphatase 2B inhibitor). Phosphoinositide 3-kinase (PI3K) inhibitors had an additive effect, whereas Erk1/2 (extracellular signal activated kinase 1/2), p38MAPK, protein phosphatase 1/2A (PP1/2A), and reactive oxygen species (ROS) were not involved. Conclusion: TCDC regulates bile salt transport at the sinusoidal membrane by protein kinase C-and protein phosphatase 2B-mediated retrieval of Ntcp from the plasma membrane. During increased portal bile salt load this mechanism may adjust bile salt uptake along the acinus and protect periportal hepatocytes from harmful bile salt concentrations

Regulation of Plasma Membrane Localization of the Na+-Taurocholate Cotransporting Polypeptide (Ntcp) by Hyperosmolarity and Tauroursodeoxycholate

“…It was suggested that choleretic and cholestatic effects may involve different PKC isoforms; however, the picture is not entirely consistent. The toxic bile acid TCDC inhibits bile salt transport across the sinusoidal mem- brane by PKC-and PP2B-mediated retrieval of Ntcp from the plasma membrane (33). Phorbol ester-induced endocytosis of Ntcp was shown to be mediated in part by Ca 2ϩ -dependent PKCs (56).…”

“…Recent studies suggest that the cholestatic bile salt taurolithocholate inhibits hepatic TC uptake and decreases plasma membrane levels of Ntcp (32). Also, taurochenodeoxycholate (TCDC) inhibits TC uptake at the sinusoidal membrane in a chelerythrine-and cypermethrin-dependent way (33). Ntcp is a serine/threonine phosphorylated protein (34) and underlies complex regulation (35).…”

Phosphorylation of RS1 (RSC1A1) Steers Inhibition of Different Exocytotic Pathways for Glucose Transporter SGLT1 and Nucleoside Transporter CNT1, and an RS1-Derived Peptide Inhibits Glucose Absorption

“…Post-translational short-term regulations of plasma membrane transporters adapt transporter activities according to physiologic demands (Zhang et al, 2008;Kock et al, 2010;Vina-Vilaseca et al, 2011;Gorboulev et al, 2012;Leto and Saltiel, 2012;Mühlfeld et al, 2012;Zhang et al, 2013). Physiologically important examples are insulin-induced recruitment of glucose transporter 4 (GLUT4) to the plasma membrane of adipocytes (Leto and Saltiel, 2012), protein kinase C-dependent endocytosis of organic anion transporter 1 (OAT1) (Zhang et al, 2008(Zhang et al, , 2013, and glucose-induced incorporation of the Na 1 -D-glucose cotransporter SGLT1 into brush-border membranes (BBMs) of small intestinal enterocytes (Gorboulev et al, 2012).…”

Deciphering the mystery of hepatitis B virus receptors: A historical perspective

“…These includes Myrcludex-B [43], Cyclosporin A (CsA), progesterone, propranolol and bosentan [73]. NTCP substrates, such as taurocholate, tauroursodeoxycholate and bromosulfophthalein, also inhibited HBV infection [43,49,73].…”