Tauroursodeoxycholic acid exerts anticholestatic effects by a cooperative cPKC -/PKA-dependent mechanism in rat liver

Wimmer, Ralf; Hohenester, Simon; Pusl, Thomas; Denk, Gerald; Rust, Christian; Beuers, Ulrich

doi:10.1136/gut.2007.140871

Cited by 58 publications

(64 citation statements)

References 44 publications

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“…7 Advances have been made in understanding the mechanisms and sites of action of ursodeoxycholic acid (UDCA) in the therapy of chronic cholangiopathies. 45,46 Our data might emphasize its putative beneficial action as a hepatocyte 47,48 and cholangiocyte 49,50 HCO À 3 secretagogue, particularly for small intrahepatic bile ductules affected in PBC. Our data may also explain, in part, the superiority of norUDCA above UDCA in the treatment of experimental cholangiopathy in Mdr2 À/À mice, a disease affecting also medium-and large-sized ducts, such as PSC 51 : Exogenous norUDCA has been shown to represent the strongest biliary HCO À earlier described for melanoma cells, 29 thus contributing to the biliary HCO À 3 umbrella to prohibit apolar hydrophobic bile acids from entering the cell.…”

Section: Discussionmentioning

confidence: 69%

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

et al. 2011

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Human cholangiocytes are continuously exposed to millimolar levels of hydrophobic bile salt monomers. We recently hypothesized that an apical biliary HCO À 3 umbrella might prevent the protonation of biliary glycine-conjugated bile salts and uncontrolled cell entry of the corresponding bile acids, and that defects in this biliary HCO À 3 umbrella might predispose to chronic cholangiopathies. Here, we tested in vitro whether human cholangiocyte integrity in the presence of millimolar bile salt monomers is dependent on (1) pH, (2) adequate expression of the key HCO À 3 exporter, anion exchanger 2 (AE2), and (3) an intact cholangiocyte glycocalyx. To address these questions, human immortalized cholangiocytes and cholangiocarcinoma cells were exposed to chenodeoxycholate and its glycine/taurine conjugates at different pH levels. Bile acid uptake was determined radiochemically. Cell viability and apoptosis were measured enzymatically. AE2 was knocked down by lentiviral short hairpin RNA. A cholangiocyte glycocalyx was identified by electron microscopy, was enzymatically desialylated, and sialylation was quantified by flow cytometry. We found that bile acid uptake and toxicity in human immortalized cholangiocytes and cholangiocarcinoma cell lines in vitro were pH and AE2 dependent, with the highest rates at low pH and when AE2 expression was defective. An apical glycocalyx was identified on cholangiocytes in vitro by electron microscopic techniques. Desialylation of this protective layer increased cholangiocellular vulnerability in a pH-dependent manner. Conclusion: A biliary HCO À 3 umbrella protects human cholangiocytes against damage by bile acid monomers. An intact glycocalyx and adequate AE2 expression are crucial in this process. Defects of the biliary HCO À 3 umbrella may lead to the development of chronic cholangiopathies.

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Section: Discussionmentioning

confidence: 69%

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

et al. 2011

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“…Additionally, cholestatic stimuli also induce Mrp2 retrieval from the canalicular membrane, including estradiol-17b-D-glucuronide, taurolithocholate (TLC), and taurochenodeoxycholate (Mottino et al, 2002;Rost et al, 2008;Schonhoff et al, 2013). Conversely, choleretic stimuli such as taurodeoxycholic acid and tauroursodeoxycholic acid can activate Mrp2 insertion back into the canalicular membrane, in a cAMP-regulated process (Beuers et al, 2001;Schonhoff et al, 2008;Wimmer et al, 2008). Mrp2 mislocalization by oxidative stress is similarly reversible by replenishment of GSH and may even be prevented by antioxidants (Sekine et al, 2008(Sekine et al, , 2010.…”

Section: Introductionmentioning

confidence: 95%

Nonalcoholic Steatohepatitis Modulates Membrane Protein Retrieval and Insertion Processes

Dzierlenga

Clarke

Cherrington

2016

Drug Metabolism and Disposition

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Interindividual variability in drug response in nonalcoholic steatohepatitis (NASH) can be mediated by altered regulation of drug metabolizing enzymes and transporters. Among these is the mislocalization of multidrug resistance-associated protein (MRP2)/ Mrp2 away from the canalicular membrane, which results in decreased transport of MRP2/Mrp2 substrates. The exact mechanism of this mislocalization is unknown, although increased activation of membrane retrieval processes may be one possibility. The current study measures the activation status of various mediators implicated in the active membrane retrieval or insertion of membrane proteins to identify which processes may be important in rodent methionine and choline deficient diet-induced NASH. The mediators currently known to be associated with transporter mislocalization are stimulated by oxidative stressors and choleretic stimuli, which play a role in the pathogenesis of NASH. The activation of protein kinases PKA, PKCa, PKCd, and PKC« and substrates radixin, myristoylated alanine-rich C-kinase substrate, and Rab11 were measured by comparing the expression, phosphorylation, and membrane translocation between control and NASH. Many of the mediators exhibited altered activation in NASH rats. Consistent with membrane retrieval of Mrp2, NASH rats exhibited a decreased phosphorylation of radixin and increased membrane localization of PKCd and PKC«, thought to be mediators of radixin dephosphorylation. Altered activation of PKCd, PKA, and PKCa may impair the Rab11-mediated active insertion of Mrp2. Overall, these data suggest alterations in membrane retrieval and insertion processes that may contribute to altered localization of membrane proteins in NASH.

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“…We have recently reported that the internalization of Abcc2 induced by oxidative stress is regulated by novel PKC (nPKC) in rat liver (Sekine et al, 2006), whereas Kubitz et al (2001) reported that activation of PKC by phorbol ester caused redistribution of ABCC2/Abcc2 from the bile canalicular (apical) membrane to the sinusoidal (basolateral) membrane in a human hepatoma cell line and in rat liver accompanied by cholestasis. Indeed, Abcc2 is known to be phosphorylated by PKC␣ [one of the conventional PKC (cPKC) family] and PKC (nPKC) in vitro Wimmer et al, 2008). Despite growing evidence showing the contribution of PKCs to the post-translational regulation of Abcc2 in hepatocytes, little is known about whether it holds true for other tissues.…”

mentioning

confidence: 99%

Correlation between Apical Localization of Abcc2/Mrp2 and Phosphorylation Status of Ezrin in Rat Intestine

Nakano

Sekine²,

Ito

et al. 2009

Drug Metab Dispos

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ABSTRACT:The multidrug resistance-associated protein 2/ATP-binding cassette transporter family C2 (Mrp2/Abcc2) is an ATP-dependent export pump that mediates the transport of a variety of organic anions. Abcc2 is mainly expressed on the canalicular membrane of hepatocytes and also the brush-border membrane of intestinal epithelial cells. We have previously reported that Abcc2 is rapidly internalized from the canalicular membrane during acute oxidative stress, which induces protein kinase C (PKC) activation in rat liver. However, it has not been elucidated whether PKC is involved in the regulation of Abcc2 localization in other tissues. In this study, we investigated this issue in rat intestinal epithelia. Exposure to thymeleatoxin, a conventional PKC (cPKC) activator, for 20 min reduced the cumulative glutathione S-bimane efflux for 40 min via Abcc2 from 30.3 ؎ 2.1 nmol/cm to 18.1 ؎ 1.6 nmol/cm. Likewise, the Abcc2 expression in the brush-border membrane of the small intestine was reduced to half that of the control without changing the total amount of Abcc2 present in the homogenate. Immunoprecipitation analysis suggested an interaction between Abcc2 and ezrin, a scaffolding protein that is dominantly expressed in the intestine. Thymeleatoxin treatment decreased the amount of the active form (C-terminally phosphorylated form) of ezrin and the amount of Abcc2 that coimmunoprecipitated with ezrin. These results indicate that cPKC activation diminishes the protein-protein interaction between ezrin and Abcc2. In conclusion, the phosphorylation status of ezrin correlates with the cell surface expression of Abcc2 in the rat small intestine, which may be regulated by cPKC.The small intestine is a highly differentiated organ with a barrier function against xenobiotics and a gateway function for nutrients. The ATP-binding cassette (ABC) transporter family, including P-glycoprotein/multidrug resistance protein 1 (P-gp/Mdr1/Abcb1), breast cancer resistant protein (Bcrp/Abcg2), and multidrug resistance-associated protein 2 (Mrp2/Abcc2), are well known efflux transporters that are located on the brush-border membrane (BBM) of small intestinal epithelia to limit the absorption of a broad range of compounds (Takano et al., 2006). The distinct but sometimes overlapping substrate specificities of these efflux transporters have been shown previously (Chan et al., 2004). Indeed, a significant increase in the oral absorption of their substrates, including drugs and carcinogens, was confirmed in animals genetically deficient in these transporters (Dietrich et al., 2001;Yamaguchi et al., 2002).Several reports indicated the disparity between mRNA and protein expression of Abcc2 in the intestine. Naud et al. (2007) reported that Abcc2 protein expression was reduced to approximately 40% of that of the control during chronic renal failure in rats, but its mRNA expression was unaffected. Dietrich et al. (2004) also reported ABCC2 protein expression was reduced to approximately 27% of that of the control patients in the human intestine du...

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Tauroursodeoxycholic acid exerts anticholestatic effects by a cooperative cPKC -/PKA-dependent mechanism in rat liver

Abstract: ABSTRACT

Cited by 58 publications

References 44 publications

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

Nonalcoholic Steatohepatitis Modulates Membrane Protein Retrieval and Insertion Processes

Correlation between Apical Localization of Abcc2/Mrp2 and Phosphorylation Status of Ezrin in Rat Intestine

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Tauroursodeoxycholic acid exerts anticholestatic effects by a cooperative cPKC -/PKA-dependent mechanism in rat liver

Abstract: ABSTRACT

Cited by 58 publications

References 44 publications

A biliary HCO3−umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO3−umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

Nonalcoholic Steatohepatitis Modulates Membrane Protein Retrieval and Insertion Processes

Correlation between Apical Localization of Abcc2/Mrp2 and Phosphorylation Status of Ezrin in Rat Intestine

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A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes