Z Gastroenterol 2012; 50 - P2_26
DOI: 10.1055/s-0031-1295823

Src kinase Fyn mediates hyperosmolarity-induced Mrp2- and Bsep-retrieval from the canalicular membrane in a cortactin dependent way

R Reinehr 1, M Cantore 1, A Sommerfeld 1, M Becker 1, D Häussinger 1
  • 1Klinik für Gastroenterologie, Hepatologie und Infektiologie; Universitätsklinikum Düsseldorf, Düsseldorf

Introduction: Hyperosmolarity induces Mrp2-/Bsep-retrieval from the canalicular membrane leading to cholestasis.1,2 The underlying signaling events remained unclear. Methods: Rat livers were perfused with either normo- (305mOsm) or hyperosmolarity (385mOsm) following Mrp2-/Bsep-staining and analyzation of transporter localization. Bile flow was measured by biliary excretion of CDNB-glutathione conjugate in perfused liver and using CLF-secretion in hepatocyte couplets. Results: In perfused rat liver, hyperosmolarity induced within 30min a Mrp2/Bsep-retrieval from the canalicular membrane, which was paralleled by activation of Src-kinases Fyn and Yes. Both, hyperosmotic transporter retrieval and Src kinase activation were sensitive to apocynin, N-acetylcysteine (NAC) and SU6656. Also PP–2, which inhibited hyperosmotic Fyn, but not Yes activation, prevented hyperosmotic transporter retrieval suggesting that Fyn is involved. Hyperosmotic activation of JNKs was sensitive to apocynin and NAC, but insensitive to SU6656 and PP–2 indicating that JNKs are not involved in transporter retrieval, as also evidenced by experiments using JNK-inhibitors (L-JNKI1, SP6001255). Hyperosmotic Mrp2-/Bsep-retrieval was accompanied by a NAC-sensitive inhibition of biliary excretion of the CDNB-glutathione conjugate in perfused rat liver and and by a decrease in CLF secretion into the pseudocanaliculi formed by hepatocyte couplets in a NAC- and PP–2-sensitive way. In hepatocyte couplets, hyperosmolarity triggered an association between Fyn and cortactin and increased the amount of phosphorylated cortactin underneath the canalicular membrane, whereas cortactin/actin association decreased. Conclusion: Hyperosmotic cholestasis is triggered by a NADPH oxidase-driven ROS formation which mediates Fyn-dependent Mrp2-/Bsep-retrieval of the transporters from the canalicular membrane which may be mediated by increased cortactin phosphorylation and subsequent reduction of cortactin/actin association.

Literatur: 1) Kubitz et al., Gastroenterology. 1997;113:1438-42. 2) Schmitt et al., Hepatology. 2001;33:509-18.

bile acid transport - cholestasis - osmosignaling