The secretin dependent biliary secretion of ions and water by transporters and/or channels, which are located at apical membrane of cholangiocytes, is essential for the regulation of biliary flow. The cystic fibrosis transmembrane conductance regulator (CFTR) plays a key role in the chloride secretion into the bile. In the cystic fibrosis (CF) patients, totally 5 to 10% of patients develop the progressive biliary fibrosis resembling primary sclerosing cholangitis. The loss of cystic fibrosis transmembrane conductance regulator (CFTR) leads to the onset of liver disease in human. Ezrin, radixin and moesin (ERM) proteins are identified as cross-linkers between the plasma membrane proteins and actin cytoskeleton. Ezrin interacts with Na+/H+ exchanger regulatory factor-1 (NHERF1) via its N-terminal binding domain and with actin cytoskeleton via its C-terminal actin-binding domain. CFTR is associated with NHERF1 via its c-terminal PDZ binding motif. In the liver, ezrin, but not radixin or moesin, is only expressed in the cholangiocytes and colocalizes with CFTR and NHERF1 at apical membrane of cholangiocyte. In the present study, we used ezrin knockdown (Vil2kd/kd) mice to investigate the physiological roles of ezrin in the liver (1). All work with animals was performed with approval from the Animal Ethics Committee of Ritsumeikan University. We have found that Vil2kd/kd mice develop severe hepatic failure characterized by extensive bile duct proliferation, periductular fibrosis, intrahepatic bile acid accumulation and reduced bile flow. Immunofluorescent analysis revealed that apical membrane localizations of CFTR and NHERF1 were disturbed in the bile ducts of Vil2kd/kd mice. To determine the physiological roles of ezrin in the regulation of apical membrane localizations of these proteins, we utilized mouse-derived immortalized cholangiocytes. Stable expression of a dominant negative form of ezrin in immortalized mouse cholangiocytes led to the reduction of the apical surface expression of CFTR. Reduced surface expression of these transport proteins was accompanied by reduced CFTR-mediated Cl- efflux activity. These data suggest that dysfunction of ezrin in cholangiocytes mimics important aspects of the pathological mechanisms responsible for cholangiopathies and ezrin has important roles in the regulation of bile duct function.
Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCA119
Poster Communications: Novel physiological roles of ezrin in the regulation of bile fluidity
R. Hatano1, K. Akiyama1, A. Tamura2, S. Hosogi3, Y. Marunaka3, M. J. Caplan4, S. Tsukita2, S. Asano1
1. Department of Molecular Physiology, College of Pharmaceutical Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan. 2. Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Osaka, Japan. 3. Department of Molecular Cell Physiology and Bio-Ionomics, Kyoto Prefectural University of Medicine, Kyoto, Kyoto, Japan. 4. Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States.
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Where applicable, experiments conform with Society ethical requirements.