Selective degradation of E-cadherin and dissolution of E-cadherin-catenin complexes in epithelial ischemia.
Ischemic epithelial cells are characterized by disruption of intercellular junctions and loss of apical-basolateral protein polarity, which are normally dependent on the integrity of the adherens junction (AJ). Biochemical analysis of both whole ischemic kidneys and ATP-depleted Madin-Darby canine kidney (MDCK) cells demonstrated a striking loss of E-cadherin (the transmembrane protein of the AJ) with the appearance and accumulation of an approximately 80-kDa fragment reactive with anti-E-cadherin antibodies on Western blots of ATP-depleted MDCK cells. This apparent ischemia-induced degradation of E-cadherin was not blocked by either inhibitors of the major proteolytic pathways (i.e., proteasome, lysosome, or calpain), or by chelation of intracellular calcium, suggesting the involvement of a protease capable of functioning at low ATP and low calcium levels. Immunocytochemistry revealed the movement of several proteins normally comprising the AJ, including E-cadherin and beta-catenin, away from lateral portions of the plasma membrane to intracellular sites. Moreover, rate-zonal centrifugation and immunoprecipitation with anti-E-cadherin and anti-beta-catenin antibodies indicated that ATP depletion disrupted normal E-cadherin-catenin interactions, resulting in the dissociation of alpha- and gamma-catenin from E-cadherin and beta-catenin-containing complexes. Because the generation and maintenance of polarized epithelial cells are dependent upon E-cadherin-mediated cell-cell adhesion and normal AJ function, we propose that the rapid degradation of E-cadherin and dissolution of the AJ is a key step in the development of the ischemic epithelial cell phenotype. Furthermore, we hypothesize that the reassembly of the AJ after ischemia/ATP depletion may require a novel bioassembly mechanism involving recombination of newly synthesized and sorted E-cadherin with preexisting pools of catenins that have (temporally) redistributed intracellularly.
Bush
K T
KT
Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0693, USA.
Tsukamoto
T
T
Nigam
S K
SK
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015820:Cadherins / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D016764:Cell Polarity; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D007365:Intercellular Junctions / Q000378:metabolism; D007511:Ischemia / Q000378:metabolism*; D007668:Kidney / Q000098:blood supply* / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015534:Trans-Activators; D051176:beta Catenin
D015820:Cadherins; C495268:Ctnnb1 protein, rat; D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D051176:beta Catenin; D000255:Adenosine Triphosphate