The glomerular epithelial cell anti-adhesin podocalyxin associates with the actin cytoskeleton through interactions with ezrin.
During development, renal glomerular epithelial cells (podocytes) undergo extensive morphologic changes necessary for creation of the glomerular filtration apparatus. These changes include formation of interdigitating foot processes, replacement of tight junctions with slit diaphragms, and the concomitant opening of intercellular urinary spaces. It was postulated previously and confirmed recently that podocalyxin, a sialomucin, plays a major role in maintaining the urinary space open by virtue of the physicochemical properties of its highly negatively charged ectodomain. This study examined whether the highly conserved cytoplasmic tail of podocalyxin also contributes to the unique organization of podocytes by interacting with the cytoskeletal network found in their cell bodies and foot processes. By immunocytochemistry, it was shown that podocalyxin and the actin binding protein ezrin are co-expressed in podocytes and co-localize along the apical plasma membrane, where they form a co-immunoprecipitable complex. Selective detergent extraction followed by differential centrifugation revealed that some of the podocalyxin cosediments with actin filaments. Moreover, its sedimentation is dependent on polymerized actin and is mediated by complex formation with ezrin. Once formed, podocalyxin/ezrin complexes are very stable, because they are insensitive to actin depolymerization or inactivation of Rho kinase, which is known to be necessary for regulation of ezrin and to mediate Rho-dependent actin organization. These data indicate that in podocytes, podocalyxin is complexed with ezrin, which mediates its link to the actin cytoskeleton. Thus, in addition to its ectodomain, the cytoplasmic tail of podocalyxin also likely contributes to maintaining the unique podocyte morphology.
Orlando
Robert A
RA
Department of Pathology, University of California, San Diego, California.
Takeda
Tetsuro
T
Department of Cellular and Molecular Medicine, University of California, San Diego, California.
Zak
Beverly
B
Department of Pathology, University of California, San Diego, California.
Schmieder
Sandra
S
Department of Cellular and Molecular Medicine, University of California, San Diego, California.
Benoit
Vivian M
VM
Department of Cellular and Molecular Medicine, University of California, San Diego, California.
McQuistan
Tammie
T
Department of Cellular and Molecular Medicine, University of California, San Diego, California.
Furthmayr
Heinz
H
Department of Pathology, Stanford University School of Medicine, Stanford, California.
Farquhar
Marilyn G
MG
Department of Pathology, University of California, San Diego, California.|Department of Cellular and Molecular Medicine, University of California, San Diego, California.
D000199:Actins / Q000502:physiology*; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000502:physiology*; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007678:Kidney Glomerulus / Q000166:cytology / Q000378:metabolism*; D009439:Neuraminidase / Q000494:pharmacology; D010750:Phosphoproteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D012795:Sialoglycoproteins / Q000502:physiology*; D014018:Tissue Distribution; D054460:rho-Associated Kinases; D000099149:Ezrin
D000199:Actins; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009439:Neuraminidase; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D012795:Sialoglycoproteins; D054460:rho-Associated Kinases; D000099149:Ezrin; C001643:podocalyxin