Nephrin forms a complex with adherens junction proteins and CASK in podocytes and in Madin-Darby canine kidney cells expressing nephrin.
Mutations in the NPHS1 gene encoding nephrin lead to congenital nephrotic syndrome of the Finnish type. Nephrin is a key component of the glomerular slit diaphragms between epithelial foot processes, but its role in the pathogenesis of this disease is poorly understood. To further clarify the molecular mechanisms involved we investigated the interactions between nephrin and other components of the foot processes and filtration slits, especially adherens junction proteins, and searched for novel nephrin interacting proteins. Using co-immunoprecipitation and pull-down assays we show here that nephrin forms a multiprotein complex with cadherins and p120 catenin and with three scaffolding proteins, ZO-1, CD2AP, and CASK, in kidney glomeruli and when expressed in Madin-Darby canine kidney cells. CASK was identified as a novel binding partner of nephrin by mass spectrometry and was localized to podocytes in the glomerulus. CASK is a scaffolding protein that participates in maintenance of polarized epithelial cell architecture by linking membrane proteins and signaling molecules to the actin cytoskeleton. Our results support a model whereby the glomerular slit diaphragms are composed of cell adhesion molecules of the immunoglobulin and cadherin superfamilies that are connected to each other and to the actin cytoskeleton and signaling networks via the cytoplasmic scaffolding proteins CASK, CD2AP, and ZO-1.
Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, California, USA.
Sanna
S
Lehtonen
Eero
E
Lehtonen
Krystyna
K
Kudlicka
Harry
H
Holthöfer
Marilyn G
MG
Farquhar
D048868:Adaptor Proteins, Signal Transducing; D022005:Adherens Junctions / Q000502:physiology*; D000818:Animals; D015820:Cadherins / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D051177:Catenins; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D006031:Glycosylation; D051528:Guanylate Kinases; D006801:Humans; D007678:Kidney Glomerulus / Q000378:metabolism* / Q000473:pathology; D007684:Kidney Tubules / Q000378:metabolism* / Q000473:pathology; D008297:Male; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D062826:Zonula Occludens-1 Protein; D018909:src Homology Domains; D000095002:Delta Catenin
D048868:Adaptor Proteins, Signal Transducing; C114545:CD2-associated protein; D015820:Cadherins; D051177:Catenins; D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D010750:Phosphoproteins; D011506:Proteins; C569042:TJP1 protein, human; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein; C113267:nephrin; C106868:CASK kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D051528:Guanylate Kinases; D000095002:Delta Catenin