title: Slit diaphragms contain tight junction proteins.
abstract: Slit diaphragms are essential components of the glomerular filtration apparatus, as changes in these junctions are the hallmark of proteinuric diseases. Slit diaphragms, considered specialized adherens junctions, contain both unique membrane proteins (e.g., nephrin, podocin, and Neph1) and typical adherens junction proteins (e.g., P-cadherin, FAT, and catenins). Whether slit diaphragms also contain tight junction proteins is unknown. Here, immunofluorescence, immunogold labeling, and cell fractionation demonstrated that rat slit diaphragms contain the tight junction proteins JAM-A (junctional adhesion molecule A), occludin, and cingulin. We found these proteins in the same protein complexes as nephrin, podocin, CD2AP, ZO-1, and Neph1 by cosedimentation, coimmunoprecipitation, and pull-down assays. PAN nephrosis increased the protein levels of JAM-A, occludin, cingulin, and ZO-1 several-fold in glomeruli and loosened their attachment to the actin cytoskeleton. These data extend current information about the molecular composition of slit diaphragms by demonstrating the presence of tight junction proteins, although slit diaphragms lack the characteristic morphologic features of tight junctions. The contribution of these proteins to the assembly of slit diaphragms and potential signaling cascades requires further investigation.
authors.affiliation: Department of Cellular and Molecular Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0651, USA.
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Fukasawa
authors.forename: Scott
authors.initials: S
authors.lastname: Bornheimer
authors.forename: Krystyna
authors.initials: K
authors.lastname: Kudlicka
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Farquhar
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D003599:Cytoskeleton / Q000378:metabolism; D004195:Disease Models, Animal; D051528:Guanylate Kinases / Q000378:metabolism; D062726:Junctional Adhesion Molecules; D007678:Kidney Glomerulus / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009401:Nephrosis / Q000378:metabolism / Q000473:pathology; D062793:Occludin; D010750:Phosphoproteins / Q000378:metabolism; D050199:Podocytes / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019108:Tight Junctions / Q000378:metabolism*; D062826:Zonula Occludens-1 Protein
chemical_list: D000199:Actins; D015815:Cell Adhesion Molecules; D062726:Junctional Adhesion Molecules; D008565:Membrane Proteins; D062793:Occludin; C568987:Ocln protein, rat; D010750:Phosphoproteins; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein; C106868:CASK kinases; D051528:Guanylate Kinases