title: Syndecan-4 ectodomain evokes mobilization of podocyte TRPC6 channels and their associated pathways: An essential role for integrin signaling.
abstract: PodocyteTRPC6 channels have been implicated in glomerular diseases. Syndecan-4 (Sdc4) is a membrane proteoglycan that can be cleaved to release a soluble ectodomain capable of paracrine and autocrine signaling. We have confirmed that overexpression of Sdc4 core protein increases surface abundance of TRPC6 channels in cultured podocytes, whereas Sdc4 knockdown has the opposite effect. Exposure to soluble Sdc4 ectodomain also increased the surface abundance of TRPC6, and increased cationic currents evoked by a diacylglycerol analog in podocytes. Sdc4 ectodomain increased generation of reactive oxygen species (ROS), reduced activation of RhoA, increased activation of Rac1, increased nuclear abundance of NFATc1, and increased total β3-integrin. The effects of Sdc4 ectodomain on cell-surface TRPC6 were blocked by the ROS quencher TEMPOL, and by the Rac1 inhibitor NSC-23766, but were not blocked by inhibition of calcineurin-NFATc1 signaling. The Sdc4 core protein co-immunoprecipitates with β3-integrin in cultured podocytes. Moreover, effects of Sdc4 ectodomain on TRPC6, ROS generation, Rac1 and RhoA modulation, and NFATc1 activation were blocked by cilengitide, a selective inhibitor of outside-in signaling through αv-containing integrins. Exposure to TNF, or serum from three patients with recurrent FSGS in relapse, increased shedding of podocyte Sdc4 ectodomains into the surrounding medium. This was also observed after treating podocytes with the metalloproteinase ADAM17 or after overexpression of the Sdc4 core protein. Increased concentrations of Sdc4 ectodomain were detected in urine of rats during acute puromycin aminonucleoside nephrosis. Locally generated Sdc4 may play a role in regulating TRPC6 channels, and may contribute to glomerular pathology.
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, TX, USA. Electronic address: kimey732000@yahoo.com.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, TX, USA. Electronic address: hroshanr@Central.UH.EDU.
authors.forename: Hila
authors.initials: H
authors.lastname: Roshanravan
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, TX, USA; Division of Nephrology, Baylor College of Medicine, Houston, TX, USA. Electronic address: SDryer@uh.edu.
authors.forename: Stuart E
authors.initials: SE
authors.lastname: Dryer
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000009:adverse effects / Q000494:pharmacology; D002460:Cell Line; D039564:Integrin alphaV / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D009401:Nephrosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D050199:Podocytes / Q000378:metabolism* / Q000473:pathology; D011692:Puromycin Aminonucleoside / Q000009:adverse effects / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D053671:Syndecan-4 / Q000235:genetics / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*; D000074287:TRPC6 Cation Channel; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
chemical_list: D000964:Antimetabolites, Antineoplastic; D039564:Integrin alphaV; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D017382:Reactive Oxygen Species; C508306:Sdc4 protein, mouse; C508307:Sdc4 protein, rat; D053671:Syndecan-4; D050052:TRPC Cation Channels; D000074287:TRPC6 Cation Channel; C492146:Trpc6 protein, mouse; C492145:Trpc6 protein, rat; D011692:Puromycin Aminonucleoside; C499134:Rac1 protein, rat; C526380:RhoA protein, mouse; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein
keywords: Calcium; FSGS; Inflammation; Metalloproteinase; Oxidative stress; Proteoglycan