Fyn binds to and phosphorylates the kidney slit diaphragm component Nephrin.
Recent investigations have focused on characterizing the molecular components of the podocyte intercellular junction, because several of these components, including Nephrin, are functionally necessary for development of normal podocyte structure and filter integrity. Accumulating evidence suggests that the Nephrin-associated protein complex is a signaling nexus. As such, Nephrin-dependent signaling might be mediated in part through Nephrin phosphorylation. Described are biochemical and mouse genetics experiments demonstrating that membrane-associated Nephrin is tyrosine-phosphorylated by the Src family kinase Fyn. Nephrin fractionated in detergent-resistant glomerular membrane fractions with Fyn and Yes. Fyn directly bound Nephrin via its SH3 domain, and Fyn directly phosphorylated Nephrin. Glomeruli in which Fyn, Yes, or Fyn and Yes were genetically deleted in mice were characterized to explore the relationship between these kinases and Nephrin. Fyn deletion resulted in coarsening of podocyte foot processes and marked attenuation of Nephrin phosphorylation in isolated glomerular detergent-resistant membrane fractions. Yes deletion had no identifiable effect on podocyte morphology but dramatically increased Nephrin phosphorylating activity. Similar to Fyn deletion, simultaneous deletion of Fyn and Yes reduced Nephrin phosphorylating activity. These results demonstrate that endogenous Fyn catalyzes Nephrin phosphorylation in podocyte detergent-resistant membrane fractions. Although Yes appears to effect the regulation of Nephrin phosphorylation, the mechanism by which this occurs requires investigation.
Verma
Rakesh
R
Department of Veterans Affairs, Ann Arbor, Michigan 48105, USA.
Wharram
Bryan
B
Kovari
Iulia
I
Kunkel
Robin
R
Nihalani
Deepak
D
Wary
Kishore K
KK
Wiggins
Roger C
RC
Killen
Paul
P
Holzman
Lawrence B
LB
D000818:Animals; D019556:COS Cells; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D003902:Detergents; D005260:Female; D007678:Kidney Glomerulus / Q000201:enzymology*; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D017830:Octoxynol; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D051575:Proto-Oncogene Proteins c-yes; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology; D013379:Substrate Specificity; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases
D003902:Detergents; D008565:Membrane Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; C113267:nephrin; D014443:Tyrosine; D017830:Octoxynol; C494960:Fyn protein, mouse; C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn; D051575:Proto-Oncogene Proteins c-yes; C496639:Yes1 protein, mouse; D019061:src-Family Kinases