Neph1 cooperates with nephrin to transduce a signal that induces actin polymerization.
While the mechanisms that regulate actin dynamics in cellular motility are intensively studied, relatively little is known about signaling events that transmit outside-in signals and direct assembly and regulation of actin polymerization complexes at the cell membrane. The kidney podocyte provides a unique model for investigating these mechanisms since deletion of Nephrin or Neph1, two interacting components of the specialized podocyte intercellular junction, results in abnormal podocyte morphogenesis and junction formation. We provide evidence that extends the existing model by which the Nephrin-Neph1 complex transduces phosphorylation-mediated signals that assemble an actin polymerization complex at the podocyte intercellular junction. Upon engagement, Neph1 is phosphorylated on specific tyrosine residues by Fyn, which results in the recruitment of Grb2, an event that is necessary for Neph1-induced actin polymerization at the plasma membrane. Importantly, Neph1 and Nephrin directly interact and, by juxtaposing Grb2 and Nck1/2 at the membrane following complex activation, cooperate to augment the efficiency of actin polymerization. These data provide evidence for a mechanism reminiscent of that employed by vaccinia virus and other pathogens, by which a signaling complex transduces an outside-in signal that results in actin filament polymerization at the plasma membrane.
Garg
Puneet
P
University of Michigan Medical School, Division of Nephrology, Ann Arbor, MI 48109-5676, USA.
Verma
Rakesh
R
Nihalani
Deepak
D
Johnstone
Duncan B
DB
Holzman
Lawrence B
LB
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D005260:Female; D051380:GRB2 Adaptor Protein / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D019000:Phosphotyrosine / Q000378:metabolism; D050199:Podocytes / Q000473:pathology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D051076:Proto-Oncogene Proteins c-fyn / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D000199:Actins; D051380:GRB2 Adaptor Protein; C486606:Kirrel1 protein, mouse; D008565:Membrane Proteins; C113267:nephrin; D019000:Phosphotyrosine; C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn