Nephrin ectodomain engagement results in Src kinase activation, nephrin phosphorylation, Nck recruitment, and actin polymerization.
A properly established and maintained podocyte intercellular junction, or slit diaphragm, is a necessary component of the selective permeability barrier of the kidney glomerulus. The observation that mutation or deletion of the slit diaphragm transmembrane protein nephrin results in failure of podocyte foot process morphogenesis and concomitant proteinuria first suggested the hypothesis that nephrin serves as a component of a signaling complex that directly integrates podocyte junctional integrity with cytoskeletal dynamics. The observations made herein provide the first direct evidence to our knowledge for a phosphorylation-mediated signaling mechanism by which this integrative function is derived. Our data support the model that during podocyte intercellular junction formation, engagement of the nephrin ectodomain induces transient Fyn catalytic activity that results in nephrin phosphorylation on specific nephrin cytoplasmic domain tyrosine residues. We found that this nephrin phosphorylation event resulted in recruitment of the SH2-SH3 domain-containing adapter protein Nck and assembly of actin filaments in an Nck-dependent fashion. Considered in the context of the role of nephrin family proteins in other organisms and the integral relationship of actin dynamics and junction formation, these observations establish a function for nephrin in regulating actin cytoskeletal dynamics.
Division of Nephrology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0676, USA.
Rakesh
R
Verma
Iulia
I
Kovari
Abdul
A
Soofi
Deepak
D
Nihalani
Kevin
K
Patrie
Lawrence B
LB
Holzman
D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D006801:Humans; D007678:Kidney Glomerulus / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D051379:Mice; D015513:Oncogene Proteins / Q000378:metabolism*; D010766:Phosphorylation; D050199:Podocytes / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019061:src-Family Kinases / Q000378:metabolism*
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D008565:Membrane Proteins; C078332:Nck protein; D015513:Oncogene Proteins; C113267:nephrin; D019061:src-Family Kinases