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Molecular and Cellular Biology, July 2003, p. 4917-4928, Vol. 23, No. 14
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.14.4917-4928.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Nephrin and CD2AP Associate with Phosphoinositide 3-OH Kinase and Stimulate AKT-Dependent Signaling

Tobias B. Huber,1 Björn Hartleben,1 Jeong Kim,2 Miriam Schmidts,1 Bernhard Schermer,1 Alexander Keil,1 Lotti Egger,3 Rachel L. Lecha,2 Christoph Borner,3 Hermann Pavenstädt,1 Andrey S. Shaw,2 Gerd Walz,1* and Thomas Benzing1

Renal Division,1 Molecular Medicine, University Hospital Freiburg, D-79106 Freiburg, Germany,3 Center for Immunology and Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 631102

Received 18 December 2002/ Returned for modification 6 February 2003/ Accepted 21 April 2003

Mutations of NPHS1 or NPHS2, the genes encoding nephrin and podocin, as well as the targeted disruption of CD2-associated protein (CD2AP), lead to heavy proteinuria, suggesting that all three proteins are essential for the integrity of glomerular podocytes, the visceral glomerular epithelial cells of the kidney. It has been speculated that these proteins participate in common signaling pathways; however, it has remained unclear which signaling proteins are actually recruited by the slit diaphragm protein complex in vivo. We demonstrate that both nephrin and CD2AP interact with the p85 regulatory subunit of phosphoinositide 3-OH kinase (PI3K) in vivo, recruit PI3K to the plasma membrane, and, together with podocin, stimulate PI3K-dependent AKT signaling in podocytes. Using two-dimensional gel analysis in combination with a phosphoserine-specific antiserum, we demonstrate that the nephrin-induced AKT mediates phosphorylation of several target proteins in podocytes. One such target is Bad; its phosphorylation and inactivation by 14-3-3 protects podocytes against detachment-induced cell death, suggesting that the nephrin-CD2AP-mediated AKT activity can regulate complex biological programs. Our findings reveal a novel role for the slit diaphragm proteins nephrin, CD2AP, and podocin and demonstrate that these three proteins, in addition to their structural functions, initiate PI3K/AKT-dependent signal transduction in glomerular podocytes.


* Corresponding author. Mailing adress: Renal Division, University Hospital Freiburg, Hugstetterstrasse 55, 79106 Freiburg, Germany. Phone: (0761) 270 3250. Fax: (0761) 270 3245. E-mail: walz{at}med1.ukl.uni-freiburg.de.


Molecular and Cellular Biology, July 2003, p. 4917-4928, Vol. 23, No. 14
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.14.4917-4928.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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