CD2AP/CIN85 Balance Determines Receptor Tyrosine Kinase Signaling Response in Podocytes

Irini Tossidou,Christian Kardinal,Imke Peters,Wilhelm Kriz,Andrey Shaw,Ivan Dikic,Sergej Tkachuk,Inna Dumler,Hermann Haller,Mario Schiffer

doi:10.1074/jbc.m608519200

Abstract

Defects in podocyte signaling are the basis of many inherited glomerular diseases leading to glomerulosclerosis. CD2-associated protein (CD2AP) is highly expressed in podocytes and is considered to play an important role in the maintenance of the glomerular slit diaphragm. Mice deficient for CD2AP (CD2AP(-/-)) appear normal at birth but develop a rapid onset nephrotic syndrome at 3 weeks of age. We demonstrate that impaired intracellular signaling with subsequent podocyte damage is the reason for this delayed podocyte injury in CD2AP(-/-) mice. We document that CD2AP deficiency in podocytes leads to diminished signal initiation and termination of signaling pathways mediated by receptor tyrosine kinases (RTKs). In addition, we demonstrate that CIN85, a paralog of CD2AP, is involved in termination of RTK signaling in podocytes. CIN85 protein expression is increased in CD2AP(-/-) podocytes in vitro. Stimulation of CD2AP(-/-) podocytes with various growth factors, including insulin-like growth factor 1, vascular endothelial growth factor, and fibroblast growth factor, resulted in a significantly decreased phosphatidylinositol 3-kinase/AKT and ERK signaling response. Moreover, increased CIN85 protein is detectable in podocytes in diseased CD2AP(-/-) mice, leading to decreased base-line activation of ERK and decreased phosphorylation after growth factor stimulation in vivo. Because repression of CIN85 protein leads to a restored RTK signaling response, our results support an important role of CD2AP/CIN85 protein balance in the normal signaling response of podocytes.

Highlights

In this study we demonstrate that CD2-associated protein (CD2AP) and CIN85 contribute to the balance of receptor tyrosine kinases (RTKs) signaling in podocytes
Podocyte Damage in 3-Week-old CD2APϪ/Ϫ Mice Occurs Simultaneously in All Glomeruli—Previously we described that podocyte apoptosis is an early lesion during the development of the disease in CD2APϪ/Ϫ mice and that apoptotic cell death is detectable in the endocapillary/mesangial compartments only at later time points [3]
We found in CD2APϪ/Ϫ mice at 2 weeks of age no mesangial matrix accumulation or damage in 221 examined glomerular profiles

Summary

Introduction

Increased CIN85 protein is detectable in podocytes in diseased CD2AP؊/؊ mice, leading to decreased base-line activation of ERK and decreased phosphorylation after growth factor stimulation in vivo. Preincubation of the cells with farnesylthiosalicylic acid or PD98059 for specific inhibition of Ras and MEK activation resulted in complete abrogation of ERK1/2 phosphorylation but no effect was detectable on PI3K/AKT signaling.

Results

Conclusion