Nuclear relocation of the nephrin and CD2AP-binding protein dendrin promotes apoptosis of podocytes

Abstract

Kidney podocytes and their slit diaphragms (SDs) form the final barrier to urinary protein loss. There is mounting evidence that SD proteins also participate in intracellular signaling pathways. The SD protein nephrin serves as a component of a signaling complex that directly links podocyte junctional integrity to actin cytoskeletal dynamics. Another SD protein, CD2-associated protein (CD2AP), is an adaptor molecule involved in podocyte homeostasis that can repress proapoptotic TGF-␤ signaling in podocytes. Here we show that dendrin, a protein originally identified in telencephalic dendrites, is a constituent of the SD complex, where it directly binds to nephrin and CD2AP. In experimental glomerulonephritis, dendrin relocates from the SD to the nucleus of injured podocytes. High-dose, proapoptotic TGF-␤1 directly promotes the nuclear import of dendrin, and nuclear dendrin enhances both staurosporine-and TGF-␤1-mediated apoptosis. In summary, our results identify dendrin as an SD protein with proapoptotic signaling properties that accumulates in the podocyte nucleus in response to glomerular injury and provides a molecular target to tackle proteinuric kidney diseases. Nuclear relocation of dendrin may provide a mechanism whereby changes in SD integrity could translate into alterations of podocyte survival under pathological conditions. glomerular injury ͉ proapoptotic signaling ͉ TGF-␤ signaling ͉ slit diaphragm G lomerular podocytes serve as the final barrier to urinary protein loss by the formation and maintenance of podocyte foot processes (FP) and the interposed slit diaphragm (SD) (1). All forms of nephrotic syndrome are characterized by abnormalities in podocytes, including retraction (effacement) of podocyte FP and/or molecular reorganization of the SD (1). The discovery of several podocyte proteins and their mutation analysis, including nephrin (2), CD2-associated protein (CD2AP) (3), ␣-actinin-4 (4), podocin (5), TRPC6 (6, 7), and neph1 (8), have shed light on the pathogenesis of proteinuria and emphasized the critical role of the podocyte and the SD in maintaining the function of the glomerular filtration barrier. At the cytoplasmic insertion site of the SD, ZO-1 (9), ␣-, ␤-, ␥-catenins (10), podocin (11), and CD2AP (3) are present. In nephrotic syndrome, the normal podocyte substructure is lost, with effacement of podocyte FP, proteinuria (1), as well as altered phosphorylation of ZO-1 (12) and nephrin (13,14).Dendrin is a proline-rich protein of unknown function that was originally identified in telencephalic dendrites of sleep-deprived rats (15). In the brain, two protein variants (81 kDa, 89 kDa) were identified in cytosolic and membranous protein fractions (15). More recently, KIBRA, a WW domain-containing protein, was identified as a dendrin-interacting protein, but the functional relevance of this interaction remains to be established (16). Here we show that dendrin is a component of the SD complex. We further show that dendrin relocates to the nucleus of injured podocytes in a murine model of cr...

Structure of the Kidney Slit Diaphragm Adapter Protein CD2-Associated Protein as Determined with Electron Microscopy

“…26 Cathepsin L cleaves CD2AP at two sites: between SH3B and SH3C and between the first and second proline-rich regions that follow SH3C. 26 The latter cleavage generates a C-terminal fragment of CD2AP (P32) that remains bound to the podocyte cytoskeleton but releases its binding partner, dendrin, 57 that can now travel to the podocyte nucleus to promote apoptosis. 26 The organization of the CD2AP tetramer leaves both cleavage sites exposed, flanking SH3C at the outer radius of the tetramer (Figure 3).…”

Notch2 activation ameliorates nephrosis

“…Apoptotic cells were identified by staining with allophycocyanin (APC)-labelled annexin V and propidium iodide 42 by using Annexin V Apoptosis Detection Kit APC (eBioscience, CA, USA). The cells were collected at 8 h after ADR treatment, washed and suspended in the binding solution.…”

Podocyte loss and albuminuria of KK-Ay mouse: A spontaneous animal model for human type 2 diabetic nephropathy

“…In human diabetic nephropathy, there is no evidence of necrosis and no direct evidence for apoptosis as a major mechanism of podocyte loss. However, apoptosis of podocytes has been determined in cell cultures [18,19]. Gu et al reported that monocyte chemoattractant protein-1 (MCP-1) was induced by advanced glycation end-products and carboxymethllysine (CML) in differentiated podocytes [20].…”