A Novel Role for the Adaptor Molecule CD2-associated Protein in Transforming Growth Factor-β-induced Apoptosis

Abstract

CD2-associated protein (CD2AP) is an adaptor molecule involved in T cell receptor signaling and podocyte homeostasis. CD2AP-deficient mice develop nephrotic syndrome and renal failure caused by glomerulosclerosis. Here we report that increased transforming growth factor-␤1 (TGF-␤1) expression and apoptosis were present in podocytes at the onset of albuminuria and were followed by depletion of podocytes associated with progressive focal-segmental glomerulosclerosis in CD2AP؊/؊ mice. Conditionally immortalized podocytes derived from CD2AP؊/؊ mice were more susceptible to TGF-␤-induced apoptosis compared with CD2AP؉/؉ podocytes. Reconstitution of CD2AP rescued CD2AP؊/؊ podocytes from TGF-␤-induced apoptosis. CD2AP was required for early activation of anti-apoptotic phosphatidylinositol 3-kinase (PI3K)/AKT and extracellular signal-regulated kinase 1/2 by TGF-␤. In contrast, activation of pro-apoptotic p38 MAPK by TGF-␤ was accelerated and enhanced in the absence of CD2AP. CD2AP was not required for PI3K/AKT activation by insulin and epidermal growth factor, indicating that CD2AP is a selective mediator of anti-apoptotic TGF-␤ signaling. In summary, we identified CD2AP as a novel mediator for selective activation of survival pathways and repression of apoptosis signaling by TGF-␤ in podocytes. Together, our in vitro and in vivo findings suggest that TGF-␤-induced podocyte apoptosis is an early pathomechanism in mice developing focal-segmental glomerulosclerosis associated with functional impairment of CD2AP.The transforming growth factor-␤ (TGF-␤) 1 superfamily consists of secreted peptides, of which the three TGF-␤ isoforms (TGF-␤1-3), activins, and bone morphogenetic proteins are best known in mammalian development, homeostasis, and pathobiology. The TGF-␤ isoforms are widely expressed and act on virtually every cell type in mammals by engaging a ubiquitous intracellular signaling cascade of Smad family proteins through ligand-induced activation of heteromeric transmembrane TGF-␤ receptor kinases. Receptor-activated Smad protein complexes accumulate in the nucleus where they participate directly in transcriptional activation of target genes. In addition, TGF-␤ receptors can activate Smad-independent signaling mechanisms, including mitogen-activated protein kinases (MAPKs), and PI3K (1, 2). However, molecular mechanisms of activation of Smad-independent pathways by TGF-␤ receptors remain unclear.The mouse CD2 receptor-associated protein (CD2AP) and its human orthologue Cas ligand with multiple SH3 domains (CMS) belong to a family of ubiquitously expressed adaptor molecules that also includes the human Cbl-interacting protein of 85 kDa (CIN85) and its rat and mouse orthologue regulator of ubiquitous kinase (Ruk) and SH3 domain-containing gene expressed in tumorigenic astrocytes (SETA) (for review, see Ref.3). These proteins are defined as cytoplasmic adaptor or scaffolding proteins by three N-terminal SH3 domains, a proline-rich domain, and a C-terminal coiled-coil domain. CIN85/ CMS family proteins have been shown t...

FOG2 Protein Down-regulation by Transforming Growth Factor-β1-induced MicroRNA-200b/c Leads to Akt Kinase Activation and Glomerular Mesangial Hypertrophy Related to Diabetic Nephropathy

“…TGF-␤ also enhances Akt phosphorylation in multiple renal cells, including glomerular mesangial cells, podocytes, and renal tubular cells (15,19,37,55,56). However, in hematopoietic cells, TGF-␤ has been shown to inhibit Akt phosphorylation by inducing the phosphatase SHIP, an inhibitor of Akt activation (57).…”

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

“…Based on recent data, it appears that at least two major SD signaling pathways can be discerned: (i) acute, reversible phosphotyrosine-based ZO-1 (12) and nephrin (13,(42)(43)(44) signaling leading to P-nephrin-Nck-mediated actin reorganization (14,45). (ii) Chronic calcium (6, 7) and phosphoserine/ threonine signaling-mediated regulation of cytoskeleton dynam- ics and podocyte survival (29,46,47). Both CD2AP and nephrin interact with the p85 regulatory subunit of phosphatidylinositol 3-kinase in vivo, stimulating antiapoptotic Akt signaling (47).…”

“…Both CD2AP and nephrin interact with the p85 regulatory subunit of phosphatidylinositol 3-kinase in vivo, stimulating antiapoptotic Akt signaling (47). Podocytes lacking CD2AP are more susceptible to apoptosis, and mice lacking CD2AP show increased podocyte apoptosis in the early stages of progressive glomerulosclerosis (46). Hence, CD2AP appears to have an antiapoptotic role, with apoptosis considered a critically important mechanism in podocyte depletion.…”

1,25-Dihydroxyvitamin D3 Ameliorates Podocytopenia in Rats with Adriamycin-induced Nephropathy

“…Then, 3-μm sections were stained with Wilms tumor antigen-1 (WT-1) antibody (1 : 50; rabbit polyclonal) (Santa Cruz Biotechnology, Inc., Santa Cruz, CA, USA). Thirty glomeruli in cross section were randomly selected and the number of WT-1 positive cells was counted (14). Results were presented as average podocyte number per glomerulus crosssection.…”