Xavier Sandhya, Niranjan Thiruvur, Krick Stefanie, Zhang Taoran, Ju Wenjun, Shaw Andrey S, Schiffer Mario, Böttinger Erwin P
Division of Nephrology, Department of Medicine, Charles R Bronfman Institute for Personalized Medicine, Mount Sinai School of Medicine, New York, New York 10029, USA.
J Am Soc Nephrol. 2009 Oct;20(10):2127-37. doi: 10.1681/ASN.2008070806. Epub 2009 Aug 13.
TGF-beta regulates differentiation, growth, and apoptosis of podocytes and mediates podocyte depletion in glomerulosclerosis. TGF-beta promotes proapoptotic signaling mediated by Smad3 but also activates prosurvival pathways such as phosphoinositide-3 kinase (PI3K)/AKT; the latter requires the CD2-associated adaptor protein (CD2AP) in podocytes. Whether the opposing activities mediated by Smad proteins and CD2AP involve molecular cross-talk is unknown. Here, we report that CD2AP-dependent early activation of the antiapoptotic PI3K/AKT pathway does not require TGF-beta receptor-regulated Smad2 and Smad3. We found that the C-terminal region of CD2AP interacts directly with the cytoplasmic tail of the TGF-beta receptor type I (TbetaRI) in a kinase-dependent manner and that the interaction between the TbetaRI and the p85 subunit of PI3K requires CD2AP. Consistent with the proapoptotic function of Smad signaling, Smad2/3-deficient podocytes were hyperproliferative and resistant to TGF-beta-induced growth inhibition and apoptosis. In contrast, CD2AP-deficient cells were hypoproliferative and hypersensitive to TGF-beta-induced apoptosis. In vivo, to determine the effects of reduced Smad3 or CD2AP gene dosage on podocyte apoptosis and proteinuria characteristic of TGF-beta1 transgenic mice, we generated TGF-beta1 transgenic mice deficient for Smad3 or heterozygous for CD2AP. Smad3 deficiency ameliorated podocyte apoptosis, and CD2AP heterozygosity increased both podocyte apoptosis and proteinuria. These data define distinct canonical (Smad) and noncanonical (CD2AP/PI3K/AKT) pathways that arise from direct, independent interactions with the TbetaRI and that mediate opposing signals for podocyte death or survival.
转化生长因子-β（TGF-β）调节足细胞的分化、生长和凋亡，并介导肾小球硬化中足细胞的缺失。TGF-β促进由Smad3介导的促凋亡信号传导，但也激活诸如磷酸肌醇-3激酶（PI3K）/AKT等促存活途径；后者在足细胞中需要CD2相关衔接蛋白（CD2AP）。Smad蛋白和CD2AP介导的相反活性是否涉及分子间相互作用尚不清楚。在此，我们报告抗凋亡PI3K/AKT途径的CD2AP依赖性早期激活不需要TGF-β受体调节的Smad2和Smad3。我们发现，CD2AP的C末端区域以激酶依赖性方式直接与I型TGF-β受体（TβRI）的胞质尾部相互作用，并且TβRI与PI3K的p85亚基之间的相互作用需要CD2AP。与Smad信号传导的促凋亡功能一致，Smad2/3缺陷型足细胞过度增殖，并且对TGF-β诱导的生长抑制和凋亡具有抗性。相反，CD2AP缺陷型细胞增殖不足，并且对TGF-β诱导的凋亡高度敏感。在体内，为了确定Smad3基因剂量减少或CD2AP基因剂量减少对TGF-β1转基因小鼠足细胞凋亡和蛋白尿特征的影响，我们生成了Smad3缺陷型或CD2AP杂合型的TGF-β1转基因小鼠。Smad3缺陷改善了足细胞凋亡，而CD2AP杂合性增加了足细胞凋亡和蛋白尿。这些数据定义了由与TβRI的直接、独立相互作用产生的不同的经典（Smad）和非经典（CD2AP/PI3K/AKT）途径，它们介导足细胞死亡或存活的相反信号。
