Cell junction-associated proteins IQGAP1, MAGI-2, CASK, spectrins, and α-actinin are components of the nephrin multiprotein complex
Cell junction-associated proteins IQGAP1, MAGI-2, CASK, spectrins, and α-actinin are components of the nephrin multiprotein complex
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DOI：
10.1073/pnas.0504166102
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发表时间：
2005-07-12
影响因子：
11.1
通讯作者：
Farquhar, MG
中科院分区：
文献类型：
--
作者：
Lehtonen, S;Ryan, JJ;Farquhar, MG
Nephrin是IG超家族的细胞表面受体，其定位于狭缝隔膜，狭缝隔膜是肾脏中肾小球上皮（足细胞）的交错足突之间的特化连接。编码nephrin的NPHS 1基因突变导致蛋白尿和先天性肾病综合征，表明nephrin对正常肾小球发育和功能至关重要。为了确定nephrin结合蛋白，我们进行了质谱分析从下拉分析与GST-nephrin胞质结构域的蛋白质。Nephrin特异性地从肾小球裂解物中拉下六种蛋白，MAGI-2/S-SCAM（膜相关鸟苷酸激酶反向2/突触支架分子）、IQGAP 1（含有IQ基序的GTP酶激活蛋白1）、CASK（钙/钙调蛋白依赖性丝氨酸蛋白激酶）、α-辅肌动蛋白、全血影蛋白和β II血影蛋白。所有这些支架蛋白通常与细胞连接有关。通过免疫荧光，这些蛋白质在肾小球上皮细胞中表达，在那里它们与足突中的nephrin共定位。在肾小球发育过程中，IQGAP 1在最早可识别的足细胞之间的连接复合体中表达，MAGI-2/S-SCAM在足细胞迁移到细胞基底后首先在足细胞的连接复合体中检测到。因此，肾蛋白裂隔膜蛋白复合物包含一组支架蛋白，其功能是将连接膜蛋白连接到肌动蛋白细胞骨架和信号级联。尽管其特殊的形态和功能，有相当大的组成相似性之间的足细胞狭缝隔膜和其他上皮细胞的典型连接复合物。
Nephrin is a cell surface receptor of the Ig superfamily that localizes to slit diaphragms, the specialized junctions between the interdigitating foot processes of the glomerular epithelium (podocytes) in the kidney. Mutations in the NPHS1 gene encoding nephrin lead to proteinuria and congenital nephrotic syndrome, indicating that nephrin is essential for normal glomerular development and function. To identify nephrin-binding proteins, we performed mass spectrometry on proteins obtained from pull-down assays with GST-nephrin cytoplasmic domain. Nephrin specifically pulled down six proteins from glomerular lysates, MAGI-2/S-SCAM (membrane-associated guanylate kinase inverted 2/synaptic scaffolding molecule), IQGAP1 (IQ motif-containing GTPase-activating protein 1), CASK (calcium/calmodulin-dependent serine protein kinase), a-actinin, all spectrin, and beta II spectrin. All of these scaffolding proteins are often associated with cell junctions. By immunofluorescence these proteins are expressed in glomerular epithelial cells, where they colocalize with nephrin in the foot processes. During glomerular development, IQGAP1 is expressed in the junctional complexes between the earliest identifiable podocytes, MAGI-2/S-SCAM is first detected in junctional complexes in podocytes after their migration to the base of the cells. Thus, the nephrin-slit diaphragm protein complex contains a group of scaffolding proteins that function to connect junctional membrane proteins to the actin cytoskeleton and signaling cascades. Despite their special morphology and function, there is considerable compositional similarity between the podocyte slit diaphragm and typical junctional complexes of other epithelial cells.