MAGI-1 Interacts with Nephrin to Maintain Slit Diaphragm Structure through Enhanced Rap1 Activation in Podocytes.
MAGI-1 Interacts with Nephrin to Maintain Slit Diaphragm Structure through Enhanced Rap1 Activation in Podocytes.
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DOI：
10.1074/jbc.m116.745026
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发表时间：
2016-11-18
期刊：
影响因子：
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通讯作者：
Kaufman L
中科院分区：
文献类型：
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作者：
Ni J;Bao S;Johnson RI;Zhu B;Li J;Vadaparampil J;Smith CM;Campbell KN;Grahammer F;Huber TB;He JC;D'Agati VD;Chan A;Kaufman L
MAGI-1 是一种多结构域胞质支架蛋白，在肾脏中专门位于足细胞裂隙隔膜处，这是一种在蛋白尿疾病中普遍受损的特殊连接处。在那里，它与几种重要分子相互作用，包括去氧肾上腺素和 neph1，这些分子是狭缝隔膜形成和作为细胞内信号中枢所必需的。在这里，我们发现培养的足细胞中 MAGI-1 表达的减少会减少去氧肾上腺素和 neph1 的膜定位，并削弱紧密连接的完整性。然而，全 Magi1 基因敲除小鼠在成年期仍表现出正常的肾小球组织学和功能。我们假设第二次轻微但互补的遗传损伤可能会诱发这些小鼠的肾小球疾病易感性。为了识别这样的基因，我们利用发育中的蝇眼来测试 MAGI 与其结合伙伴之间的功能互补。通过这种方式，我们发现果蝇 Hibris（nephrin）或 Roughest（neph1）表达的减少会显着加剧 MAGI 耗竭的影响。事实上，当在小鼠中研究这些组合时，添加 nephrin 而不是 neph1、MAGI-1 纯合缺失的杂合性导致自发性肾小球硬化。在培养的足细胞中，MAGI-1 耗竭减少了细胞间接触诱导的 Rap1 激活，这是足细胞正常功能的关键途径。同样，magi1 基因敲除小鼠的肾小球 Rap1 激活减弱，这种效应因伴随的去氧肾上腺素单倍体不足而显着增强。最后，MAGI-1 和去氧肾上腺素的联合过度表达增加了 Rap1 的激活，但当替换不能结合去氧肾上腺素的突变体 MAGI-1 时则不会增加。我们得出的结论是，nephrin 和 MAGI-1 之间的相互作用调节足细胞中 Rap1 的激活，以维持长期的裂隙隔膜结构。
MAGI-1 is a multidomain cytosolic scaffolding protein that in the kidney is specifically located at the podocyte slit diaphragm, a specialized junction that is universally injured in proteinuric diseases. There it interacts with several essential molecules, including nephrin and neph1, which are required for slit diaphragm formation and as an intracellular signaling hub. Here, we show that diminished MAGI-1 expression in cultured podocytes reduced nephrin and neph1 membrane localization and weakened tight junction integrity. Global magi1 knock-out mice, however, demonstrated normal glomerular histology and function into adulthood. We hypothesized that a second mild but complementary genetic insult might induce glomerular disease susceptibility in these mice. To identify such a gene, we utilized the developing fly eye to test for functional complementation between MAGI and its binding partners. In this way, we identified diminished expression of fly Hibris (nephrin) or Roughest (neph1) as dramatically exacerbating the effects of MAGI depletion. Indeed, when these combinations were studied in mice, the addition of nephrin, but not neph1, heterozygosity to homozygous deletion of MAGI-1 resulted in spontaneous glomerulosclerosis. In cultured podocytes, MAGI-1 depletion reduced intercellular contact-induced Rap1 activation, a pathway critical for proper podocyte function. Similarly, magi1 knock-out mice showed diminished glomerular Rap1 activation, an effect dramatically enhanced by concomitant nephrin haploinsufficiency. Finally, combined overexpression of MAGI-1 and nephrin increased Rap1 activation, but not when substituting a mutant MAGI-1 that cannot bind nephrin. We conclude that the interaction between nephrin and MAGI-1 regulates Rap1 activation in podocytes to maintain long term slit diaphragm structure.