Rinschen Markus M, Bharill Puneet, Wu Xiongwu, Kohli Priyanka, Reinert Matthäus J, Kretz Oliver, Saez Isabel, Schermer Bernhard, Höhne Martin, Bartram Malte P, Aravamudhan Sriram, Brooks Bernard R, Vilchez David, Huber Tobias B, Müller Roman-Ulrich, Krüger Marcus, Benzing Thomas
Department II of Internal Medicine, Center for Molecular Medicine Cologne, Cologne Excellence Cluster on Cellular Stress Responses in Aging Associated Diseases (CECAD) and Systems Biology of Ageing Cologne (Sybacol), University of Cologne, Cologne, Germany,
Department II of Internal Medicine, Systems Biology of Ageing Cologne (Sybacol), University of Cologne, Cologne, Germany.
Hum Mol Genet. 2016 Apr 1;25(7):1328-44. doi: 10.1093/hmg/ddw016. Epub 2016 Jan 19.
The PHB-domain protein podocin maintains the renal filtration barrier and its mutation is an important cause of hereditary nephrotic syndrome. Podocin and its Caenorhabditis elegans orthologue MEC-2 have emerged as key components of mechanosensitive membrane protein signalling complexes. Whereas podocin resides at a specialized cell junction at the podocyte slit diaphragm, MEC-2 is found in neurons required for touch sensitivity. Here, we show that the ubiquitin ligase Ubr4 is a key component of the podocin interactome purified both from cultured podocytes and native glomeruli. It colocalizes with podocin and regulates its stability. In C. elegans, this process is conserved. Here, Ubr4 is responsible for the degradation of mislocalized MEC-2 multimers. Ubiquitylomic analysis of mouse glomeruli revealed that podocin is ubiquitylated at two lysine residues. These sites were Ubr4-dependent and were conserved across species. Molecular dynamics simulations revealed that ubiquitylation of one site, K301, do not only target podocin/MEC-2 for proteasomal degradation, but may also affect stability and disassembly of the multimeric complex. We suggest that Ubr4 is a key regulator of podocyte foot process proteostasis.
PHB 结构域蛋白足突蛋白维持肾脏滤过屏障，其突变是遗传性肾病综合征的重要病因。足突蛋白及其秀丽隐杆线虫同源物 MEC-2 已成为机械敏感膜蛋白信号复合物的关键组成部分。足突蛋白位于足细胞裂孔隔膜的特殊细胞连接处，而 MEC-2 则存在于触觉敏感所需的神经元中。在此，我们表明泛素连接酶 Ubr4 是从培养的足细胞和天然肾小球中纯化出的足突蛋白相互作用组的关键组成部分。它与足突蛋白共定位并调节其稳定性。在秀丽隐杆线虫中，这一过程是保守的。在这里，Ubr4 负责错误定位的 MEC-2 多聚体的降解。对小鼠肾小球的泛素化组分析表明，足突蛋白在两个赖氨酸残基处被泛素化。这些位点依赖于 Ubr4，并且在物种间保守。分子动力学模拟表明，一个位点 K301 的泛素化不仅靶向足突蛋白/MEC-2 进行蛋白酶体降解，还可能影响多聚体复合物的稳定性和解聚。我们认为 Ubr4 是足细胞足突蛋白稳态的关键调节因子。
