Williquett Jillian, Perez-Gill Chandra, Allamargot Chantal, Rooney Faith, Pollak Martin R, Sun Hua
Division of Nephrology, Stead Family Department of Pediatrics, Carver College of Medicine, The University of Iowa, Iowa City, Iowa.
Department of Pathology, University of Colorado Anschutz Medical Campus, Aurora, Colorado.
Kidney360. 2025 Jan 1;6(1):38-48. doi: 10.34067/KID.0000000659. Epub 2024 Dec 2.
The R218Q mutation disrupts sequestration of Dynll1 by inverted formin 2, promotes Dynll1-PI31 interaction, and enhances proteasome-mediated nephrin degradation. Suppression of proteasome-mediated proteolysis with proteasome inhibitors is a new therapeutic strategy for inverted formin 2-mediated FSGS.
The p.Arg218Gln (R218Q) mutation in the inverted formin 2 () gene causes podocytopathy prone to FSGS. This mutation disrupts the ability of INF2 to sequester dynein light chain 1 (DYNLL1), thus promoting dynein-mediated mistrafficking of the slit diaphragm protein, nephrin, to proteolytic pathways. Bortezomib, a proteasome inhibitor, stabilizes nephrin in R218Q knockin (KI) podocytes, suggesting a role for the ubiquitin proteasome system (UPS) in dynein-driven pathogenesis. However, the link between dynein and the UPS is unknown. This study tested the hypothesis that INF2 R218Q promotes proteasome-mediated degradation of nephrin through an increased interaction between Dynll1 and the proteasomal inhibitor of 31kD (PI31), a Dynll1 adaptor that potentially couples the UPS with dynein cargoes.
The essential role of PI31 in UPS-mediated degradation of nephrin, a known dynein cargo, was studied in cultured R218Q KI mouse podocytes by applying genetic or chemical interventions to inhibit the activity of PI31 or of the proteasome. The protective effect of bortezomib in dynein-driven podocytopathy and FSGS was tested in R218Q KI mice challenged with puromycin aminonucleoside, a murine model of FSGS.
The R218Q mutation in INF2 disrupted sequestration of Dynll1 by INF2, allowing Dynll1 to be captured by PI31 and promoting dynein-mediated transport of nephrin to the proteasome. Each of the following manipulations was sufficient to restore nephrin proteostasis in R218Q KI podocytes: knocking down or , inactivating dynein, or inhibiting the activity of the proteasome. In R218Q KI mice challenged with puromycin aminonucleoside, dynein-mediated mistrafficking and depletion of nephrin were correlated with increased Dynll1-PI31 interaction; the resulting podocytopathy and FSGS were ameliorated by bortezomib.
The Dynll1-PI31 interaction facilitates dynein-driven trafficking of nephrin to the proteasome and proteasome-mediated degradation of nephrin in INF2-R218Q-mediated podocytopathy. This mechanism offers new therapeutic strategies for INF2-related FSGS by using pharmacologically available proteasome inhibitors.
R218Q突变破坏了反向formin 2对动力蛋白轻链1（Dynll1）的隔离，促进了Dynll1与PI31的相互作用，并增强了蛋白酶体介导的nephrin降解。用蛋白酶体抑制剂抑制蛋白酶体介导的蛋白水解是针对反向formin 2介导的局灶节段性肾小球硬化（FSGS）的一种新的治疗策略。
反向formin 2（INF2）基因中的p.Arg218Gln（R218Q）突变导致易患FSGS的足细胞病变。该突变破坏了INF2隔离动力蛋白轻链1（DYNLL1）的能力，从而促进了动力蛋白介导的裂孔隔膜蛋白nephrin向蛋白水解途径的错误运输。蛋白酶体抑制剂硼替佐米可使R218Q基因敲入（KI）足细胞中的nephrin稳定，提示泛素蛋白酶体系统（UPS）在动力蛋白驱动的发病机制中起作用。然而，动力蛋白与UPS之间的联系尚不清楚。本研究检验了以下假设：INF2 R218Q通过增加Dynll1与31kD蛋白酶体抑制剂（PI31）之间的相互作用来促进蛋白酶体介导的nephrin降解，PI31是一种Dynll1衔接蛋白，可能将UPS与动力蛋白货物偶联。
通过应用基因或化学干预措施抑制PI31或蛋白酶体的活性，在培养的R218Q KI小鼠足细胞中研究PI31在UPS介导的已知动力蛋白货物nephrin降解中的重要作用。在嘌呤霉素氨基核苷攻击的R218Q KI小鼠中测试硼替佐米在动力蛋白驱动的足细胞病变和FSGS中的保护作用，嘌呤霉素氨基核苷是FSGS的小鼠模型。
INF2中的R218Q突变破坏了INF2对Dynll1的隔离，使Dynll1被PI31捕获，并促进了动力蛋白介导的nephrin向蛋白酶体的运输。以下每种操作都足以恢复R218Q KI足细胞中的nephrin蛋白稳态：敲低PI31或Dynll1、使动力蛋白失活或抑制蛋白酶体的活性。在嘌呤霉素氨基核苷攻击的R218Q KI小鼠中，动力蛋白介导的nephrin错误运输和消耗与Dynll1-PI31相互作用增加相关；硼替佐米改善了由此导致的足细胞病变和FSGS。
在INF2-R218Q介导的足细胞病变中，Dynll1-PI31相互作用促进了动力蛋白驱动的nephrin向蛋白酶体的运输以及蛋白酶体介导的nephrin降解。该机制通过使用药理学上可用的蛋白酶体抑制剂为INF2相关的FSGS提供了新的治疗策略。
