Maywald Mee-Ling, Picciotto Cara, Lepa Carolin, Bertgen Luisa, Yousaf Farwah Sanam, Ricker Andrea, Klingauf Jürgen, Krahn Michael P, Pavenstädt Hermann, George Britta
Medizinische Klinik D, University Hospital Münster, Münster, Germany.
Institute of Medical Physics and Biophysics, Westfälische Wilhelms-University Münster, Münster, Germany.
Front Cell Dev Biol. 2022 Mar 18;10:790365. doi: 10.3389/fcell.2022.790365. eCollection 2022.
Glomerular podocytes build, with their intercellular junctions, part of the kidney filter. The podocyte cell adhesion protein, nephrin, is essential for developing and maintaining slit diaphragms as functional loss in humans results in heavy proteinuria. Nephrin expression and function are also altered in many adult-onset glomerulopathies. Nephrin signals from the slit diaphragm to the actin cytoskeleton and integrin β1 at focal adhesions by recruiting Crk family proteins, which can interact with the Rap guanine nucleotide exchange factor 1 C3G. As Rap1 activity affects focal adhesion formation, we hypothesize that nephrin signals Rap1 to integrin β. To address this issue, we combined and mammalian cell culture experiments. We find that Rap1 is necessary for correct targeting of integrin β to focal adhesions in nephrocytes, which also form slit diaphragm-like structures. In the fly, the Rap1 activity is important for signaling of the nephrin ortholog to integrin β, as well as for nephrin-dependent slit diaphragm integrity. We show by genetic interaction experiments that Rap1 functions downstream of nephrin signaling to integrin β and downstream of nephrin signaling necessary for slit diaphragm integrity. Similarly, in human podocyte culture, nephrin activation results in increased activation of Rap1. Thus, Rap1 is necessary for downstream signal transduction of nephrin to integrin β.
肾小球足细胞及其细胞间连接构成了肾脏滤过器的一部分。足细胞细胞黏附蛋白nephrin对于裂隙隔膜的发育和维持至关重要，因为人类中该蛋白功能丧失会导致大量蛋白尿。在许多成人发病的肾小球病中，nephrin的表达和功能也会发生改变。Nephrin通过募集Crk家族蛋白从裂隙隔膜向肌动蛋白细胞骨架和黏着斑处的整合素β1发出信号，Crk家族蛋白可与Rap鸟嘌呤核苷酸交换因子1 C3G相互作用。由于Rap1活性影响黏着斑的形成，我们推测nephrin将Rap1信号传递给整合素β。为解决这个问题，我们结合了果蝇和哺乳动物细胞培养实验。我们发现Rap1对于整合素β在果蝇肾细胞中正确靶向黏着斑是必需的，果蝇肾细胞也形成类似裂隙隔膜的结构。在果蝇中，Rap1活性对于nephrin直系同源物向整合素β的信号传导以及对于nephrin依赖的裂隙隔膜完整性都很重要。我们通过基因相互作用实验表明，Rap1在nephrin向整合素β的信号传导下游以及在裂隙隔膜完整性所需的nephrin信号传导下游发挥作用。同样，在人足细胞培养中，nephrin激活导致Rap1的激活增加。因此，Rap1对于nephrin向整合素β的下游信号转导是必需的。
