RED CELL CYTOSKELETON PROTEIN 4.1R IN KIDNEY FUNCTION

蛋白4.1R是红细胞骨架蛋白，其通过将血影蛋白-肌动蛋白细胞骨架桥接至特异性跨膜蛋白而在维持红细胞形状和变形性中起关键作用。 沿着在有核细胞的各种细胞器中4.1 R的鉴定以及最近与4.1 R共享非常高的同源性的三个新基因的表征，增加了研究蛋白4.1家族成员在非红细胞中的作用的兴趣。 在过去的几年中，已经清楚的是，细胞骨架不仅为质膜提供支持或将膜蛋白分离在专门的结构域中，而且它还可以调节这些膜蛋白包括各种转运蛋白的功能。 在肾上皮细胞中，选择性溶质转运蛋白的功能和紧密连接的选择性通透性依赖于肌动蛋白细胞骨架的完整性。 四个4.1基因的探针的原位杂交表明，蛋白质4.1家族的成员可能采取特定的分布在选定的组织，包括脑和肾。在肾脏中，4.1R似乎主要积聚在肾单位的近端小管中，这是发生大部分肾重吸收和/或水和溶质分泌的区域。 我们的工作假设是，4.1R可能通过与肾单位上皮的膜转运蛋白相互作用来调节近端小管的这些功能。 为了研究这种可能性，我们建议1）鉴定4.1R及其同源物的肾脏亚型并表征其在肾脏内的分布模式，2）鉴定肾脏中4.1R的结合伴侣，3）比较野生型和4.1R缺失小鼠的肾功能，以解释4.1R可能调节重吸收和/或重吸收的机制。或分泌，并研究在4.1R基因敲除小鼠中紧密连接的组织是否受损。 我们预计，详细了解肾单位上皮中蛋白质4.1家族成员的功能，将有助于了解与细胞骨架蛋白缺陷相关的肾脏病理。

Protein 4.1R is a red cell cytoskeletal protein which plays a key role in maintaining erythrocyte shape and deformability by bridging the spectrin-actin cytoskeleton to specific transmembrane proteins. The identification of 4.1R in various organelles of nucleated cells along with the recent characterization of three novel genes sharing very high homology with 4.1R have escalated the interest in studying the role of members of the protein 4.1 family in non erythroid cells. Over the past years, it has become clear that the cytoskeleton does not only provide support for the plasma membrane or segregate membrane proteins in specialized domains, but that it can also regulate the functions of such membrane proteins including various transporters. In kidney epithelia, functions of selected solute transporters and selective permeability of tight junctions depend on the integrity of the actin cytoskeleton. In situ hybridization of probes specific for each of the four 4.1 genes suggest that members of the protein 4.1 family may adopt specific distribution within selected tissues including brain and kidney. In the kidney, 4.1R seems to accumulate predominantly in the proximal tubule of the nephron, a region where most of renal reabsorption and/or secretion of water and solutes occur. Our working hypothesis is that 4.1R may regulate such functions of the proximal tubule by interacting with membrane transporters of the nephron epithelium. To investigate this possibility, we propose to 1) identify the renal isoforms of 4.1R and its homologs and characterize their distribution pattern within the kidney, 2) identify binding partners for 4.1R in the kidney, focusing in particular on membrane transporters and 3) compare renal function in wild type and 4.1R null mice in order to decipher the mechanisms by which 4.1R may regulate reabsorption and/or secretion by selected transporters and investigate whether the organization of tight junctions is compromised in 4.1R knock out mice. We anticipate that a detailed understanding of the functions of members of the protein 4.1 family in the epithelium of the nephron will shed light on kidney pathologies related to defects in cytoskeletal proteins.