RED CELL CYTOSKELETON PROTEIN 4.1R IN KIDNEY FUNCTION

4.1R蛋白是一种红细胞细胞骨架蛋白，通过连接血影蛋白-肌动蛋白细胞骨架与特定的跨膜蛋白，在维持红细胞形状和变形能力方面发挥关键作用。随着4.1R在有核细胞的各种细胞器中的鉴定，以及最近发现的三个与4.1R有很高同源性的新基因，人们对研究蛋白4.1家族成员在非红系细胞中的作用产生了兴趣。在过去的几年里，细胞骨架不仅为质膜提供支持或在特定的领域分离膜蛋白，而且它还可以调节这些膜蛋白的功能，包括各种转运蛋白。在肾上皮细胞中，选择性溶质转运体的功能和紧密连接的选择性通透性取决于肌动蛋白细胞骨架的完整性。四个4.1基因中每一个的特异性探针的原位杂交表明，蛋白4.1家族的成员可能在选定的组织中采取特定的分布，包括大脑和肾脏。在肾脏，4.1R似乎主要积聚在肾单位的近端小管，这是肾脏重吸收和/或分泌水分和溶质的主要区域。我们的工作假设是，4.1R可能通过与肾单位上皮膜转运蛋白相互作用来调节近端小管的这种功能。为了研究这种可能性，我们建议1)鉴定4.1R及其同系物的肾脏异构体，并确定它们在肾脏中的分布模式；2)鉴定4.1R在肾脏中的结合伙伴，特别是膜转运蛋白；3)比较野生型和4.1R缺失型小鼠的肾功能，以破译4.1R可能调节选定转运体重吸收和/或分泌的机制，并调查4.1R基因敲除小鼠紧密连接的组织是否受到损害。我们预计，对蛋白4.1家族成员在肾单位上皮细胞中的功能的详细了解将有助于揭示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.