Receptor-associated protein is important for normal processing of megalin in kidney proximal tubules
Receptor-associated protein is important for normal processing of megalin in kidney proximal tubules
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DOI：
10.1681/asn.v112191
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发表时间：
2000-02-01
影响因子：
13.6
通讯作者：
Christensen, EI
中科院分区：
文献类型：
--
作者：
Birn, H;Vorum, H;Christensen, EI
受体相关蛋白（RAP）已被鉴定为调节LDL受体相关蛋白表达和加工的分子伴侣。RAP还结合到相关的600-kD多配体内吞受体megalin表达在许多吸收上皮细胞，包括肾近曲小管。本研究检测RAP基因破坏对巨蛋白表达和近端小管亚细胞分布的影响以及对肾小管蛋白重吸收的影响。研究表明，RAP对megalin的正常表达和功能具有重要意义。通过免疫印迹估计，巨蛋白表达降低至约23%，并通过免疫细胞化学和RAP亲和层析回收的巨蛋白量得到支持。光和电子显微镜免疫细胞化学以及分离的膜组分的分析表明，巨蛋白的亚细胞分布的显着变化。在正常刷状缘标记的显着减少，观察与增加标记的粗糙内质网和沿着基底外侧膜的平滑膜旁内质网。RAP缺乏与尿蛋白组成的变化有关，这使得α-淀粉酶能够被鉴定为巨蛋白的新配体。此外，维生素D结合蛋白（最近鉴定的巨蛋白配体）的排泄增加，观察到支持肾小管蛋白重吸收的变化。目前的数据表明，RAP是至关重要的正常加工和功能的巨蛋白，这表明这种蛋白质在肾脏近端小管的伴侣样功能。
The receptor-associated protein (RAP) has been identified as a chaperone regulating the expression and processing of the LDL receptor-related protein. RAP also binds to the related 600-kD multiligand endocytic receptor megalin expressed in many absorptive epithelia including renal proximal tubule. The present study examines the effect of RAP gene disruption on megalin expression and subcellular distribution in the proximal tubule as well as the effect on tubular protein reabsorption. It is shown that RAP is important for the normal expression and function of megalin. Megalin expression was reduced to approximately 23% estimated by immunoblotting and supported by immunocytochemistry and by the amount of megalin recovered by RAP affinity chromatography. Light- and electron microscope immunocytochemistry as well as analyses on separated membrane fractions showed significant changes in the subcellular distribution of megalin. A significant reduction in the normal brush border labeling was observed in association with increased labeling of rough endoplasmic reticulum and the smooth paramembranous endoplasmic reticulum along the basolateral membranes. RAP deficiency was associated with changes in urinary protein composition, enabling the identification of alpha-amylase as a new ligand for megalin. In addition, an increased excretion of vitamin D-binding protein, a recently identified ligand to megalin, was observed supporting changes in tubular protein reabsorption. The present data show that RAP is of crucial importance for normal processing and function of megalin, suggesting a chaperone-like function of this protein in the kidney proximal tubule.