Receptor-mediated endocytosis of albumin by kidney proximal tubule cells is regulated by phosphatidylinositide 3-kinase
Receptor-mediated endocytosis of albumin by kidney proximal tubule cells is regulated by phosphatidylinositide 3-kinase
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DOI：
10.1172/jci1923
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发表时间：
1998-05-15
影响因子：
15.9
通讯作者：
Nahorski, S
中科院分区：
文献类型：
--
作者：
Brunskill, NJ;Stuart, S;Nahorski, S
受体介导的白蛋白内吞作用是肾近端小管上皮细胞的重要功能。我们测量了负鼠肾脏细胞[I-125]-白蛋白的内吞作用，并检测了磷脂酰肌醇3-激酶(PI-3-K)对这一过程的调节。Wortmannin(IC50 6.9 nM)和LY294002(IC50 6.5 mU M)均能抑制白蛋白内吞作用，提示PI-3-K参与了白蛋白内吞的调节。回收利用率没有受到影响。用LacSwitch表达系统将野生型P85亚基和显性阴性P85亚基(DeltaP85)导入OK细胞，用抗PI3K抗体进行免疫印迹筛选，在基础条件下不表达P85或DeltaP85，但经IPTG处理后表达明显增强(EC50为13.7mM)。经胰岛素刺激的转基因细胞的抗磷酸化酪氨酸免疫沉淀物的体外激酶实验证实Delta P85对PI 3-K的活性有抑制作用。DeltaP85的表达显著抑制白蛋白内吞作用，这主要是由于转运过程的V-max降低所致。P85的表达对白蛋白摄取无明显影响。结果表明，PI3K在受体介导的肾小管上皮细胞白蛋白内吞过程中起早期调节作用。
Receptor-mediated endocytosis of albumin is an important function of the kidney proximal tubule epithelium. We have measured endocytosis of [I-125]-albumin in opossum kidney cells and examined the regulation of this process by phosphatidylinositide 3-kinase (PI 3-kinase). Albumin endocytosis was inhibited by both wortmannin (IC50 6.9 nM) and LY294002 (IC50 6.5 mu M) at concentrations that suggested the involvement of PI 3-kinase in its regulation. Recycling rates were unaffected. We transfected OK cells with either a wild-type p85 subunit of PI 3-kinase, or a dominant negative form of the p85 subunit (Delta p85) using the LacSwitch expression system, Transfects were screened by immunoblotting with anti-PI 3-kinase antibodies, Under basal conditions, transfects demonstrated no expression of p85 or Delta p85, but expression was briskly induced by treatment of the cells with IPTG (EC50 13.7 mu M). Inhibition of PI 3-kinase activity by Delta p85 was confirmed by in vitro kinase assay of anti-phosphotyrosine immunoprecipitates from transfected cells stimulated with insulin. Expression of Delta p85 resulted in marked inhibition of albumin endocytosis, predominantly as a result of reduction of the V-max of the transport process. Expression of p85 had no significant effect on albumin uptake. The results demonstrate that PI 3-kinase regulates an early step in the receptor-mediated endocytosis of albumin by kidney proximal tubular cells.