Kinetics of internalization and recycling of transferrin and the transferrin receptor in a human hepatoma cell line. Effect of lysosomotropic agents.
Kinetics of internalization and recycling of transferrin and the transferrin receptor in a human hepatoma cell line. Effect of lysosomotropic agents.
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DOI：
10.1016/s0021-9258(17)44551-0
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发表时间：
1983-08
期刊：
影响因子：
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通讯作者：
A. Ciechanover;A. Schwartz;A. Dautry‐Varsat;H. Lodish
中科院分区：
文献类型：
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作者：
A. Ciechanover;A. Schwartz;A. Dautry‐Varsat;H. Lodish
生长的HepG 2细胞含有50，000个功能性表面转铁蛋白结合位点（Ciechanover，A.，Schwartz，A.L.，和Lodish，H.F.（1983）Cell 32，267 -275）和100，000个细胞内位点。在饱和浓度的[59 Fe]转铁蛋白，并在蛋白质合成被阻断的条件下，铁的吸收是线性的几个小时的速率为9,500转铁蛋白分子/细胞/分钟。因此，每个受体必须回收配体，平均每15.8分钟。表面结合的转铁蛋白被迅速内吞（t1/2 = 3.5分钟）。所有的铁保留在细胞内，而脱铁转铁蛋白迅速（t1/2 = 5.0分钟）分泌到培养基中。之前，我们展示了（Dautry-Varsat，A.，Ciechanover，A.，和Lodish，H.F.等人（1983）Proc. Acad. Sci. U.S.A.80，2258-2262），铁转铁蛋白-受体复合物暴露于pH小于5.0的介质导致铁解离，但脱铁转铁蛋白保持与其受体结合。如果pH升高到7.0，例如当酸性胞内囊泡与质膜融合时会发生，脱铁转铁蛋白非常迅速地从其受体解离（t1/2 = 17 s，37 ℃）。总之，这些结果表明，转铁蛋白保持结合到其受体在整个内吞循环。在本研究中，我们直接测量了转铁蛋白受体循环中涉及的所有动力学参数。它们与同一细胞系中的去唾液酸糖蛋白受体相似，可以用一个简单的动力学模型描述。在促溶酶体剂的存在下，铁转铁蛋白与其表面受体结合并被正常内化。然而，铁不从转铁蛋白解离，并且铁转铁蛋白粘附回到细胞表面并分泌到培养基中。我们的结论是，低pH值的内吞囊泡是必不可少的铁从转铁蛋白和其交付到细胞的解离，但不需要回收的转铁蛋白，大概是其受体。
Growing HepG2 cells contain 50,000 functional surface transferrin-binding sites (Ciechanover, A., Schwartz, A.L., and Lodish, H.F. (1983) Cell 32,267-275) and 100,000 intracellular sites. At saturating concentrations of [59Fe]transferrin, and under conditions in which protein synthesis is blocked, iron uptake is linear for several hours at a rate of 9,500 transferrin molecules/cell/min. Thus, each receptor must recycle a ligand, on the average, each 15.8 min. Surface-bound transferrin is rapidly endocytosed (t1/2 = 3.5 min). All of the iron remains within the cell, while the apotransferrin is rapidly (t1/2 = 5.0 min) secreted into the medium. Previously, we showed (Dautry-Varsat, A., Ciechanover, A., and Lodish, H.F. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 2258-2262) that exposure of a ferrotransferrin-receptor complex to medium of pH less than 5.0 results in dissociation of iron, but that apotransferrin remains bound to its receptor. If the pH is raised to 7.0, such as would occur when an acidic intracellular vesicle fuses with the plasma membrane, apotransferrin is very rapidly dissociated (t1/2 = 17 s at 37 degrees C) from its receptor. Taken together, these results indicate that transferrin remains bound to its receptor throughout the endocytic cycle. In the present study, we have directly measured all the kinetic parameters involved in the transferrin receptor cycle. They are similar to those of the asialoglycoprotein receptor in the same cell line, and can be described by a simple kinetic model. In the presence of lysosomotropic agents, ferrotransferrin binds to its surface receptor and is internalized normally. However, iron is not dissociated from transferrin, and ferrotransferrin recycles back to the cell surface and is secreted into the medium. We conclude that the low pH in endocytic vesicles is essential for the dissociation of iron from transferrin and its delivery to the cell, but is not required for recycling of transferrin, and presumably of its receptor.