Rosenfeld M E, Bowen-Pope D F, Ross R
J Cell Physiol. 1984 Nov;121(2):263-74. doi: 10.1002/jcp.1041210202.
Kinetic studies of binding and internalization of 125I-platelet-derived growth factor (PDGF) demonstrate that up to 15% of membrane-associated radioactivity is internalized within 2 minutes after warming to 37 degrees C in a variety of cell types. The T 1/2 for internalization is approximately 20 minutes. The T 1/2 for the subsequent appearance of degradation products in the culture medium is between 60-90 minutes following initiation of internalization. Internalization and lysosomal association of 125I-PDGF were confirmed by EM autoradiography. Quantitative studies using PDGF adsorbed to colloidal gold (gold-PDGF) demonstrate that 17% of the cell-associated sites are along coated regions of the plasma membrane (1.0 sites/micron), while 82% are associated with noncoated membrane (0.2 sites/micron). There is a significant redistribution of the gold-PDGF complexes upon warming. Within 1-2 minutes at 37 degrees C, gold particles are found within endocytic vesicles, endosomes (0.09-0.3 micron diameter), and lysosomes (greater than 0.2 micron diameter). At this time the vesicle/endosome compartment comprises 15% of the total sites and contains 0.9 sites per micron2 of surface area. The lysosomes account for 8% of the total sites and contain 0.8 sites per micron2 of surface area. Simultaneously, there is an increase in the number of gold-PDGF binding sites within coated-pits (1.6 sites/micron, 18% of the total sites) and a decrease along noncoated regions of the membrane (0.11 sites/micron, 58% of the total sites). After 15 minutes at 37 degrees C, 26% of the total sites (1.4 sites/micron2) are highly concentrated within lysosomes, while sites in the vesicle/endosome compartment remain constant. At the same time, binding sites within coated pits decrease substantially (0.5 sites/micron, 4% of the total sites), while the number of sites along noncoated regions of the membrane remain constant. Gold-PDGF was not observed associated with the Golgi complex at any time up to 120 minutes following warming. We conclude that gold-PDGF is processed via both receptor-mediated and nonspecific endocytosis and follows an intracellular pathway comparable to that followed by some other protein ligands.
对125I-血小板衍生生长因子（PDGF）结合与内化的动力学研究表明，在多种细胞类型中，升温至37℃后2分钟内，高达15%的膜相关放射性物质会被内化。内化的半衰期约为20分钟。内化开始后，培养基中降解产物随后出现的半衰期在60 - 90分钟之间。125I-PDGF的内化和溶酶体结合通过电子显微镜放射自显影得到证实。使用吸附在胶体金上的PDGF（金-PDGF）进行的定量研究表明，17%的细胞相关位点位于质膜的被膜区（1.0个位点/微米），而82%与非被膜膜相关（0.2个位点/微米）。升温后金-PDGF复合物会发生显著的重新分布。在37℃下1 - 2分钟内，在内吞小泡、内体（直径0.09 - 0.3微米）和溶酶体（直径大于0.2微米）中发现金颗粒。此时，小泡/内体区室占总位点的15%，每平方微米表面积含有0.9个位点。溶酶体占总位点的8%，每平方微米表面积含有0.8个位点。同时，被膜小窝内金-PDGF结合位点的数量增加（1.6个位点/微米，占总位点的18%），而膜的非被膜区的位点数量减少（0.11个位点/微米，占总位点的58%）。在37℃下15分钟后，26%的总位点（1.4个位点/平方微米）高度集中在溶酶体内，而小泡/内体区室中的位点保持不变。与此同时，被膜小窝内的结合位点大幅减少（0.5个位点/微米，占总位点的4%），而膜的非被膜区的位点数量保持不变。在升温后长达120分钟的任何时间都未观察到金-PDGF与高尔基体复合物相关。我们得出结论，金-PDGF通过受体介导的和非特异性的内吞作用进行处理，并且遵循与其他一些蛋白质配体类似的细胞内途径。
