ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Kinetic studies of binding and internalization of 125 I-platelet-derived growth factor (PDGF) demonstrate that up to 15% of membrane-associated radioactivity is internalized within 2 minutes after warming to 37°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/μm), while 82% are associated with noncoated membrane (0.2 sites/μm). There is a significant redistribution of the gold-PDGF complexes upon warming. Within 1-2 minutes at 37°C, gold particles are found within endocytic vesicles, endosomes (0.09-0.3 μm diameter), and lysosomes (〉 0.2 μm diameter). At this time the vesicle/endosome compartment comprises 15% of the total sites and contains 0.9 sites per μm2 of surface area. The lysosomes account for 8% of the total sites and contain 0.8 sites per μm2 of surface area. Simultaneously, there is an increase in the number of gold-PDGF binding sites within coated-pits (1.6 sites/μm, 18% of the total sites) and a decrease along noncoated regions of the membrane (0.11 sites/μm, 58% of the total sites). After 15 minutes at 37°C, 26% of the total sites (1.4 sites/μm2) 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/μm, 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.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041210202
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