期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1979
卷号：76
期号：11
页码：5689-5693
DOI：10.1073/pnas.76.11.5689
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Previous studies using a biologically active 1:1 conjugate of EGF and ferritin (F-EGF) have traced the binding and internalization of the hormone molecules. In the present report, we develop ultrastructural criteria for identification of the F-EGF{middle dot}receptor complex, and, thereby, enable utilization of the F-EGF as an indirect marker to localize the receptor for this peptide hormone. The ferritin cores of bound F-EGF are situated 4-6 nm from the extracellular surface of the membrane. When cells were incubated for up to 30 min at 37{degrees}C, this characteristic spatial relationship was observed in all uptake stages (surface clustering, endocytosis, and incorporation into multivesicular bodies), indicating that the hormone{middle dot}receptor complex remains intact through these steps. However, when incubation was continued for periods sufficient to allow hormone degradation (30-60 min), pools of free ferritin were observed in lysosomes. In the presence of various amine inhibitors of hormone degradation, internalization and multivesicular body incorporation proceeded, but hormone{middle dot}receptor degradation was blocked as evidenced by preservation of the ferritin--membrane relationship; i.e., no pools of free ferritin were seen after 60 min. These data provide morphological support for the hypothesis that down-regulation of surface receptors involves internalization of intact hormone{middle dot}receptor complexes. In addition, we have developed a method for viewing the surface of intact cells en face, allowing closer scrutiny of the clustering of F-EGF{middle dot}receptor complexes in the plane of the membrane prior to internalization. The particles in the F-EGF clusters observed by this method are spaced at 12 nm center-to-center, serving to set upper limits on the packing dimensions of the EGF{middle dot}receptor complex.
