Binding, internalization, and intracellular localization of interleukin-1 beta in human diploid fibroblasts.
This study demonstrates internalization of interleukin-1 (IL-1) via its cell surface receptor on human diploid fibroblasts and shows intracellular localization of IL-1 beta. Binding experiments at 8 degrees C using confluent fibroblast monolayers revealed 5,000-15,000 IL-1 receptors/cell that bound both IL-1 alpha and IL-1 beta. Incubation of monolayers with 125I-IL-1 beta (10(-9) M) at 8 degrees C and then at 37 degrees C for various times up to 8 h revealed a t1/2 for internalization of receptor-bound IL-1 beta of about 1.5 h. In addition, it was shown that IL-1 beta internalized via receptors was undegraded and retained binding activity. Electron microscopic autoradiography of monolayers incubated with 125I-IL-1 beta, as above, showed a progressive increase in the ratio of cytoplasmic to cell surface-associated grains. Grains at the cell surface were primarily localized at cell processes or attachment sites, frequently close to intra- and extracellular filamentous material. During incubation at 37 degrees C, most grains were free in the cytoplasm, with few present in lysosomes or vesicles. After 1 h, approximately 15% of the grains were over nuclei. Control cultures incubated at 37 degrees C with 125I-IL-1 beta and 100-fold excess unlabeled IL-1 beta showed increased uptake of label into lysosomes and little into nuclei. This study shows that IL-1 receptors are primarily located at fibroblast processes and that receptor-mediated internalization of the ligand is slow. Nuclear localization apparently requires IL-1 receptor-specific internalization of IL-1 beta, suggesting a possible role for this process in eliciting the IL-1 signal.
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Department of Pathology, University of Washington, Seattle 98195.
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D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism*; D005881:Gingiva / Q000166:cytology; D006801:Humans; D007375:Interleukin-1 / Q000493:pharmacokinetics*; D008854:Microscopy, Electron; D011971:Receptors, Immunologic / Q000378:metabolism; D017472:Receptors, Interleukin-1
D007375:Interleukin-1; D011971:Receptors, Immunologic; D017472:Receptors, Interleukin-1