Binding, internalization, and intracellular localization of interleukin-1 beta in human diploid fibroblasts

• Published in: The Journal of biological chemistry Vol. 263; no. 17; pp. 8261 - 8269
• Main Authors: Qwarnstrom, E E, Page, R C, Gillis, S, Dower, S K
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 15-06-1988; American Society for Biochemistry and Molecular Biology
• Subjects: Biological and medical sciences; Cell Membrane - metabolism; Cell physiology; Electrophoresis, Polyacrylamide Gel; Endocytosis; Fibroblasts - metabolism; Fundamental and applied biological sciences. Psychology; Gingiva - cytology; Humans; Interleukin-1 - pharmacokinetics; Microscopy, Electron; Molecular and cellular biology; Receptors, Immunologic - metabolism; Receptors, Interleukin-1; Human; Diploidy; Endocytosis; Membrane receptor; Internalization; Interleukin 1; Inflammation; Lymphokine; Intracellular; Localization; Fibroblast
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)68472-8

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.