title: Internalization and degradation of human recombinant interferon-gamma in the human histiocytic lymphoma cell line, U937: relationship to Fc receptor enhancement and antiproliferation.
abstract: This report describes the association between the intracellular fate of human recombinant interferon-gamma (rIFN-gamma) and the induction of enhanced numbers of Fc receptors and an antiproliferative effect in the human monocyte-like cell line, U937. Full receptor occupancy of Bolton-Hunter labeled 125I-rIFN-gamma occurred within 10 min at 37 degrees C. However, only 50% of those molecules bound were internalized within 30 min. Residency of rIFN-gamma within the cell was 60-120 min. Eventually, 60-70% of those molecules initially bound to the cell were completely degraded within monensin-sensitive compartments of the cell as measured by the presence of trichloroacetic acid-soluble radioactivity in the medium. Exposure of rIFN-gamma to cell extracts resulted in a shift in its pI from 8 to 6, presumably due to proteolytic cleavage of carboxy-terminal basic amino acids. A single brief exposure (5-15 min) of U937 cells to rIFN-gamma resulted in enhanced numbers of receptors for the Fc portion of 125I-IgG1 as measured 24 hr later. Eighty percent of a maximal Fc receptor response occurred at only 30% receptor occupancy (50 U/ml). In contrast, repeated daily exposure of U937 cells to moderate concentrations of rIFN-gamma (125-250 U/ml) was necessary to induce an antiproliferative effect. These data suggest that a given response of the cell to rIFN-gamma may require different intensities of the signal. This may reflect the overall complexity of the response generated.
mesh_terms: D002460:Cell Line; D002738:Chloroquine / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D003571:Cytochalasin B / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000378:metabolism*; D008985:Monensin / Q000494:pharmacology; D009000:Monocytes / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
chemical_list: D011961:Receptors, Fc; D011994:Recombinant Proteins; D003571:Cytochalasin B; D007371:Interferon-gamma; D002738:Chloroquine; D008985:Monensin; D003078:Colchicine