Internalization and Degradation of Human Recombinant Interferon-Gamma in the Human Histiocytic Lymphoma Cell Line, U937: Relationship to Fc Receptor Enhancement and Antiproliferation

摘要

This report describes the association between the intracellular fate of human recombinant interferon-y (rIFN-y) and the introduction of enhanced numbers of Fc receptors and an anti-proliferative effect in the human monocyte-like cell line, U937. Full receptor occupancy of Bolton-Hunter labeled iodine 125-rIFN-y occurred within 10 min at 37 C. However, only 50% of those molecules bound were internalized within 30 min. Residency of rIFN-y within the cell was 60-120 min. Eventually, 6-70% 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-y to cell extracts resulted in a shift in its pl from 8 to 6, presumable, due to proteolytic cleavage of carboxy-terminal basic amino acid. A single brief exposure (5-15 min) of U937 cells to rIFN-y resulted in enhanced numbers of receptors for the Fc portion of 125I-IgG 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-y (125-250 U/ml) was necessary to induce an antiproliferative effect. These data suggest that a given response of the cell to rIFN-y may require different intensities of the signal. This may reflect the overall complexity of the response generated.