title: Human interferon-gamma is internalized and degraded by cultured fibroblasts.
abstract: Human interferon-gamma (IFN-gamma) binds specifically and with high affinity to receptors on the surface of cultured fibroblasts (GM-258). At 37 degrees C about 50% of the receptor-bound IFN-gamma was rapidly internalized (t 1/2 = 4-5 min) by these cells. Following an initial lag of 15-30 min, internalized IFN-gamma was continuously degraded over a period of at least 8 h. The total uptake of IFN-gamma over this time period was found to exceed by 5 times the number of occupied IFN receptors present on the surface of these cells, suggesting that either there is a large intracellular pool of IFN-gamma receptors, or that receptors are recycled during the course of incubation. Cycloheximide (100 micrograms/ml) inhibited uptake only after the first 2 h of incubation and then only moderately. It is therefore unlikely that de novo receptor synthesis plays a major role in the observed uptake process. Both sodium azide (15 mM) and methylamine (20 mM) inhibited both the uptake and degradation of IFN-gamma at all times up to 6 h. While uptake was only slightly reduced in the presence of chloroquine (25 microM), degradation was markedly inhibited, suggesting that degradation occurs intracellularly, probably within lysosomes.
mesh_terms: D001386:Azides / Q000494:pharmacology; D001667:Binding, Competitive; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007158:Immunologic Techniques; D007371:Interferon-gamma / Q000378:metabolism*; D007700:Kinetics; D008744:Methylamines / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017471:Receptors, Interferon; D019810:Sodium Azide; D013696:Temperature
chemical_list: D001386:Azides; D008744:Methylamines; D011956:Receptors, Cell Surface; D017471:Receptors, Interferon; D007371:Interferon-gamma; D019810:Sodium Azide; D003513:Cycloheximide; C027451:methylamine