The cell dynamics of the receptor for
tumor necrosis factor (TNF) were examined in TNF-sensitive KYM cells derived from human
myosarcoma. With receptor synthesis inhibited by
cycloheximide, the half-life of the surface
TNF receptor was 2 h in the absence of TNF and 30 min in its presence, suggesting that the
TNF receptor is non-recycling and that its internalization is accelerated by TNF. During cell incubation with
TNF receptor degradation suppressed by
chloroquine, the number of surface
TNF receptors remained approximately constant, but the total number of surface and internal
TNF receptors increased gradually, at 3 h reaching 1.5 times the initial number, thus suggesting continuous synthesis, externalization, internalization, and degradation of the
TNF receptor in the absence of
cycloheximide. On cell incubation with 125I-TNF, the intracellular quantity of the pulse-labeled
TNF-receptor complex promptly increased, reaching a maximum at 20 min, and then gradually declined, thus confirming that the
TNF receptor is internalized as a
TNF-receptor complex in the presence of TNF. During incubations with
protein synthesis suppressed by
cycloheximide following surface
TNF receptor digestion by
trypsin,
TNF receptors reappeared on the cell surface, increasing in number to a peak at 60 min and gradually decreasing, and cells previously exposed to
cycloheximide with or without TNF showed no recurrence of surface
TNF receptors, suggesting that the
TNF receptor is non-recycling. The results of the study thus suggest that the
TNF receptor is continuously internalized and degraded intracellularly by lysosomes without being recycled regardless of the presence or absence of TNF and, further, that its internalization is accelerated when it is part of the
TNF-receptor complex.