The cell dynamics of the receptor on
tumor necrosis factor (TNF) were studied with the use of TNF-sensitive KYM cells derived from human
myosarcoma. With receptor synthesis inhibited by
cycloheximide, the half-life of the surface
TNF receptor was 2h in the absence of TNF and 30min in its presence, suggesting that the
TNF receptor was non-recycling and that its internalization was accelerated by TNF. During cell incubation with suppression of
TNF receptor degradation by
chloroquine, the number of surface
TNF receptors remained approximately constants, but the total number of surface and internal
TNF receptors increased gradually, at 3h reaching 1.5 times of the initial number, thus suggesting continuous synthesis, externalization, internalization, and degradation of the
TNF receptor in the absence of
cycloheximide. When the cells were incubated with 125I-TNF, the intracellular quantity of the pulse-labeled
TNF-receptor complex promptly increased, reaching a maximum at 20 min, and then declining gradually. Thus, it was confirmed that the
TNF receptor is internalized as a
TNF-receptor complex in the presence of TNF. In incubation with suppression of
protein synthesis by
cycloheximide following surface
TNF receptor digestion by
trypsin,
TNF receptors reappeared on the cell surface, increasing in the number to a peak level at 60 min and gradually decreasing. The 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 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.