WiDR colorectal carcinoma cells are highly sensitive to the synergistic cytotoxic effects of tumor necrosis factor (TNF) and γ-interferon (IFN-γ). In the present study, we have investigated the effects of recombinant human (rh) TNF and IFN-γ on the binding of both ligands in this cell line. WiDR cells exhibited high affinity binding sites for both 125I-rhIFN-γ (K(d) = 1.66 x 10-10 M, 920 sites/cell) and 125I-rhIFN-γ (K(d) = 4.15 x 10-10 M, 18,960 sites/cell). Preincubation of the cells with rhTNF (24 h) increased cell-associated 125I-rhIFN-γ radioactivity by 129% when binding was carried out at 37°C, as a result of an increase in both surface bound and internalized 125I-rhIFN-γ. However, rhTNF did not alter the degradation profile of released 125I-rhIFN-γ radioactivity. Scatchard analysis of 125I-rhIFN-γ binding data (4°C) revealed that rhTNF induced a 245% increase in 125I-rhIFN-γ binding sites. Conversely, rhIFN-γ caused a 68% increase in 125I-rhTNF binding sites and a 58% increase in receptor affinity. rhIFN-γ also increased the subsequent binding of 125I-rhIFN-γ, whereas rhTNF increased the subsequent binding of 125I-rhTNF. Furthermore, preincubation of the cells with both rhTNF and rhIFN-γ also resulted in an increase in the binding of both ligands. Actinomycin D and cycloheximide blocked all the effects of rhTNF and rhIFN-γ on ligand binding. However, the basal level of 125I-rhIFN-γ binding was insensitive to either inhibitor, whereas the basal level of 125I-rhTNF binding was decreased by both inhibitors. These data indicate that in some cell types TNF and IFN-γ may induce an increase in their own receptors (homologous up-regulation) and concomitantly increase each other's receptors (heterologous up-regulation) and that these actions are due, in part, to enhanced receptor synthesis.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1990|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology