title: Induction of receptors for tumor necrosis factor-alpha by interferons is not a major mechanism for their synergistic cytotoxic response.
abstract: We have investigated the effects of various interferons on the receptors for recombinant tumor necrosis factor-alpha (rTNF-alpha) and also their effects on rTNF-alpha-mediated cytotoxicity on human cervical carcinoma cell line ME-180. Preincubation of cells with interferon (IFN)-gamma causes a concentration- and time-dependent increase in rTNF-alpha receptor number without any change in the affinity constant of the receptors. The increase in receptor number is caused only by IFN-gamma and not by IFN-alpha or IFN-beta. Approximately 4-6 h of preincubation with IFN-gamma are required for maximum increase in rTNF-alpha binding to the cells, and this increase can be abolished by inhibitors of protein synthesis, suggesting de novo synthesis of rTNF-alpha receptors. The half-life of both uninduced and induced receptors of rTNF-alpha is approximately 2 h, indicating a rapid turnover. The binding of rTNF-alpha to the cells can also be eliminated by pretreatment of cells with trypsin. Following the removal of trypsin, binding of rTNF-alpha gradually increases, and this requires the synthesis of new proteins. The cytotoxic effect of rTNF-alpha on ME-180 cells is potentiated severalfold by the addition of either IFN-alpha, -beta, or -gamma. However, at similar concentrations, relatively higher potentiation of rTNF-alpha cytotoxicity is observed with IFN-gamma as compared to IFN-alpha and IFN-beta. The pre-exposure of cells to IFNs is as effective as co-exposure in enhancing cytotoxic effects of TNF-alpha. The induction of TNF-alpha receptors by IFNs is observed in different cell types regardless of their sensitivity to TNF-alpha, suggesting that increase in receptor number alone is not sufficient for the enhanced cytotoxic response. Because the enhancement of cytotoxic effects of TNF-alpha is observed by all IFNs but receptor induction in ME-180 cells occurs only with INF-gamma and because metabolic inhibitors which down-regulate TNF-alpha receptors also enhance cytotoxic response, we suggest that the induction of TNF-alpha receptor by IFNs is not a major mechanism of synergism between these cytokines.
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D003208:Concanavalin A / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D007372:Interferons / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000096:biosynthesis*; D018124:Receptors, Tumor Necrosis Factor; D011994:Recombinant Proteins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha; D002583:Uterine Cervical Neoplasms / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D011956:Receptors, Cell Surface; D018124:Receptors, Tumor Necrosis Factor; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D003208:Concanavalin A; D003609:Dactinomycin; D007371:Interferon-gamma; D007372:Interferons; D003513:Cycloheximide