Upregulation of interferon-gamma binding by tumor necrosis factor and lymphotoxin: disparate potencies of the cytokines and modulation of their effects by phorbol ester.
Tumor necrosis factor (TNF) and interferon-gamma (IFN-gamma) are immune-modulating cytokines that exert synergistic cytotoxic effects in several types of tumor cells, including ASPC-1 human pancreatic carcinoma cells. Lymphotoxin (LT), is a cytokine that binds to the TNF receptor and mimicks most of the biological actions of TNF. In the present study, we examined ASPC-1 cells for cytokine-mediated modulation of TNF and IFN-gamma receptors. Treatment of ASPC-1 cells with recombinant human IFN-gamma (rhIFN-gamma) did not significantly alter 125I-rhTNF binding. In contrast, treatment with rhTNF led to a dose- and time-dependent increase in 125I-rhIFN-gamma binding and internalization. Scatchard analysis revealed that rhTNF increased the number of 125I-rhIFN-gamma binding sites from 11,000 sites/cell to 23,000 sites/cell without altering receptor affinity. Although rhLT also increased 125I-rhIFN-gamma binding, it was 100-fold less potent than rhTNF. In contrast, rhLT was only 10-fold less potent than rhTNF in displacing 125I-rhTNF from its receptor. The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) blocked the rhLT- and rhTNF-mediated increase in 125I-rhIFN-gamma binding and markedly decreased 125I-rhTNF binding. These data suggest that both TNF and LT upregulate IFN-gamma receptors in ASPC-1 cells, but that LT is much less efficient than TNF. Further, the TPA-induced attenuation of IFN-gamma receptor upregulation suggests that protein kinase C activation can regulate the TNF/LT-mediated pathways involved in IFN-gamma receptor upregulation.
Raitano
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AB
Department of Microbiology and Immunology, University of Arizona, Tucson 85724.
Scuderi
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P
Korc
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M
D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008233:Lymphotoxin-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
D007457:Iodine Radioisotopes; D008233:Lymphotoxin-alpha; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D013755:Tetradecanoylphorbol Acetate