Modulation of interferon receptor expression during combination beta ser-interferon and gamma-interferon treatment of human colon carcinoma cells.

Combination treatment of SKCO1 human colon carcinoma cells with beta ser-interferon (IFN-beta ser) and gamma-interferon (IFN-gamma) results in a synergistic antiproliferative effect. The role of IFN-beta ser and IFN-gamma receptor modulation was investigated as a possible mechanism for this response. IFN-gamma (0.05-50 ng/ml) pretreatment of SKCO1 cells for 24 h decreased specific binding of 125I-IFN-beta ser by 35-60%. Scatchard analysis of binding data obtained following 24-h treatment with 5 ng/ml IFN-gamma showed that this reduction in binding was due to a decreased receptor affinity (control cells, Kd = 46 +/- 1.6 pM; IFN-gamma-treated cells, Kd = 106 +/- 6 pM, n = 2) rather than a significant change in receptor number (receptor number/control cell = 1214 +/- 471, receptor number/IFN-gamma treated cell = 1118 +/- 153, n = 2). In contrast, pretreatment of SKCO1 cells with IFN-beta ser (5 ng/ml) resulted in slight (10-35%) increases in 125I-IFN-gamma-specific binding. Scatchard analysis of binding data obtained following 24-h treatment with 5 ng/ml IFN-beta ser showed a decrease in binding affinity (control cells, Kd = 28 +/- 7 pM; IFN-beta ser-treated cells, Kd = 38 +/- 7 pM, n = 2) and a 32% increase in IFN-gamma receptor sites (receptor number/control cell = 4257 +/- 464, receptor number/IFN-beta ser-treated cell = 5570 +/- 730; n = 2). 125I-IFN-gamma internalization studies performed at 37 degrees C confirmed the cell surface binding assays; IFN-beta ser-treated cells internalized 30-50% more labeled IFN-gamma than untreated cells. However, it is unlikely that differences in binding and internalization of this magnitude play a primary role in the synergistic antiproliferative effect of IFN-gamma with IFN-beta ser in SKCO1 cells. Biochemical modulation at sites distal to the ligand receptor interaction should be investigated.