THE EFFECT OF TNFA ON BRADYKININ RECEPTOR-BINDING, PHOSPHATI-DYLINOSITOL TURNOVER AND CELL-GROWTH IN HUMAN A431 EPIDERMOID CARCINOMA-CELLS

In this study, we examined the effect of TNFa on bradykinin (BK) B2 receptor binding and function in human A431 epidermoid carcinoma cells. [H-3]BK binds to a single class of receptors on A431 cells in a saturable and reversible manner. A binding affinity (K(D)) of 3.0 +/- 0.3 nM (n = 4) and a B(max) of 151 +/- 14 fmols/10(6) Cells, representing approximately 90,000 BK receptors per cell, was observed. The rank order of potency for BK agonist peptides indicates that the A431 BK receptor appears to be of the B2 subtype. When A431 cells were incubated with TNFa (10 ng/ml) for 48 h prior to BK binding, a significant decrease in the number of BK receptors compared to control was observed. TNFa did not influence the affinity of BK binding to A431 cells and direct addition of TNFa to the binding assay did not effect BK binding. BK-stimulated IP1 formation appeared to be increased in TNFa treated cells compared to control whereas histamine-stimulated IP1 formation was not influenced. Both control and TNFa treated cells were greater than 95% viable. However, TNFa treated cells were blocked in the G1 phase of the cell cycle resulting in a decrease in DNA synthesis, This may be one mechanism for the TNFa-induced decrease in BK receptors in A431 cells.