Expression of thromboxane A2 receptor in cultured human erythroleukemia cells and its induction by 12-O-tetradecanoylphorbol-13-acetate.

Using [125I]I-S-145-OH, a radiolabeled derivative of a thromboxane (TX) A2 receptor antagonist, we have studied the expression of the TXA2 receptor in several lines of cultured leukemia cells. Specific binding of the ligand was observed in cells of two human erythroleukemia cell lines, K562 and HEL. However, only negligible binding was seen in HL-60 human promyelocytic leukemia cells and L-1210 murine leukemia cells. Scatchard analyses revealed a curvilinear plot which indicated the existence of two classes of binding sites in these cells. The Kd and Bmax values of the high and low affinity bindings in HEL cells were 2.4 nM and 24 fmol/10(6) cells, and 58 nM and 360 fmol/10(6) cells, respectively. These values in K562 cells were 2.8 nM and 16 fmol/10(6) cells, and 18 nM and 46 fmol/10(6) cells, respectively. The addition of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) to the cultures of K562 and HEL cells caused a concentration- and time-dependent increase in the binding activity. TPA at 10(-8) M increased the Bmax values of both high and low affinity bindings approximately 3 times without significant change in their Kd values and these increases were inhibited by the addition of actinomycin D. Both classes of the binding in cells of each cell line were specifically displaced by several TXA2/prostaglandin (PG) H2 analogues, although the relative specificities to the analogues were different in the two classes. These results suggest that both HEL and K562 cells express the TXA2 receptor on their cell surface and TPA strongly induces this expression in these cells.