Characterization of specific binding of 3H-phorbol dibutyrate to Friend leukemia cells

The nature of phorbol ester receptors in intact Friend erythroid leukemia cells (FLC) was examined by utilizing 3H-phorbol dibutyrate (3H-PDBu). FLC were shown to possess one class of specific and saturable 3H-PDBu receptors with high affinity, that is, with a Kd of 14.1 +/- 4.2 nM and 1.1 X 10(5) +/- 0.22 binding sites/cell, as revealed by Scatchard analysis. The specific phorbol ester binding activity of FLC was shown to be phospholipid-dependent, since it was sensitive to treatment of the cells with phospholipase A2 or C and also was inhibited competitively by phospholipid-interacting agents such as antipsychotic or anticalmodulin drugs. The relative potency of the drugs for the inhibition of PDBu binding to FLC was parallel to that for the inhibition of protein kinase C.