Modulation of H₂ histamine receptor-mediated cAMP generation and granulocytic differentiation by extracellular nucleotides via activation of protein kinase C

Extracellular ATP exerts a variety of biological actions through several kinds of P2 receptor in HL-60 promyelocytes. We show that stimulation of P2Y₂ receptors with ATP and analogs resulted in the inhibition of a subsequently histamine-induced cAMP production and functional differentiation. Treatment of the cells with phorbol 12-myristate 13-acetate also blocked the histamine-mediated cAMP generation just as ATP did. Incubation of the cells with the protein kinase C inhibitor bisindolylmaleimide (GF109203X) abolished the inhibitory effects of extracellular nucleotides, suggesting that protein kinase C may act as an inter-regulator between two receptors. However, ATP did not affect the binding affinity or total binding of [³H]histamine to membrane receptors; it also did not heterologously desensitize H₂ receptors. The ATP treatment synergistically elevated the cAMP levels induced directly by forskolin or indirectly by G protein activation after cholera toxin treatment. This indicates that the site of the protein kinase C action is not the G protein or effector enzyme. Co-stimulation of the cells with nucleotides and histamine inhibited histamine-mediated granulocytic differentiation, which was evaluated by looking at the extent of N-formyl-methionyl-leucyl-phenylalanine responses. Taken together, the results demonstrate that extracellular nucleotides are negatively involved in the modulation of hitamine signaling via activation of protein kinase C, probably by inhibiting coupling between receptor and G protein.