Differential regulation of P2Y₁₁ receptor-mediated signalling to phospholipase C and adenylyl cyclase by protein kinase C in HL-60 promyelocytes

1. The regulatory mode of the P2Y₁₁ purinoceptor-mediated signalling cascades towards phospholipase C and adenylyl cyclase was studied in HL-60 promyelocytes. 2. Treatment with the potent P2Y₁₁ receptor activator dATP evoked an elevated intracellular Ca²⁺ concentration ([Ca²⁺](i)) and inositol 1,4,5-trisphosphate (IP₃) production that was sustained for longer than 30 min. However, the dATP-induced responses were significantly inhibited by the activation of protein kinase C after a short exposure to phorbol 12-myristate 13-acetate (PMA). 3. dATP also potently stimulated cyclic AMP production with half maximum effect seen at 23±7 μM dATP. In addition, a 5-min pretreatment with PMA enhanced the dATP-stimulated cyclic AMP accumulation. 4. PMA potentiated the cyclic AMP production when adenylyl cyclase was activated directly by forskolin or indirectly by G protein activation after cholera toxin treatment. dATP also enhanced the forskolin-mediated cyclic AMP generation. 5. Treatment of the cells with 10 μM U-73122, which almost completely blocked the dATP-stimulated IP₃ production and [Ca²⁺](i) rise, had no effect on cyclic AMP accumulation, while 10 μM 9-(tetrahydro-2-furyl)adenine (SQ 22536), which inhibited the adenylyl cyclase activation, did not effect the dATP-stimulated phosphoinositide turnover. 6. Taken together, the results indicate that P2Y₁₁ receptor-mediated activation of phospholipase C and adenylyl cyclase occurs through independent pathways and is differentially regulated by protein kinase C in HL-60 cells.