EXTRACELLULAR ATP-INDUCED REGULATION OF EPIDERMAL GROWTH-FACTOR SIGNALING IN CULTURED RENAL LLC-PK1 CELLS

We investigated the effect of extracellular ATP on the interaction of epidermal growth factor (EGF) with its receptor in cultured renal epit helial cells, LLC-PK1. Pretreatment with ATP, but not adenosine, inhib ited the binding of I-125-labeled EGF. The inhibition demonstrated by ATP resulted from a decrease in the affinity of EGF receptors for its ligand, with no change in the number of EGF receptors. Incubation of p horbol 12-myristate 13-acetate (PMA) for 30 min mimicked the ATP-media ted inhibition. On the other hand, prolonged pretreatment with PMA, wh ich leads to disappearance of protein kinase C activity, reversed the inhibition. In addition, pretreatment with the protein kinase C inhibi tor 1-(5-isoquinoline sulfonyl)-2-methylpiperazine prevented the ATP-m ediated inhibition. ATP triggered an increase in inositol 1,4,5-trisph osphate levels and translocation of protein kinase C from cytosol to m embranes, consist with the stimulation of phospholipase C and the acti vation of protein kinase C. These results demonstrate that extracellul ar ATP attenuates the ligand binding affinity of EGF receptor via the stimulation of phospholipase C, leading to the activation of protein k inase C in the LLC-PK1 cells.