P2Y(AC)(-) -receptor agonists enhance the proliferation of rat C6 glioma cells through activation of the p42/44 mitogen-activated protein kinase

1 Extracellularly added P-1,P-3-di(adenosine-5') triphosphate (Ap(3)A), P-1 ,P-4-di(adenosine-5') tetraphosphate (AP(4)A), ATP, ADP, AMP and adenosine are growth inhibitory for rat C6 glioma cells. Analysis of nucleotide hydro lysis and the use of nucleotidase inhibitors demonstrated that the latter i nhibition is due to hydrolysis of the nucleotides to adenosine. 2 Agonists of the P2Y(AC)(-)-receptor enhance the growth of C6 cells if the ir hydrolysis to adenosine is inhibited by pyridoxalphosphate-6-azophenyl-2 ',4'-disulfonic acid (PPADS). In these conditions, the potency to stimulate cell growth parallels the ranking of the receptor agonists, i.e. 2-methylt hioadenosine-5'-diphosphate (2MeSADP) > AP(3)A>AP(4)A. ATP and ADP are stil l hydrolysed in the presence of PPADS and have no proliferative effect on C 6 cells. 3 The enhanced growth is due to a P2Y(AC)(-)-receptor-mediated activation o f p42/44 mitogen-activated protein kinase (MAPK) as shown by immunoblotting and protein kinase assays for active MAPK and the use of the MAPK/extracel lular signal-regulated kinase kinase (MEK) inhibitor PD98059. 4 The UTP-induced enhancement of the growth of C6 cells is due to activatio n of MAPK by a PPADS sensitive nucleotide receptor. 5 In conclusion, the effect of nucleotides on the growth of C6 cells is det ermined by ecto-nucleotidases and by activation of nucleotide receptors. Hy drolysis of nucleotides to adenosine induces growth inhibition while inhibi tion of the hydrolysis of agonists of the P2Y(AC)(-)-receptor enhances cell growth by activation of MAPK.