P2Y₂ receptor-mediated proliferation of C₆ glioma cells via activation of Ras/Raf/MEK/MAPK pathway

1. Extracellular purine and pyrimidine nucleotides have been implicated in the regulation of several cellular functions including mitogenesis. In this study, experiments were conducted to characterize the P2Y receptor on C₆ glioma cells responsible for stimulating cell proliferation associated with mitogen-activated protein kinase (MAPK) activation. 2. UTP and ATP produced a similar effect on [³H]-thymidine incorporation in a time- and concentration-dependent manner, suggesting the involvement of P2Y₂ receptor in mediating proliferation of C₆ glioma cells. 3. In response to UTP, both p42 and p44 MAPK were activated in a time- and concentration dependent manner using Western blot analysis with an anti-phospho-p42/p44 MAPK antibody. The phosphorylation reached maximal levels after 5 min and declining by 30 min. 4. Pretreatment with pertussis toxin (PTX) did not change these responses to UTP. Both DNA synthesis and phosphorylation of MAPK in response to UTP were attenuated by tyrosine kinase inhibitors, genistein and herbimycin A, protein kinase C (PKC) inhibitors, staurosporine and GF109203X, and removal of Ca²⁺ by addition of BAPTA/AM plus EGTA. 5. UTP-induced [³H]-thymidine incorporation and p42/p44 MAPK phosphorylation was completely inhibited by PD98059 (an inhibitor of MEK1/2). Furthermore, we showed that overexpression of dominant negative mutants of Ras (RasN17) and Raf (Raf-301) completely suppressed MEK1/2 and p42/p44 MAPK activation induced by ATP and UTP. 6. These results conclude that the mitogenic effect of UTP is mediated through a P2Y, receptor that involves the activation of Ras/Raf/MEK/MAPK pathway. UTP-mediated MAPK activation was modulated by Ca²⁺, PKC, and tyrosine kinase associated with cell proliferation in cultured C₆ glioma cells.