Interaction between ATP and nerve growth factor signalling in the survival and neuritic outgrowth from PC12 cells

In a previous study we used P2 receptor antagonists to inhibit diverse responses that nerve growth factor (NGF) promotes and coordinates in PC12 cells and we suggested that P2 receptors partake in the NGF signalling cascade. In this paper, we examine the direct role of extracellular P2 receptor agonists as neurotrophic factors. ATP and 2-Cl-ATP promote neurite regeneration after priming PC12 cells with NGF and the effect is dose-dependent, with an EC(50) of about 5 and 3 microM, respectively. The number of cell clumps bearing neurites was maximally induced in day 1 and it was maintained up to about one week by ATP, or up to at least 2 weeks by 2-Cl-ATP. The involvement of P1 receptors or intracellular inosine in these actions was excluded, whereas various antagonists of P2 receptors were inhibitory. Moreover, NGF and ATP caused a direct up-regulation of P2X(2), P2X(3), P2X(4) and P2Y(2), but not P2Y(4) receptor proteins under neurite-regenerating conditions, as well as extracellular signal-regulated kinase (Erk)1-2 tyrosine/threonine phosphorylation and activation. Finally, ATP, 2-Cl-ATP and ATPgammaS enhanced neurite initiation evoked by sub-optimal NGF concentrations and ATP and 2-Cl-ATP fully sustained survival of PC12 cells after serum deprivation. Our results establish that P2 receptor agonists can behave as neurotrophic factors for neuronal cells and suggest a potential interplay between ATP and NGF in the signalling pathways triggered on their target cells.