MITOGENIC SIGNALING FROM P1 AND P2 PURINERGIC RECEPTORS TO MITOGEN-ACTIVATED PROTEIN-KINASE IN HUMAN FETAL ASTROCYTE CULTURES

To investigate potential trophic actions of extracellular ATP in human astrocytes, we have examined mitogenic signaling by purinergic recept ors in cultures prepared from first trimester rostral central nervous system tissue. We found that ATP and ATP gamma S, a hydrolysis-resista nt analog, stimulated DNA synthesis, thereby indicating that P2 purine rgic receptors can stimulate mitogenic signaling in these cells. In ad dition, ATP activated a mitogen-activated protein kinase (MAPK) termed ERK (extracellular signal-regulated protein kinase), a key component of signal transduction pathways involved in cellular proliferation and differentiation. The activation of MAPK was mediated at least in part by P2 purinergic receptors, because a P2 purinoceptor antagonist, sur amin, inhibited the ATP-evoked stimulation by 50%, whereas a P1 purine rgic-receptor antagonist, 8-(para-sulfonphenyl)-theophylline, was with out effect. In contrast to rat astrocytes, adenosine/P1 purinergic-rec eptor agonists, 2-chloroadenosine and 5'-N-ethylcarboxyamidoadenosine, stimulated MAPK activity and DNA synthesis in human astrocytes. A sel ective inhibitor of protein kinase C, Ro 31-8220, blocked the ability of ATP and adenosine analogs to stimulate MAPK, thereby indicating tha t protein kinase C is upstream of MAPK in both P2- and P1-receptor sig naling pathways. An inhibitor of the MAPK activator MEK, PD 098059, ef fectively blocked ATP-and 2-chloroadenosine-induced DNA synthesis, the reby indicating that the ERK/MAPK cascade mediates mitogenic signaling by P2 and P1 purinergic receptors in human fetal astrocytes. These fi ndings suggest a role for P1 and P2 purinergic receptors in the prolif eration of human fetal astrocytes. (C) 1998 Elsevier Science Ireland L td.