Anales RANF

S2-04 CROSS-TALK BETWEEN P2 RECEPTORS AND TYROSINE KINASE RECEPTORS IN CEREBELLAR ASTROCYTES E.G: Delicado, J.C. Gil-Redondo, M.J. Queipo, L. Paniagua-Herranz, R. Pérez-Sen, M.T. Miras-Portugal Complutense University of Madrid, Madrid, Spain Cerebellar astrocytes have resulted to be a good model to study the multiple signaling pathways activated by nucleotide receptors, and their cross-talk with other extracellular relevant signals at the nervous system. At the beginning, studies focused on the identification of intracellular targets responsible for the activation of signaling pathways, such as MAP kinase cascades. We found that ERK activation was underlying the modulatory EGF receptor (EGFR) actions on P2Y signaling in these glial cells. EGFR plays a dual role in cerebellar astrocytes, depending on the cellular context and the mediators accumulating at the extracellular environment. EGFR potentiates ATP calcium responses allowing ineffective ATP concentrations per se to evoke calcium responses. The potentiation is maintained for long periods (up to 6 hours), assuring P2Y signaling at very low nucleotide concentrations. However, when nucleotides and PGE 2 accumulate at the extracellular space, EGFR contribute to the impairment of P2Y responses by the prostaglandin. Lately, we have centered on the characterization of the intracellular mechanisms responsible for dephosphorylating ERK proteins. Dual Specificity Phosphatases (DUSPs), which dephosphorylate both serine/threonine and tyrosine residues in the same substrate, are good candidates. In fact, DUSP6 appears to be one of the protein phosphatases inactivating ERK signaling at the cytosolic compartment. We have demonstrated that the metabotropic ATP nucleotide receptors, P2Y 2 and P2Y 4 , the ionotropic P2X7 receptors, and EGFR regulate the levels of the protein phosphatase with a biphasic pattern and in an ERK- dependent manner in rat cerebellar astrocytes. While short time stimulations of astrocytes with the agonists, UTP, BzATP or EGF, decrease the levels of protein phosphatase by proteosomal degradation, prolonged stimulations restore the basal levels of DUSP6 protein. We are currently investigating whether EGFR transactivation is involved in the modulation of DUSP6 levels elicited by nucleotide receptors.