P2X7/P2Z Purinoreceptor-mediated Activation of Transcription Factor NFAT in Microglial Cells

Abstract

ATP is released from neurons and other cell types during several physiological and stress conditions under which it exerts various biological effects upon binding to purinoreceptors. A rather peculiar purinoreceptor called P2X 7 /P2Z is expressed on microglial and other myeloic cells. Although increasing evidence implicates an important role for P2Z in inflammatory processes, little information exists about underlying signaling pathways. Here, we report that in N9 microglial cells, extracellular ATP potently activates nuclear factor of activated T cells (NFAT), a central transcription factor involved in cytokine gene expression. ATP activated NFAT rapidly (within 1 min), whereas activation of nuclear factor B was much delayed, with strikingly distinct kinetics. During ATP stimulation, both NFAT-1 and NFAT-2 were activated by a calcineurin-dependent pathway that required the influx of extracellular calcium ions. Based on the pharmacological profile, NFAT activation was specifically mediated by P2Z and not by other purinoreceptors. N9 cells that lacked P2Z but still expressed P2Y purinoreceptors failed to respond to NFAT activation. We conclude that P2Z-mediated NFAT activation may represent a novel mechanism by which extracellular ATP can modulate early inflammatory gene expression within the nervous and immune system.Large amounts of ATP and other nucleotides can be rapidly released from different cellular sources such as nerve terminals, antigen-stimulated T cells, activated platelets, endothelial cells, and other cell types under either physiological and pathological conditions such as hypoxia, stress, and tissue damage. Particularly in the immune and nervous system, extracellular ATP serves as a mediator of cell-to-cell communication by triggering a variety of biological responses including excitatory transmitter function, mitogenic stimulation, or induction of cell death (reviewed in Refs. 1-3). These effects are not the result of nonspecific membrane alterations but rather are mediated through the activation of specific surface molecules called P2 purinoreceptors (reviewed in Refs. 1, 4, and 5). At least two mechanistically distinct subclasses of P2 purinoreceptors are currently known. The metabotrophic P2Y receptors (formerly P2u, P2t, and P2y), which bind either UTP or ATP, initiate their biological effects through the G-proteincoupled activation of phospholipase C and subsequent Ca 2ϩ mobilization from intracellular stores. The P2X receptors are a distinct subfamily of receptors that are related to glutamate receptors and function as ligand-gated ion channels. Engagement of P2X receptors by ATP causes an increase in Ca 2ϩ permeability that is entirely dependent upon extracellular Ca 2ϩ ions. Recently, among the P2X subfamily, the molecular structure of the P2Z receptor, also called P2X 7 , has been elucidated (6, 7). The P2Z receptor contains two transmembrane domains and a large extracellular loop, structural features that are characteristic of members of the P2X family. Unlike other P2X receptors, the ...

Chemokine Production by G Protein-Coupled Receptor Activation in a Human Mast Cell Line: Roles of Extracellular Signal-Regulated Kinase and NFAT

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Expression, signaling, and function of P2X7 receptors in bone

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Overexpression of NTPDase2 in gliomas promotes systemic inflammation and pulmonary injury

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