ATP selectively suppresses the synthesis of the inflammatory protein microglial response factor (MRF)-1 through Ca2+ influx via P2X7 receptors in cultured microglia

Microglia are known to express purinergic receptors for extracellular ATP of both P2Y and P2X subtypes. In the CNS, ATP is released from neurons and acts as a signal between neurons and glia. The mrf-1 gene encodes a 17-kDa protein with a single calcium-binding (EF-hand) motif and is expressed specifically in microglia. The gene was isolated from activated microglia in response to apoptosis of cerebellar granule neurons in culture and is upregulated in response to neuronal death and degeneration in vivo. We have found that ATP suppresses the synthesis of the inflammation-related protein MRF-1 in cultured rat microglia. When microglia were treated with ATP (1 mM) for 6 h, mrf-1 mRNA levels decreased to approximately 50% compared to those in the control. This effect was dependent on both the treatment period and the dose of ATP. After ATP (1 mM) treatment for 16 h, levels of mrf-1 mRNA decreased to 37.3% and MRF-1 levels decreased to 55.0% compared to those in the control. A decrease in MRF-1 or its mRNA was also induced by benzoylbenzoyl-ATP (0.1 mM), a P2X(7) receptor-selective agonist, and by the Ca2+ ionophore A23187 (2 muM), dependent on extracellular Ca2+. Moreover, ATP modified neither the MRF-1 degradation rate nor total protein synthesis. These results indicate that ATP selectively suppresses MRF-1 synthesis at the transcription level via Ca2+ influx through P2X7 receptors. (C) 2002 Elsevier Science B.V. All rights reserved.