Retinoic acids increase P2X₂ receptor expression through the 5′-flanking region of P2rx2 gene in rat phaeochromocytoma PC-12 cells

The P2X₂ receptor is a subtype of ionotropic ATP receptor and plays a significant role in regulating fast synaptic transmission in the nervous system. Because the expression level of the P2X₂ receptor is known to determine its channel properties and functional interactions with other neurotransmitter channels, elucidating the mechanisms underlying the regulation of P2X₂ receptor expression in neuronal cells is important. Here, we identified three motifs that correspond to the retinoic acid response element in the 5′-flanking region of the rat P2X₂ gene. In rat pheochromocytoma PC-12 cells, treatment with 9-cisretinoic acid as well as all-trans-retinoic acid significantly increased the mRNA and protein level of P2X₂ receptor. In addition, in PC-12 cells transiently transfected with a luciferase reporter gene driven by the promoter region of the rat P2X₂ gene, both 9-cis-retinoic acid and all-trans-retinoic acid increased the luciferase activity, whereas their effects were diminished by truncation of the retinoic acid response elements in the promoter. Furthermore, 9-cis-retinoic acid enhanced the ATP-evoked whole cell currents and intracellular Ca²⁺- and ATP-evoked dopamine release, indicating the up-regulation of functional P2X₂ receptors on the plasma membrane. These results provide the molecular mechanism underlying the transcriptional regulation of P2X₂ receptors and suggest that retinoid is an important factor in regulating P2X₂ receptors in the nervous system.