The expression of the glutamate transporter EAAC1 is stimulated by all‐trans retinoic acid in C6 rat glioma cells

Abstract

Several mechanisms modulate the activity of EAAC1, the counterpart of the human EAAT3 carrier encoded by the gene Slc1a1, through changes in transporter trafficking and interaction with regulatory proteins. Much less is known on EAAC1 regulation at the gene level. We investigate here the effects of all‐trans retinoic acid (ATRA) on EAAC1 activity and expression in C6 rat glioma cells. ATRA induced a four‐fold increase of aspartate transport in a dose‐ and time‐dependent manner (EC50 = 120 nM). Kinetic analysis indicated that the stimulation was due to Vmax increase and functional studies pointed to EAAC1 as the target of ATRA. In agreement with these data, Slc1a1 mRNA and EAAC1 protein were much higher in ATRA‐treated cells than in control counterparts, while no expression of GLAST and GLT‐1 transporters was detected under both conditions. ATRA effects on EAAC1 activity were inhibited by the specific RAR inhibitor LE540 and mimicked by AM80, a RAR agonist, but not by the RXR agonists HX630 and PA024. In addition, Slc1a1 mRNA induction was suppressed by cycloheximide, suggesting that a protein intermediate is needed for ATRA effect. In parallel with EAAC1 induction, ATRA treatment caused a huge increase in the expression of the oligodendrocytic marker PLP (proteolipid protein). These results indicate that the expression of Slc1a1 is induced by ATRA through a RAR‐dependent mechanism.