Kainate receptor-mediated activation of the AP-1 transcription factor complex in cultured rat cerebellar granule...

The sequence-specific DNA-binding activity of the AP-1 transcription factor complex was measured in cultured rat cerebellar granule cells by electrophoretic mobility shift assay. A low concentration of kainate (KA; 10 microM), but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA; 10 microM), enhanced DNA-binding of the AP-1 transcription factor in cultures pretreated with Concanavalin A (Con A), to prevent KA receptor desensitization. In the presence of cyclothiazide (an inhibitor of AMPA receptor desensitization), KA (10 microM) caused only a slight increase of AP-1 DNA-binding, in contrast to the threefold enhancement produced by AMPA (10 or 30 microM) or by a higher concentration of KA (30 microM), suggesting that the effect of KA, in the presence of Con A, is mediated by activation of putative KA receptors. To confirm this, the effects of the AMPA receptor-selective, non-competitive antagonist, 1-(4-aminophenyl)-3-methylcarbamoyl-4-methyl-3,4-dihydro-7, 8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 53655; 50 microM), the mixed AMPA/KA receptor competitive antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 50 microM), and the AMPA and GluR5 KA receptor competitive antagonist, (-)(3S,4aR,6R, 8aR)-6-[2-(1(2)H-tetrazole-5-yl)ethyl]-1,2,3,4,4a,5,6,7,8, 8a-decahydroisoquinoline-3-carboxylic acid monohydrate (LY 326325; 100 microM), were examined on AMPA- and KA-induced AP-1 activation, respectively. Our results suggest that stimulation of native KA receptors is responsible for the observed KA-specific activation of the AP-1 transcription factor complex.