Cyclic AMP-mediated regulation of GABA(A) receptor subunit expression in mature rat cerebellar granule cells: Evidence for transcriptional and translational control

Exposure of rat cerebellar granule cells cultured to maturity in vitro to f orskolin, N-6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (Bt(2)cAMP ), and 3-isobutyl-1-methylxanthine (IBMX) down-regulated GABA(A) receptor a lpha 6 and beta 3 subunits but up-regulated alpha 1 and beta 2 subunits wit h respect to vehicle-treated controls. Dideoxyforskolin had no effect on su bunit expression. Protein kinase A inhibitors, H-89 and Rp-adenosine 3',5'- cyclic monophosphothioate, prevented these effects on alpha 1 but not alpha 6 subunit expression. Flunitrazepam-sensitive [H-3]Ro 15-4513 binding site s were increased by 144 +/- 20% following forskolin treatment. [H-3]Ro 15-4 513 photoaffinity labelling showed that the GABA(A) receptor alpha 1 subuni t was the principal locus of the increased flunitrazepam-sensitive [H-3]Ro 15-4513 binding. Forskolin decreased flunitrazepam-insensitive [H-3]Ro 15-4 513 binding sites by 25 +/- 8% and resulted in a 20% decrease in the irreve rsible incorporation of radioactivity in the alpha 6 subunit. Steady-state levels of GABA(A) receptor subunit mRNAs were determined by semiquantitativ e RT-PCR in forskolin-treated cultures. Forskolin, Bt(2)cAMP, and IBMX down -regulated GABA(A) receptor alpha 6 subunit mRNA expression; alpha 1 and be ta 3 mRNA levels were unaffected, whereas beta 2 subunit mRNA was up-regula ted. Dideoxyforskolin had no significant effect on alpha 1, alpha 6, beta 2 , and beta 3 mRNA levels. Thus, in mature cerebellar granule cells, GABA(A) receptor expression can be regulated by intracellular cyclic AMP levels. T his occurs at the level of gene transcription and/or translation by mechani sms that are only partially governed by protein kinase A.