The metabotropic GABA(B) receptor directly interacts with the activating transcription factor 4

G protein-coupled receptors regulate gene expression by cellular signaling cascades that target transcription factors and their recognition by specifi c DNA sequences, In the central nervous system, heteromeric metabotropic ga mma -aminobutyric acid type B (GABA(B)) receptors through adenylyl cyclase regulate cAMP levels, which may control transcription factor binding to the cAMP response element. Using yeast-two hybrid screens of rat brain librari es, we now demonstrate that GABA(B) receptors are engaged in a direct and s pecific interaction with the activating transcription factor 4 (ATF-4), a m ember of the cAMP response element-binding protein/ATF family. As confirmed by pull-down assays, ATF-4 associates via its conserved basic leucine zipp er domain with the C termini of both GABA(B) receptor (GABA(B)R) 1 and GABA (B)R2 at a site which serves to assemble these receptor subunits in heterod imeric complexes. Confocal fluorescence microscopy shows that GABA(B)R and ATF-4 are strongly coclustered in the soma and at the dendritic membrane su rface of both cultured hippocampal neurons as well as retinal amacrine cell s in vivo. In oocyte coexpression assays short term signaling of GABA(B)Rs via G proteins was only marginally affected by the presence of the transcri ption factor, but ATF-4 was moderately stimulated in response to receptor a ctivation in in vivo reporter assays. Thus, inhibitory metabotropic GABA(B) Rs may regulate activity-dependent gene expression via a direct interaction with ATF-4.