Rat beta 1-adrenergic receptor regulatory region containing consensus AP-2 elements recognizes novel transactivator proteins.
beta 1-Adrenergic receptors (beta1-ARs) serve as important regulators of central nervous system (CNS)-mediated behavior and several neural functions, including mood, memory, neuroendocrine control, and stimulation of autonomic function. Using beta 1-AR-luciferase reporter recombinants, we have previously determined that important beta 1-AR genetic elements controlling expression within the C6 glioma cell line are contained within the region -396 to -299, relative to the translational start site. By conducting progressive internal deletions of the rat beta 1-AR 5' flanking region and with the use of beta 1-AR-luciferase recombinants, we have verified that this region contains the primary beta 1-AR promoter and/or major regulatory elements. To begin the identification of protein factors involved in beta 1-AR transcriptional activity conferred by this beta 1-AR region and flanking sequences, we conducted electrophoretic mobility shift assays using defined beta 1-AR DNA subregion probes. One probe (GS-1), encompassing the region -396 to -367, was found to produce two major and two minor mobility shift complexes when bound to nuclear extracts from the beta 1-AR expresser C6 cell line. UV-crosslinking of DNA-protein complexes, coupled with DNase I digestion, indicated that this beta 1-AR region interacts with one major protein of approximately 117 kDa molecular weight and additional minor proteins. GS-1 DNA-protein complexes were observed using beta 1-AR expresser tissues in the CNS, including cortex, hippocampus, and olfactory bulb. No DNA-protein complexes were observed when using nuclear extracts from beta 1-AR nonexpresser tissues; in some cases, using L6 cells, previously characterized to express little or no beta1-ARs, a reduction in intensities of the DNA-protein complexes was observed. Competition experiments indicate that nuclear protein binds to one of two subregions within the GS-1 sequence that contain AP-2-like consensus elements. Recombinant AP-2 protein will bind to both the beta 1-AR GS-1 promoter fragment and commercially available AP-2 consensus element control probes. Interestingly, using antibody supershift and immunoblotting experiments, no supershifts were observed and the major 117-kDa protein was not immunoreactive to antibodies recognizing either AP-2 alpha or AP-2 beta. These results support our contention that this beta 1-AR regulatory region contains AP-2 consensus elements that recognize novel transactivator proteins.