Adrenergic receptors (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. Regulation of neurotransmitter receptor efficacy and control of neuronal plasticity, as evidenced in receptor desensitization and chronic down-regulation mechanisms, are recognized as part of the adaptive process in the brain that occurs during depression and antidepressant therapy. Beta-AR down-regulation occurs during chronic treatment with antidepressants, suggesting that the dysregulation of the beta`-adrenergic receptor (beta1-AR) subtype, the predominant (beta-AR subtype in the brain, may be associated with depression. Furthermore, the central administration of (beta-AR agonist isoproterenol in the brain induces antidepressant-like effects in the rat, and appears to specifically involve the (beta1-AR subtype. My laboratory has examined the molecular mechanisms underlying beta1AR mRNA down-regulation following agonist induction, and have identified potential transcriptional and post-transcriptional control mechanisms. We have recently identified a transcriptional represser region in the beta1-AR gene, encompassing positions -396 to -367 relative to the translational start site, and have identified the potential represser molecule as a novel bZIP-like transcription factor. This novel transcription factor contains a basic DNA-binding domain, including a leucine zipper motif (bZIP-like), and a phosphatase motif similar to those contained within the RNA polymerase II C-terminal domain (CTD) phosphatases.
The specific aims of this application are to validate the bZIP-like transcription factor as a represser of beta1-AR expression in neonatal rat cortical neurons and to test the hypothesis that this factor is a determinant in the agonist-mediated down-regulation of beta1-AR mRNAs. The primary experimental objectives of this proposal are: 1) to verify interaction of the bZIP-like transcription factor in the repression of the beta1-AR promoter in neonatal rat cortical neurons, 2) to mutagenize the phosphatase motif and basic DNA-binding domain in the transcription factor for potential development of a dominant negative mutant, 3) to identify other potential partners in the bZIP-like transactivator complex formed during beta1-AR transcriptional repression, and 4) to determine the role of the bZIP-like transcription factor in molecular mechanisms underlying agonist-mediated beta1-AR mRNA down-regulation in neonatal rat cortical neurons using both ecdysone-inducible expression and RNA interference systems. This information may provide important insights in the regulation of beta-ARs in the brain and the potential role of these neurotransmitter receptors in depression. This R21 grant application is submitted under PA-03-107 (""""""""NIH Exploratory/Developmental Grant [R21] Program"""""""").
