Rat beta 1-adrenergic receptor regulatory region containing consensus AP-2 elements recognizes novel transactivator proteins

CRM 1-mediated degradation and agonist-induced down-regulation of beta-adrenergic receptor mRNAs

The beta1-adrenergic receptor (beta1-AR) mRNAs are post-transcriptionally regulated at the level of mRNA stability and undergo accelerated agonist-mediated degradation via interaction of its 3' untranslated region (UTR) with RNA binding proteins, including the HuR nuclear protein. In a previous report [Kirigiti et al. (2001). Mol. Pharmacol. 60:1308-1324], we examined the agonist-mediated down-regulation of the rat beta1-AR mRNAs, endogenously expressed in the rat C6 cell line and ectopically expressed in transfectant hamster DDT1MF2 and rat L6 cells. In this report, we determined that isoproterenol treatment of neonatal rat cortical neurons, an important cell type expressing beta1-ARs in the brain, results in significant decreases in beta1-AR mRNA stability, while treatment with leptomycin B, an inhibitor of the nuclear export receptor CRM 1, results in significant increases in beta1-AR mRNA stability and nuclear retention. UV-crosslinking/immunoprecipitation and glycerol gradient fractionation analyses indicate that the beta1-AR 3' UTR recognize complexes composed of HuR and multiple proteins, including CRM 1. Cell-permeable peptides containing the leucine-rich nuclear export signal (NES) were used as inhibitors of CRM 1-mediated nuclear export. When DDT1MF2 transfectants were treated with isoproterenol and peptide inhibitors, only the co-addition of the NES inhibitor reversed the isoproterenol-induced reduction of beta1-AR mRNA levels. Our results suggest that CRM 1-dependent NES-mediated mechanisms influence the degradation and agonist-mediated down-regulation of the beta1-AR mRNAs.

Protein/DNA interaction profiling reveals novel regulators of the pineal transcriptome

The rat pineal gland transcriptome exhibits dynamic daily variation that reflects nocturnally restricted hormone production. Here we have used a protein/DNA interaction array to screen for day-night changes in DNA binding activity that are associated with transcriptional rhythms. Overall, 47 of 54 potential consensus binding sequence activities were detected, and of these, 29 (62%) were found to exhibit day:night differences in level. In addition to known, rhythmic pineal DNA binding activities (CRE and AP-1), multiple novel activities were observed including nocturnally elevated AP-2 consensus sequence binding activity. This array result was validated using conventional DNA binding assays, and we have also demonstrated AP-2beta and AP-2gamma proteins in the pineal gland, in addition to a nocturnally elevated AP-2alpha isoform. Our results have confirmed the presence of a complex assembly of transcriptional rhythms in the rat pineal gland and have provided details of more factors that contribute to this aspect of circadian neuroendocrine function.

The pharmacogenomics of selective serotonin reuptake inhibitors

The introduction of selective serotonin (5-HT) reuptake inhibitors (SSRIs) has significantly improved the pharmacological treatment of a range of psychiatric disorders. Nevertheless, despite the undoubted advantages of antidepressant treatment in terms of improved tolerability to therapy while maintaining a high level of efficacy, not all patients benefit from it; an appreciable proportion do not respond adequately, while others may show adverse reactions. The necessary change of the initial treatment choice often requires extended periods for the remission of symptomatology. Such difficulties could be avoided if it should be possible to determine more quickly the most suitable drug. Several factors have been thought to influence the outcome of antidepressant therapy. Among the factors influencing the interindividual variability in response to treatment with SSRI, differences in genetic features may play a significant role. Several genetic polymorphisms have been associated with therapeutic SSRI response, including genetic variants of the 5-HT transporter, 5-HT-2A-receptor, tryptophan hydroxylase, brain-derived neurotrophic factor, G-protein beta3 subunit, interleukin-1beta and angiotensin-converting enzyme, although with conflicting results; also cytochrome P450 drug-metabolising enzymes may bear a particular importance, although further corroboration of the findings is necessary, and further key participating genes remain to be identified. The hope is that the identification of these genetic components will eventually facilitate the development of a customised SSRI treatment.

Estrogen reduces cardiac injury and expression of beta1-adrenoceptor upon ischemic insult in the rat heart

To test the hypothesis that estrogen confers cardioprotection by suppressing the expression of beta-adrenoceptor (beta-AR), we first correlated the infarct size in response to ischemic insult and beta-AR stimulation with the expression of beta(1)-AR in sham, ovariectomized (Ovx) and estrogen replaced (Ovx + E(2)) rats. When beta-AR is being activated during ischemia, the infarct size was significantly greater in Ovx than in the sham and Ovx + E(2) rats. There is a negative correlation between the infarct size and the expression level of beta(1)-AR as revealed by Western blotting and supported by binding analysis. Incubation of ventricular myocytes from Ovx rats with estrogen at 10(-9) M for 24 and 48 h, but not 12 h, significantly reduced lactate dehydrogenase release when the myocytes are subjected to simulated ischemia. The cardioprotective effect of 24 h estrogen incubation was accompanied by a reduction in the protein expression level of beta(1)-AR, which is estrogen receptor-dependent, whereas the lack of protection of 12-h estrogen incubation was not accompanied by any alterations in the expression level of beta(1)-AR. Together, the result from present study suggested that it is most likely that the cardioprotective effect of long-term estrogen replacement is due to suppressing the enhanced expression of cardiac beta(1)-AR in the Ovx rats, which in turn reduces cardiac injury when beta-AR is activated by sympathetic hyperactivity during ischemia. Therefore, suppression of the enhanced expression of cardiac beta(1)-AR in Ovx rats represents a novel cardioprotective mechanism of estrogen replacement therapy.

Reciprocal regulation of beta(1)-adrenergic receptor gene transcription by Sp1 and early growth response gene 1: induction of EGR-1 inhibits the expression of the beta(1)-adrenergic receptor gene

The beta(1)-adrenergic receptor (beta(1)-AR) plays a key role in regulating heart rate and contractility in response to catecholamines. Our studies have focused on defining the factors that regulate the expression of the beta(1)-AR gene. We determined that a 65-base-pair (bp) region in the beta(1)-AR promoter between bp -394 and bp -330 directs basal transcription. An element located between -377 and -365 can bind Sp1 and Sp3. In Drosophila melanogaster SL2 cells, Sp1 stimulated the expression of the beta(1)-AR promoter, whereas Sp3 was unable to activate transcription. Site-directed mutagenesis indicated that an intact Sp1-binding site is essential for maintaining the activity of the basal promoter. In addition to binding Sp family members, the nucleotides between -381 and -367 can bind the zinc-finger transcription factor Egr-1. The Egr-1 and Sp1 binding sites are partially overlapping and their binding sequence is conserved among mammalian beta(1)-AR genes. The induction of Egr-1 in rat neonatal ventricular myocytes with phorbol-12-myristate-13-acetate or in HeLa S3 cells by regulated expression of Egr-1 in a tetracycline-responsive promoter, suppressed expression from the beta(1)-AR promoter. Overexpression of Sp1 in SK-N-MC cells increased beta(1)-AR mRNA by 2.4-fold, whereas overexpression of Egr-1 reduced beta(1)-AR mRNA by 40%. Coexpression of Egr-1 with Sp1 reduced Sp1-mediated up-regulation of beta(1)-AR mRNA by 60%. Mutagenesis revealed that an intact Sp1-binding site is essential for observing transcriptional repression by Egr-1 and that Egr-1 suppressed the transcription of the beta(1)-AR gene by competing with Sp1 for binding to their overlapping sites. These results reveal a novel physiologically relevant transcriptional mechanism for reciprocal regulation of beta(1)-AR gene expression.

Agonist-mediated down-regulation of rat beta1-adrenergic receptor transcripts: role of potential post-transcriptional degradation factors

The human beta1-adrenergic receptor (AR) and hamster beta2-AR transcripts can be post-transcriptionally regulated at the level of mRNA stability and undergo accelerated agonist-mediated degradation via interaction of their 3' untranslated regions (UTR) with RNA binding proteins. Using RNase protection assays, we have determined that chronic isoproterenol exposure of rat C6 glioma cells results in the accelerated reduction of beta1-AR mRNAs. To determine the role of cellular environment on the agonist-independent and agonist-mediated degradation of beta1-AR mRNAs, we transfected rat beta1-AR expression recombinants into both hamster DDT1MF2 cells and rat L6 cells. The rat beta1-AR mRNAs in the two transfectant cell pools retain longer agonist-independent half-lives than in the C6 environment and undergo accelerated degradation upon chronic agonist exposure. Using UV-cross-linking/immunoblot and immunoprecipitation analyses, we have determined that the rat beta1-AR 3' UTR recognizes a predominant M(r) 39,000 component, identified as the mammalian elav-like protein HuR, and several other minor components, including the heteronuclear protein hnRNP A1. HuR levels are more highly expressed in C6 cells than in DDT1MF2 and L6 cells and are induced after chronic isoproterenol treatment. Furthermore, C6 transfectants containing an HuR expression recombinant exhibit reduced beta1-AR mRNA half-lives that were statistically comparable with half-lives identified in isoproterenol-treated C6 cells. These results imply that HuR plays a potential role in the agonist-independent and agonist-mediated down-regulation of beta1-AR mRNAs.