Two alpha 1b-adrenergic receptor mRNAS expressed in Sprague-Dawley rat liver have distinct 5'-regions

Characterization of the mouse alpha1D-adrenergic receptor gene

Alpha1-adrenergic receptors (alpha1-ARs) play critical roles in the regulation of a variety of physiological processes. Increasing evidence suggests that multiple receptor subtypes of alpha1-ARs regulate these physiological processes. Molecular cloning has identified three distinct cDNAs encoding alpha1-AR subtypes (alpha1A, alpha1B and alpha1D) that are structurally homologous. Among the alpha1-AR subtypes, the function of the alpha1D-AR remains unclear. In order to examine the physiological role of alpha1D-AR, we cloned and characterized a gene for the mouse alpha1D-AR. Using a mouse alpha1D-AR cDNA as a probe, we isolated the gene for the mouse alpha1D-AR from a mouse genomic library. The alpha1D-AR consists of two exons and an intron that interrupts the coding region of the putative sixth transmembrane domain. The 5'-flanking region of exon 1 contains neither a TATA box nor a CAAT box but is high in GC content and contains several Sp1 binding sites (GC boxes). This pattern is similar to promoters described for other members of alpha1-ARs. The untranslated region also contains putative cyclic AMP response elements. Isolation of this gene will allow further investigation, via gene knock-outs and deletion mutants, of the mechanisms of transcriptional regulation and a greater understanding of the physiological role of alpha1D-AR.

Transcriptional regulation of the human alpha1a-adrenergic receptor gene. Characterization Of the 5'-regulatory and promoter region

We recently cloned cDNAs encoding three subtypes of human alpha1-adrenergic receptors (alpha1ARs), alpha1a, alpha1b, and alpha1d (Schwinn, D. A., Johnston, G. L., Page, S. O., Mosley, M. J., Wilson, K. H., Worman, N. P., Campbell, S., Fidock, M. D., Furness, L. M., Parry-Smith, D. J., Peter, B., and Bailey, D. S. (1995) J. Pharmacol. Exp. Ther. 272, 134-142) and demonstrated predominance of alpha1aARs in many human tissues (Price, D. T., Lefkowitz, R. J., Caron, M. G., Berkowitz, D., and Schwinn, D. A. (1994) Mol. Pharmacol. 45, 171-175). Several lines of evidence indicate that alpha1aARs are important in clinical diseases such as myocardial hypertrophy and benign prostatic hyperplasia. Therefore, we initiated studies to understand mechanisms underlying regulation of alpha1aAR gene transcription. A genomic clone containing 6.2 kb of 5'-untranslated region of the human alpha1aAR gene was recently isolated. Ribonuclease protection and primer extension assays indicate that alpha1aAR gene transcription occurs at multiple initiation sites with the major site located 696 base pairs upstream of the ATG, where a classic initiator sequence is located. Transfection of luciferase reporter constructs containing varying amounts of 5'-untranslated region into human SK-N-MC neuroblastoma cells indicate that a region extending 125 base pairs upstream from the main transcription initiation site contains full alpha1aAR promoter activity. Furthermore, distinct activator and suppressor elements lie 2-3 and 3-5 kilobase pairs upstream, respectively. Although the alpha1aAR promoter contains neither TATA or CAAT elements, gel shift mobility assays targeting three GC boxes immediately upstream of the main transcription initiation site confirm binding of Sp1. Activity of the alpha1aAR promoter is cell-specific, demonstrating highest activity in cells endogenously expressing alpha1aARs. The human alpha1aAR gene also contains several cis regulatory elements, including several insulin and cAMP response elements. Consistent with these observations, we provide the first evidence that treatment of SK-N-MC cells with insulin and cAMP elevating agents leads to an increase in alpha1aAR expression. In conclusion, these data represent the first characterization of the alpha1aAR gene; our findings should facilitate further studies designed to understand mechanisms regulating alpha1AR subtype-specific expression in healthy and diseased human tissue.

Evidence for alternative splicing in hepatic alpha 1B-adrenergic receptor gene expression

The interactions of catecholamines with alpha 1B-adrenergic receptors (alpha 1B-AR) located on the surface of many cell types are responsible for physiologic and pathologic functions in mammalian systems. Transcription of the alpha 1B-AR gene leads to the expression of multiple alpha 1B-AR mRNAs that are distributed in a tissue-specific fashion. The purpose of this study was to define the 5'-untranslated regions of the multiple alpha 1B-AR gene transcripts. Evidence for a previously unidentified intron in the alpha 1B-AR gene upstream of the receptor open reading frame was obtained via rapid amplification of cDNA ends. A product was amplified and was found to be missing the nucleotide interval from -708 to -194, (+1 is the start of translation). Evidence for tissue-specific alternative intron splicing was obtained from ribonuclease protection assays and RT-PCR experiments. Using an RNA probe extending from -240 to +93 and including 45 nucleotides into the putative intron, a single protected fragment was detected in heart RNA while two protected fragments were detected in liver RNA. RT-PCR amplification of the region spanning the intron resulted in detection of two PCR products in liver RNA and no detectable product in heart RNA. These findings emphasize the complexity of alpha 1B-AR gene regulation and suggest that multiple alpha 1B-AR mRNAs with different 5'-UTRs may play a role in regulating alpha 1B-adrenergic responsiveness.

Recent advances in the molecular pharmacology of the alpha 1-adrenergic receptors

This review is intended to discuss recent developments in the molecular pharmacology of the alpha 1-adrenergic receptor (alpha 1-AR) subtypes. After a brief historical development, we will focus on the more contemporary issues having to do with this receptor family. Emphasis will be put on recent data regarding the cloning, nomenclature, signalling mechanisms, and genomic organization of the alpha 1-AR subtypes. We will also highlight recent mutational studies that identify key amino acid residues involved in ligand binding, as well as the role of the alpha 1-AR subtypes in regulating physiologic processes.

Regulation of alpha 1b-adrenergic receptor gene expression in rat liver cell lines

alpha 1b-Adrenergic receptor gene expression was investigated in two rat hepatic cell lines, Clone 9 and McA-RH7777 cells. By Northern blot analysis, Clone 9 cells expressed a 2.7 kb alpha 1b-adrenergic receptor gene transcript whereas two transcripts, 3.3 kb and 2.7 kb, were observed in total cellular RNA isolated from rat liver. A binding site for the alpha 1-adrenergic antagonist [3H]prazosin was observed in Clone 9 cell membrane preparations (Bmax = 47 +/- 7 fmol/mg protein and Kd = 0.11 +/- 0.02 nM, n = 5). In contrast, alpha 1b-adrenergic receptor gene transcripts could not be detected in total cellular RNA prepared from McA-RH7777 cells by either Northern blot analysis or ribonuclease protection assays. However, results from nuclear run-off assays indicated that the alpha 1b-adrenergic receptor gene was transcribed in McA-RH7777 cells and alpha 1b-adrenergic receptor gene transcripts were observed in McA-RH7777 cell nuclear RNA. These results suggest that alpha 1b-adrenergic receptor gene expression in liver may be regulated in part post-transcriptionally and that this level of regulation may be altered or disrupted in the Clone 9 and McA-RH7777 cell lines.