Transient expression analyses of DNA extending 2.4 kb upstream of the human renin gene

Fluorescence activated cell sorting of transiently transfected As4.1 cells shows renin enhancer directs on/off switching of renin promoter in vitro

1. The proximal promoter of the renin gene is weak and its activity is influenced by a strong, far-upstream enhancer. This and the ability of renin expression in renal afferent arteriolar cells to be 'recruited' under chronic stimulation is consistent with the on/off switching (variegation) model of gene expression. If true, this would provide an example in which variegation controls a physiologically regulable gene. 2. The present study tested the hypothesis that renin promoter activity may accord with the variegation model, at least in individual juxtaglomerular (mouse As4.1) cells in vitro. 3. As4.1 cells were transiently transfected with constructs containing the mouse renin (Ren-1c) enhancer adjacent to the Ren-1c promoter and a linked reporter gene encoding enhanced green fluorescent protein (EGFP). The EGFP signal from individual cells was monitored by fluorescence activated cell sorting. 4. In the presence of the renin enhancer there was 10-fold higher EGFP expression in transfected cells compared with cells transfected with EGFP constructs containing the promoter alone. There was, moreover, an 8-fold increase in the number of EGFP expressing cells. However, EGFP expression in individual transfected cells was similar in the presence or absence of the enhancer. 5. Results from the in vitro system used suggest that the Ren-1c enhancer does not regulate the rate of promoter activity, but rather increases the probability of achieving an active transcriptional state. Limitations of these findings are discussed.

Renin: from 'pro' to promoter

Renin is the rate-limiting enzyme in a cascade that leads to production of angiotensin II, which is perhaps our most important regulator of salt and water balance and blood pressure. In this personal perspective, I describe how I entered the renin field 33 years ago by discovering that proteases increased the level of renin activity in biological fluids, so revealing the existence of a 'pro' form of the molecule. This led me on a journey that encapsulated all of the major milestones in molecular discovery for renin. These included (1) the elucidation of the steps in renin biosynthesis, (2) the cloning of renin cDNA and its gene, (3) demonstration of the structure of the renin protein, (4) using the renin gene in the first genetic studies in hypertension, (5) finding the mechanism by which the major controller, cyclic AMP, regulates the promoter, (6) showing that a strong enhancer and its weak promoter control this physiologically regulatable gene in accord with the variegation (on/off switching) model, and (7) being the first to identify molecules involved in posttranscriptional control. The renin molecule, its gene and molecular control are now very well understood, but more fine details on the topic of renin continue to emerge to delight 'reninologists' and others.

Renin gene expression: the switch and the fingers

1. Now that many of the factors and control elements that regulate renin transcription have been identified, the scene is set to address the question of the mode of control. 2. Based on current gene control theories, either renin gene transcription in each cell undergoes gradual responses over a continuous range or transcription is switched completely on or completely off. The latter model of 'binary' or 'variegated' expression fits with observations such as the 'recruitment' of new cells for renin expression during strong physiological stimulation and the progressive switching off of expression during development. 3. The renin gene offers an excellent general model for testing the mode of control of genes that are subject to continuous modulatory influences from the demands of physiological perturbations. This is because the promoter is well characterized and is subject to the influence of a strong far-upstream enhancer, one of the key elements of the variegation model. 4. Renin is also controlled at the post-transcriptional level and this, like transcriptional control, involves cAMP mechanisms. We have cloned the human and mouse homologues of a protein (ZNF265) that is important in renin mRNA processing and stability. This uses 'zinc fingers' to bind the mRNA. The role of this and other proteins in splicing and stabilization of mRNA is now being elucidated. 5. Unravelling the mechanisms that determine rate of supply of renin mRNA to the biosynthetic machinery is being assisted by advances in concepts and techniques in the rapidly moving field of genomics.

Polymorphisms of the renin gene promoter in spontaneously hypertensive and Wistar-Kyoto rats

1. In the present study, 1.39 kb of the renin gene 5' region in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was amplified by polymerase chain reaction from genomic DNA and sequenced. Consistent differences in the renin gene sequence of SHR and WKY rats were found at positions -725, -727, -979 and -1126/-1129 as numbered from the transcription start site (+1). No polymorphism was specific to hypertensive rats. 2. Gel-shift assays were performed using labelled SHR renin promotor DNA and nuclear proteins extracted from rat kidneys. The regions between -1122 and -1139 and between -701 and -797 showed protein binding.

Transcriptional regulation of the rat renin gene by regulatory elements in intron I

Renin catalyzes the rate-limiting step in the enzymatic cascade leading to the vasoactive peptide angiotensin II. Therefore, the activity of the renin-angiotensin system in a tissue is regulated significantly at the level of transcription of the renin gene. Besides transcription factor binding sites in the promoter region, the renin genes of human and rat contain regulatory elements also in intron I. Inclusion of intron I in reporter gene constructs with the renin promoter leads to a marked down-regulation of gene expression in nonrenin expressing 293 human embryonic kidney cells but has hardly any effect in renin-expressing L8 rat skeletal myoblasts. In combination with the cytomegalovirus immediate early gene promoter, the silencing occurs in both cell lines but is less pronounced in L8 cells. By partially deleting intron I in these constructs, we describe 5 negative (I-NRE) and 2 positive (I-PRE) regulatory elements responsible for these effects. Using gel-retardation and methylation-interference assays with 293-nuclear extracts, we detected a pseudo-palindromic protein-binding sequence between position +159 and +171 relative to the transcriptional start site. Binding of transcription factors to this sequence may be important for the tissue-specific silencing of the renin gene outside the juxtaglomerular cells of the kidney.

Role of proximal promoter elements in regulation of renin gene transcription

Mouse As4.1 cells, obtained after transgene-targeted oncogenesis to induce neoplasia in renal renin-expressing cells, express high levels of renin mRNA from the endogenous Ren-1(c) gene. We have used these cells to characterize the role of the Ren-1(c) proximal promoter (+6 to -117) in the regulation of renin gene transcription. It was found that 4.1 kilobases (kb) of Ren-1(c) 5'-flanking sequence, in combination with the proximal promoter, are required for strong activation (approximately 2 orders of magnitude over the basal level of the promoter alone) of the chloramphenicol acetyltransferase reporter in transfection assays. Within the 4.1-kb fragment, a 241-base pair region was identified that retains full activity in an orientation-independent manner in combination with the promoter. The resulting transcripts initiate at the normal renin start site. Electrophoretic mobility shift assays identified a sequence at approximately position -60 in the promoter region that binds nuclear proteins specific for renin-expressing As4.1 cells. Mutations in this sequence, which disrupt binding of nuclear protein(s), completely abolish activation of transcription by the 4. 1-kb fragment. Activation of transcription by the 241-base pair enhancer was still observed, although it was diminished in magnitude (60-fold over the mutated promoter alone). We present a model derived from the current data that suggests that regulation of renin expression is achieved through cooperation of transcription factors binding at the proximal promoter element and a distal enhancer element to abrogate or override the effects of an intervening negative regulatory region.

PCR-SSCP analysis of the promoter region of the renin gene in patients with aldosterone-producing adenomas

1. Aldosterone-producing adenomas (APA) of the adrenal gland may be responsive or un-responsive to the renin-angiotensin system. 2. We have described increased expression of renin mRNA in angiotensin-responsive aldosterone-producing adenomas (AII-R-APA) compared with angiotensin-un-responsive aldosterone-producing adenomas (AII-U-APA) and significantly different allelic frequencies of the BglI, TaqI and HinfI restriction fragment length polymorphisms of the renin gene between the two groups. 3. An area including the 5' flanking region -500 bp from exon 1, exon 1 and intron A contained no gross insertions or deletions when studied by a long polymerase chain reaction technique. 4. In the present study, polymerase chain reaction-single strand conformation polymorphism analysis (PCR-SSCP) revealed no single base pair alteration in the proximal promoter region (-600 bp to transcription start) of the renin gene in patients with APA (either AII-U-APA or AII-R-APA) when compared with normal subjects. 5. Therefore, mutations in this regulatory region do not appear to explain the different levels of renin gene expression observed in these two subtypes of APA.

Some physiological outcomes of renin gene studies

1. The cloning of the renin gene has permitted studies of its physiological regulation, extrarenal expression and role in disease. 2. Marked modulation of renin mRNA concentration is seen in adrenal, heart and hypothalamus in response to sodium depletion and inhibition of AII formation, as well as in models of renal and genetic hypertension in the rat. 3. One important outcome of studies of the promoter has been the discovery of a cyclic AMP-responsive sequence. 4. Sequence variations have been detected in or near the renin gene and have been used as markers in studies of its role in cardiovascular disease aetiology. 5. In conclusion, molecular biology has, in the past decade, made a significant contribution to the understanding of renin physiology and pathophysiology.

Analysis of the renin gene in patients with aldosterone-producing adenomas by polymerase chain reaction-single stranded conformational polymorphisms and long polymerase chain reaction

1. Angiotensin-responsive aldosterone-producing adenomas (AII-R-APA) have increased expression of renin mRNA compared with angiotensin-unresponsive aldosterone-producing adenomas (AII-U-APA) or normal adrenals. 2. Further, significant associations between the BglI, TaqI and HinfI RFLP and aldosterone responsiveness to the renin-angiotensin system of the two subgroups of patients have been reported. 3. Using the polymerase chain reaction based technique single stranded conformational polymorphism, we detected no alterations in exon 1 of the renin gene in peripheral blood leucocyte DNA from normal AII-U-APA and AII-R-APA subjects. 4. Using long-PCR, we amplified a fragment of the renin gene consisting of a region covering 500 bp upstream of exon 1, exon 1 and intron A. No gross changes in this area of the renin gene were found in the three groups of subjects studied. However this does not exclude small alterations in this area.

Human renin 5'-flanking DNA to nucleotide-2750

Renin is one of the most important factors in blood pressure and electrolyte regulation in mammals and the renin locus has been implicated in hypertension. To assist studies of promoter control we therefore determined the 5'-flanking sequence of the human gene (REN) to residue -2750 relative to the transcription start site (+1). Sites of homology to consensus sequences for binding of trans-acting factors involved in transcriptional control of other genes were identified, and functionality for two of these (a CRE and Pit-1 site) have so far been demonstrated.

Function of human renin proximal promoter DNA

An understanding of the mechanisms involved in the control of the human renin promoter have been hampered and confounded in work to date because of deficiencies in material available and experimental design. The promoter appears to be weak and a good cell model is lacking. Chorio-decidual cultures have been used since these have high renin synthesis, are readily available and grow well in culture. They suffer, however, from phenotypic variability and do not transfect well in transient expression analyses. Recent evidence suggests that 2.6 kb of proximal 5'-flanking DNA is unable to induce native promoter activity under basal conditions. Experiments in which an exogenous enhancer was introduced have raised the possibility that an endogenous enhancer residing outside of the 2.6 kb 5'-flanking region could be required. Cell-type specific factors also appear to be needed. The proximal flanking DNA does, however, appear to be capable of conferring activity on the promoter in chorio-decidual cells under stimulated conditions, suggesting that factors so activated may have considerable importance. Evidence suggests that forskolin-responsive signal transduction pathways may lead cyclic AMP responsive element (CRE) binding protein (CREB) to act on a CRE at -222 in the proximal REN promoter DNA. Activation of the mouse promoter by cAMP appears to involve a different element, however. Furthermore, overall control of renin synthesis is likely to involve post-transcriptional mechanisms as well. Thus, despite being the first cardiovascular gene to be cloned, much more work is required before the control of the human renin gene is fully understood.

Proximal 2.6 kb of 5'-flanking DNA is insufficient for human renin promoter activity in renin-synthesizing chorio-decidual cells

In order to determine the influence of proximal 5'-flanking DNA of the human renin gene (REN) in cells that express human renin, transient expression analyses were carried out in chorio-decidual cells. Constructs containing different lengths of REN promoter DNA, extending as far as 2595 bp upstream of the transcription start site, were unable to drive transcription of a chloramphenicol acetyl transferase reporter gene in chorio-decidual cells, nor in noncognate 293 or JEG-3 cells. The tk promoter was similarly inactive in constructs containing -2595 to -453 fragments of REN 5'-flanking DNA. In each cell type, the -2595 to -1300 DNA exerted a negative influence. Additional promoter- and cell type-dependent negative influences were noted for other regions of REN 5'-flanking DNA and the -453 to -145 DNA increased tk promoter activity 2.5-fold in chorio-decidual cells. By introducing the SV40 enhancer into constructs, a weak stimulation of the REN promoter was observed in chorio-decidual cells, but not in noncognate, JEG-3 cells, although the -2595 to -1300 DNA retained its negative influence in the cognate cell type. These results show that the proximal 2.6 kb of REN 5'-flanking DNA is unable to drive reporter gene activity in renin-synthesizing, chorio-decidual cells under basal conditions and suggest that trans-acting factors unique to at least this cell type, together with enhancer(s) located outside of the proximal 2.6 kb of REN promoter DNA tested, could be required for human renin promoter activity.

cis-regulatory elements and trans-acting factors directing basal and cAMP-stimulated human renin gene expression in chorionic cells

Much knowledge was accumulated in the regulation of plasma renin activity and renin secretion during recent years. However, the mechanisms of renin gene transcription, especially for the human gene, have been poorly studied because of the lack of cell lines expressing renin. Cells derived from chorion tissue were used to study renin gene transcription because these cells express renin and regulate renin secretion in a similar way to JG cells. The present study was performed to determine the cis-regulatory elements and the trans-acting factors involved in human renin gene expression using chorionic cells. Transient DNA transfections were performed with various constructs containing the 5'-flanking region of the human renin gene. 5'-Deletion analysis of the human renin promoter (from -2616 to -67 bp) revealed the presence of two proximal negative cis-regulatory elements between -374 and -273 bp and between -273 and -137 bp. These elements were not present in a non-renin-producing cell line, JEG-3 cells. DNase I footprinting revealed that two sequences located within these regions bind trans-factors present in chorionic cellular nuclear extract: AGE3-like sequence (-293/-273) and apolipoprotein A1 regulatory protein-1-like sequence (-259/-245). The first 110 bp of the renin promoter were sufficient to direct specific expression in chorionic cells and contained two footprints sharing homology with ets (-29/-6) and pituitary-specific factor (Pit-1) (-70/-62) sequences. Furthermore, one footprint (-234/-214) contained the sequence TAGCGTCA, which shares strong homology to the cAMP-responsive element (CRE) binding site. Gel shift analysis showed specific DNA/protein complexes within this region, which were displaced by the somatostatin consensus CRE. Finally, luciferase analysis of 5'-deletion mutant revealed that -273 to +16 bp of the renin promoter was sufficient to confer complete forskolin stimulation, whereas deletion to -130 (deletion of the CRE) decreased cAMP responsiveness by 50% and those to -67 bp (deletion of the CRE and Pit-1-like sequences) suppressed it. Thus, these latter two sequences probably act together to confer complete cAMP responsiveness.

Species differences in binding of submandibular nuclear proteins to renin promoter DNA

1. Renin is highly expressed in submandibular gland (SMG) of mouse, which has two genes, Ren-1d and Ren-2d, but not at all in rat SMG. Differences in nuclear protein binding to renin promoter DNA were, therefore, explored. 2. Rat -169 to +23 renin DNA formed complexes with both mouse and rat extract, whereas a corresponding fragment of mouse Ren-1d DNA (-121 to +4) bound with rat extract, but much less so with mouse extract. Rat extract bound a -704 to -450 fragment of the Ren-1d promoter. For Ren-2d -578 to -383 and -786 to -718 DNA bound with mouse extract and -383 to +11 and -664 to -578 DNA bound with rat extract. 3. The results support a role for differences in presence or binding of species-specific trans-acting factors in the differential regulation of the renin gene in SMG of mouse and rat. Strong binding near the rat RNA polymerase II binding site could repress transcription in rat SMG, and binding peculiar to the Ren-2d B2 element might contribute to high expression in mouse SMG.