The human renin kidney enhancer is required to maintain base-line renin expression but is dispensable for tissue-specific, cell-specific, and regulated expression

Vitamin D decreases silencer methylation to downregulate renin gene expression

Renin, encoded by REN, is an essential enzyme in the renin-angiotensin aldosterone system (RAAS) which is responsible for the maintenance of blood pressure homeostasis. Transcriptional regulation of REN has been linked to enhancer-promoter crosstalk, cAMP response element-binding protein (CREB), the active metabolite of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and a less well-characterized intronic silencer element. We hypothesized that in addition to these, differential DNA methylation is linked to REN expression and influenced by 1,25(OH)₂D₃. REN expressing cells (HEK293) were used to elucidate the effect of 1,25(OH)₂D₃ on REN methylation and expression as quantified by methylation-sensitive qPCR and RT-qPCR, respectively. In vitro 1,25(OH)₂D₃ supplementation (10 nM) induced significant hypomethylation of the REN silencer (P < 0.050), which was linked to a significant reduction in REN expression (P < 0.010) but had no effect on enhancer methylation. In addition, 1,25(OH)₂D₃ increased VDR (P < 0.05), as well as TET1 (P < 0.05) expression, suggesting an association between 1,25(OH)₂D₃ and DNA methylation. Thus, it appears that the silencer element, which is controlled by DNA methylation and influenced by 1,25(OH)₂D₃, plays an essential role in regulating REN expression.

Decipher the complexity of cis-regulatory regions by a modified Cas9

BACKGROUND

Understanding complex mechanisms of human transcriptional regulation remains a major challenge. Classical reporter studies already enabled the discovery of cis-regulatory elements within the non-coding DNA; however, the influence of genomic context and potential interactions are still largely unknown. Using a modified Cas9 activation complex we explore the complexity of renin transcription in its native genomic context.

METHODS

With the help of genomic editing, we stably tagged the native renin on chromosome 1 with the firefly luciferase and stably integrated a programmable modified Cas9 based trans-activation complex (SAM-complex) by lentiviral transduction into human cells. By delivering five specific guide-RNA homologous to specific promoter regions of renin we were able to guide this SAM-complex to these regions of interest. We measured gene expression and generated and compared computational models.

RESULTS

SAM complexes induced activation of renin in our cells after renin specific guide-RNA had been provided. All possible combinations of the five guides were subjected to model analysis in linear models. Quantifying the prediction error and the calculation of an estimator of the relative quality of the statistical models for our given set of data revealed that a model incorporating interactions in the proximal promoter is the superior model for explanation of the data.

CONCLUSION

By applying our combined experimental and modelling approach we can show that interactions occur within the selected sequences of the proximal renin promoter region. This combined approach might potentially be useful to investigate other genomic regions. Our findings may help to better understand the transcriptional regulation of human renin.

In silico analysis of human renin gene-gene interactions and neighborhood topologically associated domains suggests breakdown of insulators contribute to ageing-associated diseases

Three-dimensional chromatin architecture and gene-gene interactions impact gene expression. We assembled this information, in silico, for the human renin gene (REN). We searched for chromatin contacts and boundaries and the locations of super-enhancers that are involved in cell specific differentiation. The REN promoter was connected via RNA polymerase II binding to promoters of 12 neighboring genes on chromosome 1q32.1 over a distance of 762,497 bp. This constitutes a regulatory archipelago. The genes formed 3 topologically associated domains (TADs), as follows: TAD1: ZC3H11A, SNRPE, LINC00303; SOX13; TAD2: ETNK2, REN, KISS1, GOLT1A; TAD3: PLEKHA6, LINC00628, PPP1R15B, PIK3C2B, MDM4. REN in TAD2, was isolated from its neighboring genes in TAD1 and TAD3 by CTCF-binding sites that serve as insulators. TAD1 and TAD3 genes SOX13 and LINC00628 overlapped super-enhancers, known to reside near nodes regulating cell identity, and were co-expressed in various tissues, suggesting co-regulation. REN was also connected with 62 distant genes genome-wide, including the angiotensin II type 1 receptor gene. The findings lead us to invoke the following novel hypothesis. While the REN promoter is isolated from neighboring super-enhancers in most cells by insulators, these insulators break down with cell age to permit the inappropriate expression of REN in non-kidney cells by using the neighboring super-enhancers, resulting in expression in a wider spectrum of tissues, contributing to aging-related immune system dysregulation, cardiovascular diseases and cancers. Research is needed to confirm this hypothesis experimentally.

Genome-wide map of proximity linkage to renin proximal promoter in rat

A challenge to understanding enhancer-gene relationships is that enhancers are not always sequentially close to the gene they regulate. Physical proximity mapping through sequencing can provide an unbiased view of the chromatin close to the proximal promoter of the renin gene ( Ren). Our objective was to determine genomic regions that physically interact with the renin proximal promoter, using two different genetic backgrounds, the Dahl salt sensitive and normotensive SS-13BN, which have been shown to have different regulation of plasma renin in vivo. The chromatin conformation capture method with sequencing focused at the Ren proximal promoter in rat-derived cardiac endothelial cells was used. Cells were fixed, chromatin close to the Ren promoter was captured, and fragments were sequenced. The clustering of mapped reads produced a genome-wide map of chromatin in contact with the Ren promoter. The largest number of contacts was found on chromosome 13, the chromosome with Ren, and contacts were found on all other chromosomes except chromosome X. These contacts were significantly enriched with genes positively correlated with Ren expression and with mapped quantitative trait loci associated with blood pressure, cardiovascular, and renal phenotypes. The results were reproducible in an independent biological replicate. The findings reported here represent the first map between a critical cardiovascular gene and physical interacting loci throughout the genome and will provide the basis for several new directions of research.

Long-Range Control of Renin Gene Expression in Tsukuba Hypertensive Mice

Renin, a rate-limiting enzyme in the renin–angiotensin system, is regulated to maintain blood pressure homeostasis: renin gene expression in the kidney is suppressed in a hypertensive environment. We found that expression of a 15-kb human RENIN (hREN) transgene was aberrantly upregulated (>4.2-fold), while the endogenous mouse renin (mRen) gene was suppressed (>1.7-fold) in Tsukuba hypertensive mice (THM), a model for genetically induced hypertension. We then generated transgenic mice using a 13-kb mRen gene fragment that was homologous to the 15-kb hREN transgene and found that its expression was also upregulated (>3.1-fold) in THM, suggesting that putative silencing elements of the renin genes were distally located in the loci. We next examined the possible role of a previously identified mouse distal enhancer (mdE) located outside of the 13-kb mRen gene fragment. Deletion of the mdE in the context of a 156-kb mRen transgene did not affect its transcriptional repression in THM, implying that although the silencing element of the mRen gene is located within the 156-kb fragment tested, it is distinct from the mdE. Consistent with these results, deletion of the 63-kb region upstream of the mdE from the endogenous mRen gene locus abrogated its transcriptional repression in THM. We finally tested whether dysregulation of the short renin transgenes also occurred in the fetal or neonatal kidneys of THM and found that their expression was not aberrantly upregulated, demonstrating that aberrant regulation of short renin transgenes commences sometime between neonate and adult periods.

Selective Deletion of the Brain-Specific Isoform of Renin Causes Neurogenic Hypertension

The renin-angiotensin system (RAS) in the brain is a critical determinant of blood pressure, but the mechanisms regulating RAS activity in the brain remain unclear. Expression of brain renin (renin-b) occurs from an alternative promoter-first exon. The predicted translation product is a nonsecreted enzymatically active renin whose function is unknown. We generated a unique mouse model by selectively ablating the brain-specific isoform of renin (renin-b) while preserving the expression and function of the classical isoform expressed in the kidney (renin-a). Preservation of renal renin was confirmed by measurements of renin gene expression and immunohistochemistry. Surprisingly, renin-b-deficient mice exhibited hypertension, increased sympathetic nerve activity to the kidney and heart, and impaired baroreflex sensitivity. Whereas these mice displayed decreased circulating RAS activity, there was a paradoxical increase in brain RAS activity. Physiologically, renin-b-deficient mice exhibited an exaggerated depressor response to intracerebroventricular administration of losartan, captopril, or aliskiren. At the molecular level, renin-b-deficient mice exhibited increased expression of angiotensin-II type 1 receptor in the paraventricular nucleus, which correlated with an increased renal sympathetic nerve response to leptin, which was dependent on angiotensin-II type 1 receptor activity. Interestingly, despite an ablation of renin-b expression, expression of renin-a was significantly increased in rostral ventrolateral medulla. These data support a new paradigm for the genetic control of RAS activity in the brain by a coordinated regulation of the renin isoforms, with expression of renin-b tonically inhibiting expression of renin-a under baseline conditions. Impairment of this control mechanism causes neurogenic hypertension.

Estrogen Receptor α Is Required for Maintaining Baseline Renin Expression

Enzymatic cleavage of angiotensinogen by renin represents the critical rate-limiting step in the production of angiotensin II, but the mechanisms regulating the initial expression of the renin gene remain incomplete. The purpose of this study is to unravel the molecular mechanism controlling renin expression. We identified a subset of nuclear receptors that exhibited an expression pattern similar to renin by reanalyzing a publicly available microarray data set. Expression of some of these nuclear receptors was similarly regulated as renin in response to physiological cues, which are known to regulate renin. Among these, only estrogen receptor α (ERα) and hepatic nuclear factor α have no known function in regulating renin expression. We determined that ERα is essential for the maintenance of renin expression by transfection of small interfering RNAs targeting Esr1, the gene encoding ERα, in renin-expressing As4.1 cells. We also observed that previously characterized negative regulators of renin expression, Nr2f2 and vitamin D receptor, exhibited elevated expression in response to ERα inhibition. Therefore, we tested whether ERα regulates renin expression through an interaction with Nr2f2 and vitamin D receptor. Renin expression did not return to baseline when we concurrently suppressed both Esr1 and Nr2f2 or Esr1 and vitamin D receptor mRNAs, strongly suggesting that Esr1 regulates renin expression independent of Nr2f2 and vitamin D receptor. ERα directly binds to the hormone response element within the renin enhancer region. We conclude that ERα is a previously unknown regulator of renin that directly binds to the renin enhancer hormone response element sequence and is critical in maintaining renin expression in renin-expressing As4.1 cells.

A mouse renin distal enhancer is essential for blood pressure homeostasis in BAC-rescued renin-null mutant mice

Renin is predominantly expressed in juxtaglomerular cells in the kidney and regulates blood pressure homeostasis. To examine possible in vivo functions of a mouse distal enhancer (mdE), we generated transgenic mice (TgM) carrying either wild-type or mdE-deficient renin BACs (bacterial artificial chromosome), integrated at the identical chromosomal site. In the kidneys of the TgM, the mdE contributed 80% to basal renin promoter activity. To test for possible physiological roles for the mdE, renin BAC transgenes were used to rescue the hypotensive renin-null mice. Interestingly, renal renin expression in the Tg(BAC):renin-null compound mice was indistinguishable between the wild-type and mutant BAC carriers. Surprisingly, however, the plasma renin activity and angiotensin I concentration in the mdE compound mutant mice were significantly lower than the same parameters in the control mice, and the mutants were consistently hypotensive, demonstrating that blood pressure homeostasis is regulated through transcriptional cis elements controlling renin activity.

Control of renin [corrected] gene expression

Renin, as part of the renin-angiotensin system, plays a critical role in the regulation of blood pressure, electrolyte homeostasis, mammalian renal development, and progression of fibrotic/hypertrophic diseases. Renin gene transcription is subject to complex developmental and tissue-specific regulation. Initial studies using the mouse As4.1 cell line, which has many characteristics of the renin-expressing juxtaglomerular cells of the kidney, have identified a proximal promoter region (-197 to -50 bp) and an enhancer (-2,866 to -2,625 bp) upstream of the Ren-1(c) gene, which are critical for renin gene expression. The proximal promoter region contains several transcription factor binding sites including a binding site for the products of the developmental control genes Hox. The enhancer consists of at least 11 transcription factor binding sites and is responsive to various signal transduction pathways including cAMP, retinoic acid, endothelin-1, and cytokines, all of which are known to alter renin mRNA levels. Furthermore, in vivo models have validated several of these key components found within the proximal promoter region and the enhancer as well as other key sites necessary for renin gene transcription.

Regulation of renin expression by the orphan nuclear receptors Nr2f2 and Nr2f6

Understanding the transcriptional mechanisms of renin expression is key to understanding the regulation of the renin-angiotensin system. We previously identified the nuclear receptors RAR/RXR and Nr2f6 (EAR2) as positive and negative transcriptional regulators of renin expression, respectively (Liu X, Huang X, Sigmund CD. Circ Res 92: 1033-1040, 2003). Both mediate their effects through a hormone response element (HRE) within the renin enhancer. Here, we determined whether another nuclear receptor, Nr2f2 (Coup-TFII, Arp-1), identified in a screen of proteins that bind the HRE, also regulates renin expression. Luciferase assays indicate that Nr2f2 negatively regulates the renin promoter more potently than Nr2f6. Gel-shift and chromatin immunoprecipitation (ChIP) indicate that Nr2f2 and Nr2f6 can bind directly to the renin enhancer through the HRE. Surprisingly, baseline expression of endogenous renin was not effected when Nr2f2 was knocked down in As4.1 cells, whereas knockdown of Nr2f6 increased renin expression twofold. Interestingly, however, knockdown of Nr2f2 augmented the induction of renin expression caused by retinoic acid. These data indicate that both Nr2f6 and Nr2f2 can negatively regulate the renin promoter, under baseline conditions and in response to physiological queues, respectively. Therefore, Nr2f2 may require an initiating signal that results in a change at the chromatin level or activation of another transcription factor to exert its effects. We conclude that both Nr2f2 and Nr2f6 negatively regulate renin promoter activity, but may do so by divergent mechanisms.

Divergent mechanism regulating fluid intake and metabolism by the brain renin-angiotensin system

The purpose of this review is two-fold. First, I will highlight recent advances in our understanding of the mechanisms regulating angiotensin II (ANG II) synthesis in the brain, focusing on evidence that renin is expressed in the brain and is expressed in two forms: a secreted form, which may catalyze extracellular ANG I generation from glial or neuronal angiotensinogen (AGT), and an intracellular form, which may generate intracellular ANG in neurons that may act as a neurotransmitter. Second, I will discuss recent studies that advance the concept that the renin-angiotensin system (RAS) in the brain not only is a potent regulator of blood pressure and fluid intake but may also regulate metabolism. The efferent pathways regulating the blood pressure/dipsogenic effects and the metabolic effects of elevated central RAS activity appear different, with the former being dependent upon the hypothalamic-pituitary-adrenal axis, and the latter being dependent upon an interaction between the brain and the systemic (or adipose) RAS.

cAMP target sequences enhCRE and CNRE sense low-salt intake to increase human renin gene expression in vivo

This study aimed to assess the role of cAMP target sequences enhancer cAMP response element (enhCRE) and cAMP and overlapping negative response element (CNRE) in the control of human renin gene (REN) in vivo. enhCRE and CNRE were silenced by mutations in a 12.2-kb human renin promoter fused to LacZ reporter gene. This construct was used to generate transgenic mice (RENMut-LacZ). The expression of the transgene was correctly targeted to the juxtaglomerular portions of renal afferent arterioles which express endogenous mouse renin. Therefore, enhCRE and CNRE do not seem to be relevant for the control of the cell-specific expression of the human renin gene. The β-adrenoreceptor agonist isoproterenol (10 mg/kg/day, for 2 days) stimulated the endogenous renin, but not the LacZ mRNA expression. Treatment of RENMut-LacZ mice with the angiotensin converting enzyme inhibitor (enalapril 10 mg/kg/day, for 7 days) or their crossing to angiotensin receptor type 1a knockout mice led to increased renin and LacZ mRNA levels. Renin expression was upregulated by low-salt diet (0.03% NaCl, for 10 days) and downregulated by high-salt diet (4% NaCl, for 10 days). In contrast, low-salt diet did not influence, while high-salt diet inhibited the expression of LacZ. In summary, enhCRE and CNRE appear to be necessary for the transactivation of the human renin gene through β-adrenoreceptors and by low-salt diet. Our data also suggest that different intracellular mechanisms mediate the effect of low- and high-salt intake on renin expression in vivo.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Regulation of renin gene expression by oxidative stress

Increased arterial pressure, angiotensin II, and cytokines each result in feedback inhibition of renin gene expression. Because angiotensin II and cytokines can stimulate reactive oxygen species production, we tested the hypothesis that oxidative stress may be a mediator of this inhibition. Treatment of renin-expressing As4.1 cells with the potent cytokine tumor necrosis factor-alpha caused an increase in the steady-state levels of cellular reactive oxygen species, which was reversed by the antioxidant N-acetylcysteine. Exogenous H(2)O(2) caused a dose- and time-dependent decrease in the level of endogenous renin mRNA and decreased the transcriptional activity of a 4.1-kb renin promoter fused to luciferase, which was maximal when the renin enhancer was present. The effect of H(2)O(2) appeared to be specific to renin, because there was no change in the expression of beta-actin or cyclophilin mRNA or transcriptional activity of the SV40 promoter. The tumor necrosis factor-alpha-induced decrease in renin mRNA was partially reversed by either N-acetylcysteine or panepoxydone, a nuclear factor kappaB (NFkappaB) inhibitor. Interestingly, H(2)O(2) did not induce NFkappaB in As4.1 cells, and panepoxydone had no effect on the downregulation of renin mRNA by H(2)O(2). The transcriptional activity of a cAMP response element-luciferase construct was decreased by both tumor necrosis factor-alpha and H(2)O(2). These data suggest that cellular reactive oxygen species can negatively regulate renin gene expression via an NFkappaB-independent mechanism involving the renin enhancer and inhibiting cAMP response element-mediated transcription. Our data further suggest that tumor necrosis factor-alpha decreases renin expression through both NFkappaB-dependent and NFkappaB-independent mechanisms, the latter involving the production of reactive oxygen species.

Intrarenal renin-angiotensin system

Phylogenetically the renin-angiotensin system (RAS) is an ancient regulatory system which has attracted the attention of researchers for about a century. As a result of their efforts, different types of RAS inhibitors are now widely used as therapeutic medicines. The scientific enthusiasm toward RAS remains undiminished and new findings and discoveries are to be expected. Early investigators described the role of RAS in the local control of renal hemodynamics. This correlated well with the morphology of juxtaglomerular apparatus (JGA). Recently developed imaging techniques has allowed for in vivo visualization of cellular functions and the use of molecular biological tools have shed new light on the morphology and physiology of renal RAS, especially in connection with the tubular system. RAS has gained recognition to be more than just an endocrine regulatory system for regulating hemodynamics and water/salt metabolism. RAS is a local tissue and/or cellular regulator with a wide range of effects exerted via various receptors. Local RAS is crucially involved in basic physiological processes like ontogenesis and cell proliferation as well as pathophysiological conditions such as inflammation and tissue fibrosis. These findings may open new frontiers for novel therapeutic approaches. This review focuses only on some specific - less discussed and recently described or hypothesized - morphological and functional aspects of intrarenal RAS, including in vivo imaging of RAS, its effects on juxtaglomerular apparatus and possible cooperative mechanisms among various local renal RAS systems.

Development of vascular renin expression in the kidney critically depends on the cyclic AMP pathway

During metanephric kidney development, renin expression in the renal vasculature begins in larger vessels, shifting to smaller vessels and finally remaining restricted to the terminal portions of afferent arterioles at the entrance into the glomerular capillary network. The mechanisms determining the successive expression of renin along the vascular axis of the kidney are not well understood. Since the cAMP signaling cascade plays a central role in the regulation of both renin secretion and synthesis in the adult kidney, it seemed feasible that this pathway might also be critical for renin expression during kidney development. In the present study we determined the spatiotemporal development of renin expression and the development of the preglomerular arterial tree in mouse kidneys with renin cell-specific deletion of G(s)alpha, a core element for receptor activation of adenylyl cyclases. We found that in the absence of the G(s)alpha protein, renin expression was largely absent in the kidneys at any developmental stage, accompanied by alterations in the development of the preglomerular arterial tree. These data indicate that the maintenance of renin expression following a specific spatiotemporal pattern along the preglomerular vasculature critically depends on the availability of G(s)alpha. We infer from our data that the cAMP signaling pathway is not only critical for the regulation of renin synthesis and secretion in the mature kidney but that it also is critical for establishing the juxtaglomerular expression site of renin during development.

In vivo analysis of key elements within the renin regulatory region

Renin is responsible for initiating the enzymatic cascade that results in the production of angiotensin II, the major effector molecule of the renin-angiotensin system (RAS). Extensive information on the regulatory region of the renin gene has been derived by transient transfection studies in vitro, particularly using the As4.1 cell line. To verify key factors within the regulatory region of renin in vivo, homologous recombination was used to introduce a green fluorescent protein (GFP) cassette into exon one of the renin gene contained within a 240 kb bacterial artificial chromosome (BAC) to create a construct that has GFP expression controlled by the renin regulatory region (RenGFP BAC). Within the regulatory region of the RenGFP BAC construct we independently deleted the enhancer, as well as mutated the HOX-PBX site within the proximal promoter element. Transgenic lines were generated for each of these BAC constructs and GFP expression was analyzed throughout a spectrum of tissues positive for renin expression including the kidney, adrenal gland, gonadal artery, and submandibular gland. The results described within this manuscript support the interpretation that the renin enhancer is critical for regulating baseline expression where as the Hox/Pbx site is important for the tissue specificity of renin expression.

Endothelium-specific interference with peroxisome proliferator activated receptor gamma causes cerebral vascular dysfunction in response to a high-fat diet

The ligand-activated transcription factor peroxisome proliferator activated receptor gamma (PPARgamma) is expressed in vascular endothelium where it exerts anti-inflammatory and antioxidant effects. However, its role in regulating vascular function remains undefined. We examined endothelial function in transgenic mice expressing dominant-negative mutants of PPARgamma under the control of an endothelial-specific promoter to test the hypothesis that endothelial PPARgamma plays a protective role in the vasculature. Under baseline conditions, responses to the endothelium-dependent agonist acetylcholine were not affected in either aorta or the basilar artery in vitro. In response to feeding a high-fat diet for 12 weeks, acetylcholine produced dilation that was markedly impaired in the basilar artery of mice expressing dominant-negative mutants, but not in mice expressing wild-type PPARgamma controlled by the same promoter. Unlike basilar artery, 12 weeks of a high-fat diet was not sufficient to cause endothelial dysfunction in the aorta of mice expressing dominant-negative PPARgamma, although aortic dysfunction became evident after 25 weeks. The responses to acetylcholine in basilar artery were restored to normal after treatment with a scavenger of superoxide. Baseline blood pressure was only slightly elevated in the transgenic mice, but the pressor response to angiotensin II was augmented. Thus, interference with PPARgamma in the endothelium produces endothelial dysfunction in the cerebral circulation through a mechanism involving oxidative stress. Consistent with its role as a fatty acid sensor, these findings provide genetic evidence that endothelial PPARgamma plays a critical role in protecting blood vessels in response to a high-fat diet.

Dysregulated human renin expression in transgenic mice carrying truncated genomic constructs: evidence supporting the presence of insulators at the renin locus

We previously generated transgenic mice carrying a large P1 artificial chromosome (PAC160) encompassing a 160-kb segment containing the human renin gene, two upstream genes, and one downstream gene. We also previously generated mutant PAC160 constructs lacking the distal enhancer and concluded it is required to maintain baseline expression of human renin, but is not required for tissue-specific, cell-specific, and regulated expression of renin in vivo. We now report two additional transgenic lines carrying random truncations of PAC160 upstream of the renin gene. Southern and PCR mapping studies indicate that the truncation break points in the two lines are located approximately 10.4 and 2.5 kb upstream of the renin gene causing a deletion of all DNA upstream of the break. We tested the hypothesis that large-scale deletion of DNA upstream of the human renin gene including the enhancer would cause dysregulation of human renin expression. Phenotypically, these truncations cause a severe dysregulation of human renin expression, but remarkably, a preservation of the normal tissue-specific expression of the human ethanolamine kinase 2 (ETNK2) gene which lies immediately downstream of renin. Several functional binding sites for CTCF, a mammalian insulator protein, were identified in and around the renin and ETNK2 loci by gel shift and chromatin immunoprecipitation. We conclude that there are sequences in and around the renin and ETNK2 loci which act as boundaries between neighboring genes which insulate them from each other. The study illustrates the value of taking a much wider genomic perspective when studying mechanisms regulating gene expression.

Wilms' tumor protein (-KTS) modulates renin gene transcription

Renin plays a crucial role in the control of various physiological processes such as blood pressure and body fluid homeostasis. Here, we show that a splice variant of the Wilms' tumor protein lacking three amino acids WT1(-KTS) suppresses renin gene transcription. Using bioinformatics tools, we initially predicted that a WT1-binding site exists in a regulatory region about 12 kb upstream of the renin promoter; this was confirmed by reporter gene assays and gel shift experiments in heterologous cells. Co-expression of Wt1 and renin proteins was found in rat kidney sections, mouse kidney blood vessels, and a cell line derived from the juxtaglomerular apparatus that produces renin. Knockdown of WT1 protein by siRNA significantly increased the cellular renin mRNA content, while overexpression of WT1(-KTS) reduced renin gene expression in stable and transiently transfected cells. A mutant WT1(-KTS) protein found in Wilms' tumors failed to suppress renin gene reporter activity and endogenous renin expression. Our findings show that renin gene transcription is regulated by the WT1(-KTS) protein and this may explain findings in patients with WT1 gene mutations of increased plasma renin and hypertension.

Chorionic enhancer is dispensable for regulated expression of the human renin gene

We tested the hypothesis that a transcriptional chorionic enhancer (CE), previously identified to increase human renin expression in choriodecidual cells is required to mediate tissue-specific, cell-specific, and regulated expression of human renin in transgenic mice. Recombineering was used to delete the CE upstream of the renin gene alone or in combination with the kidney enhancer (KE) in a large artificial chromosome construct containing the entire human renin gene and extensive flanking sequences. Deletion of the CE had no qualitative or quantitative effect on the tissue-specific expression of human renin, nor on the cellular localization of human renin in the kidney or placenta. Combined deletion of both the CE and KE caused a decrease in the level of renal renin expression consistent with the established role of the KE. We also considered the possibility that the CE is a downstream enhancer of the KiSS1 gene, which lies directly upstream of renin and is also expressed in the placenta. Deletion of the CE alone, or the CE and KE together, had no effect on the level of KiSS1 expression in the placenta. These data provide convincing evidence that the CE is silent in vivo, at least in the mouse. The absence of a phenotype caused by deletion of the CE is consistent with the observation that the sequence is not evolutionarily conserved.

Peroxisome Proliferator-Activated Receptor-γ Is Involved in the Control of Renin Gene Expression

Based on the presence of a functional retinoic acid receptor/retinoid X receptor transcription factor binding sequence (hormone-responsive element) in the renin gene enhancer and on the fact that the peroxisome proliferator-activated receptors (PPARs) bind to DNA as heterodimers with retinoid X receptors, we speculated that PPARs are involved in the regulation of renin gene expression. To test this hypothesis, we used the human renin-producing cell line CaLu-6. Endogenous or pharmacological PPARγ agonists (unsaturated fatty acids and thiazolidinediones, respectively) stimulated renin gene expression. Surprisingly, we found that PPARγ targets a palindromic repeat with a 3-bp spacer (Pal3) in the proximal human renin promoter. Thus, renin is the first gene described with a functional Pal3 sequence. PPARγ agonists also stimulated renin gene expression in cultured native juxtaglomerular cells, which are the main source of renin in vivo. In summary, PPARγ was identified as a novel intracellular mediator involved in the upregulation of renin transcription.

Renin enhancer is crucial for full response in Renin expression to an in vivo stimulus

We showed recently that deletion of a strong enhancer located 2.7 kb upstream of the renin gene in mice produces a strain with mild hypotension and salt-sensitivity. Here we set out to compare responses in renin expression in kidney and extrarenal tissues in these "REKO" mice. REKO and wild-type mice were placed on a low NaCl/enalapril regimen for 1 week, and then Ren-1(c) mRNA and renin enzyme activities were measured in tissues and plasma. In untreated REKO mice, renin and Ren-1(c) mRNA were reduced significantly in kidney, submandibular gland, adrenal, heart, and brain. In situ hybridization indicated a marked reduction in Ren-1(c) mRNA in juxtaglomerular cells and granular ducts of submandibular gland. After the chronic stimulus response in renal Ren-1(c) mRNA in REKO mice was blunted by 54% compared with wild-type mice, and was accompanied by almost complete exhaustion of renin stores. Response in plasma renin was blunted by 47%, this being mirrored in heart (54% decline), in which renin is derived mostly from the bloodstream. In adrenal a 55% reduction was seen. These data are consistent with inability of REKO mice to adequately replenish renal renin stores during chronic stimulation of renin secretion. In conclusion, the renin enhancer is critical for replenishment of renin stores and response in renin to a chronic in vivo stimulus.

Functional characterization of polymorphisms in the kidney enhancer of the human renin gene

The renin gene is regulated by an enhancer located 2.6 kb upstream of the transcription start site in the mouse and 11 kb upstream in humans. Despite extensive sequence conservation, the mouse renin enhancer is transcriptionally more active than the human renin enhancer. We report that the mechanism accounting for this is a result of sequence variation in the promoter proximal half-site of a retinoic-acid response element present in the enhancer. This sequence difference also prompted us to search for naturally occurring polymorphisms in the renin enhancer among normal and hypertensive human subjects. We sequenced the kidney enhancer from 90 samples derived from the Coriell Polymorphism Discovery Resource and 95 severely hypertensive Caucasian and African-American individuals. A single relatively frequent polymorphism (7, 2, and 7%, respectively in the Coriell, African-American, and Caucasian) was identified in the enhancer, one nucleotide downstream of the promoter distal half-site of the retinoic-acid response element. This variant was transcriptionally silent in transfection assays performed in renin-expressing As4.1 cells, a model of renal juxtaglomerular cells. A singleton polymorphism in the promoter was also identified in a single African-American individual. This polymorphism was located between binding sites for CBF1 and homeobox D10 but was also transcriptionally silent either in the presence or absence of the enhancer. Our study demonstrates the presence of silent polymorphisms in the renin promoter and enhancer, thus underscoring the critical importance of performing functional analyses before initiating expensive clinical studies seeking association between polymorphisms and complex diseases such as hypertension.