Regulation of renin enhancer activity by nuclear factor I and Sp1/Sp3

Inhibition of Renin Expression Is Regulated by an Epigenetic Switch From an Active to a Poised State

BACKGROUND

Renin-expressing cells are myoendocrine cells crucial for the maintenance of homeostasis. Renin is regulated by cAMP, p300 (histone acetyltransferase p300)/CBP (CREB-binding protein), and Brd4 (bromodomain-containing protein 4) proteins and associated pathways. However, the specific regulatory changes that occur following inhibition of these pathways are not clear.

METHODS

We treated As4.1 cells (tumoral cells derived from mouse juxtaglomerular cells that constitutively express renin) with 3 inhibitors that target different factors required for renin transcription: H-89-dihydrochloride, PKA (protein kinase A) inhibitor; JQ1, Brd4 bromodomain inhibitor; and A-485, p300/CBP inhibitor. We performed assay for transposase-accessible chromatin with sequencing (ATAC-seq), single-cell RNA sequencing, cleavage under targets and tagmentation (CUT&Tag), and chromatin immunoprecipitation sequencing for H3K27ac (acetylation of lysine 27 of the histone H3 protein) and p300 binding on biological replicates of treated and control As4.1 cells.

RESULTS

In response to each inhibitor, Ren1 expression was significantly reduced and reversible upon washout. Chromatin accessibility at the Ren1 locus did not markedly change but was globally reduced at distal elements. Inhibition of PKA led to significant reductions in H3K27ac and p300 binding specifically within the Ren1 super-enhancer region. Further, we identified enriched TF (transcription factor) motifs shared across each inhibitory treatment. Finally, we identified a set of 9 genes with putative roles across each of the 3 renin regulatory pathways and observed that each displayed differentially accessible chromatin, gene expression, H3K27ac, and p300 binding at their respective loci.

CONCLUSIONS

Inhibition of renin expression in cells that constitutively synthesize and release renin is regulated by an epigenetic switch from an active to poised state associated with decreased cell-cell communication and an epithelial-mesenchymal transition. This work highlights and helps define the factors necessary for renin cells to alternate between myoendocrine and contractile phenotypes.

Determinants of renin cell differentiation: a single cell epi-transcriptomics approach

Rationale

Renin cells are essential for survival. They control the morphogenesis of the kidney arterioles, and the composition and volume of our extracellular fluid, arterial blood pressure, tissue perfusion, and oxygen delivery. It is known that renin cells and associated arteriolar cells descend from FoxD1 + progenitor cells, yet renin cells remain challenging to study due in no small part to their rarity within the kidney. As such, the molecular mechanisms underlying the differentiation and maintenance of these cells remain insufficiently understood.

Objective

We sought to comprehensively evaluate the chromatin states and transcription factors (TFs) that drive the differentiation of FoxD1 + progenitor cells into those that compose the kidney vasculature with a focus on renin cells.

Methods and Results

We isolated single nuclei of FoxD1 + progenitor cells and their descendants from FoxD1 ^cre/+ ; R26R-mTmG mice at embryonic day 12 (E12) (n _cells =1234), embryonic day 18 (E18) (n _cells =3696), postnatal day 5 (P5) (n _cells =1986), and postnatal day 30 (P30) (n _cells =1196). Using integrated scRNA-seq and scATAC-seq we established the developmental trajectory that leads to the mosaic of cells that compose the kidney arterioles, and specifically identified the factors that determine the elusive, myo-endocrine adult renin-secreting juxtaglomerular (JG) cell. We confirm the role of Nfix in JG cell development and renin expression, and identified the myocyte enhancer factor-2 (MEF2) family of TFs as putative drivers of JG cell differentiation.

Conclusions

We provide the first developmental trajectory of renin cell differentiation as they become JG cells in a single-cell atlas of kidney vascular open chromatin and highlighted novel factors important for their stage-specific differentiation. This improved understanding of the regulatory landscape of renin expressing JG cells is necessary to better learn the control and function of this rare cell population as overactivation or aberrant activity of the RAS is a key factor in cardiovascular and kidney pathologies.

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.

Superoxide via Sp3 mechanism increases renal renin activity, renal AT1 receptor function, and blood pressure in rats

We tested a hypothesis that superoxide, by inducing Sp3, increases renal renin activity, renal angiotensin II type 1 receptor (AT1R) function, and blood pressure (BP) in rats. Group 1 rats were treated with vehicle, saline. Group 2 rats were treated with superoxide dismutase (SOD) inhibitor diethylthiocarbamate (DETC). Group 3 rats were treated with DETC and an SOD mimetic, tempol. Group 4 rats were treated with tempol only. All four groups of rats were treated for 2 wk then anesthetized, and BP was recorded. Thereafter, diuresis and natriuresis in response to AT1R blocker candesartan were determined. When compared with vehicle rats, BP increased in DETC rats. The increased BP in DETC rats decreased with tempol. Diuresis and natriuresis in response to candesartan increased in controls, and this further increased in DETC rats and decreased with tempol. A second set of four groups of rats underwent the same treatment as above and were anesthetized, and their kidneys were obtained for biochemical studies. The levels of superoxide but not hydrogen peroxide increased, whereas SOD activities decreased further in the renal cortical tissues of DETC rats than vehicle rats. These effects were attenuated with tempol in DETC rats. Moreover, tissue renin activity and abundance of membranous AT1R proteins increased more in DETC rats than vehicle rats, and decreased with tempol in DETC rats. Furthermore, the levels of lysine-acetylated, but not serine-phosphorylated, Sp3 increased more in the nuclei of DETC rats than vehicle rats. The increased levels of Sp3 lysine acetylation decreased in DETC rats with tempol. Taken together, our results suggest that superoxide activates renal Sp3 via lysine acetylation increasing renin activity, AT1R function, and BP in rats.

Macroarray analysis in the hypertrophic left ventricle of renin-dependent hypertensive rats: identification of target genes for renin

Introduction The aim of this work was to identify new renin target genes in left ventricular hypertrophy during hypertension.

Materials and methods We compared left ventricle gene expression from four transgenic TGR(mRen2)27 (TG+/-) rats and four non-transgenic littermates (TG-/-) using cDNA macroarray. Hybridisation signals were quantified with a phosphorimager, and normalised to an external scale. Data analysis was performed with Statistical Analysis for Microarrays (SAM 1.21) software. The mRNA levels of candidate genes were determined by semi-quantitative RT-PCR in three different hypertensive rats: TG+/-, spontaneously hypertensive (SHR) and genetically Lyon hypertensive (LH) rats, compared to their respective controls (TG-/-, Wistar-Kyoto, Lyon low blood pressure rats).

Results Out of 1,200 genes present on the macroarray, 233 were reliably measured and only three were overexpressed (Biglycan, β1-adenosine monophosphate-activated protein kinase [AMPK] and amyloid precursor like protein 2 [APLP2]) and 19 were underexpressed in the left ventricle of TG+/compared with TG-/-. APLP2 is a member of the amyloid precursor protein (APP) family. APLP2 and APP mRNA levels were increased in TGR(mRen2)27 but significantly decreased in LH rats, while only APP was increased in SHR rats.

Conclusions We report new genes associated with renin-dependent left ventricular hypertrophy. Moreover, this work shows for the first time that the APP family gene expression could be altered in response to high renin activity and this effect is independent of cardiac remodelling and 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.

Classical Renin-Angiotensin system in kidney physiology

The renin-angiotensin system has powerful effects in control of the blood pressure and sodium homeostasis. These actions are coordinated through integrated actions in the kidney, cardiovascular system and the central nervous system. Along with its impact on blood pressure, the renin-angiotensin system also influences a range of processes from inflammation and immune responses to longevity. Here, we review the actions of the "classical" renin-angiotensin system, whereby the substrate protein angiotensinogen is processed in a two-step reaction by renin and angiotensin converting enzyme, resulting in the sequential generation of angiotensin I and angiotensin II, the major biologically active renin-angiotensin system peptide, which exerts its actions via type 1 and type 2 angiotensin receptors. In recent years, several new enzymes, peptides, and receptors related to the renin-angiotensin system have been identified, manifesting a complexity that was previously unappreciated. While the functions of these alternative pathways will be reviewed elsewhere in this journal, our focus here is on the physiological role of components of the "classical" renin-angiotensin system, with an emphasis on new developments and modern concepts.

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.

Genetic Variant of C-5312T Can Change Binding Pattern of Sp1 to Renin Enhancer that are Very Likely to Affect Renin Gene Expression

Renin distal enhancer plays a pivotal role in renin gene expression, and the genetic variants C-5312T of renin enhancer can affect renin gene transcription level. However, the mechanism associated with the transcription level changes remains unknown. Therefore, it is of interest to investigate the possible role of distal enhancer in regulating the expression of renin gene. Single nucleotide polymorphism in renin distal enhancer was identified in 34 hypertensive patients by automatic sequencing. The data showed that the renin enhancer from the patients have genetic variants C-5312T or C-5312T SNP. Hence, the functionality of the renin enhancer and influence of the genetic variants C-5312T on binding to Sp1 is studied. These results from the binding study suggested that Sp1 binds to the DNA in GC rich region. Thus, the genetic variant C-5312T has changed the binding pattern of Sp1 to renin enhancer. This is likely to influence Sp1 activity to stimulate the expression of renin gene. The binding of Sp1 to the cis-element will enhance transcription of renin gene. Thus, polymorphism within C-5312T might contribute to the reduction of renin transcription.

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.

Transcriptional regulator RBP-J regulates the number and plasticity of renin cells

Renin-expressing cells are crucial in the control of blood pressure and fluid-electrolyte homeostasis. Notch receptors convey cell-cell signals that may regulate the renin cell phenotype. Because the common downstream effector for all Notch receptors is the transcription factor RBP-J, we used a conditional knockout approach to delete RBP-J in cells of the renin lineage. The resultant RBP-J conditional knockout (cKO) mice displayed a severe reduction in the number of renin-positive juxtaglomerular apparatuses (JGA) and a reduction in the total number of renin positive cells per JGA and along the afferent arterioles. This reduction in renin protein was accompanied by a decrease in renin mRNA expression, decreased circulating renin, and low blood pressure. To investigate whether deletion of RBP-J altered the ability of mice to increase the number of renin cells normally elicited by a physiological threat, we treated RBP-J cKO mice with captopril and sodium depletion for 10 days. The resultant treated RBP-J cKO mice had a 65% reduction in renin mRNA levels (compared with treated controls) and were unable to increase circulating renin. Although these mice attempted to increase the number of renin cells, the cells were unusually thin and had few granules and barely detectable amounts of immunoreactive renin. As a consequence, the cells were incapable of fully adopting the endocrine phenotype of a renin cell. We conclude that RBP-J is required to maintain basal renin expression and the ability of smooth muscle cells along the kidney vasculature to regain the renin phenotype, a fundamental mechanism to preserve homeostasis.

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 ).

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.

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.

1,25-dihydroxyvitamin D3 suppresses renin gene transcription by blocking the activity of the cyclic AMP response element in the renin gene promoter

We have shown that 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) down-regulates renin expression. To explore the molecular mechanism, we analyzed the mouse Ren-1c gene promoter by luciferase reporter assays. Deletion analysis revealed two DNA fragments from -2,725 to -2,647 (distal fragment) and from -117 to +6 (proximal fragment) that are sufficient to mediate the repression. Mutation of the cAMP response element (CRE) in the distal fragment blunted forskolin stimulation as well as 1,25(OH)(2)D(3) inhibition of the transcriptional activity, suggesting the involvement of CRE in 1,25(OH)(2)D(3)-induced suppression. EMSA revealed that 1,25(OH)(2)D(3) markedly inhibited nuclear protein binding to the CRE in the promoter. ChIP and GST pull-down assays demonstrated that liganded VDR blocked the binding of CREB to the CRE by directly interacting with CREB with the ligand-binding domain, and the VDR-mediated repression can be rescued by CREB, CBP, or p300 overexpression. These data indicate that 1,25(OH)(2)D(3) suppresses renin gene expression at least in part by blocking the formation of CRE-CREB-CBP complex.

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.

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

Renin is the rate-limiting enzyme in the renin-angiotensin system and thus dictates the level of the pressor hormone angiotensin-II. The classical site of renin expression and secretion is the renal juxtaglomerular cell, where its expression is tightly regulated by physiological cues. An evolutionarily conserved transcriptional enhancer located 11 kb upstream of the human RENIN gene has been reported to markedly enhance transcription in renin expressing cells in vitro. However, its importance in vivo remains unclear. We tested whether this enhancer is required for appropriate tissue- and cell-specific expression, or for physiological regulation of the human RENIN gene. To accomplish this, we used a retrofitting technique employing homologous recombination in bacteria to delete the enhancer from a 160-kb P1-artificial chromosome containing human RENIN, two upstream genes and one downstream gene, and then generated two lines of transgenic mice. We previously showed that human renin expression in transgenic mice containing the wild type construct is tightly regulated as is expression of the linked genes. Deletion of the enhancer had no effect on tissue-specific expression of human RENIN, but using the downstream gene as an internal control, found that human RENIN mRNA levels were 3-10-fold decreased compared with constructs containing the enhancer. Despite this decrease in expression, renin protein remained localized to renal juxtaglomerular cells and was appropriately regulated by cues that either increase or decrease expression of renin. Our results suggest that sequences other than the enhancer may be necessary for tissue-specific, cell-specific, and regulated expression of human RENIN.

Hypertension, kidney, and transgenics: a fresh perspective

In this review, we outline the application and contribution of transgenic technology to establishing the genetic basis of blood pressure regulation and its dysfunction. Apart from a small number of examples where high blood pressure is the result of single gene mutation, essential hypertension is the sum of interactions between multiple environmental and genetic factors. Candidate genes can be identified by a variety of means including linkage analysis, quantitative trait locus analysis, association studies, and genome-wide scans. To test the validity of candidate genes, it is valuable to model hypertension in laboratory animals. Animal models generated through selective breeding strategies are often complex, and the underlying mechanism of hypertension is not clear. A complementary strategy has been the use of transgenic technology. Here one gene can be selectively, tissue specifically, or developmentally overexpressed, knocked down, or knocked out. Although resulting phenotypes may still be complicated, the underlying genetic perturbation is a starting point for identifying interactions that lead to hypertension. We recognize that the development and maintenance of hypertension may involve many systems including the vascular, cardiac, and central nervous systems. However, given the central role of the kidney in normal and abnormal blood pressure regulation, we intend to limit our review to models with a broadly renal perspective.

Role of CREB1 and NFκB-p65 in the Down-regulation of Renin Gene Expression by Tumor Necrosis Factor α

Tumor necrosis factor-alpha (TNFalpha) is a potent inhibitor of renin gene expression in renal juxtaglomerular cells. We have found that TNFalpha suppresses renin transcription via transcription factor NFkappaB, which targets a cAMP responsive element (CRE) in the renin promoter. Here we aimed to further clarify the role of NFkappaB and the canonical CRE-binding proteins of the CRE-binding protein/activating transcription factor (CREB/ATF) family in the inhibition of renin gene expression by TNFalpha in the juxtaglomerular cell line As4.1. TNFalpha caused a moderate decrease in the binding of CREB1 to its cognate CRE DNA binding site. On the other hand, NFkappaB-p65 transcriptional activity was substantially reduced by TNFalpha, which targeted a trans-activation domain at the very C terminus of the p65 molecule. Our results suggest that TNFalpha inhibits renin gene expression by decreasing the transactivating capacity of NFkappaB-p65 and partially by attenuating CREB1 binding to CRE.

Retinoic acid activates human secretin gene expression by Sp proteins and nuclear factor I in neuronal SH-SY5Y cells

Secretin is a neuropeptide that is expressed in distinct central neurones. As there is no information on how the secretin gene is regulated in neuronal cells, a well established neuronal differentiation cell model, SH-SY5Y, was used to study transcriptional regulation of the human secretin gene. High secretin transcript and peptide levels were found in this cell, and secretin gene expression and promoter activity were up-regulated upon all-trans retinoic acid (RA) treatment. Within the promoter, a functional GC-box 1 (-131 from ATG, relative to the ATG initiation codon) was found to be regulated by a brain-specific Sp protein, Sp4, and ubiquitous factors Sp1 and Sp3. The human secretin gene in SH-SY5Y cells is controlled by the (Sp1 + Sp4)/Sp3 ratio and the RA-induced activation is a partial result of a decrease in Sp3 levels. In addition to the GC-box 1, an N1 motif in close proximity was also responsible for RA-induced secretin gene activation. Competitive gel mobility shift and southwestern blot studies revealed binding of Nuclear Factor I (NFI) with the N1 motif. Overexpression of NFI-C increased promoter activity upon RA treatment. Consistent with this observation, NFI-C transcript levels were augmented after RA treatment. We conclude that RA induction of the secretin gene in neuronal cells is regulated by the combined actions of reducing Sp3 and increasing NFI-C expression.

Transcriptional Regulation of Renin

Renin, as a component of the renin-angiotensin system, plays important roles in the regulation of blood pressure, electrolyte homeostasis, and mammalian renal development. Transcription of renin genes is subject to complex developmental and tissue-specific regulation. Progress has been made recently in elucidating the molecular mechanisms involved in renin gene expression. Using mouse As4.1 cells, which have many features characteristic of the renin-expressing juxtaglomerular cells of kidney, a proximal promoter region (−197 to −50 bp) and an enhancer (−2866 to −2625 bp) have been identified in the mouse renin gene, Ren-1 c , that are critical for its expression. The proximal promoter region contains at least 7 transcription factor-binding sites, including a binding site for the products of Hox , developmental control genes. 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, to alter renin mRNA levels. Sequence highly homologous to the mouse enhancer is also found in the human and rat renin genes. How these regulatory regions function in vivo will be the focus of future study.

Enhancer-dependent inhibition of mouse renin transcription by inflammatory cytokines

Inflammatory cytokines have been shown to inhibit renin gene expression in the kidney in vivo and the kidney tumor-derived As4.1 cell line. In this report, we show that cytokines oncostatin M (OSM), IL-6, and IL-1beta inhibit transcriptional activity associated with 4.1 kb of the mouse renin 5'-flanking sequence in As4.1 cells. The 242-bp enhancer (-2866 to -2625 bp) is sufficient to mediate the observed inhibitory effects. Sequences within the enhancer required for inhibition by each of these cytokines have been determined by deletional and mutational analysis. Results indicate that a 39-bp region (CEC) containing a cAMP-responsive element, an E-box, and a steroid receptor-binding site, previously identified as the most critical elements for enhancer activity, is sufficient for the inhibition induced by IL-1beta. However, mutation of each of the three component sites does not abolish the inhibition by IL-1beta, suggesting that the target(s) of cytokine action may not be the transcription factors binding directly to these sites. This CEC region is also critical, but not sufficient, for the inhibition mediated by OSM and IL-6. These data suggest that the direct target of the associated cytokines may be coactivators interacting with transcription factors binding at the enhancer. Finally, we show that OSM treatment caused a 17-fold increase in promoter activity when only 2,625 bp of the Ren-1(c) flanking sequence were tested, in which the enhancer is not present. Three regions including -2625 to -1217 bp, the HOX.PBX binding site at -60 bp, and -59 to +6 bp have been found to contribute to this induction.

NFI-C2 negatively regulates α-sarcoglycan promoter activity in C2C12 myoblasts

alpha-Sarcoglycan striated muscle-specific protein is a member of the sarcoglycan-sarcospan complex. Positive and negative transcriptional regulation of sarcoglycan genes are important in sarcoglycan's intracellular localization and sarcolemmal stability. In the present work we assessed the function of NFI transcription factors in the regulation of alpha-sarcoglycan promoter through the C2C12 cell line differentiation. NFI factors act alternatively as activators and negative modulators of alpha-sarcoglycan promoter activity. In myoblasts NFI-A1.1 and NFI-B2 are activators, whereas NFI-C2 and NFI-X2 are negative regulators. In myotubes, all NFI members are activators, being NFI-C2 the less potent. We identified the alpha-sarcoglycan promoter NFI-C2 response element by testing progressive deletion constructs and point mutations in C2C12 cells over-expressing NFI-C2. Gel-shift and chromatin immunoprecipitation experiments demonstrated that NFI factors are indeed interacting in vitro and in vivo with the binding sequence. These results suggest a NFI role in C2C12 cell differentiation.

Differential expression of the closely linked KISS1, REN, and FLJ10761 genes in transgenic mice

We previously reported the development and characterization of transgenic mice containing a large 160-kb P1 artificial chromosome (PAC) encompassing the renin (REN) locus from human chromosome 1. Here we demonstrate that PAC160 not only encodes REN, but also complete copies of the next upstream (KISS1) and downstream ( FLJ10761 ) gene along human chromosome 1. Incomplete copies of the second upstream (PEPP3) and downstream (SOX13) genes are also present. The gene order PEPP3-KISS1-REN-FLJ10761-SOX13 is conserved in mice containing either one or two copies of the REN locus. Despite the close localization of KISS1, REN, and FLJ10761 , they each exhibit distinct, yet overlapping tissue-specific expression profiles in humans. The tissue-specific expression patterns of REN and FLJ10761 were retained in transgenic mice containing PAC160. Expression of REN and FLJ10761 were also proportional to copy number. Expression of KISS1 in PAC160 mice showed both similarities and differences to humans. These data suggest that expression of gene blocks encoded on large genomic clones are retained when the clones are used to generate transgenic mice. Genomic elements which act to insulate genes from their neighbors are also apparently retained.

Identification of a novel region in the proximal promoter of the mouse renin gene critical for expression

An enhancer at -2.6 kb and a HOX.PBX-binding site at -60 bp have been demonstrated to be critical to expression of the mouse renin gene (Ren-1(c)) in As4.1 cells. In this report, we show that a region (-197 to -70) immediately 5' to the HOX.PBX-binding site is also critical for Ren-1(c) expression. Deletion of this region in a construct containing 4.1 kb of the Ren-1(c) 5'-flanking sequence resulted in a 99% reduction in Ren-1(c) promoter activity in As4.1 cells, suggesting the pivotal role for the region in the regulation of the mouse renin gene. Electrophoretic mobility shift and supershift assays have identified two nuclear factor I-binding sites and a Sp1/Sp3-binding site within the distal portion of the region (-197 to -103). Mutation of these three sites caused a 90% decrease in Ren-1(c) promoter activity. Mutational analysis and electrophoretic mobility shift assays have also identified three additional transcription factor-binding sites within the region from -103 to -69, each of which contributes to high-level expression of Ren-1(c) in As4.1 cells. Finally, we have shown that the Ren-1(c) enhancer is the target for endothelin-1 (ET-1)-induced inhibition of Ren-1(c) expression and the transcription factor-binding sites in the proximal promoter are required for the maximal ET-1 inhibitory effect.