Identification of negative and positive regulatory elements in the human renin gene

Renin and the IGFII/M6P receptor system in cardiac biology

Nonenzymatic cardiac activities of renin are well described during the last years and contribute either to cardiac-specific effects of the renin-angiotensin-aldosterone-system (RAAS) or to the pharmacological effects of RAAS inhibition. The interaction of renin with insulin-like growth factor II/mannose-6-phosphate (IGFII/M6P) receptors participates in nonclassical renin effects and contributes to cardiac remodelling caused by RAAS activation. The current findings suggest an important role for renin IGFII/M6P receptor interaction in cardiac adaptation to stress and support the idea that excessive accumulation of renin during inhibition of RAAS directly contributes to blood pressure-independent effects of these pharmacological interventions. It becomes a challenge for future studies focussing on chronic hypertension or myocardial infarction to comprise regulatory adaptations of the kidney, the main source of plasma renin and prorenin, because they directly contribute to key steps in regulation of cardiac (mal)adaptation via IGFII/M6P receptors. This receptor system is part of peptide/receptor interactions that modifies and possibly limits adverse remodelling effects caused by angiotensin II. Evaluation of interactions of renin with other pro-hypertrophic agonists is required to decide whether this receptor may become a target of pharmacological intervention.

Chicken ovalbumin upstream promoter transcription factor II regulates renin gene expression

This study aimed to investigate the possible involvement of the orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) in the regulation of renin gene expression. COUP-TFII colocalized with renin in the juxtaglomerular cells of the kidney, which are the main source of renin in vivo. Protein-DNA binding studies demonstrated that COUP-TFII binds to an imperfect direct repeat COUP-TFII recognition sequence (termed hereafter proxDR) in the proximal renin promoter. Because cAMP signaling plays a central role in the control of the renin gene expression, we suggested that COUP-TFII may modulate this cAMP effect. Accordingly, knockdown of COUP-TFII in the clonal renin-producing cell lines As4.1 and Calu-6 diminished the stimulation of the renin mRNA expression by cAMP agonists. In addition, the mutation of the proxDR element in renin promoter reporter gene constructs abrogated the inducibility by cAMP. The proxDR sequence was found to be necessary for the function of a proximal renin promoter cAMP-response element (CRE). Knockdown of COUP-TFII or cAMP-binding protein (CREB), which is the archetypal transcription factor binding to CRE, decreased the basal renin gene expression. However, the deficiency of COUP-TFII did not further diminish the renin expression when CREB was knocked down. In agreement with the cell culture studies, mutant mice deficient in COUP-TFII have lower renin expression than their control strain. Altogether our data show that COUP-TFII is involved in the control of renin gene expression.

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.

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 ).

Mesenchymal stem cells differentiate into renin-producing juxtaglomerular (JG)-like cells under the control of liver X receptor-alpha

Renin is a key enzyme for cardiovascular and renal homeostasis and is produced by highly specialized endocrine cells in the kidney, known as juxtaglomerular (JG) cells. The nature and origin of these cells remain as mysteries. Previously, we have shown that the nuclear hormone receptor liver X receptor-alpha (LXRalpha) is a major transcriptional regulator of the expression of renin, c-myc, and other genes involved with growth/differentiation. In this study we test the hypothesis that LXRalpha plays an important role not only in renin expression but also in renin-containing cell differentiation, specifically from the mesenchymal stem cell (MSC), which may be the origin of the JG cell. Indeed, our data demonstrated that LXRalpha activation by its ligands or cAMP stimulated renin gene expression in both murine and human MSCs. Furthermore, sustained cAMP stimulation of murine MSCs overexpressing LXRalpha led to their differentiation into JG-like cells expressing renin and alpha-smooth muscle actin. These MSC-derived JG-like cells contained renin in secretory granules and released active renin in response to cAMP. In conclusion, the activation of LXRalpha stimulates renin expression and induces MSCs differentiation into renin-secreting, JG-like cells. Our results suggest that the MSC may be the origin of the juxtaglomerular cell and provide insight into novel understanding of pathophysiology of the renin-angiotensin system.

A proximal direct repeat motif characterized as a negative regulatory element in the human renin gene

The regulation of renin gene expression is thought to be fundamental to regulation of the total renin-angiotensin system. The human renin gene contains a direct repeat (DR) motif AGGGGTCAC-AGGGCCA in the proximal region (-259/-245 bp), which contains similar sequence for nuclear receptor superfamily binding core motif, AGGTCA, and is the most similar to COUP-TFII consensus. The DR motif was evaluated as a functional cis-element with renal cortex and chorio-decidual cells by footprint assay, electromobility shift assay (EMSA) and reporter assay. The DR motif site was protected by footprint analysis with a clear hypersensitive and a minor hypersensitive region in good accordance with the DR of the consensus. One of the binding proteins was strongly suspected to be COUP-TFII-consensus-specific by EMSA. The DNA/protein complexes obtained with nuclear extract of renin producing cells could be completely blocked by homologous competitor and strongly blocked by the second-half mutant oligonucleotide of the DR motif but not by the first-half mutant oligonucleotide. Finally, the transcriptional activity of second-half mutant construct is slightly elevated and that first-half mutant construct is significantly stronger by twofold compared with wild type construct in reporter assay. These findings suggest that the DR motif site of the human renin gene functions as a negative regulatory element involved in a twofold repression of transcription and that member(s) of nucleic receptor superfamily bind the site and play important roles in the human renin gene expression with a possibility that one of the binding protein is COUP-TFII.

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.

Nuclear receptor LXRalpha is involved in cAMP-mediated human renin gene expression

The cAMP-signaling pathway plays a crucial role in the regulation of the renin gene, but the mechanism involved remains poorly understood. We have focused our studies of renin gene regulation on the unique cAMP responsive element (huREN/CNRE, -135 to -107) in the human renin promoter. We have cloned a protein that binds to this unique CNRE and demonstrated that this protein is liver X receptor-alpha (LXRalpha), a transcriptional factor of the nuclear receptor family. Transient expression of LXRalpha in human renin-producing Calu-6 cells increased cAMP inducibility of human renin promoter. Similarly, LXRalpha-stably transfected Calu-6 cells exhibited increased cAMP inducibility of renin promoter as well as the endogenous renin gene. Site-directed mutation of huREN/CNRE, which disrupted LXRalpha binding, decreased cAMP-induced transcriptional activity of human renin promoter. Furthermore, we demonstrated that the binding of LXRalpha derived from human juxtaglomerular cells, the main production site of renin in the kidney, to the huREN/CNRE in vivo. These results suggest that LXRalpha plays an important role in the cAMP-mediated regulation of human renin gene transcription by binding to CNRE.

Identification of a novel set of genes regulated by a unique liver X receptor-alpha -mediated transcription mechanism

We have reported previously that liver X receptor-alpha (LXRalpha) can mediate a novel cAMP-dependent increase in renin and c-myc gene transcription by binding as a monomer to a unique regulatory element termed the cAMP-negative response element (CNRE). To determine whether this novel action of LXRalpha has global implications on gene regulation, we employed expression profiling to identify other genes regulated by this unique mechanism. Here we report the existence of a set of known and unknown transcripts regulated in parallel with renin. Querying the Celera Mouse Genome Assembly revealed that a majority of these genes contained the consensus CNRE. We have confirmed the functionality of these CNREs by competition for LXRalpha binding via electrophoretic mobility shift assays (EMSA) and by the use of CNRE decoy molecules documenting the abolishment of the cAMP-mediated gene induction. Taken together, these results demonstrate that the interaction between cAMP-activated LXRalpha and the CNRE enhancer element is responsible for widespread changes in gene expression and identify a set of LXRalpha/cAMP-regulated genes that may have important biological implications.

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.

LXRalpha functions as a cAMP-responsive transcriptional regulator of gene expression

LXRalpha is a member of a nuclear receptor superfamily that regulates transcription. LXRalpha forms a heterodimer with RXRalpha, another member of this family, to regulate the expression of cholesterol 7alpha-hydroxylase by means of binding to the DR4-type cis-element. Here, we describe a function for LXRalpha as a cAMP-responsive regulator of renin and c-myc gene transcriptions by the interaction with a specific cis-acting DNA element, CNRE (an overlapping cAMP response element and a negative response element). Our previous studies showed that renin gene expression is regulated by cAMP, at least partly, through the CNRE sequence in its 5'-flanking region. This sequence is also found in c-myc and several other genes. Based on our cloning results using the yeast one-hybrid system, we discovered that the mouse homologue of human LXRalpha binds to the CNRE and demonstrated that it binds as a monomer. To define the function of LXRalpha on gene expression, we transfected the renin-producing renal As4.1 cells with LXRalpha expression plasmid. Overexpression of LXRalpha in As4.1 cells confers cAMP inducibility to reporter constructs containing the renin CNRE. After stable transfection of LXRalpha, As4.1 cells show a cAMP-inducible up-regulation of renin mRNA expression. In parallel experiments, we demonstrated that LXRalpha can also bind to the homologous CNRE in the c-myc promoter. cAMP promotes transcription through c-myc/CNRE:LXRalpha interaction in LXRalpha transiently transfected cells and increases c-myc mRNA expression in stably transfected cells. Identification of LXRalpha as a cAMP-responsive nuclear modulator of renin and c-myc expression not only has cardiovascular significance but may have generalized implication in the regulation of gene transcription.

Association of some potential hormone response elements in human genes with the Alu family repeats

Short interspersed repeats of the Alu family located in promoters of some human genes contain high-affinity binding sites for thyroid hormone receptor, retinoic acid receptor and estrogen receptor. The standard binding sites for the receptors represent variants of duplicated AGGTCA motif with different spacing and orientation (direct, DR, or inverted, IR), and Alu sequences were found to have functional DR-4, DR-2 or variant IR-3/IR-17 elements. In this study we analyzed distribution and abundance of the elements in a set of human genomic sequences from GenBank and their association with Alu repeats. Our results indicate that a major fraction of potentially active DR-4, DR-2 and variant IR-3/IR-17 elements in the genes is located within Alu repeats. Alu-associated DR-2 elements are conserved in primate evolution. However, very few Alu have potential DR-3 glucocorticoid-response elements. Gel-shift experiments with the probe (AUB) corresponding to the consensus Alu sequence just upstream of the RNA polymerase III promoter B-box and containing duplicated AGGTCA motif indicate that the probe interacts in a sequence-specific manner with human nuclear proteins which bind to standard IR-0, DR-1, DR-4 or DR-5 elements. The AUB sequence was also able to promote thyroid hormone-dependent trans-activation of a reporter gene. The results support the view that Alu retroposons played an important role in evolution of regulation of the primate gene expression by nuclear hormone receptors.

Developmental changes in renal renin mRNA half-life and responses to stimulation in fetal lambs

In the perinatal period there is increased renin gene expression in the kidney compared with other stages of development. This may be related to changes in responsiveness of the renin gene to stimulation and/or differences in renin mRNA stability as development progresses. To ascertain if either responsiveness or stability changes in fetal life, we studied renin mRNA levels in primary cultures of renal cortical cells obtained from fetal lamb kidneys at two stages (0.7 and 0.9) of gestation after stimulation with isoproterenol, forskolin, or isobutyl methylxanthine and after inhibition of transcription with actinomycin D. Forskolin and isobutyl methylxanthine rapidly increased renin mRNA by at least twofold in the cultured cells from fetuses of both ages, with the sensitivity to stimulation higher in the cells from the mature fetal kidneys. Isoproterenol was effective only in mature fetal cells. In addition, the decay of renin mRNA after cessation of transcription was slower in mature cells compared with immature cells, the half-life being 11.6 +/- 0.8 h in mature cells and 6.6 +/- 0.6 h in immature cells (P < 0.05). The data suggest that increases in both renin mRNA sensitivity to stimulation and in stability can contribute to the enhanced renin expression in the perinatal period.

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.

Regulation of human renin gene promoter activity: a new negative regulatory region determines the responsiveness to TNF alpha

BACKGROUND

The renin-angiotensin system has been known to regulate blood pressure and body fluid homeostasis. Several lines of evidence have shown that renin gene expression and release are up-regulated by beta-adrenergic stimulation, sodium depletion, and angiotensin converting enzyme inhibition, but down-regulated by cytokines. To further characterize the human renin gene (hREN) promoter structure, its regulation, and to identify an appropriate cell system for study, we examined five cell lines and investigated drug effects on the hREN promoter expression.

METHODS

Using the hREN-luciferase reporter gene constructs in the DNA transfection assays, approximately 5 kb of the hREN 5' flanking region was assessed for promoter activity in five different cell lines. Regulation of the hREN promoter activity was investigated using Y-1 adrenal cells that were transfected with the hREN-luciferase DNA and were treated with forskolin, calcium ionophore A23187, phorbol ester, angiotensin II (Ang II), or cytokines.

RESULTS

Transient transfection analysis showed that the 5 kb hREN 5' flanking DNA alone was able to confer significant promoter activity in Y-1 adrenal cells. In transfected Y-1 cells, luciferase reporter expression was induced by forskolin, suppressed by the calcium ionophore A23187, and phorbol ester in a dose-dependent manner, but was unaffected by angiotensin II (Ang II). However, when Y-1 reporter cells were transfected with human angiotensin II receptor type 1 (AT1) cDNA, hREN promoter activity was dose-dependently down-regulated by Ang II, which was blockable by losartan, an AT1-selective antagonist. Further studies also showed that hREN promoter activity in Y-1 cells was selectively down-regulated by TNF alpha. Deletion of the hREN promoter sequences between position -3916 and -2822 not only enhanced hREN promoter activity by approximately tenfold, but also caused a failure of down-regulation by TNF alpha. In contrast, neither interleukin (IL)-1 alpha, IL-1 beta, IL-2, nor IL-6 exerted any significant effect.

CONCLUSIONS

Together the results suggest that TNF alpha is a negative regulator of the hREN expression in the adrenal cells, and that the TNF alpha responsiveness may be controlled by elements located between the positions -3916 and -2822 of the hREN promoter. Moreover, the Y-1 cell line may provide a valuable model system for studying renin gene regulation.

Identification of a novel inhibitor of mitogen-activated protein kinase kinase

The compound U0126 (1,4-diamino-2,3-dicyano-1, 4-bis[2-aminophenylthio]butadiene) was identified as an inhibitor of AP-1 transactivation in a cell-based reporter assay. U0126 was also shown to inhibit endogenous promoters containing AP-1 response elements but did not affect genes lacking an AP-1 response element in their promoters. These effects of U0126 result from direct inhibition of the mitogen-activated protein kinase kinase family members, MEK-1 and MEK-2. Inhibition is selective for MEK-1 and -2, as U0126 shows little, if any, effect on the kinase activities of protein kinase C, Abl, Raf, MEKK, ERK, JNK, MKK-3, MKK-4/SEK, MKK-6, Cdk2, or Cdk4. Comparative kinetic analysis of U0126 and the MEK inhibitor PD098059 (Dudley, D. T., Pang, L., Decker, S. J., Bridges, A. J., and Saltiel, A. R. (1995) Proc. Natl. Acad. Sci U. S. A. 92, 7686-7689) demonstrates that U0126 and PD098059 are noncompetitive inhibitors with respect to both MEK substrates, ATP and ERK. We further demonstrate that the two compounds bind to deltaN3-S218E/S222D MEK in a mutually exclusive fashion, suggesting that they may share a common or overlapping binding site(s). Quantitative evaluation of the steady state kinetics of MEK inhibition by these compounds reveals that U0126 has approximately 100-fold higher affinity for deltaN3-S218E/S222D MEK than does PD098059. We further tested the effects of these compounds on the activity of wild type MEK isolated after activation from stimulated cells. Surprisingly, we observe a significant diminution in affinity of both compounds for wild type MEK as compared with the deltaN3-S218E/S222D mutant enzyme. These results suggest that the affinity of both compounds is mediated by subtle conformational differences between the two activated MEK forms. The MEK affinity of U0126, its selectivity for MEK over other kinases, and its cellular efficacy suggest that this compound will serve as a powerful tool for in vitro and cellular investigations of mitogen-activated protein kinase-mediated signal transduction.

The human placental renin-angiotensin system

The human placenta and related tissues are considered to be examples of the recently accepted local renin-angiotensin systems (RAS). The brain is another example of a system that is thought to be regulated independently of the kidney and the role of angiotensin within the CNS as a neural mediator has drawn considerable attention. It has been known for a long time that many of the neuroendocrine mediators and receptors are expressed in the placenta and it has been suggested that there are many parallels between the classical neuroendocrine system and the placental one. The present review summarizes information that components of the RAS are expressed in uteroplacental tissues, are regulated by endogenous substances, and have important biological functions within this reproductive system. A comparison of similarities and differences between the classical and the placental RAS may provide clues to functions in other endocrine and neuroendocrine systems. The major components of the placental RAS that are considered are renin, prorenin, angiotensin I, angiotensin II, angiotensin converting enzyme (ACE), angiotensin receptors, and angiotensinogen (renin substrate). The factors that regulate these components at the cellular and the nuclear level are described. It is concluded that prorenin via angiotensin-dependent and angiotensin-independent mechanisms influences functions within uteroplacental tissues. Some of these actions are direct and others are mediated by the release of different signalling molecules. These features are similar to many neuroendocrine systems and utilize some of the same messengers.

A novel proximal element mediates the regulation of mouse Ren-1C promoter by retinoblastoma protein in cultured cells

The protein product of the retinoblastoma susceptibility gene, RB, is a nuclear phosphoprotein that modulates transcription of genes involved in growth control via interactions with transcription factors. Renin is a rate-limiting enzyme of the renin-angiotensin system that regulates blood pressure and water-electrolyte balance. Renin gene expression is regulated in a tissue-specific and developmentally linked manner. Similarly, the expression of RB is controlled in a differentiation-linked manner. Thus, to investigate whether RB is involved in the regulation of renin gene expression, we examined the effects of RB on transcriptional activity of the mouse renin (Ren-1C) promoter. The Ren-1C promoter contains two transcriptionally important elements; the RU-1 (-224 to -138) and RP-2 (-75 to -47) elements. RB activated the Ren-1C promoter in human embryonic kidney cells. The promoter element responsible for RB-mediated transcriptional regulation was the RP-2 element. The results of DNA-protein binding experiments showed that RB increased nuclear binding activity to the RP-2 element, and site-directed mutation which disrupted binding of nuclear factors to the RP-2 element markedly reduced RB-mediated activation of Ren-1C promoter in human embryonic kidney cells. These results indicate that the RP-2 element plays an important role in RB-mediated transcriptional regulation of Ren-1C promoter activity in human embryonic kidney cells, thereby suggesting an interesting mechanism by which RB may modulate the renin-angiotensin system.

Transactivation of the human renin promoter by the cyclic AMP/protein kinase A pathway is mediated by both cAMP-responsive element binding protein-1 (CREB)-dependent and CREB-independent mechanisms in Calu-6 cells

We examined the DNA sequence and transcription factor requirements for cAMP-induced transactivation of the human renin promoter using Calu-6 cells that express human renin mRNA endogenously. A series of constructs containing 896 base pairs of human renin 5'-flanking DNA fused to the luciferase gene and containing either the native, a consensus, or a nonfunctional cAMP response element (CRE) were used to assess DNA sequence requirements mediating the cAMP response. Expression vectors encoding the CREB-1 transcription factor, a dominant negative mutant form of CREB-1, and the catalytic subunit of protein kinase A (PKA) were used to assess transcription factor requirements mediating the cAMP response. Forskolin treatment alone only caused a 2-3-fold activation of the HREN promoter in Calu-6 cells, but nearly a 10-fold activation in JEG-3 cells, which do not express renin but are highly responsive to cAMP. Gel shift assays revealed the binding of five specific DNA-protein complexes consisting of the ATF-1 and CREB-1 transcription factors, one of which was an ATF-1.CREB-1 heterodimer suggesting the potential for regulation of CREB-1 activity by ATF-1. However, over-expression of CREB-1 did not significantly enhance forskolin-induced human renin transcriptional activity. Transfection of both Calu-6 and JEG-3 cells with a PKA expression vector resulted in a 10-fold induction of human renin transcriptional activity in constructs containing the native or consensus CRE and 5-fold activation in a construct containing a nonfunctional CRE. We confirmed that the PKA response has both a CREB-dependent and CREB-independent component by demonstrating that the PKA response was abolished by co-transfection of a dominant negative mutant form of CREB-1 into cells containing the native or consensus CRE construct but not in cells containing the nonfunctional CRE construct. We therefore conclude that the human renin promoter can be transcriptionally activated in a renin expressing cell line through the cAMP-PKA pathway and is mediated by both a CREB-dependent and CREB-independent mechanism.

In vivo gene transfer and gene modulation in hypertension research

Transgenic technologies and homologous recombination approaches have been useful for studying the roles of specific genes in systemic hypertension. Recently, we and others have introduced the use of in vivo gene transfer to study the effects of local gene overexpression or inactivation in hypertension. Using in vivo gene transfer for the blood vessel, we have documented the direct hypertrophic action of local angiotensin and the growth-inhibitory effect of nitric oxide. In vivo gene transfer is also an effective method for discovering the unknown functions of a newly cloned gene. Using this approach, we identified the in vivo growth-inhibitory action of the angiotensin II type 2 receptor. In addition, we have developed a novel strategy using transcriptional factor "decoy" oligonucleotides to regulate the interaction of cis- and trans-acting factors involved in the modulation of gene expression in vivo. Thus, the decoy approach can "switch" on or off specific genes in selective tissues in vivo, thereby influencing local gene expression and tissue function. For example, using decoy oligonucleotides, we have "turned on" renin gene expression in the rat liver, in which it is usually not expressed, resulting in increased hepatic and plasma renin levels. Thus, in vivo gene transfer technology provides us with a new tool for in vivo characterization of genes involved in hypertension that has potential application in human therapy.

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.

Molecular basis of human hypertension: the role of angiotensin

On the basis of recent advances in molecular biology and statistical genetics, it has become possible to search for chromosome regions that contain genes predisposing to hypertension and to directly link specific mutations on candidate genes to hypertension. As the human genome has been extensively mapped, highly informative, polymorphic markers are available, which can be used to detect genes in their proximity with 'hypertensinogenic' alleles. Some of these markers have been shown to be tightly linked to the genes of the renin-angiotensin system. Furthermore, the coding and regulatory regions of the genes encoding for renin, ACE, angiotensinogen and the AT1 receptor have been partially characterized. This provides a basis for further definition of specific polymorphisms within these genes that are of functional importance and that can be used to examine their contribution to the inheritance of primary hypertension. The first studies of these links have already emerged and have been reviewed in this article. Several problems arise in performing such linkage studies in human primary hypertension, however. It is difficult to define the genetic background of heterogeneous, multigenetic and multifactorial diseases such as human hypertension. Extensive studies of population genetics, including the analysis of large numbers of generations and controlled breeding experiments, cannot be performed, for obvious reasons. Blood pressure is not a convenient study trait, because it exhibits great intraindividual variance and also because of the relatively low reliability of just a few indirect measurements obtained under loosely controlled environmental conditions. Twenty-four-hour ambulatory blood pressure measurements may improve such investigations in the near future. Ravogli et al (1990) reported that the 24-hour ambulatory systolic blood pressure is higher in normotensive subjects of hypertensive parents than in normotensive subjects of normotensive parents--a finding that had not been previously reported using the conventional method of measurement. Hypertension as a trait per se is also problematic: its classification (above 140/90 mmHg) is purely artefactual, and its aetiology is highly heterogeneous. Thus, we have to keep in mind that even strong gene effects, if present in only a small subgroup of hypertensives, may not be detected in these studies. Attempts are being made to strengthen the analysis by characterizing physiologically distinct subgroups. In addition, the investigation of intermediate phenotypes, such as plasma parameters, which are more reliable and less subject to variations, may be helpful.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Endogenous human renin expression and promoter activity in CALU-6, a pulmonary carcinoma cell line

We have previously reported that transgenic mice containing the human renin gene express high levels of human renin mRNA in the lung. We show in this report that human renin expression in two lines of transgenic mice is developmentally regulated. Human renin expression is not evident in the transgenic mouse lung at 15.5 days of gestation, is detectable at 17.5 days of gestation, peaks around birth, and remains elevated into adulthood. In situ hybridization of mouse fetal lung samples at 18.5 days of gestation revealed that human renin was exclusively expressed in pulmonary type II epithelial cells. A survey of the medical literature revealed a number of clinical cases in which hypertension was caused by renin-secreting pulmonary tumors and a fairly widespread occurrence of immunoreactive renin in banked pulmonary tumors of diverse origin. This prompted us to examine a number of pulmonary tumor cell lines to determine whether they express human renin mRNA. One pulmonary carcinoma cell line, CALU-6, expressed human renin mRNA endogenously. Human renin expression in these cells was induced approximately 100-fold after treatment with forskolin, 8-bromoadenosine 3':5'-cyclic monophosphate, or N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate. Transfection analysis of human renin promoter-luciferase fusion constructs revealed the presence of cell-specific positive and negative regulatory elements in the human renin 5'-flanking DNA. This cell line is the only immortalized human cell line that expresses high levels of endogenous human renin mRNA and should provide an excellent tool for studying the regulation of human renin expression in vitro.

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.

Transcriptional silencer in intron I of the rat renin gene

In the present study we investigated the influence of intron I of the rat renin gene on the transcriptional activity of its promoter in cell culture. The presence of intron I abolished the transcription of reporter genes (luciferase and lacZ) in the non-renin-expressing human embryonic kidney cell line 293, while it did not significantly affect the activity of the rat renin promoter in rat sceletal myoblast line L8 expressing renin. We conclude from these results that intron I of the rat renin gene contains a tissue-specific silencer element probably also responsible for the transcriptional repression of the endogeneous renin gene in 293 cells.

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.

Pituitary-specific transcription factor (Pit-1) binding site in the human renin gene 5'-flanking DNA stimulates promoter activity in placental cell primary cultures and pituitary lactosomatotropic cell lines

Renin gene expression is limited to a number of specific tissues, including the kidney, adrenal glands, reproductive organs (of particular relevance to this study, the placenta), and the pituitary gland. In the present study, we investigated the human renin (hRen) 5'-flanking DNA sequences required to drive the expression of a luciferase reporter gene in placental and pituitary cells and in two cell lines, 293 and JEG-3, which have been proposed as model systems with which to study transcriptional regulation of renin genes. The activities of specific sequences in the hRen 5'-flanking DNA sequences in human placental cell primary cultures were very similar to those that we previously reported in pituitary cells, suggesting the involvement of common promoter elements and related transcription factors. Accordingly, the binding site for the pituitary-specific transcription factor (Pit-1) was the major determinant of renin promoter activity in both pituitary and placental cells. Gel mobility shift analysis showed a placental nuclear factor with a gel mobility different from that of Pit-1. However, Northern blot analysis failed to demonstrate abundant Pit-1-related mRNAs in renin-expressing cultures of chorionic and decidual cells, suggesting that the placental factor is not closely related to Pit-1. Although a factor from 293 cells also bound to the Pit-1 site, it had gel mobility shift characteristics different from Pit-1 and the placental factor. Moreover, the low promoter activity in 293 cells was independent of this site or, indeed, of sequences upstream from the TATA box. In JEG-3 cells, renin 5'-flanking DNA sequences showed virtually no transcriptional activity.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Regulated tissue- and cell-specific expression of the human renin gene in transgenic mice

Transgenic mice containing the human renin gene were constructed with the aim of examining the tissue- and cell-specific expression of human renin. The human renin transgene used consisted of a genomic sequence extending approximately 900 bp upstream and 400 bp downstream of the coding region and included all exon and intron sequences. Two assays were developed to differentiate human renin transcripts from endogenous mouse renin transcripts at the whole-tissue level. High level human renin expression was evident in the kidney, adrenal gland, ovary, testis, lung, and adipose tissue of all four transgenic lines examined. Human renin mRNA could also be detected at lower levels in the submandibular gland and heart of two different individual lines. No expression was evident in the liver or brain of any line tested. In situ hybridization revealed the human renin mRNA to be localized and exquisitely restricted to renal juxtaglomerular cells. Treatment of transgenic mice with captopril resulted in an increase in the accumulation of renal renin mRNAs derived from both the mouse and human renin genes. Plasma renin activity assays using synthetic human renin substrate clearly demonstrated the elaboration of active human renin into the systemic circulation of transgenic mice. These data strongly suggest that the human renin transgene exhibits both tissue- and cell-specific expression in transgenic mice. Its expression is entrained to the same regulatory signals as the endogenous renin gene in kidney, and active human renin is released into the plasma of the transgenic mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Strategies towards a transgenic model of essential hypertension

The generation of genetically modified animals by transgenic technology has proven to be a surprisingly versatile resource for researchers, providing an increasing number of new tools for biological investigation. As well as permitting the analysis of gene function and regulation in vivo, modifications of the techniques are being used to suppress or abolish the expression of specific genes, and further refinements have permitted the ablation of specific cell-types and the development of differentiated cell lines from tissue-specific tumours. In hypertension research, where many important questions have been frustratingly difficult to address by previously available methods, the advances afforded by transgenic studies have already been significant and are likely to be even more profound in the future. With the further development of these techniques, it may be possible to produce new and more representative models of essential hypertension.

Identification of a previously unrecognized production site of human renin

We found expression of the renin gene in the intestine of human, mouse and the transgenic mouse in which the 3' flanking sequences of the human renin gene function as a tissue-specific promoter. A cotransfection analysis showed that the promoter is activated by the product of adenovirus E1A 13S mRNA in cells originated from extrarenal tissues.

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

The influence on homologous and heterologous promoter activity of DNA extending 2.4 kb upstream of the human renin gene (REN) was examined by transient expression assay in JEG-3 cells, using the gene for chloramphenicol acetyl transferase (CAT) as reporter, and cotransfection with pCH110 to control for transfection efficiency. Analyses of constituent subfragments of the region 5' of residue -144, using the herpes simplex virus thymidine kinase (tk) promoter to drive transcription, provided no evidence for negative regulatory influences within the -2400 to -144 DNA. That distal 5'-flanking DNA may have little influence on promoter activity is further supported by a sharp decline in nucleotide homology between human, rat and mouse renin genes further upstream than human residue -604. Constructs containing renin DNA to residue +13, i.e., which retained the REN promoter, all displayed very low CAT activities, consistent with negative cis-acting control within the -149 to +13 region. This finding contrasts with results of similar studies for mouse, in which renin gene control was suggested to be mediated primarily via cell-specific trans-acting activator(s) acting on yet-to-be identified enhancer(s). Mouse renin genes have, however, a common DNA insertion that could have disrupted the negative element in this region, and which might contain enhancer target(s) for trans-acting factor(s). In conclusion, the present study involving JEG-3 cells has demonstrated that distal human renin 5'-flanking DNA has little cis-acting influence on promoter activity, whereas DNA located within 100 base pairs of the renin promoter may have a negative regulatory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Purkinje cell protein-2 regulatory regions and transgene expression in cerebellar compartments

The Purkinje cell protein 2 (Pcp-2) is expressed in cerebellar Purkinje cells and retinal bipolar neurons. To illuminate how Pcp-2 expression is restricted to only two neuronal types and to derive tools to express heterologous genes in these neuronal subpopulations, genomic sequences of the mouse Pcp-2 gene have been cloned and flanking sequences have been evaluated as a source of neuron-specific regulatory elements. An upstream region with homology to other genes expressed in neurons was identified and a hybrid gene containing this sequence was constructed by ligating 0.4 kb of upstream and 0.3 kb of downstream Pcp-2-flanking DNA to lacZ. Transgenic mice bearing this construct exhibited beta-galactosidase in a wide array of neuron types, suggesting that this sequence may play an important role in specifying neuronal expression. Addition of a further 3.1 kb of Pcp-2 upstream sequences restricted expression of beta-galactosidase to a small number of neuron types and most notably to Purkinje cells within parasagitally oriented cerebellar compartments. The presence of elements lying within the 3.1-kb upstream region and acting to specifically restrict Pcp-2 expression is therefore suggested. Moreover, as beta-galactosidase was not expressed in the bipolar cells of these transgenic mice, retinal expression of the endogenous Pcp-2 gene must involve elements in addition to those conferring expression within Purkinje cells.

Molecular biology of human renin and its gene

This article describes investigations of several aspects of the molecular biology of the human renin gene and the three-dimensional structure of renin and its precursor, prorenin. Because of the importance of the RAS in hypertension, heart failure, renal failure, and possibly other disorders such as atherosclerosis, it is critical to understand the detailed control of this system. This control involves regulation at the transcriptional level, folding of prorenin, sorting of prorenin to a regulated pathway where it is proteolytically cleaved to renin and released in response to secretogogues, constitutive release of uncleaved prorenin, and nonproteolytic activation of prorenin. Currently there is great interest not only in the control of renin in the kidney, the sole source of circulating renin, but also at extrarenal sites where RAS activity may regulate cardiovascular functions. The renin gene was found to be expressed significantly in the renal juxtaglomerular cells and several other cell types. Most tissue culture cells did not express the gene; exceptions were cultured SK-LMS-1 cells and cAMP-stimulated human lung fibroblasts. Cultured human uterine-placental cells expressed the human renin gene at levels higher than in other cell types assessed. Renin mRNA had the same start site in the placental cells as the kidney and was regulated by calcium ionophores and cAMP. Thus, these cells provide primary nontransformed human cells to study the homologous human promoter. Transfected renin promoters showed cell type-specific expression and cAMP responsiveness in these cells in constructs containing as few as 102 bp of 5'-flanking DNA. DNA upstream from this appears to contain an inhibitory element(s) that may have some tissue specificity in its distribution. The cAMP response is not due to cAMP induction of a transcription factor that secondarily affects the renin promoter. A novel element may be involved, since the promoter does not contain a CRE element that mediates many cAMP responses, and the cells do not appear to respond to another known cAMP-responsive transcription factor, AP-2. Studies with transfected vectors expressing a mutant cAMP-responsive protein kinase A regulatory subunit suggest that cAMP is not responsible for basal renin promoter activity in the placental cells. By contrast, cAMP induces in essence gene activation in WI26VA4 transformed human lung fibroblasts in which renin mRNA levels increase by up to 150-fold in response to forskolin. Thus, cAMP may activate renin gene expression under certain circumstances and tissue-specific renin gene expression may be directed by more than one mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)