Genomic structure, organization, and promoter region analysis of murine guanylyl cyclase/atrial natriuretic peptide receptor-A gene

Guanylyl cyclase/natriuretic peptide receptor-A: Identification, molecular characterization, and physiological genomics

The natriuretic peptides (NPs) hormone family, which consists mainly of atrial, brain, and C-type NPs (ANP, BNP, and CNP), play diverse roles in mammalian species, ranging from renal, cardiac, endocrine, neural, and vascular hemodynamics to metabolic regulations, immune responsiveness, and energy distributions. Over the last four decades, new data has transpired regarding the biochemical and molecular compositions, signaling mechanisms, and physiological and pathophysiological functions of NPs and their receptors. NPs are incremented mainly in eliciting natriuretic, diuretic, endocrine, vasodilatory, and neurological activities, along with antiproliferative, antimitogenic, antiinflammatory, and antifibrotic responses. The main locus responsible in the biological and physiological regulatory actions of NPs (ANP and BNP) is the plasma membrane guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), a member of the growing multi-limbed GC family of receptors. Advances in this field have provided tremendous insights into the critical role of Npr1 (encoding GC-A/NPRA) in the reduction of fluid volume and blood pressure homeostasis, protection against renal and cardiac remodeling, and moderation and mediation of neurological disorders. The generation and use of genetically engineered animals, including gene-targeted (gene-knockout and gene-duplication) and transgenic mutant mouse models has revealed and clarified the varied roles and pleiotropic functions of GC-A/NPRA in vivo in intact animals. This review provides a chronological development of the biochemical, molecular, physiological, and pathophysiological functions of GC-A/NPRA, including signaling pathways, genomics, and gene regulation in both normal and disease states.

Ligand-Dependent Downregulation of Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Role of miR-128 and miR-195

Cardiac hormones act on the regulation of blood pressure (BP) and cardiovascular homeostasis. These hormones include atrial and brain natriuretic peptides (ANP, BNP) and activate natriuretic peptide receptor-A (NPRA), which enhance natriuresis, diuresis, and vasorelaxation. In this study, we established the ANP-dependent homologous downregulation of NPRA using human embryonic kidney-293 (HEK-293) cells expressing recombinant receptor and MA-10 cells harboring native endogenous NPRA. The prolonged pretreatment of cells with ANP caused a time- and dose-dependent decrease in ¹²⁵I-ANP binding, Guanylyl cyclase (GC) activity of receptor, and intracellular accumulation of cGMP leading to downregulation of NPRA. Treatment with ANP (100 nM) for 12 h led to an 80% decrease in ¹²⁵I-ANP binding to its receptor, and BNP decreased it by 62%. Neither 100 nM c-ANF (truncated ANF) nor C-type natriuretic peptide (CNP) had any effect. ANP (100 nM) treatment also decreased GC activity by 68% and intracellular accumulation cGMP levels by 45%, while the NPRA antagonist A71915 (1 µM) almost completely blocked ANP-dependent downregulation of NPRA. Treatment with the protein kinase G (PKG) stimulator 8-(4-chlorophenylthio)-cGMP (CPT-cGMP) (1 µM) caused a significant increase in ¹²⁵I-ANP binding, whereas the PKG inhibitor KT 5823 (1 µM) potentiated the effect of ANP on the downregulation of NPRA. The transfection of miR-128 significantly reduced NPRA protein levels by threefold compared to control cells. These results suggest that ligand-dependent mechanisms play important roles in the downregulation of NPRA in target cells.

Angiotensin II represses Npr1 expression and receptor function by recruitment of transcription factors CREB and HSF-4a and activation of HDACs

The two vasoactive hormones, angiotensin II (ANG II; vasoconstrictive) and atrial natriuretic peptide (ANP; vasodilatory) antagonize the biological actions of each other. ANP acting through natriuretic peptide receptor-A (NPRA) lowers blood pressure and blood volume. We tested hypothesis that ANG II plays critical roles in the transcriptional repression of Npr1 (encoding NPRA) and receptor function. ANG II significantly decreased NPRA mRNA and protein levels and cGMP accumulation in cultured mesangial cells and attenuated ANP-mediated relaxation of aortic rings ex vivo. The transcription factors, cAMP-response element-binding protein (CREB) and heat-shock factor-4a (HSF-4a) facilitated the ANG II-mediated repressive effects on Npr1 transcription. Tyrosine kinase (TK) inhibitor, genistein and phosphatidylinositol 3-kinase (PI-3K) inhibitor, wortmannin reversed the ANG II-dependent repression of Npr1 transcription and receptor function. ANG II enhanced the activities of Class I histone deacetylases (HDACs 1/2), thereby decreased histone acetylation of H3K9/14ac and H4K8ac. The repressive effect of ANG II on Npr1 transcription and receptor signaling seems to be transduced by TK and PI-3K pathways and modulated by CREB, HSF-4a, HDACs, and modified histones. The current findings suggest that ANG II-mediated repressive mechanisms of Npr1 transcription and receptor function may provide new molecular targets for treatment and prevention of hypertension and cardiovascular diseases.

Transforming growth factor β1 antagonizes the transcription, expression and vascular signaling of guanylyl cyclase/natriuretic peptide receptor A - role of δEF1

The objective of this study was to determine the role of transforming growth factor β1 (TGF-β1) in transcriptional regulation and function of the guanylyl cyclase A/natriuretic peptide receptor A gene (Npr1) and whether cross-talk exists between these two hormonal systems in target cells. After treatment of primary cultured rat thoracic aortic vascular smooth muscle cells and mouse mesangial cells with TGF-β1, the Npr1 promoter construct containing a δ-crystallin enhancer binding factor 1 (δEF1) site showed 85% reduction in luciferase activity in a time- and dose-dependent manner. TGF-β1 also significantly attenuated luciferase activity of the Npr1 promoter by 62%, and decreased atrial natriuretic peptide-mediated relaxation of mouse denuded aortic rings ex vivo. Treatment of cells with TGF-β1 increased the protein levels of δEF1 by 2.4-2.8-fold, and also significantly enhanced the phosphorylation of Smad 2/3, but markedly reduced Npr1 mRNA and receptor protein levels. Over-expression of δEF1 showed a reduction in Npr1 promoter activity by 75%, while deletion or site-directed mutagenesis of δEF1 sites in the Npr1 promoter eliminated the TGF-β1-mediated repression of Npr1 transcription. TGF-β1 significantly increased the expression of α-smooth muscle actin and collagen type I α2 in rat thoracic aortic vascular smooth muscle cells, which was markedly attenuated by atrial natriuretic peptide in cells over-expressing natriuretic peptide receptor A. Together, the present results suggest that an antagonistic cascade exists between the TGF-β1/Smad/δEF1 pathways and Npr1 expression and receptor signaling that is relevant to renal and vascular remodeling, and may be critical in the regulation of blood pressure and cardiovascular homeostasis.

Endocytosis and Trafficking of Natriuretic Peptide Receptor-A: Potential Role of Short Sequence Motifs

The targeted endocytosis and redistribution of transmembrane receptors among membrane-bound subcellular organelles are vital for their correct signaling and physiological functions. Membrane receptors committed for internalization and trafficking pathways are sorted into coated vesicles. Cardiac hormones, atrial and brain natriuretic peptides (ANP and BNP) bind to guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and elicit the generation of intracellular second messenger cyclic guanosine 3',5'-monophosphate (cGMP), which lowers blood pressure and incidence of heart failure. After ligand binding, the receptor is rapidly internalized, sequestrated, and redistributed into intracellular locations. Thus, NPRA is considered a dynamic cellular macromolecule that traverses different subcellular locations through its lifetime. The utilization of pharmacologic and molecular perturbants has helped in delineating the pathways of endocytosis, trafficking, down-regulation, and degradation of membrane receptors in intact cells. This review describes the investigation of the mechanisms of internalization, trafficking, and redistribution of NPRA compared with other cell surface receptors from the plasma membrane into the cell interior. The roles of different short-signal peptide sequence motifs in the internalization and trafficking of other membrane receptors have been briefly reviewed and their potential significance in the internalization and trafficking of NPRA is discussed.

Coordinate control of adipose 'browning' and energy expenditure by β-adrenergic and natriuretic peptide signalling

The catecholamines and the adrenergic receptors have been long known to be vital components in the regulation of fat cell metabolism. Whether in response to stress, cold temperature or diet, the β-adrenergic receptors (βARs) respond to epinephrine/norepinephrine to activate a signalling cascade that drives triglyceride hydrolysis to free fatty acids for use as fuel for skeletal and cardiac muscle work. The βARs also are well-established activators of brown fat for the conversion of substrate energy to generate heat from the oxidation of glucose and fatty acids. Long thought to be irrelevant to the biology of adult humans, the realization that there is indeed functional brown fat in humans has now created great interest and enthusiasm over the possibility that recruiting brown fat to target obesity and metabolic disease could represent a viable therapeutic option. Coupled with newer evidence that various stimuli independent of the βARs may also be able to increase active brown adipocytes, including the cardiac natriuretic peptides, it is an exciting time to be working in this area. This review will focus on the catecholamines and natriuretic peptides as cooperative actors in promoting fat metabolism, and will consider areas in need of further research.

Genetically altered mutant mouse models of guanylyl cyclase/natriuretic peptide receptor-A exhibit the cardiac expression of proinflammatory mediators in a gene-dose-dependent manner

The objective of this study was to examine whether genetically determined differences in the guanylyl cyclase/natriuretic peptide receptor-A gene (Npr1) affect cardiac expression of proinflammatory cytokines, hypertrophic markers, nuclear factor-κB (NF-κB), and activating protein-1 (AP-1) in am Npr1 gene-dose-dependent manner. In the present studies, adult male Npr1 gene-disrupted (Npr1(-/-)), wild-type (Npr1(+/+)), and gene-duplicated (Npr1(++/++)) mice were used. The Npr1(-/-) mice showed 41 mm Hg higher systolic blood pressure and 60% greater heart weight to body weight (HW/BW) ratio; however, Npr1(++/++) mice exhibited 15 mm Hg lower systolic blood pressure and 12% reduced HW/BW ratio compared with Npr1(+/+) mice. Significant upregulation of gene expression of proinflammatory cytokines and hypertrophic markers along with enhanced NF-κB/AP-1 binding activities were observed in the Npr1(-/-) mouse hearts. Conversely, hypertrophic markers and proinflammatory cytokines gene expression as well as NF-κB/AP-1 binding activities were markedly decreased in Npr1(++/++) mouse hearts compared with wild-type mice. The ventricular guanylyl cyclase activity and cGMP levels were reduced by 96% and 87%, respectively, in Npr1(-/-) mice; however, these parameters were amplified by 2.8-fold and 3.8-fold, respectively, in Npr1(++/++) mice. Echocardiographic analysis revealed significantly increased fractional shortening in Npr1(++/++) mice (P < .05) but greatly decreased in Npr1(-/-) mice (P < .01) hearts compared with Npr1(+/+) mice. The present findings suggest that Npr1 represses the expression of cardiac proinflammatory mediators, hypertrophic markers, and NF-κB/AP-1-mediated mechanisms, which seem to be associated in an Npr1 gene-dose-dependent manner.

Histone deacetylase inhibitors modulate the transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-a gene: interactive roles of modified histones, histone acetyltransferase, p300, AND Sp1

Atrial natriuretic peptide (ANP) binds guanylyl cyclase-A/natriuretic peptide receptor-A (GC-A/NPRA) and produces the intracellular second messenger, cGMP, which regulates cardiovascular homeostasis. We sought to determine the function of histone deacetylases (HDACs) in regulating Npr1 (coding for GC-A/NPRA) gene transcription, using primary mouse mesangial cells treated with class-specific HDAC inhibitors (HDACi). Trichostatin A, a pan inhibitor, and mocetinostat (MGCD0103), a class I HDAC inhibitor, significantly enhanced Npr1 promoter activity (by 8- and 10-fold, respectively), mRNA levels (4- and 5.3-fold, respectively), and NPRA protein (2.7- and 3.5-fold, respectively). However, MC1568 (class II HDAC inhibitor) had no discernible effect. Overexpression of HDAC1 and HDAC2 significantly attenuated Npr1 promoter activity, whereas HDAC3 and HDAC8 had no effect. HDACi-treated cultured cells in vitro and intact animals in vivo showed significantly reduced binding of HDAC1 and -2 and increased accumulation of acetylated H3-K9/14 and H4-K12 at the Npr1 promoter. Deletional analyses of the Npr1 promoter along with ectopic overexpression and inhibition of Sp1 confirmed that HDACi-induced Npr1 gene transcription is accomplished by Sp1 activation. Furthermore, HDACi attenuated the interaction of Sp1 with HDAC1/2 and promoted Sp1 association with p300 and p300/cAMP-binding protein-associated factor; it also promoted the recruitment of p300 and p300/cAMP-binding protein-associated factor to the Npr1 promoter. Our results demonstrate that trichostatin A and MGCD0103 enhanced Npr1 gene expression through inhibition of HDAC1/2 and increased both acetylation of histones (H3-K9/14, H4-K12) and Sp1 by p300, and their recruitment to Npr1 promoter. Our findings define a novel epigenetic regulatory mechanism that governs Npr1 gene transcription.

Interactive roles of NPR1 gene-dosage and salt diets on cardiac angiotensin II, aldosterone and pro-inflammatory cytokines levels in mutant mice

OBJECTIVE

The objective of the present study was to elucidate the interactive roles of guanylyl cyclase/natriuretic peptide receptor-A (NPRA) gene (Npr1) and salt diets on cardiac angiotensin II (ANG II), aldosterone and pro-inflammatory cytokines levels in Npr1 gene-targeted (1-copy, 2-copy, 3-copy, 4-copy) mice.

METHODS

Npr1 genotypes included 1-copy gene-disrupted heterozygous (+/-), 2-copy wild-type (+/+), 3-copy gene-duplicated heterozygous (++/+) and 4-copy gene-duplicated homozygous (++/++) mice. Animals were fed low, normal and high-salt diets. Plasma and cardiac levels of ANG II, aldosterone and pro-inflammatory cytokines were determined.

RESULTS

With a high-salt diet, cardiac ANG II levels were increased (+) in 1-copy mice (13.7 ± 2.8 fmol/mg protein, 111%) compared with 2-copy mice (6.5 ± 0.6), but decreased (-) in 4-copy (4.0 ± 0.5, 38%) mice. Cardiac aldosterone levels were increased (+) in 1-copy mice (80 ± 4 fmol/mg protein, 79%) compared with 2-copy mice (38 ± 3). Plasma tumour necrosis factor alpha was increased (+) in 1-copy mice (30.27 ± 2.32 pg/ml, 38%), compared with 2-copy mice (19.36 ± 2.49, 24%), but decreased (-) in 3-copy (11.59 ± 1.51, 12%) and 4-copy (7.13 ± 0.52, 22%) mice. Plasma interleukin (IL)-6 and IL-1α levels were also significantly increased (+) in 1-copy compared with 2-copy mice but decreased (-) in 3-copy and 4-copy mice.

CONCLUSION

These results demonstrate that a high-salt diet aggravates cardiac ANG II, aldosterone and pro-inflammatory cytokine levels in Npr1 gene-disrupted 1-copy mice, whereas, in Npr1 gene-duplicated (3-copy and 4-copy) mice, high salt did not render such elevation, suggesting the potential roles of Npr1 against salt loading.

Interactive roles of Ets-1, Sp1, and acetylated histones in the retinoic acid-dependent activation of guanylyl cyclase/atrial natriuretic peptide receptor-A gene transcription

Cardiac hormones atrial and brain natriuretic peptides activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which plays a critical role in reduction of blood pressure and blood volume. Currently, the mechanisms responsible for regulating the Npr1 gene (coding for GC-A/NPRA) transcription are not well understood. The present study was conducted to examine the interactive roles of all-trans retinoic acid (ATRA), Ets-1, Sp1, and histone acetylation on the transcriptional regulation and function of the Npr1 gene. Deletion analysis of the Npr1 promoter and luciferase assays showed that ATRA enhanced a 16-fold Npr1 promoter activity and greatly stimulated guanylyl cyclase (GC) activity of the receptor protein in both atrial natriuretic peptide (ANP)-dependent and -independent manner. As confirmed by gel shift and chromatin immunoprecipitation assays, ATRA enhanced the binding of both Ets-1 and Sp1 to the Npr1 promoter. The retinoic acid receptor α (RARα) was recruited by Ets-1 and Sp1 to form a transcriptional activator complex with their binding sites in the Npr1 promoter. Interestingly, ATRA also increased the acetylation of histones H3 and H4 and enhanced their recruitment to Ets-1 and Sp1 binding sites within the Npr1 promoter. Collectively, the present results demonstrate that ATRA regulates Npr1 gene transcription and GC activity of the receptor by involving the interactive actions of Ets-1, Sp1, and histone acetylation.

Ligand-mediated endocytosis and intracellular sequestration of guanylyl cyclase/natriuretic peptide receptors: role of GDAY motif

The guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), also referred to as GC-A, is a single polypeptide molecule having a critical function in blood pressure regulation and cardiovascular homeostasis. GC-A/NPRA, which resides in the plasma membrane, consists of an extracellular ligand-binding domain, a single transmembrane domain, and an intracellular cytoplasmic region containing a protein kinase-like homology domain (KHD) and a guanylyl cyclase (GC) catalytic domain. After binding with atrial and brain natriuretic peptides (ANP and BNP), GC-A/NPRA is internalized and sequestered into intracellular compartments. Therefore, GC-A/NPRA is a dynamic cellular macromolecule that traverses different subcellular compartments through its lifetime. This review describes the roles of short-signal sequences in the internalization, trafficking, and intracellular redistribution of GC-A/NPRA from cell surface to cell interior. Evidence indicates that, after internalization, the ligand-receptor complexes dissociate inside the cell and a population of GC-A/NPRA recycles back to the plasma membrane. Subsequently, the disassociated ligands are degraded in the lysosomes. However, a small percentage of the ligand escapes the lysosomal degradative pathway, and is released intact into culture medium. Using pharmacologic and molecular perturbants, emphasis has been placed on the cellular regulation and processing of ligand-bound GC-A/NPRA in terms of receptor trafficking and down-regulation in intact cells. The discussion is concluded by examining the functions of short-signal sequence motifs in the cellular life-cycle of GC-A/NPRA, including endocytosis, trafficking, metabolic processing, inactivation, and/or down-regulation in model cell systems.

Regulation of natriuretic peptide receptor-A gene expression and stimulation of its guanylate cyclase activity by transcription factor Ets-1

ANP (atrial natriuretic peptide) exerts its biological effects by binding to GC (guanylate cyclase)-A/NPR (natriuretic peptide receptor)-A, which generates the second messenger cGMP. The molecular mechanism mediating Npr1 (coding for GC-A/NPRA) gene regulation and expression is not well understood. The objective of the present study was to elucidate the mechanism by which Ets-1 [Ets (E twenty-six) transformation-specific sequence] contributes to the regulation of Npr1 gene transcription and expression. Chromatin immunoprecipitation and gel-shift assays confirmed the in vivo and in vitro binding of Ets-1 to the Npr1 promoter. Overexpression of Ets-1 enhanced significantly Npr1 mRNA levels, protein expression, GC activity and ANP-stimulated intracellular accumulation of cGMP in transfected cells. Depletion of endogenous Ets-1 by siRNA (small interfering RNA) dramatically decreased promoter activity by 80%. Moreover, methylation of the Npr1 promoter region (-356 to +55) reduced significantly the promoter activity and hypermethylation around the Ets-1 binding sites directly reduced Ets-1 binding to the Npr1 promoter. Collectively, the present study demonstrates that Npr1 gene transcription and GC activity of the receptor are critically controlled by Ets-1 in target cells.

Guanylyl cyclase/natriuretic peptide receptor-A gene disruption causes increased adrenal angiotensin II and aldosterone levels

Disruption of the guanylyl cyclase-A/natriuretic peptide receptor-A (GC-A/NPRA) gene leads to elevated arterial blood pressure and congestive heart failure in mice lacking NPRA. This study was aimed at determining whether Npr1 (coding for GC-A/NPRA) gene copy number affects adrenal ANG II and aldosterone (Aldo) levels in a gene-dose-dependent manner in Npr1 gene-targeted mice. Adrenal ANG II and Aldo levels increased in 1-copy mice compared with 2-copy mice, but decreased in 3-copy and 4-copy mice. In contrast, renal ANG II levels decreased in 1-copy (25%), 3-copy (38%), and 4-copy (39%) mice compared with 2-copy mice. The low-salt diet stimulated adrenal ANG II and Aldo levels in 1-copy (20 and 2,441%), 2-copy (15 and 2,339%), 3-copy (20 and 424%), and 4-copy (31 and 486%) mice, respectively. The high-salt diet suppressed adrenal ANG II and Aldo levels in 1-copy (46 and 29%) and 2-copy (38 and 17%) mice. On the other hand, the low-salt diet stimulated renal ANG II levels in 1-copy (45%), 2-copy (45%), 3-copy (59%), and 4-copy (48%) mice. However, the high-salt diet suppressed renal ANG II levels in 1-copy (28%) and 2-copy (27%) mice. In conclusion, NPRA signaling antagonizes adrenal ANG II and Aldo levels in a gene-dose dependent manner. Increased adrenal ANG II and Aldo levels may play an important role in elevated arterial blood pressure and progressive hypertension, leading to renal and vascular injury in Npr1 gene-disrupted mice.

Transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-A gene

Activation of natriuretic peptide receptor-A (NPRA) produces the second messenger cGMP, which plays a pivotal role in maintaining blood pressure and cardiovascular homeostasis. In the present study, we have examined the role of trans-acting factor Ets-1 in transcriptional regulation of Npr1 gene (coding for NPRA). Using deletional analysis of the Npr1 promoter, we have defined a 400 base pair (bp) region as the core promoter, which contains consensus binding sites for transcription factors including: Ets-1, Lyf-1, and GATA-1/2. Overexpression of Ets-1 in mouse mesangial cells (MMCs) enhanced Npr1 gene transcription by 12-fold. However, overexpression of GATA-1 or Lyf-1 repressed Npr1 basal promoter activity by 50% and 80%, respectively. The constructs having a mutant Ets-1 binding site or lacking this site failed to respond to Ets-1 activation of Npr1 gene transcription. Collectively, the present results demonstrate that Ets-1 greatly stimulates Npr1 gene promoter activity, implicating its critical role in the regulation and function of NPRA at the molecular level.

Genome-wide analysis and experimentation of plant serine/ threonine/tyrosine-specific protein kinases

Protein tyrosine phosphorylation plays an important role in cell growth, development and oncogenesis. No classical protein tyrosine kinase has hitherto been cloned from plants. Does protein tyrosine kinase exist in plants? To address this, we have performed a genomic survey of protein tyrosine kinase motifs in plants using the delineated tyrosine phosphorylation motifs from the animal system. The Arabidopsis thaliana genome encodes 57 different protein kinases that have tyrosine kinase motifs. Animal non-receptor tyrosine kinases, SRC, ABL, LYN, FES, SEK, KIN and RAS have structural relationship with putative plant tyrosine kinases. In an extended analysis, animal receptor and non-receptor kinases, Raf and Ras kinases, mixed lineage kinases and plant serine/threonine/tyrosine (STY) protein kinases, form a well-supported group sharing a common origin within the superfamily of STY kinases. We report that plants lack bona fide tyrosine kinases, which raise an intriguing possibility that tyrosine phosphorylation is carried out by dual-specificity STY protein kinases in plants. The distribution pattern of STY protein kinase families on Arabidopsis chromosomes indicates that this gene family is partly a consequence of duplication and reshuffling of the Arabidopsis genome and of the generation of tandem repeats. Genome-wide analysis is supported by the functional expression and characterization of At2g24360 and phosphoproteomics of Arabidopsis. Evidence for tyrosine phosphorylated proteins is provided by alkaline hydrolysis, anti-phosphotyrosine immunoblotting, phosphoamino acid analysis and peptide mass fingerprinting. These results report the first comprehensive survey of genome-wide and tyrosine phosphoproteome analysis of plant STY protein kinases.

Transcriptional response in the unaffected kidney after contralateral hydronephrosis or nephrectomy

BACKGROUND

Unilateral loss of kidney function is followed by compensatory contralateral growth. The early, genome-wide transcriptional response of the untouched kidney to unilateral ureteral obstruction (UUO) or unilateral nephrectomy is unknown.

METHODS

Twelve adult male Sprague-Dawley rats were subjected to UUO and twelve rats to unilateral nephrectomy. At time points 12, 24, and 72 hours after insult four rats each were sacrificed and the contralateral kidney harvested for genome-wide gene expression analysis, transcription factor analysis, and histomorphology.

RESULTS

Microarray studies revealed that the majority of differentially expressed transcripts were suppressed in UUO and unilateral nephrectomy compared to control kidneys. The function of these suppressed genes is predominantly growth inhibition and apoptosis suggesting a net pro-hypertrophic response. Insulin-like growth factor-2 (IGF-2)-binding protein was one of the few activated genes. We observed a distinctly different molecular signature between UUO and unilateral nephrectomy at the three time points investigated. The early response in UUO rats suggests a counterbalance to the nonfiltering kidney by activation of transport pathways such as the aquaporins. Unilateral nephrectomy kidneys, on the other hand, respond immediately to contralateral nephrectomy by activation of cell cycle regulators such as the cyclin family. Several genes with weakly defined function were found to be associated with either UUO or unilateral nephrectomy. Transcription factor analysis of the identified transcripts suggests common regulation at least of some of these genes. All kidneys showed normal histology.

CONCLUSION

Release of growth inhibition by nephrectomy leads to immediate cell cycle activation after unilateral nephrectomy, whereas UUO kidneys counterbalance filtration failure by activation of several transporters.

An Unsuspected Metabolic Role for Atrial Natriuretic Peptides

In normal and obese humans, lipid mobilization and systemic nonesterified fatty acid levels are thought to be acutely controlled by catecholamines (ie, epinephrine and norepinephrine) and insulin. Natriuretic peptides (NPs) are known to play a key role in the regulation of salt and water balance and blood pressure homeostasis. They are involved in the pathophysiology of hypertension and heart failure. NPs have recently been found to exert potent lipolytic effects (ie, activating the breakdown of stored triacylglycerols) in isolated human fat cells and to promote lipid mobilization in vivo. Atrial natriuretic peptide increases the intracellular 3', 5'-cyclic guanosine monophosphate (cGMP) concentration which activates cGMP-dependent protein kinase leading to perilipin and hormone-sensitive lipase phosphorylation and lipolysis. NPs promote lipid mobilization when administered intravenously. NPs are also responsible for the residual lipid-mobilizing action observed under oral beta-blockade in subjects performing physical exercise. NPs are therefore novel factors which may open promising research pathways to explain the control of lipid mobilization in physiological and pathological conditions. The metabolic impact of altered production and circulation of NPs remains to be established. The potential influence of NPs on the development of lipid disorders, obesity-related cardiovascular events, and cardiac cachexia will be discussed in this review.

Regulation of guanylyl cyclase/natriuretic peptide receptor-A gene expression

Natriuretic peptide receptor-A (NPRA) is the biological receptor of the peptide hormones atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The level and activity of this receptor determines the biological effects of ANP and BNP in different tissues mainly directed towards the maintenance of salt and water homeostasis. The core transcriptional machinery of the TATA-less Npr1 gene, which encodes NPRA, consists of three SP1 binding sites and the inverted CCAAT box. This promoter region of Npr1 gene has been shown to contain several putative binding sites for the known transcription factors, but the functional significance of most of these regulatory sequences is yet to be elucidated. The present review discusses the current knowledge of the functional significance of the promoter region of Npr1 gene and its transcriptional regulation by a number of factors including different hormones, growth factors, changes in extracellular osmolarity, and certain physiological and patho-physiological conditions.

Characterization of a cGMP-response element in the guanylyl cyclase/natriuretic peptide receptor A gene promoter

Previous studies have shown that atrial natriuretic peptide (ANP) can inhibit transcription of its receptor, guanylyl cyclase A, by a mechanism dependent on cGMP and have suggested the presence of a putative cGMP-response element (cGMP-RE) in the Npr1 gene promoter. To localize and characterize the putative cis-acting element, we have subcloned a 1520-bp fragment of the rat Npr1 promoter in an expression vector containing the luciferase reporter gene. Several fragments, generated by exonuclease III-directed deletions, were transiently transfected into cells to measure their promoter activity. Deletion from -1520 to -1396 of a 1520-bp-long Npr1 promoter led to a 5-fold increase in luciferase activity. Subsequent deletion to the position -1307 resulted in a decrease of luciferase activity by 90%. Preincubation of cells with 100 nM of ANP or 100 microM 8-bromo-cGMP inhibited luciferase activity of the 1520-bp and 1396-bp-long fragments, but not the activity of the 1307-bp fragment, suggesting that the cGMP-RE is localized between positions -1396 and -1307. The cGMP regulatory region was narrowed by gel shift assays and footprinting to position -1372 to -1354 from the transcription start site of Npr1 and indicated its interaction with transcriptional factor(s). Cross-competition experiments with mutated oligonucleotides led to the definition of a consensus sequence (-1372 AaAtRKaNTTCaAcAKTY -1354) for the novel cGMP-RE, which is conserved in the human (75% identity) and mouse (95% identity) Npr1 promoters.

Novel isoforms of the sodium channels Nav1.8 and Nav1.5 are produced by a conserved mechanism in mouse and rat

The voltage-gated sodium channel Na(v)1.8 is only expressed in subsets of neurons in dorsal root ganglia (DRG) and trigeminal and nodose ganglia. We have isolated mouse partial length Na(v)1.8 cDNA clones spanning the exon 17 sequence, which have 17 nucleotide substitutions and 12 predicted amino acid differences from the published sequence. The absence of a mutually exclusive alternative exon 17 was confirmed by sequencing 4.1 kilobases of genomic DNA spanning exons 16-18 of Scn10a. A novel cDNA isoform was identified, designated Na(v)1.8c, which results from alternative 3'-splice site selection at a CAG/CAG motif to exclude the codon for glutamine 1031 within the interdomain cytoplasmic loop IDII/III. The ratio of Na(v)1.8c (CAG-skipped) to Na(v)1.8 (CAG-inclusive) mRNA in mouse is approximately 2:1 in adult DRG, trigeminal ganglion, and neonatal DRG. A Na(v)1.8c isoform also occurs in rat DRG, but is less common. Of the two other tetrodotoxin-resistant channels, no analogous alternative splicing of mouse Na(v)1.9 was detected, whereas rare alternative splicing of Na(v)1.5 at a CAG/CAG motif resulted in the introduction of a CAG trinucleotide. This isoform, designated Na(v)1.5c, is conserved in rat and encodes an additional glutamine residue that disrupts a putative CK2 phosphorylation site. In summary, novel isoforms of Na(v)1.8 and Na(v)1.5 are each generated by alternative splicing at CAG/CAG motifs, which result in the absence or presence of predicted glutamine residues within the interdomain cytoplasmic loop IDII/III. Mutations of sodium channels within this cytoplasmic loop have previously been demonstrated to alter electrophysiological properties and cause cardiac arrhythmias and epilepsy.

Angiotensin II-mediated negative regulation of Npr1 promoter activity and gene transcription

Atrial natriuretic peptide receptor A (NPRA) plays important role(s) in the control of extracellular fluid volume and blood pressure homeostasis. We have determined and analyzed the functional promoter region of Npr1 gene (coding for NPRA) and studied the effect of angiotensin (Ang) II on its promoter activity and expression in cultured mouse mesangial cells. The promoter analysis of Npr1 gene revealed the presence of positive regulatory cis-elements in the regions -1982 to -1841 bp and -916 to -496 bp and of the repressor elements in the regions -1841 to -916 bp and 56 to 382 bp relative to transcription start site. The Ang II pretreatment of cultured mouse mesangial cells transiently transfected with the promoter construct pNPRA-luc1 significantly inhibited the promoter activity in a time- and dose-dependent manner, with a maximum inhibition at 24 hours. The Ang II-dependent repression of Npr1 promoter activity was partially blocked by both angiotensin type 1 and type 2 antagonists candesartan and PD 123,319, respectively. The mRNA level of NPRA was also downregulated by Ang II treatment as determined by semiquantitative reverse transcriptase-polymerase chain reaction assay. The deletion analysis showed that the promoter region approximately 916 bp upstream of transcription start site contains the cis-elements involved in Ang II-mediated repression of transcription of Npr1 gene. The present study thus reveals the presence of functional cis-regulatory elements in the promoter region of the murine Npr1 gene and its transcriptional downregulation by vasoactive peptide Ang II.