Atrial natriuretic peptide inhibits the phosphoinositide hydrolysis in murine Leydig tumor cells

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.

Guanylyl cyclase/natriuretic peptide receptor-A signaling antagonizes phosphoinositide hydrolysis, Ca(2+) release, and activation of protein kinase C

Thus far, three related natriuretic peptides (NPs) and three distinct sub-types of cognate NP receptors have been identified and characterized based on the specific ligand binding affinities, guanylyl cyclase activity, and generation of intracellular cGMP. Atrial and brain natriuretic peptides (ANP and BNP) specifically bind and activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), and C-type natriuretic peptide (CNP) shows specificity to activate guanylyl cyclase/natriuretic peptide receptor-B (GC-B/NPRB). All three NPs bind to natriuretic peptide receptor-C (NPRC), which is also known as clearance or silent receptor. The NPRA is considered the principal biologically active receptor of NP family; however, the molecular signaling mechanisms of NP receptors are not well understood. The activation of NPRA and NPRB produces the intracellular second messenger cGMP, which serves as the major signaling molecule of all three NPs. The activation of NPRB in response to CNP also produces the intracellular cGMP; however, at lower magnitude than that of NPRA, which is activated by ANP and BNP. In addition to enhanced accumulation of intracellular cGMP in response to all three NPs, the levels of cAMP, Ca²⁺ and inositol triphosphate (IP₃) have also been reported to be altered in different cells and tissue types. Interestingly, ANP has been found to lower the concentrations of cAMP, Ca²⁺, and IP₃; however, NPRC has been proposed to increase the levels of these metabolic signaling molecules. The mechanistic studies of decreased and/or increased levels of cAMP, Ca²⁺, and IP₃ in response to NPs and their receptors have not yet been clearly established. This review focuses on the signaling mechanisms of ANP/NPRA and their biological effects involving an increased level of intracellular accumulation of cGMP and a decreased level of cAMP, Ca²⁺, and IP₃ in different cells and tissue systems.

All-trans retinoic acid and sodium butyrate enhance natriuretic peptide receptor a gene transcription: role of histone modification

The objective of the present study was to delineate the mechanisms of GC-A/natriuretic peptide receptor-A (GC-A/NPRA) gene (Npr1) expression in vivo. We used all-trans retinoic acid (ATRA) and histone deacetylase (HDAC) inhibitor, sodium butyrate (NaBu) to examine the expression and function of Npr1 using gene-disrupted heterozygous (1-copy; +/-), wild-type (2-copy; +/+), and gene-duplicated heterozygous (3-copy; ++/+) mice. Npr1(+/-) mice exhibited increased renal HDAC and reduced histone acetyltransferase (HAT) activity; on the contrary, Npr1(++/+) mice showed decreased HDAC and enhanced HAT activity compared with Npr1(+)(/+) mice. ATRA and NaBu promoted global acetylation of histones H3-K9/14 and H4-K12, reduced methylation of H3-K9 and H3-K27, and enriched accumulation of active chromatin marks at the Npr1 promoter. A combination of ATRA-NaBu promoted recruitment of activator-complex containing E26 transformation-specific 1, retinoic acid receptor α, and HATs (p300 and p300/cAMP response element-binding protein-binding protein-associated factor) at the Npr1 promoter, and significantly increased renal NPRA expression, GC activity, and cGMP levels. Untreated 1-copy mice showed significantly increased systolic blood pressure and renal expression of α-smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) compared with 2- and 3-copy mice. Treatment with ATRA and NaBu synergistically attenuated the expression of α-SMA and PCNA and reduced systolic blood pressure in Npr1(+/-) mice. Our findings demonstrate that epigenetic upregulation of Npr1 gene transcription by ATRA and NaBu leads to attenuation of renal fibrotic markers and systolic blood pressure in mice with reduced Npr1 gene copy number, which will have important implications in prevention and treatment of hypertension-related renal pathophysiological conditions.

Guanylyl cyclase / atrial natriuretic peptide receptor-A: role in the pathophysiology of cardiovascular regulation

Atrial natriuretic factor (ANF), also known as atrial natriuretic peptide (ANP), is an endogenous and potent hypotensive hormone that elicits natriuretic, diuretic, vasorelaxant, and anti-proliferative effects, which are important in the control of blood pressure and cardiovascular events. One principal locus involved in the regulatory action of ANP and brain natriuretic peptide (BNP) is guanylyl cyclase / natriuretic peptide receptor-A (GC-A/NPRA). Studies on ANP, BNP, and their receptor, GC-A/NPRA, have greatly increased our knowledge of the control of hypertension and cardiovascular disorders. Cellular, biochemical, and molecular studies have helped to delineate the receptor function and signaling mechanisms of NPRA. Gene-targeted and transgenic mouse models have advanced our understanding of the importance of ANP, BNP, and GC-A/NPRA in disease states at the molecular level. Importantly, ANP and BNP are used as critical markers of cardiac events; however, their therapeutic potentials for the diagnosis and treatment of hypertension, heart failure, and stroke have just begun to be realized. We are now just at the initial stage of molecular therapeutics and pharmacogenomic advancement of the natriuretic peptides. More investigations should be undertaken and ongoing ones be extended in this important field.

The functional genomics of guanylyl cyclase/natriuretic peptide receptor-A: perspectives and paradigms

The cardiac hormones atrial natriuretic peptide and B-type natriuretic peptide (brain natriuretic peptide) activate guanylyl cyclase (GC)-A/natriuretic peptide receptor-A (NPRA) and produce the second messenger cGMP. GC-A/NPRA is a member of the growing family of GC receptors. The recent biochemical, molecular and genomic studies on GC-A/NPRA have provided important insights into the regulation and functional activity of this receptor protein, with a particular emphasis on cardiac and renal protective roles in hypertension and cardiovascular disease states. The progress in this field of research has significantly strengthened and advanced our knowledge about the critical roles of Npr1 (coding for GC-A/NPRA) in the control of fluid volume, blood pressure, cardiac remodeling, and other physiological functions and pathological states. Overall, this review attempts to provide insights and to delineate the current concepts in the field of functional genomics and signaling of GC-A/NPRA in hypertension and cardiovascular disease states at the molecular level.

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.

Diminished mesenteric vaso- and venoconstriction and elevated plasma ANP and BNP with simulated microgravity

Diminished constriction of arteries and veins following exposure to microgravity or bed rest is associated with a reduced ability to augment peripheral vascular resistance (PVR) and stroke volume during orthostasis. We tested the hypothesis that small mesenteric arteries and veins, which are not exposed to large pressure shifts during simulated microgravity via head-down tail suspension (HDT), will exhibit decrements in adrenergic constriction after HDT in rats. Small mesenteric arteries and veins from control (Con; n = 41) and HDT (n = 35) male Sprague-Dawley rats were studied in vitro. Vasoactive responsiveness to norepinephrine (NE) in arteries (10(-9) to 10(-4) M) and veins (pressure-diameter responses from 2 to 12 cmH(2)O after incubation in 10(-6) or 10(-4) M NE) were evaluated. Plasma concentrations of atrial (ANP) and NH(2)-terminal prohormone brain (NT-proBNP) natriuretic peptides were also measured. In mesenteric arteries, sensitivity and maximal responsiveness to NE were reduced with HDT. In mesenteric veins there was a diminished venoconstriction to NE at any given pressure in HDT. Plasma concentrations of both ANP and NT-proBNP were increased with HDT, and maximal arterial and venous constrictor responses to NE after incubation with 10(-7) M ANP or brain natriuretic peptide (BNP) were diminished. These data demonstrate that, in a vascular bed not subjected to large hydrodynamic differences with HDT, both small arteries and veins have a reduced responsiveness to adrenergic stimulation. Elevated levels of circulating ANP or NT-proBNP could adversely affect the ability of these vascular beds to constrict in vivo and conceivably could alter the intrinsic constrictor properties of these vessels with long-term exposure.

Biology of natriuretic peptides and their receptors

Increasing evidence suggests that natriuretic peptides (NPs) play diverse roles in mammals, including renal hemodynamics, neuroendocrine, and cardiovascular functions. Collectively, NPs are classified as hypotensive hormones; the main actions of NPs are implicated in eliciting natriuretic, diuretic, steroidogenic, antiproliferative, and vasorelaxant effects, important factors in the control of body fluid volume and blood pressure homeostasis. One of the principal loci involved in the regulatory actions of NPs is their cognate plasma membrane receptor molecules, which are activated by binding with specific NPs. Interaction of NPs with their receptors plays a central role in physiology and pathophysiology of hypertension and cardiovascular disorders. Gaining insight into the intricacies of NPs-specific receptor signaling pathways is of pivotal importance for understanding both hormone-receptor biology and the disease states arising from abnormal hormone receptor interplay. During the last decade there has been a surge in interest in NP receptors; consequently, a wealth of information has emerged concerning molecular structure and function, signaling mechanisms, and use of transgenics and gene-targeted mouse models. The objective of this present review is to summarize and document the previous findings and recent discoveries in the field of the natriuretic peptide hormone family and receptor systems with emphasis on the structure-function relationship, signaling mechanisms, and the physiological and pathophysiological significance in health and disease.

Expression of atrial natriuretic peptide receptor-A antagonizes the mitogen-activated protein kinases (Erk2 and P38MAPK) in cultured human vascular smooth muscle cells

To understand the signaling mechanisms of atrial natriuretic peptide (ANP) receptor-A (NPRA), we studied the effect of the ANP/NPRA system on mitogen-activated protein kinases (MAPKs), with particular emphasis on the extracellular-regulated kinase (Erk2) and stress-activated protein kinase (p38MAPK) in cultured human vascular smooth muscle cells (HVSMC). Angiotensin II (ANG II) and platelet-derived growth factor (PDGF) stimulated the immunoreactive Erk2 and p38MAPK activities and their protein levels by 2-4 fold. The pretreatment of cells with ANP significantly inhibited the agonist-stimulated Erk2 and p38MAPK activities and protein expression by 65-75% in HVSMC transiently transfected with NPRA, as compared with only 18-22% inhibition in vector-transfected cells. The pretreatment of cells with KT5823, an inhibitor of cGMP-dependent protein kinase (PKG), reversed the inhibitory effects of ANP on MAPK activities and protein expression by 90-95%. PD98059, which inhibits Erk2 by directly inhibiting the MAPK-kinase (MEK), and SB202192, a selective antagonist of p38MAPK, blocked the Erk2 and p38MAPK activities, respectively. Interestingly, ANP stimulated the MAPK-phosphatase-3 (MKP-3) protein levels by more than 3-fold in HVSMC over-expressing NPRA, suggesting that ANP-dependent inhibition of MAPKs may also proceed by stimulating the phosphatase cascade. These present findings provide the evidence that ANP exerts inhibitory effects on agonist-stimulated MAPKs (Erk2 and p38MAPK) activities and protein levels in a 2-fold manner: by antagonizing the up-stream signaling pathways and by activation of MKP-3 to counter-regulate MAPKs in a cGMP and PKG-dependent manner. Our results identify a signal transduction pathway in HVSMC that could contribute to vascular remodeling and structural changes in human hypertension.

Stimulation of atrial natriuretic peptide receptor/guanylyl cyclase- A signaling pathway antagonizes the activation of protein kinase C-alpha in murine Leydig cells

Atrial natriuretic peptide (ANP) regulates diverse physiological responses by binding to its specific guanylyl cyclase-A receptor (Npra) which synthesizes the intracellular second messenger cGMP. To understand the molecular mechanisms of cellular signaling of ANP, we have studied its effect on the enzymatic activity of overexpressed protein kinase C (PKC) in murine Leydig tumor (MA-10) cells which were transfected with PKC-alpha cDNA. Treatments with 12-O-tetradecanoylphorbol-13-acetate (TPA), angiotensin II (ANG II) and endothelin-1 (ET-1) stimulated the PKC activity by 4-5-fold in PKC-alpha cDNA transfected MA-10 cells. The pretreatment of PKC-alpha transfected cells with ANP significantly inhibited the TPA-, ANG II- and ET-1-stimulated PKC activity. The agonist-stimulated PKC activity was also inhibited in the presence of 8-bromo-cGMP, however, cAMP had no effect on stimulatory PKC activity. The exposure of cells to Npra- antagonist A71915, which blocks the production of cGMP, significantly reduced the inhibitory effect of ANP on agonist-stimulated PKC activity and accumulation of intracellular cGMP in MA-10 cells. Similarly, inhibition of cGMP-dependent protein kinase by KT5823, restored the stimulatory levels of PKC activity in the presence of ANP. These results provide direct evidence that ANP antagonizes the agonist-stimulated PKC activity in MA-10 cells, involving the specific receptor Npra, its second messenger cGMP and cGMP-dependent protein kinase. Together, these findings implicate that ANP may act as a negative mediator of 'cross-talk' between PKC-alpha and Npra signaling pathway in MA-10 cells.