Two distinct forms of receptors for atrial natriuretic factor in bovine adrenocortical cells. Purification, ligand binding, and peptide mapping

Multilimbed membrane guanylate cyclase signaling system, evolutionary ladder

One monumental discovery in the field of cell biology is the establishment of the membrane guanylate cyclase signal transduction system. Decoding its fundamental, molecular, biochemical, and genetic features revolutionized the processes of developing therapies for diseases of endocrinology, cardio-vasculature, and sensory neurons; lastly, it has started to leave its imprints with the atmospheric carbon dioxide. The membrane guanylate cyclase does so via its multi-limbed structure. The inter-netted limbs throughout the central, sympathetic, and parasympathetic systems perform these functions. They generate their common second messenger, cyclic GMP to affect the physiology. This review describes an historical account of their sequential evolutionary development, their structural components and their mechanisms of interaction. The foundational principles were laid down by the discovery of its first limb, the ACTH modulated signaling pathway (the companion monograph). It challenged two general existing dogmas at the time. First, there was the question of the existence of a membrane guanylate cyclase independent from a soluble form that was heme-regulated. Second, the sole known cyclic AMP three-component-transduction system was modulated by GTP-binding proteins, so there was the question of whether a one-component transduction system could exclusively modulate cyclic GMP in response to the polypeptide hormone, ACTH. The present review moves past the first question and narrates the evolution and complexity of the cyclic GMP signaling pathway. Besides ACTH, there are at least five additional limbs. Each embodies a unique modular design to perform a specific physiological function; exemplified by ATP binding and phosphorylation, Ca²⁺-sensor proteins that either increase or decrease cyclic GMP synthesis, co-expression of antithetical Ca²⁺ sensors, GCAP1 and S100B, and modulation by atmospheric carbon dioxide and temperature. The complexity provided by these various manners of operation enables membrane guanylate cyclase to conduct diverse functions, exemplified by the control over cardiovasculature, sensory neurons and, endocrine systems.

Venom natriuretic peptides guide the design of heart failure therapeutics

Heart failure (HF) affects over 26 million people world-wide. It is a syndrome triggered by loss of normal cardiac function due to many acute (eg myocardial infarction) and/or chronic (eg hypertension) causes and characterized by mixed beneficial and deleterious activation of a complex of multifaceted neurohormonal systems the net effect of which frequently is further adverse disruption of pressure-volume homeostasis. Unlike the situation in chronic heart failure, current strategies for treatment of acute heart failure are empirical and lack a strong evidence base. Management includes any of a combination of vasodilators, diuretics and ionotropic agents depending on the hemodynamic profile of the patient. Despite the improvement in the options available to improve outcomes in patients with chronic HF, for several decades little gain has been made in the treatment of the acute decompensated state. Morbidity and mortality rates remain high necessitating new therapeutic agents. The cardiac natriuretic peptides (NPs) are key hormones in pressure-volume homoeostasis. There are three isoforms of mammalian NPs, namely ANP, BNP and CNP. These peptides bind to membrane-bound NP receptors (NPRs) on the heart, vasculature and kidney to lower blood pressure and circulating volume. Intravenous infusion of NPs in HF patients improves hemodynamic status but is associated with occasional severe hypotension. Apart from mammalian NPs, snake venom NPs are an excellent source of pharmacologically distinct ligands that offer the possibility of engineering NPs for therapeutic purposes. Venom NPs have long half-lives, differential NPR activation profiles and varied NPR specificity. The scaffolds of venom NPs encode the molecular information for designing NPs with longer half-lives and improved and differential vascular and renal functions. This review focuses on the structure-function paradigm of mammalian and venom NPs and the different peptide engineering strategies that have been utilized in the design of clinically relevant new NP-analogues.

Membrane guanylate cyclase, a multimodal transduction machine: history, present, and future directions

A sequel to these authors' earlier comprehensive reviews which covered the field of mammalian membrane guanylate cyclase (MGC) from its origin to the year 2010, this article contains 13 sections. The first is historical and covers MGC from the year 1963–1987, summarizing its colorful developmental stages from its passionate pursuit to its consolidation. The second deals with the establishment of its biochemical identity. MGC becomes the transducer of a hormonal signal and founder of the peptide hormone receptor family, and creates the notion that hormone signal transduction is its sole physiological function. The third defines its expansion. The discovery of ROS-GC subfamily is made and it links ROS-GC with the physiology of phototransduction. Sections ROS-GC, a Ca²⁺-Modulated Two Component Transduction System to Migration Patterns and Translations of the GCAP Signals Into Production of Cyclic GMP are Different cover its biochemistry and physiology. The noteworthy events are that augmented by GCAPs, ROS-GC proves to be a transducer of the free Ca²⁺ signals generated within neurons; ROS-GC becomes a two-component transduction system and establishes itself as a source of cyclic GMP, the second messenger of phototransduction. Section ROS-GC1 Gene Linked Retinal Dystrophies demonstrates how this knowledge begins to be translated into the diagnosis and providing the molecular definition of retinal dystrophies. Section Controlled By Low and High Levels of [Ca²⁺]_i, ROS-GC1 is a Bimodal Transduction Switch discusses a striking property of ROS-GC where it becomes a “[Ca²⁺]_i bimodal switch” and transcends its signaling role in other neural processes. In this course, discovery of the first CD-GCAP (Ca²⁺-dependent guanylate cyclase activator), the S100B protein, is made. It extends the role of the ROS-GC transduction system beyond the phototransduction to the signaling processes in the synapse region between photoreceptor and cone ON-bipolar cells; in section Ca²⁺-Modulated Neurocalcin δ ROS-GC1 Transduction System Exists in the Inner Plexiform Layer (IPL) of the Retinal Neurons, discovery of another CD-GCAP, NCδ, is made and its linkage with signaling of the inner plexiform layer neurons is established. Section ROS-GC Linkage With Other Than Vision-Linked Neurons discusses linkage of the ROS-GC transduction system with other sensory transduction processes: Pineal gland, Olfaction and Gustation. In the next, section Evolution of a General Ca²⁺-Interlocked ROS-GC Signal Transduction Concept in Sensory and Sensory-Linked Neurons, a theoretical concept is proposed where “Ca²⁺-interlocked ROS-GC signal transduction” machinery becomes a common signaling component of the sensory and sensory-linked neurons. Closure to the review is brought by the conclusion and future directions.

Ca(2+) modulation of ANF-RGC: new signaling paradigm interlocked with blood pressure regulation

ANF-RGC is the prototype receptor membrane guanylate cyclase that is both the receptor and the signal transducer of the most hypotensive hormones, ANF and BNP. It is a single-transmembrane protein. After binding these hormones at the extracellular domain, ANF-RGC at its intracellular domain signals the activation of the C-terminal catalytic module and accelerates the production of the second messenger, cyclic GMP, which controls blood pressure, cardiac vasculature, and fluid secretion. At present, this is the sole transduction mechanism and the physiological function of ANF-RGC. Through comprehensive studies involving biochemistry, immunohistochemistry, and blood pressure measurements in mice with targeted gene deletions, this study demonstrates a new signaling model of ANF-RGC that also controls blood pressure. In this model, (1) ANF-RGC is not the transducer of ANF and BNP, (2) its extracellular domain is not used for signaling, and (3) the signal flow is not downstream from the extracellular domain to the core catalytic domain. Instead, the signal is the intracellular Ca(2+), which is translated at the site of its reception, at the core catalytic domain of ANF-RGC. A model for this Ca(2+) signal transduction is diagrammed. It captures Ca(2+) through its Ca(2+) sensor myristoylated neurocalcin δ and upregulates ANF-RGC activity with a K(1/2) of 0.5 μM. The neurocalcin δ-modulated domain resides in the (849)DIVGFTALSAESTPMQVV(866) segment of ANF-RGC, which is a part of the core catalytic domain. Thereby, ANF-RGC is primed to receive, transmit, and translate the Ca(2+) signals into the generation of cyclic GMP at a rapid rate. The study defines a new paradigm of membrane guanylate cyclase signaling, which is linked to the physiology of cardiac vasculature regulation and possibly also to fluid secretion.

Guanylyl cyclases A and B are asymmetric dimers that are allosterically activated by ATP binding to the catalytic domain

It is not known how natriuretic peptides and adenosine triphosphate (ATP) activate guanylyl cyclase A (GC-A) and GC-B, which generate the second messenger cyclic guanosine monophosphate. We determined that natriuretic peptides increased the maximum rate of these enzymes >10-fold in a positive cooperative manner in the absence of ATP. In the absence of natriuretic peptides, ATP shifted substrate-velocity profiles from cooperative to linear but did not increase the affinity of GCs for the substrate guanosine triphosphate (GTP) since the Michaelis constant was unchanged. However, in the presence of natriuretic peptides, ATP competed with GTP for binding to an allosteric site, which enhanced the activation of GCs by decreasing the Michaelis constant. Thus, natriuretic peptide binding was required for communication of the allosteric activation signal to the catalytic site. The ability of ATP to activate GCs decreased and enzyme potency (a measure of sensitivity to stimulation) increased with increasing GTP concentrations. Point mutations in the purine-binding site of the catalytic domain abolished GC activity but not allosteric activation. Coexpression of inactive mutants produced half the activity expected for symmetric catalytic dimers. 2'-Deoxy-ATP and 2'-deoxy-GTP were poor allosteric activators, but 2'-deoxy-GTP was an effective substrate, consistent with distinct binding requirements for the allosteric and catalytic sites. We conclude that membrane GC domains are asymmetric homodimers with distinct and reciprocally regulated catalytic and allosteric sites that bind to GTP and ATP, respectively. These data define a new membrane GC activation model and provide evidence of a previously unidentified GC drug interaction site.

Structure, signaling mechanism and regulation of the natriuretic peptide receptor guanylate cyclase

Atrial natriuretic peptide (ANP) and the homologous B-type natriuretic peptide are cardiac hormones that dilate blood vessels and stimulate natriuresis and diuresis, thereby lowering blood pressure and blood volume. ANP and B-type natriuretic peptide counterbalance the actions of the renin-angiotensin-aldosterone and neurohormonal systems, and play a central role in cardiovascular regulation. These activities are mediated by natriuretic peptide receptor-A (NPRA), a single transmembrane segment, guanylyl cyclase (GC)-linked receptor that occurs as a homodimer. Here, we present an overview of the structure, possible chloride-mediated regulation and signaling mechanism of NPRA and other receptor GCs. Earlier, we determined the crystal structures of the NPRA extracellular domain with and without bound ANP. Their structural comparison has revealed a novel ANP-induced rotation mechanism occurring in the juxtamembrane region that apparently triggers transmembrane signal transduction. More recently, the crystal structures of the dimerized catalytic domain of green algae GC Cyg12 and that of cyanobacterium GC Cya2 have been reported. These structures closely resemble that of the adenylyl cyclase catalytic domain, consisting of a C1 and C2 subdomain heterodimer. Adenylyl cyclase is activated by binding of G(s)α to C2 and the ensuing 7° rotation of C1 around an axis parallel to the central cleft, thereby inducing the heterodimer to adopt a catalytically active conformation. We speculate that, in NPRA, the ANP-induced rotation of the juxtamembrane domains, transmitted across the transmembrane helices, may induce a similar rotation in each of the dimerized GC catalytic domains, leading to the stimulation of the GC catalytic activity.

Allosteric modification, the primary ATP activation mechanism of atrial natriuretic factor receptor guanylate cyclase

ANF-RGC is the prototype receptor membrane guanylate cyclase being both the receptor and the signal transducer of the most hypotensive hormones, ANF and BNP. It is a single transmembrane-spanning protein. After binding these hormones at the extracellular domain it at its intracellular domain signals activation of the C-terminal catalytic module and accelerates the production of its second messenger, cyclic GMP, which controls blood pressure, cardiac vasculature, and fluid secretion. ATP is obligatory for the posttransmembrane dynamic events leading to ANF-RGC activation. It functions through the ATP-regulated module, ARM (KHD) domain, of ANF-RGC. In the current over a decade held model "phosphorylation of the KHD is absolutely required for hormone-dependent activation of NPR-A" [Potter, L. R., and Hunter, T. (1998) Mol. Cell. Biol. 18, 2164-2172]. The presented study challenges this concept. It demonstrates that, instead, ATP allosteric modification of ARM is the primary signaling step of ANF-GC activation. In this two-step new dynamic model, ATP in the first step binds ARM. This triggers in it a chain of transduction events, which cause its allosteric modification. The modification partially activates (about 50%) ANF-RGC and, concomitantly, also prepares the ARM for the second successive step. In this second step, ARM is phosphorylated and ANF-RGC achieves additional (∼50%) full catalytic activation. The study defines a new paradigm of the ANF-RGC signaling mechanism.

Membrane guanylate cyclase is a beautiful signal transduction machine: overview

This article is a sequel to the four earlier comprehensive reviews which covered the field of membrane guanylate cyclase from its origin to the year 2002 (Sharma in Mol Cell Biochem 230:3-30, 2002) and then to the year 2004 (Duda et al. in Peptides 26:969-984, 2005); and of the Ca(2+)-modulated membrane guanylate cyclase to the year 1997 (Pugh et al. in Biosci Rep 17:429-473, 1997) and then to 2004 (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). This article contains three parts. The first part is "Historical"; it is brief, general, and freely borrowed from the earlier reviews, covering the field from its origin to the year 2004 (Sharma in Mol Cell Biochem, 230:3-30, 2002; Duda et al. in Peptides 26:969-984, 2005). The second part focuses on the "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily". It is divided into two sections. Section "Historical" and covers the area from its inception to the year 2004. It is also freely borrowed from an earlier review (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). Section "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily" covers the area from the year 2004 to May 2009. The objective is to focus on the chronological development, recognize major contributions of the original investigators, correct misplaced facts, and project on the future trend of the field of mammalian membrane guanylate cyclase. The third portion covers the present status and concludes with future directions in the field.

Expression, purification, and characterization of the intra-cellular domain of the ANP receptor

The membrane-bound atrial natriuretic peptide receptor (GCA) catalyzes the formation of cGMP from GTP in response to natriuretic peptide hormones. Previous structural studies have focused on the extra-cellular hormone binding domain of this receptor whereas its intra-cellular domain has not yet been amenable to such studies. We report here the baculovirus expression and purification of the GCA intra-cellular domain construct GCA(ID) comprising the complete intra-cellular region which includes the kinase-homology domain, coiled-coil region, and catalytic cyclase domain. The intra-cellular domain was enzymatically characterized in terms of guanylyl cyclase activity and the effects of ATP, manganese, and Triton X-100. Our results indicate that the activity of the intra-cellular domain of the ANP receptor is about 2 fold less active compared to a truncated cyclase domain construct lacking the kinase-like domain that was also expressed and purified. In addition, unlike the full length receptor, the intra-cellular domain could not be activated by Triton X-100/Mn(2+) or its activity stimulated by ATP. These data therefore indicate that the major part of the transition from the basal state to the fully, ANP/ATP-dependent, activated state as well its stimulation/enhancement by Triton X-100/Mn(2+) requires the full length receptor. These receptor insights could aid in the development of novel therapeutics as the GCA receptor is a key drug target for cardiovascular diseases.

Identification and synergism of cis-acting elements essential for basal promoter activity of the human type 1 angiotensin II receptor gene in PLC-PRF-5 cells

The basal promoter activity of the human AT(1) receptor gene was characterized using a human hepatoma cell line with a considerably high expression of AT(1), PLC-PRF-5. Four cis-acting, positively regulating elements termed AT(1)PRE1 (-113 to -102 bp), AT(1)PRE2 (-49 to -43 bp), AT(1)PRE3 (-5 to -2 bp) and AT(1)PRE4 (+44 to +50 bp) were identified. AT(1)PRE2 contained a GC-box-like sequence and bound to Sp1. AT(1)PRE1 contained two tandem GC-boxes and was bound to several nuclear proteins in addition to Sp1. Nuclear proteins that were bound sequence-specifically to AT(1)PRE1, AT(1)PRE2 and AT(1)PRE4 were found in both PLC-PRF-5 cells and 8505C cells, while those bound to AT(1)PRE3 were not found in 8505C cells, which showed no expression of AT(1) and almost no promoter activity for the AT(1) gene. Significant promoter activity was still observed even when AT(1)PRE1, AT(1)PRE2 and AT(1)PRE4 were all mutated. Mutagenesis of AT(1)PRE3, however, substantially inactivated promoter activity. AT(1)PRE1, AT(1)PRE2 and AT(1)PRE4 synergistically enhanced AT(1) gene transcription promoted by AT(1)PRE3. These results suggested that AT(1)PRE3 is responsible for the tissue-specific expression of the human AT(1) gene, and that AT(1)PRE1, AT(1)PRE2 and AT(1)PRE4 function as a general enhancer in liver-derived cells.

Different effect of ATP on ANP receptor guanylyl cyclase in spontaneously hypertensive and normotensive rats

AIM

Natriuretic peptide receptor A (NPR-A) is the main physiological receptor for atrial natriuretic peptide (ANP). Maximal activation of NPR-A guanylyl cyclase (GC) requires ANP binding and ATP interaction with a putative cytoplasmic site. This study investigates the regulatory effect of ATP on GC-coupled NPR-A activity in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR).

METHODS

Cyclic GMP production and competitive inhibition of [(125)I]ANP(1-28) binding were performed in solubilized glomerular and papillary renal membranes.

RESULTS

Here, we report that incubation of renal glomerular and papillary membranes with ATP induced a concentration-dependent increase in basal and ANP(1-28)-stimulated GC activity that was significantly greater in SHR than in age-matched WKY. ATPgammaS was more effective than ATP and induced a greater stimulation of cGMP production in SHR than in WKY. In contrast, in solubilized membranes ATP exerted an inhibitory role on basal and ANP(1-28)-induced GC activity, suggesting that an accessory protein is required for ATP-induced GC activation. ATP increases NPR-A affinity for ANP(1-28) and decreased B(max) in crude and solubilized membranes. Kinetic analysis of GC-coupled NPR-A revealed that ATP reduced the Km and increased the V(max), an effect that was greater in SHR.

CONCLUSION

Our observations indicate that ATP exerts a greater net effect on NPR-A in SHR than in WKY, which might explain the greater rate of cGMP production observed in SHR compared to WKY.

Natriuretic peptides, their receptors, and cyclic guanosine monophosphate-dependent signaling functions

Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide, B-type natriuretic peptide, C-type natriuretic peptide, and possibly osteocrin/musclin. Three single membrane-spanning natriuretic peptide receptors (NPRs) have been identified. Two, NPR-A/GC-A/NPR1 and NPR-B/GC-B/NPR2, are transmembrane guanylyl cyclases, enzymes that catalyze the synthesis of cGMP. One, NPR-C/NPR3, lacks intrinsic enzymatic activity and controls the local concentrations of natriuretic peptides through constitutive receptor-mediated internalization and degradation. Single allele-inactivating mutations in the promoter of human NPR-A are associated with hypertension and heart failure, whereas homozygous inactivating mutations in human NPR-B cause a form of short-limbed dwarfism known as acromesomelic dysplasia type Maroteaux. The physiological effects of natriuretic peptides are elicited through three classes of cGMP binding proteins: cGMP-dependent protein kinases, cGMP-regulated phosphodiesterases, and cyclic nucleotide-gated ion channels. In this comprehensive review, the structure, function, regulation, and biological consequences of natriuretic peptides and their associated signaling proteins are described.

Diverse Forms of Guanylyl Cyclases in Medaka Fish – Their Genomic Structure and Phylogenetic Relationships to those in Vertebrates and Invertebrates

Fish species such as medaka fish, fugu, and zebrafish contain more guanylyl cyclases (GCs) than do mammals. These GCs can be divided into two types: soluble GCs and membrane GCs. The latter are further divided into four subfamilies: (i) natriuretic peptide receptors, (ii) STa/guanylin receptors, (iii) sensory-organ-specific membrane GCs, and (iv) orphan receptors. Phylogenetic analyses of medaka fish GCs, along with those of fugu and zebrafish, suggest that medaka fish is a much closer relative to fugu than to zebrafish. Analyses of nucleotide data available on a web site (http://www.ncbi. nlm.nih.gov/) of GCs from a range of organisms from bacteria to vertebrates suggest that gene duplication, and possibly chromosomal duplication, play important roles in the divergence of GCs. In particular, the membrane GC genes were generated by chromosomal duplication before the divergence of tetrapods and teleosts.

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.

ATP-regulated module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

ATP is an obligatory agent for the atrial natriuretic factor (ANF) and the type C natriuretic peptide (CNP) signaling of their respective receptor guanylate cyclases, ANF-RGC and CNP-RGC. Through a common mechanism, it binds to a defined ARM domain of the cyclase, activates the cyclase and transduces the signal into generation of the second messenger cyclic GMP. In this presentation, the authors review the ATP-regulated transduction mechanism and refine the previously simulated three-dimensional ARM model (Duda T, Yadav P, Jankowska A, Venkataraman V, Sharma RK. Three dimensional atomic model and experimental validation for the ATP-regulated module (ARM) of the atrial natriuretic factor receptor guanylate cyclase. Mol Cell Biochem 2000;214:7-14; reviewed in: Sharma RK, Yadav P, Duda T. Allosteric regulatory step and configuration of the ATP-binding pocket in atrial natriuretic factor receptor guanylate cyclase transduction mechanism. Can J Physiol Pharmacol 2001;79: 682-91; Sharma RK. Evolution of the membrane guanylate cyclase transduction system. Mol Cell Biochem 2002;230:3-30). The model depicts the ATP-binding dependent configurational changes in the ARM and supports the concept that in the first step, ATP partially activates the cyclase and primes it for the subsequent transduction steps, resulting in full activation of the cyclase.

Structural studies of the natriuretic peptide receptor: a novel hormone-induced rotation mechanism for transmembrane signal transduction

The atrial natriuretic peptide (ANP) receptor is a single-span transmembrane receptor that is coupled to its intrinsic intracellular guanylate cyclase (GCase) catalytic activity. To investigate the mechanisms of hormone binding and signal transduction, we have expressed the extracellular hormone-binding domain of the ANP receptor (ANPR) and characterized its structure and function. The disulfide-bond structure, state of glycosylation, binding-site residues, chloride-dependence of ANP binding, dimerization, and binding stoichiometry have been determined. More recently, the crystal structures of both the apoANPR dimer and ANP-bound complex have been determined. The structural comparison between the two has shown that, upon ANP binding, two ANPR molecules in the dimer undergo an inter-molecular twist with little intra-molecular conformational change. This motion produces a Ferris wheel-like translocation of two juxtamembrane domains with essentially no change in the inter-domain distance. This movement alters the relative orientation of the two domains equivalent to counter-clockwise rotation of each by 24 degrees . These results suggest that transmembrane signaling by the ANP receptor is mediated by a novel hormone-induced rotation mechanism.

Allosteric regulatory step and configuration of the ATP-binding pocket in atrial natriuretic factor receptor guanylate cyclase transduction mechanism

The atrial natriuretic factor (ANF) signal transduction mechanism consists of the transformation of the signal information into the production of cyclic GMP. The binding of ANF to its receptor, which is also a guanylate cyclase, generates the signal. This cyclase has been termed atrial natriuretic factor receptor guanylate cyclase, ANF-RGC. ANF-RGC is a single transmembrane-spanning protein. The ANF receptor domain resides in the extracellular region of the protein, and the catalytic domain is located in the intracellular region at the C-terminus of the protein. Thus, the signal is relayed progressively from the receptor domain to the catalytic domain, where it is converted into the formation of cyclic GMP. The first transduction step is the direct binding of ATP with ANF-RGC. This causes allosteric regulation of the enzyme and primes it for the activation of its catalytic moiety. The partial structural motif of the ATP binding domain in ANF-RGC has been elucidated, and it has been named ATP regulatory module (ARM). In this presentation, we provide a brief review of the ATP-regulated transduction mechanism and the ARM model. The model depicts a configuration of the ATP-binding pocket that has been experimentally validated, and the model shows that the ATP-dependent transduction process is a two- (or more) step event. The first step involves the binding of ATP with its ARM. This partially activates the cyclase and prepares it for the subsequent steps, which are consistent with its being phosphorylated and attaining the fully activated state.Key words: ANF, ANF-receptor guanylate cyclase (ANF-RGC), ATP, ATP-regulatory module (ARM).

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

Ligand binding-dependent limited proteolysis of the atrial natriuretic peptide receptor: juxtamembrane hinge structure essential for transmembrane signal transduction

The atrial natriuretic peptide (ANP) receptor is a 130-kDa transmembrane protein containing an extracellular ANP-binding domain, a single transmembrane sequence, an intracellular kinase-homologous domain, and a guanylate cyclase (GCase) domain. We observed that the receptor, when bound with ANP, was rapidly cleaved by endogenous or exogenously added protease to yield a 65-kDa ANP-binding fragment. No cleavage occurred without bound ANP. This ligand-induced cleavage abolished GCase activation by ANP. Cleavage occurred in an extracellular, juxtamembrane region containing six closely spaced Pro residues and a disulfide bond. Such structural features are shared among the A-type and B-type ANP receptors but not by ANP clearance receptors. The potential role of the hinge structure was examined by mutagenesis experiments. Mutation of Pro(417), but not other Pro residues, to Ala abolished GCase activation by ANP. Elimination of the disulfide bond by Cys to Ser mutations yielded a constitutively active receptor. Pro(417), and Cys(423) and Cys(432) forming the disulfide bond are strictly conserved among GCase-coupled receptors, while other residues are largely variable. The conserved Pro(417) and the disulfide bond may represent a consensus signaling motif in the juxtamembrane hinge structure that undergoes a marked conformational change upon ligand binding and apparently mediates transmembrane signal transduction.

The guanylyl cyclase family of natriuretic peptide receptors

Guanylyl cyclases are cytoplasmic and membrane-associated enzymes that catalyze the conversion of GTP to cyclic GMP, an intracellular signaling molecule. Molecular cloning has identified a multigene family encoding both soluble and particulate forms of the enzymes. Diffusible agents such as nitric oxide and carbon monoxide activate the soluble guanylyl cyclases. The particulate members of the family share a characteristic domain arrangement, with a single transmembrane span separating a variable extracellular ligand-binding domain from a conserved intracellular regulatory and cyclase catalytic domain. Seven members of the particulate guanylyl cyclase family have been identified, and they include the receptors for natriuretic peptides and Escherichia coli heat-stable enterotoxin. Recently, animal models have been developed to study the role of natriuretic peptides and their guanylyl cyclase-coupled receptors in renal and cardiovascular physiology.

Expression and purification of the extracellular ligand-binding domain of the atrial natriuretic peptide (ANP) receptor: monovalent binding with ANP induces 2:2 complexes

The receptor for atrial natriuretic peptide (ANP) is a type-I transmembrane protein containing an extracellular ligand-binding domain, a single transmembrane sequence, an intracellular kinase-homologous domain, and a guanylate cyclase (GCase) domain. Binding of ANP to the extracellular domain causes activation of the GCase domain by an as yet unknown mechanism. To facilitate studies of the receptor structure and signaling mechanism, we have expressed the extracellular ANP-binding domain of rat ANP receptor (NPR-ECD) in a water-soluble form. NPR-ECD was purified to homogeneity by ANP-affinity chromatography. SDS-PAGE gave a single 61-kDa band, which coincided with a radioactive band obtained by photoaffinity-labeling with N4alpha-azidobenzoyl-125I-ANP(4-28). Edman degradation gave a single amino-terminal sequence expected for the mature protein. Both trifluoromethanesulfonic acid and peptide-N-glycosidase F treatments yielded a 50-kDa band, indicating N-glycosylation. The molecular mass of 57 725 Da determined by mass spectrometry indicates the carbohydrate content at 16%. NPR-ECD bound ANP with an affinity comparable to that of the full-length receptor. The ligand selectivity of NPR-ECD (in the order ANP > brain natriuretic peptide >> C-type natriuretic peptide) was also similar to that of the full-length receptor. HPLC gel filtration of NPR-ECD gave a peak with an apparent mass of 74 kDa. Preincubation with ANP generated a new 150-kDa peak with a concomitant decrease of the 74-kDa peak. This shift in peak positions was ANP concentration-dependent and was complete at the NPR-ECD-to-ANP molar ratio of 1:1, indicating equimolar binding. The change in the apparent native molecular weight from 74 to 150 kDa suggests that binding causes dimerization of the NPR-ECD:ANP complex to yield an [NPR-ECD:ANP]2 complex.

Characteristics of ANP-binding sites in the adrenal capsules of term-pregnant rats

Significant increases of circulatory volume and plasma aldosterone levels are observed in pregnancy. We investigated whether a decrease of atrial natriuretic peptide (ANP) receptors in the adrenal zona glomerulosa (ZG) could explain the marked elevation of plasma aldosterone occurring during pregnancy. 125I-ANP binding was measured in competition experiments using rANP(1-28), ANP(4-23), a truncated analog which has high specificity for the ANP-C receptor, or a combination of both. Western blot experiments were also performed with an investigation into the effect of ANP on aldosterone secretion in adrenal capsule suspensions. 125I-ANP binding on adrenal ZG membranes was displaced by ANP(1-28) with an affinity (Kd) of 313 +/- 39 and 323 +/- 60 pM (NS) for pregnant and non-pregnant rats, respectively. The density of sites (Bmax) decreased slightly but not significantly during pregnancy. Displacement experiments with ANP(4-23) demonstrated a Bmax of 137 and 134 fmol/mg of proteins (NS) for pregnant and non pregnant rats, respectively. Studies were performed to block the ANP-C site. Displacing the remaining 125I-ANP binding with ANP(1-28) led to an affinity constant and receptor density which were not significantly different between the two groups of rats. The results obtained with Western blots showed a single band of 123 kDa with no significant variations in ANP-R1 receptors in the ZG during gestation. The sensitivity of potassium-, ACTH- or angiotensin II-stimulated aldosterone secretion to ANP was not altered by gestation. These data show that the apparent hyperaldosteronism found in normal term-pregnant rats is not the consequence of modifications in the affinity, number and properties of ANP receptor types or in the sensitivity of the aldosterone response to ANP.

Localization of atrial natriuretic factor receptors in the mesenteric arterial bed. Comparison with angiotensin II and endothelin receptors

Although receptors for atrial natriuretic factor (ANF) and angiotensin II (Ang II) have been reported in rat mesenteric arteries, both peptides induce weak biological responses. Endothelin-1 (ET-1) evokes a potent vasoconstriction in the mesenteric artery. To identify the tissue localization of ANF, Ang II, and ET-1 receptors, radioligand binding experiments with 125I-ANF, 125I-[Sar1,Ile8]Ang II, and 125I-ET-1 were performed in defatted mesenteric arteries and in the surrounding adipose tissue. 125I-ANF binding assays in adipose tissue showed a single class of high-affinity binding sites (Bmax, 420 +/- 16 fmol/mg protein; Kd, 343 +/- 16 pmol/L). In vascular membranes, most 125I-ANF binding was nonspecific. The majority of receptors present in adipose tissue recognized ANF, C-type natriuretic peptide (CNP), and des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANF-(4- 23) (C-ANF) with close affinities, with C-ANF competing for > 98% of the binding sites. In adipocytes, ANF and CNP stimulated cGMP generation. cGMP production by mesenteric arteries was stimulated by sodium nitroprusside but not by ANF or CNP. Autoradiographic localization of 125I-ANF and 125I-ET-1 showed that in the case of ANF, most specific binding occurred in adipocytes, whereas for ET-1, specific binding was present in both adipose tissue and mesenteric arteries. Cross-linking of 125I-ANF followed by SDS-PAGE revealed two receptor species of 130 and 70 kD in adipose membranes and none in vascular tissue. Both were completely displaced by ANF, CNP, and C-ANF. 125I-[Sar1,Ile8]Ang II binding assays in adipose tissue exhibited a single class of binding sites (Bmax, 211 +/- 4 fmol/mg protein; Kd, 520 +/- 10 pmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutational inactivation of the catalytic domain of guanylate cyclase-A receptor

Guanylate cyclase-A, the receptor for atrial natriuretic factor, contains a protein kinase-like domain and a catalytic domain in the intracellular region. To investigate the active site (the catalytic cavity) of guanylate cyclase-A, we amplified the catalytic domain plus three amino acids from the kinase-like domain of guanylate cyclase-A (GC-c) with polymerase chain reaction (PCR) and expressed it in Escherichia coli. During the screening of the PCR-cloned gene products with guanylate cyclase assay, a mutant that lacks enzyme activity was identified. Results of cDNA sequencing revealed that Leu 817 was replaced by an Arg residue in the mutated protein. The mutated GC-c bound to GTP-agarose as well as the wild-type protein, indicating that the binding capability of mutated GC-c to GTP is not significantly affected by the Arg substitution. Gel-filtration column chromatography showed that, like the wild-type GC-c, the mutated protein also formed a high-molecular-weight complex. Since mutation of Leu 817 to Arg abolishes the catalytic activity, Leu 817 is likely located near the active site of guanylate cyclase-A. These results demonstrate that the carboxyl fragment of guanylate cyclase-A is an ideal system for studying the active site of guanylate cyclase-A.

Interaction of atrial natriuretic peptide with its receptors in bovine lung membranes

In bovine lung membranes, atrial natriuretic peptide (ANP) showed temperature-dependent binding to guanylate cyclase-natriuretic peptide receptor (NPR-GC). Photoaffinity labeling of the receptors with 4-azidobenzoyl (AZB)-125I-ANP and competitive binding studies with 125I-ANP, ANP, and atriopeptin I (API) revealed that NPR-GC was detected as the predominant ANP-binding protein at 0 degrees C, whereas at 37 degrees C natriuretic peptide clearance receptor (NPR-C) was detected as the predominant protein. The ratio of NPR-GC and NPR-C was 89:11 at 0 degrees C for 40 min, respectively, whereas 6:94 at 37 degrees C. AZB-125I-ANP bound to NPR-GC dissociated from the binding site within 5 min at 37 degrees C but not at 0 degrees C, whereas ANP bound to NPR-C did not dissociate from the binding site at 0 and 37 degrees C. The dissociated AZB-125I-ANP rapidly rebound to NPR-GC at 37 degrees C but not to NPR-C, and the dissociated NPR-GC was capable of binding. Some AZB-125I-ANP was hydrolyzed by a membrane-bound proteinase(s). Phosphoramidon inhibited the hydrolysis of AZB-125I-ANP. Thus, the dissociated AZB-125I-ANP rebound to NPR-GC and NPR-C. These results suggest that usually intact ANP repeatedly binds to NPR-GC until hydrolysis. Furthermore, the majority of ANP bind to NPR-GC before binding to NPR-C under physiological temperature.

Dominant negative mutations of the guanylyl cyclase-A receptor. Extracellular domain deletion and catalytic domain point mutations

Guanylyl cyclase-A (GC-A), a receptor for A-type natriuretic peptide (ANP), contains an extracellular ligand-binding domain, a single transmembrane domain, and intracellular protein kinase-like and cyclase catalytic domains. Expression of the putative cyclase catalytic region (HCAT) resulted in the formation of an active enzyme that migrated as a homodimer on gel filtration columns; treatment with sodium trichloroacetate caused dissociation of the dimer and a loss of cyclase activity. Co-transfection of HCAT and full-length GC-A led to elevated basal intact cell cGMP concentrations and increased cell homogenate guanylyl cyclase activity. However, atrial natriuretic peptide-induced elevations of cGMP and cyclase activity were inhibited by the introduction of HCAT. Alanine scanning mutagenesis of highly conserved residues within HCAT identified one mutation (D893A) that destroyed enzyme activity but not the ability of the mutant subunit to form homodimers. The mutant subunit inhibited the cyclase activity of wild-type HCAT (approximately 70%) as well as that of full-length GC-A (approximately 85%) in co-expression studies where the amount of wild-type HCAT or full-length GC-A was not altered. Unlike co-transfection with wild-type HCAT, co-transfection of HCA-TD893A and GC-A did not result in elevated basal intact cell cGMP concentrations. For the first time we describe deletion and point mutations within the plasma membrane family of guanylyl cyclase receptors that result in the formation of effective dominant negative proteins.

Hormonal modulation of atrial natriuretic factor receptors in adrenal fasciculata cells from female rats

We recently reported that the hormonal status of female rats modified atrial natriuretic factor (ANF) receptors and the aldosterone-suppressant activity of ANF in adrenal glomerulosa cells; here we investigated if this was also true for adrenal fasciculata cells. Adrenal fasciculata cells from animals in different hormonal states contained guanylate cyclase linked ANF-R1 receptors but not ANF-R2 (clearance) receptors. The concentration of ANF-R1 receptors in cells from intact virgin rats was insignificantly higher than in cells from 13- to 15-day pregnant rats and significantly higher than in cells from ovariectomized (OVX), OVX beta-estradiol-treated, and OVX progesterone-treated rats. Under none of the hormonal states did ANF suppress adrenocorticotropic hormone (ACTH) stimulated corticosterone secretion. Data suggest that the interactions between ANF and ACTH on mineralocorticoid and glucocorticoid synthesis markedly differ.

Developmental changes in ANP-stimulated guanylyl cyclase activity enhanced by ATP in rat lung membrane fractions

1. ANP (atrial natriuretic peptides)- or ANP/ATP-stimulated guanylyl cyclase activities were compared in adult (2 month old) and neonatal (5-7 day old) rat lung membrane fractions. 2. The enzyme activities of both membranes depended on the incubation time and ATP concentration: although the activities of both membranes were similar after a short incubation time (4 min), those in adult membranes were lower than those of neonatal membranes after longer incubation times (10 and 30 min) or at lower concentrations of ATP. 3. ANP/ATP gamma S-stimulated guanylyl cyclase activities, which were much higher than ANP/ATP-stimulated activities, were similar in both membranes. 4. ATPase activity of adult membranes was higher than that of neonatal membranes, suggesting that hydrolysis of ATP leads to a decrease of ANP/ATP-guanylyl cyclase activity in adult membranes. Triton X-100 enhanced and diminished ANP/ATP-stimulated guanylyl cyclase activities of adult and neonatal membranes, respectively, and thereby abolished the adult/neonatal difference in the membrane response to ATP. 5. ANP-stimulated activities of both membranes were much more activated by pre-incubation with ATP gamma S than those induced by simultaneous addition of ATP gamma S. The former activities were decreased to levels of the latter by Triton X-100. The latter activities were not affected by Triton X-100. 6. The present results suggested that conformation of lung plasma membranes is related to activation of the ANP receptor/guanylyl cyclase system.

Atrial natriuretic factor as a volume regulator

Atrial natriuretic factor, originally isolated from the atrium of the heart, has been found to consist of three major groups: atrial natriuretic peptide (ANP), B-form natriuretic peptide (BNP), and C-form natriuretic peptide (CNP). In addition, ANP exists in its precursor form, pro-ANP, an active ANP with a longer peptide chain (urodilatin) and an antiparallel dimer of active ANP. Sites and production of these diverse forms of the peptides are also diverse, depending on pathologic states. Three major subtypes of ANP receptors exist; these include a clearance receptor and two types of a transmembrane receptor with guanylyl cyclase structures in their intracellular domain. The latter exists at least in two forms, one of which is found mainly in the brain. All the actions of ANP mediated by the transmembrane form of ANP receptors are mediated by cGMP generated by the guanylyl cyclase in the cytosolic domain of the receptor. Among the numerous effects of ANP, its major effects are stimulation of natriuresis and diuresis by the kidney through its hemodynamic and tubular effects. In addition, ANP causes vasodilatation and fluid volume reduction by direct actions on vascular smooth muscle cells, and inhibition of secretion of hormones, such as aldosterone, from adrenal cortex and norepinephrine from peripheral adrenergic neurons. Centrally mediated effects on the regulation of the fluid volume may also be important.

Modulation of exogenous and endogenous atrial natriuretic peptide by a receptor inhibitor

Atrial natriuretic peptide is an important peptide hormone of cardiac origin that functions to regulate cardiac preload via the regulation of sodium excretion. This natriuretic action occurs through activation of the particulate guanylyl cyclase-linked natriuretic peptide-A receptor. HS-142-1 is a newly discovered antagonist of the natriuretic peptide-A receptor that permits insight into the functional role of atrial natriuretic peptide in cardiorenal homeostasis. The first objective of this study was to define for the first time the intrarenal action of HS-142-1 on exogenous atrial natriuretic peptide-mediated natriuresis in anesthetized normal dogs. In group 1 (n = 6), which received intravenous atrial natriuretic peptide at 100 ng/kg per minute, intrarenal HS-142-1 (0.5 mg/kg bolus) attenuated atrial natriuretic peptide-induced increases in glomerular filtration rate, urine flow, sodium excretion, and renal cyclic GMP generation and decreases in distal tubular sodium reabsorption. The second objective was to determine whether endogenous atrial natriuretic peptide participates in the regulation of basal sodium excretion. In group 2 (n = 6), intrarenal HS-142-1 alone decreased both absolute and fractional sodium excretion and renal cyclic GMP generation and increased distal tubular sodium reabsorption. These studies demonstrate that HS-142-1 markedly attenuates exogenous atrial natriuretic peptide-mediated natriuresis via enhancement of distal tubular reabsorption and blunting of increases in glomerular filtration rate. Second, the current studies support a functional role for endogenous atrial natriuretic peptide in the regulation of basal sodium excretion.

AP-811, a novel ANP-C receptor selective agonist

AP-811 is a derivative of the Phe8-Ile15 region of atrial natriuretic peptide (ANP) and is one of the smallest linear ligands for ANP receptors. The binding and agonist activities of AP-811 have been compared with those of other ANP analogs for the ANP-A and ANP-C receptors. AP-811 binds with a high binding affinity to and is a strong agonist for the ANP-C receptor, indicating that the binding and agonist sites for this receptor are the same or near each other in the ANP sequence. In contrast, AP-811 showed no agonistic effect for the ANP-A receptor, although it could bind to this receptor. Comparing the biological activities of AP-811 with those of other ANP analogs, we propose that the binding and agonist sites for the ANP-A receptor may consist of separate regions of ANP. In conclusion, AP-811 is the smallest C-receptor-selective agonist.

Cloning of guanylyl cyclase isoforms

The cloning of particulate and soluble guanylyl cyclases is summarized in Table I. With respect to transmembrane signal transduction systems, guanylyl and adenylyl cyclases can be grouped together with some protein tyrosine kinases and protein tyrosine phosphatases to form a diverse protein family with various structural and functional similarities (Garbers, 1989, 1991, 1992; Koesling et al., 1991; Chinkers and Garbers, 1991; Fig. 1). Particulate guanylyl cyclase contains a single transmembrane domain, and the peptide-binding portion (ligand receptor) is on the exterior surface and the catalytic region on the interior, similar to the protein tyrosine kinase/receptor and the protein tyrosine phosphatase/receptor families (Yarden et al., 1986; Charbonneau et al., 1988; Tonks et al., 1988). Protein tyrosine kinases and phosphatases are also activated by ligand binding to the extracellular domain, which in turn results in phosphorylation or dephosphorylation. On the other hand, soluble guanylyl cyclase exists as a heterodimer with two putative catalytic domains, and both subunits are essential for enzyme activity and activation by nitric oxide. It is thus particularly interesting that adenylyl cyclase also contains two catalytic domains, which are both necessary for catalytic activity (Tang et al., 1991). It is possible that particulate guanylyl cyclase may also dimerize on hormonal stimulation and two catalytic domains from two monomers form a functional catalytic center capable of forming cyclic GMP. The catalytic core of GC-A expressed in bacteria was shown to form a homodimer with positively cooperative kinetics (Thorpe et al., 1991). The physiological significance of the existence of multiple forms of soluble guanylyl cyclase subunits remains unclear. Future studies should reveal the differences in tissue distribution and activation by nitrovasodilators in various heterodimers of soluble guanylyl cyclase.

Hormonal modulation of atrial natriuretic factor receptors and effects on adrenal glomerulosa cells of female rats

This study was done to determine if a decrease in the aldosterone-suppressant effect of atrial natriuretic factor (ANF) by progesterone and an increase by estrogen was caused by modulation of adrenal zona glomerulosa ANF receptors. Freshly dispersed glomerulosa cells from virgin, 13-15 day pregnant, ovariectomized (OVX) estradiol-17 beta-treated and OVX progesterone-treated rats were used. Competitive displacement of specifically bound [125I]ANF1-28 with unlabelled ANF1-28 yielded concentrations of guanylate cyclase-linked ANF-R1 plus ANF-R2 (clearance) receptors and the displacement with unlabelled ANF4-23 yielded ANF-R2 receptors; the difference between the two was treated as the concentration of ANF-R1 receptors. Pregnancy and progesterone decreased and estrogen increased the number of glomerulosa ANF-R1 receptors. ANF produced a significantly greater suppression of potassium-induced aldosterone secretion in cells from OVX estradiol-treated rats than in cells from OVX progesterone-treated animals. These data suggest that the inhibition of the aldosterone-suppressant activity of ANF by progesterone is the result of a downregulation of ANF-R1 receptors.

The glycine residue of ATP regulatory module in receptor guanylate cyclases that is essential in natriuretic factor signaling

Atrial natriuretic factor (ANF) and C-type natriuretic peptide (CNP)-activated guanylate cyclases are single-chain transmembrane-spanning proteins, containing both ligand binding and catalytic activities. In both proteins, ligand binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an ATP-dependent step. ATP directly binds to a defined ATP-regulatory module (ARM) sequence motif in the cyclases and through ARM bridges the events of ligand binding and signal transduction. These ARM sequence motifs are respectively represented by Gly503-Xa-Gly505-Xa-Xa-Xa-Gly509 and Gly499-Xa-Xa-Xa-Gly503 in the case of ANF receptor guanylate cyclase (ANF-RGC) and CNP receptor guanylate cyclase (CNP-RGC). Through genetic remodeling techniques, we now show that ARM-Gly505 in ANF-RGC and the corresponding ARM-Gly499 in CNP-RGC are critical for ANF and CNP signaling, and other ARM-Gly residues have minimal effect in the respective signaling processes.

Structural requirements of mastoparan for activation of membrane-bound guanylate cyclase

Mastoparan activated membrane-bound guanylate cyclase and potentiated the effect of atrial natriuretic factor (ANF) and ATP on guanylate cyclase activity in rat lung membranes. Mastoparan is a cationic, amphiphilic tetradecapeptide with an amidated carboxyl terminus. It takes the alpha-helical conformation upon interacting with the membrane. Several analogs were synthesized to study the role of the positive charges, the carboxyl amino group and the alpha-helical conformation of mastoparan in the activation of guanylate cyclase. The results showed that substitution of the C-terminal amide group of mastoparan with a carboxyl group significantly reduced its potency on the activation of guanylate cyclase. Replacement of three lysine residues of mastoparan with aspartic acid or serine residues completely abolished the stimulatory effect of mastoparan. When the alanine at position 10 of mastoparan was substituted by a proline, the resulting analog had no effect on guanylate cyclase activity. These results demonstrate that the positive charges and the helical structure of mastoparan are critical determinants for the activation of guanylate cyclase.

Aortic smooth muscle contains guanylate-cyclase-coupled 130-kDa atrial natriuretic factor receptor as predominant receptor form. Spontaneous switching to 60-kDa C-receptor upon cell culturing

Photoaffinity labeling of atrial natriuretic factor (ANF) receptor in the plasma membranes from bovine aortic smooth muscle tissue using N alpha 5-(4-azidobenzoyl)-ANF-(5-28)- peptide labeled with 125I yielded a 130-kDa band. However, when smooth muscle cells from the same bovine aorta were placed in culture, the 130-kDa receptor quickly disappeared and a 60-kDa band began to appear at high density. After three passages, essentially no 130-kDa band was found and only the 60-kDa band was strongly labeled. The primary structures of the two receptor forms were compared by radiochemical peptide mapping after endoproteinase Glu-C digestion of photoaffinity-labeled and detergent-solubilized 130-kDa receptor from the aorta or the 60-kDa receptor from the cultured cells. The peptide mapping showed courses of digestion that were significantly different from each other, suggesting difference in their primary structures. The basal guanylate cyclase activity in the aortic membranes was 1.0 pmol cGMP produced.min-1.mg protein-1 at 37 degrees C using Mn(2+)-GTP as substrate. The corresponding activity in the membranes from the cultured cells was 20 fmol cGMP.min-1.mg protein-1. Binding studies gave a density of binding sites (Bmax) of 82 fmol/mg protein for the aortic membranes and 850 fmol/mg protein for the cultured cell membranes. These data suggest that the major form of ANF receptor in the cultured cells, namely the 60-kDa receptor, lacked guanylate cyclase activity. Northern blot analysis of poly(A)-RNA extracted form bovine thoracic aorta or adrenal cortex gave a single 3.6-kb band when 32P-labeled human A-type ANF receptor cDNA was used as a hybridization probe. However, no band was detected when C-receptor cDNA was used as a probe. In addition to the major 130-kDa band, extended SDS/PAGE revealed two additional faint bands with estimated molecular masses of 126 kDa and 135 kDa. Treatment with endoglycosidase H resulted in disappearance of the 126-kDa band and appearance of a 100-kDa band. The 130-kDa and 135-kDa bands were unchanged. Treatment by endoglycosidase F or glycopeptidase F reduced all three bands to a single 100-kDa band. These results suggest that the slight difference in mobility is due to different states of glycosylation.(ABSTRACT TRUNCATED AT 400 WORDS)

Down-regulation of protein kinase C potentiates atrial natriuretic peptide-stimulated cGMP accumulation in vascular smooth-muscle cells

It has been reported that atrial natriuretic peptide (ANP) produces inositol phosphates and diacylglycerol in vascular smooth muscle cells (VSMC). The purpose of this study is to investigate whether diacylglycerol produced by ANP affects ANP-induced cyclic GMP (cGMP) accumulation through the activation of protein kinase C. Short-term (15 min) treatment of rat aortic VSMC with protein kinase C activating phorbol 12-myristate 13-acetate (PMA, 100 nM) decreased ANP (100 nM)-induced cGMP accumulation by 34.7% in the presence of IBMX (0.5 mM). However, the long-term (24 h) treatment to decrease the activity of protein kinase C led to an enhancement of the cGMP accumulation by 69.6% compared with that of control VSMC. There were no significant differences in Bmax and Kd for ANP and ANP-dependent particular guanylyl cyclase activity between long-term PMA-treated and control VSMC. In the present study, we show that the activation of protein kinase C attenuates the cGMP accumulation induced by ANP and that down-regulation of protein kinase C results in an enhancement of the cGMP accumulation. These data are consistent with the role of protein kinase C as a negative regulator in ANP-receptor/guanylyl cyclase pathway.

Induction of nitric oxide synthase regulates atrial natriuretic peptide receptors in vascular smooth muscle cells

In a previous study, we reported that cyclic GMP (cGMP) selectively down-regulates the atrial natriuretic peptide clearance receptor (ANPC receptor) in the vascular endothelial cells. The aim of the present study is to determine whether nitric oxide (NO) regulates ANP receptor by accumulating intracellular cGMP in cultured rabbit aortic smooth muscle cells. Treatment with interleukin-1 beta (IL-1), a cytokine known to induce NO synthase, dose-dependently increased the basal level of intracellular cGMP with a concomitant increase of nitrite in the conditioned media. These effects of IL-1 were attenuated in the presence of N omega-nitro-L-arginine. IL-1 (40 pM) significantly (P < 0.01) decreased [125I]atriopeptin III binding to the cells, an effect that was inhibited by N omega-nitro-L-arginine. Treatment with sodium nitroprusside (SNP) which releases NO also decreased [125I]atriopeptin III binding to the cells. In addition, further decrease in [125I]atriopeptin III binding following IL-1 or SNP treatment was observed in the presence of 0.1 mM zaprinast, a cGMP-specific phosphodiesterase inhibitor. Scatchard analysis of the binding data in the treated cells showed a decrease in Bmax without a significant change in Kd. Affinity cross-linking of [125I]atriopeptin III to the treated cells demonstrated a decrease in 70-kDa band corresponding to the ANPC receptor. MEanwhile, intracellular cGMP response to atriopeptin III was significantly (P < 0.01) enhanced in the cells pretreated with IL-1 or SNP despite the decrease in receptor density. These findings suggest that NO down-regulates the ANPC receptor by the accumulation of intracellular cGMP in cultured rabbit aortic smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Core sequence of ATP regulatory module in receptor guanylate cyclases

Atrial natriuretic factor (ANF) and C-type natriuretic peptide (CNP)-activated guanylate cyclases are single-chain transmembrane-spanning proteins, containing both ligand binding and catalytic activities. In both proteins, ligand binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Studies with ANF receptor guanylate cyclase (ANF-RGC) have indicated that obligatory in this activation process is an ATP-dependent step. ATP directly binds to the cyclase and bridges the events of ligand binding and signal transduction. A defined ATP-regulated module (ARM) sequence (Gly503-Arg-Gly-Ser-Asn-Tyr-Gly509) in the cyclase is critical in the ATP-mediated event. Through genetic remodeling techniques, we have now identified the core ARM sequence that is essential in both ANF and CNP signaling. This sequence is Gly-Xa-Xa-Xa-Gly, represented by Gly505-Ser-Asn-Tyr-Gly509 in the case of ANF-RGC ARM and by Gly499-Ser-Ser-Tyr-Gly503 in the CNP receptor guanylate cyclase ARM.

Inhibition of the aldosterone-suppressant activity of atrial natriuretic factor by progesterone and pregnancy in rats

Angiotensin II (AII) caused concentration-dependent increase in aldosterone secretion by dispersed zona glomerulosa cells from non-ovariectomized (non-OVX) and ovariectomized (OVX) rats treated with the vehicle (peanut oil), beta-estradiol (0.1 mg/kg/d x 3) or progesterone (2 mg/kg/d x 3); this effect of AII was greater on cells from progesterone- than from estrogen-treated animals. In contrast, atrial natriuretic factor (ANF) was 100- to 1,000-fold less effective in suppressing AII-stimulated aldosterone production by cells from progesterone-treated (both non-OVX and OVX) and pregnant (17-20 day) rats than by cells from nonpregnant controls and estrogen-treated animals. To our knowledge, this is the first demonstration of an inhibition of an important action of ANF by another hormone and our data suggest that increased circulating levels of progesterone during pregnancy produce a relative refractoriness to the aldosterone-suppressant activity of ANF, which favors fluid/salt expansion.