Characterization and regulation by protein kinase C of renal glomerular atrial natriuretic peptide receptor-coupled guanylate cyclase

Phosphorylation-Dependent Regulation of Guanylyl Cyclase (GC)-A and Other Membrane GC Receptors

Receptor guanylyl cyclases (GCs) are single membrane spanning, multidomain enzymes, that synthesize cGMP in response to natriuretic peptides or other ligands. They are evolutionarily conserved from sea urchins to humans and regulate diverse physiologies. Most family members are phosphorylated on 4 to 7 conserved serines or threonines at the beginning of their kinase homology domains. This review describes studies that demonstrate that phosphorylation and dephosphorylation are required for activation and inactivation of these enzymes, respectively. Phosphorylation sites in GC-A, GC-B, GC-E, and sea urchin receptors are discussed, as are mutant receptors that mimic the dephosphorylated inactive or phosphorylated active forms of GC-A and GC-B, respectively. A salt bridge model is described that explains why phosphorylation is required for enzyme activation. Potential kinases, phosphatases, and ATP regulation of GC receptors are also discussed. Critically, knock-in mice with glutamate substitutions for receptor phosphorylation sites are described. The inability of opposing signaling pathways to inhibit cGMP synthesis in mice where GC-A or GC-B cannot be dephosphorylated demonstrates the necessity of receptor dephosphorylation in vivo. Cardiac hypertrophy, oocyte meiosis, long-bone growth/achondroplasia, and bone density are regulated by GC phosphorylation, but additional processes are likely to be identified in the future.

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.

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.

Integrative Signaling Networks of Membrane Guanylate Cyclases: Biochemistry and Physiology

This monograph presents a historical perspective of cornerstone developments on the biochemistry and physiology of mammalian membrane guanylate cyclases (MGCs), highlighting contributions made by the authors and their collaborators. Upon resolution of early contentious studies, cyclic GMP emerged alongside cyclic AMP, as an important intracellular second messenger for hormonal signaling. However, the two signaling pathways differ in significant ways. In the cyclic AMP pathway, hormone binding to a G protein coupled receptor leads to stimulation or inhibition of an adenylate cyclase, whereas the cyclic GMP pathway dispenses with intermediaries; hormone binds to an MGC to affect its activity. Although the cyclic GMP pathway is direct, it is by no means simple. The modular design of the molecule incorporates regulation by ATP binding and phosphorylation. MGCs can form complexes with Ca²⁺-sensing subunits that either increase or decrease cyclic GMP synthesis, depending on subunit identity. In some systems, co-expression of two Ca²⁺ sensors, GCAP1 and S100B with ROS-GC1 confers bimodal signaling marked by increases in cyclic GMP synthesis when intracellular Ca²⁺ concentration rises or falls. Some MGCs monitor or are modulated by carbon dioxide via its conversion to bicarbonate. One MGC even functions as a thermosensor as well as a chemosensor; activity reaches a maximum with a mild drop in temperature. The complexity afforded by these multiple limbs of operation enables MGC networks to perform transductions traditionally reserved for G protein coupled receptors and Transient Receptor Potential (TRP) ion channels and to serve a diverse array of functions, including control over cardiac vasculature, smooth muscle relaxation, blood pressure regulation, cellular growth, sensory transductions, neural plasticity and memory.

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.

Plasma membrane guanylate cyclase is a multimodule transduction system

This minireview highlights the studies which suggest that guanylate cyclase is a single-component transducing system, containing distinct signaling modules in a single membrane-spanning protein. A guanylate cyclase signaling model is proposed which envisions the following sequential events: (1) a signal is initiated by the binding of the hormone to the ligand binding module; (2) the signal is potentiated by ATP at ARM; and (3) the amplified signal is finally transduced at the catalytic site. All of these signaling steps together constitute a switch, which when turned on, generates the second messenger cyclic GMP.

The ANF-RGC gene motif (669)WTAPELL(675) is vital for blood pressure regulation: biochemical mechanism

ANF-RGC is the prototype membrane guanylate cyclase, both the receptor and the signal transducer of the hormones ANF and BNP. After binding them at the extracellular domain, it, at its intracellular domain, signals activation of the C-terminal catalytic module and accelerates production of the second messenger, cyclic GMP. This, in turn, controls the physiological processes of blood pressure, cardiovascular function, fluid secretion, and others: metabolic syndrome, obesity, and apoptosis. The biochemical mechanism by which this single molecule controls these diverse processes, explicitly blood pressure regulation, is the subject of this study. In line with the concept that the structural modules of ANF-RGC are designed to respond to more than one yet distinctive signals, the study demonstrates the construction of a novel ANF-RGC-In-gene-(669)WTAPELL(675) mouse model. Through this model, the study establishes that (669)WTAPELL(675) is a vital ANF signal transducer motif of the guanylate cyclase. Its striking physiological features linked with their biochemistry are the following. (1) It controls the hormonally dependent cyclic GMP production in the kidney and the adrenal gland. Its deletion causes (2) hypertension and (3) cardiac hypertrophy. (4) These mice show higher levels of the plasma aldosterone. For the first time, a mere seven-amino acid-encoded motif of the mouse gene has been directly linked with the physiological control of blood pressure regulation, a detailed biochemistry of this linkage has been established, and a model for this linkage has been described.

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 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.

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.

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.

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.

Brain natriuretic peptide: role in cardiovascular and volume homeostasis

The identification of natriuretic peptides as key regulators of natriuresis and vasodilatation, and the appreciation that their secretion is under the control of cardiac hemodynamic and neurohumoral factors, has caused wide interest. The natriuretic peptides are structurally similar, but genetically distinct peptides that have diverse actions on cardiovascular, renal, and endocrine homeostasis. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are of myocardial cell origin, while cardiac natriuretic peptide (CNP) is of endothelial origin. ANP and BNP bind to the natriuretic peptide receptor (NPR-A) which, via 3' 5'-cyclic guanosine monophosphate (cGMP), mediates natriuresis, vasodialation, renin inhibition, and antimitogenic properties. CNP lacks natriuretic action but possesses vasodilating and growth inhibiting effects via the guanyl cyclase linked natriuretic peptide-B (NPR-B) receptor. All three peptides are cleared by natriuretic peptide-C receptor (NPR-C) and degraded by neutral endopeptidase, both of which are widely expressed in kidney, lung, and vascular wall. Recently, a fourth member of the natriuretic peptide, dendroaspsis natriuretic peptide (DNP) has been reported to be present in human plasma and atrial myocardium.

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.

Mesangial cells from diabetic NOD mice constitutively express increased density of atrial natriuretic peptide C receptors

BACKGROUND

Experimental evidence shows that natriuretic peptides (NPs) play a pathophysiological role in the glomerular hemodynamic abnormalities that occur in diabetes mellitus.

METHODS

In this study, the cGMP response to NPs and the different subtypes of NP receptors were examined in mesangial cells derived from a genetic model of diabetes, the nonobese diabetic (NOD) mouse. Multiple mesangial cell lines were derived from diabetic (D-NOD) and nondiabetic (ND-NOD) adult mice and were studied at different passages.

RESULTS

cGMP accumulation after stimulation by atrial NP (ANP) or C-type NP (CNP) was markedly inhibited in D-NOD cells irrespective of the glucose concentration (6 or 20 mM) in the culture medium. In contrast, NP receptor density measured from [125I]-ANP saturation binding curves was 7.5 times greater in D-NOD than in ND-NOD cells. No change in KD (200 pM in both cell lines) was observed. Competitive inhibition studies showed that 4-23 C-ANP, which is specific of clearance receptors (NPR-C), displaced 90% of the maximum fraction bound, suggesting the predominance of NPR-C in both cell lines. Further identification was obtained from RNase protection assay and reverse transcription-polymerase chain reaction, which also demonstrated the higher expression of NPR-C mRNA in D-NOD cells. In contrast, NPR-A mRNA was not modified. Increased expression of NPR-C in D-NOD cells was associated with an increase of ANP internalization rate at 37 degrees C, indicating that these receptors were functional.

CONCLUSIONS

These studies demonstrate that the constitutive overexpression of NPR-C in D-NOD mesangial cells is associated with a decreased response of cGMP to ANP or CNP treatment. This could be due to the lesser availability of the peptides for binding to NPR-A or NPR-B or to an inhibitory effect on NP-dependent guanylate cyclase activity via the activation of NPR-C.

Atrial natriuretic peptide induces acrosomal exocytosis of human spermatozoa

Acrosomal exocytosis in mammalian spermatozoa is a process essential for fertilization. We report here that atrial natriuretic peptide (ANP) markedly stimulates acrosomal exocytosis of capacitated human spermatozoa. Typically, ANP exerts some of its actions via activation of the ANP receptor (ANPR-A), a particulate guanylyl cyclase-linked receptor, and subsequent formation of guanosine 3',5'-cyclic monophosphate (cGMP). We found that ANP-stimulated acrosome reaction was inhibited by the competitive ANPR-A antagonist anantin, indicating a receptor-mediated process. A linear fragment of ANP, ANP-(13-28), and another ANP-like compound, brain natriuretic peptide, were inactive. The stimulatory effect of ANP on acrosome reaction was mimicked by the permeable cGMP analog, 8-bromo-cGMP (8-BrcGMP). Addition of the protein kinase C (PKC) inhibitors, staurosporine and GF-109203X, resulted in a dose-related inhibition of ANP-induced acrosome reaction. Also, downregulation of endogeneous PKC activity resulted in inhibition of ANP- but not 8-BrcGMP-induced acrosome reaction. Removal of extracellular Ca2+ abolished ANP-induced acrosome reaction. Thus ANP via Ca2+ influx, PKC activation, and stimulation of particulate guanylyl cyclase may play a role in the induction of acrosome reaction of human spermatozoa.

Endothelin-3 reduces C-type natriuretic peptide-induced cyclic GMP formation in C6 glioma cells

The effect of endothelin-3 (ET-3) on C-type natriuretic peptide (CNP)-induced guanosine 3',5'-cyclic monophosphate (cGMP) was examined in C6 glioma cells, CNP-induced cGMP formation was both time- and dose-dependent, with an EC50 value of about 10 nM. While ET-3 and phorbol 12-myristate 13-acetate (PMA) had no effect on basal cGMP production, both compounds were potent inhibitors of CNP-induced cGMP formation, with IC50 values of approximately 10 and 2 nM, respectively. Although protein kinase C (PKC) inhibitors had no effect on basal cGMP formation, Ro 31-8220, a PKC inhibitor, reversed the ET-3 inhibition on CNP-induced cGMP formation by 63% and that of PMA almost completely. Our findings suggest that stimulation of cGMP formation by CNP in C6 glioma cells is negatively modulated by PKC activation, and that the inhibitory action of ET-3 on CNP-stimulated cGMP formation is mediated partly by PKC.

Differential regulation of natriuretic peptide receptors on ciliary body epithelial cells

Atrionatriuretic peptide (ANP) lowers intraocular pressure in the eyes of humans and rabbits. We examined the effects of natriuretic peptides on cGMP formation and 125I-labelled-ANP binding to cultured cells derived from ciliary body epithelium, the site of aqueous humour formation in the eye. ANP, brain natriuretic peptide (BNP) and C-natriuretic peptide (CNP) at 1 microM stimulated cGMP formation 8.2(+/-1.2)-fold, 4.8(+/-0.6)-fold and 87.3(+/-12.1)-fold respectively. 125I-ANP bound to intact cells at a single site, with a dissociation constant KD=0.30+/-0.01 nM. BNP was as effective as ANP in displacing 125I-ANP, whereas CNP displaced label with a slightly higher IC50. 125I-ANP binding was displaced >95% by c-ANP, a specific ligand for natriuretic peptide C receptors (NPR-C). Cross-linking of 125I-ANP to cells labelled predominantly a protein of Mr 62000. These data suggest that 125I-ANP binding was primarily to NPR-C, whereas cGMP stimulation occurred primarily via natriuretic peptide B receptors (NPR-B). Vasopressin and histamine, both activators of the inositol phosphate/diacylglycerol phosphate pathway in non-pigmented ciliary epithelial cells, inhibited CNP stimulation of guanylate cyclase (NPR-B) and 125I-ANP binding (NPR-C) by 30-38%. Inhibition was mimicked by PMA, dioctanoylglycerol and phorbol didecanoate, whereas 4alpha phorbol didecanoate had no effect. Staurosporine and bisindolylmaleimide both blocked inhibition of 125I-ANP binding and cGMP formation by PMA. These results suggest that protein kinase C (PKC) down-regulates both NPR-B and NPR-C. PKC down-regulation of NPR-B varied inversely with CNP concentration. Inhibition by 1 microM PMA was 30.6(+/-4.0)% with 500 nM CNP, but 83.4(+/-8.8)% with 10 nM CNP, indicating that increasing CNP could partially overcome inhibition by PMA. Since extracellular CNP levels were not affected by PKC activation, the effect of PKC on NPR-B is best explained as a reduction in NPR-B affinity for CNP. NPR-C measured as 125I-ANP binding was likewise reduced 36.4(+/-5.1)% by exposure to PMA. In contrast with NPR-B inhibition, however, inhibition of NPR-C was due largely to a reduction in the number of receptor binding sites per cell rather than a reduction in receptor affinity for ligand. The data therefore suggest that both NPR-B and NPR-C are down-regulated by PKC, but that the mechanisms of down-regulation of the two receptors are different.

Protein kinase A activity modulates natriuretic peptide-dependent cGMP accumulation in renal cells

The purpose of this work was to examine whether the level of cAMP accumulation and protein kinase A (PKA) activity influence atrial natriuretic factor (ANF)-dependent guanosine 3',5'-cyclic monophosphate (cGMP) production in two renal cell types: rabbit cortical vascular smooth muscle cells (RCSMC) and SV-40-transformed human glomerular visceral epithelial cells (HGVEC-SV1). N-[2-(p-bromocinnamylamino)ethyl]- 5-isoquinolinesulfonamide (H-89), a PKA inhibitor, decreased ANF-stimulated cGMP production in RCSMC in a time- and concentration-dependent manner. ANF-stimulated cGMP production was markedly inhibited after prolonged 9- and 18-h incubations with 25 microM H-89 (52 and 65%, respectively) but was not altered after exposure of cells to this agent for 1 h. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine and N-(2-[methylamino]ethyl)-5-isoquinolinesulfonamide, protein kinase inhibitors not selective for PKA, did not reproduce the effect of H-89, even at higher concentrations (50 and 100 microM). Cycloheximide (10 microM), a protein synthesis inhibitor, limited the inhibitory effect of H-89, although alone it did not modify the ANF-stimulated cGMP production. H-89 did not affect cGMP production when it was stimulated by SIN-1, a nitric oxide donor. Prolonged incubation (18 h) with 8-bromo cAMP or cholera toxin, an activator of Gs protein resulting in adenylate cyclase stimulation, enhanced ANF-dependent cGMP production by 225 and 176%, respectively. This stimulatory effect was blocked by 25 microM H-89. 125I-ANF binding to RCSMC at 4 degrees C was not affected by preincubation of the cells with H-89. There was a 44% decrease in the expression of ANF C receptors measured as the ANF-(4-23)-displaceable 125I-ANF binding at 37 degrees C, which could not, however, explain the inhibitory effect of H-89 on cGMP production. Modulation of ANF- and C-type natriuretic peptide-dependent cGMP production by H-89 and cholera toxin was also found in HGVEC-SV1 with the same characteristics as in RCSMC. Taken together, these results suggest that PKA activity controls the function of natriuretic peptide guanylate cyclase-coupled receptors in the two cell types studied. PKA-dependent inhibition of a negatively regulatory protein distinct from the receptor itself seems necessary for a full cGMP response.

Endothelin-3 attenuates the cyclic GMP responses to C-type natriuretic peptide in cultured mouse astrocytes

The effect of endothelin-3 (ET-3) on cyclic GMP (cGMP) responses to C-type natriuretic peptide (CNP) was studied in primary cultures of mouse astrocytes. Attenuation of CNP-stimulated cGMP formation by ET-3 was time-dependent, with maximum inhibition achieved at 30 min of preincubation. ET-3 suppressed cGMP production in response to 10 nM CNP in a dose-dependent fashion, with an IC50 of 0.04 nM and a maximal inhibitory concentration of 1 microM, which led to a 66% reduction of the cGMP increment from 45.0 +/- 4.2 pmol/mg protein to 15.4 +/- 2.6 pmol/mg protein. ET-1, ET-2, and ET-3 were equipotent in suppressing the CNP-induced cGMP response, suggesting that this effect was mediated by ETB receptors. Staurosporine, Ro 31-8220, calcium-free medium, nifedipine, verapamil, lanthanum, thapsigargin, BAPTA, W7, calmidazolium, U-73122, neomycin, quinacrine, wortmannin, herbimycin-A, okadaic acid, and sodium orthovanadate failed to block the effect of ET-3. Cycloheximide (100 microM), however, partially but significantly reversed the inhibitory effect of ET-3 on CNP-induced cGMP from 48.2 to 73.3% of the control value. The results support the premise that ET-3 and CNP interact within the central nervous system. The data also suggest that cGMP accumulation in mouse astrocytes is mediated by activation of certain kinases through as yet undefined mechanisms and not by protein kinase C, increased intracellular calcium, or other second messenger pathways such as phospholipases A2, C, D, tyrosine kinase, or protein phosphatases.

Regulation of human erythrocyte Na+/H+ exchange by soluble and particulate guanylate cyclase

Guanylate cyclase activity in human erythrocytes is investigated by evaluating the intracellular guanosine 3',5'-cyclic monophosphate (cGMP) content in the presence of various agents that exert specific effects on soluble or particulate guanylate cyclase. The increase in the intraerythrocyte cGMP content by the soluble guanylate cyclase activators nitroprusside and NaNO2 suggests the presence of this enzyme in human erythrocytes. The effects of four different atrial natriuretic peptide (ANP) fragments on the intraerythrocyte cGMP content is also studied. ANP II and ANP III increase the intraerythrocyte cGMP content, whereas ANP I and des-Ser5,des-Ser6-ANP III are ineffective. Thus our data show that human erythrocytes possess particulate guanylate cyclase together with the soluble enzyme. The ANP fragments ANP II and ANP III also activate the erythrocyte Na+/H+ exchange. Nitroprusside, M & B 22948 (an inhibitor of cGMP phosphodiesterase), and the cGMP analogues dibutyryl cGMP and 8-bromoguanosine 3',5'-cyclic monophosphate also increase the erythrocyte Na+/H+ exchange rate. The latter data also suggest that the erythrocyte Na+/H+ exchange is regulated by cGMP.

Specific potentiation by cyclic AMP of natriuretic peptide-mediated cyclic GMP production in adipose tissue

Adipose tissue of the mesenteric territory contains large quantities of natriuretic peptide receptors (NPR) mainly of the NPR-C subtype. Guanylyl cyclase-bound receptors are also present since atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are equally potent in activating this enzyme. While searching for a potential biological role for NP in adipocytes we observed that ANP-mediated generation of cyclic GMP (cGMP) was potentiated when the cells were simultaneously treated with isoproterenol. Indeed, isoproterenol, a beta-adrenergic agonist, and forskolin, an activator of adenylyl cyclase, can both double or triple cGMP production in response to ANF stimulation. There was a direct correlation between the level of cyclic AMP (cAMP) generated and the level of NP-mediated cGMP production suggesting that a cAMP-dependent mechanism may be responsible of this potentiation. To determine whether or not this phenomenon was unique to adipocytes, NPR subtypes were characterized in 4 established cell lines and their cAMP-dependent cGMP behavior examined. A10 and A7r5 smooth muscle cells showed identical ratio of NPR subtypes with about 95% NPR-C and 5% NPR-B. PC12 cells presented 100% NPR-A and NIH 3T3 fibroblasts 50% NPR-C and 50% NPR-B. Regardless of the NPR subtype, forskolin could not potentiate the cGMP generation in these cell lines. These data indicate that the cAMP-dependent potentiation of the NP-mediated cGMP production is unique to adipocytes, appears independent of the guanylyl cyclase-linked NPR subtypes and may be involved in the sensitization of the guanylyl cyclase domain of NPR for a potential biological role of NP in the adipose tissue.

The significance of Ser1029 of the heat-stable enterotoxin receptor (STaR): relation of STa-mediated guanylyl cyclase activation and signaling by phorbol myristate acetate

To characterize Ser1029 in STaR at a consensus sequence of phosphorylation site by PKC, two mutants of mS1029A with replacement of Ser1029 to Ala1029 and C delta 1029 lacking 22 amino acids including Ser1029 were prepared. Preincubation of the wild type-STaR (wt-STaR) transfectant with 1 microM PMA caused additional STa-mediated guanylyl cyclase (GC) activation compared to control, whereas the mS1029A- and C delta 1029-transfected cells did not show a similar enhanced GC activation by PMA. After metabolic labeling with [32P]phosphate, transfected cells with wt-STaR and mutants were incubated with 1 microM PMA. Subsequent 32P-radiolabeled proteins were immunoprecipitated using anti-STaR antibody, and analyzed by autoradiography after separation on SDS-PAGE. The immunoprecipitated wt-STaR but not mS1029A and C delta 1029 had a significant radioactivity. These results suggest that the effect of PMA on wt-STaR transfectants may be caused by phosphorylation of Ser1029. The C delta 1012 mutant, with further truncation (Gln1012-Phe1050) of the carboxy terminus, did not show STa-mediated GC activation. Based on these data, these 17 amino acids (Gln1012-Ala1028), essential for signaling of GC activation by STa, have an abundance of basic amino acids which might be functionally influenced by phosphorylation of Ser1029.

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.

Adenosine 5'-triphosphate, phorbol ester, and pertussis toxin effects on atrial natriuretic peptide stimulation of guanylate cyclase in a human renal cell line

We examined adenosine 5'-triphosphate (ATP), pertussis toxin (PT) and phorbol myristate acetate (PMA), a protein kinase C (PKC) activator, modulation of atrial natriuretic peptide (ANP)-stimulated cell-membrane guanylate cyclase (ANP-s-GC) activity and ANP stimulation of whole-cell cGMP accumulation (ANP-s-cGMP) in an ANP-receptor-transduction cell model, the human renal cell line (SK-NEP-1). Acute and long-term effects of PMA on PKC isotype activity are different: Acute (20-min) PMA activation of PKC inhibits ANP-s-cGMP and ANP-s-GC; whereas, long-term (36-h) PMA treatment inhibits slightly less by only partially down-regulating PKC activity, the type-III PKC isotype being 36-h resistant. Long-term 10(-7)M PMA treatment of cells neither affected membrane basal GC activity nor ANP-s-GC activity but partially inhibited ATP enhancement of ANP-s-GC. This partial inhibition was completely reversed by the PKC inhibitor H7 and a PKC inhibitory antibody but only partially reversed by the antibody to the catalytic domain of PKC type III. The EC50 for ATP and its non-phosphorylating analog ATP gamma S in the presence of acute PMA inhibition of ANP-s-cGMP was similar (approximately 10(-9)). This enhancement of PMA inhibition was two orders of magnitude more sensitive (EC50 10(-7)M) than inhibition of ANP-s-cGMP that we previously reported for acute PMA treatment of whole SK-NEP-1 cells. The three- to four-fold ATP enhancement of cell membrane ANP-s-GC was not blocked by 12-hour preincubation of cells with 150 ng/mL PT but was completely blocked if 2-x-10(-7)M PMA was then added for 20 minutes, indicating that acute activation of PKC by PMA does not require a functional "G-type" protein. Acute PMA inhibition of ANP-s-cGMP was reversed by permeabilizing SK-NEP-1 cells to a specific PKC inhibitory peptide, further confirming that PMA inhibition was mediated through PKC activation. These data demonstrated that ANP-s-GC and ANP-s-cGMP were modified through non-phosphorylating interactions with ATP, by multiple PMA activatable PKC isoforms, and that neither were affected by PT-sensitive guanine-nucleotide-binding (G)-protein(s).

Characterization of binding sites in rat for A, B and C-type natriuretic peptides

Binding studies, affinity cross-linking and guanylate cyclase assays allowed a comparison of receptors with which the rat forms of atrial/A-type natriuretic peptide (rANP), brain/B-type natriuretic peptide (rBNP) and C-type natriuretic peptide (rCNP) interact in rat kidney cortex and lung. This work represents the first study in which the rat form of BNP (= rBNP-45/iso-rANP(1-45)) has been used as a radiolabelled tracer to further characterize its receptors in these tissues. In addition, these studies stress the use of the same species of natriuretic peptide and assay system, an important experimental des ign given that BNPs show species-specific differences in structure. rBNP-45 bound with lower affinity to rANP (99-126) receptors, namely guanylate cyclase-linked receptor(s) and C-receptor. No receptor which interacted with only rBNP-45 was detectable in lung and kidney cortex. Since rBNP-45 interacted preferentially with the C-receptor and was less potent than rANP(99-126) in stimulating glomerular guanylate cyclase, rBNP-45 may signal through another second messenger in addition to cyclic GMP. Work with truncated analogues of this hormone pinpointed regions of this peptide which may contribute to receptor binding affinity and guanylate cyclase activation. CNP-22 bound to only a subset of ANP receptors and was least effective in stimulating glomerular guanylate cyclase, suggesting a differential mode of action from ANP.

Activation of soluble guanylate cyclase through phosphorylation by protein kinase C in intact PC12 cells

Soluble guanylate cyclase was found to be phosphorylated by protein kinase C in intact PC12 pheochromocytoma cells. The phosphate incorporation into guanylate cyclase upon addition of phorbol 12-O-myristate 13-acetate (PMA) to PC12 cells in culture coincided with an increased intracellular cGMP level. A strong correlation between phosphate incorporation into guanylate cyclase and increased cGMP level was also observed by time-course and dose-response studies of the PMA effect, as well as when cells were treated with various phorbol esters and diacylglycerols or with various protein kinase C inhibitors. The cAMP system and the presence of extracellular Ca2+ were found not to be involved in guanylate cyclase phosphorylation. The phosphorylation and activation of guanylate cyclase by protein kinase C represent a possible mechanism whereby agonist-stimulation of receptors coupled to phosphoinositide hydrolysis induces cGMP synthesis.

Interaction of atrial natriuretic factor and endothelin-1 signals through receptor guanylate cyclase in pulmonary artery endothelial cells

The endothelial cell has a unique intrinsic feature: it produces a most potent vasopressor peptide hormone, endothelin (ET-1), yet it also contains a signaling system of an equally potent hypotensive hormone, atrial natriuretic factor (ANF). This raises two related curious questions: does the endothelial cell also contain an ET-1 signaling system? If yes, how do the two systems interact with each other? The present investigation was undertaken to determine such a possibility. Bovine pulmonary artery endothelial (BPAE) cells were chosen as a model system. Identity of the ANF receptor guanylate cyclase was probed with a specific polyclonal antibody to the 180 kDa membrane guanylate cyclase (mGC) ANF receptor. A Western-blot analysis of GTP-affinity-purified endothelial cell membrane proteins recognized a 180 kDa band; the same antibody inhibited the ANF-stimulated guanylate cyclase activity; the ANF-dependent rise of cyclic GMP in the intact cells was dose-dependent. By affinity cross-linking technique, a predominant 55 kDa membrane protein band was specifically labeled with [125I]ET-1. ET-1 treatment of the cells showed a migration of the protein kinase C (PKC) activity from cytosol to the plasma membrane; ET-1 inhibited the ANF-dependent production of cyclic GMP in a dose-dependent fashion with an EC50 of 100 nM. This inhibitory effect was duplicated by phorbol 12-myristate 13-acetate (PMA), a known PKC-activator. The EC50 of PMA was 5 nM. A PKC inhibitor, 1-(5-isoquinolinyl-sulfonyl)-2-methyl piperazine (H-7), blocked the PMA-dependent attenuation of ANF-dependent cyclic GMP formation. These results demonstrate that the 180 kDa mGC-coupled ANF and ET-1 signaling systems coexist in endothelial cells and that the ET-1 signal negates the ANF-dependent guanylate cyclase activity and cyclic GMP formation. Furthermore, these results support the paracrine and/or autocrine role of ET-1.

Regulation of intestinal guanylate cyclase by the heat-stable enterotoxin of Escherichia coli (STa) and protein kinase C

The heat-stable enterotoxin of Escherichia coli (STa) stimulates membrane-bound guanylate cyclase in intestinal epithelium and induces fluid and ion secretion. Using the T84 human colon carcinoma cell line as a model, we observed that phorbol esters markedly enhanced STa-stimulated cyclic GMP accumulation in T84 cells (C. S. Weikel, C. L. Spann, C. P. Chambers, J. K. Crane, J. Linden, and E. L. Hewlett, Infect. Immun. 58:1402-1407, 1990). In this study we document that the phorbol ester treatment increases 125I-STa-binding sites as well as membrane-bound guanylate cyclase activity in T84 cells and provide evidence that both effects are mediated by phosphorylation. Guanylate cyclase activity was increased approximately 50% in membranes prepared from intact T84 cells treated with phorbol-12,13-dibutyrate (beta-PDB) and after treatment of homogenates with beta-PDB in a manner dependent on ATP, MgCl2, and cytosol. Similarly, treatment of membranes with purified bovine brain protein kinase C in the presence of appropriate cofactors and beta-PDB resulted in an increase in STa-stimulated guanylate cyclase activity of about 70%. Likewise, the number of 125I-STa-binding sites was increased by about 25 to 40% in membranes prepared from intact cells or homogenates treated with beta-PDB; no effect on binding affinity (Kd = 0.15 nM) was noted. These experiments suggest that protein kinase C may phosphorylate the STa receptor-guanylate cyclase or a closely related protein and increase guanylate cyclase activity. The stimulatory effects of protein kinase C on STa-sensitive guanylate cyclase are opposite in direction to the profound inhibitory effects of the kinase on atrial natriuretic peptide-stimulated guanylate cyclase, demonstrating differential regulation by protein kinases within the guanylate cyclase-receptor family.

Phosphorylation of atrial natriuretic factor R1 receptor by serine/threonine protein kinases: evidences for receptor regulation

The 130 kDa atrial natriuretic factor receptor (ANF-R1) purified from bovine adrenal zona glomerulosa is phosphorylated in vitro by serine/threonine protein kinases such as cAMP-, cGMP-dependent and protein kinase C. This phosphorylation is independent of the presence of ANF (99-126) and there is no detectable intrinsic kinase activity associated with the ANF-R1 receptor or with its activated form. In bovine adrenal zona glomerulosa cells, TPA (phorbol ester) induces a marked inhibition of the ANF-stimulated cGMP accumulation as well as of the membrane ANF-sensitive guanylate cyclase catalytic activity without any change in the binding capacity or affinity for 125I-ANF. However, we have demonstrated a significant 32P incorporation in the ANF-R1 receptor of the TPA-treated cells. The effect of TPA on the zona glomerulosa ANF-R1 receptors was abolished by calphostin C, a specific protein kinase C inhibitor. Altered ANF actions due to blunted response of guanylate cyclase to ANF could be a consequence of the ANF receptor phosphorylation by excessive activity of protein kinase C and might be involved in the pathogenesis of hypertension.

Characterization of rat glomerular thromboxane A2 receptors: comparison to rat platelets

This study was designed to characterize rat glomerular thromboxane A2 (TxA2) receptors and compare them to rat platelet TxA2 receptors. The radioligand binding characteristics of the receptors were characterized using [125I][1S-(1 alpha,2 beta(5Z),3 alpha-(1E,3R*),4 alpha]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo- [2.2.1]heptan-2yl]-5-heptenoic acid ([125I]BOP), a TxA2 agonist. Equilibrium binding with [125I]BOP, as well as competitive binding assays between [125I]BOP and 13-azapinane TxA2 receptors antagonists, were performed in rat glomerular membranes (RGM) and washed rat platelets (WRP). [125I]BOP identified a single class of TxA2 receptor sites in glomerular membranes with a Kd of 318 +/- 55 pM and a Bmax of 260 +/- 62 fmol/mg protein (n = 14). [125I]BOP was displaced by the TxA2 agonist 15S-hydroxy-11 alpha,9 alpha(epoxymethano)-prosta-5Z,13E-dienoic acid (U-46,619) (IC50 = 22 +/- 6 nM, n = 3), the antagonist SQ-29,548 (IC50 = 41 +/- 7 nM, n = 4), and stereoselectively by the antagonists (-)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,925) (IC50 = 0.27 +/- 0.04 nM, n = 3) and (+)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,926) (IC50 = 124 +/- 0 nM, n = 2). The ability of six 13-azapinane TxA2 antagonists to compete with [125I]BOP was evaluated. The rank orders for the 13-azapinanes showed no significant correlation between RGM and WRP.(ABSTRACT TRUNCATED AT 250 WORDS)

The angiotensin AT2 receptor stimulates protein tyrosine phosphatase activity and mediates inhibition of particulate guanylate cyclase

The signalling mechanism and cellular targets of the AT2 receptor are still unknown. We report that angiotensin II (Ang II) inhibits basal and atrial natriuretic peptide stimulated particulate guanylate cyclase (pGC) activity through AT2 receptors in rat adrenal glomerulosa and PC12W cells. This inhibition is blocked by the phosphotyrosine phosphatase (PTPase) inhibitor orthovanadate but not by the Ser/Thr phosphatase inhibitor okadaic acid, suggesting the involvement of a PTPase in this process. Moreover, Ang II induces a rapid, transient and orthovanadate sensitive dephosphorylation of phosphotyrosine containing proteins in PC12W cells. Our findings suggest that AT2 receptors signal through stimulation of a PTPase and that this mechanism is implicated in the regulation of pGC activity. This observation is also the first example of hormonal inhibition of basal pGC activity.

Regulation of atrial natriuretic peptide-stimulated cGMP production in the inner medulla

Studies were performed to examine the regulation of atrial natriuretic peptide- (ANP) stimulated guanylate cyclase in the the inner medulla. Primary cultures of rat inner medullary collecting tubular cells exposed to 10(-7) M ANP increased cGMP formation to 31.2 +/- 1.8 compared to the basal production of 2.1 +/- 0.6 fm/micrograms protein. This response did not appear to be transduced via a Gi protein, as preincubation with pertussis toxin did not alter the response to 10(-7) M ANP, and saponized cells exposed to 10 microM GTP gamma S did not enhance the response to ANP (77.3 +/- 5.9 vs. 86.7 +/- 6.3 g/micrograms). Likewise, changes in extracellular Ca2+ from 0.5 to 3.0 mM, decrements in intracellular Ca2+ with EGTA or increments in intracellular Ca2+ with ionomycin (5 microM) did not significantly alter the response to ANP. Neither activation of protein kinase A with forskolin (36.5 +/- 5.1) nor of protein kinase C with s,n-1,2-dioctanoylglycerol (33.2 +/- 2.5) altered the response to 10(-7) M ANP (32.2 +/- 3.3, NS). As the inner medullary environment was hypertonic, the effect of altering tonicity was studied. Cells grown for 48 hours in hypertonic media (600 mOsm/kg H2O) displayed enhanced response to 10(-8) and 10(-7) M ANP when osmolality was raised by either Na+ alone or in combination with urea, but not by urea alone. Our studies demonstrate that ANP-stimulated guanylate cyclase is insensitive to alterations in either intra- or extracellular Ca2+, is not subject to inhibition by protein kinase, and does not involve a pertussis-sensitive G protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium and calmodulin regulate atrial natriuretic factor stimulation of cyclic GMP in a human renal cell line

We examined calcium and calmodulin regulation of atrial natriuretic factor stimulation of particulate-membrane guanylate cyclase (ANF-s-GC) in SK-NEP-1 cells. W7 and trifluoropiperazine, but not W5, inhibited whole cellular ANF-stimulated cyclic GMP accumulation (ANF-s-cGMP). EGTA and LaCl3 decreased ANF-s-GC and calmodulin reversed this inhibition. A23187-induced inhibition of ANF-s-cGMP was only partly reversible by IBMX. H7 or staurosporine counteracted the inhibitory effect of A23187. Calcium inhibited basal and ANF-s-GC. These data suggest that at low concentrations of calcium, ANF-s-GC was calcium-calmodulin dependent but high concentrations of calcium inhibited ANF-s-GC through phosphodiesterase, through inhibition of GC, and probably through protein kinase C.

Stimulatory effects of brain natriuretic peptide on cyclic GMP accumulation and tyrosine hydroxylase activity in cultured bovine adrenal medullary cells

We studied the effect of brain natriuretic peptide (BNP) on the accumulation of cyclic GMP and the phosphorylation and activity of tyrosine hydroxylase, compared with that of atrial natriuretic peptide (ANP), in cultured bovine adrenal medullary cells. 1. BNP as well as ANP increased cellular cyclic GMP accumulation in a concentration-dependent manner (10-1000 nmol/l). BNP (1 mumol/l) and ANP (1 mumol/l) produced a 60-fold and 30-fold increase in cyclic GMP accumulation, respectively. 2. The stimulatory effects of BNP and ANP on cyclic GMP accumulation were observed even when Ca2+ or Na+ was removed from the incubation medium. 3. 12-O-Tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, inhibited the stimulatory effect of BNP on cyclic GMP accumulation in a concentration-dependent manner (1-100 nmol/l). Furthermore, the BNP-induced accumulation of cyclic GMP was attenuated by forskolin (1 mumol/l), an activator of adenylate cyclase. 4. BNP (1 mumol/l) and ANP (1 mumol/l) caused a significant increase in phosphorylation and activity of tyrosine hydroxylase in the cells. 5. In digitonin-permeabilized cells, cyclic GMP (1-100 mumol/l) activated tyrosine hydroxylase in the presence of ATP and Mg2+. These results suggest that BNP stimulates the accumulation of cyclic GMP in a manner similar to that of ANP. The increased accumulation of cyclic GMP by these peptides may be negatively modulated by protein kinase C and cyclic AMP and may cause the phosphorylation and activation of tyrosine hydroxylase in cultured bovine adrenal medullary cells.

Phorbol and calcium decreased atriopeptin response in a human renal cell line

We investigated regulation of atrial natriuretic factor (ANF)-stimulated cellular cGMP accumulation (ANF-s-cGMP) in an ANF-responsive human renal cell line, SK-NEP-1. Dose-response data indicated that the EC50 for ANF(99-126) was 1.1 x 10(-9) M. Brain natriuretic peptide (10(-6) M) increased cGMP to a level indistinguishable from that of ANF (10(-6) M). [Met-(O)]ANF was only half as potent as ANF, and atriopeptin I (10(-6) M) did not increase cGMP over basal levels. Preincubation of SK-NEP-1 cells with ANF, but not atriopeptin I (API), for two hours or longer, caused a concentration-dependent down-regulation of ANF-s-cGMP. Phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, and A23187 and its 4-bromo derivative, calcium ionophores, inhibited ANF-s-cGMP in a dose-dependent manner. A23187 inhibition was calcium dependent and promoted net cGMP degradation. Thirty-six hour preincubation with PMA, a procedure used to down-regulate PKC, abolished acute PMA inhibition of ANF-s-cGMP without having an effect on ANF-s-cGMP or on 4-bromo-A23187 inhibition thereof. These data indicate that PKC activation specifically inhibited ANF-s-cGMP but that PKC was not required for ANF-s-cGMP in SK-NEP-1 cells. Thus structurally related ANF peptides, protein kinase C (PKC) activators, calcium ionophores are potential modulators of ANF-s-cGMP in cells from this human renal cell line.

The opposing effects of calmodulin, adenosine 5'-triphosphate, and pertussis toxin on phorbol ester induced inhibition of atrial natriuretic factor stimulated guanylate cyclase in SK-NEP-1 cells

In the present study, we investigated the effects of calmodulin, adenosine 5'-triphosphate (ATP) and pertussis toxin (PT) on phorbol ester (PMA) (a protein kinase C activator) induced inhibition of ANF-stimulated cyclic GMP formation in cells from the human renal cell line, SK-NEP-1. PMA inhibited ANF-stimulated guanylate cyclase activity in particulate membranes by about 65%. Calmodulin reversed this inhibition in a dose dependent manner. ATP potentiated Mg++ but not Mn++ supported guanylate cyclase activity. In PMA treated membranes, ATP potentiating effects were abolished. PMA also inhibited ANF-stimulated cGMP accumulation, but pretreatment with PT prevented this PMA inhibition. PT did not affect basal or ANF-stimulated cGMP accumulation. In conclusion, these results demonstrated that PMA (activated protein kinase C) inhibited ANF stimulation of particulate guanylate cyclase in opposition to the activating effects of calmodulin or ATP in SK-NEP-1 cells. The protein kinase C inhibitory effects appeared to be mediated via a PT-sensitive G protein.

Characterization and physiologic regulation of atrial natriuretic factor receptors in rabbit preglomerular renal microvessels

There has been no direct demonstration of the presence of guanylate cyclase-linked atrial natriuretic factor receptors in renal preglomerular microvasculature. Using [125I]ANF, we have demonstrated the presence of high affinity (Kd = 80 pM) and low affinity (Kd = 7.2 nM) ANF receptors in membranes derived from rabbit renal preglomerular microvessels (afferent arterioles and interlobular arteries). These microvessels also exhibited the presence of particulate bound ANF-sensitive guanylate cyclase. The density of the high affinity ANF receptor in desoxycorticosterone-treated rabbits on a high-salt diet (31 +/- 3 fmol/mg protein) was nearly half of that seen in rabbits on a normal diet (53 +/- 4 fmol/mg protein; p less than 0.01, n = 4). Data from this study demonstrated the presence of renal preglomerular ANF receptors and suggested that these receptors (perhaps in addition to glomerular ANF receptors) may participate in the regulation of extracellular volume.

Evidence for particulate guanylate cyclase in rat kidney after stimulation by atrial natriuretic factor. An ultracytochemical study

Cytochemical localization of particulate guanylate cyclase (GC) in rat kidney, after stimulation with atrial natriuretic factor (ANF), was studied by electron microscopy. In the renal corpuscle GC reaction was localized on podocytes. Other segments of the nephron that showed ultracytochemical evidence of GC activity were the proximal convoluted tubule, the thick ascending limb of the loop of Henle and the collecting tubule. All GC positivity was associated with plasma membranes. Samples incubated in basal conditions (without ANF) did not reveal any GC reaction product. These results indicate that ANF is a strong activator of particulate GC. Our data also suggests that, through the enzyme, ANF acts directly on epithelial cells of tubules where Na+ reabsorption occurs. This is in agreement with the hypothesis that ANF has a direct tubular effect on natriuresis.

Cyclic GMP and the second messenger hypothesis

A plasma membrane form of guanylate cyclase appears to contain a single transmembrane domain that divides the protein into a highly conserved intracellular domain and a variable extracellular domain. Various extracellular peptides can bind directly to guanylate cyclase to increase the production of the second messenger, cyclic GMP.

Production and characterization of monoclonal antibodies against particulate guanylate cyclase in porcine kidney

Three monoclonal antibodies (Ig G1 type) to particulate guanylate cyclase from porcine kidney cortex have been produced by fusing spleen cells from immunized BALB/c mouse with P3X63 myeloma cells. The antibodies were detected by their ability to bind immobilized antigen and by immunoprecipitation of enzyme activity. After subcloning by limiting dilution, hybridomas were injected intraperitoneally into mice to produce ascitic fluid. The antibodies recognized a 180,000 dalton protein in Lubrol-PX extract of porcine kidney cortex membrane, and when immobilized on Sepharose 4B, they co-precipitated both [125I]human atrial natriuretic peptide (ANP)-receptor complex and guanylate cyclase activity. The antibodies caused a greater increase in generation of cGMP than that of ANP.