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.

Natriuretic peptides are a family of three structurally related hormone/paracrine factors. Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted from the cardiac atria and ventricles, respectively. ANP signals in an endocrine and paracrine manner to decrease blood pressure and cardiac hypertrophy. BNP acts locally to reduce ventricular fibrosis. C-type natriuretic peptide (CNP) primarily stimulates long bone growth but likely serves unappreciated functions as well. ANP and BNP activate the transmembrane guanylyl cyclase, natriuretic peptide receptor-A (NPR-A). CNP activates a related cyclase, natriuretic peptide receptor-B (NPR-B). Both receptors catalyze the synthesis of cGMP, which mediates most known effects of natriuretic peptides. A third natriuretic peptide receptor, natriuretic peptide receptor-C (NPR-C), clears natriuretic peptides from the circulation through receptor-mediated internalization and degradation. However, a signaling function for the receptor has been suggested as well. Targeted disruptions of the genes encoding all natriuretic peptides and their receptors have been generated in mice, which display unique physiologies. A few mutations in these proteins have been reported in humans. Synthetic analogs of ANP (anaritide and carperitide) and BNP (nesiritide) have been investigated as potential therapies for the treatment of decompensated heart failure and other diseases. Anaritide and nesiritide are approved for use in acute decompensated heart failure, but recent studies have cast doubt on their safety and effectiveness. New clinical trials are examining the effect of nesiritide and novel peptides, like CD-NP, on these critical parameters. In this review, the history, structure, function, and clinical applications of natriuretic peptides and their receptors are discussed.

ADP-ribosyl cyclase catalyzes the cyclization of NAD+ to produce cyclic ADP-ribose (cADPR), which is emerging as an endogenous regulator of the Ca(2+)-induced Ca2+ release mechanism in cells. CD38 is a lymphocyte differentiation antigen which has recently been shown to be a bifunctional enzyme that can synthesize cADPR from NAD+ as well as hydrolyze cADPR to ADP-ribose. In this study, we show that both the cyclase and CD38 can also catalyze the exchange of the nicotinamide group of NADP+ with nicotine acid (NA). The product is nicotinic acid adenine dinucleotide phosphate (NAADP+), a metabolite we have previously shown to be potent in Ca2+ mobilization (Lee, H. C., and Aarhus, R. (1995) J. Biol. Chem. 270, 2152-2157). The switch of the catalysis to the exchange reaction requires acidic pH and NA. The half-maximal effective concentration of NA is about 5 mM for both the cyclase and CD38. In the absence of NA or at neutral pH, the cyclase converts NADP+ to another metabolite, which is identified as cyclic ADP-ribose 2'-phosphate. Under the same conditions, CD38 converts NADP+ to ADP-ribose 2'-phosphate instead, which is the hydrolysis product of cyclic ADP-ribose 2'-phosphate. That two different products of ADP-ribosyl cyclase and CD38, cADPR and NAADP+, are both involved in Ca2+ mobilization suggests a crucial role of these enzymes in Ca2+ signaling.

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The functional activity of integrins is dynamically regulated by T cell receptor stimulation and by protein kinase C (PKC). We report a novel function for the PKC effector protein kinase D1 (PKD1) in integrin activation. Constitutively active and kinase-inactive PKD1 mutants lacking the PKD1 pleckstrin homology (PH) domain block phorbol ester- and TCR-mediated activation and clustering of beta1 integrins. The PH domain of PKD1 mediates the association of PKD1 with the GTPase Rap1 and is central to Rap1 activation and membrane translocation in T cells. Furthermore, PKD1 and Rap1 associate with beta1 integrins in a manner that is dependent on the carboxy-terminal end of the beta1 integrin subunit cytoplasmic domain. beta1 integrin expression is required for Rap1 activation and membrane localization of the PKD1-Rap1 complex. Therefore, PKD1 promotes integrin activation in T cells by regulating Rap1 activation and membrane translocation via interactions with the beta1 integrin subunit cytoplasmic domain.

1 The sea urchin egg homogenate is an ideal model to characterize Ca 2+ -release mechanisms because of its reliability and high signal-to-noise-ratio. Apart from the InsP 3 -and ryanodine-sensitive Ca 2+ -release mechanisms, it has been recently demonstrated that this model is responsive to a third independent mechanism, that has the pyridine nucleotide, nicotinic acid adenine dinucleotide phosphate (NAADP), as an endogenous agonist. 2 The sea urchin egg homogenate was used to characterize the pharmacological and biochemical characteristics of the novel Ca 2+ -releasing agent, NAADP, compared to inositol trisphosphate (InsP 3 ) and cyclic ADP ribose (cyclic ADPR), an endogenous activator of ryanodine receptors. 3 NAADP-induced Ca 2+ -release was blocked by L-type Ca 2+ -channel blockers and by Bay K 8644, while InsP 3 -and cyclic ADPR-induced Ca 2+ -release were insensitive to these agents. L-type Ca 2+ -channel blockers did not displace [ 32 P]-NAADP binding, suggesting that their binding site was di erent. Moreover, stopped-¯ow kinetic studies revealed that these agents blocked NAADP in a all-or-none fashion. 4 Similarly, a number of K + -channel antagonists blocked NAADP-induced Ca 2+ -release selectively over InsP 3 -and cyclic ADPR-induced Ca 2+ -release. Radioligand studies showed that these agents were not competitive antagonists. 5 As has been shown for InsP 3 and ryanodine receptors, NAADP receptors were sensitive to calmodulin antagonists, suggesting that this protein could be a common regulatory feature of intracellular Ca 2+ -release mechanisms. 6 The presence of K + was not essential for NAADP-induced Ca 2+ -release, since substitution of K + with other monovalent cations in the experimental media did not signi®cantly alter Ca 2+ release by NAADP. On the contrary, cyclic ADPR and InsP 3 -sensitive mechanisms were a ected profoundly, although to a di erent extent depending on the monovalent cation which substituted for K + . Similarly, modi®cations of the pH in the experimental media from 7.2 to 6.7 or 8.0 only slightly a ected NAADPinduced Ca 2+ -release. While the alkaline condition permitted InsP 3 and cyclic ADPR-induced Ca 2+ -release, the acidic condition completely hampered both Ca 2+ -release mechanisms. 7 The present results characterize pharmacologically and biochemically the novel Ca 2+ -release mechanism sensitive to NAADP. Such characterization will help future research aimed at understanding the role of NAADP in mammalian systems.

The meiotic cell cycle of mammalian oocytes starts during embryogenesis and then pauses until luteinizing hormone (LH) acts on the granulosa cells of the follicle surrounding the oocyte to restart the cell cycle. An essential event in this process is a decrease in cyclic GMP in the granulosa cells, and part of the cGMP decrease results from dephosphorylation and inactivation of the natriuretic peptide receptor 2 (NPR2) guanylyl cyclase, also known as guanylyl cyclase B. However, it is unknown whether NPR2 dephosphorylation is essential for LH-induced meiotic resumption. Here, we prevented NPR2 dephosphorylation by generating a mouse line in which the seven regulatory serines and threonines of NPR2 were changed to the phosphomimetic amino acid glutamate (Npr2–7E). Npr2–7E/7E follicles failed to show a decrease in enzyme activity in response to LH, and the cGMP decrease was attenuated; correspondingly, LH-induced meiotic resumption was delayed. Meiotic resumption in response to EGF receptor activation was likewise delayed, indicating that NPR2 dephosphorylation is a component of the pathway by which EGF receptor activation mediates LH signaling. We also found that most of the NPR2 protein in the follicle was present in the mural granulosa cells. These findings indicate that NPR2 dephosphorylation in the mural granulosa cells is essential for the normal progression of meiosis in response to LH and EGF receptor activation. In addition, these studies provide the first demonstration that a change in phosphorylation of a transmembrane guanylyl cyclase regulates a physiological process, a mechanism that may also control other developmental events.

Synthetic atrial natriuretic peptide (carperitide) and B-type natriuretic peptide (BNP; nesiritide) are used to treat congestive heart failure. However, despite beneficial cardiac unloading properties, reductions in renal perfusion pressures limit their clinical effectiveness. Recently, CD-NP, a chimeric peptide composed of C-type natriuretic peptide (CNP) fused to the C-terminal tail of Dendroaspis natriuretic peptide (DNP), was shown to be more glomerular filtration rate-enhancing than BNP in dogs. However, the molecular basis for the increased responsiveness was not determined. Here, we show that the DNP tail has a striking effect on CNP, converting it from a nonagonist to a partial agonist of natriuretic peptide receptor (NPR)-A while maintaining the ability to activate NPR-B. This effect is specific for human receptors because CD-NP was only a slightly better activator of rat NPR-A due to the promiscuous nature of CNP in this species. Interesting, the DNP tail alone had no effect on any NPR even though it is effective in vivo. To further increase the potency of CD-NP for NPR-A, we converted two different triplet sequences within the CNP ring to their corresponding residues in BNP. Both variants demonstrated increased affinity and full agonist activity for NPR-A, whereas one was as potent as any NPR-A activator known. In contrast to a previous report, we found that DNP binds the natriuretic peptide clearance receptor (NPR-C). However, none of the chimeric peptides bound NPR-C with significantly higher affinity than endogenous ligands. We suggest that bifunctional chimeric peptides represent a new generation of natriuretic peptide therapeutics.The human natriuretic peptide system consists of atrial natriuretic peptide (ANP), 2 B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and an N-terminally extended renal form of ANP called urodilatin (1). ANP, BNP, and urodilatin bind natriuretic peptide receptor (NPR)-A, whereas CNP binds NPR-B. Both receptors are transmembrane guanylyl cyclases, which when activated catalyze the synthesis of cGMP. The natriuretic peptide clearance receptor (NPR-C) lacks guanylyl cyclase activity and functions primarily to clear natriuretic peptides from the circulation. However, a signaling function has been proposed for this receptor as well (2).Both ANP and BNP reduce blood pressure by increasing natriuresis, diuresis, vasodilation, and endothelial permeability. They also prevent cardiac hypertrophy and suppress the reninangiotensin-aldosterone systems. In 2001, BNP was approved by the United States Food and Drug Administration for the treatment of acutely decompensated heart failure. However, recent reports have suggested impaired renal function, which may be related to excessive hypotension (3, 4).CD-NP represents a new class of natriuretic peptide drug that may circumvent the hypotensive nature of BNP and preserve or augment renal function in the congestive heart failure setting. CD-NP contains the full-length 22-amino acid human CNP fused to the 15-amino acid C...