A G protein-coupled receptor from zebrafish is activated by human parathyroid hormone and not by human or teleost parathyroid hormone-related peptide. Implications for the evolutionary conservation of calcium-regulating peptide hormones.
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Genomic and cDNA clones encoding portions of a putative catfish parathyroid hormone (PTH) 2 receptor (PTH2R) led to the isolation of a cDNA encoding a full-length zebrafish PTH2R (zPTH2R). The zPTH2R shared 63 and 60% amino acid sequence identity with human and rat PTH2Rs, respectively, 47-52% identity with mammalian and frog PTH/PTHrP receptors (PTH1R), and less than 37% with other members of this family of G protein-coupled receptors. COS-7 cells expressing zPTH2R(43), a 5' splice variant that lacked 17 amino acids in the amino-terminal extracellular domain, showed cAMP accumulation when challenged with [Tyr(34)]hPTH(1-34)-amide (hPTH) (EC(50), 1.64 +/- 0. 95 nM) and [Ile(5),Trp(23),Tyr(36)]hPTHrP-(1-36)-amide ([Ile(5), Trp(23)]hPTHrP) (EC(50), 46.8 +/- 12.1 nM) but not when stimulated with [Tyr(36)]hPTHrP-(1-36)-amide (hPTHrP), [Trp(23), Tyr(36)]hPTHrP-(1-36)-amide ([Trp(23)]hPTHrP), or [Ala(29),Glu(30), Ala(34),Glu(35),Tyr(36)]fugufish PTHrP-(1-36)amide (fuguPTHrP). FuguPTHrP also failed to activate the human PTH2R but had similar efficiency and efficacy as hPTH and hPTHrP when tested with cells expressing the human PTH1R. Agonist-dependent activation of zPTH2R was less efficient than that of zPTH2R(43), and both receptor variants showed no cAMP accumulation when stimulated with either secretin, growth hormone-releasing hormone, or calcitonin. The zPTH2R thus has ligand specificity similar to that of the human homolog, which raises the possibility that a PTH-like molecule exists in zebrafish, species which lack parathyroid glands. (+info)
Molecular determinants of tuberoinfundibular peptide of 39 residues (TIP39) selectivity for the parathyroid hormone-2 (PTH2) receptor. N-terminal truncation of TIP39 reverses PTH2 receptor/PTH1 receptor binding selectivity.
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Tuberoinfundibular peptide of 39 residues (TIP39) and the parathyroid hormone-2 (PTH2) receptor form part of an extended family of related signaling molecules that includes the PTH1 receptor, which responds to PTH and PTH-related protein. TIP39 does not appreciably activate the PTH1 receptor, but in this study it is shown to bind the receptor with moderate affinity (59 nm). In this study, we investigated the molecular determinants of both ligand and receptor for the PTH2 receptor selectivity of TIP39 and quantitatively evaluated the role of molecular elements in the binding of TIP39 to the PTH2 and PTH1 receptors. A chimeric receptor composed of the N-terminal extracellular domain of the PTH1 receptor and the remainder (juxtamembrane domain) of the PTH2 receptor (P2-NP1) was fully activated by TIP39 (E(max) = 98% of the rPTH-(1-34), E(max), EC(50) = 2.0 nm). This receptor chimera bound TIP39 with an equivalent affinity to the wild-type PTH2 receptor (2. 3 and 2.0 nm, respectively). The reciprocal chimeric receptor (P1-NP2) was not activated by TIP39 and bound the ligand with an affinity equivalent to that of the PTH1 receptor. Thus, the juxtamembrane receptor domain specifies the signaling and binding selectivity of TIP39 for the PTH2 receptor over the PTH1 receptor. Removing six N-terminal residues of TIP39 eliminated activation of the PTH2 receptor and reduced binding affinity 70-fold. In contrast, this truncation increased affinity for the PTH1 receptor 10-fold, reversing the PTH2/PTH1 receptor binding selectivity and resulting in a high affinity interaction of TIP-(7-39) with the PTH1 receptor (6 nm). These findings can be explained by a strong interaction between the N-terminal region of TIP39 and the juxtamembrane domain of the PTH2 receptor, with the corresponding domain of the PTH1 receptor acting as a selectivity barrier against high affinity binding of TIP39. As a result, TIP-(7-39) is a highly potent, selective antagonist for the PTH1 receptor. (+info)
Tuberoinfundibular peptide (7-39) [TIP(7-39)], a novel, selective, high-affinity antagonist for the parathyroid hormone-1 receptor with no detectable agonist activity.
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The parathyroid hormone (PTH)-1 receptor mediates the pathophysiological effects of PTH in hyperparathyroidism and PTH-related protein (PTHrP) in humoral hypercalcemia of malignancy. A PTH1 receptor antagonist may be of therapeutic utility in these disorders. We recently identified a novel antagonist, tuberoinfundibular peptide (7-39) [TIP(7-39)], derived from the likely endogenous ligand for the PTH2 receptor TIP39. In this study its in vitro profile is evaluated and compared with that of [D-Trp(12),Tyr(34)]bPTH(7-34) and PTHrP(7-34), representing the two previously known structural classes of PTH1 receptor antagonists. TIP(7-39) binds with higher affinity (6.2 nM) to the PTH1 receptor than [D-Trp(12),Tyr(34)]bPTH(7-34) (45 nM) and PTHrP(7-34) (65 nM) and displays a 5.5-fold greater PTH1/PTH2 receptor selectivity. TIP(7-39) does not stimulate cAMP accumulation via the PTH1 receptor [in a sensitive assay that detects the activity of the weak partial agonist [Nle(8,18),Tyr(34)]bPTH(3-34)] and does not increase intracellular calcium. Schild analysis for TIP(7-39) was consistent with purely competitive antagonism of PTH(1-34)'s stimulation of cAMP accumulation (slope = 0.99 +/- 0.24). The pK(B) for TIP(7-39) (7.1 +/- 0.3) was higher than that for [D-Trp(12),Tyr(34)]bPTH(7-34) (6.5 +/- 0.0) and PTHrP(7-34) (6.0 +/- 0.1). Binding of (125)I-TIP(7-39) to the PTH1 receptor could be measured (K(D) = 1.3 +/- 0.1 nM, B(max) = 1.3 +/- 0.1 pmol/mg), whereas binding of (125)I-[Nle(8,18),D-Trp(12),Tyr(34)]bPTH(7-34) could not be detected. Kinetic analysis indicated that (125)I-TIP(7-39) dissociates much more slowly (t(1/2) = 14 min) than [D-Trp(12),Tyr(34)]bPTH(7-34) (13 s) and PTHrP(7-34) (9 s). The novel antagonist TIP(7-39) therefore displays a more favorable in vitro pharmacological profile than antagonists derived from PTH and PTHrP and may be useful for demonstrating the utility of PTH1 receptor antagonism in the treatment of hypercalcemia. (+info)
Regions in rat and human parathyroid hormone (PTH) 2 receptors controlling receptor interaction with PTH and with antagonist ligands.
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The parathyroid hormone (PTH) 2 receptor is potently activated by tuberoinfundibular peptide (TIP39). Rat and human PTH2 receptors differ considerably in their PTH responsiveness. PTH weakly stimulates cAMP accumulation via the rat receptor, and here we show it did not detectably increase intracellular calcium ([Ca2+]i) and bound with low affinity (450 nM). For the human PTH2 receptor PTH was a full agonist for increasing cAMP, a partial agonist for increasing [Ca2+]i, and bound with high affinity (18 nM). In addition, the antagonists PTH(7-34) and TIP(7-39) bound with 10- to 49-fold lower affinity to the rat receptor. We investigated the molecular basis of differential PTH and antagonist interaction with human and rat PTH2 receptors by using chimeric human/rat PTH2 receptors. PTH cAMP-signaling efficacy (Emax) was determined by extracellular loop (EL) 1 and a region including EL2 and EL3. The N-terminal domain determined PTH binding selectivity at the inactive receptor state. Multiple regions throughout the receptor are required for the PTH-PTH2 receptor complex to adopt a high-affinity active state: inserting the rat receptor's N-terminal domain, EL1 or EL2/3, into the human receptor increased PTH's EC50 and reciprocal exchanges did not reduce EC50. This suggests the global receptor conformation prevents the rat receptor from adopting a high-affinity state when in complex with PTH. N-terminal ligand truncation, producing the antagonists PTH(7-34) and TIP(7-39), altered ligand interaction with the membrane-embedded domain of the receptor, eliminating EL2/3 as a specificity determinant and lowering binding affinity. These insights should contribute to the development of a high-affinity PTH2 receptor antagonist, for investigating the receptor's physiological role. (+info)
Anatomical and physiological evidence for involvement of tuberoinfundibular peptide of 39 residues in nociception.
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The parathyroid hormone 2 (PTH2) receptor's anatomical distribution suggests that, among other functions, it may be involved in modulation of nociception. We localized PTH2 receptor protein to spinal cord lamina II and showed that it is synthesized by subpopulations of primary sensory neurons and intrinsic spinal cord dorsal horn neurons. Tuberoinfundibular peptide of 39 residues (TIP39) selectively activates the PTH2 receptor. Intraplantar microinjection of TIP39 caused a paw-withdrawal response and intrathecal injection caused scratching, biting, and licking, a nocifensive response. Intrathecal administration of a TIP39 antibody decreased sensitivity in tail-flick and paw-pressure assays. Intrathecal administration of TIP39 potentiated responses in these assays. We determined the sequence of TIP39's precursor and found that mRNA encoding TIP39 and TIP39-like immunoreactivity is concentrated in two brainstem areas, the subparafascicular area and the caudal paralemniscal nucleus. Cells in these areas project to the superficial dorsal horn of the spinal cord. Our data suggest that TIP39 released from supraspinal fibers potentiates aspects of nociception within the spinal cord. (+info)
A spectroscopic study of the membrane interaction of tuberoinfundibular peptide of 39 residues (TIP39).
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The membrane interaction of tuberoinfundibular peptide of 39 residues (TIP39), which selectively activates the parathyroid hormone 2 (PTH2) receptor (PTH2-R), has been studied by fluorescence and NMR spectroscopic techniques. Membrane binding would be the first step of a potential membrane-bound activation pathway which has been discussed for a number of neuropeptides and G-protein coupled receptors (GPCRs). Here, the orientation of TIP39 on the surface of membrane mimicking dodecyl-phosphocholine (DPC) micelles was monitored by Photo-CIDNP (chemically-induced dynamic nuclear polarization) NMR which indicates that both Trp25 and Tyr29 face the membrane surface. However, the PTH2 receptor is located in the hypothalamus membrane, for which a more realistic model is required. Therefore, liposomes containing different mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS) and cholesterol were used for fluorescence and solid-state NMR spectroscopy. Fluorescence spectroscopy showed that a large proportion of TIP39 added to these liposomes binds to the membrane surface. Proton-decoupled 31P-MAS NMR is used to investigate the potential role of individual lipid headgroups in peptide binding. Significant line-broadening in POPC/cholesterol and POPC/POPS liposomes upon TIP39 association supports a surface binding model and indicates an interaction which is slightly mediated by the presence of POPS and cholesterol. Furthermore, smoothed order parameter profiles obtained from 2H powder spectra of liposomes containing POPC-d31 as bulk lipid in addition to POPS and cholesterol show that TIP39 does not penetrate beyond the headgroup region. Spectra of similar bilayers with POPS-d31 show a small increase in segmental chain order parameters which is interpreted as a small but specific interaction between the peptide and POPS. Our data demonstrate that TIP39 belongs to a class of signaling peptides that associate weakly with the membrane surface but do not proceed to insert into the membrane hydrophobic compartment. (+info)
Postnatal development and gender-dependent expression of TIP39 in the rat brain.
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Tuberoinfundibular peptide of 39 residues (TIP39) is a selective agonist of the parathyroid hormone 2 (PTH2) receptor. The topographical distributions of TIP39 and the PTH2 receptor in the brain, described for young male rats, suggested that TIP39 has limbic and endocrine functions. In the present study, we investigated the expression of TIP39 and the PTH2 receptor in male and female rat brain during postnatal development by means of in situ hybridization histochemistry, quantitative RT-PCR, and immunocytochemistry. TIP39's distribution and expression levels are similar in young female and male brains. TIP39 mRNA levels peak at postnatal day 14 and subsequently decline both in the subparafascicular area and in the medial paralemniscal nucleus, the two major sites where TIP39 is synthesized. A greater developmental decrease in TIP39 expression in males leads to greater levels in older females than older males. The decrease is partially reversed by prepubertal but not postpubertal gonadectomy. TIP39 peptide levels in cell bodies change in parallel with mRNA levels, whereas TIP39 appears and disappears somewhat later in nerve fibers. In addition, TIP39 peptide levels are also sexually dimorphic in older rats. In contrast, PTH2 receptor expression in the brain does not decrease during puberty and is not sexually dimorphic even in old animals. The appearance of TIP39 during early, and decline during late, postnatal development together with the gender-dependent levels in mature animals suggests that TIP39 may play a role in sexual maturation or gender-specific functions. (+info)
Strong linkage on 2q33.3 to familial early-onset generalized osteoarthritis and a consideration of two positional candidate genes.
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A genomewide screen was performed in four extended families with early-onset generalized osteoarthritis (FOA) without dysplasia. The FOA phenotype within these families shows a dominant Mendelian inheritance pattern and may represent common osteoarthritis (OA) at later ages. An initial locus was confirmed by three additional families and refined by 14 markers to a two-point logarithm of odds score of 6.05 (theta=0.00) for marker D2S155 at chromosome 2q33.3. This locus coincided with the highest multipoint nonparametric linkage score of 4.70 (P-value=0.0013) at marker D2S2358. Haplotype analysis of family members delineated a narrow region with a number of possible positional candidates, of which we investigate here the two most likely ones: PTHR2, encoding parathyroid hormone receptor 2, and FZD5, encoding frizzled receptor 5. For FZD5, we did not observe a segregating variant, however, for PTHR2, a missense variant (A225S) cosegregated with FOA in one family. The frequency of the PTHR2 variant was rare in a population-based sample, aged 55-70 years (N=1228, 0.4%). Of the 11 carriers, 36% showed generalized radiographic OA as compared to 23% in the remaining population. None of the other families that contributed to the linkage revealed a segregating variant. Together, we have identified a locus on chromosome 2q33.3 for FOA. Candidate gene analysis suggested a possible association of a PTHR2 variant with generalized radiographic OA; it is, however, unlikely the major disease gene for the observed linkage to the FOA phenotype. (+info)