Adenosine does not bind to the growth hormone secretagogue receptor type-1a (GHS-R1a)

Carreira, Marcos C.; Camiña, Jesús P.; Díaz‐Rodriguez, Esther; Alvear-Perez, Rodrigo; Llorens-Cortes, Catherine; Casanueva, Felipe F.

doi:10.1677/joe.1.06714

Cited by 18 publications

(15 citation statements)

References 31 publications

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“…This observation fits in well with the kinetics of receptor endocytosis described for ghrelin in the present and previous works (27). It is important to emphasize that this effect is different from that described for adenosine in the same cellular model (22). The binding analyses showed the same number of adenosine binding sites in both HEK 293 wild-type and HEK-GHSR1a cells corresponding to a similar endogenous expression of adenosine receptors, types 2b and 3, in both cell lines.…”

Section: Discussionsupporting

confidence: 90%

“…However, the functionality of GHRH was not affected after depleting cellular levels of this receptor by transfecting siRNA specially directed against this isoform, ruling out this hypothesis. Furthermore, the GHRH actions here reported were not under the regulation of PKC, since phorbol ester PMA failed to suppress the GHRH-induced calcium response such as occurs for ghrelin-induced signal (22). As a proof of concept hGHRH analogs, JI-34 and JI-36, were able to induce a rise in intracellular calcium.…”

Section: Discussionmentioning

confidence: 80%

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Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Casanueva

Camiña

Carreira

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Ghrelin synergizes with growth hormone-releasing hormone (GHRH) to potentiate growth hormone (GH) response through a mechanism not yet fully characterized. This study was conducted to analyze the role of GHRH as a potential ligand of the ghrelin receptor, GHS-R1a. The results show that hGHRH(1-29)NH 2 (GHRH) induces a dose-dependent calcium mobilization in HEK 293 cells stably transfected with GHS-R1a an effect not observed in wildtype HEK 293 cells. This calcium rise is also observed using the GHRH receptor agonists JI-34 and JI-36. Radioligand binding and cross-linking studies revealed that calcium response to GHRH is mediated by the ghrelin receptor GHS-R1a. GHRH activates the signaling route of inositol phosphate and potentiates the maximal response to ghrelin measured in inositol phosphate turnover. The presence of GHRH increases the binding capacity of 125 I-ghrelin in a dose dependent-fashion showing a positive binding cooperativity. In addition, confocal microscopy in CHO cells transfected with GHS-R1a tagged with enhanced green fluorescent protein shows that GHRH activates the GHS-R1a endocytosis. Furthermore, the selective GHRH-R antagonists, JV-1-42 and JMR-132, act also as antagonists of the ghrelin receptor GHS-R1a. Our findings suggest that GHRH interacts with ghrelin receptor GHS-R1a, and, in consequence, modifies the ghrelin-associated intracellular signaling pathway. This interaction may represent a form of regulation, which could play a putative role in the physiology of GH regulation and appetite control.Ghrelin ͉ Ghrelin receptor ͉ GHRH T he recognition of ghrelin as the natural ligand for the growth hormone secretagogue receptor type 1a (GHS-R1a) added a new element to the complex physiological regulation for growth hormone (GH) secretion and clarified some of its aspects that were previously not fully understood (1, 2). However, this system is not as simple as it was initially thought. Ghrelin and its receptor became recognized not only for stimulating GH release but also for the findings that they exert an important role on several aspects of energy homeostasis and perhaps contribute to the metabolic syndrome (3, 4). One of the peculiar features of ghrelin and GH secretagogues (GHS) is the synergistic relationship with growth hormone-releasing hormone (GHRH) in the release of GH (5Ϫ7). The mechanism of this synergistic interaction remains a subject of debate in view of the fact that ghrelin and GHS act on both the hypothalamus and the pituitary. The evidence that this interaction requires a functional hypothalamus was obtained from patients with tumoral mass producing a hypothalamoϪpituitary disconnection in whom GH secretion is preserved after GHRH stimulation while GHS/ghrelin-induced GH secretion is blocked and the synergistic action between GHRH and GHS is absent (8, 9). Similar findings were observed in children with neonatal stalk transection (10). These observations led to the hypothesis that the action of ghrelin/GHS is mediated through an unknown hypothalamic factor with GHreleasi...

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 80%

Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Casanueva

Camiña

Carreira

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…Densitometry was performed using ImageJ software (http:// rsbweb.nih.gov/ij/index.html). In all cases, the major protein detected by each antibody reflected the expected size of the product based on manufacturers' specifications and previously published data using these antibodies (8,20).…”

Section: Methodsmentioning

confidence: 79%

Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1^−/− mice

Bone

Choi

Coe

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

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Bone DB, Choi DS, Coe IR, Hammond JR. Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1 Ϫ/Ϫ mice. Am J Physiol Heart Circ Physiol 299: H847-H856, 2010. First published June 11, 2010; doi:10.1152/ajpheart.00018.2010.-Nucleoside and nucleobase uptake is integral to mammalian cell function, and its disruption has significant effects on the cardiovasculature. The predominant transporters in this regard are the equilibrative nucleoside transporter subtypes 1 (ENT1) and 2 (ENT2). To examine the role of ENT1 in more detail, we have assessed the mechanisms by which microvascular endothelial cells (MVECs) from ENT1 Ϫ/Ϫ mice transport and metabolize nucleosides and nucleobases. Wild-type murine MVECs express mainly the ENT1 subtype with only trace levels of ENT2. These cells also have a Na ϩ -independent equilibrative nucleobase transport mechanism for hypoxanthine (ENBT1). In the ENT1Ϫ/Ϫ cells, there is no change in ENT2 or ENBT1, resulting in a very low level of nucleoside uptake in these cells, but a high capacity for nucleobase accumulation. Whereas there were no significant changes in nucleoside transporter subtype expression, there was a dramatic increase in adenosine deaminase and adenosine A 2a receptors (both transcript and protein) in the ENT1 Ϫ/Ϫ tissues compared with WT. These changes in adenosine deaminase and A 2a receptors likely reflect adaptive cellular mechanisms in response to reduced adenosine flux across the membranes of ENT1 Ϫ/Ϫ cells. Our study also revealed that mouse MVECs have a nucleoside/nucleobase transport profile that is more similar to human MVECs than to rat MVECs. Thus mouse MVECs from transgenic animals may prove to be a useful preclinical model for studies of the effects of purine metabolite modifiers on vascular function. adenosine; microvasculature; heart; transgenic; equilibrative nucleoside transporter ALL MAMMALIAN CELLS express at least one form of equilibrative transporter responsible for the cellular uptake and release of endogenous nucleosides such as adenosine. The predominant transporters are equilibrative nucleoside transporter subtypes 1 (ENT1; SLC29A1) and 2 (ENT2; SLC29A2) (3). The inhibition of ENTs has been shown to enhance the cardioprotective (21) and neuroprotective (13) actions of adenosine. These transporters are also responsible for the cellular uptake of cytotoxic nucleoside analogs used to treat cancer and viral infections (25).An ENT1-null (ENT1 Ϫ/Ϫ ) mouse model has been generated by Choi and colleagues (10). The ENT1 Ϫ/Ϫ mice are phenotypically normal with the only difference from wild-type (WT) littermates being a slight (Ͻ10%) decrease in body weight and some differences in their behavioral characteristics. The ENT1-null mice are less sensitive to the intoxicating effects of ethanol compared with their WT littermates (10), and they also display less anxiety-like behavior (9). It has been noted that there is less tonic A 1 adenosine receptor signaling in the brains of ENT1 Ϫ/Ϫ mice (10), reflecting either re...

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“…By contrast, UAG does not bind GHS-R1a [69, 70, 118]. Adenosine was initially proposed to be a partial agonist for GHS-R1a [119,120,121], but this has been questioned [122, 123]. A series of other molecules apparently unrelated to ghrelin have also been shown to bind GHS-R1a, such as the natural SRIH-like neuropeptide cortistatin, some synthetic SRIH-mimetic octapeptides (octreotide, lanreotide and vapreotide) [124,125,126] and the atypical L-type Ca 2+ channel blocker diltiazem [127].…”

Section: Type 1a Ghs Receptormentioning

confidence: 99%

Heterogeneity of Ghrelin/Growth Hormone Secretagogue Receptors

Muccioli¹,

Baragli²,

Granata³

et al. 2007

Neuroendocrinology

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Ghrelin is a gastric polypeptide displaying strong GH-releasing activity by activation of the type 1a GH secretagogue receptor (GHS-R1a) located in the hypothalamus-pituitary axis. GHS-R1a is a G-protein-coupled receptor that, upon the binding of ghrelin or synthetic peptidyl and non-peptidyl ghrelin-mimetic agents known as GHS, preferentially couples to G_q, ultimately leading to increased intracellular calcium content. Beside the potent GH-releasing action, ghrelin and GHS influence food intake, gut motility, sleep, memory and behavior, glucose and lipid metabolism, cardiovascular performances, cell proliferation, immunological responses and reproduction. A growing body of evidence suggests that the cloned GHS-R1a alone cannot be the responsible for all these effects. The cloned GHS-R1b splice variant is apparently non-ghrelin/GHS-responsive, despite demonstration of expression in neoplastic tissues responsive to ghrelin not expressing GHS-R1a; GHS-R1a homologues sensitive to ghrelin are capable of interaction with GHS-R1b, forming heterodimeric species. Furthermore, GHS-R1a-deficient mice do not show evident abnormalities in growth and diet-induced obesity, suggesting the involvement of another receptor. Additional evidence of the existence of another receptor is that ghrelin and GHS do not always share the same biological activities and activate a variety of intracellular signalling systems besides G_q. The biological actions on the heart, adipose tissue, pancreas, cancer cells and brain shared by ghrelin and the non-acylated form of ghrelin (des-octanoyl ghrelin), which does not bind GHS-R1a, represent the best evidence for the existence of a still unknown, functionally active binding site for this family of molecules. Finally, located in the heart and blood vessels is the scavenger receptor CD36, involved in the endocytosis of the pro-atherogenic oxidized low-density lipoproteins, which is a pharmacologically and structurally distinct receptor for peptidyl GHS and not for ghrelin. This review highlights the most recently discovered features of GHS-R1a and the emerging evidence for a novel group of receptors that are not of the GHS1a type; these appear involved in the transduction of the multiple levels of information provided by GHS and ghrelin.

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Adenosine does not bind to the growth hormone secretagogue receptor type-1a (GHS-R1a)

Cited by 18 publications

References 31 publications

Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1^−/− mice

Heterogeneity of Ghrelin/Growth Hormone Secretagogue Receptors

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Adenosine does not bind to the growth hormone secretagogue receptor type-1a (GHS-R1a)

Cited by 18 publications

References 31 publications

Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a

Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1−/− mice

Heterogeneity of Ghrelin/Growth Hormone Secretagogue Receptors

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Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1^−/− mice