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      Cloning, Pharmacological Characterization and Brain Distribution of the Rat Apelin Receptor

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      Neuroendocrinology
      S. Karger AG

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          Abstract

          The peptide apelin, recently isolated from bovine stomach tissue extracts, has been identified as an endogenous ligand of the human putative receptor protein related to the angiotensin receptor AT<sub>1</sub> (APJ). In this article, we report cloning of the rat apelin receptor cDNA. The sequence shares 90% identity with the human APJ receptor and 31% with the rat AT<sub>1A</sub> angiotensin receptor. Subsequently a stable CHO cell line expressing the receptor fused at its C-terminal part with the enhanced green fluorescent protein (EGFP) was established, allowing to verify its cell surface distribution and to determine the affinity of various apelin and angiotensin fragments on the cloned receptor. As shown for the human APJ receptor, the rat apelin receptor expressed in the cell line was negatively coupled to adenylate cyclase. The apelin fragment K17F (Lys<sup>1</sup>-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe<sup>17</sup>) inhibited forskolin-stimulated cAMP production at sub-nanomolar concentrations whereas angiotensin II and angiotensin III were inactive. N-terminal elongation of K17F with a tyrosine or the N-terminal deletion of the first four amino acids did not modify the inhibitory action of K17F on cAMP production. In contrast, deletion of the first seven amino acids of K17F or substitution of phenylalanine by an alanine residue at the C-terminus completely abolished the activity of the peptide. In situ hybridization analysis of apelin receptor mRNA expression in the adult rat brain showed intense labeling in the hypothalamus, especially in the supraoptic and the paraventricular nuclei. The anterior and intermediate lobes of the pituitary were also highly labeled, as well as the pineal gland. Labeling was also found in extrahypothalamic structures such as the piriform cortex, the nucleus of the lateral olfactory tract, the central grey matter, the pars compacta of the substantia nigra, the dorsal raphe nucleus, the entorhinal cortex, the dentate gyrus and the Ammon’s horn. The hypothalamic and hypophyseal distribution of the receptor suggests an involvement of apelin in the control of neuro- and adenohypophyseal hormone release, whereas its presence in the pineal gland and in discrete higher brain structures points out to possible roles in the regulation of circadian rhythms and of water and food intake behavior.

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          Molecular and functional characteristics of APJ. Tissue distribution of mRNA and interaction with the endogenous ligand apelin.

          We have recently identified apelin as the endogenous ligand for human APJ. In rats, the highest expression of APJ mRNA was detected in the lung, suggesting that APJ and its ligand play an important role in the pulmonary system. When apelin-36 and its pyroglutamylated C-terminal peptide, [
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            Isolation of a cDNA encoding the vascular type-1 angiotensin II receptor.

            Angiotensin II is an important effector molecule controlling blood pressure and volume in the cardiovascular system. Its importance is manifested by the efficacy of angiotensin-converting enzyme inhibitors in the treatment of hypertension and congestive heart failure. Angiotensin II interacts with two pharmacologically distinct subtypes of cell-surface receptors, AT1 and AT2. AT1 receptors seem to mediate the major cardiovascular effects of angiotensin II. Here we report the isolation by expression cloning of a complementary DNA encoding a unique protein with the pharmacological specificity of a vascular AT1 receptor. Hydropathic modelling of the deduced protein suggests that it shares the seven-transmembrane-region motif with the G protein-coupled receptor superfamily. Knowledge of the AT1 receptor primary sequence should now permit structural analysis, definition of the angiotensin II receptor gene family and delineation of the contribution of AT receptors to the genetic component of hypertension.
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              Characterization of Apelin, the Ligand for the APJ Receptor

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                Author and article information

                Journal
                Neuroendocrinology
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                December 1 2000
                2000
                December 22 2000
                : 72
                : 6
                : 400-407
                Article
                10.1159/000054609
                64967d04-e5a3-4834-871a-95d9b828a30e
                © 2000

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