Cloning and Functional Characterization of the Ornithokinin Receptor

Abstract

Kinins are proinflammatory peptides that dilate vessels, increase vascular permeability, contract smooth muscles, and provoke pain. In mammals two principal types of kinin receptors, B1 and B2, with distinct pharmacological properties have been cloned and characterized (1-4). Their ligands are derived from bradykinin, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg. Expression of the B1 receptor is induced under pathophysiological conditions such as injury, infection, or chronic inflammation where it mediates hyperalgesia and sensitization (5, 6). The B2 receptor is constitutively expressed in fibroblasts and in epithelial, endothelial, neuronal, and smooth muscle cells (7,8 (11,12). HOE140, a synthetic peptide derived from the bradykinin sequence, is a selective and tightly binding B2 receptor antagonist (13, 14) that lacks partial agonistic activity in most physiological settings (15).Kinins are well conserved peptides that have been identified in invertebrates, e.g. in the wasp (16). In fact the non-mammalian kinins are identical to their human counterpart including a 4-hydroxylation of a proline residue at position 3 (16). Kinins are present in all the major vertebrate classes including reptiles, amphibia, fish, and birds (8). The avian kinin, first described in 1967 (17), and aptly named ornithokinin, differs from the human bradykinin in two positions: Thr substitutes for Ser at position 6, and Leu for Phe at position 8. Ornithokinin, i.e. [Ser 6 ,Leu 8 ]bradykinin, induces transient hypotension in the chicken and contracts smooth muscle cells of the oviduct (17, 18), two physiological activities reminiscent of the kinin effects in mammals. To date the receptor underlying ornithokinin's effects has not been defined. Unlike most of the insect kinins ornithokinin has no effect on the human kinin system, and vice versa (18). The differential binding profiles are likely to reflect distinct structures of the ligand-binding sites of the corresponding receptors, however, the lack of non-mammalian kinin receptor sequences has precluded such comparisons.Here we describe the cloning of an avian kinin receptor using a PCR 1 -based strategy. Expression of the biologically active chicken ornithokinin receptor revealed the unexpected finding that HOE140, the principal antagonist of the mammalian B2 receptors, is a full agonist of the avian receptor as is ornithokinin, whereas bradykinin and [des-Arg 9 ]bradykinin have no effect. Sequence analyses indicate that avian and mammalian kinin receptors are only distantly related. Our results suggest that the ornithokinin receptor is the first member of a novel type of kinin receptors. More importantly, having available a receptor in which HOE140 acts as a full agonist will make the ornithokinin receptor a unique tool to study ligand binding and receptor function at the molecular level. EXPERIMENTAL PROCEDURESSources of Reagents-The pCDNA3, pVL-1392 vectors, and the Liposome Kit were from Invitrogen; oligonucleotides from MWG-Biotech;

Fate of bradykinin on the rat liver when administered by the venous or arterial route

“…This result was reproduced in assays with isolated cells (cytosensor microphysiometer), in which HOE-140 elicited a HSC and SEC/KC response when above 0.001 mM. Schroeder et al 25 showed that HOE-140 is indeed an agonist for the kinin receptor in birds. In certain tumor cell lines this B2 receptor antagonist may act as a mitogenic agonist.…”

Ornithokinin (avian bradykinin) from the skin of the Chinese bamboo odorous frog, Odorrana versabilis

“…As mentioned previously, it has been shown that the highly selective mammalian bradykinin B 2 ‐receptor antagonist, HOE140, is a potent agonist for the ornithokinin receptor, whereas canonical mammalian bradykinin is almost ineffective . When characterized against the mammalian bradykinin B 1 ‐receptor, desArg 9 ‐bradykinin is a full agonist, whereas desArg 9 , Leu 8 ‐bradykinin is a potent antagonist . The bradykinin B 1 ‐receptor thus appears not to have an absolute requirement for a C‐terminal Arg residue in a peptide ligand or indeed such a requirement for any residue in this position.…”

In various tumour cell lines the peptide bradykinin B2 receptor antagonist, Hoe 140 (Icatibant), may act as mitogenic agonist

“…Thus, although Hoe 140 was shown to be devoid of agonistic activity in nearly all human and animal preparations ( Regoli et al ., 1998 ) in sheep femoral artery Hoe 140 acts with high efficacy and potency as partial agonist ( Félétou et al ., 1994 ). Recently, Hoe 140 was also described to act as a full agonist at the chicken kinin receptor designated ornithokinin receptor ( Schroeder et al ., 1997 ). Furthermore, Hoe 140 is a competive antagonist in most biological assays but displays also non‐competitive properties in several tissues ( Rhaleb et al ., 1992 ; Liebmann et al ., 1993 ; Félétou et al ., 1994 ).…”