Different Binding Modes of Amphibian and Human Corticotropin-Releasing Factor Type 1 and Type 2 Receptors: Evidence for Evolutionary Differences

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 296; no. 1; pp. 113 - 120
• Main Authors: Dautzenberg, F M, Py-Lang, G, Higelin, J, Fischer, C, Wright, M B, Huber, G
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.01.2001
• Subjects: Animals; Binding, Competitive; Biological Evolution; Cell Line; Corticotropin-Releasing Hormone - analogs & derivatives; Corticotropin-Releasing Hormone - metabolism; Cyclic AMP - biosynthesis; Humans; Iodine Radioisotopes; Ligands; Peptides - metabolism; Radioligand Assay; Rats; Receptors, Corticotropin-Releasing Hormone - agonists; Receptors, Corticotropin-Releasing Hormone - antagonists & inhibitors; Receptors, Corticotropin-Releasing Hormone - metabolism; Xenopus
• ISSN: 0022-3565; 1521-0103

The binding characteristics of corticotropin-releasing factor (CRF) type 1 (CRF 1 ) and type 2 (CRF 2 ) receptors from human (hCRF 1 and hCRF 2α ) and Xenopus (xCRF 1 and xCRF 2 ) were compared using four different 125 I-labeled CRF analogs, the agonists 125 I-CRF and 125 I-sauvagine, and the antagonists 125 I-astressin ( 125 I-AST) and 125 I-antisauvagine-30 ( 125 I-aSVG). The hCRF 2α and xCRF 2 receptors bound all four radioligands with different affinities, whereas hCRF 1 did not bind 125 I-aSVG, and xCRF 1 bound neither 125 I-sauvagine nor 125 I-aSVG. Competitive binding studies using unlabeled agonists and antagonists with hCRF 1 and hCRF 2α receptors revealed that most agonists exhibited higher affinity in displacing agonist radioligands compared with displacement of antagonist radioligands. Exceptions were the agonists human and rat urocortin, which displayed high-affinity binding in the presence of either 125 I-labeled agonist or antagonist ligands. In contrast, the affinities of antagonists were independent of the nature of the radioligand. We also found that, in contrast to the mammalian CRF receptors, the affinity of ligand binding to xCRF 1 and xCRF 2 receptors strongly depended on the nature of the radioligand used for competition. For xCRF 1 , competitors showed different rank order binding profiles with 125 I-CRF compared with 125 I-AST as the displaceable ligand. Similarly, binding of competitors to the xCRF 2 receptor showed markedly different profiles with 125 I-CRF as the competed ligand compared with the other radioligands. These data demonstrate that amphibian CRF receptors have distinctly different binding modes compared with their mammalian counterparts.