Molecular cloning and pharmacological characterization of bovine calcitonin receptor-like receptor from bovine aortic endothelial cells.

A complementary DNA encoding calcitonin receptor-like receptor (CRLR) was isolated from a bovine aortic endothelial cell library. The bovine CRLR has 462 amino acids and 92% homology with the human CRLR. In a reverse transcriptase–polymerase chain reaction assay, bovine CRLR was found to be widely distributed, including in the heart and lungs. Stable transfection of bovine CRLR in human embryonic kidney cells (HEK-293) resulted in specific high-affinity [125I] rat adrenomedulin (rADM)-binding (dissociation constant=145±15pM). ADM-stimulated adenylyl cyclase activity with an ec50 value of 5.0±1.2nM. The human ADM receptor antagonist hADM(22-52) inhibited [125I]rADM-binding and ADM-stimulated adenylyl cyclase activity. Interactions between bovine CRLR and individual receptor activity modifying proteins (RAMPs) were also investigated. Transient co-transfection of bovine CRLR cDNA with human receptor activity modifying protein 1 (hRAMP1) cDNA in HEK-293 cells resulted in the expression of a CRLR that displayed high-affinity binding to calcitonin gene-related peptide. Co-transfection of bovine CRLR with human RAMP2 or RAMP3 cDNAs in HEK-293 cells displayed high-affinity ADM receptors. These observations suggest that in the absence of exogenous RAMPs heterologous expression of bovine CRLR results in an ADM receptor phenotype.