Specificity of porcine calcitonin receptor and calcitonin receptor-like receptor in the presence of receptor-activity-modifying proteins

Adrenomedullin (AM), calcitonin gene-related peptide (CGRP), amylin (AMY) and calcitonin (CT) are members of the CGRP/CT superfamily of peptides. Among them, AM and CGRP are reported to share a core receptor, the calcitonin receptor-like receptor (CRLR), and the specificity of the CRLR is determined by the expression levels of receptor-activity-modifying proteins (RAMPs). In the case of AMY, co-expression of the calcitonin receptor (CTR) and RAMPs was recently reported to form its specific receptor. However, detailed analysis of the receptor specificity of the CRLR and CTR in the presence of RAMPs has so far been performed mainly in the human system. Thus, we cloned cDNAs encoding porcine CRLR, RAMP1, RAMP2 and RAMP3 precursors from a porcine lung and hypothalamus cDNA library, and determined their sequences. Then, porcine RAMPs, CRLR and CTR were expressed in COS-7 or porcine vascular smooth muscle cells, and the resulting receptor complexes were analyzed by the cyclic adenosine 3',5'-monophosphate (cAMP) production assay. The specificity of CRLR was clearly determined by the expression of RAMPs; RAMP1 converted CRLR to CGRP receptor, while RAMP2 and RAMP3 converted it to AM receptor, but the affinity of CTR for AMY was not increased by the expression of any known RAMPs. In contrast to previous findings, porcine CTR and RAMP did not appear to form an AMY receptor having sufficient affinity and specificity for the physiological interaction.