CHARACTERIZATION OF THE STRUCTURAL AND FUNCTIONAL-PROPERTIES OF CLONED CALCITONIN RECEPTOR CDNAS

We have recently cloned CTRs from cDNA libraries prepared from porcine renal and human ovarian cell lines. In situ hybridization and Norther n analysis confirm the widespread distribution of CTR mRNA in numerous tissues. Hydropathy plots of the predicted amino acid sequence of the receptors demonstrate multiple hydrophobic regions that could generat e 7 transmembrane spanning domains, similar to other G protein-coupled receptors. Searches of databanks for proteins with related amino acid sequences reveals that the CTRs are closely related to the receptors for parathyroid hormone/parathyroid hormone related peptide, secretin, vasoactive intestinal peptide, growth hormone releasing hormone, gluc agon-like peptide-1 and glucagon. These receptors have no significant sequence homology to other G protein-coupled receptors, and therefore, appear to comprise a distinct receptor family. Expression of the hCTR or pCTR in COS cells results in expression of high affinity CTRs whic h are coupled to adenylate cyclase (AC). The hCTR, however, demonstrat es higher affinity for human and salmon CT compared to the pCTR. Both CTRs demonstrate low affinity binding and AC activation in response to calcitonin gene related peptide, amylin or secretin, providing a poss ible explanation for the cross-reactivity among these peptides in vivo . Stable transfectants expressing the pCTR increase cAMP levels and in creases in cytosolic free Ca2+ concentration consistent with dual coup ling to AC and phospholipase C. Additional studies will help to establ ish the structural basis for this functional property as well as the e volutionary relationship of the members of this newly identified famil y of receptors.