CLONING AND EXPRESSION OF A NEW MEMBER OF THE MELANOCYTE-STIMULATING HORMONE-RECEPTOR FAMILY

A new member of the G protein-coupled receptor superfamily has been isolated from an ovine genomic library with a probe generated by the application of the PCR technique, using cDNA synthesized on a mRNA template isolated from the ovine pars tuberalis. This genomic clone encodes a novel receptor of 325 amino acids with seven transmembrane domains. These domains share homology with other members of this family, but the best homology is with the recently cloned human MC-1 (50% in the transmembrane domains) and MC-3 (69% in the transmembrane domains) MSH receptors and the human ACTH (42% in the transmembrane domains) receptor. When this receptor was expressed in Cos7 cells, it was able to bind a potent analogue of alpha-MSH, [Nle(4),D-Phe(7)]-alpha-MSH (NDP-MSH), with high affinity. This binding could be displaced by pro-opiomelanocortin-derived and related peptides, with the order of potency NDP-MSH>alpha-MSH=ACTH>beta-MSH and with no effect of gamma-MSH, delta-MSH or beta-endorphin. The expressed receptor was demonstrated to be functionally coupled to the adenylate cyclase second messenger pathway, with alpha-MSH, beta-MSH and ACTH stimulating cyclic AMP production. The amount of the mRNA for this receptor was found to be very low. The tissue distribution of this receptor could only be observed using the reverse transcription-PCR technique and the receptor was found to be present in a number of somatic tissues. These data indicate that this is a new and distinct member of the melanocortin receptor family.