Molecular cloning and pharmacological characterization of porcine melanocortin-3 receptor.

Mouse gene targeting studies revealed that the melanocortin-3 receptor (MC3R) affected feeding efficiency and fat storage in mice. The functions of the MC3R in other mammalian species remain to be investigated. We are interested in exploring the functions of the porcine MC3R (pMC3R) in regulating fat storage because of the economical importance of swine industry. Although nucleotide sequences of MC3Rs from several species have been reported, pMC3R had not been cloned and sequenced. We reported herein the molecular cloning and pharmacological analysis of the pMC3R. Sequence analysis revealed that pMC3R was highly homologous (>80%) at nucleotide and amino acid sequences to human, rat, and mouse MC3Rs. With human MC3R (hMC3R) as a control, the binding and signaling properties of pMC3R were investigated using several agonists including alpha- and gamma-melanocyte-stimulating hormone (alpha- and gamma-MSH), D-Trp(8)-gamma-MSH, and [Nle(4)-D-Phe(7)]-MSH (NDP-MSH) and the natural antagonist agouti-related protein (AgRP). The results showed that pMC3R bound NDP-MSH with the highest affinity followed by D-Trp(8)-gammaMSH, gamma-, and alpha-MSH. The same ranking was also found for hMC3R, although pMC3R had two- to ninefold higher affinities for these ligands. Both pMC3R and hMC3R bound AgRP with high affinity. D-Trp(8)-gamma-MSH was the most potent agonist to stimulate cAMP generation followed by NDP-, alpha-, and gamma-MSH. This ranking was the same as that of hMC3R. The availability of pMC3R and its pharmacological characteristics will facilitate the investigation of pMC3R in regulating food intake and fat storage.