Cloning and molecular characterization of the novel human melanin-concentrating hormone receptor MCH2

Using a genomics-based approach for screening orphan G-protein-coupled rece ptors, we have identified and cloned a novel high-affinity, melanin-concent rating hormone (MCH) receptor. This receptor, named S643b, displays the gre atest overall identity (32%) with the previously reported human SLC-1 recep tor (MCH1) and to a lesser extent with the somatostatin receptor subtypes. The gene encoding the S643b receptor spans more than 23 kilobase pairs (kb) and was mapped, by radiation hybrid experiments, on chromosome 6q14.3-q15. Comparison of the S643b cDNA with human genomic sequence reveals that the 340-amino-acid receptor is encoded by five exons. Its tissue distribution, as determined by Northern blot and reverse transcription-polymerase chain r eaction analysis, indicates that a 4-kb transcript is predominantly express ed in the brain. When expressed in Chinese hamster ovary (CHO) cells, the S 643b receptor displays a strong, dose-dependent, transient elevation of int racellular calcium in response to MCH (EC50 = 9.5 nM). During the present s tudy, we isolated a splice variant, designated S643a, encoding for a recept or that was not activated by MCH in a cellular calcium mobilization assay. Comparative pharmacological studies using CHO cells stably expressing eithe r SLC-1 or S643b receptors demonstrated that similar structural features of MCH are required to stimulate intracellular Ca2+ mobilization at both rece ptors. The identification and localization of this new MCH receptor (MCH2) provides further insight into the physiological implication of MCH in modul ating behavioral responses, including food intake.