Molecular cloning and functional characterization of MCH2, a novel human MCH receptor

Melanin-concentrating hormone (MCH) is involved in the regulation of feeding and energy homeostasis. Recently, a 353-amino acid splice variant form of the human orphan receptor SLC-1 (1) (hereafter referred to as MCH1) was identified as an MCH receptor. This report describes the cloning and functional characterization of a novel second human MCH receptor, which we designate MCH2, initially identified in a genomic survey sequence as being homologous to MCH1 receptors, Using this sequence, a full-length cDNA was generated with an open reading frame of 1023 base pairs, encoding a polypeptide of 340 amino acids, with 38% identity to MCH1 and with many of the structural features conserved in G protein-coupled receptors, This newly discovered receptor belongs to class 1 (rhodopsin-like) of the G protein-coupled receptor superfamily, HEK293 cells transfected with MCH2 receptors responded to nanomolar concentrations of MCH with an increase in intracellular Ca2+ levels and increased cellular extrusion of protons. In addition, fluorescently labeled MCH bound with nanomolar affinity to these cells. The tissue localization of MCH2 receptor mRNA, as determined by quantitative reverse transcription-polymerase chain reaction, was similar to that of MCH1 in that both receptors are expressed predominantly in the brain. The discovery of a novel MCH receptor represents a new potential drug target and will allow the further elucidation of MCH-mediated responses.