Molecular characterization and distribution of the opioid growth factor receptor (OGFr) in mouse

The native opioid growth factor (OGF), [Met(5)]-enkephalin, is a tonic inhibitory peptide that modulates cell proliferation and tissue organization during development, cancer, cellular renewal, wound healing, and angiogenesis. OGF action is mediated by a receptor mechanism. The receptor for OGF, OGFr, has been cloned and sequenced in humans and rats. Using primers based on the rat OGFr cDNA, and a mouse embryo expressed sequence tag, the full-length 2.1 kb mouse OGFr cDNA was sequenced. The open reading frame was found to encode a protein of 634 amino acids, and 14 imperfect repeats of 9 amino acids each were a prominent feature. The molecular weight of OGFr was calculated as 70679, and the isoelectric point was 4.5. Northern blot analysis revealed a 2.1 kb OGFr mRNA transcript in adult mouse brain, heart, lung, liver, kidney, and triceps surae muscle. The amino acids for mouse and rat OGFr were 93% similar and 91% identical, but the mouse and human shared only a 70% similarity and a 58% identity. These results emphasize the molecular validity of OGFr, and explain the interaction of OGF with respect to normal and abnormal growth in mouse cells and tissues.