Molecular characterization of a second mouse pancreatic polypeptide receptor and its inactivated human homologue

The family of mammalian neuropeptide Y (NPY)/peptide YY (PW)/pancreatic polypeptide (PP) receptors comprises several G protein-coupled receptors, i.e. Y1, Y2, and Y4/PP1. We now report cloning of a novel member of this family named PP2, The coding region of the mouse PP2 gene reveals no introns and predicts a seven transmembrane domain (TM) receptor of 371 amino acids, Percent identities of the mouse PP2 to mouse Y1, mouse Y4/PP1 and human Y2 receptors are 53, 42, and 31, respectively, The mouse PP2 receptor expressed in COS cells binds rat I-125-PP With high affinity, i.e. IC50 = 65 pM. Pharmacological characterization of I-125-PP binding shows a rank order of potency of PP much greater than PYY greater than or equal to NPY, which is similar to that of the mouse Y4/PP1 receptor. Mouse PP2 transcripts were not detectable by Northern analysis ill adult tissues and in 11-, 15-, and 17-day-old embryos. However, a 9.8-kb PP2 transcript was detectable in 7-day-old mouse embryo, i.e. prior to the organogenesis of pancreas and the onset of PP production. We have also cloned the human homologue of PP2, which is a single copy gene and maps to human chromosome 5q31. Surprisingly, the human PP2 cDNAs and gene sequences display a single base deletion in the coding region. This frameshifting mutation predicts a truncated receptor of 290 amino acids without TM7. Transfection of COS-7 cells with several different human PP2 expression constructs failed to confirm any specific binding of I-125-PP, I-125-PYY, Or I-125-NPY to cell membranes. These data suggest that in mouse there are at least tyro PP receptors, Y4/PP1 and PP2, whereas in humans, PP2 is either functionally inactive or it has acquired a PP-independent function.