MOLECULAR-CLONING AND EXPRESSION OF PEPTIDE-23, A GROWTH HORMONE-RELEASING HORMONE-INDUCIBLE PITUITARY PROTEIN

Peptide 23 is a newly identified protein secreted by rat pituitary cel ls in primary culture. Although the secretion of this protein is stimu lated by GH-releasing hormone and inhibited by somatostatin, the N-ter minal amino acid sequence of peptide 23 shows no homology to rat GH. U sing the polymerase chain reaction technique, we cloned and sequenced the peptide 23 complementary DNA (cDNA). By means of the mixed oligonu cleotide-primed amplification of cDNA technique, primers corresponding to the NH2-amino acid sequence of peptide 23 were used to amplify, cl one, and sequence a 74-basepair cDNA of peptide 23. This polymerase ch ain reaction product was then used as a primer to amplify the complete peptide 23 cDNA by means of the rapid amplification of cDNA ends proc edure. The cDNA of peptide 23 obtained by the rapid amplification of c DNA ends procedure contained 777 nucleotides and encoded a 175-amino a cid protein with a 26-amino acid putative signal peptide. The calculat ed mol wt of the mature protein (16,613 daltons) was in good agreement with that estimated by polyacrylamide gel electrophoresis (16 kilodal tons). Northern blot analysis revealed a major messenger RNA species o f about 0.9 kilobase and a minor species of about 1.7 kilobases in cul tured rat anterior pituitary cells. In rats, peptide 23 was most abund ant in the pancreas and gastrointestinal tract. A GenBank sequence sea rch revealed complete sequence identify between peptide 23 cDNA and pa ncreatitis-associated protein cDNA, an approximately 73% homology with human hepatocellular carcinoma cDNA from human hepatocellular carcino ma, 64% homology with bovine pancreatic thread protein cDNA, and 55% h omology with rat and human reg cDNAs, which have been reported to be e xpressed in regenerating pancreatic islets. Therefore, peptide 23 is i dentical to pancreatitis-associated protein and a member of the C-type lectin supergene family.