Abstract
Pancreatic polypeptide (PP) is initially synthesized as a larger precursor that requires post-translational processing to produce the biologically active hexatriacontapeptide. These steps include tryptic cleavage at paired basic residues, their subsequent removal by a carboxypeptidase B-like enzyme, and formation of a carboxyl-terminal amide moiety via the action of peptidyl-glycyl alpha-amidating monooxygenase. To examine these reactions further, we utilized the pZIPneo(SVX) retroviral vector to express a cDNA clone encoding human PP in several cell lines including a fibroblast line (psi-2), two endocrine cell lines known to produce amidated peptides (AtT-20 and PC12), and two lines that do not ordinarily produce amidated peptides (RIN5-f and GH3). Transfected psi-2 cells produced an unprocessed precursor of PP that appeared to be secreted constitutively with little remaining in intracellular stores. No post-translational processing of the PP precursor was evident in these cells. By contrast, all 4 endocrine-derived cell lines, regardless of the nature of their endogenous products, were capable of expressing fully processed and carboxyl-terminally amidated PP. Moreover, these lines had the ability to store the processed products. Our results support the notion that post-translational processing of peptide hormone precursors requires storage in secretory granules that contain the appropriate processing enzymes. Furthermore, enzymes such as peptidyl-glycyl alpha-amidating monooxygenase that are required for processing peptides may be a common feature of endocrine-derived cells regardless of the requirement for their activity to process endogenous products.
Highlights
Expression ofHuman Pancreatic Polypeptide in Heterologous Cell Lines*Processing to produce thbeiologically active hexatria- The carboxyl-terminal amino acid of the bioactive hormone contapeptide
Pancreatic polypeptide (PP) is initially synthesized large precursorthatsubsequently undergoes post-translaas a larger precursor that requires post-translational tional processing to form the biologically active peptide [1]
To examine (Fig. 1) is presumed to involve tryptic cleavage of the basic these reactions further, wuetilized the pZIPneo(SVX) retroviral vector to express a cDNA clone encoding human PP in several cell lines including a fibroblast line, two endocrinceell lines known to produce amidated peptides (AtT-20 and PC12), and two lines thatdonotordinarilyproduceamidatedpeptides residues, followed by digestion with a carboxypeptidaseB-like enzyme resulting in the formation of a glycine-extended intermediate that serves as a substrate for the peptide a-amidating reaction (4, 5 )
Summary
Processing to produce thbeiologically active hexatria- The carboxyl-terminal amino acid of the bioactive hormone contapeptide These steps include tryptic cleavage a t of PP is followed in the structure of its precursor by glycine paired basic residues, their subsequent removal by a and two basic amino acids [2]. To examine (Fig. 1) is presumed to involve tryptic cleavage of the basic these reactions further, wuetilized the pZIPneo(SVX) retroviral vector to express a cDNA clone encoding human PP in several cell lines including a fibroblast line (psi-a), two endocrinceell lines known to produce amidated peptides (AtT-20 and PC12), and two lines thatdonotordinarilyproduceamidatedpeptides residues, followed by digestion with a carboxypeptidaseB-like enzyme resulting in the formation of a glycine-extended intermediate that serves as a substrate for the peptide a-amidating reaction (4, 5 ). MATERIALSANDMETHODS of their endogenous products,were capableof expressing fully processed and carboxyl-terminally amidated
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