Expression and processing of human preprogastrin in murine medullary thyroid carcinoma cells

Gastrin, the primary hormonal mediator of postprandial gastric acid secretion, is produced from its precursor progastrin by a series of posttranslational processing reactions including dibasic residue cleavage and carboxyl-terminal alpha-amidation. Progastrin contains three dibasic cleavage signals, Arg57Arg58, Lys74Lys75, and Arg94Arg95, that appear to be cleaved differently in different tissues. Differential processing is a potential means by which the production of biologically active peptides may be regulated in a tissue-specific manner. To study these reactions further, we used the pZipNeo SV(X) retroviral vector to express human gastrin cDNA in a heterologous cell line (MTC 6-23) known to be capable of processing other peptide precursors. The psi 2 packaging cell line transfected with the gastrin cDNA-retroviral construct (pSVXgas) produced progastrin, but no substantial amounts of processed amidated gastrin were detected. amounts of processed amidated gastrin were detected. In contrast, MTC 6-23 cells infected with the viral stock obtained from the supernatant of pSVXgas-transfected psi 2 cells produced carboxyl-terminally amidated gastrin in all of its standard molecular forms, including sulfated and nonsulfated forms of tetratriacontagastrin (G-34), heptadecagastrin (G-17), and tetradecagastrin (G-14). These studies indicate that heterologous endocrine cell lines infected with a retroviral-peptide cDNA construct can serve as useful models for peptide hormone posttranslational processing.