Background & aims: The gastrin precursor progastrin produces multiple alternative active products, but the pathways of posttranslational processing in human antral mucosa have not yet been studied directly. The aim of this study was to investigate the biosynthetic relationships and release kinetics of newly synthesized progastrin-derived peptides in the antrum of patients with pernicious anemia.
Methods: Antral mucosal explants were incubated with [35S]sulfate and [3H]tyrosine to label progastrin and its derivatives, which were detected by online scintillation counting after immunoprecipitation and high-performance liquid chromatography.
Results: [35S]- and [3H]progastrin were detected within 2.5 hours, and labeled G34Gly and G34 were readily detected after 5-hour incubation. Pulse-chase studies indicated conversion of progastrin to G17 via G34Gly and G34. Secretion of newly synthesized G34, but not G34Gly, was routinely detected; G17Gly was present only in trace quantities in cell extracts and media. In control samples, progastrin synthesis was about 10 times lower than in pernicious anemia samples, although the proportions of different labeled amidated gastrins after 5-hour incubation were similar.
Conclusions: In the antrum of patients with pernicious anemia, Gly-gastrins, particularly G34Gly, are biosynthetic intermediates and not major secretory products. Some G34 is secreted preferentially under basal conditions.