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Amine precursor uptake and decarboxylation: significance for processing of the rat gastrin precursor
Author(s) -
Voronina Svetlana,
Henry Julie,
Vaillant Camille,
Dockray Graham J.,
Varro Andrea
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.363bn.x
Subject(s) - chemistry , gastrin , biochemistry , bafilomycin , stereochemistry , secretion , apoptosis , autophagy
1 Conversion of prohormone precursors to smaller active products occurs in secretory granules, which also have the capacity to concentrate biogenic amines. We have examined how processing of the gastrin precursor, progastrin, in rat antral mucosa is influenced by modulation of the biogenic amine content of secretory granules. 2 Newly synthesized progastrin‐derived peptides in rat antral mucosa were labelled in vitro with 35 SO 4 2− using a pulse–chase protocol and detected after immunoprecipitation by HPLC with on‐line liquid scintillation counting. Secretory granule morphology was examined by electron microscopy. The effects of experimentally manipulating secretory granule pH and amine content were examined. 3 The dopamine precursor l ‐β‐3,4‐dihydroxyphenylalanine ( l ‐DOPA) inhibited cleavage of 35 S‐labelled thirty‐four amino acid amidated gastrin, i.e. [ 35 S]G34, and of [ 35 S]G34 with COOH‐terminal glycine, i.e. [ 35 S]G34–Gly, at a pair of lysine residues, but did not influence cleavage of progastrin at pairs of arginine residues. The effect of l ‐DOPA was reversed by reserpine, which inhibits the amine–proton exchangers VMAT 1 and VMAT 2 , and by carbidopa, which inhibits aromatic L‐amino acid decarboxylase. 4 Treatments that raise intragranular pH, e.g. the weak base chloroquine, the ionophore monensin and the vacuolar proton pump inhibitor bafilomycin A 1 , had similar effects to l ‐DOPA. 5 Electron microscopical studies showed that the electron‐dense aggregrates in gastrin cell secretory granules were lost after inhibition of the vacuolar proton pump. Treatment with l ‐DOPA produced reserpine‐sensitive dissipation of the electron‐dense aggregates, compatible with the idea that increased amine delivery raised intragranular pH. 6 The data suggest that the processes of amine precursor uptake, decarboxylation and sequestration in secretory granules are associated with selective modulation of progastrin cleavage, possibly by raising intragranular pH and thereby inhibiting pH‐sensitive prohormone convertases.