Modulation of the cleavage of the gastrin precursor by prohormone phosphorylation.
OBJECTIVE
Amidated gastrins are acid secretagogues and growth factors. Their precursor, progastrin, is a growth factor but not a secretagogue. Cleavage of progastrin at Arg94/95 determines the expression of these two alternative patterns of biological activity. We examined the hypothesis that cleavage at Arg94/95 is regulated by phosphorylation of the adjacent Ser96 residue.


METHODS
Hamster insulinoma cells were stably transfected with wild-type rat preprogastrin and phosphorylation site mutants; biosynthesis was studied by a pulse-chase protocol.


RESULTS
Rates of cleavage at Arg94/95 were increased in Ser96-->Ala compared with wild-type progastrin. Mutation of Glu98 to Ala inhibited incorporation of [32P]phosphate into progastrin and increased the rate of cleavage at Arg94/95. Conversely, mutation of Ser96 to Asp reduced rates of cleavage at Arg94/95. Depletion of calcium stores decreased phosphorylation of Ser96 and increased cleavage at Arg94/95. Modulation of Ser96 phosphorylation also directly influenced the ratio of progastrin-cleavage products (progastrin/CFP; G17Gly/G34Gly) secreted into the medium.


CONCLUSIONS
Phosphorylation of progastrin is dependent on calcium stores, determines prohormone cleavage rates, and thereby controls the production of the alternative active products of preprogastrin translation.
Bishop
L
L
Physiological Laboratory, University of Liverpool, Liverpool, England.
Dimaline
R
R
Blackmore
C
C
Deavall
D
D
Dockray
G J
GJ
Varro
A
A
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000502:physiology; D047388:Casein Kinases; D006224:Cricetinae; D005755:Gastrins / Q000235:genetics* / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D009154:Mutation / Q000502:physiology; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D014162:Transfection; D014407:Tumor Cells, Cultured
D005755:Gastrins; D010446:Peptide Fragments; D011498:Protein Precursors; C013706:big gastrin; D011494:Protein Kinases; D047388:Casein Kinases; D002118:Calcium