Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 295 ( Pt 3) (Pt 3), 813-9

Post-translational Processing of Progastrin: Inhibition of Cleavage, Phosphorylation and Sulphation by Brefeldin A

Affiliations

Post-translational Processing of Progastrin: Inhibition of Cleavage, Phosphorylation and Sulphation by Brefeldin A

A Varro et al. Biochem J.

Abstract

The precursor for the acid-stimulating hormone gastrin provides a useful model for studies of post-translational processing because defined sites of cleavage, amidation, sulphation and phosphorylation occur within a dodecapeptide sequence. The factors determining these post-translational processing events are still poorly understood. We have used brefeldin A, which disrupts transport from rough endoplasmic reticulum to the Golgi complex, to examine the mechanisms of cleavage, phosphorylation and sulphation of rat progastrin-derived peptides. Biosynthetic products were detected after immunoprecipitation using antibodies specific for the extreme C-terminus of progastrin, followed by reversed-phase and ion-exchange h.p.l.c. Gastrin cells incorporated [3H]tyrosine, [32P]phosphate and [35S]sulphate into both progastrin and its extreme C-terminal tryptic (nona-) peptide. Ion-exchange chromatography resolved four forms of the C-terminal tryptic fragment of progastrin which differed in whether they were phosphorylated at Ser96, sulphated at Tyr103, both or neither. The specific activity of [3H]tyrosine in the peak that was both phosphorylated and sulphated was higher than in the others. Brefeldin A inhibited the appearance of [3H]tyrosine-labelled C-terminal tryptic fragment but there was an accumulation of labelled progastrin and a peptide corresponding to the C-terminal 46 residues of progastrin. Brefeldin A also inhibited incorporation of 32P and 35S into both progastrin and its C-terminal fragment. Thus phosphorylation of Ser96, sulphation of Tyr103 and cleavage at Arg94-Arg95 depend on passage of newly synthesized progastrin along the secretory pathway; as brefeldin A is thought to act proximal to the trans-Golgi, these processing steps would appear to occur distal to this point. The data also indicate that the stores of unphosphorylated C-terminal tryptic fragment are not available for phosphorylation, implying that this modification occurs proximal to the secretory granule; cleavage is known to occur in the secretory granule which suggests that it occurs after phosphorylation.

Similar articles

See all similar articles

Cited by 6 PubMed Central articles

See all "Cited by" articles

References

    1. J Biol Chem. 1982 Apr 10;257(7):3837-46 - PubMed
    1. J Physiol. 1991 Feb;433:483-93 - PubMed
    1. Annu Rev Physiol. 1982;44:625-38 - PubMed
    1. Biochem J. 1984 Apr 1;219(1):181-7 - PubMed
    1. J Biol Chem. 1984 Nov 10;259(21):13246-52 - PubMed

Publication types

Feedback