Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17

Jens F. Rehfeld (1) , Xiaorong Zhu , Christina Norrbom , Jens R Bundgaard , Anders H Johnsen , John E Nielsen , Jonas Vikesaa , Jeffrey Stein , Arunangsu Dey , Donald F Steiner , Lennart Friis-Hansen

1 Diagnostic Investigations, Clinical Biochemistry

Cellular synthesis of peptide hormones requires prohormone convertases (PCs) for the endoproteolysis of prohormones. Antral G-cells synthesize most gastrin and express PC1/3, 2 and 5/6 in rat and man. But the cleavage sites in progastrin for each PC have not been determined. Therefore, we measured the concentrations of progastrin, processing intermediates and α-amidated gastrins in antral extracts from PC1/3 null-mice and compared the results to those in mice lacking PC2 and wild-type controls. The expression of PCs was examined by immunocytochemistry and in situ hybridisation of mouse G-cells. Finally, the in vitro effect of recombinant PC5/6 on progastrin and progastrin fragments containing the relevant dibasic cleavage sites was also examined. The results showed that also mouse G-cells express PC1/3, 2 and 5/6. The concentration of progastrin in PC1/3 null-mice was threefold elevated. Chromatography showed that cleavage of the R36R37 and R73R74 sites were grossly decreased. Accordingly, the concentrations of progastrin products were markedly reduced, α-amidated gastrins (-34 and -17) being 25% of normal. Lack of PC1/3 was without effect on the third dibasic site (K53K54), which is the only processing site for PC2. Recombinant PC5/6 did not cleave any of the dibasic processing sites in progastrin and fragments containing the relevant dibasic processing sites. The complementary cleavages of PC1/3 and 2, however, suffice to explain most of the normal endoproteolysis of progastrin. Moreover, the results show that prohormone convertases react differently to the same dibasic sequences, suggesting that additional structural factors modulate the substrate specificity.

Mots clés: Life Sciences

Jens F. Rehfeld, Xiaorong Zhu, Christina Norrbom, Jens R Bundgaard, Anders H Johnsen, et al.. Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17. Biochemical Journal, 2008, 415 (1), pp.35-43. ⟨10.1042/BJ20080881⟩. ⟨hal-00479018⟩