Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17.
Cellular synthesis of peptide hormones requires PCs (prohormone convertases) for the endoproteolysis of prohormones. Antral G-cells synthesize the most gastrin and express PC1/3, 2 and 5/6 in the rat and human. But the cleavage sites in progastrin for each PC have not been determined. Therefore, in the present study, we measured the concentrations of progastrin, processing intermediates and alpha-amidated gastrins in antral extracts from PC1/3-null mice and compared the results with those in mice lacking PC2 and wild-type controls. The expression of PCs was examined by immunocytochemistry and in situ hybridization 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 mouse G-cells express PC1/3, 2 and 5/6. The concentration of progastrin in PC1/3-null mice was elevated 3-fold. Chromatography showed that cleavage of the Arg(36)Arg(37) and Arg(73)Arg(74) sites were grossly decreased. Accordingly, the concentrations of progastrin products were markedly reduced, alpha-amidated gastrins (-34 and -17) being 25% of normal. Lack of PC1/3 was without effect on the third dibasic site (Lys(53)Lys(54)), 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 PCs react differently to the same dibasic sequences, suggesting that additional structural factors modulate the substrate specificity.
Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark. jens.f.rehfeld@rh.regionh.dk
Jens F
JF
Rehfeld
Xiaorong
X
Zhu
Christina
C
Norrbom
Jens R
JR
Bundgaard
Anders H
AH
Johnsen
John E
JE
Nielsen
Jonas
J
Vikesaa
Jeffrey
J
Stein
Arunangsu
A
Dey
Donald F
DF
Steiner
Lennart
L
Friis-Hansen
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019863:Gastrin-Secreting Cells / Q000378:metabolism; D005755:Gastrins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D045664:Proprotein Convertase 1 / Q000378:metabolism*; D045706:Proprotein Convertase 2 / Q000378:metabolism; D045702:Proprotein Convertase 5 / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D011706:Pyloric Antrum / Q000737:chemistry; D011994:Recombinant Proteins / Q000378:metabolism
D005755:Gastrins; D011498:Protein Precursors; D011994:Recombinant Proteins; C013706:big gastrin; C013550:gastrin 17; D045702:Proprotein Convertase 5; D045664:Proprotein Convertase 1; D045706:Proprotein Convertase 2