Severe block in processing of proinsulin to insulin accompanied by elevation of des-64,65 proinsulin intermediates in islets of mice lacking prohormone convertase 1/3.
The neuroendocrine processing endoproteases PC2 and PC1/3 are expressed in the beta cells of the islets of Langerhans and participate in the processing of proinsulin to insulin and C-peptide. We have previously shown that disruption of PC2 (SPC2) expression significantly impairs proinsulin processing. Here we report that disruption of the expression of PC1/3 (SPC3) produces a much more severe block in proinsulin conversion. In nulls, pancreatic and circulating proinsulin-like components comprise 87% and 91%, respectively, of total insulin-related immunoreactivity. Heterozygotes also show a more than 2-fold elevation in proinsulin levels to approximately 12%. Immunocytochemical and ultrastructural studies of the beta cells reveal the nearly complete absence of mature insulin immunoreactivity and its replacement by that of proinsulin in abundant immature-appearing secretory granules. In contrast, alpha cell morphology and glucagon processing are normal, and there is also no defect in somatostatin-14 generation. Pulse-chase labeling studies confirm the existence of a major block in proinsulin processing in PC1/3 nulls with prolongation of half-times of conversion by 7- and 10-fold for proinsulins I and II, respectively. Lack of PC1/3 also results in increased levels of des-64,65 proinsulin intermediates generated by PC2, in contrast to PC2 nulls, in which des- 31,32 proinsulin intermediates predominate. These results confirm that PC1/3 plays a major role in processing proinsulin, but that its coordinated action with PC2 is necessary for the most efficient and complete processing of this prohormone.
Zhu
Xiaorong
X
Department of Biochemistry and Molecular Biology and Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA.
Orci
Lelio
L
Carroll
Raymond
R
Norrbom
Christina
C
Ravazzola
Mariella
M
Steiner
Donald F
DF
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000096:biosynthesis*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010446:Peptide Fragments / Q000378:metabolism*; D011384:Proinsulin / Q000378:metabolism*; D045664:Proprotein Convertase 1; D043484:Proprotein Convertases; D011499:Protein Processing, Post-Translational
D007328:Insulin; D010446:Peptide Fragments; C088305:proinsulin, des(Lys(64),Arg(65)); D011384:Proinsulin; D043484:Proprotein Convertases; C473656:Pcsk1 protein, mouse; D045664:Proprotein Convertase 1; D016282:Aspartic Acid Endopeptidases