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.
Department of Biochemistry and Molecular Biology and Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA.
Xiaorong
X
Zhu
Lelio
L
Orci
Raymond
R
Carroll
Christina
C
Norrbom
Mariella
M
Ravazzola
Donald F
DF
Steiner
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