Ramzy_Asadi_Kieffer_-_Online_appendix_-_09Mar2020.pdf (2.2 MB)
Download fileRevisiting proinsulin processing: Evidence that human β-cells process proinsulin with prohormone convertase (PC) 1/3 but not PC2
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posted on 2020-04-14, 22:40 authored by Ada AdminAda Admin, Adam Ramzy, Ali Asadi, Timothy J KiefferInsulin is first produced in pancreatic
β-cells as the precursor prohormone proinsulin. Defective proinsulin processing
has been implicated in the pathogenesis of both type 1 and type 2 diabetes.
Though there is substantial evidence that mouse β-cells process proinsulin
using prohormone convertase 1/3 (PC1/3) then prohormone convertase 2 (PC2),
this finding has not been verified in human β-cells. Immunofluorescence with
validated antibodies reveals that there was no detectable PC2 immunoreactivity
in human β-cells and little PCSK2 mRNA by in situ
hybridization. Similarly, rat β-cells were not immunoreactive for PC2. In all
histological experiments, PC2 immunoreactivity in neighbouring α-cells acts as
a positive control. In donors with type 2 diabetes, β-cells had elevated PC2
immunoreactivity, suggesting that aberrant PC2 expression may contribute to
impaired proinsulin processing in β-cells of patients with diabetes. To support
histological findings using a biochemical approach, human islets were used for
pulse-chase experiments. Despite inhibition of PC2 function by temperature
blockade, brefeldin-A, chloroquine, and multiple inhibitors that blocked
production of mature glucagon from proglucagon, β-cells retained the ability to
produce mature insulin. Conversely, suppression of PC1/3 blocked processing of
proinsulin but not proglucagon. By demonstrating that healthy human β-cells
process proinsulin by PC1/3 but not PC2 we suggest that there is a need to
revise the longstanding theory of proinsulin processing.