Effects of carboxypeptidase E overexpression on insulin mRNA levels, regulated insulin secretion, and proinsulin processing of pituitary GH3 cells transfected with a furin-cleavable human proinsulin cDNA

Luca Polastri, Francesca Galbiati, Franco Folli, Alberto M. Davalli

Research output: Contribution to journalArticle

Abstract

We recently developed two rat pituitary GH3 cell clones engineered to secrete human insulin (InsGH3). InsGH3 cells convert proinsulin into mature insulin, which is partially stored into a readily releasable pool of secretory granules. The efficiency of these processes, however, is relatively low in these cells, either in vitro or in vivo. This study was aimed at determining whether carboxypeptidase E (Cpe) overexpression can increase proinsulin processing and regulated secretion by InsGH3 clones. Indeed, in its membrane-bound form Cpe works as sorting receptor for the regulated secretory pathway of many hormones while, in its soluble form, Cpe takes part to the late step of insulin maturation. We obtained two Cpe-overexpressing cell lines from two different InsGH3 clones (InsGH3/C1 and C7). In the Cpe-overexpressing cell lines, derived from InsGH3 of clone 1 (InsGH3/C1-HACpe), in which the membrane-bound form of exogenous Cpe is accounted for by 90% of total Cpe immunoreactivity, we observed an increase in proinsulin gene expression, and in basal and stimulated insulin secretion compared with the original clone. In contrast, in the Cpe-overexpressing cell line derived from InsGH3 of clone 7 (InsGH3/C7-HACpe), where the exogenous membrane-bound form was only 60% of total Cpe, we detected a decrease in basal insulin release and a modest, albeit significant, increase in intracellular proinsulin processing. In conclusion, Cpe overexpression can increase regulated insulin secretion and proinsulin processing in InsGH3 cells; however, such improvements appear quantitatively and qualitatively modest.

Original languageEnglish
Pages (from-to)803-811
Number of pages9
JournalCell Transplantation
Volume11
Issue number8
Publication statusPublished - 2002

Keywords

  • Bioenegineering
  • Carboxypeptidase E
  • Insulin secretion
  • Pituitary cells

ASJC Scopus subject areas

  • Cell Biology
  • Transplantation

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