Proteasome Inhibition Alters Glucose-stimulated (Pro)insulin Secretion and Turnover in Pancreatic {beta}-Cells.
Document Type
Article
Publication Date
2005
First Page
15727
Last Page
15734
JAX Source
J Biol Chem 2005 Apr; 280(16):15727-34.
Abstract
Metabolic labeling studies were conducted in freshly isolated mouse islets and a beta-cell line (MIN6) to examine the effects of proteasome inhibition on glucose-stimulated (pro)insulin synthesis and secretion. Glucose-stimulated (pro)insulin synthesis, as determined by the incorporation of [(3)H]tyrosine, decreased significantly by 90% in islets and 71% in MIN6 cells pretreated with the proteasome inhibitor lactacystin (10 mum) for 2 h. To follow the fate of newly synthesized (pro)insulin, islets were pulse-labeled with [(3)H]tyrosine (40 muCi) for 20 min and chased +/- lactacystin (10 mum) for up to 4 h. The release of newly synthesized (pro)insulin ([(3)H]tyrosine-labeled) was similar between lactacystin-treated and control islets despite a 51% decrease (p <0.05) in total immunoreactive (pro)insulin secretion by lactacystin-treated islets. The specific radioactivity of [(3)H]tyrosine-labeled (pro)insulin in the extracellular medium of lactacystin-treated islets (0.52 +/- 0.16 cpm/microunits) was 2-fold greater relative to control islets (0.25 +/- 0.06 cpm/microunits). Induction of the unfolded protein response by lactacystin, as evidenced by the up-regulation of endoplasmic reticulum (ER) chaperones (GRP78/BiP, GRP94, protein disulfide isomerase) and induction of the stress-inducible transcription factor C/EBP-homologous protein/GADD153 (CHOP/GADD153), likely contributed to the release of newly synthesized (pro)insulin to relieve ER stress. The present data indicate proteasome inhibition did not prevent, but increased (p <0.05), the intracellular degradation of [(3)H]tyrosine-labeled (pro-)insulin from 8 to 24% in islets. Collectively, these data indicate beta-cells may balance glucose-stimulated (pro)insulin synthesis and secretion with the activity of the proteasome to regulate protein concentrations in the ER.
Recommended Citation
Kitiphongspattana K,
Mathews CE,
Leiter EH,
Gaskins HR.
Proteasome Inhibition Alters Glucose-stimulated (Pro)insulin Secretion and Turnover in Pancreatic {beta}-Cells. J Biol Chem 2005 Apr; 280(16):15727-34.