Ubiquitinated-Protein Aggregates Form in Pancreatic β-Cells During Diabetes-Induced Oxidative Stress and Are Regulated by Autophagy

作者：Natalia A. Kaniuk, Michael A. Kiràly, Holly E. Bates, Mladen Vranić, Allen Volchuk, John Hunter Brumell · 发表于：Diabetes · 年份：2007 · DOI：10.2337/db06-1160 · 被引用次数：221 · 研究领域：Autophagy in Disease and Therapy、Pancreatic function and diabetes、Endoplasmic Reticulum Stress and Disease

Diabetes-induced oxidative stress can lead to protein misfolding and degradation by the ubiquitin-proteasome system. This study examined protein ubiquitination in pancreatic sections from Zucker diabetic fatty rats. We observed large aggregates of ubiquitinated proteins (Ub-proteins) in insulin-expressing beta-cells and surrounding acinar cells. The formation of these aggregates was also observed in INS1 832/13 beta-cells after exposure to high glucose (30 mmol/l) for 8-72 h, allowing us to further characterize this phenotype. Oxidative stress induced by aminotriazole (ATZ) was sufficient to stimulate Ub-protein aggregate formation. Furthermore, the addition of the antioxidants N-acetyl cysteine (NAC) and taurine resulted in a significant decrease in formation of Ub-protein aggregates in high glucose. Puromycin, which induces defective ribosomal product (DRiP) formation was sufficient to induce Ub-protein aggregates in INS1 832/13 cells. However, cycloheximide (which blocks translation) did not impair Ub-protein aggregate formation at high glucose levels, suggesting that long-lived proteins are targeted to these structures. Clearance of Ub-protein aggregates was observed during recovery in normal medium (11 mmol/l glucose). Despite the fact that 20S proteasome was localized to Ub-protein aggregates, epoxomicin treatment did not affect clearance, indicating that the proteasome does not degrade proteins localized to these structures. The autophagy inhibitor 3MA blocked aggregat...