title: The Effect of Tribbles-Related Protein 3 on ER Stress-Suppressed Insulin Gene Expression in INS-1 Cells.
abstract: BACKGROUND
  The highly developed endoplasmic reticulum (ER) structure in pancreatic beta cells is heavily involved in insulin biosynthesis. Thus, any perturbation in ER function inevitably impacts insulin biosynthesis. Recent studies showed that the expression of tribbles-related protein 3 (TRB3), a mammalian homolog of Drosophilia tribbles, in various cell types is induced by ER stress. Here, we examined whether ER stress induces TRB3 expression in INS-1 cells and found that TRB3 mediates ER stress-induced suppression of insulin gene expression.
  
  
  METHODS
  The effects of tunicamycin and thapsigargin on insulin and TRB3 expression in INS-1 cells were measured by Northern and Western blot analysis, respectively. The effects of adenovirus-mediated overexpression of TRB3 on insulin, PDX-1 and MafA gene expression in INS-1 cells were measured by Northern blot analysis. The effect of TRB3 on insulin promoter was measured by transient transfection study with constructs of human insulin promoter.
  
  
  RESULTS
  The treatment of INS-1 cells with tunicamycin and thapsigargin decreased insulin mRNA expression, but increased TRB3 protein expression. Adenovirus-mediated overexpression of TRB3 decreased insulin gene expression in a dose-dependent manner. A transient transfection study showed that TRB3 inhibited insulin promoter activity, suggesting that TRB3 inhibited insulin gene expression at transcriptional level. Adenovirus-mediated overexpression of TRB3 also decreased PDX-1 mRNA expression, but did not influence MafA mRNA expression.
  
  
  CONCLUSIONS
  This study showed that ER stress induced TRB3 expression, but decreased both insulin and PDX-1 gene expression in INS-1 cells. Our data suggest that TRB3 plays an important role in ER stress-induced beta cell dysfunction.
authors.affiliation: Department of Internal Medicine, Keimyung University School of Medicine, Daegu, Korea.
authors.forename: Young Yun
authors.initials: YY
authors.lastname: Jang
authors.forename: Nam Keong
authors.initials: NK
authors.lastname: Kim
authors.forename: Mi Kyung
authors.initials: MK
authors.lastname: Kim
authors.forename: Ho Young
authors.initials: HY
authors.lastname: Lee
authors.forename: Sang Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Hye Soon
authors.initials: HS
authors.lastname: Kim
authors.forename: Hye-Young
authors.initials: HY
authors.lastname: Seo
authors.forename: In Kyu
authors.initials: IK
authors.lastname: Lee
authors.forename: Keun Gyu
authors.initials: KG
authors.lastname: Park