The No-Go and Nonsense-Mediated RNA Decay Pathways Are Regulated by Inflammatory Cytokines in Insulin-Producing Cells and Human Islets and Determine β-Cell Insulin Biosynthesis and Survival

Abstract

Stress-related changes in β-cell mRNA levels result from a balance between gene transcription and mRNA decay. The regulation of RNA decay pathways has not been investigated in pancreatic β-cells. We found that no-go and nonsense-mediated RNA decay pathway components (RDPCs) and exoribonuclease complexes were expressed in INS-1 cells and human islets. Pelo, Dcp2, Dis3L2, Upf2, and Smg1/5/6/7 were upregulated by inflammatory cytokines in INS-1 cells under conditions where central β-cell mRNAs were downregulated. These changes in RDPC mRNA or corresponding protein levels were largely confirmed in INS-1 cells and rat/human islets. Cytokine-induced upregulation of Pelo, Xrn1, Dis3L2, Upf2, and Smg1/6 was reduced by inducible nitric oxide synthase inhibition, as were endoplasmic reticulum (ER) stress, inhibition of Ins1/2 mRNA, and accumulated insulin secretion. Reactive oxygen species inhibition or iron chelation did not affect RDPC expression. Pelo or Xrn1 knockdown (KD) aggravated, whereas Smg6 KD ameliorated, cytokine-induced INS-1 cell death without affecting ER stress; both increased insulin biosynthesis and medium accumulation but not glucose-stimulated insulin secretion in cytokine-exposed INS-1 cells. In conclusion, RDPCs are regulated by inflammatory stress in β-cells. RDPC KD improved insulin biosynthesis, likely by preventing Ins1/2 mRNA clearance. Pelo/Xrn1 KD aggravated, but Smg6 KD ameliorated, cytokine-mediated β-cell death, possibly through prevention of proapoptotic and antiapoptotic mRNA degradation, respectively.