Protein-Binding Function of RNA-Dependent Protein Kinase Promotes Proliferation through TRAF2/RIP1/NF-κB/c-Myc Pathway in Pancreatic β cells

Mol Med. 2015 Feb 18;21(1):154-66. doi: 10.2119/molmed.2014.00235.

Abstract

Double-stranded RNA-dependent protein kinase (PKR), an intracellular pathogen recognition receptor, is involved both in insulin resistance in peripheral tissues and in downregulation of pancreatic β-cell function in a kinase-dependent manner, indicating PKR as a core component in the progression of type 2 diabetes. PKR also acts as an adaptor protein via its protein-binding domain. Here, the PKR protein-binding function promoted β-cell proliferation without its kinase activity, which is associated with enhanced physical interaction with tumor necrosis factor receptor-associated factor 2 (TRAF2) and TRAF6. In addition, the transcription of the nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB)-dependent survival gene c-Myc was upregulated significantly and is necessary for proliferation. Upregulation of the PKR protein-binding function induced the NF-κB pathway, as observed by dose-dependent degradation of IκBα, induced nuclear translocation of p65 and elevated NF-κB-dependent reporter gene expression. NF-κB-dependent reporter activity and β-cell proliferation both were suppressed by TRAF2-siRNA, but not by TRAF6-siRNA. TRAF2-siRNA blocked the ubiquitination of receptor-interacting serine/threonine-protein kinase 1 (RIP1) induced by PKR protein binding. Furthermore, RIP1-siRNA inhibited β-cell proliferation. Proinflammatory cytokines (TNFα) and glucolipitoxicity also promoted the physical interaction of PKR with TRAF2. Collectively, these data indicate a pivotal role for PKR's protein-binding function on the proliferation of pancreatic β cells through TRAF2/RIP1/NF-κB/c-Myc pathways. Therapeutic opportunities for type 2 diabetes may arise when its kinase catalytic function, but not its protein-binding function, is downregulated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Catalysis
  • Cell Proliferation / drug effects
  • Cell Survival
  • GTPase-Activating Proteins / metabolism*
  • Gene Expression Regulation
  • Humans
  • Insulin-Secreting Cells / metabolism*
  • Mice
  • NF-kappa B / metabolism*
  • Protein Binding
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / metabolism*
  • Signal Transduction*
  • TNF Receptor-Associated Factor 2 / metabolism*
  • Transcription, Genetic
  • Tumor Necrosis Factor-alpha / metabolism
  • Tumor Necrosis Factor-alpha / pharmacology
  • eIF-2 Kinase / metabolism*

Substances

  • GTPase-Activating Proteins
  • NF-kappa B
  • Proto-Oncogene Proteins c-myc
  • Ralbp1 protein, mouse
  • TNF Receptor-Associated Factor 2
  • Tumor Necrosis Factor-alpha
  • eIF-2 Kinase