Silver nanoparticles induce degradation of the endoplasmic reticulum stress sensor activating transcription factor-6 leading to activation of the NLRP-3 inflammasome

J Biol Chem. 2015 Feb 27;290(9):5926-39. doi: 10.1074/jbc.M114.610899. Epub 2015 Jan 15.

Abstract

In the past decade, the increasing amount of nanoparticles (NP) and nanomaterials used in multiple applications led the scientific community to investigate the potential toxicity of NP. Many studies highlighted the cytotoxic effects of various NP, including titanium dioxide, zinc oxide, and silver nanoparticles (AgNP). In a few studies, endoplasmic reticulum (ER) stress was found to be associated with NP cytotoxicity leading to apoptosis in different cell types. In this study, we report for the first time that silver nanoparticles of 15 nm (AgNP15), depending on the concentration, induced different signature ER stress markers in human THP-1 monocytes leading to a rapid ER stress response with degradation of the ATF-6 sensor. Also, AgNP15 induced pyroptosis and activation of the NLRP-3 inflammasome as demonstrated by the processing and increased activity of caspase-1 and secretion of IL-1β and ASC (apoptosis-associated speck-like protein containing a CARD domain) pyroptosome formation. Transfection of THP-1 cells with siRNA targeting NLRP-3 decreased the AgNP15-induced IL-1β production. The absence of caspase-4 expression resulted in a significant reduction of pro-IL-1β. However, caspase-1 activity was significantly higher in caspase-4-deficient cells when compared with WT cells. Inhibition of AgNP15-induced ATF-6 degradation with Site-2 protease inhibitors completely blocked the effect of AgNP15 on pyroptosis and secretion of IL-1β, indicating that ATF-6 is crucial for the induction of this type of cell death. We conclude that AgNP15 induce degradation of the ER stress sensor ATF-6, leading to activation of the NLRP-3 inflammasome regulated by caspase-4 in human monocytes.

Keywords: Caspase; Caspase 1 (CASP1); Caspase 4; Endoplasmic Reticulum Stress (ER Stress); Inflammasome; NLRP-3 Inflammasome; Nanotechnology; Pyroptosis; Silver Nanoparticles.

MeSH terms

  • Activating Transcription Factor 6 / metabolism*
  • Apoptosis / drug effects
  • Blotting, Western
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Caspase 1 / metabolism
  • Cell Death / drug effects
  • Cell Line, Tumor
  • Cells, Cultured
  • Endoplasmic Reticulum Stress / drug effects
  • Enzyme Activation / drug effects
  • Humans
  • Inflammasomes / drug effects*
  • Inflammasomes / metabolism
  • Interleukin-1beta / metabolism
  • Metal Nanoparticles / chemistry
  • Metal Nanoparticles / toxicity*
  • Metal Nanoparticles / ultrastructure
  • Microscopy, Confocal
  • Microscopy, Electron, Transmission
  • Monocytes / drug effects
  • Monocytes / metabolism
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • Proteolysis / drug effects
  • RNA Interference
  • Silver / chemistry*

Substances

  • ATF6 protein, human
  • Activating Transcription Factor 6
  • Carrier Proteins
  • Inflammasomes
  • Interleukin-1beta
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • NLRP3 protein, human
  • Silver
  • Caspase 1