TNF-selectively activates the IRE1-/XBP1 endoplasmic reticulum stress pathway in human airway smooth muscle cells

John Yap, Xujiao Chen, Philippe Delmotte, Gary C. Sieck, Gary C. Sieck

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

TNF_selectively activates the IRE1_/XBP1 endoplasmic reticulum stress pathway in human airway smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 318: L483-L493, 2020. First published January 15, 2020; doi:10.1152/ajplung.00212.2019.-Airway inflammation is a key aspect of diseases such as asthma. Proinflammatory cytokines such as TNF_mediate the inflammatory response. In various diseases, inflammation leads to endoplasmic reticulum (ER) stress, the accumulation of unfolded proteins, which triggers homeostatic responses to restore normal cellular function. We hypothesized that TNF_triggers ER stress through an increase in reactive oxygen species generation in human airway smooth muscle (hASM) with a downstream effect on mitofusin 2 (Mfn2). In hASM cells isolated from lung specimens incidental to patient surgery, dose- A nd time-dependent effects of TNF_exposure were assessed. Exposure of hASM to tunicamycin was used as a positive control. Tempol (500_M) was used as superoxide scavenger. Activation of three ER stress pathways were evaluated by Western blotting: 1) autophosphorylation of inositolrequiring enzyme1 (IRE1_) leading to splicing of X-box binding protein 1 (XBP1); 2) autophosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) leading to phosphorylation of eukaryotic initiation factor 2_; and 3) translocation and cleavage of activating transcription factor 6 (ATF6). We found that exposure of hASM cells to tunicamycin activated all three ER stress pathways. In contrast, TNF_selectively activated the IRE1_/XBP1 pathway in a dose- A nd time-dependent fashion. Our results indicate that TNF_does not activate the PERK and ATF6 pathways. Exposure of hASM cells to TNF_also decreased Mfn2 protein expression. Concurrent exposure to TNF_and tempol reversed the effect of TNF_on IRE1_phosphorylation and Mfn2 protein expression. Selective activation of the IRE1_/XBP1 pathway in hASM cells after exposure to TNF_may reflect a unique homeostatic role of this pathway in the inflammatory response of hASM cells.

Original languageEnglish (US)
Pages (from-to)L483-L493
JournalAmerican Journal of Physiology - Lung Cellular and Molecular Physiology
Volume318
Issue number3
DOIs
StatePublished - Mar 2020

Keywords

  • Airway smooth muscle
  • Asthma
  • Er stress
  • Inflammation
  • Tnf_

ASJC Scopus subject areas

  • Physiology
  • Pulmonary and Respiratory Medicine
  • Physiology (medical)
  • Cell Biology

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