Phosphorylation of TRIM28 Enhances the Expression of IFN-β and Proinflammatory Cytokines During HPAIV Infection of Human Lung Epithelial Cells

Front Immunol. 2018 Sep 28:9:2229. doi: 10.3389/fimmu.2018.02229. eCollection 2018.


Human infection with highly pathogenic avian influenza viruses (HPAIV) is often associated with severe tissue damage due to hyperinduction of interferons and proinflammatory cytokines. The reasons for this excessive cytokine expression are still incompletely understood, which has hampered the development of efficient immunomodulatory treatment options. The host protein TRIM28 associates to the promoter regions of over 13,000 genes and is recognized as a genomic corepressor and negative immune regulator. TRIM28 corepressor activity is regulated by post-translational modifications, specifically phosphorylation of S473, which modulates binding of TRIM28 to the heterochromatin-binding protein HP1. Here, we identified TRIM28 as a key immune regulator leading to increased IFN-β and proinflammatory cytokine levels during infection with HPAIV. Using influenza A virus strains of the subtype H1N1 as well as HPAIV of subtypes H7N7, H7N9, and H5N1, we could demonstrate that strain-specific phosphorylation of TRIM28 S473 is induced by a signaling cascade constituted of PKR, p38 MAPK, and MSK1 in response to RIG-I independent sensing of viral RNA. Furthermore, using chemical inhibitors as well as knockout cell lines, our results suggest that phosphorylation of S473 facilitates a functional switch leading to increased levels of IFN-β, IL-6, and IL-8. In summary, we have identified TRIM28 as a critical factor controlling excessive expression of type I IFNs as well as proinflammatory cytokines during infection with H5N1, H7N7, and H7N9 HPAIV. In addition, our data indicate a novel mechanism of PKR-mediated IFN-β expression, which could lay the ground for novel treatment options aiming at rebalancing dysregulated immune responses during severe HPAIV infection.

Keywords: IFN-β; KAP1; PKR; RIG-I; TIF1-beta; TRIM28; influenza; innate immunity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • A549 Cells
  • Analysis of Variance
  • Animals
  • CRISPR-Cas Systems / genetics
  • Chlorocebus aethiops
  • DEAD Box Protein 58 / metabolism
  • Epithelial Cells / virology*
  • Gene Knockdown Techniques
  • Gene Transfer Techniques
  • HEK293 Cells
  • Human Umbilical Vein Endothelial Cells
  • Humans
  • Influenza A virus / metabolism*
  • Influenza, Human / metabolism*
  • Interferon-beta / metabolism*
  • Lung / virology*
  • Phosphorylation
  • Receptors, Immunologic
  • Ribosomal Protein S6 Kinases, 90-kDa / metabolism
  • Tripartite Motif-Containing Protein 28 / genetics*
  • Tripartite Motif-Containing Protein 28 / metabolism*
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • Receptors, Immunologic
  • Interferon-beta
  • TRIM28 protein, human
  • Tripartite Motif-Containing Protein 28
  • Ribosomal Protein S6 Kinases, 90-kDa
  • mitogen and stress-activated protein kinase 1
  • p38 Mitogen-Activated Protein Kinases
  • RIGI protein, human
  • DEAD Box Protein 58