The TLR4 adaptor TRAM controls the phagocytosis of Gram-negative bacteria by interacting with the Rab11-family interacting protein 2

PLoS Pathog. 2019 Mar 18;15(3):e1007684. doi: 10.1371/journal.ppat.1007684. eCollection 2019 Mar.

Abstract

Phagocytosis is a complex process that eliminates microbes and is performed by specialised cells such as macrophages. Toll-like receptor 4 (TLR4) is expressed on the surface of macrophages and recognizes Gram-negative bacteria. Moreover, TLR4 has been suggested to play a role in the phagocytosis of Gram-negative bacteria, but the mechanisms remain unclear. Here we have used primary human macrophages and engineered THP-1 monocytes to show that the TLR4 sorting adapter, TRAM, is instrumental for phagocytosis of Escherichia coli as well as Staphylococcus aureus. We find that TRAM forms a complex with Rab11 family interacting protein 2 (FIP2) that is recruited to the phagocytic cups of E. coli. This promotes activation of the actin-regulatory GTPases Rac1 and Cdc42. Our results show that FIP2 guided TRAM recruitment orchestrates actin remodelling and IRF3 activation, two events that are both required for phagocytosis of Gram-negative bacteria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Adaptor Proteins, Signal Transducing / physiology*
  • Animals
  • Carrier Proteins / metabolism*
  • Carrier Proteins / physiology
  • Endocytosis
  • Endosomes
  • Escherichia coli / pathogenicity
  • HEK293 Cells
  • Humans
  • Interferon Regulatory Factor-3
  • Lipopolysaccharides
  • Macrophages / immunology
  • Macrophages / metabolism
  • Membrane Proteins / metabolism*
  • Membrane Proteins / physiology
  • Mice
  • Mice, Inbred C57BL
  • Myeloid Differentiation Factor 88
  • Phagocytosis / physiology*
  • Primary Cell Culture
  • Protein Transport
  • Signal Transduction
  • Staphylococcus aureus / pathogenicity
  • THP-1 Cells
  • Toll-Like Receptor 4 / metabolism
  • cdc42 GTP-Binding Protein
  • rab GTP-Binding Proteins
  • rac1 GTP-Binding Protein

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • IRF3 protein, human
  • Interferon Regulatory Factor-3
  • Lipopolysaccharides
  • Membrane Proteins
  • Myeloid Differentiation Factor 88
  • RAC1 protein, human
  • TICAM2 protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 4
  • CDC42 protein, human
  • RAB11FIP2 protein, human
  • cdc42 GTP-Binding Protein
  • rab GTP-Binding Proteins
  • rac1 GTP-Binding Protein

Grants and funding

The Research Committee between St. Olavs Hospital and Faculty of Medicine and Health Science, NTNU,, https://www.ntnu.no/documents/10268/1221071659/Tildeling+av+forskningsmidler+fra+Felles+Forskningsutvalg_rev2015.pdf/15944b9a-115c-48d6-b56f-b2f8e8e855a0sff, awarded the grant # 46082500 to HH, that financed this study. The NTNU’s Onsager Fellowship, https://www.ntnu.edu/research/onsager-fellowship, awarded the grant #80420223 to RKK, that financed this study. The Research Council of Norway through its Centers of Excellence funding scheme, https://www.forskningsradet.no/prognett-sff/Home_page/1224067001813, awarded the grant #223255/F50 to TE, that financed this study. The Research Council of Norway, FRIMEDBIO program,, file:///Users/haraldhu/Downloads/NyeprosjekterFRIMEDBIO2017NorskogEngelsk-2.pdf, awarded the grant # 275876 to TE, that financed this study. The Liaison Committee for education, research and innovation in Central Norway,, https://helse-midt.no/samarbeidsorganetfelles forskingsutvalg, awarded the grant # 50052400 to TE, that financed this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.