A scaffold for signaling of Tim-4-mediated efferocytosis is formed by fibronectin

Cell Death Differ. 2019 Sep;26(9):1646-1655. doi: 10.1038/s41418-018-0238-9. Epub 2018 Nov 19.

Abstract

An essential step during clearance of apoptotic cells is the recognition of phosphatidylserine (PS) exposed on apoptotic cells by its receptors on phagocytes. Tim-4 directly binding to PS and functioning as a tethering receptor for phagocytosis of apoptotic cells has been extensively studied over the past decade. However, the molecular mechanisms by which Tim-4 collaborates with other engulfment receptors during efferocytosis remain elusive. By comparing efferocytosis induced by Tim-4 with that by Anxa5-GPI, an artificial tethering receptor, we found that Tim-4 possesses auxiliary machinery to induce a higher level of efferocytosis than Anxa5-GPI. To search for that, we performed a yeast two-hybrid screen and identified Fibronectin (Fn1) as a novel Tim-4-associating protein. Tim-4 directly associated with Fn1 and formed a complex with integrins via the association of Fn1. Through Tim-4-/- mice and cell-based assays, we found that modulation of the Fn1 level affected efferocytosis induced by Tim-4 and disruption of the interaction between Tim-4 and Fn1 abrogated Tim-4-mediated efferocytosis. In addition, Tim-4 depletion attenuated integrin signaling activation and perturbation of integrin signaling suppressed Tim-4-promoted efferocytosis. Taken together, the data suggest that Fn1 locates Tim-4 and integrins in close proximity by acting as a scaffold, resulting in synergistic cooperation of Tim-4 with integrins for efficient efferocytosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Annexin A5 / genetics
  • Apoptosis / genetics*
  • Cytokines / genetics
  • Fibronectins / genetics*
  • Glucose-6-Phosphate Isomerase / genetics
  • Humans
  • Macrophages / metabolism
  • Membrane Proteins / genetics*
  • Mice
  • Mice, Knockout
  • Phagocytes / metabolism
  • Phagocytosis / genetics
  • Phosphatidylserines / metabolism
  • Signal Transduction / genetics

Substances

  • Annexin A5
  • Anxa5 protein, mouse
  • Cytokines
  • FN1 protein, human
  • Fibronectins
  • Membrane Proteins
  • Phosphatidylserines
  • TIM-4 protein, mouse
  • GPI protein, human
  • Glucose-6-Phosphate Isomerase