Two-step engulfment of apoptotic cells.
Apoptotic cells expose phosphatidylserine on their surface as an "eat me" signal, and macrophages respond by engulfing them. Although several molecules that specifically bind phosphatidylserine have been identified, the molecular mechanism that triggers engulfment remains elusive. Here, using a mouse pro-B cell line, Ba/F3, that grows in suspension, we reconstituted the engulfment of apoptotic cells. The parental Ba/F3 cells did not engulf apoptotic cells. Ba/F3 transformants expressing T cell immunoglobulin- and mucin-domain-containing molecule 4 (Tim4), a type I membrane protein that specifically binds phosphatidylserine, efficiently bound apoptotic cells in a phosphatidylserine-dependent manner but did not engulf them. However, Ba/F3 transformants expressing both Tim4 and the integrin α(v)β(3) complex bound to and engulfed apoptotic cells in the presence of milk fat globule epidermal growth factor factor VIII (MFG-E8), a secreted protein that can bind phosphatidylserine and integrin α(v)β(3). These results indicate that the engulfment of apoptotic cells proceeds in two steps: Tim4 tethers apoptotic cells, and the integrin α(v)β(3) complex mediates engulfment in coordination with MFG-E8. A similar two-step engulfment of apoptotic cells was observed with mouse resident peritoneal macrophages. Furthermore, the Tim4/integrin-mediated engulfment by the Ba/F3 cells was enhanced in cells expressing Rac1 and Rab5, suggesting that this system well reproduces the engulfment of apoptotic cells by macrophages.
Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Yoshida-konoe, Kyoto, Japan.
Satoshi
S
Toda
Rikinari
R
Hanayama
Shigekazu
S
Nagata
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010587:Phagocytosis; D010718:Phosphatidylserines / Q000378:metabolism*; D054448:Precursor Cells, B-Lymphoid / Q000166:cytology* / Q000378:metabolism; D011485:Protein Binding; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D039302:Integrin alphaVbeta3; D008565:Membrane Proteins; D010718:Phosphatidylserines; C500399:TIM-4 protein, mouse; D020696:rab5 GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein