Externalization and recognition by macrophages of large subunit of eukaryotic translation initiation factor 3 in apoptotic cells.
We previously isolated a monoclonal antibody named PH2 that inhibits phosphatidylserine-mediated phagocytosis of apoptotic cells by macrophages. We report here the identification of the cognate antigen. A protein bound by PH2 in Western blotting was identified as the 170-kDa subunit of eukaryotic translation initiation factor 3 (eIF3 p170/eIF3a). When eIF3a was expressed in a culture cell line as a protein fused to green fluorescence protein, the fusion protein was detected at the cell surface only after the induction of apoptosis. The same phenomenon was seen when the localization of endogenous eIF3a was determined using anti-eIF3a antibody, and eIF3a seemed to be partially degraded during apoptosis. Furthermore, bacterially expressed N-terminal half of eIF3a fused to glutathione S-transferase bound to the surface of macrophages and inhibited phagocytosis of apoptotic cells by macrophages when it was added to phagocytosis reactions. These results collectively suggest that eIF3a translocates to the cell surface upon apoptosis, probably after partial degradation, and bridges apoptotic cells and macrophages to enhance phagocytosis.
Graduate School of Natural Science and Technology, Kanazawa University, Shizenken, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan.
Yuji
Y
Nakai
Akiko
A
Shiratsuchi
Junko
J
Manaka
Hiroshi
H
Nakayama
Koji
K
Takio
Jian-Ting
JT
Zhang
Tatsuo
T
Suganuma
Yoshinobu
Y
Nakanishi
D000818:Animals; D000911:Antibodies, Monoclonal; D017209:Apoptosis; D002460:Cell Line; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism*; D005982:Glutathione Transferase; D049452:Green Fluorescent Proteins; D006801:Humans; D008264:Macrophages / Q000473:pathology / Q000502:physiology*; D051379:Mice; D010587:Phagocytosis; D021122:Protein Subunits / Q000378:metabolism; D011993:Recombinant Fusion Proteins
D000911:Antibodies, Monoclonal; D039621:Eukaryotic Initiation Factor-3; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005982:Glutathione Transferase