Human CD300a binds to phosphatidylethanolamine and phosphatidylserine, and modulates the phagocytosis of dead cells.
CD300a is an immunoreceptor tyrosine-based inhibitory motif (ITIM) containing molecule that belongs to the CD300 family of paired activating/inhibitory receptors. It has been shown that its ligation inhibits activation signals on cells of both myeloid and lymphoid lineages. The ligands for CD300a have not been identified. Here, we show that a CD300a-Ig fusion protein specifically binds to apoptotic cells that are evolutionary apart, such as human and insect cells, suggesting that the ligand has to be conserved. Using surface plasmon resonance, ultracentrifugation, ELISA, and reporter cell assays, we identified phosphatidylethanolamine (PE) and phosphatidylserine (PS), 2 phospholipids that translocate to the outer leaflet of the plasma membrane of dead cells, as the ligands for CD300a. Mutational and structural modeling studies identified residues that are involved in the binding of CD300a to PE and PS and that form a cavity where the hydrophilic heads of PE and PS, can penetrate. CD300a down-regulates the uptake of apoptotic cells by macrophages and its ectopic expression in CD300a-negative cell lines also decreased the engulfment of dead cells. Collectively, our results indicate that PE and PS are ligands for CD300a, and that this interaction plays an important role in regulating the removal of dead cells.
Laboratory of Molecular and Developmental Immunology, Division of Monoclonal Antibodies, Office of Biotechnology Products, Center for Drug Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA.
Venkateswara R
VR
Simhadri
John F
JF
Andersen
Eric
E
Calvo
Seung-Chul
SC
Choi
John E
JE
Coligan
Francisco
F
Borrego
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry* / Q000378:metabolism*; D016923:Cell Death; D005434:Flow Cytometry; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010587:Phagocytosis / Q000502:physiology*; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D010718:Phosphatidylserines / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D020349:Surface Plasmon Resonance; D014461:Ultracentrifugation
D015703:Antigens, CD; C515070:CD300A protein, human; D008024:Ligands; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; C483858:phosphatidylethanolamine