Pretaporter, a Drosophila protein serving as a ligand for Draper in the phagocytosis of apoptotic cells

Abstract

Phagocytic removal of cells undergoing apoptosis is necessary for animal development and tissue homeostasis. Draper, a homologue of the Caenorhabditis elegans phagocytosis receptor CED‐1, is responsible for the phagocytosis of apoptotic cells in Drosophila, but its ligand presumably present on apoptotic cells remains unknown. An endoplasmic reticulum protein that binds to the extracellular region of Draper was isolated. Loss of this protein, which we name Pretaporter, led to a reduced level of apoptotic cell clearance in embryos, and the overexpression of pretaporter in the mutant flies rescued this defect. Results from genetic analyses suggested that Pretaporter functionally interacts with Draper and the corresponding signal mediators. Pretaporter was exposed at the cell surface after the induction of apoptosis, and cells artificially expressing Pretaporter at their surface became susceptible to Draper‐mediated phagocytosis. Finally, the incubation with Pretaporter augmented the tyrosine‐phosphorylation of Draper in phagocytic cells. These results collectively suggest that Pretaporter relocates from the endoplasmic reticulum to the cell surface during apoptosis to serve as a ligand for Draper in the phagocytosis of apoptotic cells.

Apoptosis-dependent Externalization and Involvement in Apoptotic Cell Clearance of DmCaBP1, an Endoplasmic Reticulum Protein of Drosophila

“…Antibody and Immunochemistry-The generation and use of anti-Draper (14), anti-Croquemort (14), anti-focal adhesion kinase (21), anti-Pretaporter (17), and anti-Calreticulin (22,23) antibodies were reported previously. Anti-Drosophila DmCaBP1 antibody was raised by immunizing rats with recombinant DmCaBP1 expressed in E. coli as a protein fused to GST.…”

“…Western blotting using alkaline phosphatase-or HRP-labeled secondary antibody was carried out as described previously (14). Immunocytochemical detection of DmCaBP1 was performed as described in our previous paper (17). To immunoprecipitate DmCaBP1, cell lysates or culture media were incubated with anti-DmCaBP1 antiserum, and proteins bound to the antibody were recovered using protein G-Sepharose (GE Healthcare).…”

“…We previously identified a protein we named Pretaporter as a ligand for Draper, a Drosophila homologue of CED-1, by affinity chromatography (17). Pretaporter is a protein residing in the endoplasmic reticulum (ER) 3 and seems to be relocated to the cell surface after the induction of apoptosis (17). While isolating Pretaporter, we noticed the presence of another protein that bound to and eluted from the Draperconjugated matrix.…”

“…However, it is almost obscure how CED-1 and its counterparts are activated for the induction of engulfment in phagocytes. We previously identified a protein we named Pretaporter as a ligand for Draper, a Drosophila homologue of CED-1, by affinity chromatography (17). Pretaporter is a protein residing in the endoplasmic reticulum (ER) 3 and seems to be relocated to the cell surface after the induction of apoptosis (17).…”

Innate recognition of apoptotic cells: novel apoptotic cell-associated molecular patterns revealed by crossreactivity of anti-LPS antibodies

“…Recently in Drosophila, two proteins of the endoplasmic reticulum, Pretaporter and DmCaBP1, have been observed to become externalised in apoptosis aiding phagocytosis mediated by Draper, a fly hemocyte receptor for apoptotic cells that is homologous to CED-1. 33,34 We established that LBP/p40 translocates from its intracellular location to the plasma membrane surface during apoptosis. In light of our observations (e.g.…”