PT  - JOURNAL ARTICLE
AU  - Adam P. Williamson
AU  - Ronald D. Vale
TI  - Cellular reconstitution of apoptotic cell clearance reveals a multi-step phosphorylation mechanism for Draper receptor triggering
AID  - 10.1101/198986
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 198986
4099  - http://biorxiv.org/content/early/2017/10/05/198986.short
4100  - http://biorxiv.org/content/early/2017/10/05/198986.full
AB  - Apoptotic cells are cleared after exposing “eat me” ligands, including phosphatidylserine (PS), but the signaling pathway in the phagocytic cell that leads to engulfment remains poorly understood. Here, by transfecting the engulfment receptor Draper into Drosophila S2 cells and using PS-coated beads to mimic apoptotic cells, we have created a simplified system for studying this process. We show that ligand-bound Draper forms mobile microclusters that recruit effector proteins and exclude a transmembrane phosphatase, suggesting a kinetic segregation mechanism for receptor activation similar to T cell receptors. Like the TCR, Draper’s extracellular domain and ligand can be replaced with other interacting modules. We show that phosphorylation of Draper’s ITAM motif occurs first and is a dominant contributor to signaling. After ITAM phosphorylation, additional residues become phosphorylated and contribute to signaling efficiency. Our results demonstrate broad mechanistic similarities between Draper and mammalian immune receptor activation and an ability to reprogram engulfment signaling.