MEGF10 is a mammalian ortholog of CED-1 that interacts with clathrin assembly protein complex 2 medium chain and induces large vacuole formation

Abstract

The mechanisms underlying the engulfment of apoptotic corpses, which is involved in development, cellular homeostasis, and autoimmunity, remain largely unknown in mammals. MEGF10 is a mammalian ortholog of nematode CED-1, a transmembrane protein involved in engulfment of apoptotic corpses. MEGF10-expressing cells display an irregular, mosaic-like pattern of MEGF10, causing cells to tightly adhere to coated glass dishes. This restricted cell motility caused cells to adopt a flat appearance. In the present study, we observed that these cells formed unusually large vacuoles, the formation of which we linked to the cytoplasmic domain of MEGF10. While investigating the signaling pathway and trafficking of MEGF10, we identified an interaction between MEGF10 and clathrin assembly protein complex 2 medium chain (AP50), a component of clathrin-coated pits. In cells co-expressing MEGF10 and AP50, MEGF10 and AP50 colocalized and mirrored the adhesion pattern of MEGF10. LC-MS/MS and immunoblot analyses revealed that the MEGF10 associated with AP2 alpha and beta subunits in addition to associating with AP50 and beta-actin, and that MEGF10 was ubiquitinated and tyrosine phosphorylated. Moreover, we observed that MEGF10 mRNA expression is primarily restricted to the brain, with robust expression in the stellate cells of the cerebellum. Elucidating the trafficking and regulatory machinery of MEGF10 will guide us in having a deeper understanding of the mechanisms involved in clearing apoptotic cells.