Phosphatidylserine clustering by membrane receptors triggers LC3-associated phagocytosis

LC3-associated phagocytosis (LAP) represents a non-canonical function of autophagy proteins in which ATG8 family proteins (LC3 and GABARAP proteins) are lipidated onto single-membrane phagosomes as particles are engulfed by phagocytic cells 1–4 . LAP plays roles in innate immunity 5 , inflammation and anti-cancer 6 responses and is initiated upon phagocytosis of particles that stimulate Toll-like receptors (TLR), Fc-receptors, and upon engulfment of dying cells 6 . However, how this molecular route is initiated remains elusive. Here we report that receptors that engage LAP enrich phosphatidylserine (PS) in the phagosome membrane via membrane-proximal domains that are necessary and sufficient for LAP to proceed. Subsequently, PS recruits the Rubicon-containing PI3-kinase complex to initiate the enzymatic cascade leading to LAP. Manipulation of plasma membrane PS content, PS-binding by Rubicon, or the PS-clustering domains of receptors prevents LAP and phagosome maturation. We found that pharmacologic inhibition of PS clustering promotes the ability of dendritic cells to induce anti-cancer responses to engulfed tumor cells. Therefore, the initiation of LAP represents a novel mechanism of PS-mediated signal transduction upon ligation of surface receptors.