Clathrin and AP2 Are Required for Phagocytic Receptor-Mediated Apoptotic Cell Clearance in Caenorhabditis elegans

Abstract

Clathrin and the multi-subunit adaptor protein complex AP2 are central players in clathrin-mediated endocytosis by which the cell selectively internalizes surface materials. Here, we report the essential role of clathrin and AP2 in phagocytosis of apoptotic cells. In Caenorhabditis elegans, depletion of the clathrin heavy chain CHC-1 and individual components of AP2 led to a significant accumulation of germ cell corpses, which resulted from defects in both cell corpse engulfment and phagosome maturation required for corpse removal. CHC-1 and AP2 components associate with phagosomes in an inter-dependent manner. Importantly, we found that the phagocytic receptor CED-1 interacts with the α subunit of AP2, while the CED-6/Gulp adaptor forms a complex with both CHC-1 and the AP2 complex, which likely mediates the rearrangement of the actin cytoskeleton required for cell corpse engulfment triggered by the CED-1 signaling pathway. In addition, CHC-1 and AP2 promote the phagosomal association of LST-4/Snx9/18/33 and DYN-1/dynamin by forming a complex with them, thereby facilitating the maturation of phagosomes necessary for corpse degradation. These findings reveal a non-classical role of clathrin and AP2 and establish them as indispensable regulators in phagocytic receptor-mediated apoptotic cell clearance.

Dictyostelium EHD associates with Dynamin and participates in phagosome maturation

“…Interestingly, previous studies in C. elegans have suggested that dynamin might contribute to Rab5 recruitment to phagosomes during phagocytosis of apoptotic cells (Kinchen et al, 2008). More recently, in C. elegans, dynamin has been shown to form a complex with clathrin, clathrin adaptor protein complex 2 (AP2), and LST-4 (the C. elegans homolog of mammalian proteins Snx9, Snx18 and Snx33) to promote phagosome maturation during apoptotic cell corpse clearance (Chen et al, 2013). Therefore, dynamin might have more than one function in phagocytosis.…”

Resolving the homology—function relationship through comparative genomics of membrane-trafficking machinery and parasite cell biology

“…Subunits of the AP-1 and AP-2 complexes, as well as retromer, are found at phagosomes, and, while this may seem superficially like a case of neofunctionalization, is consistent with a role for AP-1 in phagocytosis in murine macrophages [75], and evidence for roles for both AP-2 and retromer in phagocytic clearance of apoptotically killed cells in Caenorhabditis elegans [201,202]. Therefore, many seemingly non-canonical functions of trafficking factors in E. histolytica may represent specialization common to professional phagocytic cells.…”

Degron-tagged reporters probe membrane topology and enable the specific labelling of membrane-wrapped structures

“…Degron-tagged reporters also allow the specific labelling of a single membrane or surface of a membrane. The close proximity of the corpse plasma membrane and the engulfing phagosome membrane make it difficult to distinguish their signals using fluorescence microscopy 26,27 , unless cells have distinct transcriptional programs, i.e. neuronal corpses engulfed by non-neuronal cells.…”