Phagocytic receptor signaling regulates clathrin and epsin-mediated cytoskeletal remodeling during apoptotic cell engulfment in C. elegans
The engulfment and subsequent degradation of apoptotic cells by phagocytes is an evolutionarily conserved process that efficiently eliminates dying cells during development. In this study, we demonstrate that clathrin heavy chain (CHC-1), a membrane coat protein known for its role in receptor-mediated endocytosis, and its adaptor epsin (EPN-1), are essential for the removal of apoptotic cells in Caenorhabditis elegans. Disrupting epn-1 or chc-1 impairs engulfment by inhibiting actin polymerization. This defect is partially rescued by inactivating UNC-60, a cofilin ortholog that functions in actin severing and depolymerization, suggesting that EPN-1 and CHC-1 regulate actin assembly during pseudopod extension. Both CHC-1 and EPN-1 are enriched on extending pseudopods in an EPN-1-dependent manner. Epistasis analysis places epn-1 and chc-1 in the same cell-corpse engulfment pathway as ced-1, ced-6, and dyn-1. The signaling of CED-1 is required for the enrichment of EPN-1 and CHC-1 on pseudopods. Like EPN-1 and CHC-1, CED-1, CED-6, and DYN-1 are crucial for the assembly and stability of F-actin beneath pseudopods. We propose that in response to CED-1 signaling, CHC-1 is recruited to the phagocytic cup via EPN-1, where it acts as a scaffold protein to organize actin remodeling. Our findings reveal novel roles for clathrin and epsin in apoptotic cell internalization, suggest a Hip1/R-independent mechanism linking clathrin to actin assembly, and connect the CED-1 pathway to cytoskeletal UNC 3230 remodeling.