NECAP antagonizes light-induced Rhodopsin-1 internalization to promote photoreceptor homeostasis.

AP-2 is a key mediator of clathrin-mediated endocytosis (CME) that internalizes cargo from the plasma membrane. NECAP proteins physically bind phosphorylated AP-2 during CME, but their roles during endocytosis remain unresolved, with conflicting reports about their function. Here, we report that Drosophila NECAP is dispensable for development, but antagonizes light-dependent Rhodopsin-1 (Rh1) internalization, a process that occurs through AP-2-mediated endocytosis. Specifically, loss of Drosophila NECAP causes excessive light-dependent Rh1 internalization and an age-related retinal degeneration that can be rescued by photoreceptor-specific expression of a wild-type transgenic NECAP. A Drosophila NECAP mutant transgene, equivalent to a canine NECAP1 variant associated with retinal atrophy, failed to rescue the NECAP loss-of-function phenotype in the eye. Furthermore, overexpression of wild-type NECAP suppressed massive Rh1 internalization in a distinct Drosophila model of light-dependent Rh1 endocytosis and retinal degeneration. These results establish NECAP as a negative regulator of light-dependent Rh1 internalization essential for photoreceptor survival.