Hsc70 is required for endocytosis and clathrin function in Drosophila

By screening for Drosophila mutants exhibiting aberrant bride of sevenless (Boss) staining patterns on eye imaginal disc epithelia, we have recovered a point mutation in Hsc70-4, the closest homologue to bovine clathrin uncoating ATPase. Although the mutant allele was lethal, analysis of mutant clones generated by FLP/FRT recombination demonstrated that the Sevenless-mediated internalization of Boss was blocked in mutant Hsc70-4 eye disc epithelial cells. Endocytosis of other probes was also greatly inhibited in larval Garland cells. Immunostaining and EM analysis of the mutant cells revealed disruptions in the organization of endosomal/lysosomal compartments, including a substantial reduction in the number of clathrin-coated structures in Garland cells. The Hsc70-4 mutation also interacted genetically with a dominant-negative mutant of dynamin, a gene required for the budding of clathrin-coated vesicles (CCVs). Consistent with these phenotypes, recombinant mutant Hsc70 proteins exhibited diminished clathrin uncoating activity in vitro. Together, these data provide genetic support for the long-suspected role of Hsc70 in clathrin-mediated endocytosis, at least in part by inhibiting the uncoating of CCVs

Developmental Control of Endocytosis in Dendritic Cells by Cdc42

AbstractDendritic cells (DCs) developmentally regulate antigen uptake by controlling their endocytic capacity. Immature DCs actively internalize antigen. However, mature DCs are poorly endocytic, functioning instead to present antigens to T cells. We have found that endocytic downregulation reflects a decrease in endocytic activity controlled by Rho family GTPases, especially Cdc42. Blocking Cdc42 function by Toxin B treatment or injection of dominant-negative inhibitors of Cdc42 abrogates endocytosis in immature DCs. In mature DCs, injection of constitutively active Cdc42 or microbial delivery of a Cdc42 nucleotide exchange factor reactivates endocytosis. DCs regulate endogenous levels of Cdc42-GTP with activated Cdc42 detectable only in immature cells. We conclude that DCs developmentally regulate endocytosis at least in part by controlling levels of activated Cdc42