Antibodies to clathrin inhibit endocytosis but not recycling to the trans Golgi network in vitro

Mannose 6-phosphate receptors carry newly synthesized lysosomal enzymes from the trans Golgi network (TGN) to prelysosomes and then return to the TGN to carry out another round of lysosomal enzyme delivery. Although clathrin-coated vesicles mediate the export of mannose 6-phosphate receptors from the TGN, nothing is known about the transport vesicles used to carry these receptors back to the TGN. Two different in vitro assays used in this study show that an antibody that interferes with clathrin assembly blocks receptor-mediated endocytosis of transferrin, but has no effect on the recycling of the 300-kilodalton mannose 6-phosphate receptor from prelysosomes to the TGN. These results suggest that the transport of mannose 6-phosphate receptors from prelysosomes to the TGN does not involve clathrin.