Role of dynactin in endocytic traffic: Effects of dynamitin overexpressionand colocalization with CLIP-170

The flow of material from peripheral, early endosomes to-late endosomes req uires microtubules and is thought to be facilitated by the minus end-direct ed motor cytoplasmic dynein and its activator dynactin. The microtubule-bin ding protein CLIP-170 may also play a role by providing an early link to en dosomes. Here, we show that perturbation of dynactin function in vivo affec ts endosome dynamics and trafficking. Endosome movement, which is normally bidirectional, is completely inhibited. Receptor-mediated uptake and recycl ing occur normally, but cells are less susceptible to infection by envelope d viruses that require: delivery to late endosomes, and they show reduced a ccumulation of lysosomally targeted probes. Dynactin colocalizes at microtu bule plus ends with CLIP-170 in a way that depends on CLIP-170's putative c argo-binding domain. Overexpression studies using p150(Glued), the microtub ule-binding subunit of dynactin, and mutant and wild-type forms of CLIP-170 indicate that CLIP-170 recruits dynactin to microtubule ends. These data s uggest a new model for the formation of motile complexes of endosomes and m icrotubules early in the endocytic pathway.