Role for dynamin in late endosome dynamics and trafficking of the cation-independent mannose 6-phosphate receptor

It is well established that dynamin is involved in clathrin-dependent endoc ytosis, but relatively little is known about possible intracellular functio ns of this GTPase. Using confocal imaging, we found that endogenous dynamin was associated with the plasma membrane, the trans-Golgi network, and a pe rinuclear cluster of cation-independent mannose 6-phosphate receptor (CI-MP R)-containing, structures. By electron microscopy (EM), it was shown that t hese structures were late endosomes and that the endogenous dynamin was pre ferentially localized to tubulovesicular appendices on these late endosomes . Upon induction of the dominant-negative dynK44A mutant, confocal microsco py demonstrated a redistribution of the CI-MPR in mutant expressing cells. Quantitative EM analysis of the ratio of CI-MPR to lysosome-associated memb rane protein-1 in endosome profiles revealed a higher colocalization of the two markers in dynK44A-expressing cells than in control cells. Western blo t analysis showed that dynK44A-expressing cells had an increased cellular p rocathepsin D content. Finally, EM revealed that in dynK44A-expressing cell s, endosomal tubules containing CI-MPR were formed. These results are in co ntrast to recent reports that dynamin-2 is exclusively associated with endo cytic structures at the plasma membrane. They suggest instead that endogeno us dynamin also plays an important role in the molecular machinery behind t he recycling of the CI-MPR from endosomes to the trans-Golgi network, and w e propose that dynamin is required for the final scission of vesicles buddi ng from endosome tubules.