Acts as an adapter protein linking the dynein motor complex to various cargos and converts dynein from a non-processive to a highly processive motor in the presence of dynactin. Facilitates the interaction between dynein and dynactin and activates dynein processivity (the ability to move along a microtubule for a long distance without falling off the track). Predominantly recruits 2 dyneins, which increases both the force and speed of the microtubule motor. Component of secretory vesicle machinery in developing neurons that acts as a regulator of neurite outgrowth. Regulates the secretory vesicle transport by controlling the accumulation of Rab6-containing secretory vesicles in the pericentrosomal region restricting anterograde secretory transport during the early phase of neuronal differentiation, thereby inhibiting neuritogenesis.