Dynamic association of cytoplasmic dynein heavy chain 1a with the Golgi apparatus and intermediate compartment

Microtubule motors, such as the minus end-directed motor, cytoplasmic dynei n, play an important role in maintaining the integrity, intracellular locat ion,;and function of the Golgi apparatus, as well as in the translocation o f membrane between the endoplasmic reticulum and Golgi apparatus. We have i mmunolocalised conventional cytoplasmic dynein heavy chain to the Golgi app aratus in cultured vertebrate cells. In addition, we present evidence that cytoplasmic dynein heavy chain cycles constitutively between the endoplasmi c reticulum and Golgi apparatus: it colocalises partially with the intermed iate compartment, it is found on nocodazole-induced peripheral Golgi elemen ts and, most strikingly, on Brefeldin A-induced tubules that are moving tow ards microtubule plus ends. The direction of movement of membrane between t he endoplasmic reticulum and Golgi apparatus is therefore unlikely to be re gulated by controlling motor-membrane interactions: rather, the motors prob ably remain bound throughout the whole cycle, with their activity being mod ulated instead, We also report that the overexpression of p50/dynamitin res ults in the loss of cytoplasmic dynein heavy chain from the membrane of per ipheral Golgi elements. These results explain how dynamitin overexpression causes the inhibition of endoplasmic reticulum-to-Golgi transport complex m ovement towards the centrosomal region, and support the general model that an intact dynactin complex is required for cytoplasmic dynein binding to al l cargoes.