Regulation of the intracellular distribution of cytoplasmic dynein by serum factors and calcium.

Previous work has indicated that cytoplasmic dynein localizes primarily to lysosomes in cultured fibroblasts, consistent with a function for dynein in retrograde movement. We now show that dynein can be redistributed from a lysosome-associated pool to a more diffuse cytoplasmic pool upon shifting fibroblasts to culture medium lacking serum for several hours. This effect on dynein localization is readily reversed upon addition of serum, with a substantial return to a control appearance of punctate staining within 10 minutes. The serum effect appears to be selective for dynein, in that the localization of kinesin and the overall morphology of intracellular organelles does not change. However, the distribution of kinesin-positive vesicles and lysosomes does appear to be altered during serum starvation, in that these organelles are located to greater extents in the peripheral regions of the cell. Dynein is also associated with the mitotic apparatus, but this localization does not change in response to serum starvation. Removal of calcium from the extracellular medium also results in the loss of punctate dynein staining, which can be recovered upon addition of calcium to calcium-free medium. The redistribution of dynein observed under these experimental conditions may reflect the activity of a regulatory process controlling the association of dynein with organelles, thereby providing one means of modulating intracellular transport.