Localization of myosin Va is dependent on the cytoskeletal organization inthe cell

Myosin V plays an important role in membrane trafficking events. Its implic ation in the transport of pigment granules in melanocytes and synaptic vesi cles in neurons is now well established. However, less is known about its f unction(s) in other cell types. Finding a common function is complicated by the diversity of myosin V expression in different tissues and organisms an d by its association with different subcellular compartments. Here we show that myosin V is present in a variety of cells. Within the same cell type u nder different physiological conditions, we observed two main cellular loca tions for myosin V that were dependent on the dynamics of the plasma membra ne: in cells with highly dynamic membranes, myosin V was specifically conce ntrated at the leading edge in membrane ruffles, whereas in cells with less dynamic membranes, myosin V was enriched around the microtubule-organizing center. The presence of myosin V in the leading ruffling edge of the cell was induced by growth factor stimulation and was dependent on the presence of a functional motor domain. Moreover, myosin V localization at the microt ubule-organizing center was dependent on the integrity of the microtubules. In polarized epithelial cells (WIF-B), where the microtubule-organizing re gion is close to the actin-rich apical surface, one single pool of myosin V , sensitive to the integrity of both microtubules and actin filaments, was observed.