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Cell migration, which involves acto-myosin dynamics, cell adhesion, membrane trafficking and signal transduction, is a prerequisite for cancer cell metastasis. Here, we report that an actin-dependent molecular motor, unconventional myosin Va, is involved in this process and implicated in cancer metastasis. The mRNA expression of myosin Va is increased in a number of highly metastatic cancer cell lines and metastatic colorectal cancer tissues. Suppressing the expression of myosin Va by lentivirus-based RNA interference in highly metastatic cancer cells impeded their migration and metastasis capabilities both in vitro and in vivo. In addition, the levels of myosin Va in cancer cell lines are positively correlated with the expression of Snail, a transcriptional repressor that triggers epithelial-mesenchymal transition. Repression or overexpression of Snail in cancer cells caused reduced or elevated levels of myosin Va, respectively. Furthermore, Snail can bind to an E-box of the myosin Va promoter and induce its activity, which indicates that Snail might act as a transcriptional activator. These data demonstrate an essential role of myosin Va in cancer cell migration and metastasis, and suggest a novel target for Snail in its regulation of cancer progression.

An essential feature of dendritic cell immune surveillance is endocytic sampling of the environment for non-self antigens primarily via macropinocytosis and phagocytosis. The role of several members of the myosin family of actin based molecular motors in dendritic cell endocytosis and endocytic vesicle movement was assessed through analysis of dendritic cells derived from mice with functionally null myosin mutations. These include the dilute (myosin Va), Snell's waltzer (myosin VI) and shaker-1 (myosin VIIa) mouse lines. Non muscle myosin II function was assessed by treatment with the inhibitor, blebbistatin. Flow cytometric analysis of dextran uptake by dendritic cells revealed that macropinocytosis was enhanced in Snell's waltzer dendritic cells while shaker-1 and blebbistatin-treated cells were comparable to controls. Comparison of fluid phase uptake using pH insensitive versus pH sensitive fluorescent dextrans revealed that in dilute cells rates of uptake were normal but endosomal acidification was accelerated. Phagocytosis, as quantified by uptake of E. coli, was normal in dilute while dendritic cells from Snell's waltzer, shaker-1 and blebbistatin treated cells exhibited decreased uptake. Microtubule mediated movements of dextran-or transferrin-tagged endocytic vesicles were significantly faster in dendritic cells lacking myosin Va. Loss of myosin II, VI or VIIa function had no significant effects on rates of endocytic vesicle movement., ((c) 2007 Wiley-Liss, Inc.)

Cytokinesis in fission yeast involves the coordination of septum deposition with the contraction of a cytokinetic actomyosin ring. We have examined the role of the type V myosin Myo52 in the coupling of these two events by the construction of a series of deletion mutants of the Myo52 tail and a further mutant within the ATP binding domain of the head. Each mutant protein was ectopically expressed in fission yeast cells. Each truncation was assayed for the ability to localize to the cell poles and septum (the normal cellular locations of Myo52) and to rescue the morphology defects and temperature sensitivity of a myo52Delta strain. A region within the Myo52 tail (amino acids 1320-1503), with a high degree of similarity to the vesicle-binding domain of the budding yeast type V myosin Myo2p, was essential for Myo52's role in the maintenance of growth polarity and cell division. A separate region (amino acids 1180-1320) was required for Myo52 foci to move throughout the cytoplasm; however, constructs lacking this region, but which retained the ability to dimerize still associated with actin at sites of cell growth. Not all of the Myo52 truncations which localized rescued the morphological defects of myo52Delta, demonstrating that loss of function was not simply brought about by an inability of mutant proteins to target the correct cellular location. By contrast, Myo52 motor activity was required for both localization and cellular function. myo52Delta cells were unable to efficiently localize the beta-1,3-glucan synthase, Bgs1, either at the cell poles or at the division septum, regions of cell wall deposition. Bgs1 and Myo52 localized to vesicle-like dots at the poles in interphase and these moved together to the septum at division. These data have led to the formulation of a model in which Myo52 is responsible for the delivery of Bgs1 and associated molecules to polar cell growth regions during interphase. On the commencement of septum formation, Myo52 transports Bgs1 to the cell equator, thus ensuring the accurate deposition of beta-1,3-glucan at the leading edge of the primary septum., (Copyright (c) 2006 Wiley-Liss, Inc.)

The presence of Myosin Va (an actin-based molecular motor) in the peripheral nervous system was examined and its subcellular distribution within the axons of the sciatic nerve was demonstrated via immunocytochemistry. Myosin Va (M-Va) in the nerve was detected by using SDS-PAGE and Western blot techniques with a polyclonal antibody specifically raised against the M-Va globular tail domain. In addition, purification of M-Va from the rat sciatic nerve prior to immunoblotting yielded a M-Va standard band. Likewise, optical immunocytochemical procedures revealed the presence of M-Va, particularly in the cortical axoplasmic territory, but also in the Schwann cell soma. The above experiments were carried out both on intact as well as on severed sciatic nerves with similar results. The proximal stumps of severed sciatic nerves (from 0 to 72 h after injury) were labelled in vivo with (35)S-methionine. SDS-PAGE autoradiography of the immunoabsorbed M-Va from the radiolabelled homogenized nerve tissue showed a significant increment of the radioactive intensity of M-Va heavy chain band through time. Moreover, a significant increment of transcripts coding for M-Va heavy chain was detected through time using RT-PCR after nerve injury and compared to intact nerves. This data suggest that M-Va is up-regulated in a time-dependent manner. The latter suggests a possible involvement of M-Va in nerve regeneration processes., (Copyright 2002 Wiley-Liss, Inc.)