Myosin X is required for efficient melanoblast migration and melanoma initiation and metastasis

Hiroshi Tokuo,Lynne M Coluccio,Jag Bhawan

doi:10.1038/s41598-018-28717-y

Abstract

Myosin X (Myo10), an actin-associated molecular motor, has a clear role in filopodia induction and cell migration in vitro, but its role in vivo in mammals is not well understood. Here, we investigate the role of Myo10 in melanocyte lineage and melanoma induction. We found that Myo10 knockout (Myo10KO) mice exhibit a white spot on their belly caused by reduced melanoblast migration. Myo10KO mice crossed with available mice that conditionally express in melanocytes the BRAFV600E mutation combined with Pten silencing exhibited reduced melanoma development and metastasis, which extended medial survival time. Knockdown of Myo10 (Myo10kd) in B16F1 mouse melanoma cell lines decreased lung colonization after tail-vein injection. Myo10kd also inhibited long protrusion (LP) formation by reducing the transportation of its cargo molecule vasodilator-stimulated phosphoprotein (VASP) to the leading edge of migrating cells. These findings provide the first genetic evidence for the involvement of Myo10 not only in melanoblast migration, but also in melanoma development and metastasis.

Highlights

Myo[10] is one of several actin-based motor molecules in the myosin superfamily
Previous studies have shown that Myo[10] promotes filopodia formation by delivering specific cargos to the cell periphery, e.g., Mena/vasodilator-stimulated phosphoprotein (VASP), which binds to the tail domain[5,6], and integrins[7], netrin receptors[8], and VE-cadherin[9], which bind to the FERM domain
Myo[10] is expressed ubiquitously in vertebrate tissues[2,11,12], and its functional importance has been found in a variety of cells/tissues, e.g., phagocytosis cup formation in leukocytes[13], nuclear anchoring and spindle assembly in Xenopus laevis[14], orientation of the mitotic spindle in cultured cells[15], endothelial cell migration and angiogenesis[16], axonal path-finding regulated by netrin[8], cranial neural crest cell migration in Xenopus[17,18], sealing zone patterning[19] and differentiation[20] in osteoclasts, tight junction barrier formation in polarized epithelial cells[21], axon outgrowth in cortical neurons[22], formation of Shigella-induced membrane protrusions and cell-to-cell spreading[23], dendritic spine development by VASP trafficking[6], and leukocyte extravasation through cultured endothelial cells[24]

Summary

Introduction

Myo[10] is one of several actin-based motor molecules in the myosin superfamily. It has a motor or head domain with a nucleotide-binding site and an actin-binding site, an IQ or neck domain, which binds three molecules of calmodulin, and a C-terminal tail domain that has a single α-helix (SAH) region followed by a coiled-coil region presumably involved in dimerization, 3 PEST sequences, which are rich in proline, glutamate, serine and threonine and confer sensitivity to certain proteases, 3 pleckstrin homology (PH) domains, a Myosin Tail Homology 4 (MyTH4) domain, which binds to microtubules, and a band 4.1, Ezrin, Radixin, Merlin (FERM) domain[1]. Myo[10] localizes to the tips of filopodia, actin-rich finger-like protrusions found at the leading edge of cells[2] and believed to be involved in numerous cellular processes including cell migration, wound healing, adhesion to the extracellular matrix, guidance towards chemoattractants, neuronal growth-cone path finding and embryonic development[3]. Most recently, reduced filopodia formation was observed in isolated macrophages from Myo10KO mice[25] and in retinal angiogenesis in the eyes of Myo10KO mice[26]. In spite of these studies, the physiological and pathological functions of Myo[10] in murine or human organs is still largely unknown. In aggressive non-small cell lung cancer[30]; Myo[10] was a target of microRNA-340, which inhibits the metastasis of breast cancer[31]; MYO10 expression was higher in prostate cancer than in normal tissue; and Myo10kd reduced the migration speed and directional persistence of a prostate cancer cell line[32]

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Conclusion