A myosin-Va tail fragment sequesters dynein light chains leading to apoptosis in melanoma cells

Abstract

Previous studies proposed that myosin-Va regulates apoptosis by sequestering pro-apoptotic Bmf to the actin cytoskeleton through dynein light chain-2 (DLC2). Adhesion loss or other cytoskeletal perturbations would unleash Bmf, allowing it to bind and inhibit pro-survival Bcl2 proteins. Here, we demonstrated that overexpression of a myosin-Va medial tail fragment (MVaf) harboring the binding site for DLC2 dramatically decreased melanoma cell viability. Morphological and molecular changes, including surface blebbing, mitochondrial outer membrane permeabilization, cytochrome-c and Smac release, as well as caspase-9/-3 activation and DNA fragmentation indicated that melanoma cells died of apoptosis. Immobilized MVaf interacted directly with DLCs, but complexed MVaf/DLCs did not interact with Bmf. Overexpression of DLC2 attenuated MVaf-induced apoptosis. Thus, we suggest that, MVaf induces apoptosis by sequestering DLC2 and DLC1, thereby unleashing the pair of sensitizer and activator BH3-only proteins Bmf and Bim. Murine embryonic fibroblasts (MEFs) lacking Bim and Bmf or Bax and Bak were less sensitive to apoptosis caused by MVaf expression than wild-type MEFs, strengthening the putative role of the intrinsic apoptotic pathway in this response. Finally, MVaf expression attenuated B16-F10 solid tumor growth in mice, suggesting that this peptide may be useful as an apoptosis-inducing tool for basic and translational studies.

A novel role for Myosin-Va in mitochondrial fission

“…It is now widely known that the Warburg effect favors biomass building of proliferative tissues 45 . Therefore, the reduced clonogenic ability of myosin-Va knockdown cells is consistent with our metabolic data and corroborates previous findings 1,15 . Exploring the possibility that myosin-Va functions as an effector molecule of the MAPK pathway to enhance mitochondrial fragmentation induced by oncogenic transformation is an intriguing possibility worthy of further exploration.…”

“…In addition, by sequestering the pro-apoptotic factor Bmf 16 , myosin-Va modulates apoptosis triggered by mitochondrial outer membrane permeabilization (MOMP). Interfering in this pathway by overexpressing a small fragment of the myosin-Va tail, which encompasses the DYNLL2 binding site, induces apoptosis in melanoma cells 1 . The myosin-Va ortholog, Myo2p, is required for mitochondrial transport and mitochondrial inheritance in daughter cells in the budding yeast Saccharomyces cerevisiae 17 .…”

Non‐muscle myosins in tumor progression, cancer cell invasion, and metastasis

“…In case of Bmf‐Myo5a complex, sequestration of Bmf to the actin cytoskeleton via binding to Myo5a may prevent apoptosis, allowing cancer cell survival. Expression of a Myo5a tail fragment that disrupts Bmf sequestration resulted in enhanced apoptosis of melanoma cells and decreased melanoma growth in mice, indicating that Myo5a may regulate tumor cell death [Izidoro‐Toledo et al, ]. Further, Myo5a is highly expressed in metastatic cancer cell lines derived from various tissue types, and its knockdown disrupted tumor cell spreading and migration in vitro and decreased pulmonary metastasis of tumor cells in a chick embryo chorioallantoic membrane model in vivo [Lan et al, ].…”

Two pathways regulate cortical granule translocation to prevent polyspermy in mouse oocytes

“…We investigated whether myosin Va might similarly be involved in the transport of cortical granules by expressing the dominant-negative tail construct MyoVa LT , which did not affect Rab11a motility in a previous study20. We note that the MyoVa LT construct used here is reported to bind dynein light chain 8 (refs 30, 31). However, given that our results demonstrated clearly that the translocation of cortical granules is independent of microtubules (Fig.…”