Myosin VI Is Differentially Regulated by DNA Damage in p53- and Cell Type-dependent Manners

Abstract

Myosin VI is an unconventional motor protein and functions in a variety of intracellular processes such as cell migration, vesicular trafficking, and homeostasis of the Golgi complex. Previously, we found that myosin VI is up-regulated in RKO, LS174T, and H1299 cells by DNA damage in a p53-dependent manner and mediates the pro-survival function of p53. Here, we showed that the levels of myosin VI protein were markedly inhibited in MCF7 and LNCaP cells by topoisomerase I-II inhibitors. However, the levels of myosin VI transcript were decreased only by topoisomerase I inhibitors. We also found that the levels of myosin VI protein were markedly inhibited in MCF7 cells by wild-type p53 but not tumor-derived mutant p53. Surprisingly, we found that the level of myosin VI transcript was slightly increased instead of decreased in MCF7 cells by p53, suggesting that a mechanism other than transcriptional repression is involved. Additionally, we found that on the myosin VI promoter, the level of acetylated histone H3 was markedly decreased, whereas that of p53 and acetylated histone H4 was slightly increased in MCF7 cells upon treatment with topoisomerase I-II inhibitors. Finally, we showed that overexpression of myosin VI enhances, whereas knockdown of myosin VI decreases, DNA damage-induced stabilization of p53, and consequently, knockdown of myosin VI de-sensitizes MCF7 cells to DNA damage-induced apoptosis. Taken together, as a mediator of the p53 pro-survival pathway and a marker of malignancy in some tumors, differential regulation of myosin VI in various tumor cells by topoisomerase inhibitors dictates whether knockdown of myosin VI inhibits, rather than enhances, the susceptibility of tumor cells to some therapeutic agents, which might be explored for designing a proper therapeutic strategy.Myosins are motor proteins to move cargos along actin filaments using the energy derived from ATP hydrolysis by actinactivated Mg 2ϩ -dependent ATPase activity (1-3). Myosins are categorized into 18 distinct classes according to variations of their amino acid sequence in the motor domain. The differences in motor and tail domains are linked to their specific biological functions in the cell (4 -5). Myosin VI is an unconventional actin-based motor protein and carries out a diverse set of functions such as maintenance of the Golgi complex, cargo sorting and vesicle formation, protein secretion, endocytosis, cell migration, spindle orientation, spermatogenesis, and cell-cell contacts (1, 6 -10). In addition, myosin VI was shown to enhance RNA polymerase II-dependent transcription through physical interaction with RNA polymerase II (11), suggesting that myosin VI has a critical function in the nucleus as well as in the cytoplasm and on the plasma membrane.Myosin VI was found to be overexpressed in high-grade ovarian carcinoma cells and knockdown of myosin VI led to impediment of cell spreading, migration, and dissemination (12). Myosin VI was also found to be one of the highly expressed genes in clinical prostate specimens and knock...

Feeding Blueberry Diets in Early Life Prevent Senescence of Osteoblasts and Bone Loss in Ovariectomized Adult Female Rats

“…To maintain this complex at the appropriate functional level may be particularly important, because significantly reduced expression of Runx2 level will not only suppress osteoblast differentiation, but also result in a cell entering the senescent stage. This is consistent with previous published evidence showing that Runx2 interacts with histone deacetylase 6 to repress the p21 gene, known as a downstream effecter of p53 that is associated with cell senescence [30] Moreover, it has been shown that myosin VI DNA damage is p53-dependent [31]. Consuming BB early in life contributes to development or maintenance of the myosin-dependent Runx2 shuttle, and this may also be important to preserve the ability of mesenchymal stromal cells to differentiate into functional osteoblasts later in life under inappropriate stress.…”

Myosin VI in the nucleus of neurosecretory PC12 cells: Stimulation-dependent nuclear translocation and interaction with nuclear proteins

“…In the nucleus, MVI was found in chromatin-free regions, where it was associated with the RNA polymerase II transcription machinery indicating its potential involvement in gene transcription [ 25–27 ]. This notion was also confirmed by the studies demonstrating involvement of MVI in the p53-dependent pro-survival pathway [ 25 , 28 ] and suggesting its modulatory role in androgen-dependent gene expression [ 29 ]. Recently, it has been shown that this molecular motor regulates gene pairing and transcriptional pause release in T cells [ 30 ].…”

“…Of note, it is interesting why colocalization with PML bodies does not depend on cell stimulation. It should be recalled that other groups showed involvement of MVI in RNAPII activity, p53-dependent DNA damage and chromosome pairing [ 27 , 28 , 30 ].…”

Myosin Motors: Novel Regulators and Therapeutic Targets in Colorectal Cancer

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