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.