MYH9 is a novel cancer stem cell marker and prognostic indicator in esophageal cancer that promotes oncogenesis through the PI3K/AKT/mTOR axis

MYH9 encodes the heavy chain of nonmuscle myosin IIA, a ubiquitously expressed cytoplasmic myosin that regulates the actin cytoskeleton, cell migration, cell polarization, and signal transduction in cancer cells. Here, we investigated the role of MYH9 in cancer stem cells (CSCs) associated with esophageal cancer (EC). The subcellular localization of MYH9 was investigated in SKGT-4 cells through immunofluorescent analysis. MYH9+ and MYH9- spheroid cells were derived from SKGT-4 cells by flow cytometry and compared for self-renewal capacity, tumorigenicity, CD133 positivity, cisplatin resistance, and phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) activity. MYH9 messenger RNA expression was assessed in 30 EC patients by quantitative reverse transcription-polymerase chain reaction. Kaplan-Meier curves were plotted to explore the influence of MYH9 on EC survival. MYH9 localized to the plasma membrane, cytoplasm, and nucleus of SKGT-4 cells. Spheroid cells displayed higher MYH9 expression and positivity compared to parental SKGT-4 cells. MYH9+ cells showed strong CSC characteristics, including in vivo tumorigenicity, migration, invasion, cisplatin resistance, and CD133+ positivity. MYH9 activated the PI3K/AKT/mTOR axis in CSCs and was upregulated in EC patients with poor survival. Collectively, these data show that MYH9 significantly promotes tumorigenesis by regulating PI3K/AKT/mTOR signaling in EC. MYH9 expression remarkably correlates with poor prognosis and represents a novel biomarker and drug target for the diagnosis and treatment of EC.