Here we report that, in comparison with K12 cells, K7M2 cells feature rapamycin-sensitive mTOR signaling which promotes cellular behaviors associated with metastasis, including higher ALDH activity, increased resistance to oxidative stress, proliferation, migration, invasion, and upregulation of BMP2 and VEGF expression. cell cycle in G1-phase [14]. mTOR signaling regulates a number of crucial cellular processes including cellular growth, metabolism, and aging via an extraordinarily complex intercellular signaling network [15, 16]. Dysregulation of this mTOR signaling network can participate in a variety of human disease processes including malignancy [17]. In mammals, mTOR associates with the proteins Raptor or Rictor to form mTOR complexes 1 and 2 (mTORC1 and 2), respectively. mTORC1 activity is usually sensitive to rapamycin, whereas mTORC2 is not [18, 19]. The best characterized substrates of mTORC1 are p70 ribosomal protein S6 kinase (S6?K1) and the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), through AMI5 which mTOR activity can regulate protein synthesis and cell growth [17]. A role for rapamycin-sensitive and rapamycin-insensitive mTOR signaling in cell motility and malignancy metastasis is usually evolving but our current understanding is limited [14]. It is, however, widely recognized that mTOR signaling plays a critical role in protein synthesis, cell proliferation, growth, and survival [10, 20C22]. Dysregulated mTOR signaling is found in a variety of human cancers including hematologic, lung, SYNS1 breast, liver, pancreas, renal, skin, and gastrointestinal tract neoplasms [17]. In addition, it was recently discovered that mTOR signaling is AMI5 usually activated in human osteosarcoma and correlates with surgical stage, metastasis, and disease-free survival [23]. The primary goal of this study was to investigate the role of mTOR signaling in OS metastasis and mTOR inhibition with rapamycin. K7M2 and K12 are related murine OS cell populations derived from the same spontaneously-occurring OS in a Balb-C mouse. K7M2 cells are highly metastatic to the lungs and were clonally derived from the much less metastatic K12 cells [24]. K7M2 and K12 cells are thus very similar genetically but differ significantly in their metastatic potentials. As such, they represent excellent tools for determining crucial biochemical pathways in OS metastasis. It has been reported that mTOR signaling activity is usually enhanced in K7M2 cells compared to K12 cells [25]. Here we statement that mTOR signaling in K7M2 cells is usually associated with higher aldehyde dehydrogenase (ALDH, a malignancy stem cell marker) activity, increased resistance AMI5 to oxidative stress, increased proliferation, migration, and invasion, and higher bone morphogenetic protein (BMP2) and vascular endothelial growth factor (VEGF) expression than in the less metastatic K12 cells. All of these metastatic phenotypes were reversed with rapamycin treatment. Interestingly, we also statement that ALDH inhibition with disulfiram is usually correlated with decreased mTOR activity and causes morphological alterations to K7M2 cells. This study provides evidence that this mTOR pathway promotes ALDH activity and metastatic potential in OS cells. We conclude that mTOR and ALDH are potential therapeutic targets in the treatment and prevention of OS metastasis. 2. Materials and Methods 2.1. Cell Culture and Rapamycin Treatment K7M2 cells and K12 cells were cultured with proliferation medium (PM; DMEM with 10% FBS and 5% penicillin and streptomycin). For mTORC1 inhibition of K7M2 cells, rapamycin (Sigma) was dissolved in DMSO (10?mM) and diluted 1?:?1000 in proliferation medium to a working concentration of 10?= cell number at harvest time/cell number in the beginning plated; Single Cell Migration Assay An automated time-lapsed microscopy system (Biorad) was used to track the single cell migration on plastic surface. Cells were observed at 15 minute increments over 96 hours, the composite images were analyzed, the songs of migration of 10 preselected single cells were monitored for each cell group, and cell velocities were calculated. 2.6. Cell Invasion Assay invasion capacity of K7M2 cells with or without rapamycin treatment, as well as ALDH-high and ALDH-low fractions of untreated K7M2 cells, was assessed using a real-time cell invasion and migration (RT-CIM) assay system (ACEA Biosciences, Inc.), with a 16-well trans-well plate (CIM-plate 16, AMI5 Roche Diagnostics GmbH). The surface of the wells in the upper chamber was coated with Matrigel (BD BioSciences, Bedford, MA USA).