Corticotropin-Releasing Factor Receptors

Supplementary Materialsmain

Supplementary Materialsmain. Furthermore, prolonged TGF- exposure enhanced mammalian target of rapamycin (mTOR) signaling. A bitopic mTOR inhibitor repressed CSC generation, anchorage-independence, cell survival, and chemoresistance, and efficiently inhibited tumorigenesis in mice. These results reveal a role for mTOR in the stabilization of stemness and drug resistance of breast cancer cells and position mTOR inhibition as a treatment strategy to target CSCs. Introduction The cell heterogeneity of tumors is a major cause Rabbit Polyclonal to eIF4B (phospho-Ser422) of problems in therapeutically interfering with cancer progression. Epithelial tumors, or carcinomas, comprise heterogeneous cancer cell populations, including cancer stem cells (CSCs), differentiated cancer cells, stromal cancer-associated fibroblasts, immune cells and endothelial cells. CSCs are a small population of self-renewing Bisacodyl cells with the ability to initiate tumor formation. In contrast to a linear model of CSC differentiation, epithelial cancer cells are now seen to have substantial differentiation plasticity (1, 2). This plasticity allows a dynamic balance between dedifferentiated CSCs and differentiated cancer cells. In carcinomas, dedifferentiation of cancer cells and generation of CSCs correlate with epithelial plasticity through a process called epithelial-mesenchymal transition (EMT) (3C5). As epithelial cells progress through EMT, they lose epithelial cell-cell contacts and apical-basal polarity, reorganize their cytoskeleton and reprogram gene expression to enable, among many changes, increased deposition of extracellular matrix components and matrix metalloproteases (6). EMT is essential in development, and is repurposed in cancer progression to enable cancer cell invasion, contribute to cancer stroma formation, generate CSCs and decrease sensitivity to anticancer drugs (7, 8). EMT is thought of as a reversible process, whereby cancer cells that acquired mesenchymal properties can revert to an epithelial state through mesenchymal-epithelial transition, which has been correlated with CSC differentiation. The epithelial plasticity is controlled by signals from the cancer microenvironment. Among the many signals in the cancer microenvironment, transforming growth factor- (TGF-) signaling, which is commonly upregulated in carcinomas, often initiates and drives EMT of carcinoma cells (9). Associated with EMT, and perhaps best illustrated with breast carcinomas, TGF- potently induces carcinoma Bisacodyl cell invasion and CSC generation Bisacodyl (10). TGF- signaling is initiated upon ligand binding to a cell surface complex of two TGF- type II receptors (TRII) and two TGF- type I receptors (TRI), which then activates the signaling effectors Smad2 and Smad3 through C-terminal phosphorylation (11). The activated Smad proteins form complexes with Smad4 and regulate target gene expression through association with high-affinity DNA-binding transcription factors at regulatory sequences (11, 12). TGF–induced, Smad3/4-mediated gene expression drives the gene reprogramming that characterizes the EMT process, starting with activation of expression of EMT master transcription factors, such as Snail, ZEB1 and ZEB2, and Twist, and cooperation of Smad3/4 complexes with these transcription factors in driving EMT (6). In addition to Smad signaling, TGF- also activates phosphoinositide 3-kinase (PI3K)CAKT, extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK), p38 Bisacodyl Bisacodyl MAPK, and Rho-guanosine triphosphatase (GTPase) pathways (11, 13). Among these, TGF–induced signaling through the PI3K-AKT-mammalian target of rapamycin (mTOR) pathway is required for progression through EMT (14, 15). Cell culture studies enable the dissection of the TGF–induced EMT program, and documented its reversible nature upon TGF- withdrawal (16). In breast cancer progression, the exposure of carcinoma cells to increased TGF- signaling from either the carcinoma cells themselves or the stromal cells is not likely to be limited to a few days that would mimic the cell culture conditions used by most researchers. Because there is no evidence for dramatic TGF- level changes within the tumor, it is logical to assume that the carcinoma cells are exposed to TGF- for longer times (17, 18). This raises the question whether prolonged exposure to TGF-, rather than short-term exposure, as routinely done in cell culture, allows the carcinoma cells to maintain the reversible character of EMT, and may result in additional changes of relevance for cancer progression. In this study, we addressed this question using an established human mammary epithelial cell population and a derivative, H-Ras-transformed carcinoma cell population that have been previously studied (3, 19C21). We found that prolonged TGF- exposure stabilized the mesenchymal phenotype, and enhanced the stemness and resistance to anticancer drugs, in contrast to and beyond what is seen in reversible EMT following short-term TGF- exposure. Reversible EMT and stabilized EMT contributed differently to tumorigenesis and dissemination in vivo. Stabilized EMT is suggested to contribute more to tumor latency and persistence, and less to cancer dissemination, which is strongly enhanced by reversible EMT. We.