For every experiment 510 images were acquired for each condition and 50100 cells were analyzed. that increase in hypoxia. Genetic and pharmacologic inhibition of BMI-1 and EZH2, respectively, restoreKCNA5expression, which sensitizes cells to stress-induced death. In addition , ectopic expression of the Kv1. 5 channel induces apoptotic cell death under conditions of hypoxia. These findings identify a novel role for PcG proteins in promoting cancer cell survival via repression ofKCNA5. Keywords: KCNA5, potassium channel, Kv1. 5, polycomb, stress, cancer == Introduction == The ability to resist cell death is a hallmark of cancer (1). Cancer cells are able to survive despite exposure to cell intrinsic (e. g. metabolic and genotoxic) and extrinsic (e. g. hypoxia, nutrient deprivation) stress (1). This ability to survive conditions of stress UF010 allows cancer cells to escape physiologic death responses that are induced upon exposure to hostile microenvironments. In UF010 rapidly growing solid tumors the cancer outstrips its blood supply, thereby subjecting the cancer cells to a hostile microenvironment that is characterized by oxygen, growth factor and nutrient deprivation (1, 2). Furthermore, chemotherapy and radiation exacerbate the hostile local microenvironment by inducing tumor necrosis. Despite exposure to these tremendous stresses, however , solid tumors often recur after clinical remission and relapse remains a leading cause of cancer-associated death. The mechanisms of tumor relapse are both diverse and complex but elucidating how cancer cells resist stress-induced death has the potential to uncover novel opportunities for cancer therapy. Stem cells harbor the ability to self-renew indefinitely and are epigenetically Rabbit Polyclonal to SIRT2 programmed to resist differentiation and to survive in hypoxic niche environments (3). Tumor cells often hijack normal stem cell processes to support their propagation and this is particularly evident in cancer cell populations that display tumor-initiating properties (1, 4). Although the mechanisms that support maintenance of stem cell traits are complex (3), chromatin repressive complexes are essential mediators of stemness and also crucial contributors to cancer pathogenesis (5). Among the best characterized of the chromatin repressive UF010 complexes are the polycomb group protein complexes PRC1 and PRC2 (reviewed in (5) and (6)). Polycomb proteins function to silence target gene lociviadirect post-translational modification of histones. In particular, the PRC1 complex proteins BMI-1 and RING1B cooperate to induce ubiquitination of histone 2A at lysine residue 119 (H2AubK119), while the PRC2 member EZH2 mediates methylation of histone 3 at lysine residue 27 (H3K27me3) (5). Together these chromatin marks support maintenance of a repressed chromatin state that inhibits transcriptional activation (6). Both BMI-1 and EZH2 are highly over-expressed by many human cancers and play central roles in tumor initiation and tumor progression (6). In particular, over-expression of polycomb proteins is evident in tumor-initiating cell populations (7) and in the aggressive pediatric solid tumors Ewing sarcoma (ES) and neuroblastoma (NB) (812). The precise targets of polycomb-dependent regulation are cell type and context specific but , in general, polycomb repressive complexes support maintenance of stemness and oncogenesis by suppressing the expression of tumor suppressor genes and developmental regulators (6, 13) Controlled regulation of intracellular levels of elemental ions is essential for normal cellular homeostasis. Transmembrane channels control ion flux across cellular membranes and there is abundant evidence that deregulation of calcium and sodium channel function can contribute to cancer pathogenesis in diverse fashions (14, 15). In addition , altered expression, regulation and function of potassium ion channels has been implicated in.