Aberrant expression of long noncoding RNAs (lncRNAs) is associated with various human cancers. However, the role of lncRNAs in Bcr-Abl-mediated chronic myeloid leukemia (CML) is unknown. In this study, we performed a comprehensive analysis of lncRNAs in human CML cells using an lncRNA cDNA microarray and identified an lncRNA termed lncRNA-BGL3 that acted as a key regulator of Bcr-Abl-mediated cellular transformation. Notably, we observed that lncRNA-BGL3 was highly induced in response to disruption of Bcr-Abl expression or by inhibiting Bcr-Abl kinase activity in K562 cells and leukemic cells derived from CML patients. Ectopic expression of lncRNA-BGL3 sensitized leukemic cells to undergo apoptosis and inhibited Bcr-Abl-induced tumorigenesis. Furthermore, transgenic (TG) mice expressing lncRNA-BGL3 were generated. We found that TG expression of lncRNA-BGL3 alone in mice was sufficient to impair primary bone marrow transformation by Bcr-Abl. Interestingly, we identified that lncRNA-BGL3 was a target of miR-17, miR-93, miR-20a, miR-20b, miR-106a and miR-106b, microRNAs that repress mRNA of phosphatase and tensin homolog (PTEN). Further experiments demonstrated that lncRNA-BGL3 functioned as a competitive endogenous RNA for binding these microRNAs to cross-regulate PTEN expression. Additionally, our experiments have begun to address the mechanism of how lncRNA-BGL3 is regulated in the leukemic cells and showed that Bcr-Abl repressed lncRNA-BGL3 expression through c-Myc-dependent DNA methylation. Taken together, these results reveal that Bcr-Abl-mediated cellular transformation critically requires silence of tumor-suppressor lncRNA-BGL3 and suggest a potential strategy for the treatment of Bcr-Abl-positive leukemia.

T cell activation, a critical event in adaptive immune responses, follows productive interactions between T cell receptors (TCRs) and antigens, in the form of peptide-bound major histocompatibility complexes (pMHCs) on the surfaces of antigen-presenting-cells. Upon activation, T cells can lyse infected cells, secrete cytokines, such as interferon-γ (IFN-γ), and perform other effector functions with various efficiencies that directly depend on the binding parameters of the TCR-pMHC complex. The mechanism that relates binding parameters to the efficiency of activation of the T cell remains controversial; some studies suggest that the dissociation constant (K D ) determines the response (the "affinity model"), whereas others suggest that the off-rate (k off ) is critical (the "productive hit rate model"). Here, we used mathematical modeling to show that antigen potency, as determined by the EC 50 , the functional correlate that is used to support K D -based models, could not be used to discriminate between the affinity and productive hit rate models. Our theoretical work showed that both models predicted a correlation between antigen potency and K D , but only the productive hit rate model predicted a correlation between maximal efficacy (E max ) and k off . We confirmed the predictions made by the productive hit rate model in experiments with cytotoxic T cell clones and a panel of pMHC variants. Therefore, we suggest that the activity of an antigen is determined by both its potency and maximal efficacy. We discuss the implications of our findings to the practical evaluation of T cell activation, for example in adoptive immunotherapies, and relate our work to the pharmacological theory of dose-response. † To whom correspondence should be addressed. omer.dushek@path.ox.ac.uk (O.D.); anton.vandermerwe@path.ox.ac.uk (P.A.V.D.M.) . ‡ Present address: Immunocore Limited, Abingdon, OX14 4RX, UK.