Tcf/Lef-b-catenin in T cell identity and cancer

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 DESCRIPTION (provided by applicant): Immunodeficiencies (inherited or acquired) and lymphocyte malignancy are two major immune disorders that pose grave threats to public health. Firstly, loss of T cells in adults (e.g. due to chemotherapy or ageing) severely compromises cellular immunity. How the distinct CD4+ and CD8+ T cell identities are established and maintained remains an unanswered puzzling question at present. Secondly, acute T cell lymphoblastic leukemia/lymphomas (T-ALLs) is induced by the transformation of developing T cells in the thymus. Elucidation of factors/pathways contributing to initiation and propagation of T-ALLs is required to improve diagnosis and develop novel targeted therapies. Tcf1 and Lef1 transcription factors are well documented to have essential roles in T cell development. We also showed that Tcf1 functions as a tumor suppressor by restraining Lef1 and Notch expression in early thymocytes. Tcf1 and Lef1 are most notably associated with the Wnt-ß-catenin pathway; however, the long- standing controversies regarding the physiological roles of ß-catenin in T cell development and malignancy remain unresolved. By conditionally targeting both Tcf1 and Lef1 at CD4+CD8+ double positive (DP) thymocytes, we found that Tcf1/Lef1 double deficient CD8+ T cells showed inappropriate expression of CD4+ lineage genes including the CD4 coreceptor itself, CD40 ligand, Rorgt and Foxp3 without prior activation. We hypothesize that Tcf1 and Lef1 seal off CD8+ T cell identity by epigenetically silencing CD4+-associated genes. We have generated a true ß-catenin null mutant and another mouse strain where Tcf1 long isoforms are ablated and hence Tcf1-ß- catenin interaction is abrogated. With these new tools, we will test the hypothesis that Tcf1 and Lef1 use both ß-catenin-dependent and -independent mechanisms to regulate thymocyte maturation and transformation. Our specific aims are: Specific Aim 1. To investigate the mechanisms by which Tcf1 and Lef1 regulate CD8+ T cell identity. Specific Aim 2. To elucidate the requirements of ß-catenin and its interaction with Tcf1/Lef1 in T cell development and malignancy. These studies will identify the first transcription factors and their interaction with epigenetic machinery that re responsible for regulation of CD8+ T cell identity. The new animal models will ensure unprecedented clarity to resolve the long-standing controversies over ß-catenin. The outcomes will establish new paradigms in immune cell identity and the involvement of Wnt-ß-catenin pathway. The information will identify critical regulatory points in directing hematopoietic progenitors or iPS cells to mature T cells with desired antigen specificity and thus help improve immune reconstitution and targeted, cell-based cancer therapy.