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Notch 1 mediated inhibition of Nur77-induced apoptosis: implications for T-cell leukemia
It is widely accepted that activating mutations of genes encoding the Notch family of transmembrane receptors, specifically Notch1, are associated with oncogenic transformation. Previous data from our lab has shown that an active form of Notch1 (Nic) provides a protective effect against apoptosis in D011.10 T cells, and that this effect may be attributed to Nic binding the pro-apoptotic protein Nur77. Nur77 is an immediate early gene that is upregulated during negative selection of thymocytes and activation-induced apoptosis in D011.10 T cells. Nur77 upregulation is tightly regulated and requires MEF2D, NFAT, and the co-activator, p300, to effectively respond to apoptotic stimuli. In this report we show that Nic has the ability to interfere with the induction of transcription of Nur77, and that this interference is directly related to the inability of p300 to bind the Nur77 promoter in the presence of Nic. We also show that blocking Notch activation through gamma secretase-inhibitors or siRNA directed against Notch1 in T cell acute lymphoblastic leukemia (T-ALL) cell lines restores Nur77 upregulation in response stimuli. These observations support a model in which during thymocytes negative selection activating mutations of Notch1 inhibit the upregulation of a crucial proapoptotic molecule. Studies to determine the mechanism by which Nur77 induces apoptosis have indentified a unique translocation of Nur77 from the nucleus to the cytosol. It has been determined that once in the cytosol Nur77 interacts with members of the Bcl-2 family of proteins at the mitochondrial membrane. This interaction induces a conformational change of Bcl-2 so that is becomes pro-apoptotic instead of protective. Of similar interest is the role that Nur77 itself plays during the induction of activation-induced apoptosis which may be independent of Bcl-2 conformational change. In an effort to describe possible functions of Nur77, DO11.10 cells that have Nur77 under a tet-inducible promoter were observed for changes IP3R. Initial results from our lab suggest that Nur77 alone has the ability to induce cell death in DO11.10 cells using this tet-inducible system. Interestingly we have been able to identify distinct changes in IP3R isoforms during stimulation induced apoptosis and Nur77-dependent apoptosis. Current experiments are focused on a mechanism beyond the known function of the Nur77/Bcl-2 interaction; that Nur77 may also be acting as a physical barrier between the known anti-apoptotic interaction of IP3R and Bcl-2, leading to sustained calcium flux.
Molecular biology|Cellular biology|Immunology
Rud, Jonathan G, "Notch 1 mediated inhibition of Nur77-induced apoptosis: implications for T-cell leukemia" (2010). Doctoral Dissertations Available from Proquest. AAI3409650.