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Notch signaling deregulation is linked to the onset of several tumors including T-cell acute lymphoblastic leukemia (T-ALL). Deregulated microRNA (miRNA) expression is also associated with several cancers, including leukemias. However, the transcriptional regulators of miRNAs, as well as the relationships between Notch signaling and miRNA deregulation, are poorly understood. To identify miRNAs regulated by Notch pathway, we performed microarray-based miRNA profiling of several Notch-expressing T-ALL models. Among seven miRNAs, consistently regulated by overexpressing or silencing Notch3, we focused our attention on miR-223, whose putative promoter analysis revealed a conserved RBPjk binding site, which was nested to an NF-kB consensus. Luciferase and chromatin immunoprecipitation assays on the promoter region of miR-223 show that both Notch and NF-kB are novel coregulatory signals of miR-223 expression, being able to activate cooperatively the transcriptional activity of miR-223 promoter. Notably, the Notch-mediated activation of miR-223 represses the tumor suppressor FBXW7 in T-ALL cell lines. Moreover, we observed the inverse correlation of miR-223 and FBXW7 expression in a panel of T-ALL patient-derived xenografts. Finally, we show that miR-223 inhibition prevents T-ALL resistance to γ-secretase inhibitor (GSI) treatment, suggesting that miR-223 could be involved in GSI sensitivity and its inhibition may be exploited in target therapy protocols. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented which discusses the study regarding the relationship between Notch1/Hes-1 expression and glucocorticoid sensitivity in lymphoblastic leukemia.

Notch3 and pTα signaling events are essential for T-cell leukemogenesis and characterize murine and human T-cell acute lymphoblastic leukemia. Genetic ablation of pTα expression in Notch3 transgenic mice abrogates tumor development, indicating that pTα signaling is crucial to the Notch3-mediated leukemogenesis. Here we report a novel direct interaction between Notch3 and pTα. This interaction leads to the recruitment and persistence of the E3 ligase protein c-Cbl to the lipid rafts in Notch3-IC transgenic thymocytes. Conversely, deletion of pTα in Notch3 transgenic mice leads to cytoplasmic retention of c-Cbl that targets Notch3 protein to the proteasomal-degradative pathway. It appears that protein kinase C θ (PKCθ), by regulating tyrosine and serine phosphorylation of Cbl, is able to control its function. We report here that the increased Notch3-IC degradation correlates with higher levels of c-Cbl tyrosine phosphorylation in Notch3-IC/pTα−/− double-mutant thymocytes, which also display a decreased PKCθ activity. Our data indicate that pTα/pre-T-cell receptor is able to regulate the different subcellular localization of c-Cbl and, by regulating PKCθ activity, is also able to influence its ubiquitin ligase activity upon Notch3 protein. [ABSTRACT FROM AUTHOR]