NOTCH1 dimeric signaling is essential for T-cell leukemogenesis and leukemia maintenance.

abstractT-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy that is characterized by an expansion of T-cell progenitors and DNA mutations that lead to overactive NOTCH1 signaling in >50% of T-ALL cases. Using synthetic models of human T-ALL, we report that NOTCH1 dimeric signaling was crucial for the leukemogenesis of human hematopoietic stem/progenitor cells (HSPCs) from cord blood. We also identified a Notch dimerization-dependent gene signature, including the HES4 transcription factor, which induced a proliferative advantage in human HSPCs and in Notch dimerization-dependent, patient-derived xenografts of T-ALL. Interestingly, in human T-ALL cells, HES4 enforced the expression of the Δ133p53 isoform with the concomitant block of proapoptotic p53 target genes and the induction of BCL2L1 gene expression and antiapoptotic B-cell lymphoma extra-large protein. In addition, through an integrated experimental approach that included genetically modified cell lines, RNA/chromatin immunoprecipitation sequencing, and single-cell RNA sequencing profiles of primary T-ALL samples, we revealed cell subsets with Notch dimerization-dependent gene signatures, which indirectly correlated with proapoptotic genes and directly associated with cell markers of poor clinical outcome in primary T-ALL samples. Taken together, these findings highlight the crucial role of NOTCH1 dimeric signaling in human T-cell leukemogenesis and T-ALL maintenance, suggesting that a possible benefit can be obtained with a therapeutic strategy that target NOTCH1 dimer signaling or its downstream effectors.