The viral oncogene Np9 acts as a critical molecular switch for co-activating β-catenin, ERK, Akt and Notch1 and promoting the growth of human leukemia stem/progenitor cells.
In mice, loss of KLF4 accelerated the development of NOTCH1-induced T-ALL by enhancing the G1-to-S transition in leukemic cells and promoting the expansion of leukemia-initiating cells.
In this murine model, we identified a new, Rag1-independent leukemia-initiating mechanism originating from a Sca1(+)CD19(+) precursor cell population and showed that Notch1 expression accelerates the cells' self-renewal capacity in vitro.
To identify Notch1 target genes in leukemia, we developed mouse T-cell leukemic lines that express intracellular Notch1 in a doxycycline-dependent manner.
Mechanistically, loss of SH2B3 increases Janus kinase-signal transducer and activator of transcription signaling, promotes lymphoid cell proliferation, and accelerates leukemia development in a mouse model of NOTCH1-induced ALL.
We sequenced the heterodimerization domain and the PEST domain of Notch1 in our mouse model of TAL1-induced leukemia and found that 74% of the tumors harbor activating mutations in Notch1.
Leukemia initiating cells (LIC) contribute to therapeutic resistance through acquisition of mutations in signaling pathways, such as NOTCH1, that promote self-renewal and survival within supportive niches.
In contrast to the strict and differential use of ADAM10 and ADAM17 in normal and dysregulated signaling, respectively, both proteases participated in signaling intrinsic to N1 mutations associated with leukemia.
PTEN/AKT mutations were especially abundant in TAL- or LMO-rearranged leukemia but nearly absent in TLX3-rearranged patients (P=0.03), the opposite to that observed for NOTCH1-activating mutations.
Several genetic alterations are intuitively "druggable" with existing agents, for example, kinase-activating lesions in high-risk B-cell ALL, NOTCH1 in both leukemia and lymphoma, and BRAF in hairy cell leukemia.
Together these results identify N-Me as a long-range oncogenic enhancer implicated directly in the pathogenesis of human leukemia and highlight the importance of the NOTCH1-MYC regulatory axis in T cell transformation and as a therapeutic target in T-ALL.
We found activating mutations in NOTCH1 in a single M0 primary AML sample, in three (ML1, ML2 and CTV-1) out of 23 AML cell lines and in the diagnostic (myeloid) and relapsed (T-lymphoid) clones in a patient with lineage switch leukemia.
We demonstrate that ubiquitin-specific protease 7 (USP7) interacts with NOTCH1 and controls leukemia growth by stabilizing the levels of NOTCH1 and JMJD3 histone demethylase.
NOTCH1 mRNA and surface protein expression levels were independent of the NOTCH1 gene mutational status, consistent with the requirement for NOTCH1 signaling in this leukemia.
Together, these data identify a mechanism for enhancing the oncogenic potential of weak Notch1 mutants in leukemia models, and they reveal the MAFB-ETS2 transcriptional axis as a potential therapeutic target in T-ALL.
These proof-of-concept studies support the further optimization of this first-in-class NOTCH1 inhibitor with dual selectivity: leukemia over normal cells and NOTCH1 mutants over wild-type receptors.
Although these mutations are not detected at the pre-leukemia stage, incremental up-regulation of NOTCH1 surface expression is observed at the pre-leukemia and leukemia stages.
These markers included various first- and second-hit genetic alterations (TCRD-LMO2 breakpoint regions, n = 2; TAL1 deletions, n = 3; Notch1 mutations, n = 1) and nononcogenic T-cell receptor rearrangements (n = 13) that were derived from leukemias of 16 children who were 1.5 to 11.2 years old at diagnosis of leukemia.