3160 – MYCN IS AN ESSENTIAL IMMATURE T-ALL ONCOGENIC DRIVER MARKED BY BROAD H3K4ME3

• Published in: Experimental hematology 2024-08, Vol.137, p.104480, Article 104480
• Main Authors: Segat, Gabriela, Sun, Ann, Zhu, Alice, Foo, Marissa, Rodriguez, Claudia Barreto, Wong, Rachel, Gusscott, Sammuel, Behzad, Hayedeh, Chen, Carol, Eaves, Connie, Hirst, Martin, Weng, Andrew
• Format: Article
• Language: English
• ISSN: 0301-472X
• DOI: 10.1016/j.exphem.2024.104480

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive leukemia of immature T-cells. The outcome for patients with intrinsic therapy resistance or disease relapse remains poor, and the biological bases for aggressive disease remain ill-defined. Using our synthetic leukemia model from human CD34+ cord blood (CB) cells, we performed RNA-Seq on 32 synthetic leukemias (SynLs) generated with Notch1 (N), LMO2 (L), TAL1 (T), and/or BMI1 (B) oncogenes. Genetic loss-of-function approaches were used to assess potential dependencies of oncogene-transduced CB cells and SynLs. Transcriptomic analysis of SynLs revealed two types of disease corresponding to early (ETP-like) and later (post beta-selection) T-cell development stages. Interestingly, early vs. late SynLs could be distinguished by MYCN expression level, the highest being in early SynLs. Notably, T-ALL patients with high MYCN expression present a shorter survival (TARGET cohort). To assess MYCN's contribution to T-ALL, we performed MYCN knockdown (KD)/knockout (KO) in NLTB-transduced CB or early SynLs and observed significantly reduced cell growth and clonogenic activity. Conversely, overexpression of MYCN along with Notch1 in CB cells increased clonogenic activity in vitro but was insufficient to generate leukemia in vivo. To explore mechanisms of MYCN gene regulation, we performed histone ChIP-Seq on NLTB-transduced CB and early SynLs. NLTB transduction resulted in global gain of H3K4me3, often distributed over gene bodies including MYCN. KD of the H3K4 methyltransferase complex components WDR5 and KMT2D led to reduced growth/survival of NLTB-transduced CB and early SynLs, while normal T-progenitors appeared unaffected by KMT2D KD. Our results reveal MYCN as a critical oncogene associated with immature tumors and suggest that epigenetic regulation may drive consistent oncogene expression and malignant identity.