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Selinexor, a first-in-class exportin1 (XPO1) inhibitor, is an attractive anti-tumor agent because of its unique mechanisms of action; however, its dose-dependent toxicity and lack of biomarkers preclude its wide use in clinical applications. To identify key molecules/pathways regulating selinexor sensitivity, we performed genome-wide CRISPR/Cas9 dropout screens using two B-ALL lines. We identified, for the first time, that paralogous DDX19A and DDX19B RNA helicases modulate selinexor sensitivity by regulating MCL1 mRNA nuclear export. While single depletion of either DDX19A or DDX19B barely altered MCL1 protein levels, depletion of both significantly attenuated MCL1 mRNA nuclear export, reducing MCL1 protein levels. Importantly, combining selinexor treatment with depletion of either DDX19A or DDX19B markedly induced intrinsic apoptosis of leukemia cells, an effect rescued by MCL1 overexpression. Analysis of Depmap datasets indicated that a subset of T-ALL lines expresses minimal DDX19B mRNA levels. Moreover, we found that either selinexor treatment or DDX19A depletion effectively induced apoptosis of T-ALL lines expressing low DDX19B levels. We conclude that XPO1 and DDX19A/B coordinately regulate cellular MCL1 levels and propose that DDX19A/B could serve as biomarkers for selinexor treatment. Moreover, pharmacological targeting of DDX19 paralogs may represent a potential strategy to induce intrinsic apoptosis in leukemia cells., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

To identify molecules/pathways governing Venetoclax (VEN) sensitivity, we performed genome-wide CRISPR/Cas9 screens using a mouse AML line insensitive to VEN-induced mitochondrial apoptosis. Levels of sgRNAs targeting March5, Ube2j2 or Ube2k significantly decreased upon VEN treatment, suggesting synthetic lethal interaction. Depletion of either Ube2j2 or Ube2k sensitized AML cells to VEN only in the presence of March5, suggesting coordinate function of the E2s Ube2j2 and Ube2k with the E3 ligase March5. We next performed CRISPR screens using March5 knockout cells and identified Noxa as a key March5 substrate. Mechanistically, Bax released from Bcl2 upon VEN treatment was entrapped by Mcl1 and Bcl-XL and failed to induce apoptosis in March5 intact AML cells. By contrast, in March5 knockout cells, liberated Bax did not bind to Mcl1, as Noxa likely occupied Mcl1 BH3-binding grooves and efficiently induced mitochondrial apoptosis. We reveal molecular mechanisms underlying AML cell-intrinsic VEN resistance and suggest a novel means to sensitize AML cells to VEN., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Cord blood transplantation (CBT) is an alternative donor transplantation method and has the advantages of rapid availability and the possibility of inducing a more potent graft-versus-leukemia effect, leading to a lower relapse rate for patients with non-remission relapse and refractory acute myeloid leukemia (R/R AML). This study aimed to investigate the impact of CBT, compared to human leukocyte antigen-matched related donor transplantation (MRDT). This study included 2451 adult patients with non-remission R/R AML who received CBT (1738 patients) or MRDT (713 patients) between January 2009 and December 2018. Five-year progression-free survival (PFS) and the prognostic impact of CBT were evaluated using a propensity score (PS) matching analysis. After PS matching, the patient characteristics were well balanced between the groups. The five-year PFS was 25.2% (95% confidence interval [CI]: 21.2-29.5%) in the CBT group and 18.1% (95% CI: 14.5-22.0%) in the MRDT group (P = 0.009). The adjusted hazard ratio (HR) was 0.83 (95% CI: 0.69-1.00, P = 0.045); this was due to a more pronounced decrease in the relapse rate (HR: 0.78, 95% CI: 0.69-0.89, P < 0.001) than an increase in the NRM (1.42, 1.15-1.76, P = 0.001). In this population, CBT was associated with a better 5-year PFS than MRDT after allogeneic HSCT., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Deficiency of the transcription factor GATA2 is a highly penetrant genetic disorder predisposing to myelodysplastic syndromes (MDS) and immunodeficiency. It has been recognized as the most common cause underlying primary MDS in children. Triggered by the discovery of a recurrent synonymous GATA2 variant, we systematically investigated 911 patients with phenotype of pediatric MDS or cellular deficiencies for the presence of synonymous alterations in GATA2. In total, we identified nine individuals with five heterozygous synonymous mutations: c.351C>G, p.T117T (N = 4); c.649C>T, p.L217L; c.981G>A, p.G327G; c.1023C>T, p.A341A; and c.1416G>A, p.P472P (N = 2). They accounted for 8.2% (9/110) of cases with GATA2 deficiency in our cohort and resulted in selective loss of mutant RNA. While for the hotspot mutation (c.351C>G) a splicing error leading to RNA and protein reduction was identified, severe, likely late stage RNA loss without splicing disruption was found for other mutations. Finally, the synonymous mutations did not alter protein function or stability. In summary, synonymous GATA2 substitutions are a new common cause of GATA2 deficiency. These findings have broad implications for genetic counseling and pathogenic variant discovery in Mendelian disorders.