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Metabolic reprogramming of amino acids represents a vulnerability in cancer cells, yet the mechanisms underlying serine metabolism in acute myeloid leukemia (AML) and leukemia stem/initiating cells (LSCs/LICs) remain unclear. Here, we identify RNA N 6 -methyladenosine (m 6 A) modification as a key regulator of serine biosynthesis in AML. Using a CRISPR/Cas9 screen, we find that depletion of m 6 A regulators IGF2BP3 or METTL14 sensitizes AML cells to serine and glycine (SG) deprivation. IGF2BP3 recognizies m 6 A on mRNAs of key serine synthesis pathway (SSP) genes (e.g., ATF4 , PHGDH , PSAT1 ), stabilizing these transcripts and sustaining serine production to meet the high metabolic demand of AML cells and LSCs/LICs. IGF2BP3 silencing combined with dietary SG restriction potently inhibits AML in vitro and in vivo, while its deletion spares normal hematopoiesis. Our findings reveal the critical role of m 6 A modification in the serine metabolic vulnerability of AML and highlight the IGF2BP3/m 6 A/SSP axis as a promising therapeutic target. Subject terms: Acute myeloid leukaemia, Cancer metabolism

Aplastic anemia (AA) is a life-threatening bone marrow (BM) failure syndrome characterized by pancytopenia. Recent studies revealed that dysfunctional endothelial progenitor cells (EPCs), critical components of the BM microenvironment, are involved in hematopoietic-dysfunction-related diseases, including AA. However, the mechanism underlying EPC damage in AA remains unknown. Here we find that transforming growth factor-β (TGF-β) signaling is hyperactive in dysfunctional AA EPCs with impaired hematopoietic support and immune regulatory ability, and TGF-β inhibition promotes hematopoiesis and immune rebalance by repairing dysfunctional EPCs. Through impaired EPC and AA murine models, we validated that TGF-β inhibition restores EPC dysfunction to improve hematopoiesis and immune status in vitro and in vivo. RNA sequencing and real-time quantitative polymerase chain reaction provided further validation. These results indicate that dysfunctional BM EPCs with hyperactive TGF-β signaling are involved in AA. TGF-β inhibition promotes multilineage hematopoiesis recovery and immune balance by repairing dysfunctional EPCs, providing a potential therapeutic strategy for AA. Subject terms: Experimental models of disease, Translational research

VEXAS syndrome is a clonal hematopoietic disorder characterized by hyperinflammation, bone marrow failure, and high mortality. The molecular hallmark of VEXAS is somatic mutations at methionine 41 (M41) in the E1 ubiquitin enzyme, UBA1. These mutations induce a protein isoform switch, but the mechanisms underlying disease pathogenesis remain unclear. Here, we developed a human cell model of VEXAS syndrome by engineering the male monocytic THP1 cell line to express the common UBA1 M41V mutation. We found that mutant UBA1 M41V cells exhibit aberrant UBA1 isoform expression, increased vacuolization, and upregulation of the unfolded protein response, recapitulating key features of VEXAS. Moreover, proteomic analyses revealed dysregulated ubiquitination and proteotoxic stress in UBA1 M41V cells, with alterations in inflammatory and stress-response pathways. Functional studies demonstrated that UBA1 M41V cells were highly sensitive to genetic or pharmacological inhibition of E1 ubiquitin enzymes. Treatment with the E1 enzyme inhibitor TAK-243 preferentially suppressed colony formation of UBA1 M41V cells as compared to WT cells. Moreover, UBA1 M41V cells exhibited greater sensitivity to TAK-243 in competition assays and showed increased apoptosis. Interestingly, TAK-243 preferentially inhibited UBA6 activity over UBA1, suggesting that UBA6 may compensate for UBA1 dysfunction in UBA1 M41V cells. Targeting UBA6 using shRNA or the UBA6-specific inhibitor phytic acid further revealed an acquired dependency on UBA6 in UBA1 M41V cells. Phytic acid selectively impaired growth and colony formation in UBA1 M41V cells while sparing WT cells, highlighting a potential therapeutic vulnerability. Together, these findings establish a novel human model of VEXAS syndrome, identify key roles for UBA1 and UBA6 in disease pathogenesis, and demonstrate that UBA6 inhibition represents a promising therapeutic strategy for selectively targeting UBA1 mutant clones. Subject terms: Haematological cancer, Cell signalling