Acute myeloid leukemia (AML) is an aggressive hematological malignancy arising from hematopoietic stem and progenitor cells (HSPCs). Current treatments often fail to eradicate AML; therefore, new therapeutic strategies are essential. Here, we reveal that RNA terminal uridylyl transferase enzymes 4 and 7 (TUT4/7) are druggable therapeutic targets, whose genetic deletion suppresses AML growth, induces apoptosis, and improves the survival in leukemic mouse models. Notably, a preclinical TUT4/7 inhibitor promotes cell death in samples from patients with AML and synergizes with venetoclax. Mechanistically, TUT4/7 inactivation suppresses mevalonate pathway gene expression, compromising the cholesterol synthesis pathway. Current AML therapies often cause severe hematopoietic toxicity. Although Tut4/7 deletion results in inflammatory activation throughout the hematopoietic system, this is permissive to a normal life span and Tut4/7 deficiency does not compromise HSPC function. Together, these findings identify TUT4/7 as druggable targets, whose inactivation suppresses AML while sparing normal hematopoiesis. In combination with venetoclax, this represents a promising therapeutic strategy.

Resistance to standard and novel therapies remains the main obstacle to cure in acute myeloid leukaemia (AML) and is often driven by metabolic adaptations which are therapeutically actionable. Here we identify inhibition of mannose-6-phosphate isomerase (MPI), the first enzyme in the mannose metabolism pathway, as a sensitizer to both cytarabine and FLT3 inhibitors across multiple AML models. Mechanistically, we identify a connection between mannose metabolism and fatty acid metabolism, that is mediated via preferential activation of the ATF6 arm of the unfolded protein response (UPR). This in turn leads to cellular accumulation of polyunsaturated fatty acids, lipid peroxidation and ferroptotic cell death in AML cells. Our findings provide further support to the role of rewired metabolism in AML therapy resistance, unveil a connection between two apparently independent metabolic pathways and support further efforts to achieve eradication of therapy-resistant AML cells by sensitizing them to ferroptotic cell death.

Resistance to standard and novel therapies remains the main obstacle to cure in acute myeloid leukemia (AML) and is often driven by metabolic adaptations which are therapeutically actionable. Here we identify inhibition of mannose-6-phosphate isomerase (MPI), the first enzyme in the mannose metabolism pathway, as a sensitizer to both cytarabine and FLT3 inhibitors across multiple AML models. Mechanistically, we identify a connection between mannose metabolism and fatty acid metabolism, that is mediated via preferential activation of the ATF6 arm of the unfolded protein response (UPR). This in turn leads to cellular accumulation of polyunsaturated fatty acids, lipid peroxidation and ferroptotic cell death in AML cells. Our findings provide further support to the role of rewired metabolism in AML therapy resistance, unveil a novel connection between two apparently independent metabolic pathways and support further efforts to achieve eradication of therapy-resistant AML cells by sensitizing them to ferroptotic cell death.

Peptidylarginine deiminases (PADIs) are strongly associated with the development of autoimmunity, neurodegeneration and cancer but their physiological roles are ill-defined. The nuclear deiminase PADI4 regulates pluripotency in the mammalian pre-implantation embryo but its function in tissue development is unknown. PADI4 is primarily expressed in the bone marrow, as part of a self-renewal-associated gene signature. It has been shown to regulate the proliferation of multipotent haematopoietic progenitors and proposed to impact on the differentiation of haematopoietic stem cells (HSCs), suggesting that it controls haematopoietic development or regeneration. Using conditional in vivo models of steady state and acute Padi4 ablation, we examined the role of PADI4 in the development and function of the haematopoietic system. We found that PADI4 loss does not significantly affect HSC self-renewal or differentiation potential upon injury or serial transplantation, nor does it lead to HSC exhaustion or premature ageing. Thus PADI4 is dispensable for cell-autonomous HSC maintenance, differentiation and haematopoietic regeneration. This work represents the first study of PADI4 in tissue development and indicates that pharmacological PADI4 inhibition may be tolerated without adverse effects.

Current therapies for blood malignancies fail to eradicate disease in many patients. Optimal new strategies would complement existing therapies, target cancer stem cells and have little to no effect upon normal haematopoiesis.Regulation of normal and malignant haematopoiesis by degradation and reshaping of the transcriptome is currently poorly understood. Our data suggests this constitutes a novel and untapped therapeutic vulnerability in acute myeloid leukaemia (AML). We have identified that two epitranscriptomic systems for targeted RNA decay are required for AML initiation and maintenance, but do not impact steady state normal haematopoiesis. Firstly, binding of YTHDF2 to - N6-Methyladenosine (m6A) modified mRNA and second, uridylation of mRNA by Poly(A) Uridyltransferases. Inactivation of YTHDF2 or Uridyltransferases in murine models of AML significantly reduces leukaemic propagation and improves survival in vivo. In normal haematopoietic stem and progenitor cells, YTHDF2 and Uridyltransferases are key control nodes for a novel mechanism to degrade and repress inflammatory mRNA transcripts. However, they are dispensable for steady state survival. We therefore identify novel therapeutic pathways to eradicate AML while preserving steady state haematopoiesis.

Peptidylarginine deiminases (PADIs, or PADs) are emerging as key regulators of human physiology and pathophysiology. The nuclear deiminase PADI4 regulates embryonic stem cell pluripotency, however its role in adult stem cells is unknown. PADI4 is expressed most highly in the bone marrow (BM), where it is found as part of a self-renewal-associated gene signature and shown to modulate the function of critical transcriptional regulators such as Tal1 and c-Myc, suggesting that it regulates haematopoietic development or regeneration. We investigated the functional significance of PADI4 in haematopoietic stem cell (HSC) biology and normal haematopoiesis. We employed two conditional mouse models of tissue-specific Padi4 ablation, where Padi4 was completely deleted either after the emergence of HSCs, or acutely in the BM of adult mice. We found that loss of PADI4 does not significantly affect HSC self-renewal or differentiation potential upon injury or serial transplantation, nor does it lead to exhaustion or premature ageing of HSCs. Thus, surprisingly, PADI4 is dispensable for cell-autonomous HSC maintenance, differentiation and haematopoietic regeneration. This work has important implications for the clinical use of PADI4 inhibitors as therapeutic agents in autoimmunity and cancer. Key Points PADI4 is dispensable for steady-state and post-transplantation haematopoiesis HSCs do not require intrinsic PADI4 activity to respond to haematopoietic injury PADI4 deficiency does not lead to premature HSC ageing or exhaustion

Hematopoietic stem cells (HSCs) reside at the apex of the hematopoietic differentiation hierarchy and sustain multilineage hematopoiesis. Here, we show that the transcriptional regulator CITED2 is essential for life-long HSC maintenance. While hematopoietic-specific Cited2 deletion has a minor impact on steady-state hematopoiesis, Cited2-deficient HSCs are severely depleted in young mice and fail to expand upon aging. Moreover, although they home normally to the bone marrow, they fail to reconstitute hematopoiesis upon transplantation. Mechanistically, CITED2 is required for expression of key HSC regulators, including GATA2, MCL-1, and PTEN. Hematopoietic-specific expression of anti-apoptotic MCL-1 partially rescues the Cited2-deficient HSC pool and restores their reconstitution potential. To interrogate the Cited2→Pten pathway in HSCs, we generated Cited2;Pten compound heterozygous mice, which had a decreased number of HSCs that failed to reconstitute the HSC compartment. In addition, CITED2 represses multiple pathways whose elevated activity causes HSC exhaustion. Thus, CITED2 promotes pathways necessary for HSC maintenance and suppresses those detrimental to HSC integrity.

The mRNA N-6-methyladenosine (m(6)A) modification has emerged as an essential regulator of normal and malignant hematopoiesis. Inactivation of the m(6)A mRNA reader YTHDF2, which recognizes m(6)A-modified transcripts to promote m(6)A-mRNA degradation, results in hematopoietic stem cell (HSC) expansion and compromises acute myeloid leukemia. Here we investigate the long-term impact of YTHDF2 deletion on HSC maintenance and multilineage hematopoiesis. We demonstrate that Ythdf2-deficient HSCs from young mice fail upon serial transplantation, display increased abundance of multiple m(6)A-modified inflammation-related transcripts, and chronically activate proinflammatory pathways. Consistent with the detrimental consequences of chronic activation of inflammatory pathways in HSCs, hematopoiesis-specific Ythdf2 deficiency results in a progressive myeloid bias, loss of lymphoid potential, HSC expansion, and failure of aged Ythdf2-deficient HSCs to reconstitute multilineage hematopoiesis. Experimentally induced inflammation increases YTHDF2 expression, and YTHDF2 is required to protect HSCs from this insult. Thus, our study positions YTHDF2 as a repressor of inflammatory pathways in HSCs and highlights the significance of m(6)A in long-term HSC maintenance.

, The mRNA N 6 -methyladenosine (m 6 A) modification has emerged as an essential regulator of normal and malignant hematopoiesis. Inactivation of the m 6 A mRNA reader YTHDF2, which recognizes m 6 A-modified transcripts to promote m 6 A-mRNA degradation, results in hematopoietic stem cell (HSC) expansion and compromises acute myeloid leukemia. Here we investigate the long-term impact of YTHDF2 deletion on HSC maintenance and multilineage hematopoiesis. We demonstrate that Ythdf2 -deficient HSCs from young mice fail upon serial transplantation, display increased abundance of multiple m 6 A-modified inflammation-related transcripts, and chronically activate proinflammatory pathways. Consistent with the detrimental consequences of chronic activation of inflammatory pathways in HSCs, hematopoiesis-specific Ythdf2 deficiency results in a progressive myeloid bias, loss of lymphoid potential, HSC expansion, and failure of aged Ythdf2 -deficient HSCs to reconstitute multilineage hematopoiesis. Experimentally induced inflammation increases YTHDF2 expression, and YTHDF2 is required to protect HSCs from this insult. Thus, our study positions YTHDF2 as a repressor of inflammatory pathways in HSCs

Acute myeloid leukemia (AML) is an aggressive clonal disorder of hematopoietic stem cells (HSCs) and primitive progenitors that blocks their myeloid differentiation, generating self-renewing leukemic stem cells (LSCs). Here, we show that the mRNA m6A reader YTHDF2 is overexpressed in a broad spectrum of human AML and is required for disease initiation as well as propagation in mouse and human AML. YTHDF2 decreases the half-life of diverse m6A transcripts that contribute to the overall integrity of LSC function, including the tumor necrosis factor receptor Tnfrsf2, whose upregulation in Ythdf2-deficient LSCs primes cells for apoptosis. Intriguingly, YTHDF2 is not essential for normal HSC function, with YTHDF2 deficiency actually enhancing HSC activity. Thus, we identify YTHDF2 as a unique therapeutic target whose inhibition selectively targets LSCs while promoting HSC expansion.

Citation for published version: Paris, J, Morgan, M, Monteiro De Campos, J, Spencer, G, Shmakova, A, Ivanova, I, Mapperley, C, Lawson, H, Wotherspoon, D, Pires Sepulveda, C, Vukovic, M, Allen, L, Sarapuu, A, Tavosanis, A, Guitart, A, Villacreces, A, Much, C, Junho, C, Anvari Azar, A, Van De Lagemaat, L, Vernimmen, D, Nehme, A, Mazurier, F, Somervaille, T, Gregory, R, O'Carroll, D & Kranc, K 2019, 'Targeting the RNA m6A reader YTHDF2 selectively compromises cancer stem cells in acute myeloid leukemia', Cell Stem Cell, vol. 25. https://doi.org/10.1016/j.stem.2019.03.021