Promyelomonocytic leukemia (PML) is a prominent oncosuppressor whose inactivation is involved in the pathogenesis of hematological and epithelial cancers. Here, we report that PML aggregated in nuclear bodies in syncytia elicited by the envelope glycoprotein complex (Env) of human immunodeficiency virus-1 (HIV-1) in vitro. PML aggregation occurred after the fusion of nuclei (karyogamy) within syncytia but before the apoptotic program was activated. The aggregation of PML was detectable in syncytia present in the brain or lymph nodes from patients with HIV-1 infection, as well as in a fraction of blood leukocytes, correlating with viral status. Using a range of specific inhibitors of PML (the oncogenic PML/RARα fusion product or specific small interfering RNAs), we demonstrated that, in Env-elicited syncytia, PML was required for activating phosphorylation of ataxia telangiectasia mutated (ATM), which colocalized with PML in nuclear bodies, in a molecular complex that also involved topoisomerase IIβ-binding protein 1. PML knockdown thus inhibited the ATM-dependent DNA damage response that culminates in the activation of p53, p53-dependent transcription of pro-apoptotic genes and cell death. Infection of CD4-expressing cells with HIV-1 also induced syncytial apoptosis, which could be suppressed by inhibiting PML. Altogether, these data indicate that PML activation is a critical early event that participates in the apoptotic demise of HIV-1-elicited syncytia.

While acute promyelocytic leukemia (APL) is always driven by fusions involving one of the three retinoic acid receptors, why PML and RARA are the preferred fusion partners has remained largely unsettled. Here, we demonstrate that corepressor (NCoR) binding onto the RARA moiety of PML::RARA is required for hematopoietic progenitor immortalization. We establish that PML-mediated tethering of the UBC9 SUMO-conjugating enzyme onto PML::RARA enforces SUMO2 conjugation of multiple RARA partner proteins, notably the NCoR complex, boosting its repressive power. PML mutants that fail to recruit UBC9 yield PML::RARA fusions that promote neither NCoR sumoylation nor transformation. Conversely, direct UBC9/RARA fusion drives both efficient corepressor complex sumoylation and immortalization. Sumoylation inhibitors reactivate retinoic acid target genes in PML::RARA-expressing, but not in RARA-expressing, progenitors and trigger APL differentiation. Thus, fusion of PML to RARA entails an unexpected gain of function that boosts RARA-mediated transcriptional repression through sumoylation of PML::RARA-bound proteins, explaining the recurrent implication of PML and RARA in APL pathogenesis.

Although most patients with T-cell acute lymphoblastic leukemia (T-ALL) achieve remission with chemotherapy, many relapse with a poor prognosis, treatment-resistant disease. The mechanisms driving chemoresistance remain largely elusive, in part due to the lack of faithful experimental models. Here, we generated isogenic patient-derived xenograft (PDX) pairs at diagnosis and relapse from T-ALL cases harboring TP53 alterations at relapse (TP53alt, TP53 mutation and/or deletion). These models faithfully captured the genomic and functional features of both the diagnosis and the relapse primary leukemias. Despite inter-T-ALL variability, comparative functional analyses revealed a unique, cell-intrinsic relapse phenotype that includes enhanced leukemia-initiating capacity and which can be experimentally conferred to diagnosis cells by TP53 silencing. Deregulated metabolic pathways and increased MYC signaling are prominent in the relapse phenotype. Ultra-sensitive backtracking of TP53-mutant cells and single-cell expression profiling revealed cellular heterogeneity at diagnosis, with sequential progression from a minor subpopulation toward a biallelic TP53alt relapse. Our findings support a model in which T-ALL relapse originates from a pre-existing transcriptional state with deregulated metabolism that is selected under therapeutic pressure, opening monitoring prospects for precision medicine. ### Competing Interest Statement The authors have declared no competing interest.

Most acute promyelocytic leukemia (APL), driven by the PML::RARA fusion, are now cured with targeted therapies combining all-trans retinoic acid (ATRA) and arsenic trioxide. Some patients treated with earlier ATRA/chemotherapy regimen developed resistance associated with mutations that most often preclude PML::RARA ATRA-binding. Here, we characterized a subset of clustered mutations associated with ATRA-resistance, but not predicted to affect ATRA binding. Most mutants indeed retained full ligand responsiveness, but displayed a basal super-repressive phenotype which did not result from an increased affinity for known corepressors such as NCoR and SMRT. Our findings suggest these mutations are gain-of-function associated with enhanced interactions with unidentified RARA partners with repressive ability. Similar to ATRA-resistant PLZF::RARA variants, these observations stress the role of persistent transcriptional repression of some retinoic acid target genes in acquired ATRA-resistance.

Germinal mono-allelic loss-of-function mutations of NEK1 drive amyotrophic lateral sclerosis (ALS) at variable penetrance, presumably through haploinsufficiency. Modeling the ALS-associated Arg812Ter mutation in mice revealed that the resulting truncated Nek1 (Nek1t) is aggregation-prone, particularly in alpha-motoneurons (αMNs), and drives canonical ALS symptoms when bi-allelically expressed (Nek1t/t). Promyelocytic leukemia (Pml) ablation allows for ALS symptoms to occur even in heterozygote Nek1wt/t animals, mimicking the human situation. Pml precludes disease occurrence by promoting SUMO-facilitated degradation of Nek1t proteins through PML nuclear bodies (NBs). Conversely, Pml induction, achieved by activating the interferon pathway via poly(I:C) treatment, clears Nek1t puncta in αMNs, dramatically reducing ALS-associated symptoms and extending survival by 5 months. Our studies highlight the role of mutant NEK1 expression in ALS pathogenesis and identifies activation of interferon pathways as a candidate therapeutic strategy that promotes Pml-triggered SUMOylation/degradation of toxic misfolded proteins in vivo, yielding dramatic clinical improvement. These observations provide strong proof-of-concept support to validate PML as a relevant therapeutic target in neurodegenerative conditions associated with protein misfolding and putative aggregation.

Neutrophil differentiation is governed by a precise transcriptional and epigenetic program. Here, we identify the zinc finger protein 711 (Znf711) and its partner, the histone demethylase PHD finger protein 8 (Phf8), as essential regulators of terminal granulopoiesis. Contrary to their established role as a transcriptional activatorcoactivator pair, we found that the Znf711-Phf8 complex operates through a repressive mechanism. Znf711 promotes neutrophil maturation in a DNA-binding-independent manner by sequestering Phf8. Upon loss of Znf711, Phf8 is recruited by the growth factor independent 1 transcription repressor (Gfi1aa) to the promoter of the master regulator c/ebpα, where SUMOylated Phf8 acts as a corepressor to inhibit its transcription. Furthermore, we delineate a positive feedback loop wherein C/ebpα directly activates znf711 expression, ensuring a high level of c/ebpα at the onset of differentiation. Our findings define the Znf711-Phf8 complex as a critical transcriptional rheostat in neutrophil development.

Cellular senescence is a dynamic cancer cell condition with both tumor-suppressive and relapse-promoting features. While terminating cell proliferation, it may sustain disease persistence through its senescence-associated secretory phenotype (SASP), immune alteration, and stem-like reprogramming. Here, we identify therapy-induced senescence (TIS) as a unifying, plastic state across newly diagnosed (nd), genetically diverse non-M3 acute myeloid leukemias (AML) that reprograms blasts towards an acute promyelocytic leukemia (APL)-like phenotype with distinct plasticity-related therapeutic vulnerabilities. We established a short-term ex vivo chemotherapy assay to quantify the patient-individual TIS capacity of primary AML blasts by fluorescent senescence-associated β-galactosidase activity, further characterized by p16INK4a expression, Ki67 loss, and H3K9me3 heterochromatin remodeling. Like daunorubicin or cytarabin, hypomethylating agents, hydroxyurea, and anti-CD33 antibody-drug conjugates also triggered TIS to varying extents, showing that diverse agents converge on senescence and prime AML cells for potential senolytic elimination. Probing baseline transcriptomes of nd AML samples by an AML TIS-high signature of the top-100 differentially expressed genes failed to stratify outcomes across TCGA (n=172), OHSU Beat AML (n=405), and MLL Munich Leukemia Laboratory (n=433) cohorts. Unexpectedly, a 13-gene subclassifier, determined by unsupervised cluster analysis of the top-100 genes and unrelated to the M3-typical t(15;17) PML::RARA translocation, identified 65 of 67 genetically defined APL cases across these nearly 1,000 all-subtype AML transcriptomes, suggesting that TIS rendered non-M3 AML APL-like. Multi-omic analyses including bulk and single-cell RNA sequencing plus PRC2/SUZ12 and H3K27me3 ChIP-seq unveiled TIS-related loss of polycomb repression, epigenetic remodeling, and transcriptional reprogramming, yet independent of PML::RARA, as the underlying molecular mechanism. Functionally, TIS-associated APL-like plasticity conferred sensitivity to differentiation therapies such as all-trans retinoic acid (ATRA) and histone deacetylase inhibitors, and to Bcl2-targeting agents with senolytic activity. Patient-derived xenograft models validated these vulnerabilities as sequential TIS followed by senescence targeting achieved durable control exclusively in models able to mount a senescence response. Given the biologically unifying and ATRA-sensitizing role of TIS-associated M3-like plasticity, we assessed its clinical relevance in three independent cohorts totaling 92 newly diagnosed patients. TIS capacity at diagnosis robustly stratified outcomes, predicted superior disease-free and overall survival, and was associated with favorable ELN classification, normal cytogenetics, and NPM1 or DNMT3A mutations, while being lowest in adverse-risk SRSF2-mutant AML. Our findings uncover TIS-related M3-like plasticity as a novel state exploitable by a two-punch strategy of senesence induction first followed by targeted interventions through pro-differentiation or senolytic approaches, establishing a new therapeutic paradigm with immediate clinical potential and broader relevance to other malignancies where therapy-induced plasticity dictates outcome.

Nucleophosmin-1 (NPM1) is a nucleolar chaperone protein frequently mutated in acute myeloid leukemia (AML). ARF and Sentrin/SUMO Specific Peptidase 3 (SENP3) control NPM1 functions through dynamic SUMOylation/de-SUMOylation. Mutated NPM1 is an oncoprotein that exhibits an aberrant cytoplasmic localization (NPM1c) and disrupts PML/P53 signaling. Studies reported increased survival of patients with NPM1c AML when retinoic acid (RA) was added to chemotherapy or hypomethylating agents. Ex vivo, RA initiates NPM1c degradation, P53 activation and cell death. Yet, the molecular mechanisms involved remain elusive. Here we show that in NPM1c AML cell lines or patients’ blasts, NPM1c-triggered mitochondrial dysfunction and oxidative stress drive NPM1c stabilization through SENP3 upregulation. RA decreases mitochondrial ROS production, driving degradation of SENP3, ARF stabilization, PML-dependent NPM1c hyperSUMOylation followed by RNF4-dependent ubiquitination and degradation. Thus, the feedback loop stabilizing NPM1c protein can be interrupted by RA-triggered enhanced mitochondrial fitness, mechanistically explaining the benefit of RA in chemotherapy or hypomethylating agents-treated AMLs.

The ubiquitination or SUMOylation of hematopoietic-related factors plays pivotal roles in hematopoiesis. RNF111, known as a ubiquitin ligase, is a newly discovered SUMO-targeted ubiquitin ligase involved in multiple signaling pathways mediated by transforming growth factor (TGF)-β family members. However, its role in hematopoiesis remains unclear. Herein, a heritable Rnf111 mutant zebrafish line was generated by CRISPR/Cas9-mediated genome editing. Impairment of hematopoietic stem and progenitor cells (HSPC) of definitive hematopoiesis was found in Rnf111-deficient mutants. Ablation of Rnf111 resulted in decreased phosphorylation of Smad2/3 in HSPC. Definitive endoderm 2 inducer (IDE2), which specifically activates TGF-β signaling and downstream Smad2 phosphorylation, could restore definitive hematopoiesis in Rnf111-deficient embryos. Further molecular mechanism studies revealed that Gcsfr/NO signaling was an important target pathway of Smad2/3 involved in Rnf111-mediated HSPC development. In conclusion, our study demonstrated that Rnf111 contributes to the development of HSPC by maintaining Smad2/3 phosphorylation and activation of the Gcsfr/NO signaling pathway.

Neutrophils are key component of the innate immune system in vertebrates. Diverse transcription factors and cofactors act in a well-coordinated manner to ensure proper neutrophil development. Dysregulation of the transcriptional program triggering neutrophil differentiation is associated with various human hematologic disorders such as neutropenia, neutrophilia, and leukemia. In the current study we show the zinc finger protein Znf687 is a lineage-preferential transcription factor, whose deficiency leads to an impaired neutrophil development in zebrafish. Mechanistically, Znf687 functions as a negative regulator of gfi1aa , a pivotal modulator in terminal granulopoiesis, to regulate neutrophil maturation. Moreover, we found BRD4, an important epigenetic regulator, directly interacts with ZNF687 in neutrophils. Deficiency of brd4 results in similar defective neutrophil development as observed in znf687 mutant zebrafish. Biochemical and genetic analyses further reveal that instead of serving as a canonical transcriptional coactivator, Brd4 directly interacts and bridges Znf687 and Smrt nuclear corepressor on gfi1aa gene’s promoter to exert transcription repression. In addition, the ZNF687-BRD4-SMRT-GFI1 transcriptional regulatory network is evolutionary conserved in higher vertebrate. Overall, our work indicates Znf687 and Brd4 are two novel master regulators in promoting terminal granulopoiesis.

AbstractUnderstanding the regulation of normal erythroid development will help to develop new potential therapeutic strategies for disorders of the erythroid lineage. Cellular repressor of E1A‐stimulated genes 1 (CREG1) is a glycoprotein that has been implicated in the regulation of tissue homeostasis. However, its role in erythropoiesis remains largely undefined. In this study, it is found that CREG1 expression increases progressively during erythroid differentiation. In zebrafish, creg1 mRNA is preferentially expressed within the intermediate cell mass (ICM)/peripheral blood island (PBI) region where primitive erythropoiesis occurs. Loss of creg1 leads to anemia caused by defective erythroid differentiation and excessive apoptosis of erythroid progenitors. Mechanistically, creg1 deficiency results in reduced activation of TGF‐β/Smad2 signaling pathway. Treatment with an agonist of the Smad2 pathway (IDE2) could significantly restore the defective erythroid development in creg1−/− mutants. Further, Klf1, identified as a key target gene downstream of the TGF‐β/Smad2 signaling pathway, is involved in creg1 deficiency‐induced aberrant erythropoiesis. Thus, this study reveals a previously unrecognized role for Creg1 as a critical regulator of erythropoiesis, mediated at least in part by the TGF‐β/Smad2‐Klf1 axis. This finding may contribute to the understanding of normal erythropoiesis and the pathogenesis of erythroid disorders.

Germinal mono-allelic loss-of-function mutations of NEK1 drive Amyotrophic Lateral Sclerosis (ALS) at variable penetrance, potentially through haploinsufficiency. Modeling the ALS-associated Arg812Ter mutation in mice revealed that the resulting truncated NEK1 (NEK1t) is aggregation-prone, notably in alpha-motoneurons (alphaMNs), and drives multiple ALS-like symptoms when bi-allelically expressed. Promyelocytic leukemia (Pml) is a key genetic interactor, since its loss allows for ALS symptoms to occur even in Nek1wt/t animals, mimicking the human situation. Pml precludes disease onset by promoting SUMO-facilitated degradation of NEK1t proteins. Pml upregulation by interferon alpha or poly(I:C) eliminates NEK1t aggregates in alphaMNs of Nek1t/t animals, dramatically improving ALS-associated symptoms and extending survival by 6 months. Our study highlights the role of NEK1 aggregates in ALS pathogenesis and identifies interferon or poly(I:C) as a promising candidate therapy acting through Pml-triggered degradation of toxic misfolded proteins. ### Competing Interest Statement The authors have declared no competing interest.

The story of acute promyelocytic leukemia (APL) discovery, physiopathology, and treatment is a unique journey, transforming the most aggressive form of leukemia to the most curable. It followed an empirical route fueled by clinical breakthroughs driving major advances in biochemistry and cell biology, including the discovery of PML nuclear bodies (PML NBs) and their central role in APL physiopathology. Beyond APL, PML NBs have emerged as key players in a wide variety of biological functions, including tumor-suppression and SUMO-initiated protein degradation, underscoring their broad importance. The APL story is an example of how clinical observations led to the incremental development of the first targeted leukemia therapy. The understanding of APL pathogenesis and the basis for cure now opens new insights in the treatment of other diseases, especially other acute myeloid leukemias.

Acute promyelocytic leukemia (APL) is driven by the promyelocytic leukemia (PML)/retinoic acid receptor α (RARA) fusion oncoprotein. Over the years, it has emerged as a model system to understand how this simple (and sometimes sole) genetic alteration can transform hematopoietic progenitors through the acquisition of dominant-negative properties toward both transcriptional control by nuclear receptors and PML-mediated senescence. The fortuitous identification of two drugs, arsenic trioxide (ATO) and all-trans-retinoic acid (ATRA), that respectively bind PML and RARA to initiate PML/RARA degradation, has allowed an unprecedented dissection of the cellular and molecular mechanisms involved in patients' cure by the ATO/ATRA combination. This analysis has unraveled the dual and complementary roles of RARA and PML in both APL initiation and cure by the ATRA/ATO combination. We discuss how some of the features unraveled by APL studies may be more broadly applicable to some other forms of leukemia. In particular, the functional synergy between drugs that promote differentiation and those that initiate apoptosis/senescence to impede self-renewal could pave the way to novel curative combinations.

In recent decades, millions of patients with cancer have been cured by chemotherapy alone. By 'cure', we mean that patients with cancers that would be fatal if left untreated receive a time-limited course of chemotherapy and their cancer disappears, never to return. In an era when hundreds of thousands of cancer genomes have been sequenced, a remarkable fact persists: in most patients who have been cured, we still do not fully understand the mechanisms underlying the therapeutic index by which the tumour cells are killed, but normal cells are somehow spared. In contrast, in more recent years, patients with cancer have benefited from targeted therapies that usually do not cure but whose mechanisms of therapeutic index are, at least superficially, understood. In this Perspective, we will explore the various and sometimes contradictory models that have attempted to explain why chemotherapy can cure some patients with cancer, and what gaps in our understanding of the therapeutic index of chemotherapy remain to be filled. We will summarize principles which have benefited curative conventional chemotherapy regimens in the past, principles which might be deployed in constructing combinations that include modern targeted therapies.

Differentially expressed genes in Xenograted T-ALL shSYNCRIP-SNHG5 versus ShCtrl

Abstract YPEL5 is a member of the Yippee-like (YPEL) gene family that is evolutionarily conserved in eukaryotic species. To date, the physiological function of YPEL5 has not been assessed due to a paucity of genetic animal models. Here, using CRISPR/Cas9-mediated genome editing, we generated a stable ypel5−/− mutant zebrafish line. Disruption of ypel5 expression leads to liver enlargement associated with hepatic cell proliferation. Meanwhile, hepatic metabolism and function are dysregulated in ypel5−/− mutant zebrafish, as revealed by metabolomic and transcriptomic analyses. Mechanistically, Hnf4a is identified as a crucial downstream mediator that is positively regulated by Ypel5. Zebrafish hnf4a overexpression could largely rescue ypel5 deficiency-induced hepatic defects. Furthermore, PPARα signaling mediates the regulation of Hnf4a by Ypel5 through directly binding to the transcriptional enhancer of the Hnf4a gene. Herein, this work demonstrates an essential role of Ypel5 in hepatocyte proliferation and function and provides the first in vivo evidence for a physiological role of the ypel5 gene in vertebrates.