Structural Maintenance Of Chromosomes Proteins Research Articles

Identification of two novel heterozygous variants of SMC3 with Cornelia de Lange syndrome.

Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder, and cases caused by variants in the structural maintenance of chromosomes protein 3 (SMC3) gene are uncommon. Here, we report two cases of CdLS associated with novel pathogenic variants in SMC3 from two Chinese families. Clinical presentations of two patients with CdLS were evaluated, and specimens from the patients and other family members were collected for Trio-based whole-exome sequencing. Pyrosequencing, chip-based digital PCR, minigene splicing assay, and in silico analysis were carried out to elucidate the impact of novel variants. Novel heterozygous variants in SMC3 were identified in each proband. One harbored a novel splicing and mosaic variant (c.2535+1G>A) in SMC3. The mutated allele G>A conversion was approximately 23.1% by digital PCR, which indicated that 46.2% of peripheral blood cells had this variant. Additionally, invitro minigene splicing analysis validated that the c.2535+1G>A variant led to an exon skipping in messenger RNA splicing. The other carried a heterozygous variant (c.435C>A), which was predicted to be pathogenic as well as significantly altered in local electrical potential. The former showed multiple abnormalities and marked clinical severity, and the latter mainly exhibited a speech developmental disorder and slightly facial anomalies. Both patients were clinically diagnosed with Cornelia de Lange syndrome 3 (CdLS3). The newly identified SMC3 gene variants can expand the understanding of CdLS3 and provide reliable evidence for genetic counseling to the affected family.

Structural Maintenance of Chromosome Protein 4 Promotes the Progression of Cardia Adenocarcinoma via Regulation of the Wnt/β-catenin Signaling Pathway.

Structural maintenance of chromosome protein 4 (SMC4) is crucial for chromosome assembly and separation, but its role and mechanism in cardia adenocarcinoma (CA) are unknown. SMC4 expression levels were initially detected by protein profiling in 20 pairs of CA tumor tissues and adjacent normal tissues. The level of SMC4 expression in CA cells was then evaluated using a western blot analysis. Cell proliferation was evaluated by CCK-8 and clone formation tests. Scratch and transwell tests were used to investigate cell migration as well as invasion, while through the flow cytometry, we examined the cell apoptosis and progression of the cell cycle. The regulatory effects of the epithelial-mesenchymal transition (EMT) and the Wnt/β- catenin pathway were investigated using western blot. A tumorigenesis experiment was used to investigate the influence of SMC4 on tumor development in nude mice. This study showed overexpression of SMC4 in CA tissues and cells. Knockdown of SMC4 can significantly inhibit the proliferation, migration and invasion, stimulate cell apoptosis, induce cell cycle arrest in the G0/G1 phase of CA cells, and inhibit tumor growth in vivo. In addition, down-regulation of SMC4 resulted in decreased expression of Bcl-2, Cyclin D1, CDK4, CDK6, β-catenin, phosphorylated GSK-3β, N-cadherin, and Vimentin, with an increased level of proteins, i.e., Bax, cleaved-caspase3, and E-cadherin. When SMC4 was overexpressed, these effects were reversed. SMC4 can facilitate the biological progression of CA, suggesting that SMC4 could be a potential therapeutic target for the disease.

Chromosome architecture in an archaeal species naturally lacking structural maintenance of chromosomes proteins

Proteins in the structural maintenance of chromosomes (SMC) superfamily play key roles in chromosome organization and are ubiquitous across all domains of life. However, SMC proteins are notably absent in the Desulfurococcales of phylum Crenarchaeota. Intrigued by this observation, we performed chromosome conformation capture experiments in the model Desulfurococcales species Aeropyrum pernix. As in other archaea, we observe chromosomal interaction domains across the chromosome. The boundaries between chromosomal interaction domains show a dependence on transcription and translation for their definition. Importantly, however, we reveal an additional higher-order, bipartite organization of the chromosome—with a small high-gene-expression and self-interacting domain that is defined by transcriptional activity and loop structures. Viewing these data in the context of the distribution of SMC superfamily proteins in the Crenarchaeota, we suggest that the organization of the Aeropyrum genome represents an evolutionary antecedent of the compartmentalized architecture observed in the Sulfolobus lineage.

Structural maintenance of chromosomes (SMC) proteins are required for DNA elimination in Paramecium.

Chromosome (SMC) proteins are a large family of ATPases that play important roles in the organization and dynamics of chromatin. They are central regulators of chromosome dynamics and the core component of condensin. DNA elimination during zygotic somatic genome development is a characteristic feature of ciliated protozoa such as Paramecium This process occurs after meiosis, mitosis, karyogamy, and another mitosis, which result in the formation of a new germline and somatic nuclei. The series of nuclear divisions implies an important role of SMC proteins in Paramecium sexual development. The relationship between DNA elimination and SMC has not yet been described. Here, we applied RNA interference, genome sequencing, mRNA sequencing, immunofluorescence, and mass spectrometry to investigate the roles of SMC components in DNA elimination. Our results show that SMC4-2 is required for genome rearrangement, whereas SMC4-1 is not. Functional diversification of SMC4 in Paramecium led to a formation of two paralogues where SMC4-2 acquired a novel, development-specific function and differs from SMC4-1. Moreover, our study suggests a competitive relationship between these two proteins.

Current working models of SMC-driven DNA-loop extrusion.

Structural maintenance of chromosome (SMC) proteins play a key roles in the chromosome organization by condensing two meters of DNA into cell-sized structures considered as the SMC protein extrudes DNA loop. Recent sequencing-based high-throughput chromosome conformation capture technique (Hi-C) and single-molecule experiments have provided direct evidence of DNA-loop extrusion. However, the molecular mechanism by which SMCs extrude a DNA loop is still under debate. Here, we review DNA-loop extrusion studies with single-molecule assays and introduce recent structural studies of how the ATP-hydrolysis cycle is coupled to the conformational changes of SMCs for DNA-loop extrusion. In addition, we explain the conservation of the DNA-binding sites that are vital for dynamic DNA-loop extrusion by comparing Cryo-EM structures of SMC complexes. Based on this information, we compare and discuss four compelling working models that explain how the SMC complex extrudes a DNA loop.

Identification of candidate genes associated with body weight in swimming crab (Portunus trituberculatus) according to conjunctive analyses of BSA-seq and RNA-seq

The swimming crab (Portunus trituberculatus) is a valuable crustacean species extensively cultivated in China, owing to its fast development, palatability, and rich nutrition. However, the genetic factors regulating its growth remain elusive, impeding the progress of breeding initiatives for this economically important species. In this study, we combined bulk segregation analysis sequencing (BSA-seq) and transcriptome sequencing (RNA-seq) to identify potential candidate genes related to the body weight of P. trituberculatus using a full-sib family. BSA-seq successfully identified five candidate intervals on chromosomes 31, 38, and 47, spanning a total length of 9.76 Mb, which encompassed 137 annotated genes. By conducting RNA-seq analysis on swimming crab individuals in two extreme weight groups, 1581 genes were mined as differentially expressed genes (DEGs), involving 357 up-regulated and 1224 down-regulated genes. GO enrichment analysis demonstrated that DEGs were significantly enriched in proteolysis, obsolete oxidation-reduction process, nucleus, cytoplasm, molecular function, and metal ion binding. KEGG enrichment analysis showed that the proteasome signaling pathway could play a prominent role in the growth difference of P. trituberculatus. The conjunctive analyses of BSA-seq and RNA-seq led to the identification of eight critical DEGs, including peripheral plasma membrane protein CASK (CASK), cytoplasmic dynein 2 heavy chain 1 (Dyh1b), RNA-binding protein 5 (Rbm5), structural maintenance of chromosomes protein 3 (Smc3), hemicentin-2 (Hmcn1), A-kinase anchor protein 13 (Akap13), zinc finger MYM-type protein 2 (Zmym3), and extracellular matrix protein FRAS1 (Fras1), which exert influence over the growth of P. trituberculatus. This study not only enhances our understanding of the molecular mechanism governing the growth of P. trituberculatus but also provides valuable insights for future aquaculture programs aimed at selective breeding of this species.

Sequencing, Functional Annotation, and Interaction Prediction of mRNAs and Candidate Long Noncoding RNAs Originating from Tea Leaves During Infection by the Fungal Pathogen Causing Tea Leaf Spot, Didymella bellidis.

Tea leaf spot caused by Didymella bellidis can seriously reduce the productivity and quality of tea (Camellia sinensis var. sinensis) leaves in Guizhou Province, southwest China. Analysis of the relationship between messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs) of tea could provide insights into the plant-pathogen interaction. In this study, high-throughput sequencing of mRNAs and lncRNAs from tea leaves during infection by D. bellidis was conducted using the Illumina Novaseq 6000 platform. Infection by D. bellidis hyphae resulted in up- or downregulation of 553 and 191 of the differentially expressed mRNAs (DEmRNAs), respectively. As the S gene number (total number of genes with significantly differential expression annotated in the specified Gene Ontology [GO] database), three were enriched with respect to the defense response to the fungus at the biological process level. Expression of the DEmRNAs peroxidase 21 (TEA000222.1) and mcht-2 (TEA013240.1) originating from tea leaves were upregulated during challenge by D. bellidis hyphae, whereas expression of the LRR receptor-like serine/threonine-protein kinase ERECTA (TEA016781.1) gene was downregulated. The infection of D. bellidis hyphae resulted in up- or downregulation of 227 and 958 of the differentially expressed lncRNAs (DElncRNAs). The DEmRNAs associated with uncharacterized LOC101499401 (TEA015626.1), uncharacterized protein (TEA014125.1), structural maintenance of chromosomes protein 1 (TEA001660.1), and uncharacterized protein (TEA017727.1) occurred as a result of cis regulation by DElncRNAs MSTRG.20036, MSTRG.3843, MSTRG.26132, and MSTRG.56701, respectively. The expression profiling and lncRNA/mRNA association prediction in the tea leaves infected by D. bellidis will provide a valuable resource for further research into disease resistance.

Cohesin contributes to transcriptional repression of stage-specific genes in the human malaria parasite.

The complex life cycle of the human malaria parasite, Plasmodium falciparum, is driven by specific transcriptional programs, but it is unclear how most genes are activated or silenced at specific times. There is an association between transcription and spatial organization; however, the molecular mechanisms behind genome organization are unclear. While P. falciparum lacks key genome-organizing proteins found in metazoans, it has all core components of the cohesin complex. To investigate the role of cohesin in P. falciparum, we functionally characterize the cohesin subunit Structural Maintenance of Chromosomes protein 3 (SMC3). SMC3 knockdown during early stages of the intraerythrocytic developmental cycle (IDC) upregulates a subset of genes involved in erythrocyte egress and invasion, which are normally expressed at later stages. ChIP-seq analyses reveal that during the IDC, SMC3 enrichment at the promoter regions of these genes inversely correlates with gene expression and chromatin accessibility. These data suggest that SMC3 binding contributes to the repression of specific genes until their appropriate time of expression, revealing a new mode of stage-specific gene repression in P. falciparum.

Looping the Genome with SMC Complexes.

SMC (structural maintenance of chromosomes) protein complexes are an evolutionarily conserved family of motor proteins that hold sister chromatids together and fold genomes throughout the cell cycle by DNA loop extrusion. These complexes play a key role in a variety of functions in the packaging and regulation of chromosomes, and they have been intensely studied in recent years. Despite their importance, the detailed molecular mechanism for DNA loop extrusion by SMC complexes remains unresolved. Here, we describe the roles of SMCs in chromosome biology and particularly review in vitro single-molecule studies that have recently advanced our understanding of SMC proteins. We describe the mechanistic biophysical aspects of loop extrusion that govern genome organization and its consequences.

Function and Evolution of the Loop Extrusion Machinery in Animals.

Structural maintenance of chromosomes (SMC) complexes are essential proteins found in genomes of all cellular organisms. Essential functions of these proteins, such as mitotic chromosome formation and sister chromatid cohesion, were discovered a long time ago. Recent advances in chromatin biology showed that SMC proteins are involved in many other genomic processes, acting as active motors extruding DNA, which leads to the formation of chromatin loops. Some loops formed by SMC proteins are highly cell type and developmental stage specific, such as SMC-mediated DNA loops required for VDJ recombination in B-cell progenitors, or dosage compensation in Caenorhabditis elegans and X-chromosome inactivation in mice. In this review, we focus on the extrusion-based mechanisms that are common for multiple cell types and species. We will first describe an anatomy of SMC complexes and their accessory proteins. Next, we provide biochemical details of the extrusion process. We follow this by the sections describing the role of SMC complexes in gene regulation, DNA repair, and chromatin topology.

Revealing and manipulating the structure of mitotic chromosomes using atomic force microscopy

Although the mitotic cell cycle has been extensively characterized, very little is known about the highly condensed structure of metaphase chromosomes. The hierarchical organization of the chromatin fibers and their extrusion into complex loop structures by the Structural Maintenance of Chromosome (SMC) proteins are widely acknowledged features of the chromosomal architecture; however, the small size and complex topology of these structures are hindering their unequivocal detection and characterization. Even though Atomic Force Microscopy (AFM) has the potential to access these features, chromosome deformability and susceptibility to alterations to their external environment have so far limited the application of this technique. In the present work we overcome these issues and employ AFM to study the structure of human metaphase chromosomes in a liquid environment that closely resembles their physiological conditions, without the use of fixation agents and enzymatic treatments. Our analysis reveals the finer details of the unperturbed chromosome structure, shedding light on the organization of the chromatin fiber network and testing its stability against changes in the environment ionic conditions. Moreover, by complementing the image analysis with AFM-based Force Spectroscopy we probe the response of mitotic chromosomes to nanoscale deformations in the presence and absence of specific SMC proteins, namely Condensin I and II, thereby providing new insights into their contribution to the chromosome structural stability. The presented results enrich our current understanding of chromosome organization and provide new valuable tools to study the structure of mitotic chromosomes in both healthy and pathological conditions.

Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled coil arms

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elongated coiled coils (CC). Recent studies found that variable CC conformations including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed description of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale conformational changes—most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hinders folding of the consecutive CC region and leads frequently to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly links the sensitive CC architecture to the biological function of cohesin.

Condensin pinches a short negatively supercoiled DNA loop during each round of ATP usage.

Condensin, an SMC (structural maintenance of chromosomes) protein complex, extrudes DNA loops using an ATP-dependent mechanism that remains to be elucidated. Here, we show how condensin activity alters the topology of the interacting DNA. High condensin concentrations restrain positive DNA supercoils. However, in experimental conditions of DNA loop extrusion, condensin restrains negative supercoils. Namely, following ATP-mediated loading onto DNA, each condensin complex constrains a DNA linking number difference (∆Lk) of -0.4. This ∆Lk increases to -0.8 during ATP binding and resets to -0.4 upon ATP hydrolysis. These changes in DNA topology do not involve DNA unwinding, do not spread outside the condensin-DNA complex and can occur in the absence of the condensin subunit Ycg1. These findings indicate that during ATP binding, a short DNA domain delimited by condensin is pinched into a negatively supercoiled loop. We propose that this loop is the feeding segment of DNA that is subsequently merged to enlarge an extruding loop. Such a "pinch and merge" mechanism implies that two DNA-binding sites produce the feeding loop, while a third site, plausibly involving Ycg1, might anchor the extruding loop.

Profiling a single-stranded DNA region within an rDNA segment that affects the loading of bacterial condensin.

Bacterial condensin preferentially loads onto single-stranded DNA (ssDNA) invitro and onto rDNA invivo to support proper chromosome compaction. Thus, the actively transcribing rDNA would provide the ssDNA region for the loading of bacterial condensin. We attempted to detect the ssDNA region in the rrnI gene in situ. Non-denaturing sodium bisulfite treatment catalyzed the conversion of cytosines to thymines (CT-conversion) at the melted DNA of a genome. Using next-generation sequencing, we generated an average of 11,000 reads covering each cytosine on the rDNA segment. In principle, the CT-conversion rate is an accurate guide to detect ssDNA segment. We detected multiple ssDNA segments throughout the rDNA. The deletion mutations of the rDNA hindered the ssDNA formation at the 100-500bp segment downstream of the promoter. These data support the idea that the ssDNA segment plays a crucial role as the condensin-loading site and suggest the mechanism of condensin loading onto rDNA.

Disruption of SMC-related genes promotes recombinant cholesterol esterase production in Burkholderia stabilis.

Burkholderia stabilis strain FERMP-21014 secretes cholesterol esterase (BsChe), which is used in clinical settings to determine serum cholesterol levels. Previously, we constructed an expression plasmid with an endogenous constitutive promoter to enable the production of recombinant BsChe. In this study, we obtained one mutant strain with 13.1-fold higher BsChe activity than the wild type, using N-methyl-N'-nitro-N-nitrosoguanidine as a mutagen. DNA-sequencing analysis revealed that the strain had lost chromosome 3 (∆Chr3), suggesting that the genes hindering BsChe production may be encoded on Chr3. We also identified common mutations in the functionally unknown BSFP_068720/30 genes in the top 10 active strains generated during transposon mutagenesis. As BSFP_068720/30/40 comprised an operon on Chr3, we created the BSFP_068720/30/40 disruption mutant and confirmed that each disruption mutant containing the expression plasmid exhibited ~ 16.1-fold higher BsChe activity than the wild type. Quantitative PCR showed that each disruption mutant and ΔChr3 had a ~ 9.4-fold higher plasmid copy number than the wild type. Structural prediction models indicate that BSFP_068730/40 is structurally homologous to the structural maintenance of chromosomes (SMC) protein MukBE, which is responsible for chromosome segregation during cell division. Conversely, BSFP_068720/30/40 disruption did not lead to a Chr3 drop-out. These results imply that BSFP_068720/30/40 is not a SMC protein but is involved in destabilizing foreign plasmids to prevent the influx of genetic information from the environment. In conclusion, the disruption of BSFP_068720/30/40 improved plasmid stability and copy number, resulting in exceptionally high BsChe production. KEY POINTS: • Disruption of BSFP_068720/30/40 enabled mass production of Burkholderia Che/Lip. • BSFP_068730/40 is an SMC protein homolog not involved in chromosome retention. • BSFP_068720/30/40 is likely responsible for the exclusion of exogenous plasmids.

SMC protein RecN drives RecA filament translocation for in vivo homology search

While the molecular repertoire of the homologous recombination pathways is well studied, the search mechanism that enables recombination between distant homologous regions is poorly understood. Earlier work suggests that the recombinase RecA, an essential component for homology search, forms an elongated filament, nucleating at the break site. How this RecA structure carries out long-distance search remains unclear. Here, we follow the dynamics of RecA after induction of a single double-strand break on the Caulobacter chromosome. We find that the RecA-nucleoprotein filament, once formed, rapidly translocates in a directional manner in the cell, undergoing several pole-to-pole traversals, until homology search is complete. Concomitant with translocation, we observe dynamic variation in the length of the filament. Importantly invivo, the RecA filament alone is incapable of such long-distance movement; both translocation and associated length variations are contingent on action of structural maintenance of chromosome (SMC)-like protein RecN, via its ATPase cycle. In summary, we have uncovered the three key elements of homology search driven by RecN: mobility of a finite segment of RecA, changes in filament length, and ability to conduct multiple pole-to-pole traversals, which together point to an optimal search strategy.

Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled-coil arms

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elongated coiled-coils (CCs). Recent studies found that variable CC conformations, including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed description of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale conformational changes, most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hinders folding of the consecutive CC region and frequently leads to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly link the sensitive CC architecture to the biological function of cohesin.

How in vitro maturation changes the proteome of ovine cumulus-oocyte complexes?

The present study evaluated the effects of in vitro maturation (IVM) on the proteome of cumulus-oocyte complexes (COCs) from ewes. Extracted COC proteins were analyzed by LC-MS/MS. Differences in protein abundances (p < 0.05) and functional enrichments in immature versusin vitro-matured COCs were evaluated using bioinformatics tools. There were 2550 proteins identified in the COCs, with 89 and 87 proteins exclusive to immature and mature COCs, respectively. IVM caused downregulation of 84 and upregulation of 34 proteins. Major upregulated proteins in mature COCs were dopey_N domain-containing protein, structural maintenance of chromosomes protein, ubiquitin-like modifier-activating enzyme 2. Main downregulated proteins in mature COCs were immunoglobulin heavy constant mu, inter-alpha-trypsin inhibitor heavy chain 2, alpha-2-macroglobulin. Proteins exclusive to mature COCs and upregulated after IVM related to immune response, complement cascade, vesicle-mediated transport, cell cycle, and extracellular matrix organization. Proteins of immature COCs and downregulated after IVM were linked to metabolic processes, immune response, and complement cascade. KEGG pathways and miRNA-regulated genes attributed to downregulated and mature COC proteins related to complement and coagulation cascades, metabolism, humoral response, and B cell-mediated immunity. Thus, IVM influenced the ovine COC proteome. This knowledge supports the future development of efficient IVM protocols for Ovis aries.

DNA sliding and loop formation by E. coli SMC complex: MukBEF

SMC (structural maintenance of chromosomes) complexes share conserved architectures and function in chromosome maintenance via an unknown mechanism. Here we have used single-molecule techniques to study MukBEF, the SMC complex in Escherichia coli. Real-time movies show MukB alone can compact DNA and ATP inhibits DNA compaction by MukB. We observed that DNA unidirectionally slides through MukB, potentially by a ratchet mechanism, and the sliding speed depends on the elastic energy stored in the DNA. MukE, MukF and ATP binding stabilize MukB and DNA interaction, and ATP hydrolysis regulates the loading/unloading of MukBEF from DNA. Our data suggests a new model for how MukBEF organizes the bacterial chromosome in vivo; and this model will be relevant for other SMC proteins.

Npm1 haploinsufficiency in collaboration with MEIS1 is sufficient to induce AML in mice

AbstractNPM1 is among the most frequently mutated genes in acute myeloid leukemia (AML). Mutations in the NPM1 gene result in the increased export of NPM1 to the cytoplasm (NPM1c) and are associated with multiple transforming events including the aberrant upregulation of MEIS1 that maintains stem cell and cell cycle–associated pathways in NPM1c AML. However, another consequence of the NPM1c mutation is the inadequate levels of NPM1 wild-type in the nucleus and nucleolus, caused by the loss of one wild-type allele in addition to enforced NPM1 nuclear export. The contribution of NPM1 haploinsufficiency independently of the NPM1 mutation to AML development and its relationship with MEIS1 function is poorly understood. Using mouse models, our study shows that NPM1 haploinsufficiency paired with MEIS1 overexpression is sufficient to induce a fully penetrant AML in mice that transcriptionally resembles human NPM1c AML. NPM1 haploinsufficiency alters MEIS1-binding occupancies such that it binds the promoter of the oncogene structural maintenance of chromosome protein 4 (SMC4) in NPM1 haploinsufficient AML cells but not in NPM1 wild-type–harboring Hoxa9/Meis1-transformed cells. SMC4 is higher expressed in haploinsufficient and NPM1c+ AML cells, which are more vulnerable to the disruption of the MEIS1-SMC4 axis compared with AML cells with nonmutated NPM1. Taken together, our study underlines that NPM1 haploinsufficiency on its own is a key factor of myeloid leukemogenesis and characterizes the MEIS1-SMC4 axis as a potential therapeutic target in this AML subtype.