Frequent pathway mutations of splicing machinery in myelodysplasia

Decoding cancer etiology with cellular reprogramming

Cancer research remains clinically unmet in many areas due to limited access to patient samples and the lack of reliable model systems that truly reflect human cancer biology. The emergence of patient-derived induced pluripotent stem cells and engineered human pluripotent stem cells (hPSCs) has helped overcome these challenges, offering a versatile alternative platform for advancing cancer research. These hPSCs are already proving to be valuable models for studying specific cancer driver mutations, offering insights into cancer origins, pathogenesis, tumor heterogeneity, clonal evolution, and facilitating drug discovery and testing. This article reviews recent progress in utilizing hPSCs for clinically relevant cancer models and highlights efforts to deepen our understanding of fundamental cancer biology.

The Ataxia-telangiectasia mutated (ATM) is the most important gene for repairing the DNA in Myelodysplastic Neoplasm

Myelodysplastic Neoplasm (MDS) is a cancer associated with aging, often leading to acute myeloid leukemia (AML). One of its hallmarks is hypermethylation, particularly in genes responsible for DNA repair. This study aimed to evaluate the methylation and mutation status of DNA repair genes (single-strand - XPA, XPC, XPG, CSA, CSB and double-strand - ATM, BRCA1, BRCA2, LIG4, RAD51) in MDS across three patient cohorts (Cohort A-56, Cohort B-100, Cohort C-76), using methods like pyrosequencing, real-time PCR, immunohistochemistry, and mutation screening. Results showed that XPA had higher methylation in low-risk MDS compared to high-risk MDS. For double-strand repair genes, ATM displayed higher methylation in patients who transformed to AML (p = 0.016). ATM gene expression was downregulated in MDS compared to controls (p = 0.042). When patients were classified according to the WHO 2022 guidelines, ATM expression progressively decreased from low-risk subtypes (e.g., Hypoplastic MDS) to high-risk MDS and AML. Patients who transformed to AML had a higher 5mC/5hmC ratio compared to those who didn't (p = 0.045). Additionally, poor cytogenetic risk patients had higher tissue methylation scores than those with good risk (p = 0.035). Analysis using the cBioPortal platform identified ATM as the most frequently mutated DNA repair gene, with various mutations, such as frameshift and missense, most of which were classified as oncogenic. The findings suggest that ATM is frequently silenced or downregulated in MDS due to methylation or mutations, contributing to the progression to AML. This highlights ATM's potential role in the disease's advancement and as a target for future therapeutic strategies.

Covalent targeting of splicing in T cells

Despite significant interest in therapeutic targeting of splicing, few chemical probes are available for the proteins involved in splicing. Here, we show that elaborated stereoisomeric acrylamide EV96 and its analogues lead to a selective T cell state-dependent loss of interleukin 2-inducible T cell kinase (ITK) by targeting one of the core splicing factors SF3B1. Mechanistic investigations suggest that the state-dependency stems from a combination of differential protein turnover rates and extensive ITK mRNA alternative splicing. We further introduce the most comprehensive list to date of proteins involved in splicing and leverage cysteine- and protein-directed activity-based protein profiling with electrophilic scout fragments to demonstrate covalent ligandability for many classes of splicing factors and splicing regulators in T cells. Taken together, our findings show how chemical perturbation of splicing can lead to immune state-dependent changes in protein expression and provide evidence for the broad potential to target splicing factors with covalent chemistry.

U2AF1 mutation causes an oxidative stress and DNA repair defect in hematopoietic and leukemic cells

U2AF1 is a core component of spliceosome and controls cell-fate specific alternative splicing. U2AF1 mutations have been frequently identified in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) patients, and mutations in U2AF1 are associated with poor prognosis in hematopoietic malignant diseases. Here, by forced expression of mutant U2AF1 (U2AF1 S34F) in hematopoietic and leukemic cell lines, we find that U2AF1 S34F causes increased reactive oxygen species (ROS) production. In hematopoietic cell line, a defect in mitochondrial function and DNA damage response deficiency are found in U2AF1 S34F expressing 32D cells. In leukemic cell line Molm13 cells, U2AF1 mutation leads to resistance to DNA damaging agents. Accumulation of DNA damage is also found in U2AF1 S34F expressing leukemic cells when treated with DNA damage agent. Finally, in our established hematopoietic-specific U2af1 S34F knock-in mice model, U2AF1 mutation leads to the development of myelodysplastic/myeloproliferative neoplasm (MDS/MPN) and causes DNA damage accumulation in hematopoietic cells. Our study provides evidence that U2AF1 mutation causes DNA damage response deficiency and DNA damage accumulation in hematopoietic cells, and suggests that mutant U2AF1 induced higher ROS production, resistance to DNA damaging agents and increased genomic instability may contribute to poor prognosis of AML patients with U2AF1 mutations.

Alternative splicing of modulatory immune receptors in T lymphocytes: a newly identified and targetable mechanism for anticancer immunotherapy

Alternative splicing (AS) is a mechanism that generates translational diversity within a genome. Equally important is the dynamic adaptability of the splicing machinery, which can give preference to one isoform over others encoded by a single gene. These isoform preferences change in response to the cell's state and function. Particularly significant is the impact of physiological alternative splicing in T lymphocytes, where specific isoforms can enhance or reduce the cells' reactivity to stimuli. This process makes splicing isoforms defining features of cell states, exemplified by CD45 splice isoforms, which characterize the transition from naïve to memory states. Two developments have accelerated the use of AS dynamics for therapeutic interventions: advancements in long-read RNA sequencing and progress in nucleic acid chemical modifications. Improved oligonucleotide stability has enabled their use in directing splicing to specific sites or modifying sequences to enhance or silence particular splicing events. This review highlights immune regulatory splicing patterns with potential significance for enhancing anticancer immunotherapy.

An erythroid-specific lentiviral vector improves anemia and iron metabolism in a new model of XLSA

ABSTRACT

X-linked sideroblastic anemia (XLSA) is a congenital anemia caused by mutations in ALAS2, a gene responsible for heme synthesis. Treatments are limited to pyridoxine supplements and blood transfusions, offering no definitive cure except for allogeneic hematopoietic stem cell transplantation, only accessible to a subset of patients. The absence of a suitable animal model has hindered the development of gene therapy research for this disease. We engineered a conditional Alas2-knockout (KO) mouse model using tamoxifen administration or treatment with lipid nanoparticles carrying Cre-mRNA and conjugated to an anti-CD117 antibody. Alas2-KOBM animals displayed a severe anemic phenotype characterized by ineffective erythropoiesis (IE), leading to low numbers of red blood cells, hemoglobin, and hematocrit. In particular, erythropoiesis in these animals showed expansion of polychromatic erythroid cells, characterized by reduced oxidative phosphorylation, mitochondria's function, and activity of key tricarboxylic acid cycle enzymes. In contrast, glycolysis was increased in the unsuccessful attempt to extend cell survival despite mitochondrial dysfunction. The IE was associated with marked splenomegaly and low hepcidin levels, leading to iron accumulation in the liver, spleen, and bone marrow and the formation of ring sideroblasts. To investigate the potential of a gene therapy approach for XLSA, we developed a lentiviral vector (X-ALAS2-LV) to direct ALAS2 expression in erythroid cells. Infusion of bone marrow (BM) cells with 0.6 to 1.4 copies of the X-ALAS2-LV in Alas2-KOBM mice improved complete blood cell levels, tissue iron accumulation, and survival rates. These findings suggest our vector could be curative in patients with XLSA.

Endogenous retroelements in hematological malignancies: From epigenetic dysregulation to therapeutic targeting

Endogenous retroelements (EREs), which comprise half of the human genome, play a pivotal role in genome dynamics. Some EREs retained the ability to encode proteins, although most degenerated or served as a source for novel genes and regulatory elements during evolution. Despite ERE repression mechanisms developed to maintain genome stability, widespread pervasive ERE activation is observed in cancer including hematological malignancies. Challenging the perception of noncoding DNA as "junk," EREs are underestimated contributors to cancer driver mechanisms as well as antitumoral immunity by providing innate immune ligands and tumor antigens. This review highlights recent progress in understanding ERE co-option events in cancer and focuses on the controversial debate surrounding their causal role in shaping malignant phenotype. We provide insights into the rapidly evolving landscape of ERE research in hematological malignancies and their clinical implications in these cancers.

Somatic mutations and DNA methylation identify a subgroup of poor prognosis within lower-risk myelodysplastic syndromes

Lower risk (LR) myelodysplastic syndromes (MDS) are heterogeneous hematopoietic stem and progenitor disorders caused by the accumulation of somatic mutations in various genes including epigenetic regulators that may produce convergent DNA methylation patterns driving specific gene expression profiles. The integration of genomic, epigenomic, and transcriptomic profiling has the potential to spotlight distinct LR-MDS categories on the basis of pathophysiological mechanisms. We performed a comprehensive study of somatic mutations and DNA methylation in a large and clinically well-annotated cohort of treatment-naive patients with LR-MDS at diagnosis from the EUMDS registry (ClinicalTrials.gov.NCT00600860). Unsupervised clustering analyses identified six clusters based on genetic profiling that concentrate into four clusters on the basis of genome-wide methylation profiling with significant overlap between the two clustering modes. The four methylation clusters showed distinct clinical and genetic features and distinct methylation landscape. All clusters shared hypermethylated enhancers enriched in binding motifs for ETS and bZIP (C/EBP) transcription factor families, involved in the regulation of myeloid cell differentiation. By contrast, one cluster gathering patients with early leukemic evolution exhibited a specific pattern of hypermethylated promoters and, distinctly from other clusters, the upregulation of AP-1 complex members FOS/FOSL2 together with the absence of hypermethylation of their binding motif at target gene enhancers, which is of relevance for leukemic initiation. Among MDS patients with lower-risk IPSS-M, this cluster displayed a significantly inferior overall survival (p < 0.0001). Our study showed that genetic and DNA methylation features of LR-MDS at early stages may refine risk stratification, therefore offering the frame for a precocious therapeutic intervention.

Generation of tumor neoantigens by RNA splicing perturbation

Immunotherapy has revolutionized cancer treatment, but the limited availability of tumor-specific neoantigens still remains a challenge. The potential of alternative mRNA splicing-derived neoantigens as a source of new immunotherapy targets has gained significant attention. Tumors exhibit unique splicing changes and splicing factor mutations which are prevalent in various cancers and play a crucial role in neoantigen production. We present advances in splicing modulation approaches, including small-molecule drugs, decoy and splice-switching antisense oligonucleotides (SSOs), CRISPR, small interfering RNAs (siRNAs), and nonsense-mediated RNA decay (NMD) inhibition, that can be adapted to enhance antitumor immune responses. Finally, we explore the clinical implications of these approaches, highlighting their potential to transform cancer immunotherapy and broaden its efficacy.

[Research progress of iron metabolism and ferroptosis in myeloid neoplasms]

It is reported that iron metabolism and ferroptosis can influence the occurrence and development of myeloid tumors, which can serve as therapeutic targets. Dysregulation of iron metabolism is present in a variety of myeloid neoplasms. The prognosis of acute myeloid leukemia is related to differential expression of molecules related to iron metabolism. The prognosis of myelodysplastic syndrome patients with iron overload is poor. Myeloproliferative neoplasms are often characterized by the coexistence of iron deficiency and erythrocytosis, which can be treated by targeting hepcidin. Myeloid tumor cells are susceptible to oxidative damage caused by the accumulation of reactive oxygen species and are sensitive to ferroptosis. Ferroptosis has anti-tumor effect in acute myeloid leukemia and myelodysplastic syndrome. Targeting ferroptosis can reverse imatinib resistance in chronic myeloid leukemia. This article reviews the characteristics of iron metabolism in the development and progression of myeloid neoplasms, as well as the mechanism of ferroptosis, to provide a basis for the development of new therapeutic strategies.

SF3B1 thermostability as an assay for splicing inhibitor interactions

The spliceosome protein, SF3B1, is associated with U2 snRNP during early spliceosome assembly for pre-mRNA splicing. Frequent somatic mutations in SF3B1 observed in cancer necessitates the characterization of its role in identifying the branchpoint adenosine of introns. Remarkably, SF3B1 is the target of three distinct natural product drugs, each identified by their potent anti-tumor properties. Structural studies indicate that SF3B1 conformational flexibility is functionally important, and suggest that drug binding blocks the transition to a closed state of SF3B1 required for the next stage of spliceosome assembly. This model is confounded, however, by the antagonistic property of an inactive herboxidiene analog. In this study, we established an assay for evaluating the thermostability of SF3B1 present in the nuclear extract preparations employed for in vitro splicing studies, to investigate inhibitor interactions with SF3B1 in a functional context. We show that both active and antagonistic analogs of natural product inhibitors affect SF3B1 thermostability, consistent with binding alone being insufficient to impair SF3B1 function. Surprisingly, SF3B1 thermostability differs among nuclear extract preparations, likely reflecting its conformational status. We also investigated a synthetic SF3B1 ligand, WX-02-23, and found that it increases SF3B1 thermostability and interferes with in vitro splicing by a mechanism that strongly resembles the activity of natural product inhibitors. We propose that altered SF3B1 thermostability can serve as an indicator of inhibitor binding to complement functional assays of their general effect on splicing. It may also provide a means to investigate the factors that influence SF3B1 conformation.

Leukemia-mutated proteins PHF6 and PHIP form a chromatin complex that represses acute myeloid leukemia stemness

Myeloid leukemias are heterogeneous cancers with diverse mutations, sometimes in genes with unclear roles and unknown functional partners. PHF6 and PHIP are two poorly-understood chromatin-binding proteins recurrently mutated in acute myeloid leukemia (AML). PHF6 mutations are associated with poorer outcomes, while PHIP was recently identified as the most common selective mutation in Black patients in AML. Here, we show that PHF6 is a transcriptional repressor that suppresses a stemness gene network, and that PHF6 missense mutations, classified by current clinical algorithms as variants of unknown significance, produce unstable or non-functional protein. We present multiple lines of evidence converging on a critical mechanistic connection between PHF6 and PHIP. We show that PHIP loss phenocopies PHF6 loss, and that PHF6 requires PHIP to occupy chromatin and exert its downstream transcriptional program. Our work unifies PHF6 and PHIP, two disparate leukemia-mutated proteins, into a common functional complex that suppresses AML stemness.

Understanding Human Oncogene Function and Cooperativity in Myeloid Malignancy Using iPSCs

Myeloid malignancies are a spectrum of clonal disorders driven by genetic alterations that cooperatively confer aberrant self-renewal and differentiation of hematopoietic stem and progenitor cells (HSPCs). Induced pluripotent stem cells (iPSCs) can be differentiated into HSPCs and have been widely explored for modeling hematologic disorders and cell therapies. More recently, iPSCs models have been applied to study the origins and pathophysiology of myeloid malignancies, motivated by the appreciation for the differences in human oncogene function and the need for genetically defined models that recapitulate leukemia development. In this review, we will provide a broad overview of the rationale, the challenges, practical aspects, history, and recent advances of iPSC models for modeling myeloid neoplasms. We will focus on the insights into the previously unknown aspects of human oncogene function and cooperativity gained through the use of these models. It is now safe to say that iPSC models are a mainstay of leukemia modeling "toolbox" alongside primary human cells from normal and patient sources.

Perturbation of mRNA splicing in liver cancer: insights, opportunities and challenges

Perturbation of mRNA splicing is commonly observed in human cancers and plays a role in various aspects of cancer hallmarks. Understanding the mechanisms and functions of alternative splicing (AS) not only enables us to explore the complex regulatory network involved in tumour initiation and progression but also reveals potential for RNA-based cancer treatment strategies. This review provides a comprehensive summary of the significance of AS in liver cancer, covering the regulatory mechanisms, cancer-related AS events, abnormal splicing regulators, as well as the interplay between AS and post-transcriptional and post-translational regulations. We present the current bioinformatic approaches and databases to detect and analyse AS in cancer, and discuss the implications and perspectives of AS in the treatment of liver cancer.

Splicing dysregulation: hallmark and therapeutic opportunity in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer characterized by dismal prognosis. Late diagnosis, resistance to chemotherapy, and lack of efficacious targeted therapies render PDAC almost untreatable. Dysregulation of splicing, the process that excises the introns from nascent transcripts, is emerging as a hallmark of PDAC and a possible vulnerability of this devastating cancer. Splicing factors are deregulated in PDAC and contribute to all steps of tumorigenesis, from inflammation-related early events to metastasis and acquisition of chemoresistance. At the same time, splicing dysregulation offers a therapeutic opportunity to target cancer-specific vulnerabilities. We discuss mounting evidence that splicing plays a key role in PDAC and the opportunities that this essential process offers for developing new targeted therapies.

RNA methylation: where to from here for hematologic malignancies?

RNA methylation and the machinery that regulates or "reads" its expression has recently been implicated in the pathogenesis of acute myeloid leukemia (AML) and other hematologic malignancies. Modulation of these epigenetic marks has started to become a reality as several companies around the world seek to leverage this knowledge therapeutically in the clinic. Although the bases of observed activity in AML have been described by numerous groups, the exact context in which these therapies will ultimately be used remains to be properly determined. While context is likely to be of great importance here, a more "global" mechanism of action might allow for more widespread applicability to multiple disease subtypes. In other areas such as the myelodysplastic and other preleukemic syndromes, data remain sparse. Ongoing work is needed to determine whether therapeutic modulation of RNA modifications is a viable and biologically plausible approach in these cases. Regardless of the outcomes, this is an exciting era for "epitranscriptomics" as we navigate a pathway forward. Here, I describe the current knowledge around RNA methylation and hematologic malignancies at the end of 2024 including some of the relevant questions that are yet to be answered.

Diagnosing recipient- vs. donor-derived posttransplant myelodysplastic neoplasm via targeted single-cell mutational profiling

BACKGROUND

Distinguishing donor- vs. recipient-derived myelodysplastic neoplasm (MDS) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is challenging and has direct therapeutical implications.

METHODS

Here, we took a translational approach that we used in addition to conventional diagnostic techniques to resolve the origin of MDS in a 38-year-old patient with acquired aplastic anemia and evolving MDS after first allo-HSCT. Specifically, we used single-cell transcriptional profiling to differentiate between donor- and recipient-derived bone marrow cells and established a strategy that additionally allows identification of cells carrying the MDS-associated U2AF1S34Y variant.

RESULTS

The patient exhibited mixed donor chimerism combined with severely reduced erythropoiesis and dysplastic morphology within the granulocytic and megakaryocytic lineage along with the MDS-associated U2AF1S34Y mutation in the bone marrow. Single-cell transcriptional profiling together with targeted enrichment of the U2AF1S34Y-specific locus further revealed that, while the immune compartment was mainly populated by donor-derived cells, myelopoiesis was predominantly driven by the recipient. Additionally, concordant with recipient-derived MDS, we found that U2AF1S34Y-mutated cells were exclusively recipient derived with X but not Y chromosome-specific gene expression.

CONCLUSION

Our study highlights the clinical potential of integrating high-resolution single-cell techniques to resolve complex cases for personalized treatment decisions.

FUNDING

The study was funded by intramural resources of the Charité - Universitätsmedizin Berlin and the Berlin Institute of Health.

Cancer-associated SF3B1 mutations inhibit mRNA nuclear export by disrupting SF3B1-THOC5 interactions

Mutations in SF3B1 are common in many types of cancer, promoting cancer progression through aberrant RNA splicing. Recently, mRNA nuclear export has been reported to be defective in cells with the SF3B1 K700E mutation. However, the mechanism remains unclear. Our study reveals that the K700E mutation in SF3B1 attenuates its interaction with THOC5, an essential component of the mRNA nuclear export complex THO. Furthermore, the SF3B1 mutation caused reduced binding of THOC5 with some mRNA and inhibited the nuclear export of these mRNAs. Interestingly, overexpression of THOC5 restores the nuclear export of these mRNAs in cells with the SF3B1 K700E mutation. Importantly, other types of cancer-associated SF3B1 mutations also inhibited mRNA nuclear export similarly, suggesting that it is common for cancer-associated SF3B1 mutations to inhibit mRNA nuclear export. Our research highlights the critical role of the THOC5-SF3B1 interaction in the regulation of mRNA nuclear export and provides valuable insights into the impact of SF3B1 mutations on mRNA nuclear export.

Therapeutic strategies targeting aberrant RNA splicing in myeloid malignancies

In recent years, large-scale sequencing efforts have identified targetable driver mutations in haematopoietic stem cells. These efforts have led to the development and approval of nine novel agents for relapsed or refractory acute myelogenous leukaemia (R/R AML). However, despite an expansion in targeted therapies, achieving a durable remission in AML and high-risk myelodysplastic syndrome (HR-MDS) remains a significant challenge, and there is an urgent need for new effective treatments. Modulation of aberrant RNA splicing has emerged as a novel therapeutic approach in myeloid diseases. Aberrant splicing drives dysregulated gene expression that promotes tumourigenesis through increased proliferation and metastatic potential, immune evasion, decreased apoptosis, and chemotherapy resistance. Mutations in spliceosomal components have been identified in numerous cancer subtypes, with mutations in RNA binding proteins SF3B1, SRSF2, U2AF1, and ZRSR2 occurring frequently in AML and in up to 60% of patients with MDS, as well as in chronic myelomonocytic leukaemia and in 10% of patients with chronic lymphocytic leukaemia. In this review, we explore therapeutic strategies targeting aberrant splicing and the potential of these approaches to drive clinical responses.

RNA splicing as a therapeutic target in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a heterogeneous group of hematological disorders and are more commonly found in people over the age of 60. MDS patients exhibit peripheral blood cytopenias and carry an increased risk of disease progression to acute myeloid leukemia (AML). Splicing factor mutations (including genes SF3B1, SRSF2, U2AF1, and ZRSR2) are early events identified in more than 50% of MDS cases. These mutations cause aberrant pre-mRNA splicing and impact MDS pathophysiology. Emerging evidence shows that splicing factor-mutant cells are more sensitive to perturbations targeting the spliceosome, aberrantly spliced genes and/or their regulated molecular pathways. This review summarizes current therapeutic strategies and ongoing efforts targeting splicing factor mutations for the treatment of MDS.

Predicting which subsets of patients with myelodysplastic neoplasms are more likely to progress to overt chronic myelomonocytic leukemia

The boundary between myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML) has been revised in the latest World Health Organization classification of myeloid malignancies. These changes were motivated by the description of a subgroup of MDS patients identified as oligomonocytic chronic myelomonocytic leukemia (OM-CMML) at risk of evolving into overt CMML. Various studies will be reviewed describing the clinical and biological features of MDS patients evolving to CMML. The efforts to discover biomarkers enabling the identification of these patients at the time of MDS diagnosis will be discussed. Finally, the molecular landscape of these patients will be presented with a specific focus on the biallelic inactivation of TET2 in light of its functional impact on hematopoietic stem cells, granule-monocytic differentiation, and its tight interplay with inflammation.

SE-lncRNAs in Cancer: Classification, Subcellular Localisation, Function and Corresponding TFs

Emerging evidence highlights certain long noncoding RNAs (lncRNAs) transcribed from or interacting with super-enhancer (SE) regulatory elements. These lncRNAs, known as SE-lncRNAs, are strongly linked to cancer and regulate cancer progression through multiple interactions with downstream targets. The expression of SE-lncRNAs is controlled by various transcription factors (TFs), and dysregulation of these TFs can contribute to cancer development. In this review, we discuss the characteristics, classification and subcellular distribution of SE-lncRNAs and summarise the role of key TFs in the transcription and regulation of SE-lncRNAs. Moreover, we examine the distinct functions and potential mechanisms of SE-lncRNAs in cancer progression.

Splicing the Difference: Harnessing the Complexity of the Transcriptome in Hematopoiesis

Alternative splicing has long been recognized as a powerful tool to expand the diversity of the transcriptome and the proteome. The study of hematopoiesis, from hematopoietic stem cell maintenance and differentiation into committed progenitors to maturation into functional blood cells, has led the field of stem cell research and cellular differentiation for decades. The importance of aberrant splicing due to mutations in cis has been exemplified in thalassemias, resulting from aberrant expression of β-globin. The simultaneous development of increasingly sophisticated technologies, in particular the combination of multicolor flow cytometric cell sorting with bulk and single-cell sequencing, has provided sophisticated insights into the complex regulation of the blood system. The recognition that mutations in key splicing factors drive myeloid malignancies, in particular myelodysplastic syndromes, has galvanized research into alternative splicing in hematopoiesis and its diseases. In this review, we will update the audience on the exciting novel technologies, highlight alternative splicing events and their regulators with essential functions in hematopoiesis, and provide a high-level overview how splicing factor mutations contribute to hematologic malignancies.

Steering research on mRNA splicing in cancer towards clinical translation

Splicing factors are affected by recurrent somatic mutations and copy number variations in several types of haematologic and solid malignancies, which is often seen as prima facie evidence that splicing aberrations can drive cancer initiation and progression. However, numerous spliceosome components also 'moonlight' in DNA repair and other cellular processes, making their precise role in cancer difficult to pinpoint. Still, few would deny that dysregulated mRNA splicing is a pervasive feature of most cancers. Correctly interpreting these molecular fingerprints can reveal novel tumour vulnerabilities and untapped therapeutic opportunities. Yet multiple technological challenges, lingering misconceptions, and outstanding questions hinder clinical translation. To start with, the general landscape of splicing aberrations in cancer is not well defined, due to limitations of short-read RNA sequencing not adept at resolving complete mRNA isoforms, as well as the shallow read depth inherent in long-read RNA-sequencing, especially at single-cell level. Although individual cancer-associated isoforms are known to contribute to cancer progression, widespread splicing alterations could be an equally important and, perhaps, more readily actionable feature of human cancers. This is to say that in addition to 'repairing' mis-spliced transcripts, possible therapeutic avenues include exacerbating splicing aberration with small-molecule spliceosome inhibitors, targeting recurrent splicing aberrations with synthetic lethal approaches, and training the immune system to recognize splicing-derived neoantigens.

Genomic and transcriptomic profiling of pre- and postneoadjuvant chemotherapy triple negative breast cancer tumors

Our understanding of neoadjuvant treatment with microtubule inhibitors (MTIs) for triple negative breast cancer (TNBC) remains limited. To advance our understanding of the role of breast cancer driver genes' mutational status with pathological complete response (pCR; ypT0/isypN0) prediction and to identify distinct gene sets for MTIs like eribulin and paclitaxel, we carried out targeted genomic (n = 50) and whole transcriptomic profiling (n = 64) of TNBC tumor samples from the Japan Breast Cancer Research Group 22 (JBCRG-22) clinical trial. Lower PIK3CA, PTEN, and HRAS mutations were found in homologous recombination deficiency (HRD)-high (HRD score ≥ 42) tumors with higher pCR rates. When HRD-high tumors were stratified by tumor BRCA mutation status, the pCR rates in BRCA2-mutated tumors were higher (83% vs. 36%). Transcriptomic profiling of TP53-positive tumors identified downregulation of FGFR2 (false discovery rate p value = 2.07e-7), which was also the only common gene between HRD-high and -low tumors with pCR/quasi-pCR treated with paclitaxel and eribulin combined with carboplatin, respectively. Differential enrichment analysis of the HRD-high group posttreatment tumors revealed significant correlation (p = 0.006) of the glycan degradation pathway. FGFR2 expression and the differentially enriched pathways play a role in the response and resistance to MTIs containing carboplatin treatment in TNBC patients.

SRSF2 safeguards efficient transcription of DNA damage and repair genes

The serine-/arginine-rich splicing factor 2 (SRSF2) plays pivotal roles in pre-mRNA processing and gene transcription. Recurrent mutations, particularly a proline-to-histidine substitution at position 95 (P95H), are common in neoplastic diseases. Here, we assess SRSF2's diverse functions in squamous cell carcinoma. We show that SRSF2 deletion or homozygous P95H mutation both cause extensive DNA damage leading to cell-cycle arrest. Mechanistically, SRSF2 regulates efficient bi-directional transcription of DNA replication and repair genes, independent from its function in splicing. Further, SRSF2 haploinsufficiency induces DNA damage without halting the cell cycle. Exposing mouse skin to tumor-promoting carcinogens enhances the clonal expansion of heterozygous Srsf2 P95H epidermal cells but unexpectedly inhibits tumor formation. To survive carcinogen treatment, Srsf2 P95H+/- cells undergo substantial transcriptional rewiring and restore bi-directional gene expression. Thus, our study underscores SRSF2's importance in regulating transcription to orchestrate the cell cycle and the DNA damage response.

Cancer-associated SF3B1 mutation K700E causes widespread changes in U2/branchpoint recognition without altering splicing

Myelodysplastic syndromes and other cancers are often associated with mutations in the U2 snRNP protein SF3B1. Common SF3B1 mutations, including K700E, disrupt SF3B1 interaction with the protein SUGP1 and induce aberrant activation of cryptic 3' splice sites (ss), presumably resulting from aberrant U2/branch site (BS) recognition by the mutant spliceosome. Here, we apply the new method of U2 IP-seq to profile BS binding across the transcriptome of K562 leukemia cells carrying the SF3B1 K700E mutation. For cryptic 3' ss activated by K700E, we identify their associated BSs and show that they are indeed shifted from the WT sites. Unexpectedly, we also identify thousands of additional changes in BS binding in the mutant cells that do not alter 3' ss choice. These new BS are usually very close to the natural sites, occur upstream or downstream, and either exhibit stronger base-pairing potential with U2 snRNA or are adjacent to stronger polypyrimidine tracts than the WT sites. The widespread imprecision in BS recognition induced by K700E with limited changes in 3' ss selection supports a positive role for SUGP1 in early BS choice and expands the physiological consequences of this oncogenic mutation.

Aberrant pre-mRNA processing in cancer

Dysregulation of the flow of information from genomic DNA to RNA to protein occurs within all cancer types. In this review, we described the current state of understanding of how RNA processing is dysregulated in cancer with a focus on mutations in the RNA splicing factor machinery that are highly prevalent in hematologic malignancies. We discuss the downstream effects of these mutations highlighting both individual genes as well as common pathways that they perturb. We highlight examples of how alterations in RNA processing have been harnessed for therapeutic intent as well as to promote the selective toxicity of cancer cells.

Targeted therapies for myelodysplastic syndromes/neoplasms (MDS): current landscape and future directions

INTRODUCTION

Myelodysplastic syndromes/neoplasms (MDS) are a heterogeneous group of hematologic malignancies that are stratified into high-risk (HR-MDS) and low-risk (LR-MDS) categories. Until recently, LR-MDS has been typically managed by supportive measures and erythropoiesis-stimulating agents (ESAs); whereas management of HR-MDS typically included hypomethylating agents and allogeneic hematopoietic stem cell transplant. However, the limited rates and durations of response observed with these interventions prompted the search for targeted therapies to improve the outcomes among patients with MDS.

AREAS COVERED

Here, we review the current landscape of targeted therapies in MDS. These include pyruvate kinase and hypoxia-inducible factor (HIF) activators; TGF-beta, telomerase, BCL2 and isocitrate dehydrogenase (IDH) inhibitors; as well as novel approaches targeting inflammation, pyroptosis, immune evasion, and RNA splicing machinery.

EXPERT OPINION

This review highlights the progress and challenges in MDS treatment. Despite some promising results, many therapies remain in early development or have faced setbacks, emphasizing the need for a more comprehensive understanding of the disease's pathobiology. Continued research into targeted therapies, homogenous clinical trial designs, as well as increased incorporation of molecular prognostic tools and artificial intelligence into trial design are essential for developing effective treatments for MDS and improving patient outcomes.

TERT upregulation promotes cell proliferation via degradation of p21 and increases carcinogenic potential

Telomerase reverse transcriptase (TERT) gene aberration is detectable in >80% of cases with hepatocellular carcinoma (HCC). TERT reactivation is essential for cellular immortalization because it stabilizes telomere length, although the role of TERT in hepatocarcinogenesis remains unelucidated. To elucidate the significance of aberrant TERT expression in hepatocytes in inflammation-associated hepatocarcinogenesis, we generated Alb-Cre;TertTg mice, which overexpress TERT in the liver and examined their phenotype during chronic inflammation. Based on transcriptome data from the liver tissue of Alb-Cre;TertTg mice, we examined the role of TERT in hepatocarcinogenesis in vitro. We also evaluated the relationship between TERT and cell-cycle-related molecules, including p21, in HCC samples. The liver tumor development rate was increased by TERT overexpression during chronic inflammation, especially in the absence of p53 function. Gene set enrichment analysis of liver tissues revealed that gene sets related to TNF-NFκB signaling, cell cycle, and apoptosis were upregulated in Alb-Cre;TertTg liver. A luciferase reporter assay and immunoprecipitation revealed that TERT interacted with NFκB p65 and enhanced NFκB promoter activity. On the other hand, TERT formed protein complexes with p21, cyclin A2, and cyclin E and promoted ubiquitin-mediated degradation of p21, specifically in the G1 phase. In the clinical HCC samples, TERT was highly expressed but p21 was conversely downregulated, and TERT expression was associated with the upregulation of molecules related to the cell cycle. Taken together, the aberrant upregulation of TERT increased NFκB promoter activity and promoted cell cycle progression via p21 ubiquitination, leading to hepatocarcinogenesis. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

UBXN9 inhibits the RNA exosome function to promote T cell control of liver tumorigenesis

BACKGROUND AND AIMS

Liver tumorigenesis encompasses oncogenic activation and self-adaptation of various biological processes in premalignant hepatocytes to circumvent the pressure of cellular stress and host immune control. Ubiquitin regulatory X domain-containing proteins (UBXNs) participate in the regulation of certain signaling pathways. However, whether UBXN proteins function in the development of liver cancer remains unclear.

APPROACH AND RESULTS

Here, we demonstrated that UBXN9 (Alveolar Soft Part Sarcoma Chromosomal Region Candidate Gene 1 Protein/Alveolar Soft Part Sarcoma Locus) expression was decreased in autochthonous oncogene-induced mouse liver tumors and ~47.7% of human HCCs, and associated with poor prognosis in patients with HCC. UBXN9 attenuated liver tumorigenesis induced by different oncogenic factors and tumor growth of transplanted liver tumor cells in immuno-competent mice. Mechanistically, UBXN9 significantly inhibited the function of the RNA exosome, resulting in increased expression of RLR-stimulatory RNAs and activation of the retinoic acid-inducible gene-I-IFN-Ι signaling in tumor cells, and hence potentiated T cell recruitment and immune control of tumor growth. Abrogation of the CD8 + T cell response or inhibition of tumor cell retinoic acid-inducible gene-I signaling efficiently counteracted the UBXN9-mediated suppression of liver tumor growth.

CONCLUSIONS

Our results reveal a modality in which UBXN9 promotes the stimulatory RNA-induced retinoic acid-inducible gene-I-interferon signaling that induces anti-tumor T cell response in liver tumorigenesis. Targeted manipulation of the UBXN9-RNA exosome circuit may have the potential to reinstate the immune control of liver tumor growth.

Challenges in Therapeutically Targeting the RNA-Recognition Motif

The RNA recognition motif (RRM) is the most common RNA binding domain found in the human proteome. RRM domains provide RNA-binding proteins with sequence specific RNA recognition allowing them to participate in RNA-centric processes such as mRNA maturation, translation initiation, splicing, and RNA degradation. They are drivers of various diseases through overexpression or mutation, making them attractive therapeutic targets and addressing these proteins through their RRM domains with chemical compounds is gaining ever more attention. However, it is still very challenging to find selective and potent RNA-competitors due to the small size of the domain and high structural conservation of its RNA binding interface. Despite these challenges, a selection of compounds has been reported for several RRM containing proteins, but often with limited biophysical evidence and low selectivity. A solution to selectively targeting RRM domains might be through avoiding the RNA-binding surface altogether, but rather look for composite pockets formed with other proteins or for protein-protein interaction sites that regulate the target's activity but are less conserved. Alternative modalities, such as oligonucleotides, peptides, and molecular glues, are exciting new approaches to address these challenging targets and achieve the goal of therapeutic intervention at the RNA regulatory level.

Distinct mutation features and its clinical significance in myelodysplastic syndromes with normal karyotype

Myelodysplastic syndromes (MDS) is a highly heterogeneous myeloid neoplastic disease, which needs personalized evaluation and therapy. To analyze the features and significance of gene mutations for MDS patients with normal karyotype (NK) at diagnosis, targeted sequencing was conducted on 616 MDS patients with NK, alongside 457 MDS cases with abnormal karyotype (AK). The results showed that the incidence of somatic mutation reached 70.3% and 83.8% in the NK and AK group, respectively. Initial mutation including ASXL1, DNMT3A and TET2 were common in NK group, which is the same as AK group. Some karyotype-associated gene mutations, such as TP53 and U2AF1, were relatively rare in NK group. Moreover, 34 out of 91 samples who progressed to acute myeloid leukemia (AML) underwent repeat sequencing during follow-up. 25 cases were checked out with newly emerged mutations. The AML-associated genetic alterations mainly involved with active signaling and transcription factors. In patients with NK, serial targeted sequencing was employed for minimal residual disease (MRD) monitoring, indicating the efficacy and relapse of the patients. In summary, MDS with NK showed distinct mutation features from those with AK. High-frequency gene mutations together with the mutational evolution suggested the diagnostic and monitoring significance of next generation sequencing for NK-MDS.

Alternative Splicing: A Potential Therapeutic Target in Hematological Malignancies

Leukemia represents the most prevalent malignancy in children, constituting 30% of childhood cancer cases, with acute lymphoblastic leukemia (ALL) being particularly heterogeneous. This paper explores the role of alternative splicing in leukemia, highlighting its significance in cancer development and progression. Aberrant splicing is often driven by mutations in splicing-factor genes, which can lead to the production of variant proteins that contribute to oncogenesis. The spliceosome, a complex of small nuclear RNAs and proteins, facilitates RNA splicing, a process critical for generating diverse mRNA and protein products from single genes. Mutations in splicing factors, such as U2AF1, SF3B1, SRSF2, ZRSR2, and HNRNPH1, are frequently observed across various hematological malignancies and are associated with poor prognosis and treatment resistance. This research underscores the necessity of understanding the mechanisms of RNA splicing dysregulation in order to develop targeted therapies to correct these aberrant processes, thereby improving outcomes for patients with leukemia and related disorders.

Going Rogue: Mechanisms, Regulation, and Roles of Mutationally Activated Gα in Human Cancer

G protein-coupled receptors (GPCRs) couple to heterotrimeric G proteins, comprised of α and βγ subunits, to convert extracellular signals into activation of intracellular signaling pathways. Canonically, GPCR-mediated activation results in the exchange of GDP for GTP on G protein α subunits (Gα) and the dissociation of Gα-GTP and G protein βγ subunits (Gβγ), both of which can regulate a variety of signaling pathways. Hydrolysis of bound GTP by Gα returns the protein to Gα-GDP and allows reassociation with Gβγ to reform the inactive heterotrimer. Naturally occurring mutations in Gα have been found at conserved glutamine and arginine amino acids that disrupt the canonical G protein cycle by inhibiting GTP hydrolysis, rendering these mutants constitutively active. Interestingly, these dysregulated Gα mutants are found in many different cancers due to their ability to sustain aberrant signaling without a need for activation by GPCRs. This review will highlight an increased recognition of the prevalence of such constitutively activating Gα mutations in cancers and the signaling pathways activated. In addition, we will discuss new knowledge regarding how these constitutively active Gα are regulated, how different mutations are biochemically distinct, and how mutationally activated Gα are unique compared with GPCR-activated Gα Lastly, we will discuss recent progress in developing inhibitors directly targeting constitutively active Gα mutants. SIGNIFICANCE STATEMENT: Constitutively activating mutations in G protein α subunits (Gα) widely occur in and contribute to the development of many human cancers. To develop ways to inhibit dysregulated, oncogenic signaling by these mutant Gα, it is crucial to better understand mechanisms that lead to constitutive Gα activation and unique mechanisms that regulate mutationally activated Gα in cells. The prevalence of activating mutations in Gα in various cancers makes Gα proteins compelling targets for the development of therapeutics.

Comprehensive analysis of a necroptosis-associated diagnostic signature for myelodysplastic syndromes based on single-cell RNA-seq and bulk RNA-seq

BACKGROUND

Myelodysplastic syndromes (MDS) are heterogeneous and clonal hematological disorders. The role and mechanism of necroptosis in MDS remain poorly understood.

METHODS

mRNA expression profiles and single-cell RNA-sequencing (scRNA-seq) data were sourced from the GEO database. ScRNA-seq data were processed using the "Seurat" package. After cell annotation, necroptosis-related scores (NRscores) for each cell were calculated using the "UCell" package. Differentially expressed genes (DEGs) and their associated biological functions in NRscore-related cell populations were identified. Additionally, DEGs and necroptosis-related genes (DE-NRGs) between MDS patients and healthy controls were identified. Consensus clustering was employed to classify MDS patients into distinct subclusters based on DE-NRGs. The biological functions and immune characteristics of these classifications were analyzed. Prognostic gene signatures were determined using LASSO and SVM-RFE analyses, and a nomogram was constructed based on the prognostic gene signature.

RESULTS

A total of 12 cell types were identified in MDS and healthy controls. NRscore was found to be elevated in monocytes and common lymphoid precursors (CLPs). Enrichment analysis revealed that monocytes and CLPs with high NRscore were associated with mitochondria-related and immune-related pathways. Eleven DEGs in monocytes and CLPs between MDS patients and healthy controls were identified. Additionally, 13 DE-NRGs were identified from 951 DEGs between MDS and healthy controls. MDS patients were classified into two distinct subclusters based on these 13 DE-NRGs, revealing several immune-related processes and signaling pathways. Differences in immune subpopulations between the two subclusters were observed. A necroptosis-related diagnostic gene signature (IRF9, PLA2G4A, MLKL, BAX, JAK2, and STAT3) was identified as predictive of MDS prevalence.

CONCLUSION

Necroptosis plays a role in MDS progression by inducing inflammation. A novel necroptotic gene signature has been developed to distinguish and diagnose MDS at early stages of the disease.

Prognostic impact of next-generation sequencing on myelodysplastic syndrome: A single-center experience

Myelodysplastic syndromes (MDS) are clinically heterogeneous disorders characterized by peripheral blood cytopenias, poor differentiation, clonal hematopoiesis, and increased risk of developing acute myeloid leukemia (AML). While somatic mutations do not currently feature in prognostic scoring systems, they may impact the clinical phenotype. In recent years, next-generation sequencing (NGS) has enabled the opportunity to identify an increasing number of genetic abnormalities, including recurrent modifications in the TP53, DNMT3A, NRAS, NPM1, RUNX1, and FLT3 genes. Bone marrow aspirate samples of 56 patients with MDS were investigated for mutations using NGS. We compared the relationship between gene mutation status and laboratory characteristics, such as certain cytopenias, the revised international prognostic scoring system, MDS subtypes, karyotypes, AML development, and overall survival. Twenty-one genes were found to have gene mutations, including ASXL1, TET2, SRSF2, EZH2, CSF3R, NRAS, ETV6, SETBP1, RUNX1, DDX41, U2AF1, JAK2, FLT3ITD, SF3B1, DNAMT3A, PHF6, TP53, CEBPA, CBL, IDH2, and GATA2. At least one point mutation occurred in 64.2% of all patients, including 58.3% of those with normal cytogenetics. Thrombocytopenia (P = .016), anemia (P = .018), decreased overall survival (P = .017), and increased AML transformation (P = .023) have been revealed to be linked to non-SF3B1 mutations. MDS are frequently associated with somatic point mutations. According to early findings, NGS panels are extremely effective instruments that provide an entirely new viewpoint on the disease for particular individuals. Future prognostications will depend more on NGS because those who exhibit normal cytogenetics may additionally have gene mutations.

Helicase-assisted continuous editing for programmable mutagenesis of endogenous genomes

Deciphering the context-specific relationship between sequence and function is a major challenge in genomics. Existing tools for inducing locus-specific hypermutation and evolution in the native genome context are limited. Here we present a programmable platform for long-range, locus-specific hypermutation called helicase-assisted continuous editing (HACE). HACE leverages CRISPR-Cas9 to target a processive helicase-deaminase fusion that incurs mutations across large (>1000-base pair) genomic intervals. We applied HACE to identify mutations in mitogen-activated protein kinase kinase 1 (MEK1) that confer kinase inhibitor resistance, to dissect the impact of individual variants in splicing factor 3B subunit 1 (SF3B1)-dependent missplicing, and to evaluate noncoding variants in a stimulation-dependent immune enhancer of CD69. HACE provides a powerful tool for investigating coding and noncoding variants, uncovering combinatorial sequence-to-function relationships, and evolving new biological functions.

mRNA-Based Cancer Vaccines: Advancements and Prospects

The success of mRNA COVID-19 vaccines has reinvigorated research and interest in mRNA-based cancer vaccines. Despite promising results in clinical trials, therapeutic mRNA-based cancer vaccines have not yet been approved for human use. These vaccines are designed to trigger tumor regression, establish enduring antitumor memory, and mitigate adverse reactions. However, challenges such as tumor-induced immunosuppression and immunoresistance significantly hinder their application. Here, we provide an overview of the recent advances of neoantigen discovery and delivery systems for mRNA vaccines, focusing on improving clinical efficacy. Additionally, we summarize the recent clinical advances involving mRNA cancer vaccines and discuss prospective strategies for overcoming immuneresistance.

Molecular impact of mutations in RNA splicing factors in cancer

Somatic mutations in genes encoding components of the RNA splicing machinery occur frequently in multiple forms of cancer. The most frequently mutated RNA splicing factors in cancer impact intronic branch site and 3' splice site recognition. These include mutations in the core RNA splicing factor SF3B1 as well as mutations in the U2AF1/2 heterodimeric complex, which recruits the SF3b complex to the 3' splice site. Additionally, mutations in splicing regulatory proteins SRSF2 and RBM10 are frequent in cancer, and there has been a recent suggestion that variant forms of small nuclear RNAs (snRNAs) may contribute to splicing dysregulation in cancer. Here, we describe molecular mechanisms by which mutations in these factors alter splice site recognition and how studies of this process have yielded new insights into cancer pathogenesis and the molecular regulation of splicing. We also discuss data linking mutant RNA splicing factors to RNA metabolism beyond splicing.

The Impact of Spliceosome Inhibition in SF3B1-Mutated Uveal Melanoma

Purpose

Unfortunately, treatment of patients with uveal melanoma (UM) with metastatic disease is limited. Twenty percent of patients with UM harbor a mutation in the splicing factor gene SF3B1, suggesting that aberrant spliceosome function plays a vital role in tumorigenesis. Splicing inhibitors exploit the preferential sensitivity of spliceosome-compromised leukemic cells to these compounds.

Methods

We studied the effect of the splicing inhibitor E7107 using two UM cell lines and ex vivo cultured SF3B1- and BAP1-mutated primary UM tumor slices. These UM cell lines and ex vivo tumor slices were exposed for 24 hours to different concentrations of E7107. Tumor slices were stained with hematoxylin and eosin (H&E) and incubated with BAP1, MelanA, MIB-1, and caspase-3 antisera.

Results

The E7107-exposed UM cell lines exhibited decreased cell viability and increased apoptosis, with the greatest effect on SF3B1-mutated UM cells. A similar effect on UM tumor slices was observed upon exposure to E7107. Additionally, RNA was isolated for differential isoform expression analysis. No significant difference in isoform usage was found genome-wide. However, specific genes were differentially expressed after E7107 treatment in the SF3B1-mutated samples. Moreover, E7107 had the greatest effect on intron retention.

Conclusions

This study indicates/suggests that mutated SF3B1 UM cells are more sensitive to the splicing inhibitor E7107 than wild-type SF3B1 UM cells.

Clonal hematopoiesis and hematological malignancy

Clonal hematopoiesis (CH), the expansion of hematopoietic stem cells and their progeny driven by somatic mutations in leukemia-associated genes, is a common phenomenon that rises in prevalence with advancing age to affect most people older than 70 years. CH remains subclinical in most carriers, but, in a minority, it progresses to a myeloid neoplasm, such as acute myeloid leukemia, myelodysplastic syndrome, or myeloproliferative neoplasm. Over the last decade, advances in our understanding of CH, its molecular landscape, and the risks associated with different driver gene mutations have culminated in recent developments that allow for a more precise estimation of myeloid neoplasia risk in CH carriers. In turn, this is leading to the development of translational and clinical programs to intercept and prevent CH from developing into myeloid neoplasia. Here, we give an overview of the spectrum of CH driver mutations, what is known about their pathophysiology, and how this informs the risk of incident myeloid malignancy.

Identification of BAY61-3606 Derivatives With Improved Activity in Splicing Modulation That Induces Inclusion of Cassette Exons Similar to the Splicing Factor 3B Subunit 1 Mutation

Splicing modulation by a small compound offers therapeutic potential for diseases caused by splicing abnormality. However, only a few classes of compounds that can modulate splicing have been identified. We previously identified BAY61-3606, a multiple kinase inhibitor, as a compound that relaxes the splicing fidelity at the 3' splice site recognition. We have also reported the synthesis of derivatives of BAY61-3606. In this study, we tested those compounds for their splicing modulation capabilities and identified two contrasting compounds. These compounds were further investigated for their effects on the whole transcriptome, and analysis of changes in transcription and splicing revealed that the highly active derivative in the splicing reporter assay also showed significantly higher activity in modulating the splicing of endogenously expressed genes. Particularly, cassette exon inclusion was highly upregulated by this compound, and clustering analysis revealed that these effects resembled those in splicing factor 3b subunit 1 (SF3B1) K700E mutant cells but contrasted with those of the splicing inhibitor H3B-8800. Additionally, a group of serine/arginine-rich (SR) protein genes was identified as representatively affected, likely via modulation of poison exon inclusion. This finding could guide further analysis of the mode of action of these compounds on splicing, which could be valuable for developing drugs for diseases associated with splicing abnormalities.

Cancer-associated SF3B1-K700E mutation controls immune responses by regulating Treg function via aberrant Anapc13 splicing

Recurrent somatic mutations in spliceosome factor 3b subunit 1 (SF3B1) are identified in hematopoietic malignancies, with SF3B1-K700E being the most common one. Here, we show that regulatory T cell (Treg)-specific expression of SF3B1-K700E (Sf3b1K700Efl/+/Foxp3YFP-Cre) results in spontaneous autoimmune phenotypes. CD4+ T cells from Sf3b1K700Efl/+/Foxp3YFP-Cre mice display defective Treg differentiation and inhibitory function, which is demonstrated by failed prevention of adoptive transfer colitis by Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs. Mechanically, SF3B1-K700E induces an aberrant splicing event that results in reduced expression of a cell proliferation regulator Anapc13 due to the insertion of a 231-base pair DNA fragment to the 5' untranslated region. Forced expression of the Anapc13 gene restores the differentiation and ability of Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs to prevent adoptive transfer colitis. In addition, acute myeloid leukemia grows faster in aged, but not young, Sf3b1K700Efl/+/Foxp3YFP-Cre mice compared to Foxp3YFP-Cre mice. Our results highlight the impact of cancer-associated SF3B1 mutation on immune responses, which affect cancer development.

U2AF1 S34F enhances tumorigenic potential of lung cells by exhibiting synergy with KRAS mutation and altering response to environmental stress

Although U2AF1 S34F is a recurrent splicing factor mutation in lung adenocarcinoma (ADC), U2AF1 S34F alone is insufficient for producing tumors in previous models. Because lung ADCs with U2AF1 S34F frequently have co-occurring KRAS mutations and smoking histories, we hypothesized that tumor-forming potential arises from U2AF1 S34F interacting with oncogenic KRAS and environmental stress. To elucidate the effect of U2AF1 S34F co-occurring with a second mutation, we generated human bronchial epithelial cells (HBEC3kt) with co-occurring U2AF1 S34F and KRAS G12V . Transcriptome analysis revealed that co-occurring U2AF1 S34F and KRAS G12V differentially impacts inflammatory, cell cycle, and KRAS pathways. Subsequent phenotyping found associated suppressed cytokine production, increased proliferation, anchorage-independent growth, and tumors in mouse xenografts. Interestingly, HBEC3kts harboring only U2AF1 S34F display increased splicing in stress granule protein genes and viability in cigarette smoke concentrate. Our results suggest that U2AF1 S34F may potentiate transformation by granting precancerous cells survival advantage in environmental stress, permitting accumulation of additional mutations like KRAS G12V , which synergize with U2AF1 S34F to transform the cell.

Prognostic impact of DTA mutation and co-occurring mutations in patients with myelodysplastic syndrome

OBJECTIVE

To evaluate the frequency and prognostic significance of DTA (DNMT3A、TET2、ASXL1) gene mutation and co-occurring mutations in patients with myelodysplastic syndrome (MDS).

METHODS

The clinical data of 102 newly diagnosed MDS patients who accepted Next Generation Sequencing (NGS) was retrospectively analyzed. According to whether the patients had DTA gene mutation, the patients were divided into DTA mutated (DTA-mut) group and wild type (DTA-wt) group, and the relationship between gene mutation and clinical characteristics and prognosis was analyzed.

RESULTS

Among the 102 MDS patients, 96% (98/102) presented with mutation, while the mean number of mutations was 3.04 mutations/patient. DTA-mut was detected in 56.9% (58/102) patients. The most frequent co-mutated genes in DTA-mut group were SF3B1 (25.8%), RUNX1 (24.1%), U2AF1 (18.9%), SRSF2, EZH2, SETBP1 (17.2%), STAG2 (15.5%), IDH2 (12.1%) and BCOR, CBL (10.3%). The two groups showed no significant differences in ages, blood parameters, bone marrow blasts, WHO 2022 classification, IPSS-R risk category and rate of conversion to leukemia. Compared with the DTA-wt group, the mutation frequency of RUNX1 was higher (P = 0.02), while mutation frequency of TP53 was lower (P = 0.001) and the mutation frequency of ≥ 3 co-mutated genes was higher in DTA-mut group (P = 0.00). Survival analysis showed that the overall survivals (OS) of DTA-mut patients was significantly inferior to that of DTA-wt patients (P = 0.0332). According to IPSS-R classification, a statistically significant difference in OS was only observed in higher risk (IPSS-R > 3.5) group (P = 0.0058). In the context of DTA mutation, the OS of patients with RUNX1 mutation was shorter than that of patients without RUNX1 mutation significantly (P = 0.0074). The OS of patients with SF3B1 mutation was longer than that of patients without SF3B1 mutation, but there was no statistical difference (P = 0.0827). DTA mutations were not independent prognostic factors when DTA and co-mutated genes with frequency > 10% were considered in Cox regression model (P = 0.329). However, multivariate analysis confirmed an independently adverse prognosis of RUNX1 co-mutation (P = 0.042, HR = 2.426, 95% CI:1.031-5.711) in DTA-mut cohort. Moreover, our multivariable analysis suggests that SRSF2-mut was an independent poor prognostic factor for all MDS patients (P = 0.047), but lost significance (P = 0.103) for DTA-mut patients.

CONCLUSIONS

DTA mutations are frequently observed in patients with MDS, often accompanied by genes involved in RNA splicing and transcription factors like SF3B1 and RUNX1. DTA and concomitant mutations affect prognosis in MDS patients and RUNX1 was identified as an independent poor prognostic factor in patients with DTA mutations.

How we diagnose Myelodysplastic syndromes

The Myelodysplastic syndromes (MDS) are a heterogenous group of clonal bone marrow (BM) stem cell myeloid neoplasms, characterized by ineffective hematopoiesis that results in dysplasia in hematopoietic cells and peripheral cytopenias, especially anemia, and a propensity to leukemic transformation. The suspicion of MDS is raised by a typical but not specific clinical picture and routine laboratory findings, but the gold standard for MDS diagnosis is still BM examination with the presence of uni-or multi-lineage dysplasia and increased blast percentage, together with exclusion of other reasons. Cytogenetics is also an essential part of the diagnostic and prognostic processes. Flow cytometry and full genetic characterization are helpful but not mandatory for MDS diagnosis. This review summarizes the current steps of diagnostic approach for a patient suspected of having MDS. We also express our hopes that within the near future, non-invasive technologies, especially digital and peripheral blood genetics, will mature and be introduced into practice.

Identification of novel myelodysplastic syndromes prognostic subgroups by integration of inflammation, cell-type composition, and immune signatures in the bone marrow

Mutational profiles of myelodysplastic syndromes (MDS) have established that a relatively small number of genetic aberrations, including SF3B1 and SRSF2 spliceosome mutations, lead to specific phenotypes and prognostic subgrouping. We performed a multi-omics factor analysis (MOFA) on two published MDS cohorts of bone marrow mononuclear cells (BMMNCs) and CD34 + cells with three data modalities (clinical, genotype, and transcriptomics). Seven different views, including immune profile, inflammation/aging, retrotransposon (RTE) expression, and cell-type composition, were derived from these modalities to identify the latent factors with significant impact on MDS prognosis. SF3B1 was the only mutation among 13 mutations in the BMMNC cohort, indicating a significant association with high inflammation. This trend was also observed to a lesser extent in the CD34 + cohort. Interestingly, the MOFA factor representing the inflammation shows a good prognosis for MDS patients with high inflammation. In contrast, SRSF2 mutant cases show a granulocyte-monocyte progenitor (GMP) pattern and high levels of senescence, immunosenescence, and malignant myeloid cells, consistent with their poor prognosis. Furthermore, MOFA identified RTE expression as a risk factor for MDS. This work elucidates the efficacy of our integrative approach to assess the MDS risk that goes beyond all the scoring systems described thus far for MDS.

Altered RNA export by SF3B1 mutants confers sensitivity to nuclear export inhibition

SF3B1 mutations frequently occur in cancer yet lack targeted therapies. Clinical trials of XPO1 inhibitors, selinexor and eltanexor, in high-risk myelodysplastic neoplasms (MDS) revealed responders were enriched with SF3B1 mutations. Given that XPO1 (Exportin-1) is a nuclear exporter responsible for the export of proteins and multiple RNA species, this led to the hypothesis that SF3B1-mutant cells are sensitive to XPO1 inhibition, potentially due to altered splicing. Subsequent RNA sequencing after XPO1 inhibition in SF3B1 wildtype and mutant cells showed increased nuclear retention of RNA transcripts and increased alternative splicing in the SF3B1 mutant cells particularly of genes that impact apoptotic pathways. To identify novel drug combinations that synergize with XPO1 inhibition, a forward genetic screen was performed with eltanexor treatment implicating anti-apoptotic targets BCL2 and BCLXL, which were validated by functional testing in vitro and in vivo. These targets were tested in vivo using Sf3b1K700E conditional knock-in mice, which showed that the combination of eltanexor and venetoclax (BCL2 inhibitor) had a preferential sensitivity for SF3B1 mutant cells without excessive toxicity. In this study, we unveil the mechanisms underlying sensitization to XPO1 inhibition in SF3B1-mutant MDS and preclinically rationalize the combination of eltanexor and venetoclax for high-risk MDS.