YBX1 mediates translation of oncogenic transcripts to control cell competition in AML

The evolving landscape of epigenetic target molecules and therapies in myeloid cancers: focus on acute myeloid leukemia and myeloproliferative neoplasms

Research on myeloid neoplasms, a field that has been driving scientific advances in cancer for over 50 years, has yielded many discoveries that have fundamentally reshaped our understanding of cancer biology. These insights, often the product of leukemia research, have been instrumental in developing more mechanism-based treatments in the early 2000s [1]. Recognizing epigenetic dysregulation as a common disease mechanism in myeloid cancers has been groundbreaking regarding recent treatment developments that exploit chromatin-based oncogenic mechanisms. In the case of acute myeloid leukemia (AML), sequencing studies aimed at assessing the complement of genetic alterations demonstrated that more than 60% of AML cases harbored disease-driving mutations in epigenetic regulators. This high prevalence underscores the importance of epigenetic dysregulation in AML pathogenesis [2, 3]. Chromatin regulators commonly control disease-specific transcriptional programs, making them attractive therapeutic targets to manipulate neoplastic gene expression programs, particularly in myeloid neoplasms. Several drugs targeting epigenetic mechanisms and exploiting myeloid disease-specific dependencies have recently been approved for treating myeloid neoplasms. Many additional drugs are currently being investigated in clinical trials, and numerous new compound developments are being studied in preclinical studies. This manuscript will review (1) chromatin-based disease mechanisms, such as DNA methylation, chromatin regulatory complexes, and histone modifications, currently investigated for therapeutic exploitation in myeloid malignancies, and (2) therapeutic developments already approved or investigated for treating these diseases.

The m5C methyltransferase NSUN2 promotes progression of acute myeloid leukemia by regulating serine metabolism

Acute myeloid leukemia (AML) is one of the most prevalent heterogeneous hematologic malignancies with a complicated etiology. RNA post-transcriptional modifications have been linked to the incidence and progression of AML, while the detailed mechanism remains to be elucidated. In this study, we find that NOP2/Sun domain family member 2 (NSUN2), a methyltransferase of 5-methylcytosine (m5C) RNA methylation, is upregulated in AML and predicts a poor prognosis for patients with AML. Knockdown of NSUN2 in AML cells inhibits proliferation and colony formation and promotes apoptosis. Depletion of NSUN2 in AML mice reduces the tumor burden and prolongs survival. Mechanistically, NSUN2 promotes the expression of phosphoglycerate dehydrogenase (PHGDH) and serine hydroxymethyltransferase 2 (SHMT2), two key enzymes in the serine/glycine biosynthesis pathway, by stabilizing the corresponding mRNAs through regulation of m5C modifications. Overall, our findings demonstrate a critical role of NSUN2 in AML development and highlight the therapeutic potential of targeting the NSUN2/m5C axis for the treatment of this cancer.

m6A/IGF2BP3-driven serine biosynthesis fuels AML stemness and metabolic vulnerability

Metabolic reprogramming of amino acids represents a vulnerability in cancer cells, yet the mechanisms underlying serine metabolism in acute myeloid leukemia (AML) and leukemia stem/initiating cells (LSCs/LICs) remain unclear. Here, we identify RNA N6-methyladenosine (m6A) modification as a key regulator of serine biosynthesis in AML. Using a CRISPR/Cas9 screen, we find that depletion of m6A regulators IGF2BP3 or METTL14 sensitizes AML cells to serine and glycine (SG) deprivation. IGF2BP3 recognizies m6A on mRNAs of key serine synthesis pathway (SSP) genes (e.g., ATF4, PHGDH, PSAT1), stabilizing these transcripts and sustaining serine production to meet the high metabolic demand of AML cells and LSCs/LICs. IGF2BP3 silencing combined with dietary SG restriction potently inhibits AML in vitro and in vivo, while its deletion spares normal hematopoiesis. Our findings reveal the critical role of m6A modification in the serine metabolic vulnerability of AML and highlight the IGF2BP3/m6A/SSP axis as a promising therapeutic target.

RSK1 is an exploitable dependency in myeloproliferative neoplasms and secondary acute myeloid leukemia

Myeloid malignancies are heterogenous disorders characterized by distinct molecular drivers but share convergence of oncogenic signaling pathways and propagation by ripe pro-inflammatory niches. Here, we establish a comprehensive transcriptional atlas across the spectrum of myeloproliferative neoplasms (MPN) and secondary acute myeloid leukemia (sAML) through RNA-sequencing of 158 primary samples encompassing CD34+ hematopoietic stem/progenitor cells and CD14+ monocytes. Supported by mass cytometry (CyTOF) profiling, we reveal aberrant networks of PI3K/AKT/mTOR signalling and NFκB-mediated hyper-inflammation. Combining ATAC-Seq, CUT&Tag, RNA-seq, and CyTOF, we demonstrate that targeting of ribosomal protein S6 kinase A1 (RSK1) suppresses NFκB activation and diminishes pro-inflammatory mediators including tumor necrosis factor (TNF) associated with MPN disease severity and transformation. We further evaluate a therapeutic approach utilizing a first-in-class RSK inhibitor, PMD-026, currently in Phase 2 development for breast cancer, for use in myeloid malignancies. Treatment with PMD-026 suppressed disease burden across seven syngeneic and patient-derived xenograft leukemia mouse models spanning the spectrum of driver and disease-modifying mutations. These findings uncover a therapeutic avenue for a conserved dependency across MPN and sAML.

Glucose-induced LINC01419 reprograms the glycolytic pathway by recruiting YBX1 to enhance PDK1 mRNA stability in hepatocellular carcinoma

Metabolic reprogramming provides the necessary energy for the development of malignant tumours and is emerging as a novel tumour treatment strategy. However, the widespread expression of metabolic enzymes in diverse cell types makes the development of specific drugs that target cancer cells without affecting normal cellular functions challenging. Accumulating evidence has demonstrated the essential roles of long non-coding RNAs (lncRNAs) in the regulatory network associated with glucose metabolism in tumour cells. The mechanism and therapeutic potential of cancer-specific lncRNAs in modulating tumour glucose metabolism warrant in-depth exploration. Here we revealed that glucose-induced LINC01419 promoted the growth and metastasis of HCC cells by driving metabolic reprogramming. Mechanistically, LINC01419 directly interacted with Y-box binding protein 1 (YBX1) in the cytoplasm and facilitated its binding to PDK1 mRNA, thus enhancing PDK1 mRNA stability and increasing lactate production. Furthermore, YY1 contributed to the transcriptional activation of LINC01419 in HCC under high-glucose conditions. Notably, administration of an N-acetylgalactosamine (GalNAc)-conjugated siRNA specifically targeting LINC01419 markedly retarded the growth of orthotopic xenograft tumours. These findings provide evidence for an unprecedented regulatory mechanism of LINC01419 involving metabolic reprogramming in human cancer. The newly identified LINC01419/YBX1-PDK1 axis may represent a promising therapeutic target for HCC. Moreover, GalNAc-siLINC01419 holds significant potential for clinical application. KEY POINTS: This study highlights the considerable regulatory role of LINC01419 in the metabolism of HCC. The newly identified LINC01419/YBX1-PDK1 axis constitutes a valuable target. Hepatic-specific delivery of GalNAc-siLINC01419 presents a promising therapeutic strategy for HCC.

RNA sequestration in P-bodies sustains myeloid leukaemia

Post-transcriptional mechanisms are fundamental safeguards of progenitor cell identity and are often dysregulated in cancer. Here, we identified regulators of P-bodies as crucial vulnerabilities in acute myeloid leukaemia (AML) through genome-wide CRISPR screens in normal and malignant haematopoietic progenitors. We found that leukaemia cells harbour aberrantly elevated numbers of P-bodies and show that P-body assembly is crucial for initiation and maintenance of AML. Notably, P-body loss had little effect upon homoeostatic haematopoiesis but impacted regenerative haematopoiesis. Molecular characterization of P-bodies purified from human AML cells unveiled their critical role in sequestering messenger RNAs encoding potent tumour suppressors from the translational machinery. P-body dissolution promoted translation of these mRNAs, which in turn rewired gene expression and chromatin architecture in leukaemia cells. Collectively, our findings highlight the contrasting and unique roles of RNA sequestration in P-bodies during tissue homoeostasis and oncogenesis. These insights open potential avenues for understanding myeloid leukaemia and future therapeutic interventions.

CircSMAD3 represses SMAD3 phosphorylation and ameliorates cardiac remodeling by recruiting YBX1

Circular RNA (circRNA) has emerged as potential therapeutic targets for cardiovascular diseases. Given the central role of the TGFβ signaling pathway in cardiac remodeling and its potential as a therapeutic target, we hypothesized that a circRNA from this pathway could modulate cardiac remodeling and serve as a heart failure treatment. Therefore, we identified a circRNA, named circSMAD3, that was significantly reduced in murine heart failure models. Functionally, circSMAD3 mitigated cardiomyocyte hypertrophy and inhibited cardiac fibroblast activation in vitro. Mechanistically, circSMAD3 interacts with YBX1, stabilizing it and facilitating its binding to SMAD3 in the nucleus, disrupting the TGFβ/SMAD3 signaling pathway, and ultimately restoring cardiac remodeling. This study highlights circSMAD3 as a promising therapeutic target for heart failure treatment.

Inhibition of protein translational machinery in triple-negative breast cancer as a promising therapeutic strategy

Y-box binding protein-1 (YB-1) is a proto-oncogenic protein associated with protein translation regulation. It plays a crucial role in the development and progression of triple-negative breast cancer (TNBC). In this study, we describe a promising approach to inhibit YB-1 using SU056, a small-molecule inhibitor. SU056 physically interacts with YB-1 and reduces its expression, which helps to restrain the progression of TNBC. Proteome profiling analysis indicates that the inhibition of YB-1 by SU056 can alter the proteins that regulate protein translation, an essential process for cancer cell growth. Preclinical studies on human cells, mice, and patient-derived xenograft tumor models show the effectiveness of SU056. Moreover, toxicological studies have shown that SU056 treatment and dosing are well tolerated without any adverse effects. Overall, our study provides a strong foundation for the further development of SU056 as a potential treatment option for patients with TNBC by targeting YB-1.

Novel subsets of peripheral immune cells associated with promoting stroke recovery in mice

AIMS

Peripheral immune cells infiltrating into the brain trigger neuroinflammation after an ischemic stroke. Partial immune cells reprogram their function for neural repair. Which immune cells promote ischemic brain recovery needs further identification.

METHODS

We performed single-cell transcriptomic profiling of CD45high immune cells isolated from the ischemic hemisphere at subacute (5 days) and chronic (14 days) stages after ischemic stroke.

RESULTS

A subset of phagocytic macrophages was associated with neuron projection regeneration and tissue remodeling. We also identified a unique type of T cells with highly expressed macrophage markers, including C1q, Apoe, Hexb, and Fcer1g, which showed high abilities in tissue remodeling, myelination regulation, wound healing, and anti-neuroinflammation. Moreover, natural killer cells decreased cytotoxicity and increased energy and metabolic function in the chronic stage after ischemic stroke. Two subgroups of neutrophils upregulated CCL signals to recruit peripheral immune cells and released CXCL2 to keep self-recruiting at the chronic stage.

CONCLUSIONS

We identified subsets of peripheral immune cells that may provide potential therapeutic targets for promoting poststroke recovery.

Y-box binding protein 1 in small extracellular vesicles reduces mesenchymal stem cell differentiation to osteoblasts-implications for acute myeloid leukaemia

Small extracellular vesicles (sEVs) released by acute myeloid leukaemia (AML) cells have been reported to influence the trilineage differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs). However, it remains elusive which biological cargo from AML-sEVs is responsible for this effect. In this study, sEVs were isolated from cell-conditioned media and blood plasma using size-exclusion chromatography and ultrafiltration and characterized according to MISEV2018 guidelines. Our results demonstrated that AML-sEVs increased the proliferation of BM-MSCs. Conversely, key proteins that are important for normal haematopoiesis were downregulated in BM-MSCs. Additionally, we revealed that AML-sEVs significantly reduced the differentiation of BM-MSCs to osteoblasts without affecting adipogenic or chondrogenic differentiation. Next, LC-MS/MS proteomics elucidated that various proteins, including Y-box-binding protein 1 (YBX1), were upregulated in both AML-sEVs and BM-MSCs treated with AML-sEVs. Clinically relevant, we found that YBX1 is considerably upregulated in most paediatric AML patient-derived sEVs compared to healthy controls. Interestingly, sEVs isolated after the downregulation of YBX1 in AML cells remarkably rescued the osteoblastic differentiation of BM-MSCs. Altogether, our data demonstrate for the first time that YBX1 containing AML-sEVs is one of the key players that disrupt the normal function of bone marrow microenvironment by reducing the osteogenic differentiation of BM-MSCs.

Size-exclusion chromatography combined with DIA-MS enables deep proteome profiling of extracellular vesicles from melanoma plasma and serum

Extracellular vesicles (EVs) are important players in melanoma progression, but their use as clinical biomarkers has been limited by the difficulty of profiling blood-derived EV proteins with high depth of coverage, the requirement for large input amounts, and complex protocols. Here, we provide a streamlined and reproducible experimental workflow to identify plasma- and serum- derived EV proteins of healthy donors and melanoma patients using minimal amounts of sample input. SEC-DIA-MS couples size-exclusion chromatography to EV concentration and deep-proteomic profiling using data-independent acquisition. From as little as 200 µL of plasma per patient in a cohort of three healthy donors and six melanoma patients, we identified and quantified 2896 EV-associated proteins, achieving a 3.5-fold increase in depth compared to previously published melanoma studies. To compare the EV-proteome to unenriched blood, we employed an automated workflow to deplete the 14 most abundant proteins from plasma and serum and thereby approximately doubled protein group identifications versus native blood. The EV proteome diverged from corresponding unenriched plasma and serum, and unlike the latter, separated healthy donor and melanoma patient samples. Furthermore, known melanoma markers, such as MCAM, TNC, and TGFBI, were upregulated in melanoma EVs but not in depleted melanoma plasma, highlighting the specific information contained in EVs. Overall, EVs were significantly enriched in intact membrane proteins and proteins related to SNARE protein interactions and T-cell biology. Taken together, we demonstrated the increased sensitivity of an EV-based proteomic workflow that can be easily applied to larger melanoma cohorts and other indications.

Differential co-expression network analysis elucidated genes associated with sensitivity to farnesyltransferase inhibitor and prognosis of acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease and the most common form of acute leukemia with a poor prognosis. Due to its complexity, the disease requires the identification of biomarkers for reliable prognosis. To identify potential disease genes that regulate patient prognosis, we used differential co-expression network analysis and transcriptomics data from relapsed, refractory, and previously untreated AML patients based on their response to treatment in the present study. In addition, we combined functional genomics and transcriptomics data to identify novel and therapeutically potential systems biomarkers for patients who do or do not respond to treatment. As a result, we constructed co-expression networks for response and non-response cases and identified a highly interconnected group of genes consisting of SECISBP2L, MAN1A2, PRPF31, VASP, and SNAPC1 in the response network and a group consisting of PHTF2, SLC11A2, PDLIM5, OTUB1, and KLRD1 in the non-response network, both of which showed high prognostic performance with hazard ratios of 4.12 and 3.66, respectively. Remarkably, ETS1, GATA2, AR, YBX1, and FOXP3 were found to be important transcription factors in both networks. The prognostic indicators reported here could be considered as a resource for identifying tumorigenesis and chemoresistance to farnesyltransferase inhibitor. They could help identify important research directions for the development of new prognostic and therapeutic techniques for AML.

YB-1 activating cascades as potential targets in KRAS-mutated tumors

Y‑box binding protein‑1 (YB-1) is a multifunctional protein that is highly expressed in human solid tumors of various entities. Several cellular processes, e.g. cell cycle progression, cancer stemness and DNA damage signaling that are involved in the response to chemoradiotherapy (CRT) are tightly governed by YB‑1. KRAS gene with about 30% mutations in all cancers, is considered the most commonly mutated oncogene in human cancers. Accumulating evidence indicates that oncogenic KRAS mediates CRT resistance. AKT and p90 ribosomal S6 kinase are downstream of KRAS and are the major kinases that stimulate YB‑1 phosphorylation. Thus, there is a close link between the KRAS mutation status and YB‑1 activity. In this review paper, we highlight the importance of the KRAS/YB‑1 cascade in the response of KRAS-mutated solid tumors to CRT. Likewise, the opportunities to interfere with this pathway to improve CRT outcome are discussed in light of the current literature.

Cell fate determinant Llgl1 is required for propagation of acute myeloid leukemia

Scribble complex proteins can influence cell fate decisions and self-renewal capacity of hematopoietic cells. While specific cellular functions of Scribble complex members are conserved in mammalian hematopoiesis, they appear to be highly context dependent. Using CRISPR/Cas9-based genetic screening, we have identified Scribble complex-related liabilities in AML including LLGL1. Despite its reported suppressive function in HSC self-renewal, inactivation of LLGL1 in AML confirms its relevant role for proliferative capacity and development of AML. Its function was conserved in human and murine models of AML and across various genetic backgrounds. Inactivation of LLGL1 results in loss of stemness-associated gene-expression including HoxA-genes and induces a GMP-like phenotype in the leukemia stem cell compartment. Re-expression of HoxA9 facilitates functional and phenotypic rescue. Collectively, these data establish LLGL1 as a specific dependency and putative target in AML and emphasizes its cell-type specific functions.

YBX1 as an oncogenic factor in T-cell acute lymphoblastic leukemia

Y-box-binding protein 1 (YBX1), a member of the RNA-binding protein family, is a critical regulator of cell survival in various solid tumors and acute myeloid leukemia. However, the function of YBX1 in T-cell acute lymphoblastic leukemia (T-ALL) remains elusive. Here, we found that YBX1 was upregulated in patients with T-ALL, T-ALL cell lines, and NOTCH1-induced T-ALL mice. Furthermore, depletion of YBX1 dramatically reduced cell proliferation, induced cell apoptosis, and induced G0/G1 phase arrest in vitro. Moreover, YBX1 depletion significantly decreased the leukemia burden in the human T-ALL xenograft and NOTCH1-induced T-ALL mice model in vivo. Mechanistically, downregulation of YBX1 markedly inhibited the expression of total AKT serine/threonine kinase (AKT), p-AKT, total extracellular signal-regulated kinase (ERK), and p-ERK in T-ALL cells. Taken together, our results uncovered a critical role of YBX1 in the leukemogenesis of T-ALL, which may have great potential as a biomarker and therapeutic target in T-ALL.

Translational control of Ybx1 expression regulates cardiac function in response to pressure overload in vivo

RNA-protein interactions are central to cardiac function, but how activity of individual RNA-binding protein is regulated through signaling cascades in cardiomyocytes during heart failure development is largely unknown. The mechanistic target of rapamycin kinase is a central signaling hub that controls mRNA translation in cardiomyocytes; however, a direct link between mTOR signaling and RNA-binding proteins in the heart has not been established. Integrative transcriptome and translatome analysis revealed mTOR dependent translational upregulation of the RNA binding protein Ybx1 during early pathological remodeling independent of mRNA levels. Ybx1 is necessary for pathological cardiomyocyte growth by regulating protein synthesis. To identify the molecular mechanisms how Ybx1 regulates cellular growth and protein synthesis, we identified mRNAs bound to Ybx1. We discovered that eucaryotic elongation factor 2 (Eef2) mRNA is bound to Ybx1, and its translation is upregulated during cardiac hypertrophy dependent on Ybx1 expression. Eef2 itself is sufficient to drive pathological growth by increasing global protein translation. Finally, Ybx1 depletion in vivo preserved heart function during pathological cardiac hypertrophy. Thus, activation of mTORC1 links pathological signaling cascades to altered gene expression regulation by activation of Ybx1 which in turn promotes translation through increased expression of Eef2.

Aberrant m5C hypermethylation mediates intrinsic resistance to gefitinib through NSUN2/YBX1/QSOX1 axis in EGFR-mutant non-small-cell lung cancer

BACKGROUND

RNA 5-methylcytosine (m⁵C) modification plays critical roles in the pathogenesis of various tumors. However, the function and molecular mechanism of RNA m⁵C modification in tumor drug resistance remain unclear.

METHODS

The correlation between RNA m⁵C methylation, m⁵C writer NOP2/Sun RNA methyltransferase family member 2 (NSUN2) and EGFR-TKIs resistance was determined in non-small-cell lung cancer (NSCLC) cell lines and patient samples. The effects of NSUN2 on EGFR-TKIs resistance were investigated by gain- and loss-of-function assays in vitro and in vivo. RNA-sequencing (RNA-seq), RNA bisulfite sequencing (RNA-BisSeq) and m⁵C methylated RNA immunoprecipitation-qPCR (MeRIP-qPCR) were performed to identify the target gene of NSUN2 involved in EGFR-TKIs resistance. Furthermore, the regulatory mechanism of NSUN2 modulating the target gene expression was investigated by functional rescue and puromycin incorporation assays.

RESULTS

RNA m⁵C hypermethylation and NSUN2 were significantly correlated with intrinsic resistance to EGFR-TKIs. Overexpression of NSUN2 resulted in gefitinib resistance and tumor recurrence, while genetic inhibition of NSUN2 led to tumor regression and overcame intrinsic resistance to gefitinib in vitro and in vivo. Integrated RNA-seq and m⁵C-BisSeq analyses identified quiescin sulfhydryl oxidase 1 (QSOX1) as a potential target of aberrant m⁵C modification. NSUN2 methylated QSOX1 coding sequence region, leading to enhanced QSOX1 translation through m⁵C reader Y-box binding protein 1 (YBX1).

CONCLUSIONS

Our study reveals a critical function of aberrant RNA m⁵C modification via the NSUN2-YBX1-QSOX1 axis in mediating intrinsic resistance to gefitinib in EGFR-mutant NSCLC.

circNEIL3 inhibits tumor metastasis through recruiting the E3 ubiquitin ligase Nedd4L to degrade YBX1

Distant metastasis is a major contributor to cancer-related mortality. However, the role of circRNAs in this process remains unclear. Herein, we profiled the circRNA expression in a cohort of 68 colorectal carcinoma (CRC) primary tumors and their paired liver metastatic lesions. By overlapping with the TGFβ-responsive circRNAs, circNEIL3 (hsa_circ_0001460) was identified as a TGFβ-repressive and metastasis-related circRNA. Functionally, circNEIL3 effectively inhibited tumor metastasis in both and in vivo and in vivo models of various cancer types. Mechanistically, circNEIL3 exerts its metastasis-repressive function through its direct interaction with oncogenic protein, Y-box-binding protein 1 (YBX1), which consequently promotes the Nedd4L-mediated proteasomal degradation of YBX1. Importantly, circNEIL3 expression was negatively correlated to YBX1 protein level and metastatic tendency in CRC patient samples. Collectively, our findings indicate the YBX1-dependent antimetastatic function of circNEIL3 and highlight the potential of circNEIL3 as a biomarker and therapeutic option in cancer treatment.

YBX1 regulates the survival of chronic myeloid leukemia stem cells by modulating m6A-mediated YWHAZ stability

PURPOSE

Chronic myeloid leukemia (CML) is a myeloproliferative disease derived from hematopoietic stem cells (HSCs) that harbor Philadelphia chromosome (Ph chromosome). In clinic, leukemia stem cells (LSCs) in CML are insensitive to the treatment with tyrosine kinase inhibitors, and are responsible for disease relapse. However, the molecular mechanisms for maintaining LSCs survival remain elusive.

METHODS

CML patient-derived cell lines and BCR-ABL-induced CML mouse model were used to explore the role of YBX1 in regulating the survival of CML LSCs. Bone marrow transduction and transplantation, and colony-forming unit assay were used to investigate LSC function. The underlying mechanism of how YBX1 regulates LSCs survival were assessed using flow cytometry, RNA sequencing, western blot, RNA decay assay, co-immunoprecipitation and RNA immunoprecipitation.

RESULTS

Here we show that RNA-binding protein YBX1 plays an important role in regulating survival of CML LSCs. We find that YBX1 expression is significantly increased in CML cells, and confirm that YBX1 is required for maintaining survival of LSCs. Deletion of YBX1 impairs the propagation of CML through blocking cell proliferation and inducing apoptosis of LSCs. Mechanistically, we find that YBX1 regulates expression of apoptotic associated genes. YBX1 cooperates with RNA m⁶A reader IGF2BPs to stabilize YWHAZ transcript in an m⁶A-dependent manner, and loss of YBX1 decreases YWHAZ expression by accelerating mRNA decay. Restoration of YWHAZ efficiently rescues the defects of YBX1-deficient CML cells.

CONCLUSION

Our findings reveal a critical role of YBX1 in maintaining survival of CML LSCs, which provides a rationale for targeting YBX1 in CML treatment.

tRNA derived small RNAs—Small players with big roles

In the past 2 decades, small non-coding RNAs derived from tRNA (tsRNAs or tRNA derived fragments; tRFs) have emerged as new powerful players in the field of small RNA mediated regulation of gene expression, translation, and epigenetic control. tRFs have been identified from evolutionarily divergent organisms from Archaea, the higher plants, to humans. Recent studies have confirmed their roles in cancers and other metabolic disorders in humans and experimental models. They have been implicated in biotic and abiotic stress responses in plants as well. In this review, we summarize the current knowledge on tRFs including types of tRFs, their biogenesis, and mechanisms of action. The review also highlights recent studies involving differential expression profiling of tRFs and elucidation of specific functions of individual tRFs from various species. We also discuss potential considerations while designing experiments involving tRFs identification and characterization and list the available bioinformatics tools for this purpose.

Context-specific effects of NOX4 inactivation in acute myeloid leukemia (AML)

PURPOSE

Oxidative stress has been linked to initiation and progression of cancer and recent studies have indicated a potential translational role regarding modulation of ROS in various cancers, including acute myeloid leukemia (AML). Detailed understanding of the complex machinery regulating ROS including its producer elements in cancer is required to define potential translational therapeutic use. Based on previous studies in acute myeloid leukemia (AML) models, we considered NADPH oxidase (NOX) family members, specifically NOX4 as a potential target in AML.

METHODS

Pharmacologic inhibition and genetic inactivation of NOX4 in murine and human models of AML were used to understand its functional role. For genetic inactivation, CRISPR-Cas9 technology was used in human AML cell lines in vitro and genetically engineered knockout mice for Nox4 were used for deletion of Nox4 in hematopoietic cells via Mx1-Cre recombinase activation.

RESULTS

Pharmacologic NOX inhibitors and CRISPR-Cas9-mediated inactivation of NOX4 and p22-phox (an essential NOX component) decreased proliferative capacity and cell competition in FLT3-ITD-positive human AML cells. In contrast, conditional deletion of Nox4 enhanced the myeloproliferative phenotype of an FLT3-ITD induced knock-in mouse model. Finally, Nox4 inactivation in normal hematopoietic stem and progenitor cells (HSPCs) caused a minor reduction in HSC numbers and reconstitution capacity.

CONCLUSION

The role of NOX4 in myeloid malignancies appears highly context-dependent and its inactivation results in either enhancing or inhibitory effects. Therefore, targeting NOX4 in FLT3-ITD positive myeloid malignancies requires additional pre-clinical assessment.

Histone demethylase KDM4C is a functional dependency in JAK2-mutated neoplasms

Mutations of the JAK2 gene are frequent aberrations in the aging hematopoietic system and in myeloid neoplasms. While JAK-inhibitors efficiently reduce hyperinflammation induced by the constitutively active mutated JAK2 kinase, the malignant clone and abundance of mutated cells remains rather unaffected. Here, we sought to assess for genetic vulnerabilities of JAK2-mutated clones. We identified lysine-specific demethylase KDM4C as a selective genetic dependency that persists upon JAK-inhibitor treatment. Genetic inactivation of KDM4C in human and murine JAK2-mutated cells resulted in loss of cell competition and reduced proliferation. These findings led to reduced disease penetrance and improved survival in xenograft models of human JAK2-mutated cells. KDM4C deleted cells showed alterations in target histone residue methylation and target gene expression, resulting in induction of cellular senescence. In summary, these data establish KDM4C as a specific dependency and therapeutic target in JAK2-mutated cells that is essential for oncogenic signaling and prevents induction of senescence.

Liquid-Liquid Phase Separation in Cancer Signaling, Metabolism and Anticancer Therapy

The cancer state is thought to be maintained by genetic and epigenetic changes that drive a cancer-promoting gene expression program. However, recent results show that cellular states can be also stably maintained by the reorganization of cell structure leading to the formation of biological condensates via the process of liquid-liquid phase separation. Here, we review the data showing cancer-specific biological condensates initiated by mutant oncoproteins, RNA-binding proteins, or lincRNAs that regulate oncogenic gene expression programs and cancer metabolism. Effective anticancer drugs may specifically partition into oncogenic biological condensates (OBC).

JAK2 inhibitor persistence in MPN: uncovering a central role of ERK activation

The Philadelphia chromosome negative myeloproliferative neoplasms, including polycythemia vera, essential thrombocytosis, and myelofibrosis, are driven by hyper activation of the JAK2 tyrosine kinase, the result of mutations in three MPN driving genes: JAK2, MPL, and CALR. While the anti-inflammatory effects of JAK2 inhibitors can provide improved quality of life for many MPN patients, the upfront and persistent survival of disease-driving cells in MPN patients undergoing JAK2 inhibitor therapy thwarts potential for remission. Early studies indicated JAK2 inhibitor therapy induces heterodimeric complex formation of JAK2 with other JAK family members leading to sustained JAK2-dependent signaling. Recent work has described novel cell intrinsic details as well as cell extrinsic mechanisms that may contribute to why JAK2 inhibition may be ineffective at targeting MPN driving cells. Diverse experimental strategies aimed at uncovering mechanistic details that contribute to JAK2 inhibitor persistence have each highlighted the role of MEK/ERK activation. These approaches include, among others, phosphoproteomic analyses of JAK2 signaling as well as detailed assessment of JAK2 inhibition in mouse models of MPN. In this focused review, we highlight these and other studies that collectively suggest targeting MEK/ERK in combination with JAK2 inhibition has the potential to improve the efficacy of JAK2 inhibitors in MPN patients. As MPN patients patiently wait for improved therapies, such studies should further strengthen optimism that pre-clinical research is continuing to uncover mechanistic insights regarding the ineffectiveness of JAK2 inhibitors, which may lead to development of improved therapeutic strategies.