p53 loss promotes acute myeloid leukemia by enabling aberrant self-renewal

TP53 -Mutated Myeloid Neoplasms: 2024 Update on Diagnosis, Risk-Stratification, and Management

Alterations in the tumor suppressor gene TP53 are common in human cancers and are associated with an aggressive nature. Approximately 8%-12% of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) harbor TP53 mutations (TP53 mut) and present immense challenges due to inherent chemoresistance and poor outcomes. As TP53 mut are more common in older individuals and those with secondary/therapy-related myeloid neoplasms (MN), their incidence is expected to increase with an aging population and rising proportion of cancer survivors. Treatments used for other MN-intensive chemotherapy, hypomethylating agents, and the BCL-2 inhibitor venetoclax-do not improve the survival of TP53 mut MN patients meaningfully. Additionally, further development of many promising agents has been discontinued, highlighting the challenges. Widespread acknowledgment of these problems led to the recognition of TP53 mut MN as a distinct entity in the 5th edition of the World Health Organization and International Consensus Classifications. However, critical discrepancies between the two classifications may lead to under- or overestimation of the prognostic risk. Here, we review recent advances in the biology, diagnosis, and treatment of TP53 mut MN. The development of TP53 mut MN is positioned at the intersection of age, hereditary predisposition, and anti-cancer therapies. Precursor TP53 mut clones can be detected years prior to the eventual leukemic transformation-raising the possibility of early intervention. We discuss the two classification systems and the bearing of the discrepancies between the two on timely and effective management. We provide novel evidence in the areas of discrepancies. Finally, we review the current therapeutic landscape and the obvious limitations of the currently used therapies.

TP53 mutations and TET2 deficiency cooperate to drive leukemogenesis and establish an immunosuppressive environment

Mutations and deletions in TP53 are associated with adverse outcomes in patients with myeloid malignancies, and there is an urgent need for the development of improved therapies for TP53-mutant leukemias. Here, we identified mutations in TET2 as the most common co-occurring mutation in patients with TP53-mutant acute myeloid leukemia (AML). In mice, combined hematopoietic-specific deletion of TET2 and TP53 resulted in enhanced self-renewal compared with deletion of either gene alone. Tp53/Tet2 double-KO mice developed serially transplantable AML. Both mice and patients with AML with combined TET2/TP53 alterations upregulated innate immune signaling in malignant granulocyte-monocyte progenitors, which had leukemia-initiating capacity. A20 governs the leukemic maintenance by triggering aberrant noncanonical NF-κB signaling. Mice with Tp53/Tet2 loss had expansion of monocytic myeloid-derived suppressor cells (MDSCs), which impaired T cell proliferation and activation. Moreover, mice and patients with AML with combined TP53/TET2 alterations displayed increased expression of the TIGIT ligand, CD155, on malignant cells. TIGIT-blocking antibodies augmented NK cell-mediated killing of Tp53/Tet2 double-mutant AML cells, reduced leukemic burden, and prolonged survival in Tp53/Tet2 double-KO mice. These findings describe a leukemia-promoting link between TET2 and TP53 mutations and highlight therapeutic strategies to overcome the immunosuppressive bone marrow environment in this adverse subtype of AML.

In vivo models of subclonal oncogenesis and dependency in hematopoietic malignancy

Cancer evolution is a multifaceted process leading to dysregulation of cellular expansion and differentiation through somatic mutations and epigenetic dysfunction. Clonal expansion and evolution is driven by cell-intrinsic and -extrinsic selective pressures, which can be captured with increasing resolution by single-cell and bulk DNA sequencing. Despite the extensive genomic alterations revealed in profiling studies, there remain limited experimental systems to model and perturb evolutionary processes. Here, we integrate multi-recombinase tools for reversible, sequential mutagenesis from premalignancy to leukemia. We demonstrate that inducible Flt3 mutations differentially cooperate with Dnmt3a, Idh2, and Npm1 mutant alleles, and that changing the order of mutations influences cellular and transcriptional landscapes. We next use a generalizable, reversible approach to demonstrate that mutation reversion results in rapid leukemic regression with distinct differentiation patterns depending upon co-occurring mutations. These studies provide a path to experimentally model sequential mutagenesis, investigate mechanisms of transformation and probe oncogenic dependency in disease evolution.

Acute Erythroid Leukemia: From Molecular Biology to Clinical Outcomes

Acute Erythroid Leukemia (AEL) is a rare and aggressive subtype of Acute Myeloid Leukemia (AML). In 2022, the World Health Organization (WHO) defined AEL as a biopsy with ≥30% proerythroblasts and erythroid precursors that account for ≥80% of cellularity. The International Consensus Classification refers to this neoplasm as "AML with mutated TP53". Classification entails ≥20% blasts in blood or bone marrow biopsy and a somatic TP53 mutation (VAF > 10%). This type of leukemia is typically associated with biallelic TP53 mutations and a complex karyotype, specifically 5q and 7q deletions. Transgenic mouse models have implicated several molecules in the pathogenesis of AEL, including transcriptional master regulator GATA1 (involved in erythroid differentiation), master oncogenes, and CDX4. Recent studies have also characterized AEL by epigenetic regulator mutations and transcriptome subgroups. AEL patients have overall poor clinical outcomes, mostly related to their poor response to the standard therapies, which include hypomethylating agents and intensive chemotherapy. Allogeneic bone marrow transplantation (AlloBMT) is the only potentially curative approach but requires deep remission, which is very challenging for these patients. Age, AlloBMT, and a history of antecedent myeloid neoplasms further affect the outcomes of these patients. In this review, we will summarize the diagnostic criteria of AEL, review the current insights into the biology of AEL, and describe the treatment options and outcomes of patients with this disease.

Emerging In Vitro and In Vivo Models: Hope for the Better Understanding of Cancer Progression and Treatment

Various cancer models have been developed to aid the understanding of the underlying mechanisms of tumor development and evaluate the effectiveness of various anticancer drugs in preclinical studies. These models accurately reproduce the critical stages of tumor initiation and development to mimic the tumor microenvironment better. Using these models for target validation, tumor response evaluation, resistance modeling, and toxicity comprehension can significantly enhance the drug development process. Herein, various in vivo or animal models are presented, typically consisting of several mice and in vitro models ranging in complexity from transwell models to spheroids and CRISPR-Cas9 technologies. While in vitro models have been used for decades and dominate the early stages of drug development, they are still limited primary to simplistic tests based on testing on a single cell type cultivated in Petri dishes. Recent advancements in developing new cancer therapies necessitate the generation of complicated animal models that accurately mimic the tumor's complexity and microenvironment. Mice make effective tumor models as they are affordable, have a short reproductive cycle, exhibit rapid tumor growth, and are simple to manipulate genetically. Human cancer mouse models are crucial to understanding the neoplastic process and basic and clinical research improvements. The following review summarizes different in vitro and in vivo metastasis models, their advantages and disadvantages, and their ability to serve as a model for cancer research.

TP53 Mutations in Acute Leukemias and Myelodysplastic Syndromes: Insights and Treatment Updates

TP53 mutations are found in 5%-10% of de novo myelodysplastic syndrome (MDS) and AML cases. By contrast, in therapy related MDS and AML, mutations in TP53 are found in up to 30%-40% of patients. The majority of inactivating mutations observed in MDS and AML are missense mutations localized in a few prevalent hotspots. TP53 missense mutations together with truncating mutations or chromosomal loss of TP53 determine a loss-of-function effect on normal p53 function. Clonal expansion of TP53-mutant clones is observed under the selection pressure of chemotherapy or MDM2 inhibitor therapy. TP53-mutant clones are resistant to current chemotherapy, and when responses to treatment have been observed, they have correlated poorly with overall survival. The most heavily investigated and targeted agent for patients with TP53-mutant MDS and AML has been APR-246 (eprenetapopt) a p53 reactivator, in combination with azacitidine, but also in triplets with venetoclax. Despite positive results in phase II trials, a phase III trial did not confirm superior response or improved survival. Other agents, like magrolimab (anti-CD47 antibody), failed to demonstrate improved activity in TP53-mutant MDS and AML. Agents whose activity is not dependent on a functional apoptosis system like anti-CD123 antibodies or cellular therapies are in development and may hold promises. Delivering prognostic information in a dismal disease like TP53-mutated MDS and AML is particularly challenging. The physician should balance hope and realism, describing the trajectory of possible treatments and at the same time indicating the poor outcome, together with promoting adaptive coping in patients and elaborating on the nature of the disease.

Ppm1d truncating mutations promote the development of genotoxic stress-induced AML

Hematopoietic stem cells (HSCs) ensure blood cell production during the life-time of an organism, and to do so they need to balance self-renewal, proliferation, differentiation, and migration in a steady state as well as in response to stress or injury. Importantly, aberrant proliferation of HSCs leads to hematological malignancies, and thus, tight regulation by various tumor suppressor pathways, including p53, is essential. Protein phosphatase magnesium-dependent 1 delta (PPM1D) is a negative regulator of p53 and promotes cell survival upon induction of genotoxic stress. Truncating mutations in the last exon of PPM1D lead to the production of a stable, enzymatically active protein and are commonly associated with clonal hematopoiesis. Using a transgenic mouse model, we demonstrate that truncated PPM1D reduces self-renewal of HSCs in basal conditions but promotes the development of aggressive AML after exposure to ionizing radiation. Inhibition of PPM1D suppressed the colony growth of leukemic stem and progenitor cells carrying the truncated PPM1D, and remarkably, it provided protection against irradiation-induced cell growth. Altogether, we demonstrate that truncated PPM1D affects HSC maintenance, disrupts normal hematopoiesis, and that its inhibition could be beneficial in the context of therapy-induced AML.

Loss of p53 enhances the tumor-initiating potential and drug resistance of clonogenic multiple myeloma cells

Tumor relapse and drug resistance are major factors that limit the curability of multiple myeloma (MM). New regimens have improved overall MM survival rates, but patients with high-risk features continue to have inferior outcomes. Chromosome 17p13 deletion (del17p) that includes the loss of the TP53 gene is a high-risk cytogenetic abnormality and is associated with poor clinical outcomes owing to relatively short remissions and the development of pan-drug resistant disease. Increased relapse rates suggest that del17p enhances clonogenic growth, and we found that the loss of p53 increased both the frequency and drug resistance of tumor-initiating MM cells (TICs). Subsequent RNA sequencing (RNA-seq) studies demonstrated significant activation of the Notch signaling pathway and upregulation of inhibitor of DNA binding (ID1/ID2) genes in p53-knock out (p53-KO) cells. We found that the loss of ID1 or HES-1 expression or treatment with a gamma-secretase inhibitor (GSI) significantly decreased the clonogenic growth of p53-KO but not p53 wild-type cells. GSI treatment in a small set of MM specimens also reduced the clonogenic growth in del17p samples but not in non-del17p samples. This effect was specific as overexpression of the Notch intracellular domain (NICD) rescued the effects of GSI treatment. Our study demonstrates that the Notch signaling and ID1 expression are required for TIC expansion in p53-KO MM cells. These findings also suggest that GSI may be specifically active in patients with p53 mutant MM.

The Prognostic Value of TP53 Mutations in Adult Acute Myeloid Leukemia: A Meta-Analysis

OBJECTIVE

Mutations of the tumor protein p53 (TP53) gene were considered to be associated with an unfavorable prognosis in acute myeloid leukemia (AML). This meta-analysis aimed to systematically elucidate the prognostic value of TP53 mutation in adult patients with AML.

METHOD

A comprehensive literature search was conducted for eligible studies published before August 2021. The primary endpoint was overall survival (OS). Pooled hazard ratios (HRs) and their 95% confidence intervals (CIs) were calculated for prognostic parameters. Subgroup analyses based on intensive treatment were performed.

RESULTS

Thirty-two studies with 7,062 patients were included. As compared to wild-type carriers, AML patients with TP53 mutations had significantly shorter OS (HR: 2.40, 95% CI: 2.16-2.67, I2: 46.6%). Similar results were found in DFS (HR: 2.87, 95% CI: 1.88-4.38), EFS (HR: 2.56, 95% CI: 1.97-3.31), and RFS (HR: 2.40, 95% CI: 1.79-3.22). Mutant TP53 predicted inferior OS (HR: 2.77, 95% CI: 2.41-3.18) in the intensively treated AML subgroup, compared with the non-intensively treated group (HR: 1.89, 95% CI: 1.58-2.26). Among intensively-treated AML patients, the age of 65 did not affect the prognostic value of TP53 mutations. Besides, TP53 mutation was also strongly associated with an elevated risk of adverse cytogenetics, which conferred a dismal OS in AML patients (HR: 2.03, 95% CI: 1.74-2.37).

CONCLUSION

TP53 mutation exhibits a promising potential for discriminating AML patients with a worse prognosis, thus being capable of serving as a novel tool for prognostication and therapeutic decision-making in the management of AML.

The ADAR1 editome reveals drivers of editing-specificity for ADAR1-isoforms

Adenosine deaminase acting on RNA ADAR1 promotes A-to-I conversion in double-stranded and structured RNAs. ADAR1 has two isoforms transcribed from different promoters: cytoplasmic ADAR1p150 is interferon-inducible while ADAR1p110 is constitutively expressed and primarily localized in the nucleus. Mutations in ADAR1 cause Aicardi - Goutières syndrome (AGS), a severe autoinflammatory disease associated with aberrant IFN production. In mice, deletion of ADAR1 or the p150 isoform leads to embryonic lethality driven by overexpression of interferon-stimulated genes. This phenotype is rescued by deletion of the cytoplasmic dsRNA-sensor MDA5 indicating that the p150 isoform is indispensable and cannot be rescued by ADAR1p110. Nevertheless, editing sites uniquely targeted by ADAR1p150 remain elusive. Here, by transfection of ADAR1 isoforms into ADAR-less mouse cells we detect isoform-specific editing patterns. Using mutated ADAR variants, we test how intracellular localization and the presence of a Z-DNA binding domain-α affect editing preferences. These data show that ZBDα only minimally contributes to p150 editing-specificity while isoform-specific editing is primarily directed by the intracellular localization of ADAR1 isoforms. Our study is complemented by RIP-seq on human cells ectopically expressing tagged-ADAR1 isoforms. Both datasets reveal enrichment of intronic editing and binding by ADAR1p110 while ADAR1p150 preferentially binds and edits 3'UTRs.

Regulative Roles of Metabolic Plasticity Caused by Mitochondrial Oxidative Phosphorylation and Glycolysis on the Initiation and Progression of Tumorigenesis

One important feature of tumour development is the regulatory role of metabolic plasticity in maintaining the balance of mitochondrial oxidative phosphorylation and glycolysis in cancer cells. In recent years, the transition and/or function of metabolic phenotypes between mitochondrial oxidative phosphorylation and glycolysis in tumour cells have been extensively studied. In this review, we aimed to elucidate the characteristics of metabolic plasticity (emphasizing their effects, such as immune escape, angiogenesis migration, invasiveness, heterogeneity, adhesion, and phenotypic properties of cancers, among others) on tumour progression, including the initiation and progression phases. Thus, this article provides an overall understanding of the influence of abnormal metabolic remodeling on malignant proliferation and pathophysiological changes in carcinoma.

BRCA1 and TP53 codeficiency causes a PARP inhibitor-sensitive erythroproliferative neoplasm

Mutations in the BRCA1 tumor suppressor gene, such as 5382insC (BRCA1insC), give carriers an increased risk for breast, ovarian, prostate, and pancreatic cancers. We have previously reported that, in mice, Brca1 deficiency in the hematopoietic system leads to pancytopenia and, as a result, early lethality. We explored the cellular consequences of Brca1-null and BRCA1insC alleles in combination with Trp53 deficiency in the murine hematopoietic system. We found that Brca1 and Trp53 codeficiency led to a highly penetrant erythroproliferative disorder that is characterized by hepatosplenomegaly and by expanded megakaryocyte erythroid progenitor (MEP) and immature erythroid blast populations. The expanded erythroid progenitor populations in both BM and spleen had the capacity to transmit the disease into secondary mouse recipients, suggesting that Brca1 and Trp53 codeficiency provides a murine model of hematopoietic neoplasia. This Brca1/Trp53 model replicated Poly (ADP-ribose) polymerase (PARP) inhibitor olaparib sensitivity seen in existing Brca1/Trp53 breast cancer models and had the benefits of monitoring disease progression and drug responses via peripheral blood analyses without sacrificing experimental animals. In addition, this erythroid neoplasia developed much faster than murine breast cancer, allowing for increased efficiency of future preclinical studies.

FBP1-Altered Carbohydrate Metabolism Reduces Leukemic Viability through Activating P53 and Modulating the Mitochondrial Quality Control System In Vitro

Acute myeloid leukemia (AML)—the most frequent form of adult blood cancer—is characterized by heterogeneous mechanisms and disease progression. Developing an effective therapeutic strategy that targets metabolic homeostasis and energy production in immature leukemic cells (blasts) is essential for overcoming relapse and improving the prognosis of AML patients with different subtypes. With respect to metabolic regulation, fructose-1,6-bisphosphatase 1 (FBP1) is a gluconeogenic enzyme that is vital to carbohydrate metabolism, since gluconeogenesis is the central pathway for the production of important metabolites and energy necessary to maintain normal cellular activities. Beyond its catalytic activity, FBP1 inhibits aerobic glycolysis—known as the “Warburg effect”—in cancer cells. Importantly, while downregulation of FBP1 is associated with carcinogenesis in major human organs, restoration of FBP1 in cancer cells promotes apoptosis and prevents disease progression in solid tumors. Recently, our large-scale sequencing analyses revealed FBP1 as a novel inducible therapeutic target among 17,757 vitamin-D-responsive genes in MV4-11 or MOLM-14 blasts in vitro, both of which were derived from AML patients with FLT3 mutations. To investigate FBP1′s anti-leukemic function in this study, we generated a new AML cell line through lentiviral overexpression of an FBP1 transgene in vitro (named FBP1-MV4-11). Results showed that FBP1-MV4-11 blasts are more prone to apoptosis than MV4-11 blasts. Mechanistically, FBP1-MV4-11 blasts have significantly increased gene and protein expression of P53, as confirmed by the P53 promoter assay in vitro. However, enhanced cell death and reduced proliferation of FBP1-MV4-11 blasts could be reversed by supplementation with post-glycolytic metabolites in vitro. Additionally, FBP1-MV4-11 blasts were found to have impaired mitochondrial homeostasis through reduced cytochrome c oxidase subunit 2 (COX2 or MT-CO2) and upregulated PTEN-induced kinase (PINK1) expressions. In summary, this is the first in vitro evidence that FBP1-altered carbohydrate metabolism and FBP1-activated P53 can initiate leukemic death by activating mitochondrial reprogramming in AML blasts, supporting the clinical potential of FBP1-based therapies for AML-like cancers.

Comparison of acute myeloid leukemia and myelodysplastic syndromes with TP53 aberrations

TP53 aberrations are found in approximately 10% of patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) and are considered early driver events affecting leukemia stem cells. In this study, we compared features of a total of 84 patients with these disorders seen at a tertiary cancer center. Clinical and cytogenetic characteristics as well as immunophenotypes of immature blast cells were similar between AML and MDS patients. Median overall survival (OS) was 226 days (95% confidence interval [CI], 131-300) for the entire cohort with an estimated 3-year OS rate of 11% (95% CI, 6-22). OS showed a significant difference between MDS (median, 345 days; 95% CI, 235-590) and AML patients (median, 91 days; 95% CI, 64-226) which is likely due to a different co-mutational pattern as revealed by next-generation sequencing. Transformation of TP53 aberrant MDS occurred in 60.5% of cases and substantially reduced their survival probability. Cox regression analysis revealed treatment class and TP53 variant allele frequency as prognostically relevant parameters but not the TP53-specific prognostic scores EAp53 and RFS. These data emphasize similarities between TP53 aberrant AML and MDS and support previous notions that they should be classified and treated as a distinct disorder.

The Role of Tumor Stem Cell Exosomes in Cancer Invasion and Metastasis

Exosomes are lipid membrane bilayer-encapsulated vesicles secreted by cells into the extracellular space. They carry abundant inclusions (such as nucleic acids, proteins, and lipids) that play pivotal roles in intercellular communication. Tumor stem cells are capable of self-renewal and are crucial for survival, proliferation, drug resistance, metastasis, and recurrence of tumors. The miRNAs (microRNAs) in exosomes have various functions, such as participating in inflammatory response, cell migration, proliferation, apoptosis, autophagy, and epithelial-mesenchymal transition. Tumor stem cells secrete exosomes that act as important messengers involved in various tumor processes and several studies provide increasing evidence supporting the importance of these exosomes in tumor recurrence and metastasis. This review primarily focuses on the production and secretion of exosomes from tumors and tumor stem cells and their effects on cancer progression. Cancer stem cancer derived exosome play an important massager in the tumor microenvironment. It also emphasizes on the study of tumor stem cell exosomes in the light of cancer metastasis and recurrence aiming to provide valuable insights and novel perspectives, which could be beneficial for developing effective diagnostic and treatment strategies.

TP53 promotes lineage commitment of human embryonic stem cells through ciliogenesis and sonic hedgehog signaling

Aneuploidy, defective differentiation, and inactivation of the tumor suppressor TP53 all occur frequently during tumorigenesis. Here, we probe the potential links among these cancer traits by inactivating TP53 in human embryonic stem cells (hESCs). TP53-/- hESCs exhibit increased proliferation rates, mitotic errors, and low-grade structural aneuploidy; produce poorly differentiated immature teratomas in mice; and fail to differentiate into neural progenitor cells (NPCs) in vitro. Genome-wide CRISPR screen reveals requirements of ciliogenesis and sonic hedgehog (Shh) pathways for hESC differentiation into NPCs. TP53 deletion causes abnormal ciliogenesis in neural rosettes. In addition to restraining cell proliferation through CDKN1A, TP53 activates the transcription of BBS9, which encodes a ciliogenesis regulator required for proper Shh signaling and NPC formation. This developmentally regulated transcriptional program of TP53 promotes ciliogenesis, restrains Shh signaling, and commits hESCs to neural lineages.

Murine Models of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a phenotypically and genetically heterogeneous hematologic malignancy. Extensive sequencing efforts have mapped the genomic landscape of adult and pediatric AML revealing a number of biologically and prognostically relevant driver lesions. Beyond identifying recurrent genetic aberrations, it is of critical importance to fully delineate the complex mechanisms by which they contribute to the initiation and evolution of disease to ultimately facilitate the development of targeted therapies. Towards these aims, murine models of AML are indispensable research tools. The rapid evolution of genetic engineering techniques over the past 20 years has greatly advanced the use of murine models to mirror specific genetic subtypes of human AML, define cell-intrinsic and extrinsic disease mechanisms, study the interaction between co-occurring genetic lesions, and test novel therapeutic approaches. This review summarizes the mouse model systems that have been developed to recapitulate the most common genomic subtypes of AML. We will discuss the strengths and weaknesses of varying modeling strategies, highlight major discoveries emanating from these model systems, and outline future opportunities to leverage emerging technologies for mechanistic and preclinical investigations.

Mouse Models of Frequently Mutated Genes in Acute Myeloid Leukemia

Acute myeloid leukemia is a clinically and biologically heterogeneous blood cancer with variable prognosis and response to conventional therapies. Comprehensive sequencing enabled the discovery of recurrent mutations and chromosomal aberrations in AML. Mouse models are essential to study the biological function of these genes and to identify relevant drug targets. This comprehensive review describes the evidence currently available from mouse models for the leukemogenic function of mutations in seven functional gene groups: cell signaling genes, epigenetic modifier genes, nucleophosmin 1 (NPM1), transcription factors, tumor suppressors, spliceosome genes, and cohesin complex genes. Additionally, we provide a synergy map of frequently cooperating mutations in AML development and correlate prognosis of these mutations with leukemogenicity in mouse models to better understand the co-dependence of mutations in AML.

TP53 in Acute Myeloid Leukemia: Molecular Aspects and Patterns of Mutation

Mutation of the tumor suppressor gene, TP53, is associated with abysmal survival outcomes in acute myeloid leukemia (AML). Although it is the most commonly mutated gene in cancer, its occurrence is observed in only 5–10% of de novo AML, and in 30% of therapy related AML (t-AML). TP53 mutation serves as a prognostic marker of poor response to standard-of-care chemotherapy, particularly in t-AML and AML with complex cytogenetics. In light of a poor response to traditional chemotherapy and only a modest improvement in outcome with hypomethylation-based interventions, allogenic stem cell transplant is routinely recommended in these cases, albeit with a response that is often short lived. Despite being frequently mutated across the cancer spectrum, progress and enthusiasm for the development of p53 targeted therapeutic interventions is lacking and to date there is no approved drug that mitigates the effects of TP53 mutation. There is a mounting body of evidence indicating that p53 mutants differ in functionality and form from typical AML cases and subsequently display inconsistent responses to therapy at the cellular level. Understanding this pathobiological activity is imperative to the development of effective therapeutic strategies. This review aims to provide a comprehensive understanding of the effects of TP53 on the hematopoietic system, to describe its varying degree of functionality in tumor suppression, and to illustrate the need for the adoption of personalized therapeutic strategies to target distinct classes of the p53 mutation in AML management.

DNA-PK inhibitor peposertib enhances p53-dependent cytotoxicity of DNA double-strand break inducing therapy in acute leukemia

Peposertib (M3814) is a potent and selective DNA-PK inhibitor in early clinical development. It effectively blocks non-homologous end-joining repair of DNA double-strand breaks (DSB) and strongly potentiates the antitumor effect of ionizing radiation (IR) and topoisomerase II inhibitors. By suppressing DNA-PK catalytic activity in the presence of DNA DSB, M3814 potentiates ATM/p53 signaling leading to enhanced p53-dependent antitumor activity in tumor cells. Here, we investigated the therapeutic potential of M3814 in combination with DSB-inducing agents in leukemia cells and a patient-derived tumor. We show that in the presence of IR or topoisomerase II inhibitors, M3814 boosts the ATM/p53 response in acute leukemia cells leading to the elevation of p53 protein levels as well as its transcriptional activity. M3814 synergistically sensitized p53 wild-type, but not p53-deficient, AML cells to killing by DSB-inducing agents via p53-dependent apoptosis involving both intrinsic and extrinsic effector pathways. The antileukemic effect was further potentiated by enhancing daunorubicin-induced myeloid cell differentiation. Further, combined with the fixed-ratio liposomal formulation of daunorubicin and cytarabine, CPX-351, M3814 enhanced the efficacy against leukemia cells in vitro and in vivo without increasing hematopoietic toxicity, suggesting that DNA-PK inhibition could offer a novel clinical strategy for harnessing the anticancer potential of p53 in AML therapy.

RNA sequencing of long-term label-retaining colon cancer stem cells identifies novel regulators of quiescence

Recent data suggest that therapy-resistant quiescent cancer stem cells (qCSCs) are the source of relapse in colon cancer. Here, using colon cancer patient-derived organoids and xenografts, we identify rare long-term label-retaining qCSCs that can re-enter the cell cycle to generate new tumors. RNA sequencing analyses demonstrated that these cells display the molecular hallmarks of quiescent tissue stem cells, including expression of p53 signaling genes, and are enriched for transcripts common to damage-induced quiescent revival stem cells of the regenerating intestine. In addition, we identify negative regulators of cell cycle, downstream of p53, that we show are indicators of poor prognosis and may be targeted for qCSC abolition in both p53 wild-type and mutant tumors. These data support the temporal inhibition of downstream targets of p53 signaling, in combination with standard-of-care treatments, for the elimination of qCSCs and prevention of relapse in colon cancer.

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Colon tumors contain therapy-resistant quiescent cancer stem cells (qCSCs)

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qCSC gene expression mirrors that of quiescent stem cells of the regenerating gut

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qCSCs are enriched for p53 signaling genes

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qCSC elimination may be achieved by inhibiting downstream targets of p53 signaling

Molecular Landscapes and Models of Acute Erythroleukemia

Malignancies of the erythroid lineage are rare but aggressive diseases. Notably, the first insights into their biology emerged over half a century ago from avian and murine tumor viruses-induced erythroleukemia models providing the rationale for several transgenic mouse models that unraveled the transforming potential of signaling effectors and transcription factors in the erythroid lineage. More recently, genetic roadmaps have fueled efforts to establish models that are based on the epigenomic lesions observed in patients with erythroid malignancies. These models, together with often unexpected erythroid phenotypes in genetically modified mice, provided further insights into the molecular mechanisms of disease initiation and maintenance. Here, we review how the increasing knowledge of human erythroleukemia genetics combined with those from various mouse models indicate that the pathogenesis of the disease is based on the interplay between signaling mutations, impaired TP53 function, and altered chromatin organization. These alterations lead to aberrant activity of erythroid transcriptional master regulators like GATA1, indicating that erythroleukemia will most likely require combinatorial targeting for efficient therapeutic interventions.

Clonal hematopoiesis and risk for hematologic malignancy

Clonal hematopoiesis (CH) is common in older persons and is associated with an increased risk of hematologic cancer. Here, we review studies establishing an association between CH and hematopoietic malignancy, discuss features of CH that are predictive of leukemic progression, and explore the role of hematopoietic stressors in the evolution of CH to acute myeloid leukemia or myelodysplastic syndrome. CH due to point mutations or structural variants such as copy-number alterations is associated with an ∼10-fold increased risk of hematopoietic malignancy. Although the absolute risk of hematopoietic malignancy is low, certain features of CH may confer a higher risk of transformation, including the presence of TP53 or spliceosome gene mutations, a variant allele fraction >10%, the presence of multiple mutations, and altered red blood indices. CH in the setting of peripheral blood cytopenias carries a very high risk of progression to a myeloid malignancy and merits close observation. There is emerging evidence suggesting that hematopoietic stressors contribute to both the development of CH and progression to hematopoietic malignancy. Specifically, there is evidence that genotoxic stress from chemotherapy or radiation therapy, ribosome biogenesis stress, and possibly inflammation may increase the risk of transformation from CH to a myeloid malignancy. Models that incorporate features of CH along with an assessment of hematopoietic stressors may eventually help predict and prevent the development of hematopoietic malignancies.

The Agglutinin of Common Nettle (Urtica dioica L.) Plant Effects on Gene Expression Related to Apoptosis of Human Acute Myeloid Leukemia Cell Line

Treatment of acute myeloid leukemia (AML) requires new drugs as result of a rise in new cases and high disease relapse. Plant lectins with the ability to bind carbohydrates on the cell surface have the potential to treat cancer. Urtica dioica L. agglutinin (UDA) is a low weight lectin with anti-benign prostatic hyperplasia (BPH) impact. Here, we examine the impact of UDA on HL-60 cell line. Cytotoxicity and cytostatic effects were assessed in HL-60 cells treated with UDA and vincristine (positive control). The effects of the lectin on cell cycle phases and cell death mechanism were surveyed by propidium iodide (PI) staining and annexin V/PI, respectively. The activation status of the apoptosis pathway was determined by western blotting. Finally, the expression levels of 84 genes were examined by the Human cancer drug target gene PCR array kit. The results indicated that the increase in UDA concentration inhibited the proliferation of HL-60 cells as well as apoptosis induction. Cell cycle analysis showed that the number of sub G1 cells increased essentially. Experimental observations showed that UDA can induce cell apoptosis through a caspase 9-dependent pathway. The expression changes of 21 genes confirmed the apoptotic events in HL-60 cells treated with UDA. In this, we have presented the first investigation on the cytotoxic and apoptotic effects of a lectin isolated from rhizomes and roots of Urtica dioica L. on human AML cells. Generally, the results suggest that UDA may have therapeutic value for leukemia and would be studied further as a new drug for AML later on.

BRD4-mediated repression of p53 is a target for combination therapy in AML

Acute myeloid leukemia (AML) is a typically lethal molecularly heterogeneous disease, with few broad-spectrum therapeutic targets. Unusually, most AML retain wild-type TP53, encoding the pro-apoptotic tumor suppressor p53. MDM2 inhibitors (MDM2i), which activate wild-type p53, and BET inhibitors (BETi), targeting the BET-family co-activator BRD4, both show encouraging pre-clinical activity, but limited clinical activity as single agents. Here, we report enhanced toxicity of combined MDM2i and BETi towards AML cell lines, primary human blasts and mouse models, resulting from BETi's ability to evict an unexpected repressive form of BRD4 from p53 target genes, and hence potentiate MDM2i-induced p53 activation. These results indicate that wild-type TP53 and a transcriptional repressor function of BRD4 together represent a potential broad-spectrum synthetic therapeutic vulnerability for AML.

Cancer Stemness: p53 at the Wheel

The tumor suppressor p53 maintains an equilibrium between self-renewal and differentiation to sustain a limited repertoire of stem cells for proper development and maintenance of tissue homeostasis. Inactivation of p53 disrupts this balance and promotes pluripotency and somatic cell reprogramming. A few reports in recent years have indicated that prevalent TP53 oncogenic gain-of-function (GOF) mutations further boosts the stemness properties of cancer cells. In this review, we discuss the role of wild type p53 in regulating pluripotency of normal stem cells and various mechanisms that control the balance between self-renewal and differentiation in embryonic and adult stem cells. We also highlight how inactivating and GOF mutations in p53 stimulate stemness in cancer cells. Further, we have explored the various mechanisms of mutant p53-driven cancer stemness, particularly emphasizing on the non-coding RNA mediated epigenetic regulation. We have also analyzed the association of cancer stemness with other crucial gain-of-function properties of mutant p53 such as epithelial to mesenchymal transition phenotypes and chemoresistance to understand how activation of one affects the other. Given the critical role of cancer stem-like cells in tumor maintenance, cancer progression, and therapy resistance of mutant p53 tumors, targeting them might improve therapeutic efficacy in human cancers with TP53 mutations.

Mouse Models of Myeloid Malignancies

Mouse models of human myeloid malignancies support the detailed and focused investigation of selected driver mutations and represent powerful tools in the study of these diseases. Carefully developed murine models can closely recapitulate human myeloid malignancies in vivo, enabling the interrogation of a number of aspects of these diseases including their preclinical course, interactions with the microenvironment, effects of pharmacological agents, and the role of non-cell-autonomous factors, as well as the synergy between co-occurring mutations. Importantly, advances in gene-editing technologies, particularly CRISPR-Cas9, have opened new avenues for the development and study of genetically modified mice and also enable the direct modification of mouse and human hematopoietic cells. In this review we provide a concise overview of some of the important mouse models that have advanced our understanding of myeloid leukemogenesis with an emphasis on models relevant to clonal hematopoiesis, myelodysplastic syndromes, and acute myeloid leukemia with a normal karyotype.

Acute Myeloid Leukemia and Myelodysplastic Syndromes with TP53 Aberrations - A Distinct Stem Cell Disorder

The tumor suppressor p53 exerts pivotal roles in hematopoietic stem cell (HSC) homeostasis. Mutations of the TP53 gene have recently been described in individuals with clonal hematopoiesis conferring substantial risk of developing blood cancers. In patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), TP53 aberrations-mutations, deletions, and a combination thereof-are encountered at a constant frequency of approximately 10%. These aberrations affect HSCs transforming them into preleukemic stem cells, pinpointing their central role in leukemogenesis. AML and MDS with TP53 aberrations are characterized by complex chromosomal aberrations. Respective patients experience a dismal long-term outcome following treatment with both intensive and nonintensive regimens including novel agents like venetoclax combinations or even allogeneic HSC transplantation. However, according to the 2016 WHO classification, AML and MDS with TP53 aberrations are still regarded as separate disease entities. On the basis of their common biological and clinical features, we propose to classify AML and MDS with TP53 aberrations as a single, distinct stem cell disorder with a unique genetic make-up, comparable with the WHO classification of "AML with recurrent genetic abnormalities." This approach will have implications for basic and translational research endeavors, aid in harmonization of current treatment strategies, and facilitate the development of master trials targeting a common deleterious driver event.

Which are the most promising targets for minimal residual disease-directed therapy in acute myeloid leukemia prior to allogeneic stem cell transplant?

Minimal residual disease has emerged as an important prognostic factor for relapse and survival in acute myeloid leukemia. Eradication of minimal residual disease may increase the number of patients with long-term survival; however, to date, strategies that specifically target minimal residual disease are limited. Consensus guidelines on minimal residual disease detection by immunophenotypic and molecular methods are an essential initial step for clinical trials evaluating minimal residual disease. Here, we review promising targets of minimal residual disease prior to allogeneic stem cell transplantation. Specifically, the focus of this review is on the rationale and clinical development of therapies targeting: oncogenic driver mutations, apoptosis, methylation, and leukemic immune targets. We review the progress made in the clinical development of therapies against each target and the challenges that lie ahead.

Chetomin, a Hsp90/HIF1α pathway inhibitor, effectively targets lung cancer stem cells and non-stem cells

Non-small cell lung cancer (NSCLC) remains recalcitrant to effective treatment due to tumor relapse and acquired resistance. Cancer stem cells (CSCs) are believed to be one mechanism for relapse and resistance and are consequently considered promising drug targets. We report that chetomin, an active component of Chaetomium globosum, blocks heat shock protein 90/hypoxia-inducible factor 1 alpha (Hsp90/HIF1α) pathway activity. Chetomin also attenuated sphere-forming, a stem cell-like characteristic, of NSCLC CSCs (at ~ nM range) and the proliferation of non-CSCs NSCLC cultures and chemoresistant sublines (at ~ μM range). At these concentrations, chetomin exerted a marginal influence on noncancerous cells originating from several organs. Chetomin markedly decreased in vivo tumor formation in a spontaneous Kras ^LA1 lung cancer model, flank xenograft models, and a tumor propagation flank implanted model at doses that did not produce an observable toxicity to the animals. Chetomin blocked Hsp90/HIF1α pathway activity via inhibiting the Hsp90-HIF1α binding interaction without affecting Hsp90 or Hsp70 protein levels. This study advocates chetomin as a Hsp90/HIF1α pathway inhibitor and a potent, nontoxic NSCLC CSC-targeting molecule.

Molecular modulation of autophagy: New venture to target resistant cancer stem cells

Autophagy is a highly regulated catabolic process in which superfluous, damaged organelles and other cytoplasmic constituents are delivered to the lysosome for clearance and the generation of macromolecule substrates during basal or stressed conditions. Autophagy is a bimodal process with a context dependent role in the initiation and the development of cancers. For instance, autophagy provides an adaptive response to cancer stem cells to survive metabolic stresses, by influencing disease propagation via modulation of essential signaling pathways or by promoting resistance to chemotherapeutics. Autophagy has been implicated in a cross talk with apoptosis. Understanding the complex interactions provides an opportunity to improve cancer therapy and the clinical outcome for the cancer patients. In this review, we provide a comprehensive view on the current knowledge on autophagy and its role in cancer cells with a particular focus on cancer stem cell homeostasis.

FAM213A is linked to prognostic significance in acute myeloid leukemia through regulation of oxidative stress and myelopoiesis

Accurate prediction of malignancies is important in choosing therapeutic strategies. Although there are many genetic and cytogenetic prognostic factors for acute myeloid leukemia (AML), prognosis is difficult to predict because of the heterogeneity of AML. Prognostic factors, including messenger RNA (mRNA) expression, have been determined for other malignancies, but not for AML. A total of 402 patients from The Cancer Genome Atlas, GSE12417 (GPL96, 97), and GSE12417 (GPL570) were included in this study. In Kaplan-Meier curve analyses, high expression of family with sequence similarity 213 member A (FAM213A), which activates antioxidant proteins, was associated with worse prognosis of AML. Similar to the results of the survival curve, C-indices and area under the curve values were high. Current prognostic factors of AML, unlike those of other cancers, do not take mRNA expression into consideration. Thus, the development of mRNA-based prognostic factors would be beneficial for accurate prediction of the survival of AML patients. Additionally, in vivo validation using zebrafish revealed that fam213a is important for myelopoiesis at the developmental stage and is a negative regulator of the p53 tumor suppressor gene. The findings implicate fam213a as a novel prognostic factor for AML patients.

The role of TP53 in acute myeloid leukemia: Challenges and opportunities

The tumor suppressor gene TP53 is one of the most frequently mutated genes in human cancer. The central role of the TP53 protein in several fundamental processes such as cancer, aging, senescence, and DNA repair has ensured enormous attention. However, the role of TP53 in acute myeloid leukemia (AML) is enigmatic. Unlike many other human cancers, a vast majority of AMLs display no genomic TP53 alterations. There is now growing appreciation of the fact that the unaltered TP53 status of tumor cells can be exploited therapeutically. As most AMLs have an intact TP53 gene, its physiological tumor-suppressive roles could be harnessed. Therefore, the use of pharmacological activators of the TP53 pathway may provide clinical benefit in AML. Conversely, even though the frequency of TP53 mutations in AML is substantially lower than in other human cancers, TP53 mutations are associated with chemoresistance and high risk of relapse. In patients with TP53 mutations, these alterations may lead to novel, selective vulnerabilities, creating opportunities for therapeutic targeting of TP53 mutant AML. The mutational status of TP53 therefore poses challenges and opportunities in terms of advancing effective treatment strategies in AML. An increasing armamentarium of small-molecule activators of the TP53 pathway, and a growing understanding of molecular pathways triggered by mutant TP53 have accelerated efforts aimed at targeting TP53 function in AML. In combination with standard AML chemotherapy or emerging targeted therapies, pharmacological targeting of the TP53 pathway may provide therapeutic benefit in AML.

Dual inhibition of MDMX and MDM2 as a therapeutic strategy in leukemia

The tumor suppressor p53 is often inactivated via its interaction with endogenous inhibitors mouse double minute 4 homolog (MDM4 or MDMX) or mouse double minute 2 homolog (MDM2), which are frequently overexpressed in patients with acute myeloid leukemia (AML) and other cancers. Pharmacological disruption of both of these interactions has long been sought after as an attractive strategy to fully restore p53-dependent tumor suppressor activity in cancers with wild-type p53. Selective targeting of this pathway has thus far been limited to MDM2-only small-molecule inhibitors, which lack affinity for MDMX. We demonstrate that dual MDMX/MDM2 inhibition with a stapled α-helical peptide (ALRN-6924), which has recently entered phase I clinical testing, produces marked antileukemic effects. ALRN-6924 robustly activates p53-dependent transcription at the single-cell and single-molecule levels and exhibits biochemical and molecular biological on-target activity in leukemia cells in vitro and in vivo. Dual MDMX/MDM2 inhibition by ALRN-6924 inhibits cellular proliferation by inducing cell cycle arrest and apoptosis in cell lines and primary AML patient cells, including leukemic stem cell-enriched populations, and disrupts functional clonogenic and serial replating capacity. Furthermore, ALRN-6924 markedly improves survival in AML xenograft models. Our study provides mechanistic insight to support further testing of ALRN-6924 as a therapeutic approach in AML and other cancers with wild-type p53.

p53 and Cell Fate: Sensitizing Head and Neck Cancer Stem Cells to Chemotherapy

Head and neck cancers are deadly diseases that are diagnosed annually in approximately half a million individuals worldwide. Growing evidence supporting a role for cancer stem cells (CSCs) in the pathobiology of head and neck cancers has led to increasing interest in identifying therapeutics to target these cells. Apart from the canonical tumor-suppressor functions of p53, emerging research supports a significant role for this protein in physiological stem cell and CSC maintenance and reprogramming. Therefore, p53 has become a promising target to sensitize head and neck CSCs to chemotherapy. In this review, we highlight the role of p53 in stem cell maintenance and discuss potential implications of targeting p53 to treat patients with head and neck cancers.

Phase 1b study of the MDM2 inhibitor AMG 232 with or without trametinib in relapsed/refractory acute myeloid leukemia

This open-label, phase 1 study evaluated the safety, pharmacokinetics, and maximum tolerated dose of AMG 232, an investigational oral, selective mouse double minute 2 homolog inhibitor in relapsed/refractory acute myeloid leukemia (AML). AMG 232 was administered orally once daily for 7 days every 2 weeks (7 on/off) at 60, 120, 240, 360, 480, or 960 mg as monotherapy (arm 1) or at 60 mg with trametinib 2 mg (arm 2). Dose-limiting toxicities (DLTs), adverse events (AEs), pharmacokinetics, clinical and pharmacodynamic response, and expression of p53 target genes were assessed. All 36 patients received AMG 232. No DLTs occurred in arm 1, and 360 mg was the highest test dose; dose escalation was halted due to gastrointestinal AEs at higher doses. One of ten patients in arm 2 had a DLT (grade 3 fatigue); 60 mg was the highest dose tested with trametinib. Common treatment-related AEs (any grade) included nausea (58%), diarrhea (56%), vomiting (33%), and decreased appetite (25%). AMG 232 exhibited linear pharmacokinetics unaffected by coadministration with trametinib. Serum macrophage inhibitor cytokine-1 and bone marrow expression of BAX, PUMA, P21, and MDM2 increased during treatment. Of 30 evaluable patients, 1 achieved complete remission, 4 had morphologic leukemia-free state, and 1 had partial remission. Four of 13 (31%) TP53-wild-type patients and 0 of 3 (0%) TP53-mutant patients were responders. AMG 232 was associated with gastrointestinal AEs at higher doses but had acceptable pharmacokinetics, on-target effects, and promising clinical activity warranting further investigation in patients with relapsed/refractory AML. This trial was registered at www.clinicaltrials.gov as #NCT02016729.

A Gain-of-Function p53-Mutant Oncogene Promotes Cell Fate Plasticity and Myeloid Leukemia through the Pluripotency Factor FOXH1

Mutations in the TP53 tumor suppressor gene are common in many cancer types, including the acute myeloid leukemia (AML) subtype known as complex karyotype AML (CK-AML). Here, we identify a gain-of-function (GOF) Trp53 mutation that accelerates CK-AML initiation beyond p53 loss and, surprisingly, is required for disease maintenance. The Trp53^R172H mutation (TP53^R175H in humans) exhibits a neomorphic function by promoting aberrant self-renewal in leukemic cells, a phenotype that is present in hematopoietic stem and progenitor cells (HSPC) even prior to their transformation. We identify FOXH1 as a critical mediator of mutant p53 function that binds to and regulates stem cell-associated genes and transcriptional programs. Our results identify a context where mutant p53 acts as a bona fide oncogene that contributes to the pathogenesis of CK-AML and suggests a common biological theme for TP53 GOF in cancer. SIGNIFICANCE: Our study demonstrates how a GOF p53 mutant can hijack an embryonic transcription factor to promote aberrant self-renewal. In this context, mutant Trp53 functions as an oncogene to both initiate and sustain myeloid leukemia and suggests a potential convergent activity of mutant Trp53 across cancer types.This article is highlighted in the In This Issue feature, p. 813.

A model for RAS mutation patterns in cancers: finding the sweet spot

The three RAS genes - HRAS, NRAS and KRAS - are collectively mutated in one-third of human cancers, where they act as prototypic oncogenes. Interestingly, there are rather distinct patterns to RAS mutations; the isoform mutated as well as the position and type of substitution vary between different cancers. As RAS genes are among the earliest, if not the first, genes mutated in a variety of cancers, understanding how these mutation patterns arise could inform on not only how cancer begins but also the factors influencing this event, which has implications for cancer prevention. To this end, we suggest that there is a narrow window or 'sweet spot' by which oncogenic RAS signalling can promote tumour initiation in normal cells. As a consequence, RAS mutation patterns in each normal cell are a product of the specific RAS isoform mutated, as well as the position of the mutation and type of substitution to achieve an ideal level of signalling.

tp53 deficiency causes a wide tumor spectrum and increases embryonal rhabdomyosarcoma metastasis in zebrafish

The TP53 tumor-suppressor gene is mutated in >50% of human tumors and Li-Fraumeni patients with germ line inactivation are predisposed to developing cancer. Here, we generated tp53 deleted zebrafish that spontaneously develop malignant peripheral nerve-sheath tumors, angiosarcomas, germ cell tumors, and an aggressive Natural Killer cell-like leukemia for which no animal model has been developed. Because the tp53 deletion was generated in syngeneic zebrafish, engraftment of fluorescent-labeled tumors could be dynamically visualized over time. Importantly, engrafted tumors shared gene expression signatures with predicted cells of origin in human tissue. Finally, we showed that tp53^del/del enhanced invasion and metastasis in kRAS^G12D-induced embryonal rhabdomyosarcoma (ERMS), but did not alter the overall frequency of cancer stem cells, suggesting novel pro-metastatic roles for TP53 loss-of-function in human muscle tumors. In summary, we have developed a Li-Fraumeni zebrafish model that is amenable to large-scale transplantation and direct visualization of tumor growth in live animals.

Wiskott-Aldrich syndrome gene mutations modulate cancer susceptibility in the p53± murine model

The Wiskott-Aldrich syndrome protein (WASp) is a key regulator of the actin cytoskeleton in hematopoietic cells and mutated in two severe immunodeficiency diseases with high incidence of cancer. Wiskott-Aldrich syndrome (WAS) is caused by loss-of-function mutations in WASp and most frequently associated with lymphoreticular tumors of poor prognosis. X-linked neuropenia (XLN) is caused by gain-of-function mutations in WASp and associated with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). To understand the role of WASp in tumorigenesis, we bred WASp⁺, WASp⁻, and WASp-XLN mice onto tumor susceptible p53^+/- background and sub-lethally irradiated them to enhance tumor development. We followed the cohorts for 24 weeks and tumors were characterized by histology and flow cytometry to define the tumor incidence, onset, and cell origin. We found that p53^+/-WASp⁺ mice developed malignancies, including solid tumors and T cell lymphomas with 71.4% of survival 24 weeks after irradiation. p53^+/-WASp⁻ mice showed lower survival rate and developed various early onset malignancies. Surprisingly, the p53^+/-WASp-XLN mice developed malignancy mostly with late onset, which caused delayed mortality in this colony. This study provides evidence for that loss-of-function and gain-of-function mutations in WASp influence tumor incidence and onset.

Iron Drives T Helper Cell Pathogenicity by Promoting RNA-Binding Protein PCBP1-Mediated Proinflammatory Cytokine Production

Iron deposition is frequently observed in human autoinflammatory diseases, but its functional significance is largely unknown. Here we showed that iron promoted proinflammatory cytokine expression in T cells, including GM-CSF and IL-2, via regulating the stability of an RNA-binding protein PCBP1. Iron depletion or Pcbp1 deficiency in T cells inhibited GM-CSF production by attenuating Csf2 3' untranslated region (UTR) activity and messenger RNA stability. Pcbp1 deficiency or iron uptake blockade in autoreactive T cells abolished their capacity to induce experimental autoimmune encephalomyelitis, an animal model for multiple sclerosis. Mechanistically, intracellular iron protected PCBP1 protein from caspase-mediated proteolysis, and PCBP1 promoted messenger RNA stability of Csf2 and Il2 by recognizing UC-rich elements in the 3' UTRs. Our study suggests that iron accumulation can precipitate autoimmune diseases by promoting proinflammatory cytokine production. RNA-binding protein-mediated iron sensing may represent a simple yet effective means to adjust the inflammatory response to tissue homeostatic alterations.

USP22 deficiency leads to myeloid leukemia upon oncogenic Kras activation through a PU.1-dependent mechanism

Ras mutations are commonly observed in juvenile myelomonocytic leukemia (JMML) and chronic myelomonocytic leukemia (CMML). JMML and CMML transform into acute myeloid leukemia (AML) in about 10% and 50% of patients, respectively. However, how additional events cooperate with Ras to promote this transformation are largely unknown. We show that absence of the ubiquitin-specific peptidase 22 (USP22), a component of the Spt-Ada-GCN5-acetyltransferase chromatin-remodeling complex that is linked to cancer progression, unexpectedly promotes AML transformation in mice expressing oncogenic Kras^G12D/+ USP22 deficiency in Kras^G12D/+ mice resulted in shorter survival compared with control mice. This was due to a block in myeloid cell differentiation leading to the generation of AML. This effect was cell autonomous because mice transplanted with USP22-deficient Kras^G12D/+ cells developed an aggressive disease and died rapidly. The transcriptome profile of USP22-deficient Kras^G12D/+ progenitors resembled leukemic stem cells and was highly correlated with genes associated with poor prognosis in AML. We show that USP22 functions as a PU.1 deubiquitylase by positively regulating its protein stability and promoting the expression of PU.1 target genes. Reconstitution of PU.1 overexpression in USP22-deficient Kras^G12D/+ progenitors rescued their differentiation. Our findings uncovered an unexpected role for USP22 in Ras-induced leukemogenesis and provide further insights into the function of USP22 in carcinogenesis.

Changes of signal transductivity and robustness of gene regulatory network in the carcinogenesis of leukemic subtypes via microarray sample data

Mutation accumulation and epigenetic alterations in genes are important for carcinogenesis. Because leukemogenesis-related signal pathways have been investigated and microarray sample data have been produced in acute myeloid leukemia (AML), myelodysplastic syndromes (MDS) and normal cells, systems analysis in coupling pathways becomes possible.

Based on system modeling and identification, we could construct the coupling pathways and their associated gene regulatory networks using microarray sample data. By applying system theory to the estimated system model in coupling pathways, we can then obtain transductivity sensitivity, basal sensitivity and error sensitivity of each protein to identify the potential impact of genetic mutations, epigenetic alterations and the coupling of other pathways from the perspective of energy, respectively. By comparing the results in AML, MDS and normal cells, we investigated the potential critical genetic mutations and epigenetic alterations that activate or repress specific cellular functions to promote MDS or AML leukemogenesis. We suggested that epigenetic modification of β-catenin and signal integration of CSLs, AP-2α, STATs, c-Jun and β-catenin could contribute to cell proliferation at AML and MDS. Epigenetic regulation of ERK and genetic mutation of p53 could lead to the repressed apoptosis, cell cycle arrest and DNA repair in leukemic cells. Genetic mutation of JAK, epigenetic regulation of ERK, and signal integration of C/EBPα could result in the promotion of MDS cell differentiation. According to the results, we proposed three drugs, decitabine, genistein, and monorden for preventing AML leukemogenesis, while three drugs, decitabine, thalidomide, and geldanamycin, for preventing MDS leukemogenesis.

p53: emerging roles in stem cells, development and beyond

Most human cancers harbor mutations in the gene encoding p53. As a result, research on p53 in the past few decades has focused primarily on its role as a tumor suppressor. One consequence of this focus is that the functions of p53 in development have largely been ignored. However, recent advances, such as the genomic profiling of embryonic stem cells, have uncovered the significance and mechanisms of p53 functions in mammalian cell differentiation and development. As we review here, these recent findings reveal roles that complement the well-established roles for p53 in tumor suppression.

Rapid chromatin repression by Aire provides precise control of immune tolerance

Aire mediates the expression of tissue-specific antigens in thymic epithelial cells to promote tolerance against self-reactive T lymphocytes. However, the mechanism that allows expression of tissue-specific genes at levels that prevent harm is unknown. Here we show that Brg1 generates accessibility at tissue-specific loci to impose central tolerance. We found that Aire has an intrinsic repressive function that restricts chromatin accessibility and opposes Brg1 across the genome. Aire exerted this repressive influence within minutes after recruitment to chromatin and restrained the amplitude of active transcription. Disease-causing mutations that impair Aire-induced activation also impair the protein's repressive function, which indicates dual roles for Aire. Together, Brg1 and Aire fine-tune the expression of tissue-specific genes at levels that prevent toxicity yet promote immune tolerance.

Differentiation therapy revisited

The concept of differentiation therapy emerged from the fact that hormones or cytokines may promote differentiation ex vivo, thereby irreversibly changing the phenotype of cancer cells. Its hallmark success has been the treatment of acute promyelocytic leukaemia (APL), a condition that is now highly curable by the combination of retinoic acid (RA) and arsenic. Recently, drugs that trigger differentiation in a variety of primary tumour cells have been identified, suggesting that they are clinically useful. This Opinion article analyses the basis for the clinical successes of RA or arsenic in APL by assessing the respective roles of terminal maturation and loss of self-renewal. By reviewing other successful examples of drug-induced tumour cell differentiation, novel approaches to transform differentiating drugs into more efficient therapies are proposed.

A non-cell-autonomous role for Pml in the maintenance of leukemia from the niche

Disease recurrence after therapy, due to the persistence of resistant leukemic cells, represents a fundamental problem in the treatment of leukemia. Elucidating the mechanisms responsible for the maintenance of leukemic cells, before and after treatment, is therefore critical to identify curative modalities. It has become increasingly clear that cell-autonomous mechanisms are not solely responsible for leukemia maintenance. Here, we report a role for Pml in mesenchymal stem cells (MSCs) in supporting leukemic cells of both CML and AML. Mechanistically, we show that Pml regulates pro-inflammatory cytokines within MSCs, and that this function is critical in sustaining CML-KLS and AML ckit+ leukemic cells non-cell autonomously.

Identification of key pathways and genes in TP53 mutation acute myeloid leukemia: evidence from bioinformatics analysis

Background

Tumor protein p53 (TP53) mutations are not only a risk factor in acute myeloid leukemia (AML) but also a potential biomarker for individualized treatment options. This study aimed to investigate potential pathways and genes associated with TP53 mutations in adult de novo AML.

Methods

An RNA sequencing dataset of adult de novo AML was downloaded from The Cancer Genome Atlas database. Differentially expressed genes (DEGs) were identified by edgeR of the R platform. Key pathways and genes were identified using the following bioinformatics tools: gene set enrichment analysis (GSEA), gene ontology (GO), the Kyoto Encyclopedia of Genes and Genomes (KEGG), Search Tool for the Retrieval of Interacting Genes/Proteins, and Molecular Complex Detection.

Results

GSEA suggested that TP53 mutations were significantly associated with cell differentiation, proliferation, cell adhesion biological processes, and MAPK pathway. In total, 1,287 genes were identified as DEGs. GO and KEGG analysis suggested that upregulation of DEGs was significantly enriched in categories associated with cell adhesion biological processes, Ras-associated protein 1, PI3K-Akt pathway, and cell adhesion molecules. The top ten genes ranked by degree, CDH1, BMP2, KDR, LEP, CASR, ITGA2B, APOE, MNX1, NMU, and TRH, were identified as hub genes from the protein-protein interaction network. Survival analysis suggested that patients with TP53 mutations had a significantly increased risk of death, while the mRNA expression level in patients with TP53 mutation was similar to those carrying TP53 wild type.

Conclusion

Our findings have indicated that multiple genes and pathways may play a crucial role in TP53 mutation AML, offering candidate targets and strategies for TP53 mutation AML individualized treatment.