PAX5-ELN oncoprotein promotes multistep B-cell acute lymphoblastic leukemia in mice

Janus Kinase 3 (JAK3): A Critical Conserved Node in Immunity Disrupted in Immune Cell Cancer and Immunodeficiency

The Janus kinase (JAK) family is a small group of protein tyrosine kinases that represent a central component of intracellular signaling downstream from a myriad of cytokine receptors. The JAK3 family member performs a particularly important role in facilitating signal transduction for a key set of cytokine receptors that are essential for immune cell development and function. Mutations that impact JAK3 activity have been identified in a number of human diseases, including somatic gain-of-function (GOF) mutations associated with immune cell malignancies and germline loss-of-function (LOF) mutations associated with immunodeficiency. The structure, function and impacts of both GOF and LOF mutations of JAK3 are highly conserved, making animal models highly informative. This review details the biology of JAK3 and the impact of its perturbation in immune cell-related diseases, including relevant animal studies.

Stem cell-like reprogramming is required for leukemia-initiating activity in B-ALL

B cell acute lymphoblastic leukemia (B-ALL) is a multistep disease characterized by the hierarchical acquisition of genetic alterations. However, the question of how a primary oncogene reprograms stem cell-like properties in committed B cells and leads to a preneoplastic population remains unclear. Here, we used the PAX5::ELN oncogenic model to demonstrate a causal link between the differentiation blockade, the self-renewal, and the emergence of preleukemic stem cells (pre-LSCs). We show that PAX5::ELN disrupts the differentiation of preleukemic cells by enforcing the IL7r/JAK-STAT pathway. This disruption is associated with the induction of rare and quiescent pre-LSCs that sustain the leukemia-initiating activity, as assessed using the H2B-GFP model. Integration of transcriptomic and chromatin accessibility data reveals that those quiescent pre-LSCs lose B cell identity and reactivate an immature molecular program, reminiscent of human B-ALL chemo-resistant cells. Finally, our transcriptional regulatory network reveals the transcription factor EGR1 as a strong candidate to control quiescence/resistance of PAX5::ELN pre-LSCs as well as of blasts from human B-ALL.

Lessons from mouse models in the impact of risk factors on the genesis of childhood B-cell leukemia

B-cell acute lymphoblastic leukemia (B-ALL) stands as the primary contributor to childhood cancer-related mortality on a global scale. The development of the most conventional forms of this disease has been proposed to be conducted by two different steps influenced by different types of risk factors. The first step is led by a genetic insult that is presumably acquired before birth that transforms a healthy cell into a preleukemic one, which is maintained untransformed until the second step takes place. This necessary next step to leukemia development will be triggered by different risk factors to which children are exposed after birth. Murine models that recap the stepwise progression of B-ALL have been instrumental in identifying environmental and genetic factors that contribute to disease risk. Recent evidence from these models has demonstrated that specific environmental risk factors, such as common infections or gut microbiome dysbiosis, induce immune stress, driving the transformation of preleukemic cells, and harboring genetic alterations, into fully transformed leukemic cells. Such models serve as valuable tools for investigating the mechanisms underlying preleukemic events and can aid in the development of preventive approaches for leukemia in child. Here, we discuss the existing knowledge, learned from mouse models, of the impact of genetic and environmental risk factors on childhood B-ALL evolution and how B-ALL prevention could be reached by interfering with preleukemic cells.

PAX5 fusion genes in acute lymphoblastic leukemia: A literature review

Acute lymphoblastic leukemia (ALL) is a common cancer affecting children worldwide. The development of ALL is driven by several genes, some of which can be targeted for treatment by inhibiting gene fusions. PAX5 is frequently mutated in ALL and is involved in chromosomal rearrangements and translocations. Mutations in PAX5 interact with other genes, such as ETV6 and FOXP1, which influence B-cell development. PAX5/ETV6 has been observed in both B-ALL patients and a mouse model. The interaction between PAX5 and FOXP1 negatively suppresses the Pax5 gene in B-ALL patients. Additionally, ELN and PML genes have been found to fuse with PAX5, leading to adverse effects on B-cell differentiation. ELN-PAX5 interaction results in the decreased expression of LEF1, MB1, and BLNK, while PML-PAX5 is critical in the early stages of leukemia. PAX5 fusion genes prevent the transcription of the PAX5 gene, making it an essential target gene for the study of leukemia progression and the diagnosis of B-ALL.

PAX5 alterations in B-cell acute lymphoblastic leukemia

PAX5, a master regulator of B cell development and maintenance, is one of the most common targets of genetic alterations in B-cell acute lymphoblastic leukemia (B-ALL). PAX5 alterations consist of copy number variations (whole gene, partial, or intragenic), translocations, and point mutations, with distinct distribution across B-ALL subtypes. The multifaceted functional impacts such as haploinsufficiency and gain-of-function of PAX5 depending on specific variants have been described, thereby the connection between the blockage of B cell development and the malignant transformation of normal B cells has been established. In this review, we provide the recent advances in understanding the function of PAX5 in orchestrating the development of both normal and malignant B cells over the past decade, with a focus on the PAX5 alterations shown as the initiating or driver events in B-ALL. Recent large-scale genomic analyses of B-ALL have identified multiple novel subtypes driven by PAX5 genetic lesions, such as the one defined by a distinct gene expression profile and PAX5 P80R mutation, which is an exemplar leukemia entity driven by a missense mutation. Although altered PAX5 is shared as a driver in B-ALL, disparate disease phenotypes and clinical outcomes among the patients indicate further heterogeneity of the underlying mechanisms and disturbed gene regulation networks along the disease development. In-depth mechanistic studies in human B-ALL and animal models have demonstrated high penetrance of PAX5 variants alone or concomitant with other genetic lesions in driving B-cell malignancy, indicating the altered PAX5 and deregulated genes may serve as potential therapeutic targets in certain B-ALL cases.

The Pleiotropy of PAX5 Gene Products and Function

PAX5, a member of the Paired Box (PAX) transcription factor family, is an essential factor for B-lineage identity during lymphoid differentiation. Mechanistically, PAX5 controls gene expression profiles, which are pivotal to cellular processes such as viability, proliferation, and differentiation. Given its crucial function in B-cell development, PAX5 aberrant expression also correlates with hallmark cancer processes leading to hematological and other types of cancer lesions. Despite the well-established association of PAX5 in the development, maintenance, and progression of cancer disease, the use of PAX5 as a cancer biomarker or therapeutic target has yet to be implemented. This may be partly due to the assortment of PAX5 expressed products, which layers the complexity of their function and role in various regulatory networks and biological processes. In this review, we provide an overview of the reported data describing PAX5 products, their regulation, and function in cellular processes, cellular biology, and neoplasm.

Childhood B-Cell Preleukemia Mouse Modeling

Leukemia is the most usual childhood cancer, and B-cell acute lymphoblastic leukemia (B-ALL) is its most common presentation. It has been proposed that pediatric leukemogenesis occurs through a “multi-step” or “multi-hit” mechanism that includes both in utero and postnatal steps. Many childhood leukemia-initiating events, such as chromosomal translocations, originate in utero, and studies so far suggest that these “first-hits” occur at a far higher frequency than the incidence of childhood leukemia itself. The reason why only a small percentage of the children born with such preleukemic “hits” will develop full-blown leukemia is still a mystery. In order to better understand childhood leukemia, mouse modeling is essential, but only if the multistage process of leukemia can be recapitulated in the model. Therefore, mouse models naturally reproducing the “multi-step” process of childhood B-ALL will be essential to identify environmental or other factors that are directly linked to increased risk of disease.

In vivo impact of JAK3 A573V mutation revealed using zebrafish

Background

Janus kinase 3 (JAK3) acts downstream of the interleukin-2 (IL-2) receptor family to play a pivotal role in the regulation of lymphoid cell development. Activating JAK3 mutations are associated with a number of lymphoid and other malignancies, with mutations within the regulatory pseudokinase domain common.

Methods

The pseudokinase domain mutations A572V and A573V were separately introduced into the highly conserved zebrafish Jak3 and transiently expressed in cell lines and zebrafish embryos to examine their activity and impact on early T cells. Genome editing was subsequently used to introduce the A573V mutation into the zebrafish genome to study the effects of JAK3 activation on lymphoid cells in a physiologically relevant context throughout the life-course.

Results

Zebrafish Jak3 A573V produced the strongest activation of downstream STAT5 in vitro and elicited a significant increase in T cells in zebrafish embryos. Zebrafish carrying just a single copy of the Jak3 A573V allele displayed elevated embryonic T cells, which continued into adulthood. Hematopoietic precursors and NK cells were also increased, but not B cells. The lymphoproliferative effects of Jak3 A573V in embryos was shown to be dependent on zebrafish IL-2Rγc, JAK1 and STAT5B equivalents, and could be suppressed with the JAK3 inhibitor Tofacitinib.

Conclusions

This study demonstrates that a single JAK3 A573V allele expressed from the endogenous locus was able to enhance lymphopoiesis throughout the life-course, which was mediated via an IL-2Rγc/JAK1/JAK3/STAT5 signaling pathway and was sensitive to Tofacitinib. This extends our understanding of oncogenic JAK3 mutations and creates a novel model to underpin further translational investigations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00018-022-04361-8.

Risk Factors for Childhood Leukemia: Radiation and Beyond

Childhood leukemia (CL) is undoubtedly caused by a multifactorial process with genetic as well as environmental factors playing a role. But in spite of several efforts in a variety of scientific fields, the causes of the disease and the interplay of possible risk factors are still poorly understood. To push forward the research on the causes of CL, the German Federal Office for Radiation Protection has been organizing recurring international workshops since 2008 every two to three years. In November 2019 the 6th International Workshop on the Causes of CL was held in Freising and brought together experts from diverse disciplines. The workshop was divided into two main parts focusing on genetic and environmental risk factors, respectively. Two additional special sessions addressed the influence of natural background radiation on the risk of CL and the progress in the development of mouse models used for experimental studies on acute lymphoblastic leukemia, the most common form of leukemia worldwide. The workshop presentations highlighted the role of infections as environmental risk factor for CL, specifically for acute lymphoblastic leukemia. Major support comes from two mouse models, the Pax5+/- and Sca1-ETV6-RUNX1 mouse model, one of the major achievements made in the last years. Mice of both predisposed models only develop leukemia when exposed to common infections. These results emphasize the impact of gene-environment-interactions on the development of CL and warrant further investigation of such interactions - especially because genetic predisposition is detected with increasing frequency in CL. This article summarizes the workshop presentations and discusses the results in the context of the international literature.

Oncogene-Induced Reprogramming in Acute Lymphoblastic Leukemia: Towards Targeted Therapy of Leukemia-Initiating Cells

Simple Summary

Acute lymphoblastic leukemia is a heterogeneous disease characterized by a diversity of genetic alterations, following a sophisticated and controversial organization. In this review, we present and discuss the concepts exploring the cellular, molecular and functional heterogeneity of leukemic cells. We also review the emerging evidence indicating that cell plasticity and oncogene-induced reprogramming should be considered at the biological and clinical levels as critical mechanisms for identifying and targeting leukemia-initiating cells.

Abstract

Our understanding of the hierarchical structure of acute leukemia has yet to be fully translated into therapeutic approaches. Indeed, chemotherapy still has to take into account the possibility that leukemia-initiating cells may have a distinct chemosensitivity profile compared to the bulk of the tumor, and therefore are spared by the current treatment, causing the relapse of the disease. Therefore, the identification of the cell-of-origin of leukemia remains a longstanding question and an exciting challenge in cancer research of the last few decades. With a particular focus on acute lymphoblastic leukemia, we present in this review the previous and current concepts exploring the phenotypic, genetic and functional heterogeneity in patients. We also discuss the benefits of using engineered mouse models to explore the early steps of leukemia development and to identify the biological mechanisms driving the emergence of leukemia-initiating cells. Finally, we describe the major prospects for the discovery of new therapeutic strategies that specifically target their aberrant stem cell-like functions.

Forward and Reverse Genetics of B Cell Malignancies: From Insertional Mutagenesis to CRISPR-Cas

Cancer genome sequencing has identified dozens of mutations with a putative role in lymphomagenesis and leukemogenesis. Validation of driver mutations responsible for B cell neoplasms is complicated by the volume of mutations worthy of investigation and by the complex ways that multiple mutations arising from different stages of B cell development can cooperate. Forward and reverse genetic strategies in mice can provide complementary validation of human driver genes and in some cases comparative genomics of these models with human tumors has directed the identification of new drivers in human malignancies. We review a collection of forward genetic screens performed using insertional mutagenesis, chemical mutagenesis and exome sequencing and discuss how the high coverage of subclonal mutations in insertional mutagenesis screens can identify cooperating mutations at rates not possible using human tumor genomes. We also compare a set of independently conducted screens from Pax5 mutant mice that converge upon a common set of mutations observed in human acute lymphoblastic leukemia (ALL). We also discuss reverse genetic models and screens that use CRISPR-Cas, ORFs and shRNAs to provide high throughput in vivo proof of oncogenic function, with an emphasis on models using adoptive transfer of ex vivo cultured cells. Finally, we summarize mouse models that offer temporal regulation of candidate genes in an in vivo setting to demonstrate the potential of their encoded proteins as therapeutic targets.

PAQR3 inhibits proliferation and aggravates ferroptosis in acute lymphoblastic leukemia through modulation Nrf2 stability

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is a usual hematological tumor, which was featured by malignant proliferation of lymphoid progenitor cells. Many important factors participate into the regulation of ALL, including proteins. PAQR3 (also named RKTG) has been proved to take part in many human cancers by acting as a tumor suppressor. PAQR3 has bee n shown to repress human leukemia cells proliferation and induce cell apoptosis, but its role and relevant regulatory mechanism on cell proliferation and ferroptosis in ALL needs more exploration.

METHODS

The genes expression was detected through quantitative reverse transcription polymerase chain reaction (mRNA) or western blot (protein). The cell proliferation was assessed through Cell Counting Kit-8 and 5-ethynyl-2-deoxyuridine assays. The levels of MDA, DCF, and intracellular free Fe in ALL cells were tested through the commercial kits. The cell apoptosis was determined through flow cytometry analysis. The binding ability of PAQR3 and nuclear factor erythroid 2-related factor 2 (Nrf2) was verified through pull down assay.

RESULTS

PAQR3 expression was firstly assessed in ALL patients and cell lines, and discovered to be downregulated. It was verified that PAQR3 suppressed ALL cells proliferation. Further experiments proved that PAQR3 aggravates ferroptosis in ALL. In addition, AQR3 bound with Nrf2, and modulated its expression through ubiquitination in ALL. Finally, through rescue assays, it was demonstrated that Nrf2 overexpression reversed the effects of PAQR3 on cell proliferation and ferroptosis.

CONCLUSION

Findings from our work uncovered that PAQR3 inhibited proliferation and aggravated ferroptosis in ALL through modulation Nrf2 stability. This study suggested that PAQR3 may serve as an effective biological marker for ALL treatment.

Prognostic value of RASD1 transcript levels in adult Philadelphia-negative B-cell acute lymphoblastic leukemia

OBJECTIVES

Ras-related dexamethasone-induced 1 (RASD1) is abnormally expressed in many solid cancers. However, its potential role in adults with B-cell acute lymphoblastic leukemia (B-ALL) is unclear. Therefore, we aim to clarify the abnormal expression of the tumor-associated biomarker, RASD1, as a potential target for diagnosis and prognosis in adult Philadelphia-negative B-ALL.

METHODS

The expression of RASD1 was detected with RT-qPCR in 92 adults with de novo Ph-negative B-ALL and 40 healthy controls. The correlation between RASD1 transcript levels and relapse was assessed.

RESULTS

RASD1 transcript levels in patients with Ph-negative B-ALL (median 81.76%, range 0.22%-1824.52%) were significantly higher than those in healthy controls (7.59%, 0.46%-38.66%; P<0.0001). Patients with low RASD1 transcript levels had a lower 5-year relapse-free survival (RFS, 47.5% [32.9%, 62.1%] vs. 63.1% [49.0%, 77.2%]; P = 0.012) and a higher 5-year cumulative incidence of relapse (CIR, 52.0% [37.4%, 66.6%] vs. 36.2% [22.2%, 50.2%]; P = 0.013) especially in patients receiving chemotherapy only. Multivariate analysis showed that a low RASD1 transcript level was an independent risk factor for RFS (HR = 2.938 [1.427, 6.047], P = 0.003) and CIR (HR = 3.367 [1.668, 6.796], P = 0.001) in patients with Ph-negative B-ALL.

CONCLUSIONS

RASD1 transcript levels were significantly higher in patients with Ph-negative B-ALL and a low RASD1 transcript level was independently correlated with increased relapse risk.

Multi-Omics Analysis of Acute Lymphoblastic Leukemia Identified the Methylation and Expression Differences Between BCP-ALL and T-ALL

Acute lymphoblastic leukemia (ALL) as a common cancer is a heterogeneous disease which is mainly divided into BCP-ALL and T-ALL, accounting for 80–85% and 15–20%, respectively. There are many differences between BCP-ALL and T-ALL, including prognosis, treatment, drug screening, gene research and so on. In this study, starting with methylation and gene expression data, we analyzed the molecular differences between BCP-ALL and T-ALL and identified the multi-omics signatures using Boruta and Monte Carlo feature selection methods. There were 7 expression signature genes (CD3D, VPREB3, HLA-DRA, PAX5, BLNK, GALNT6, SLC4A8) and 168 methylation sites corresponding to 175 methylation signature genes. The overall accuracy, accuracy of BCP-ALL, accuracy of T-ALL of the RIPPER (Repeated Incremental Pruning to Produce Error Reduction) classifier using these signatures evaluated with 10-fold cross validation repeated 3 times were 0.973, 0.990, and 0.933, respectively. Two overlapped genes between 175 methylation signature genes and 7 expression signature genes were CD3D and VPREB3. The network analysis of the methylation and expression signature genes suggested that their common gene, CD3D, was not only different on both methylation and expression levels, but also played a key regulatory role as hub on the network. Our results provided insights of understanding the underlying molecular mechanisms of ALL and facilitated more precision diagnosis and treatment of ALL.

Gain of chromosome 21 in hematological malignancies: lessons from studying leukemia in children with Down syndrome

Structural and numerical alterations of chromosome 21 are extremely common in hematological malignancies. While the functional impact of chimeric transcripts from fused chromosome 21 genes such as TEL-AML1, AML1-ETO, or FUS-ERG have been extensively studied, the role of gain of chromosome 21 remains largely unknown. Gain of chromosome 21 is a frequently occurring aberration in several types of acute leukemia and can be found in up to 35% of cases. Children with Down syndrome (DS), who harbor constitutive trisomy 21, highlight the link between gain of chromosome 21 and leukemogenesis, with an increased risk of developing acute leukemia compared with other children. Clinical outcomes for DS-associated leukemia have improved over the years through the development of uniform treatment protocols facilitated by international cooperative groups. The genetic landscape has also recently been characterized, providing an insight into the molecular pathogenesis underlying DS-associated leukemia. These studies emphasize the key role of trisomy 21 in priming a developmental stage and cellular context susceptible to transformation, and have unveiled its cooperative function with additional genetic events that occur during leukemia progression. Here, using DS-leukemia as a paradigm, we aim to integrate our current understanding of the role of trisomy 21, of critical dosage-sensitive chromosome 21 genes, and of associated mechanisms underlying the development of hematological malignancies. This review will pave the way for future investigations on the broad impact of gain of chromosome 21 in hematological cancer, with a view to discovering new vulnerabilities and develop novel targeted therapies to improve long term outcomes for DS and non-DS patients.

Functional analysis of a novel fusion protein PAX5-KIDINS220 identified in a pediatric Ph-like ALL patient

PAX5-KIDINS220 (PAX5-K220) is a novel chimeric fusion gene identified in a pediatric Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL) patient, but the function of the encoded fusion protein has not yet been analyzed. Here, we report the functional analysis of PAX5-K220 in vitro. We successfully generated PAX5-K220 expressing cells and demonstrate that PAX5-K220 is a nuclear protein. Luciferase reporter assay reveals that PAX5-K220 inhibits wild-type PAX5 transcriptional activity in a dominant-negative fashion like other PAX5-related fusion proteins, and may contribute to lymphocyte differentiation block. However, although identified in Ph-like ALL, PAX5-K220 does not induce IL-3-independent proliferation when transduced in the IL-3-dependent Ba/F3 murine leukemia cells, but rather attenuates growth. These results reveal that PAX5-K220 certainly shares the character with other PAX5-related fusion proteins rather than other fusion proteins with tyrosine kinase activity identified in Ph-like ALL, and did not contribute to proliferation activity. Precise functional analysis of each differently partnered PAX5 fusion protein is warranted in the future for better understanding of PAX5-related translocations and their effects.

Immunophenotyping of Murine Precursor B-Cell Leukemia/Lymphoma: A Comparison of Immunohistochemistry and Flow Cytometry

In humans and in mouse models, precursor B-cell lymphoblastic leukemia (B-ALL)/lymphoblastic lymphoma (B-LBL) can be classified as either the pro-B or pre-B subtype. This is based on the expression of antigens associated with the pro-B and pre-B stages of B-cell development. Antigenic markers can be detected by flow cytometry or immunohistochemistry (IHC), but no comparison of results from these techniques has been reported for murine B-ALL/LBL. In our analysis of 30 cases induced by chemical or viral mutagenesis on a WT or Pax5+/- background, 18 (60%) were diagnosed as pro-B by both flow cytometry and IHC. Discordant results were found for 12 (40%); 6 were designated pro-B by IHC and pre-B by flow cytometry and the reverse for the remaining 6 cases. Discordance occurred because different markers were used to define the pro-B-to-pre-B transition by IHC vs flow cytometry. IHC expression of cytoplasmic IgM (μIgM) defined the pre-B stage, whereas the common practice of using CD25 as a surrogate marker in flow cytometry was employed here. These results show that CD25 and μIgM are not always concurrently expressed in B-ALL/LBL, in contrast to normal B-cell development. Therefore, when subtyping B-ALL/LBL in mice, an IHC panel of B220, PAX5, TdT, c-Kit/CD117, CD43, IgM, and ΚLC should be considered. For flow cytometry, cytoplasmic IgM may be an appropriate marker in conjunction with the surface markers B220, CD19, CD43, c-Kit/CD117, BP-1, and CD25.