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The PAX5-JAK2 translocation acts as a dual-hit mutation that promotes aggressive B-cell leukemia via nuclear STAT5 activation

ABSTRACT: While PAX5 is an important tumor suppressor in B-ALL, it is also involved in oncogenic translocations coding for PAX5 fusion proteins. PAX5-JAK2 encodes a protein consisting of the PAX5 DNA-binding region fused to the constitutively active JAK2 kinase domain. Here, we studied the oncogenic function of PAX5-JAK2 in a mouse model expressing it from the endogenous Pax5 locus. The Pax5Jak2/+ mice rapidly developed an aggressive B-ALL in the absence of another cooperating mutation. The DNA-binding function and kinase activity of Pax5-Jak2, as well as IL-7 signaling, all contributed to leukemia development. Interestingly, all Pax5Jak2/+ tumors lost the wild-type Pax5 allele, allowing efficient DNA binding of Pax5-Jak2. While we could not find evidence for a nuclear role of Pax5-Jak2 as an epigenetic regulator, active phosphorylated Stat5 was present at a high level in Pax5Jak2/+ B-ALL tumors, consistent with increased expression of Stat5 target genes. Together, these data identified Pax5-Jak2 as an important nuclear driver of leukemia formation by maintaining phosphorylated Stat5 levels in the nucleus.

ORGANISM(S): Mus musculus

PROVIDER: GSE174775 | GEO | 2022/02/04

REPOSITORIES: GEO

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The role of the Janus-faced transcription factor PAX5-JAK2 in acute lymphoblastic leukemia

Project description:PAX5-JAK2 has recently been identified as a novel recurrent fusion gene in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) but the function of the encoded chimeric protein has not yet been characterized in detail. Herein we show that the PAX5-JAK2 chimera, which consists of the DNA-binding paired domain of PAX5 and the active kinase domain of JAK2, is a nuclear protein that has the ability to bind to wild-type PAX5 target loci. Moreover, our data provide compelling evidence that PAX5-JAK2 functions as nuclear catalytically active kinase that autophosphorylates and in turn phosphorylates and activates downstream STATs in an apparently non-canonical mode. The chimeric protein also enables cytokine-independent growth of Ba/F3 cells and, therefore, possessing transforming potential. Importantly, the kinase activity of PAX5-JAK2 can be efficiently blocked by JAK2 inhibitors rendering it a potential target for therapeutic intervention. Together, our data show that PAX5-JAK2 simultaneously deregulates the PAX5 downstream transcriptional program and activates the JAK-STAT signaling cascade, and thus, by interfering with these two important pathways, may promote leukemogenesis.

2014-12-29 | GSE56449 | GEO

PAX5-KIDINS220 gene expression array in Ba/F3 cells

Project description: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.We successfully generated PAX5-K220 expressing cells and demonstrate that PAX5-K220 is a nuclear protein. In addition, PAX5-K220 activates JAK2-STAT5 pathway through the repression of Socs5, a known negative regulator of JAK-STAT pathway. 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. 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. 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.

2019-03-01 | GSE127485 | GEO

SPAG9-JAK2 gene expression array in Ba/F3 cells

Project description:SPAG9-JAK2 is a novel fusion gene identified in a pediatric patient with Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL). In this study, we performed functional analysis of the SPAG9-JAK2 fusion to establish molecular targeted therapy. Ba/F3 cells expressing SPAG9-JAK2 generated by retroviral transduction (Ba/F3-SPAG9-JAK2), proliferated in the absence of IL-3, and exhibited constitutive phosphorylation of the tyrosine residues in the JAK2 kinase domain of the fusion protein and STAT3/STAT5. Mutation of tyrosine residues in the JAK2 kinase domain (SPAG9-JAK2 mut) abolished IL-3 independence, but had no influence on STAT3/STAT5 phosphorylation levels. Gene expression analysis revealed that Stat1 was significantly up-regulated in Ba/F3-SPAG9-JAK2 cells. STAT1 was also phosphorylated in Ba/F3-SPAG9-JAK2 but not SPAG9-JAK2 mut cells, suggesting that STAT1 is key for SPAG9-JAK2-mediated cell proliferation. Consistently, STAT1 induced expression of the anti-apoptotic proteins, BCL-2 and MCL-1, as did SPAG9-JAK2, but not SPAG9-JAK2 mut. Ruxolitinib abrogated Ba/F3-SPAG9-JAK2-mediated proliferation in vitro, but was insufficient in vivo. Venetoclax (a BCL-2 inhibitor) or AZD5991 (an MCL-1 inhibitor) enhanced the effects of ruxolitinib on Ba/F3-SPAG9-JAK2 in vitro. These findings suggest that activation of the JAK2-STAT1-BCL-2/MCL-1 axis contributes to SPAG9-JAK2-related aberrant growth promotion. BCL-2 or MCL-1 inhibition is a potential therapeutic option for B-ALL with SPAG9-JAK2 fusion.

2021-05-18 | GSE174578 | GEO

Constitutively active STAT5 recruits p53 to alternative transcriptional targets in myeloid cancers

Project description:In several cancer types, STAT (Signal transducer and activator of transcription) transcription factors are constitutively activated. We previously identified a target gene, LPP/miR-28 (LIM domain containing preferred translocation partner in lipoma), induced by constitutive activation of STAT5, but not by transient cytokine-activated STAT5. Here, we demonstrate in transformed hematopoietic cells that binding of both STAT5B and p53 to chromatin is required for transcriptional activity of an alternative LPP/miR-28 promoter. Using a genome-wide approach, we identified 463 genomic positions at promoter regions where STAT5B and p53 are co-localized on the chromatin. At these positions, p53 chromatin binding is dependent on persistent STAT5B activation. The transcriptional activity of selected promoters bound by STAT5B and p53 was significantly changed upon STAT5 or p53 inhibition, and the transcription of these target genes is frequently altered in platelets of myeloproliferative neoplasm patients harboring mutations constitutively activating STAT5. These data suggest that the constitutive STAT5 activation recruits p53 in cancer cells and thereby activates oncogenic transcriptional programs. STAT5B and p53 ChIP-chip with or without JAK2 inhibition (ruxolitinib) to inhibit STAT5 phosphorylation and DNA binding.

2014-02-01 | E-GEOD-38143 | biostudies-arrayexpress

Ebf1 or Pax5 Haploinsufficiency Synergizes with STAT5 Activation to Initiate Acute Lymphoblastic Leukemia

Project description:STAT5 is critical for differentiation, proliferation and survival of progenitor B cells suggesting a possible role in Acute Lymphoblastic Leukemia (ALL). Herein, we show increased expression of activated STAT5 in ALL patients, which correlates with treatment outcome. Mutations in Ebf1 and Pax5, genes critical for B cell development have also been identified in human ALL. To determine whether mutations in Ebf1 or Pax5 synergize with STAT5 activation to induce ALL we crossed mice expressing a constitutively active form of STAT5 (Stat5b-CA) with mice heterozygous for Ebf1 or Pax5. Haploinsufficiency of either Pax5 or Ebf1 synergized with Stat5b-CA to rapidly induce ALL in 100% of the mice. The leukemic cells displayed reduced expression of both Pax5 and Ebf1 but this had little affect on most EBF1 or PAX5 target genes. However, a subset of these genes was deregulated and included a large percentage of potential tumor suppressor genes and oncogenes. Further, most of these genes appear to be jointly regulated by both EBF1 and PAX5. Our findings suggest a model whereby small perturbations in a self-reinforcing network of transcription factors critical for B cell development, specifically PAX5 and EBF1, cooperate with STAT5 activation to initiate ALL. Gene expression profiling was performed on cells isolated from lymph nodes of Stat5b-CA x Ebf1+/- and Stat5b-CA x Rag2-/- leukemic mice and pre B cells sorted from bone marrow of C57BL/6 mice and Stat5b-CA transgenic mice. 17 Samples.

2011-05-09 | E-GEOD-25645 | biostudies-arrayexpress

The PAX5-JAK2 translocation acts as a dual-hit mutation that promotes aggressive B-cell leukemia via nuclear STAT5 activation

Project description:The PAX5-JAK2 translocation acts as a dual-hit mutation that promotes aggressive B-cell leukemia via nuclear STAT5 activation

| PRJNA731504 | ENA

Ebf1 or Pax5 Haploinsufficiency Synergizes with STAT5 Activation to Initiate Acute Lymphoblastic Leukemia

2011-05-09 | GSE25645 | GEO

Pax5 restoration in a mouse model of B progenitor acute lymphoblastic leukemia

Project description:Hypomorphic mutations of PAX5 occur in one third of B-progenitor acute lymphoblastic leukemias (B-ALLs), however their functional consequences remain undefined. Here we employ advanced transgenic RNAi in mice to suppress endogenous Pax5 expression in the hematopoietic compartment in vivo, which co-operates with activated STAT5 to induce B-ALL. In this model, restoring endogenous Pax5 expression in established B-ALL induces transcriptional and immunophenotypic changes reminiscent of normal B cell differentiation, disabling leukemia-initiating capacity and ultimately causing leukemia clearance. Comparison of leukemias harvested from triplicate untreated mice versus triplicate Dox-treated (3 days) mice

2014-06-18 | E-GEOD-52870 | biostudies-arrayexpress

IL7R mutational activation can initiate Ph-like and PAX5 P80R precursor B-cell acute lymphoblastic leukemia

Project description:Interleukin-7 receptor α (encoded by IL7R) is essential for lymphoid development. Whether acute lymphoblastic leukemia (ALL)-related IL7R gain-of-function mutations can trigger leukemogenesis remains unclear. Here, we demonstrate that lymphoid-restricted mutant IL7R, expressed at physiological levels in conditional knock-in mice, establishes a pre-leukemia stage in which B-cell precursors display self-renewal ability, initiating precursor B-ALL that resembles PAX5 P80R or Ph-like human leukemia. Full transformation associates with transcriptional upregulation of oncogenes such as Myc or Bcl2, downregulation of tumor suppressors such as Ikzf1 or Arid2, and major IL-7R signaling upregulation (involving both JAK/STAT5 and PI3K/mTOR), required for leukemia cell viability. Accordingly, maximal signaling drives full penetrance and early leukemia onset in homozygous IL7R mutant animals. Notably, we identify 2 transcriptional subgroups in mouse and human Ph-like ALL, and show that dactolisib and sphingosine-kinase inhibitors are novel treatment avenues for IL-7R-related cases. Our model, a unique resource to explore the pathophysiology and therapeutic vulnerabilities of B-ALL, demonstrates that IL7R can initiate this malignancy.

2021-11-02 | PXD017147 | Pride

Pax5 restoration in a mouse model of B progenitor acute lymphoblastic leukemia

2014-06-18 | GSE52870 | GEO

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