Co-existence of IL7R high and SH2B3 low expression distinguishes a novel high-risk acute lymphoblastic leukemia with Ikaros dysfunction

Modulation of JAK-STAT Signaling by LNK: A Forgotten Oncogenic Pathway in Hormone Receptor-Positive Breast Cancer

Breast cancer remains the most frequently diagnosed cancer in women worldwide. Tumors that express hormone receptors account for 75% of all cases. Understanding alternative signaling cascades is important for finding new therapeutic targets for hormone receptor-positive breast cancer patients. JAK-STAT signaling is commonly activated in hormone receptor-positive breast tumors, inducing inflammation, proliferation, migration, and treatment resistance in cancer cells. In hormone receptor-positive breast cancer, the JAK-STAT cascade is stimulated by hormones and cytokines, such as prolactin and IL-6. In normal cells, JAK-STAT is inhibited by the action of the adaptor protein, LNK. However, the role of LNK in breast tumors is not fully understood. This review compiles published reports on the expression and activation of the JAK-STAT pathway by IL-6 and prolactin and potential inhibition of the cascade by LNK in hormone receptor-positive breast cancer. Additionally, it includes analyses of available datasets to determine the level of expression of LNK and various members of the JAK-STAT family for the purpose of establishing associations between expression and clinical outcomes. Together, experimental evidence and in silico studies provide a better understanding of the potential implications of the JAK-STAT-LNK loop in hormone receptor-positive breast cancer progression.

Signaling pathways and regulation of gene expression in hematopoietic cells

Cellular functions are regulated by signal transduction pathway networks consisting of protein-modifying enzymes that control the activity of many downstream proteins. Protein kinases and phosphatases regulate gene expression by reversible phosphorylation of transcriptional factors, which are their direct substrates. Casein kinase II (CK2) is a serine/threonine kinase that phosphorylates a large number of proteins that have critical roles in cellular proliferation, metabolism and survival. Altered function of CK2 has been associated with malignant transformation, immunological disorders and other types of diseases. Protein phosphatase 1 (PP1) is a serine/threonine phosphatase, which regulates the phosphorylation status of many proteins that are essential for cellular functions. IKAROS is a DNA-binding protein, which functions as a regulator of gene transcription in hematopoietic cells. CK2 directly phosphorylates IKAROS at multiple phosphosites which determines IKAROS activity as a regulator of gene expression. PP1 binds to IKAROS via the PP1-consensus recognition site and dephosphorylates serine/threonine residues that are phosphorylated by CK2. Thus, the interplay between CK2 and PP1 signaling pathways have opposing effects on the phosphorylation status of their mutual substrate - IKAROS. This review summarizes the effects of CK2 and PP1 on IKAROS role in regulation of gene expression and its function as a tumor suppressor in leukemia.

Puppet masters of B-cell progenitor acute lymphoblastic leukemia: The preB cell receptor and the interleukin 7 receptor α

B-cell progenitor acute lymphoblastic leukemia (BCP-ALL) is enriched for a preB cell phenotype, hinting at a specific vulnerability of this cell stage. Two signaling pathways via the preB cell receptor (preBCR) and the interleukin 7 receptor α (IL-7Rα) chain govern the balance between differentiation and proliferation at this stage and both receptor pathways are routinely altered in human BCP-ALL. Here, we review the immunobiology of both the preBCR as well as the IL-7Rα and analyze the human BCP-ALL spectrum in the light of these signaling complexes. Finally, we present a terminology for preBCR signaling modules that distinguishes a pro-proliferative "phase-I" module from a pro-differentiative "phase-II" module. This terminology might serve as a framework to better address shared oncogenic mechanics of preB cell stage BCP-ALL.

IKAROS in Acute Leukemia: A Positive Influencer or a Mean Hater?

One key process that controls leukemogenesis is the regulation of oncogenic gene expression by transcription factors acting as tumor suppressors. Understanding this intricate mechanism is crucial to elucidating leukemia pathophysiology and discovering new targeted treatments. In this review, we make a brief overview of the physiological role of IKAROS and the molecular pathway that contributes to acute leukemia pathogenesis through IKZF1 gene lesions. IKAROS is a zinc finger transcription factor of the Krüppel family that acts as the main character during hematopoiesis and leukemogenesis. It can activate or repress tumor suppressors or oncogenes, regulating the survival and proliferation of leukemic cells. More than 70% of Ph+ and Ph-like cases of acute lymphoblastic leukemia exhibit IKZF1 gene variants, which are linked to worse treatment outcomes in both childhood and adult B-cell precursor acute lymphoblastic leukemia. In the last few years, much evidence supporting IKAROS involvement in myeloid differentiation has been reported, suggesting that loss of IKZF1 might also be a determinant of oncogenesis in acute myeloid leukemia. Considering the complicated "social" network that IKAROS manages in hematopoietic cells, we aim to focus on its involvement and the numerous alterations of molecular pathways it can support in acute leukemias.

Clinical and Genetic Characteristics of IKZF1 Mutation in Chinese Children With B-Cell Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is a malignancy associated with altered lymphoid precursor hyperplasia and accompanied with different genetic mutations. Few studies have been reported on the association between gene mutations and clinical features of IKZF1 mutation in children with B-cell ALL (B-ALL). We investigated clinical and genetic characteristics in 200 newly diagnosed pediatric B-ALL through multiplex ligation-dependent probe amplification (MLPA) and targeted next-generation sequencing (NGS) method. We found that IKZF1 mutations, including large segment deletions, small insertions or deletions (InDels) and single nucleotide variations (SNVs), were detected in 22 patients with a positive mutation rate of 11.0%. IKZF1 mutation was significantly associated with higher WBC count (19.38 × 10⁹/L vs. 5.80 × 10⁹/L, p = 0.002). Compared with IKZF1 wild-type cases, a higher frequency of IL7R gene mutation was discovered in IKZF1 mutant cases (9.1% vs. 0.0%, p = 0.012). Patients with IKZF1 mutation were less sensitive to glucocorticoid induction than patients without IKZF1 mutation (63.6% vs. 9.0%, p < 0.001). On the 15th day of induction, minimal residual disease (MRD) > 10⁻³ level were higher in IKZF1 mutant patients than wild-type patients (45.5% vs. 22.3%, p = 0.018). In conclusion, our study reveals the association between genetic mutations and clinical features in Chinese children with B-ALL, which might contribute to molecular classification, risk stratification and prognosis evaluation, and provide new ideas for targeted therapy in ALL.

Activated interleukin-7 receptor signaling drives B-cell acute lymphoblastic leukemia in mice

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk subtype of B-ALL often associated with genetic variants that alter cytokine receptor signaling, including mutations in the interleukin-7 receptor (IL7R). To investigate whether IL7R variants are leukemia-initiating, we built mouse models expressing activated Il7r (aIL7R). B-cell intrinsic aIL7R mice developed spontaneous B-ALL, demonstrating sufficiency of Il7r activating mutations in leukemogenesis. Concomitant introduction of a knock-out allele in the associated adapter protein Lnk (encoded by Sh2b3) or a dominant-negative variant of the transcription factor Ikaros (Ikzf1) increased disease penetrance. The resulting murine leukemias displayed monoclonality and recurrent somatic Kras mutations and efficiently engrafted into immunocompetent mice. Phosphoproteomic analyses of aIL7R leukemic cells revealed constitutive Stat5 signaling and B cell receptor (BCR)-like signaling despite the absence of surface pre-BCR. Finally, in vitro treatment of aIL7R leukemic B-cells with Jak, mTOR, or Syk inhibitors blocked growth, confirming that each pathway is active in this mouse model of IL7R-driven B-ALL.

Ikaros Proteins in Tumor: Current Perspectives and New Developments

Ikaros is a zinc finger transcription factor (TF) of the Krüppel family member, which significantly regulates normal lymphopoiesis and tumorigenesis. Ikaros can directly initiate or suppress tumor suppressors or oncogenes, consequently regulating the survival and proliferation of cancer cells. Over recent decades, a series of studies have been devoted to exploring and clarifying the relationship between Ikaros and associated tumors. Therapeutic strategies targeting Ikaros have shown promising therapeutic effects in both pre-clinical and clinical trials. Nevertheless, the increasingly prominent problem of drug resistance targeted to Ikaros and its analog is gradually appearing in our field of vision. This article reviews the role of Ikaros in tumorigenesis, the mechanism of drug resistance, the progress of targeting Ikaros in both pre-clinical and clinical trials, and the potential use of associated therapy in cancer therapy.

The Role of LNK (SH2B3) in the Regulation of JAK-STAT Signalling in Haematopoiesis

LNK is a member of the SH2B family of adaptor proteins and is a non-redundant regulator of cytokine signalling. Cytokines are secreted intercellular messengers that bind to specific receptors on the surface of target cells to activate the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) signalling pathway. Activation of the JAK-STAT pathway leads to proliferative and often inflammatory effects, and so the amplitude and duration of signalling are tightly controlled. LNK binds phosphotyrosine residues to signalling proteins downstream of cytokines and constrains JAK-STAT signalling. Mutations in LNK have been identified in a range of haematological and inflammatory diseases due to increased signalling following the loss of LNK function. Here, we review the regulation of JAK-STAT signalling via the adaptor protein LNK and discuss the role of LNK in haematological diseases.

Lymphoid blast transformation in an MPN with BCR-JAK2 treated with ruxolitinib: putative mechanisms of resistance

The basis for acquired resistance to JAK inhibition in patients with JAK2-driven hematologic malignancies is not well understood. We report a patient with a myeloproliferative neoplasm (MPN) with a BCR activator of RhoGEF and GTPase (BCR)-JAK2 fusion with initial hematologic response to ruxolitinib who rapidly developed B-lymphoid blast transformation. We analyzed pre-ruxolitinib and blast transformation samples using genome sequencing, DNA mate-pair sequencing (MPseq), RNA sequencing (RNA-seq), and chromosomal microarray to characterize possible mechanisms of resistance. No resistance mutations in the BCR-JAK2 fusion gene or transcript were identified, and fusion transcript expression levels remained stable. However, at the time of blast transformation, MPseq detected a new IKZF1 copy-number loss, which is predicted to result in loss of normal IKZF1 protein translation. RNA-seq revealed significant upregulation of genes negatively regulated by IKZF1, including IL7R and CRLF2. Disease progression was also characterized by adaptation to an activated B-cell receptor (BCR)-like signaling phenotype, with marked upregulation of genes such as CD79A, CD79B, IGLL1, VPREB1, BLNK, ZAP70, RAG1, and RAG2. In summary, IKZF1 deletion and a switch from cytokine dependence to activated BCR-like signaling phenotype represent putative mechanisms of ruxolitinib resistance in this case, recapitulating preclinical data on resistance to JAK inhibition in CRLF2-rearranged Philadelphia chromosome-like acute lymphoblastic leukemia.

A New Treatment Strategy for Early T-Cell Precursor Acute Lymphoblastic Leukemia: A Case Report and Literature Review

Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is an aggressive and extremely fatal subtype of T-cell acute lymphoblastic leukemia (T-ALL), characterized by the similar transcriptional and immunophenotypic profiles to those of early T-cell precursors and positive expressions of myeloid antigens. Besides, the gene expression profile in ETP-ALL is similar to that in myeloid malignancies. The clinical characteristics, treatments and prognoses of ETP-ALL are significantly heterogeneous. In the present study, we reported a 43-year-old female patient who lacked terminal deoxynucleotidyl transferase (TDT) expression in immunophenotype and displayed mutations of fms-like tyrosine kinase-internal tandem duplication (FLT3-ITD), paired-box domain 5 (PAX5) and SH2B adaptor protein 3 (SH2B3) (PAX5 and SH2B3, the genes critical to B cell identity and function), which represent myeloid and precursor B-lineage associated gene mutations, respectively. It was a rare T-ALL or T-lineage case. Because of multiple poor prognostic factors in this case, conventional induction regimens, like hyper-CVAD (cyclophosphamide, vincristine, doxorubicin, dexamethasone), were invalid. The patient showed inadequate response, suggesting that this treatment was not employed on the basis of the immunophenotype. FLAG-IDA regimen (fludarabine, cytarabine [Ara-C], granulocyte-colony stimulating factor [G-CSF] and idarubicin), which is usually applied to eliminate leukemia cells, was administered combining with sorafenib as an effective induction chemotherapy. The case achieved long-term survival following the allogeneic hematopoietic stem cell transplantation (allo-HSCT). We recommend that adult ETP-ALL patients can be treated with a myeloid-oriented chemotherapy (as frontline induction treatment) along with gene-targeting inhibitors, followed by allo-HSCT.

Interleukin (IL)-7 Signaling in the Tumor Microenvironment

Interleukin (IL)-7 plays an important immunoregulatory role in different types of cells. Therefore, it attracts researcher's attention, but despite the fact, many aspects of its modulatory action, as well as other functionalities, are still poorly understood. The review summarizes current knowledge on the interleukin-7 and its signaling cascade in context of cancer development. Moreover, it provides a cancer-type focused description of the involvement of IL-7 in solid tumors, as well as hematological malignancies.The interleukin has been discovered as a growth factor crucial for the early lymphocyte development and supporting the growth of malignant cells in certain leukemias and lymphomas. Therefore, its targeting has been explored as a treatment modality in hematological malignancies, while the unique ability to expand lymphocyte populations selectively and without hyperinflammation has been used in experimental immunotherapies in patients with lymphopenia. Ever since the early research demonstrated a reduced growth of solid tumors in the presence of IL-7, the interleukin application in boosting up the anticancer immunity has been investigated. However, a growing body of evidence indicative of IL-7 upregulation in carcinomas, facilitating tumor growth and metastasis and aiding drug-resistance, is accumulating. It therefore becomes increasingly apparent that the response to the IL-7 stimulus strongly depends on cell type, their developmental stage, and microenvironmental context. The interleukin exerts its regulatory action mainly through phosphorylation events in JAK/STAT and PI3K/Akt pathways, while the significance of MAPK pathway seems to be limited to solid tumors. Given the unwavering interest in IL-7 application in immunotherapy, a better understanding of interleukin role, source in tumor microenvironment, and signaling pathways, as well as the identification of cells that are likely to respond should be a research priority.

Synergism between IL7R and CXCR4 drives BCR-ABL induced transformation in Philadelphia chromosome-positive acute lymphoblastic leukemia

Ph⁺ acute lymphoblastic leukemia (ALL) is characterized by the expression of an oncogenic fusion kinase termed BCR-ABL1. Here, we show that interleukin 7 receptor (IL7R) interacts with the chemokine receptor CXCR4 to recruit BCR-ABL1 and JAK kinases in close proximity. Treatment with BCR-ABL1 kinase inhibitors results in elevated expression of IL7R which enables the survival of transformed cells when IL7 was added together with the kinase inhibitors. Importantly, treatment with anti-IL7R antibodies prevents leukemia development in xenotransplantation models using patient-derived Ph⁺ ALL cells. Our results suggest that the association between IL7R and CXCR4 serves as molecular platform for BCR-ABL1-induced transformation and development of Ph⁺ ALL. Targeting this platform with anti-IL7R antibody eliminates Ph⁺ ALL cells including those with resistance to commonly used ABL1 kinase inhibitors. Thus, anti-IL7R antibodies may provide alternative treatment options for ALL in general and may suppress incurable drug-resistant leukemia forms.

The Current Genomic and Molecular Landscape of Philadelphia-like Acute Lymphoblastic Leukemia

Philadelphia (Ph)-like acute lymphoblastic leukemia (ALL) is a high-risk B-cell Acute Lymphoblastic Leukemia (B-ALL) characterized by a gene expression profile similar to Ph-positive B-ALL but lacking the BCR-ABL1 translocation. The molecular pathogenesis of Ph-like B-ALL is heterogenous and involves aberrant genomics, receptor overexpression, kinase fusions, and mutations leading to kinase signaling activation, leukemogenic cellular proliferation, and differentiation blockade. Testing for the Ph-like signature, once only a research technique, is now available to the clinical oncologist. The plethora of data pointing to poor outcomes for this ALL subset has triggered investigations into the role of targeted therapies, predominantly involving tyrosine kinase inhibitors that are showing promising results.

Regulation of Small GTPase Rab20 by Ikaros in B-Cell Acute Lymphoblastic Leukemia

Ikaros is a DNA-binding protein that regulates gene expression and functions as a tumor suppressor in B-cell acute lymphoblastic leukemia (B-ALL). The full cohort of Ikaros target genes have yet to be identified. Here, we demonstrate that Ikaros directly regulates expression of the small GTPase, Rab20. Using ChIP-seq and qChIP we assessed Ikaros binding and the epigenetic signature at the RAB20 promoter. Expression of Ikaros, CK2, and RAB20 was determined by qRT-PCR. Overexpression of Ikaros was achieved by retroviral transduction, whereas shRNA was used to knockdown Ikaros and CK2. Regulation of transcription from the RAB20 promoter was analyzed by luciferase reporter assay. The results showed that Ikaros binds the RAB20 promoter in B-ALL. Gain-of-function and loss-of-function experiments demonstrated that Ikaros represses RAB20 transcription via chromatin remodeling. Phosphorylation by CK2 kinase reduces Ikaros’ affinity toward the RAB20 promoter and abolishes its ability to repress RAB20 transcription. Dephosphorylation by PP1 phosphatase enhances both Ikaros’ DNA-binding affinity toward the RAB20 promoter and RAB20 repression. In conclusion, the results demonstrated opposing effects of CK2 and PP1 on expression of Rab20 via control of Ikaros’ activity as a transcriptional regulator. A novel regulatory signaling network in B-cell leukemia that involves CK2, PP1, Ikaros, and Rab20 is identified.

Transcriptional Regulation of Genes by Ikaros Tumor Suppressor in Acute Lymphoblastic Leukemia

Regulation of oncogenic gene expression by transcription factors that function as tumor suppressors is one of the major mechanisms that regulate leukemogenesis. Understanding this complex process is essential for explaining the pathogenesis of leukemia as well as developing targeted therapies. Here, we provide an overview of the role of Ikaros tumor suppressor and its role in regulation of gene transcription in acute leukemia. Ikaros (IKZF1) is a DNA-binding protein that functions as a master regulator of hematopoiesis and the immune system, as well as a tumor suppressor in acute lymphoblastic leukemia (ALL). Genetic alteration or functional inactivation of Ikaros results in the development of high-risk leukemia. Ikaros binds to the specific consensus binding motif at upstream regulatory elements of its target genes, recruits chromatin-remodeling complexes and activates or represses transcription via chromatin remodeling. Over the last twenty years, a large number of Ikaros target genes have been identified, and the role of Ikaros in the regulation of their expression provided insight into the mechanisms of Ikaros tumor suppressor function in leukemia. Here we summarize the role of Ikaros in the regulation of the expression of the genes whose function is critical for cellular proliferation, development, and progression of acute lymphoblastic leukemia.

Cellular signaling and epigenetic regulation of gene expression in leukemia

Alterations in normal regulation of gene expression is one of the key features of hematopoietic malignancies. In order to gain insight into the mechanisms that regulate gene expression in these diseases, we dissected the role of the Ikaros protein in leukemia. Ikaros is a DNA-binding, zinc finger protein that functions as a transcriptional regulator and a tumor suppressor in leukemia. The use of ChIP-seq, RNA-seq, and ATAC-seq—coupled with functional experiments—revealed that Ikaros regulates both the global epigenomic landscape and epigenetic signature at promoter regions of its target genes. Casein kinase II (CK2), an oncogenic kinase that is overexpressed in leukemia, directly phosphorylates Ikaros at multiple, evolutionarily-conserved residues. Phosphorylation of Ikaros impairs the protein's ability to regulate both the transcription of its target genes and global epigenetic landscape in leukemia. Treatment of leukemia cells with a specific inhibitor of CK2 restores Ikaros function, resulting in cytotoxicity of leukemia cells. Here, we review the mechanisms through which the CK2-Ikaros signaling axis regulates the global epigenomic landscape and expression of genes that control cellular proliferation in leukemia.

RAG1 high expression associated with IKZF1 dysfunction in adult B-cell acute lymphoblastic leukemia

The recombination mediated by recombination activating gene (RAG) is not only the dominant mutational process but also the predominant driver of oncogenic genomic rearrangement in acute lymphoblastic leukemia (ALL). It is further responsible for leukemic clonal evolution. In this study, significant RAG1 increase is observed in the subsets of B-ALL patients, and high expression of RAG1 is observed to be correlated with high proliferation markers. IKZF1-encoded protein, IKAROS, directly binds to the RAG1 promoter and regulates RAG1 expression in leukemic cells. CK2 inhibitor by increasing IKAROS activity significantly suppresses RAG1 expression in ALL in an IKAROS-dependent manner. Patients with IKZF1 deletion have significantly higher expression of RAG1 compared to that without IKZF1 deletion. CK2 inhibitor treatment also results in an increase in IKZF1 binding to the RAG1 promoter and suppression of RAG1 expression in primary ALL cells. Taken together, these results demonstrate that RAG1 high expression is associated with high proliferation markers in B-ALL. Our data for the first time proved that RAG1 expression is directly suppressed by IKAROS. Our results also reveal drive oncogenesis of B-ALL is driven by high expression of RAG1 with IKAROS dysfunction together, which have significance in an integrated prognostic model for adult ALL.

Ikaros tumor suppressor function includes induction of active enhancers and super-enhancers along with pioneering activity

Ikaros encodes a transcription factor that functions as a tumor suppressor in T-cell acute lymphoblastic leukemia (T-ALL). The mechanisms through which Ikaros regulates gene expression and cellular proliferation in T-ALL are unknown. Re-introduction of Ikaros into Ikaros-null T-ALL cells resulted in cessation of cellular proliferation and induction of T-cell differentiation. We performed dynamic, global, epigenomic and gene expression analyses to determine the mechanisms of Ikaros tumor suppressor activity. Our results identified novel Ikaros functions in the epigenetic regulation of gene expression: Ikaros directly regulates de novo formation and depletion of enhancers, de novo formation of active enhancers and activation of poised enhancers; Ikaros directly induces the formation of super-enhancers; and Ikaros demonstrates pioneering activity by directly regulating chromatin accessibility. Dynamic analyses demonstrate the long-lasting effects of Ikaros DNA binding on enhancer activation, de novo formation of enhancers and super-enhancers, and chromatin accessibility. Our results establish that Ikaros’ tumor suppressor function occurs via global regulation of the enhancer and super-enhancer landscape and through pioneering activity. Expression analysis identified a large number of novel signaling pathways that are directly regulated by Ikaros and Ikaros-induced enhancers, and that are responsible for the cessation of proliferation and induction of T-cell differentiation in T-ALL cells.

Keeping PACE with Ph Positive to Ph-Like Detection in B-Lineage Acute Lymphoblastic Leukemia: A Practical and Cost Effective (PACE) Approach in a Resource Constrained Setting

Philadelphia (Ph)-like or BCR-ABL like acute lymphoblastic leukemia (ALL) is defined on the basis of a gene expression profile that is similar to Ph-positive ALL. It comprises a wide spectrum of genetic lesions affecting primarily the cytokine receptor and/or kinase signalling genes. It accounts for approximately 10-15% of pediatric ALL, and is more common in patients who are high-risk according to the National Cancer Institute criteria. Presence of Ph-like mutations is an independent predictor of poor outcome. However, there is vast potential to utilize targeted therapy to improve survival in this group. The sizeable range of genetic lesions varying from translocations, fusions, point mutations and deletions make the diagnosis challenging. Hence, a practical and cost effective approach is required to enable identification in resource constrained settings. Patients with recurrent cytogenetic abnormalities such as ETV6-RUNX1, high hyperdiploidy, TCF3-PBX1, BCR-ABL1 and KMT2A (MLL) rearrangement need not be tested, as these are mutually exclusive with BCR-ABL like mutations. Detection of CRLF2 overexpression, which is the commonest abnormality, is employed as the first step. In patients lacking overexpression, testing for tyrosine kinase fusions can be performed. However, the goal should be to employ a combination of molecular diagnostic techniques such as reverse transcriptase polymerase chain reaction (PCR), real time quantitative PCR, fluorescence in situ hybridization and Sanger sequencing to detect genetic lesions that are amenable to targeted therapy.

Manic Fringe deficiency imposes Jagged1 addiction to intestinal tumor cells

Delta ligands regulate Notch signaling in normal intestinal stem cells, while Jagged1 activates Notch in intestinal adenomas carrying active β-catenin. We used the Apc^Min/+ mouse model, tumor spheroid cultures, and patient-derived orthoxenografts to address this divergent ligand-dependent Notch function and its implication in disease. We found that intestinal-specific Jag1 deletion or antibody targeting Jag1 prevents tumor initiation in mice. Addiction to Jag1 is concomitant with the absence of Manic Fringe (MFNG) in adenoma cells, and its ectopic expression reverts Jag1 dependence. In 239 human colorectal cancer patient samples, MFNG imposes a negative correlation between Jag1 and Notch, being high Jag1 in the absence of MFNG predictive of poor prognosis. Jag1 antibody treatment reduces patient-derived tumor orthoxenograft growth without affecting normal intestinal mucosa. Our data provide an explanation to Jag1 dependence in cancer, and reveal that Jag1-Notch1 interference provides therapeutic benefit in a subset of colorectal cancer and FAP syndrome patients.

The many faces of IKZF1 in B-cell precursor acute lymphoblastic leukemia

Transcription factor IKZF1 (IKAROS) acts as a critical regulator of lymphoid differentiation and is frequently deleted or mutated in B-cell precursor acute lymphoblastic leukemia. IKZF1 gene defects are associated with inferior treatment outcome in both childhood and adult B-cell precursor acute lymphoblastic leukemia and occur in more than 70% of BCR-ABL1-positive and BCR-ABL1-like cases of acute lymphoblastic leukemia. Over the past few years, much has been learned about the tumor suppressive function of IKZF1 during leukemia development and the molecular pathways that relate to its impact on treatment outcome. In this review, we provide a concise overview on the role of IKZF1 during normal lymphopoiesis and the pathways that contribute to leukemia pathogenesis as a consequence of altered IKZF1 function. Furthermore, we discuss different mechanisms by which IKZF1 alterations impose therapy resistance on leukemic cells, including enhanced cell adhesion and modulation of glucocorticoid response.

Ikaros regulation of the BCL6/BACH2 axis and its clinical relevance in acute lymphoblastic leukemia

B-Cell CLL/Lymphoma 6 (BCL6) is a proto-oncogene that is highly expressed in acute lymphoblastic leukemia (ALL). BTB and CNC Homology 1 Basic Leucine Zipper Transcription Factor 2 (BACH2) is a suppressor of transcription. The BACH2-BCL6 balance controls selection at the pre-B cell receptor checkpoint by regulating p53 expression. However, the underlying mechanism and the clinical relevance of the BCL6/BACH2 axis are unknown. Here, we found that Ikaros, a tumor suppressor encoded by IKZF1, directly binds to both the BCL6 and BACH2 promoters where it suppresses BCL6 and promotes BACH2 expression in B-cell ALL (B-ALL) cells. Casein kinase 2 (CK2) inhibitors increase Ikaros function thereby inhibiting BCL6 and promoting BACH2 expression in an Ikaros-dependent manner. We also found that the expression of BCL6 is higher while BACH2 expression is lower in patients with B-ALL than normal bone marrow control. High BCL6 and low BACH2 expression is associated with high leukemic cell proliferation, unfavorable clinical and laboratory features, and inferior outcomes. Moreover, IKZF1 deletion is associated with high BCL6 and low BACH2 expression in B-ALL patients. CK2 inhibitors increase Ikaros binding to the promoter of BCL6 and BACH2 and suppress BCL6 while promoting BACH2 expression in the primary B-ALL cells. Our data indicates that Ikaros regulates expression of the BCL6/BACH2 axis in B-ALL. High BCL6 and low BACH2 expression are associated with Ikaros dysregulation and have a potential effect on the development of B-ALL.

Casein Kinase II (CK2), Glycogen Synthase Kinase-3 (GSK-3) and Ikaros mediated regulation of leukemia

Signaling networks that regulate cellular proliferation often involve complex interactions between several signaling pathways. In this manuscript we review the crosstalk between the Casein Kinase II (CK2) and Glycogen Synthase Kinase-3 (GSK-3) pathways that plays a critical role in the regulation of cellular proliferation in leukemia. Both CK2 and GSK-3 are potential targets for anti-leukemia treatment. Previously published data suggest that CK2 and GSK-3 act synergistically to promote the phosphatidylinositol-3 kinase (PI3K) pathway via phosphorylation of PTEN. More recent data demonstrate another mechanism through which CK2 promotes the PI3K pathway - via transcriptional regulation of PI3K pathway genes by the newly-discovered CK2-Ikaros axis. Together, these data suggest that the CK2 and GSK-3 pathways regulate AKT/PI3K signaling in leukemia via two complementary mechanisms: a) direct phosphorylation of PTEN and b) transcriptional regulation of PI3K-promoting genes. Functional interactions between CK2, Ikaros and GSK3 define a novel signaling network that regulates proliferation of leukemia cells. This regulatory network involves both direct posttranslational modifications (by CK and GSK-3) and transcriptional regulation (via CK2-mediated phosphorylation of Ikaros). This information provides a basis for the development of targeted therapy for leukemia.

Regulation of cellular proliferation in acute lymphoblastic leukemia by Casein Kinase II (CK2) and Ikaros

The IKZF1 gene encodes the Ikaros protein, a zinc finger transcriptional factor that acts as a master regulator of hematopoiesis and a tumor suppressor in leukemia. Impaired activity of Ikaros is associated with the development of high-risk acute lymphoblastic leukemia (ALL) with a poor prognosis. The molecular mechanisms that regulate Ikaros' function as a tumor suppressor and regulator of cellular proliferation are not well understood. We demonstrated that Ikaros is a substrate for Casein Kinase II (CK2), an oncogenic kinase that is overexpressed in ALL. Phosphorylation of Ikaros by CK2 impairs Ikaros' DNA-binding ability, as well as Ikaros' ability to regulate gene expression and function as a tumor suppressor in leukemia. Targeting CK2 with specific inhibitors restores Ikaros' function as a transcriptional regulator and tumor suppressor resulting in a therapeutic, anti-leukemia effect in a preclinical model of ALL. Here, we review the genes and pathways that are regulated by Ikaros and the molecular mechanisms through which Ikaros and CK2 regulate cellular proliferation in leukemia.