Serine phosphorylation by SYK is critical for nuclear localization and transcription factor function of Ikaros

Syk-dependent homologous recombination activation promotes cancer resistance to DNA targeted therapy

Enhanced DNA repair is an important mechanism of inherent and acquired resistance to DNA targeted therapies, including poly ADP ribose polymerase (PARP) inhibition. Spleen associated tyrosine kinase (Syk) is a non-receptor tyrosine kinase acknowledged for its regulatory roles in immune cell function, cell adhesion, and vascular development. This study presents evidence indicating that Syk expression in high-grade serous ovarian cancer and triple-negative breast cancers promotes DNA double-strand break resection, homologous recombination (HR), and subsequent therapeutic resistance. Our investigations reveal that Syk is activated by ATM following DNA damage and is recruited to DNA double-strand breaks by NBS1. Once localized to the break site, Syk phosphorylates CtIP, a pivotal mediator of resection and HR, at Thr-847 to promote repair activity, particularly in Syk-expressing cancer cells. Inhibition of Syk or its genetic deletion impedes CtIP Thr-847 phosphorylation and overcomes the resistant phenotype. Collectively, our findings suggest a model wherein Syk fosters therapeutic resistance by promoting DNA resection and HR through a hitherto uncharacterized ATM-Syk-CtIP pathway. Moreover, Syk emerges as a promising tumor-specific target to sensitize Syk-expressing tumors to PARP inhibitors, radiation and other DNA-targeted therapies.

The transcriptomic landscape of canonical activation of NLRP3 inflammasome from bone marrow-derived macrophages

The NLRP3 inflammasome has gained significant attention due to its participation in diverse cellular processes. Nevertheless, the detailed framework of the canonical NLRP3 inflammasome assembly still remains unrevealed. This study aims to elucidate the transcriptomic landscape of the various stages involved in the canonical activation of the NLRP3 inflammasome in BMDMs by integrating RNA-seq, bioinformatics, and molecular dynamics analyses. The model for the canonical activation of the NLRP3 inflammasome was confirmed through morphological observations, functional assessments (ELISA and LDH), and protein detection (western blot). Subsequently, cells were subjected to RNA sequencing following three groups: control, priming (LPS 500 ng/ml, 4 h), and activation (LPS 500 ng/ml, 4 h; ATP 5 mM, 1 h). A total of 9116 differentially expressed genes (DEGs) were identified, which exerted regulatory effects on various pathways, including cell metabolism, ion fluxes, post-translational modifications, and organelles. Subsequently, six hub genes (Sirt3, Stat3, Syk, Trpm2, Tspo, and Txnip) were identified via integrating literature review and database screening. Finally, the three-dimensional structures of these six hub proteins were obtained using the MD-optimized RoseTTAFold and Gromacs simulations (at least 200 ns). In summary, our research offers novel insights into the transcriptomic-level understanding of the assembly of the canonical NLRP3 inflammasome.

Conserved transcriptional programming across sex and species after peripheral nerve injury predicts treatments for neuropathic pain

BACKGROUND AND PURPOSE

Chronic pain is a devastating problem affecting one in five individuals around the globe, with neuropathic pain the most debilitating and poorly treated type of chronic pain. Advances in transcriptomics have contributed to cataloguing diverse cellular pathways and transcriptomic alterations in response to peripheral nerve injury but have focused on phenomenology and classifying transcriptomic responses.

EXPERIMENTAL APPROACH

To identifying new types of pain-relieving agents, we compared transcriptional reprogramming changes in the dorsal spinal cord after peripheral nerve injury cross-sex and cross-species, and imputed commonalities, as well as differences in cellular pathways and gene regulation.

KEY RESULTS

We identified 93 transcripts in the dorsal horn that were increased by peripheral nerve injury in male and female mice and rats. Following gene ontology and transcription factor analyses, we constructed a pain interactome for the proteins encoded by the differentially expressed genes, discovering new, conserved signalling nodes. We investigated the interactome with the Drug-Gene database to predict FDA-approved medications that may modulate key nodes within the network. The top hit from the analysis was fostamatinib, the molecular target of which is the non-receptor spleen associated tyrosine kinase (Syk), which our analysis had identified as a key node in the interactome. We found that intrathecally administrating the active metabolite of fostamatinib, R406 and another Syk inhibitor P505-15, significantly reversed pain hypersensitivity in both sexes.

CONCLUSIONS AND IMPLICATIONS

Thus, we have identified and shown the efficacy of an agent that could not have been previously predicted to have analgesic properties.

IKAROS: from chromatin organization to transcriptional elongation control

IKAROS is a master regulator of cell fate determination in lymphoid and other hematopoietic cells. This transcription factor orchestrates the association of epigenetic regulators with chromatin, ensuring the expression pattern of target genes in a developmental and lineage-specific manner. Disruption of IKAROS function has been associated with the development of acute lymphocytic leukemia, lymphoma, chronic myeloid leukemia and immune disorders. Paradoxically, while IKAROS has been shown to be a tumor suppressor, it has also been identified as a key therapeutic target in the treatment of various forms of hematological malignancies, including multiple myeloma. Indeed, targeted proteolysis of IKAROS is associated with decreased proliferation and increased death of malignant cells. Although the molecular mechanisms have not been elucidated, the expression levels of IKAROS are variable during hematopoiesis and could therefore be a key determinant in explaining how its absence can have seemingly opposite effects. Mechanistically, IKAROS collaborates with a variety of proteins and complexes controlling chromatin organization at gene regulatory regions, including the Nucleosome Remodeling and Deacetylase complex, and may facilitate transcriptional repression or activation of specific genes. Several transcriptional regulatory functions of IKAROS have been proposed. An emerging mechanism of action involves the ability of IKAROS to promote gene repression or activation through its interaction with the RNA polymerase II machinery, which influences pausing and productive transcription at specific genes. This control appears to be influenced by IKAROS expression levels and isoform production. In here, we summarize the current state of knowledge about the biological roles and mechanisms by which IKAROS regulates gene expression. We highlight the dynamic regulation of this factor by post-translational modifications. Finally, potential avenues to explain how IKAROS destruction may be favorable in the treatment of certain hematological malignancies are also explored.

Syk-dependent alternative homologous recombination activation promotes cancer resistance to DNA targeted therapy

Enhanced DNA repair is an important mechanism of inherent and acquired resistance to DNA targeted therapies, including poly ADP ribose polymerase inhibition. Spleen associated tyrosine kinase (Syk) is a non-receptor tyrosine kinase known to regulate immune cell function, cell adhesion, and vascular development. Here, we report that Syk can be expressed in high grade serous ovarian cancer and triple negative breast cancers and promotes DNA double strand break resection, homologous recombination (HR) and therapeutic resistance. We found that Syk is activated by ATM following DNA damage and is recruited to DNA double strand breaks by NBS1. Once at the break site, Syk phosphorylates CtIP, a key mediator of resection and HR, at Thr-847 to promote repair activity, specifically in Syk expressing cancer cells. Syk inhibition or genetic deletion abolished CtIP Thr-847 phosphorylation and overcame the resistant phenotype. Collectively, our findings suggest that Syk drives therapeutic resistance by promoting DNA resection and HR through a novel ATM-Syk-CtIP pathway, and that Syk is a new tumor-specific target to sensitize Syk-expressing tumors to PARPi and other DNA targeted therapy.

Protein Kinase CK2 and Epstein-Barr Virus

Protein kinase CK2 is a pleiotropic protein kinase, which phosphorylates a number of cellular and viral proteins. Thereby, this kinase is implicated in the regulation of cellular signaling, controlling of cell proliferation, apoptosis, angiogenesis, immune response, migration and invasion. In general, viruses use host signaling mechanisms for the replication of their genome as well as for cell transformation leading to cancer. Therefore, it is not surprising that CK2 also plays a role in controlling viral infection and the generation of cancer cells. Epstein-Barr virus (EBV) lytically infects epithelial cells of the oropharynx and B cells. These latently infected B cells subsequently become resting memory B cells when passing the germinal center. Importantly, EBV is responsible for the generation of tumors such as Burkitt's lymphoma. EBV was one of the first human viruses, which was connected to CK2 in the early nineties of the last century. The present review shows that protein kinase CK2 phosphorylates EBV encoded proteins as well as cellular proteins, which are implicated in the lytic and persistent infection and in EBV-induced neoplastic transformation. EBV-encoded and CK2-phosphorylated proteins together with CK2-phosphorylated cellular signaling proteins have the potential to provide efficient virus replication and cell transformation. Since there are powerful inhibitors known for CK2 kinase activity, CK2 might become an attractive target for the inhibition of EBV replication and cell transformation.

ETV2 regulates PARP-1 binding protein to induce ER stress-mediated death in tuberin-deficient cells

Lymphangioleiomyomatosis (LAM) is a rare progressive disease, characterized by mutations in the tuberous sclerosis complex genes (TSC1 or TSC2) and hyperactivation of mechanistic target of rapamycin complex 1 (mTORC1). Here, we report that E26 transformation-specific (ETS) variant transcription factor 2 (ETV2) is a critical regulator of Tsc2-deficient cell survival. ETV2 nuclear localization in Tsc2-deficient cells is mTORC1-independent and is enhanced by spleen tyrosine kinase (Syk) inhibition. In the nucleus, ETV2 transcriptionally regulates poly(ADP-ribose) polymerase 1 binding protein (PARPBP) mRNA and protein expression, partially reversing the observed down-regulation of PARPBP expression induced by mTORC1 blockade during treatment with both Syk and mTORC1 inhibitors. In addition, silencing Etv2 or Parpbp in Tsc2-deficient cells induced ER stress and increased cell death in vitro and in vivo. We also found ETV2 expression in human cells with loss of heterozygosity for TSC2, lending support to the translational relevance of our findings. In conclusion, we report a novel ETV2 signaling axis unique to Syk inhibition that promotes a cytocidal response in Tsc2-deficient cells and therefore maybe a potential alternative therapeutic target in LAM.

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.

Evaluating the Immediate Response of Country-Wide Health Systems to the Covid-19 Pandemic: Applying the Gray Incidence Analysis Model

The purpose of the study is to evaluate county-wide health systems using the data set of the first wave of the COVID-19 pandemic. The overall design of study comprises a literature review, secondary data, and a mathematical analysis. It is a cross-sectional quantitative study following a deductive approach. It uses the data of the first wave of the COVID-19 pandemic taken from the website of Worldometer as of April 8, 2020. The study uses a gray incidence analysis model (commonly known as Gray Relational Analysis, i.e., GRA) as its research methodology. On the basis of the results of GRA, a classification has been made under a predetermined scheme of ensigns: much better, better, somewhat better, fair, poor, somewhat worse, and worse health systems. There are a total 211 countries that have been divided into the seven aforementioned categories. Findings of the study show that Southern Africa Development Community (SADC) countries fall predominantly under the much better ensign, whereas Organization for Economic Co-operation and Development (OECD), Schengen Area (SA), and/or European Union (EU) countries fall under the worse ensign. Pakistan falls under the ensign of poor. It is an original attempt to evaluate the response of health systems based on real data using a scientific methodology. The study provides valuable information about the health systems of the countries for forming an informed opinion about the health systems herein. The study provides useful new information for stakeholders and a new framework for future research.

IRF4 modulates the response to BCR activation in chronic lymphocytic leukemia regulating IKAROS and SYK

Interferon regulatory factor 4 (IRF4) is a transcriptional regulator of immune system development and function. Here, we investigated the role of IRF4 in controlling responsiveness to B-cell receptor (BCR) stimulation in chronic lymphocytic leukemia (CLL). We modulated IRF4 levels by transfecting CLL cells with an IRF4 vector or by silencing using small-interfering RNAs. Higher IRF4 levels attenuated BCR signaling by reducing AKT and ERK phosphorylation and calcium release. Conversely, IRF4 reduction improved the strength of the intracellular cascade activated by BCR engagement. Our results also indicated that IRF4 negatively regulates the expression of the spleen tyrosine kinase SYK, a crucial protein for propagation of BCR signaling, and the zinc finger DNA-binding protein IKAROS. We modulated IKAROS protein levels both by genetic manipulation and pharmacologically by treating CLL cells with lenalidomide and avadomide (IMIDs). IKAROS promoted BCR signaling by reducing the expression of inositol 5-phosphatase SHIP1. Lastly, IMIDs induced IRF4 expression, while down-regulating IKAROS and interfered with survival advantage mediated by BCR triggering, also in combination with ibrutinib. Overall, our findings elucidate the mechanism by which IRF4 tunes BCR signaling in CLL cells. Low IRF4 levels allow an efficient transmission of BCR signal throughout the accumulation of SYK and IKAROS.

The paradoxical pharmacological mechanisms of lenalidomide and bortezomib in the treatment of multiple myeloma

The combination of bortezomib (Velcade, PS-341) and lenalidomide (Revlimid) for the treatment of multiple myeloma was proved by USA Food and Drug Administration in 2006. Lenalidomide prevents the proliferation of multiple myeloma cells through binding to cereblon and promoting the ubiquitinational degradation of IKZF1 (Ikaros)/IKZF3 (Aiolos). However, the proteasome inhibitor bortezomib would inhibit the ubiquitinational degradation of IKZF1/IKZF3. How bortezomib could not block the antiproliferative effect of lenalidomide on multiple myeloma cells, which is the paradoxical pharmacological mechanisms in multiple myeloma. In this review, we summarized recent advances in molecular mechanisms underlying the combination of bortezomib and lenalidomide for the treatment multiple myeloma, discussed the paradoxical pharmacological mechanisms of lenalidomide and bortezomib in the treatment of multiple myeloma.

Developmental stage-specific distribution and phosphorylation of Mblk-1, a transcription factor involved in ecdysteroid-signaling in the honey bee brain

In the honey bee, the mushroom bodies (MBs), a higher-order center in insect brain, comprise interneurons termed Kenyon cells (KCs). We previously reported that Mblk-1, which encodes a transcription factor involved in ecdysteroid-signaling, is expressed preferentially in the large-type KCs (lKCs) in the pupal and adult worker brain and that phosphorylation by the Ras/MAPK pathway enhances the transcriptional activity of Mblk-1 in vitro. In the present study, we performed immunoblotting and immunofluorescence studies using affinity-purified anti-Mblk-1 and anti-phosphorylated Mblk-1 antibodies to analyze the distribution and phosphorylation of Mblk-1 in the brains of pupal and adult workers. Mblk-1 was preferentially expressed in the lKCs in both pupal and adult worker brains. In contrast, some Mblk-1 was phosphorylated almost exclusively in the pupal stages, and phosphorylated Mblk-1 was preferentially expressed in the MB neuroblasts and lKCs in pupal brains. Immunofluorescence studies revealed that both Mblk-1 and phosphorylated Mblk-1 are located in both the cytoplasm and nuclei of the lKC somata in the pupal and adult worker brains. These findings suggest that Mblk-1 plays a role in the lKCs in both pupal and adult stages and that phosphorylated Mblk-1 has pupal stage-specific functions in the MB neuroblasts and lKCs in the honey bee brain.

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.

Spleen tyrosine kinase activity regulates epidermal growth factor receptor signaling pathway in ovarian cancer

BACKGROUND

Spleen tyrosine kinase (SYK) is frequently upregulated in recurrent ovarian carcinomas, for which effective therapy is urgently needed. SYK phosphorylates several substrates, but their translational implications remain unclear. Here, we show that SYK interacts with EGFR and ERBB2, and directly enhances their phosphorylation.

METHODS

We used immunohistochemistry and immunoblotting to assess SYK and EGFR phosphorylation in ovarian serous carcinomas. Association with survival was determined by Kaplan-Meier analysis and the log-rank test. To study its role in EGFR signaling, SYK activity was modulated using a small molecule inhibitor, a syngeneic knockout, and an active kinase inducible system. We applied RNA-seq and phosphoproteomic mass spectrometry to investigate the SYK-regulated EGF-induced transcriptome and downstream substrates.

FINDINGS

Induced expression of constitutively active SYK130E reduced cellular response to EGFR/ERBB2 inhibitor, lapatinib. Expression of EGFRWT, but not SYK non-phosphorylatable EGFR3F mutant, resulted in paclitaxel resistance, a phenotype characteristic to SYK active ovarian cancers. In tumor xenografts, SYK inhibitor reduces phosphorylation of EGFR substrates. Compared to SYKWT cells, SYKKO cells have an attenuated EGFR/ERBB2-transcriptional activity and responsiveness to EGF-induced transcription. In ovarian cancer tissues, pSYK (Y525/526) levels showed a positive correlation with pEGFR (Y1187). Intense immunoreactivity of pSYK (Y525/526) correlated with poor overall survival in ovarian cancer patients.

INTERPRETATION

These findings indicate that SYK activity positively modulates the EGFR pathway, providing a biological foundation for co-targeting SYK and EGFR. FUND: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, NIH/NCI, Ovarian Cancer Research Foundation Alliance, HERA Women's Cancer Foundation and Roseman Foundation. Funders had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript and eventually in the decision to submit the manuscript.

The Transcriptional Landscape of Microglial Genes in Aging and Neurodegenerative Disease

Microglia, the brain-resident myeloid cells, are strongly implicated in Alzheimer's disease (AD) pathogenesis by human genetics. However, the mechanisms by which microglial gene expression is regulated in a region-specific manner over the course of normal aging and in neurodegenerative disease are only beginning to be deciphered. Herein, we used a specific marker of microglia (TMEM119) and a cell-type expression profiling tool (CellMapper) to identify a human microglial gene expression module. Surprisingly, we found that microglial module genes are robustly expressed in several healthy human brain regions known to be vulnerable in AD, in addition to other regions affected only later in disease or spared in AD. Surveying the microglial gene set for differential expression over the lifespan in mouse models of AD and a related tauopathy revealed that the majority of microglial module genes were significantly upregulated in cortex and hippocampus as a function of age and transgene status. Extending these results, we also observed significant upregulation of microglial module genes in several AD-affected brain regions in addition to other regions using postmortem brain tissue from human AD samples. In pathologically confirmed AD cases, we found preliminary evidence that microglial genes may be dysregulated in a sex-specific manner. Finally, we identified specific and significant overlap between the described microglial gene set—identified by unbiased co-expression analysis—and genes known to impart risk for AD. Our findings suggest that microglial genes show enriched expression in AD-vulnerable brain regions, are upregulated during aging and neurodegeneration in mice, and are upregulated in pathologically affected brain regions in AD. Taken together, our data-driven findings from multiple publicly accessible datasets reemphasize the importance of microglial gene expression alterations in AD and, more importantly, suggest that regional and sex-specific variation in microglial gene expression may be implicated in risk for and progression of neurodegenerative disease.

Optimized induction of mitochondrial apoptosis for chemotherapy-free treatment of BCR-ABL+acute lymphoblastic leukemia

BCR-ABL+acute lymphoblastic leukemia (ALL) in adults has a poor prognosis with allogeneic stem cell transplantation (SCT) considered the best curative option for suitable patients. We here characterize the curative potential of BH3-mimetics differentially targeting mitochondrial BCL2-family members using a combination therapy approach with dexamethasone and tyrosine kinase inhibitors targeting BCR-ABL. In BCR-ABL + ALL BH3-mimetics act by redistribution of mitochondrial activator BIM, which is strongly required for cytotoxicity of the BCL2-specific BH3-mimetic ABT-199, tyrosine kinase inhibitors (TKIs) and dexamethasone. BIM expression is enhanced by dexamethasone and TKIs and both synergize with ABT-199 in BCR-ABL + ALL. Triple combinations with ABT-199, dexamethasone and TKIs efficiently attenuate leukemia progression both in tissue culture and in primary cell xenotransplantation models. Notably, the dasatinib-containing combination led to treatment- and leukemia-free long-term survival in a BCR-ABL + mouse model. Finally, response to BH3-mimetics can be predicted for individual patients in a clinically relevant setting. These data demonstrate curative targeted and chemotherapy-free pharmacotherapy for BCR-ABL + ALL in a preclinical model. Clinical evaluation, in particular for patients not suitable for allogeneic SCT, is warranted.

The prognostic and predictive value of IKZF1 and IKZF3 expression in T-cells in patients with multiple myeloma

Purpose: While recent studies described the role of IKZF1/3 proteins in multiple myeloma (MM) cells, few have highlighted the significance of IKZF1/3 expression in T-cells. In this study we examine the prognostic and predictive value of IKZF1/3 expression in T-cells in patients with MM stage III. Experimental design: We analysed the IKZF1/3 expression levels in T-cells from 45 MM stage I (MMI) and 50 newly diagnosed MM stage III (MMIII) patients, according to Durie-Salmon staging system, by flow cytometry to examine their prognostic and predictive value. We also combined in vivo observations with in vitro assays to determine the effect of IKZF1/3 expression on the T-cell immunophenotype and anti-tumour T-cell response in 162 MMIII patients. Results: We found that high IKZF3, but not IKZF1, expression in T-cells correlates with superior overall survival in MMIII patients treated with immunomodulatory drugs (thalidomide, lenalidomide and pomalidomide). Moreover, we show that higher IKZF3 expression in T-cells inhibits myeloma-specific T-cell response in vitro and that the immunophenotype of patients with high IKZF3 expression shows features that are contrary to the changes induced by immunomodulatory drugs. Although we observed higher IKZF3 expression levels in T-cells from patients with MMIII compared to MMI, IKZF3 expression was unaffected by the tumour microenvironment. Conclusion: In conclusion, IKZF3 expression in T-cells is a predictive value for clinical outcome in MMIII patients treated with immunomodulatory drugs due to its profound modulation of T-cell functionality.

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.

Interdependence of JAK-STAT and MAPK signaling pathways during EGF-mediated HTR-8/SVneo cell invasion

Invasion of trophoblast cells is spatio-temporally regulated by various cytokines and growth factors. In pregnancy, complications like preeclampsia, shallow invasion of trophoblast cells and low amounts of epidermal growth factor (EGF) have been reported. In the present study, regulatory mechanisms associated with EGF-mediated invasion in HTR-8/SVneo trophoblastic cells have been delineated. Treatment of HTR-8/SVneo cells with EGF (10 ng/ml) led to eight fold increase (p < 0.05) in invasion. Increased invasion of HTR-8/SVneo cells by EGF was associated with an increase in phosphorylation of ERK½. In addition, significant phosphorylation of STAT1 (ser 727) and STAT3 (both tyr 705 and ser 727 residues) was also observed, accompanied by a decrease in total STAT1. Inhibition of ERK½ phosphorylation by U0126 (10 μM) led to a significant decrease in EGF-mediated invasion with simultaneous decrease in the phosphorylated forms of STAT3 and STAT1. Decrease in total STAT1 was also reversed on inhibition of ERK½. Interestingly, inhibition of STAT3 by siRNA led to a significant decrease in EGF-mediated invasion of HTR-8/SVneo cells and phosphorylation of STAT1, but it did not have any effect on the activation of ERK½. On the other hand, inhibition of STAT1 by siRNA, also led to a significant decrease in the EGF-mediated invasion of HTR-8/SVneo cells, showed concomitant decrease in ERK½ phosphorylation and STAT3 phosphorylation at ser 727 residue. These results suggest cross-communication between ERK½ and JAK-STAT pathways during EGF-mediated increase in invasion of trophoblast cells; phosphorylation at ser 727 residue of both STAT3 and STAT1 appears to be critical.

The Ikaros family of zinc-finger proteins

Ikaros represents a zinc-finger protein family important for lymphocyte development and certain other physiological processes. The number of family members is large, with alternative splicing producing various additional isoforms from each of the five homologous genes in the family. The functional forms of Ikaros proteins could be even more diverse due to protein–protein interactions readily established between family members. Emerging evidence suggests that targeting Ikaros proteins is feasible and effective in therapeutic applications, although the exact roles of Ikaros proteins remain elusive within the intricate regulatory networks in which they are involved. In this review we collect existing knowledge as to the functions, regulatory pathways, and molecular mechanisms of this family of proteins in an attempt to gain a better understanding through the comparison of activities and interactions among family members.

Alternative Splice Variants Modulates Dominant-Negative Function of Helios in T-Cell Leukemia

The molecular defects which lead to multistep incidences of human T-cell leukemia have yet to be identified. The DNA-binding protein Helios (known as IKZF2), a member of the Ikaros family of Krüppel-like zinc-finger proteins, functions pivotally in T-cell differentiation and activation. In this study, we identify three novel short Helios splice variants which are T-cell leukemic specific, and demonstrate their dominant-negative function. We then test the cellular localization of distinct Helios isoforms, as well as their capability to form heterodimer with Ikaros, and the association with complexes comprising histone deacetylase (HDAC). In addition, the ectopic expression of T-cell leukemic Helios isoforms interferes with T-cell proliferation and apoptosis. The gene expression profiling and pathway analysis indicated the enrichment of signaling pathways essential for gene expression, translation, cell cycle checkpoint, and response to DNA damage stimulus. These data indicate the molecular function of Helios to be involved in the leukemogenesis and phenotype of T-cell leukemia, and also reveal Helios deregulation as a novel marker for T-cell leukemia.

Sumoylation Inhibits the Growth Suppressive Properties of Ikaros

The Ikaros transcription factor is a tumor suppressor that is also important for lymphocyte development. How post-translational modifications influence Ikaros function remains partially understood. We show that Ikaros undergoes sumoylation in developing T cells that correspond to mono-, bi- or poly-sumoylation by SUMO1 and/or SUMO2/3 on three lysine residues (K58, K240 and K425). Sumoylation occurs in the nucleus and requires DNA binding by Ikaros. Sumoylated Ikaros is less effective than unsumoylated forms at inhibiting the expansion of murine leukemic cells, and Ikaros sumoylation is abundant in human B-cell acute lymphoblastic leukemic cells, but not in healthy peripheral blood leukocytes. Our results suggest that sumoylation may be important in modulating the tumor suppressor function of Ikaros.

Elucidation of tonic and activated B-cell receptor signaling in Burkitt's lymphoma provides insights into regulation of cell survival

Burkitt's lymphoma (BL) is a highly proliferative B-cell neoplasm and is treated with intensive chemotherapy that, because of its toxicity, is often not suitable for the elderly or for patients with endemic BL in developing countries. BL cell survival relies on signals transduced by B-cell antigen receptors (BCRs). However, tonic as well as activated BCR signaling networks and their relevance for targeted therapies in BL remain elusive. We have systematically characterized and compared tonic and activated BCR signaling in BL by quantitative phosphoproteomics to identify novel BCR effectors and potential drug targets. We identified and quantified ∼16,000 phospho-sites in BL cells. Among these sites, 909 were related to tonic BCR signaling, whereas 984 phospho-sites were regulated upon BCR engagement. The majority of the identified BCR signaling effectors have not been described in the context of B cells or lymphomas yet. Most of these newly identified BCR effectors are predicted to be involved in the regulation of kinases, transcription, and cytoskeleton dynamics. Although tonic and activated BCR signaling shared a considerable number of effector proteins, we identified distinct phosphorylation events in tonic BCR signaling. We investigated the functional relevance of some newly identified BCR effectors and show that ACTN4 and ARFGEF2, which have been described as regulators of membrane-trafficking and cytoskeleton-related processes, respectively, are crucial for BL cell survival. Thus, this study provides a comprehensive dataset for tonic and activated BCR signaling and identifies effector proteins that may be relevant for BL cell survival and thus may help to develop new BL treatments.

CD22ΔE12 as a molecular target for corrective repair using RNA trans-splicing: anti-leukemic activity of a rationally designed RNA trans-splicing molecule

Our recent studies have demonstrated that the CD22 exon 12 deletion (CD22ΔE12) is a characteristic genetic defect of therapy-refractory clones in pediatric B-precursor acute lymphoblastic leukemia (BPL) and implicated the CD22ΔE12 genetic defect in the aggressive biology of relapsed or therapy-refractory pediatric BPL. The purpose of the present study was to further evaluate the biologic significance of the CD22ΔE12 molecular lesion and determine if it could serve as a molecular target for corrective repair using RNA trans-splicing therapy. We show that both pediatric and adult B-lineage lymphoid malignancies are characterized by a very high incidence of the CD22ΔE12 genetic defect. We provide experimental evidence that the correction of the CD22ΔE12 genetic defect in human CD22ΔE12(+) BPL cells using a rationally designed CD22 RNA trans-splicing molecule (RTM) caused a pronounced reduction of their clonogenicity. The RTM-mediated correction replaced the downstream mutation-rich segment of Intron 12 and remaining segments of the mutant CD22 pre-mRNA with wildtype CD22 exons 10-14, thereby preventing the generation of the cis-spliced aberrant CD22ΔE12 product. The anti-leukemic activity of this RTM against BPL xenograft clones derived from CD22ΔE12(+) leukemia patients provides the preclinical proof-of-concept that correcting the CD22ΔE12 defect with rationally designed CD22 RTMs may provide the foundation for therapeutic innovations that are needed for successful treatment of high-risk and relapsed BPL patients.

Microfluidics: reframing biological enquiry

The underlying physical properties of microfluidic tools have led to new biological insights through the development of microsystems that can manipulate, mimic and measure biology at a resolution that has not been possible with macroscale tools. Microsystems readily handle sub-microlitre volumes, precisely route predictable laminar fluid flows and match both perturbations and measurements to the length scales and timescales of biological systems. The advent of fabrication techniques that do not require highly specialized engineering facilities is fuelling the broad dissemination of microfluidic systems and their adaptation to specific biological questions. We describe how our understanding of molecular and cell biology is being and will continue to be advanced by precision microfluidic approaches and posit that microfluidic tools - in conjunction with advanced imaging, bioinformatics and molecular biology approaches - will transform biology into a precision science.

Effect of IKZF1 deletions on signal transduction pathways in Philadelphia chromosome negative pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL)

Background

IKZF1 deletions are an unfavorable prognostic factor in children with Philadelphia chromosome positive (Ph⁺) as well as negative (Ph⁻) acute lymphoblastic leukemia (ALL). Although IKZF1 deletions occur in 10–15% of Ph⁻ ALL cases, effects of IKZF1 deletions on signaling pathways in this group have not been extensively studied. Therefore, in this study we aimed to study the effect of IKZF1 deletions on active signal transduction pathways.

Methods

Multiplex ligation-dependent probe amplification (MLPA) was used to determine IKZF1 deletions and other copy number alterations in 109 pediatric B-Cell Precursor ALL (BCP-ALL) patients. Kinase activity profiling of 45 primary Ph⁻ BCP-ALL patients (31 IKZF1 wild type patients and 14 patients harboring an IKZF1 alteration) and western blot analysis of 14 pediatric BCP-ALL samples was performed to determine active signal transduction pathways.

Results

Unsupervised hierarchical cluster analysis of kinome profiles of 45 pediatric Ph⁻ ALL cases showed no clustering based on IKZF1 status. Comparing the phosphorylation intensities of peptides associated with signaling pathways known to be involved in BCP-ALL maintenance, we did not observe differences between the two groups. Western blot analysis of 14 pediatric BCP-ALL samples showed large variations in phosphorylation levels between the different ALL samples, independent of IKZF1 status.

Conclusions

Based on these results we conclude that, although IKZF1 deletions appear to be an important clinical prognostic factor, we were unable to identify a unique IKZF1 dependent protein expression signature in pediatric Ph⁻ ALL and consequently no specific targets for future therapy of Ph⁻IKZF1 deleted BCP-ALL could be identified.

Electronic supplementary material

The online version of this article (doi:10.1186/s40164-015-0017-y) contains supplementary material, which is available to authorized users.

Liposomal Nanoparticles of a Spleen Tyrosine Kinase P-Site Inhibitor Amplify the Potency of Low Dose Total Body Irradiation Against Aggressive B-Precursor Leukemia and Yield Superior Survival Outcomes in Mice

This study was designed to improve the efficacy of radiation therapy against radiation-resistant leukemia. We report that the potency of low dose radiation therapy against B-precursor acute lymphoblastic leukemia (BPL) can be markedly enhanced by combining radiation with a liposomal nanoparticle (LNP) formulation of the SYK-P-site inhibitor C61 (“C61-LNP”). C61-LNP plus low dose total body irradiation (TBI) was substantially more effective than TBI alone or C61-LNP alone in improving the event-free survival outcome NOD/SCID mice challenged with an otherwise invariably fatal dose of human ALL xenograft cells derived from relapsed BPL patients. C61-LNP plus low dose TBI also yielded progression-free survival, tumor-free survival and overall survival outcomes in CD22ΔE12 × BCR–ABL double transgenic mice with advanced stage, radiation-resistant BPL with lymphomatous features that were significantly superior to those of mice treated with TBI alone or C61-LNP alone.

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Liposomal nanoparticles of C61 kill radiation-resistant leukemia cells

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Liposomal nanoparticles of C61 potentiate TBI against human leukemia cells

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Liposomal nanoparticles of C61 plus TBI improve the survival outcome of leukemic mice.

Low Dose Total Body Irradiation Combined With Recombinant CD19-Ligand × Soluble TRAIL Fusion Protein is Highly Effective Against Radiation-Resistant B-Precursor Acute Lymphoblastic Leukemia in Mice

In high-risk remission B-precursor acute lymphoblastic leukemia (BPL) patients, relapse rates have remained high post-hematopoietic stem cell transplantation (HSCT) even after the use of very intensive total body irradiation (TBI)-based conditioning regimens, especially in patients with a high “minimal residual disease” (MRD) burden. New agents capable of killing radiation-resistant BPL cells and selectively augmenting their radiation sensitivity are therefore urgently needed. We report preclinical proof-of-principle that the potency of radiation therapy against BPL can be augmented by combining radiation with recombinant human CD19-Ligand × soluble TRAIL (“CD19L–sTRAIL”) fusion protein. CD19L–sTRAIL consistently killed radiation-resistant primary leukemia cells from BPL patients as well as BPL xenograft cells and their leukemia-initiating in vivo clonogenic fraction. Low dose total body irradiation (TBI) combined with CD19L–sTRAIL was highly effective against (1) xenografted CD19⁺ radiochemotherapy-resistant human BPL in NOD/SCID (NS) mice challenged with an otherwise invariably fatal dose of xenograft cells derived from relapsed BPL patients as well as (2) radiation-resistant advanced stage CD19⁺ murine BPL with lymphomatous features in CD22ΔE12xBCR-ABL double transgenic mice. We hypothesize that the incorporation of CD19L–sTRAIL into the pre-transplant TBI regimens of patients with very high-risk BPL will improve their survival outcome after HSCT.

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CD19L–sTRAIL plus low dose radiation kills leukemia-initiating cells.

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CD19L–sTRAIL plus low dose TBI is very well tolerated in mice.

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CD19L–sTRAIL plus low dose TBI is very effective in mouse models of BPL.

CD22ΔE12 as a molecular target for RNAi therapy

B-precursor acute lymphoblastic leukaemia (BPL) is the most common form of cancer in children and adolescents. Our recent studies have demonstrated that CD22ΔE12 is a characteristic genetic defect of therapy-refractory clones in paediatric BPL and implicated the CD22ΔE12 genetic defect in the aggressive biology of relapsed or therapy-refractory paediatric BPL. The purpose of the present study is to evaluate the biological significance of the CD22ΔE12 molecular lesion in BPL and determine if it could serve as a molecular target for RNA interference (RNAi) therapy. Here we report a previously unrecognized causal link between CD22ΔE12 and aggressive biology of human BPL cells by demonstrating that siRNA-mediated knockdown of CD22ΔE12 in primary leukaemic B-cell precursors is associated with a marked inhibition of their clonogenicity. Additionally, we report a nanoscale liposomal formulation of CD22ΔE12-specific siRNA with potent in vitro and in vivo anti-leukaemic activity against primary human BPL cells as a first-in-class RNAi therapeutic candidate targeting CD22ΔE12.

Recombinant human CD19L-sTRAIL effectively targets B cell precursor acute lymphoblastic leukemia

Patients with B cell precursor acute lymphoblastic leukemia (BPL) respond well to chemotherapy at initial diagnosis; however, therapeutic options are limited for individuals with BPL who relapse. Almost all BPL cells express CD19, and we recently cloned the gene encoding a natural ligand of the human CD19 receptor (CD19L). We hypothesized that fusion of CD19L to the soluble extracellular domain of proapoptotic TNF-related apoptosis-inducing ligand (sTRAIL) would markedly enhance the potency of sTRAIL and specifically induce BPL cell apoptosis due to membrane anchoring of sTRAIL and simultaneous activation of the CD19 and TRAIL receptor (TRAIL-R) apoptosis signaling pathways. Here, we demonstrate that recombinant human CD19L-sTRAIL was substantially more potent than sTRAIL and induced apoptosis in primary leukemia cells taken directly from BPL patients. CD19L-sTRAIL effectively targeted and eliminated in vivo clonogenic BPL xenograft cells, even at femtomolar-picomolar concentrations. In mice, CD19L-sTRAIL exhibited a more favorable pharmacokinetic (PK) profile than sTRAIL and was nontoxic at doses ranging from 32 fmol/kg to 3.2 pmol/kg. CD19L-sTRAIL showed potent in vivo antileukemic activity in NOD/SCID mouse xenograft models of relapsed and chemotherapy-resistant BPL at nontoxic fmol/kg dose levels. Together, these results suggest that recombinant human CD19L-sTRAIL has clinical potential as a biotherapeutic agent against BPL.

A rationally designed nanoparticle for RNA interference therapy in B-lineage lymphoid malignancies

The purpose of the present study was to further evaluate the biologic significance of the CD22ΔE12 molecular lesion and determine if it could serve as a molecular target for RNA interference (RNAi) therapy. We show that both pediatric and adult B-lineage lymphoid malignancies are characterized by a very high incidence of the CD22ΔE12 genetic defect. We provide unprecedented experimental evidence for a previously unrecognized causal link between CD22ΔE12 and aggressive biology of BPL cells by demonstrating that siRNA-mediated knockdown of CD22ΔE12 in primary BPL cells is associated with a marked inhibition of their clonogenicity. These findings provide the preclinical proof-of-concept that siRNA-mediated depletion of CD22ΔE12 may help develop effective treatments for high-risk and relapsed BPL patients who are in urgent need for therapeutic innovations. We also describe a unique polypeptide-based nanoparticle formulation of CD22ΔE12-siRNA as an RNAi therapeutic candidate targeting CD22ΔE12 that is capable of delivering its siRNA cargo into the cytoplasm of leukemia cells causing effective CD22ΔE12 depletion and marked inhibition of leukemic cell growth. Further development and optimization of this nanoparticle or other nanoformulation platforms for CD22ΔE12-siRNA may facilitate the development of an effective therapeutic RNAi strategy against paradigm shift in therapy of aggressive or chemotherapy-resistant B-lineage lymphoid malignancies.

Calling in SYK: SYK's dual role as a tumor promoter and tumor suppressor in cancer

SYK (spleen tyrosine kinase) is well-characterized in the immune system as an essential enzyme required for signaling through multiple classes of immune recognition receptors. As a modulator of tumorigenesis, SYK has a bit of a schizophrenic reputation, acting in some cells as a tumor promoter and in others as a tumor suppressor. In many hematopoietic malignancies, SYK provides an important survival function and its inhibition or silencing frequently leads to apoptosis. In cancers of non-immune cells, SYK provides a pro-survival signal, but can also suppress tumorigenesis by restricting epithelial-mesenchymal transition, enhancing cell-cell interactions and inhibiting migration.

A PREVIOUSLY UNKNOWN UNIQUE CHALLENGE FOR INHIBITORS OF SYK ATP-BINDING SITE: ROLE OF SYK AS A CELL CYCLE CHECKPOINT REGULATOR

The identification of SYK as a molecular target in B-lineage leukemia/lymphoma cells prompted the development of SYK inhibitors as a new class of anti-cancer drug candidates. Here we report that induction of the SYK gene expression in human cells causes a significant down-regulation of evolutionarily conserved genes associated with mitosis and cell cycle progression providing unprecedented evidence that SYK is a master regulator of cell cycle regulatory checkpoint genes in human cells. We further show that SYK regulates the G₂ checkpoint by physically associating with and inhibiting the dual-specificity phosphatase CDC25C via phosphorylation of its S216 residue. SYK depletion by RNA interference or treatment with the chemical SYK inhibitor prevented nocodazole-treated human cell lines from activating the G₂ checkpoint via CDC25C S216-phosphorylation and resulted in polyploidy. Our study provides genetic and biochemical evidence that spleen tyrosine kinase (SYK) has a unique role in the activation of the G₂ checkpoint in both non-lymphohematopoietic and B-lineage lymphoid cells. This previously unknown role of SYK as a cell cycle checkpoint regulator represents an unforeseen and significant challenge for inhibitors of SYK ATP binding site.

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SYK is a cell cycle regulatory kinase that phosphorylates CDC25C at S216

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SYK is a master regulator of cell cycle regulatory checkpoint genes in human cells

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Inhibitors of SYK ATP binding site may increase the risk for secondary cancer

Getting Syk: spleen tyrosine kinase as a therapeutic target

Spleen tyrosine kinase (Syk) is a cytoplasmic protein tyrosine kinase well known for its ability to couple immune cell receptors to intracellular signaling pathways that regulate cellular responses to extracellular antigens and antigen-immunoglobulin (Ig) complexes of particular importance to the initiation of inflammatory responses. Thus, Syk is an attractive target for therapeutic kinase inhibitors designed to ameliorate the symptoms and consequences of acute and chronic inflammation. Its more recently recognized role as a promoter of cell survival in numerous cancer cell types ranging from leukemia to retinoblastoma has attracted considerable interest as a target for a new generation of anticancer drugs. This review discusses the biological processes in which Syk participates that have made this kinase such a compelling drug target.

Ikaros imposes a barrier to CD8+ T cell differentiation by restricting autocrine IL-2 production

Naive CD4(+) T cells require signals from the TCR and CD28 to produce IL-2, expand, and differentiate. However, these same signals are not sufficient to induce autocrine IL-2 production by naive CD8(+) T cells, which require cytokines provided by other cell types to drive their differentiation. The basis for failed autocrine IL-2 production by activated CD8(+) cells is unclear. We find that Ikaros, a transcriptional repressor that silences IL-2 in anergic CD4(+) T cells, also restricts autocrine IL-2 production by CD8(+) T cells. We find that CD8(+) T cell activation in vitro in the absence of exogenous cytokines and CD4 help leads to marked induction of Ikaros, a known repressor of the Il2 gene. Naive murine CD8 T cells haplo-insufficient for Ikzf1 failed to upregulate Ikaros, produced autocrine IL-2, and differentiated in an IL-2-dependent manner into IFN-γ-producing CTLs in response to TCR/CD28 stimulation alone. Furthermore, Ikzf1 haplo-insufficient CD8(+) T cells were more effective at controlling Listeria infection and B16 melanoma growth in vivo, and they could provide help to neighboring, non-IL-2-producing cells to differentiate into IFN-γ-producing effectors. Therefore, by repressing autocrine IL-2 production, Ikaros ensures that naive CD8(+) T cells remain dependent on licensing by APCs and CD4(+) T cells, and it may therefore act as a cell-intrinsic safeguard against inappropriate CTL differentiation and immunopathology.

Wnt/β-catenin signaling regulates follicular development by modulating the expression of Foxo3a signaling components

Wnt signaling is an evolutionarily conserved pathway that regulates cell proliferation, differentiation and apoptosis. To investigate the possible role of Wnt signaling in the regulation of ovarian follicular development, secondary follicles were isolated and cultured in vitro in the presence or absence of its activator (LiCl or Wnt3a) or inhibitor (IWR-1). We have demonstrated that activation of β-catenin signals by activators dramatically suppressed follicular development by increasing granulosa cell apoptosis and inhibiting follicle steroidogenesis. In contrast, inhibition of Wnt signaling by IWR-1 was observed with better developed follicles and increased steroidogenesis. Further studies have shown that the transcription factor Forkhead box O3a (Foxo3a) and its downstream target molecules were modulated by the activators or the inhibitor. These findings provide evidence that Wnt signaling might negatively regulate follicular development potentially through Foxo3a signaling components.

Epstein-Barr virus utilizes Ikaros in regulating its latent-lytic switch in B cells

Ikaros is a zinc finger DNA-binding protein that regulates chromatin remodeling and the expression of genes involved in the cell cycle, apoptosis, and Notch signaling. It is a master regulator of lymphocyte differentiation and functions as a tumor suppressor in acute lymphoblastic leukemia. Nevertheless, no previous reports described effects of Ikaros on the life cycle of any human lymphotropic virus. Here, we demonstrate that full-length Ikaros (IK-1) functions as a major factor in the maintenance of viral latency in Epstein-Barr virus (EBV)-positive Burkitt's lymphoma Sal and MutuI cell lines. Either silencing of Ikaros expression by small hairpin RNA (shRNA) knockdown or ectopic expression of a non-DNA-binding isoform induced lytic gene expression. These effects synergized with other lytic inducers of EBV, including transforming growth factor β (TGF-β) and the hypoxia mimic desferrioxamine. Data from chromatin immunoprecipitation (ChIP)-quantitative PCR (qPCR) and ChIP-sequencing (ChIP-seq) analyses indicated that Ikaros did not bind to either of the EBV immediate early genes BZLF1 and BRLF1. Rather, Ikaros affected the expression of Oct-2 and Bcl-6, other transcription factors that directly inhibit EBV reactivation and plasma cell differentiation, respectively. IK-1 also complexed with the EBV immediate early R protein in coimmunoprecipitation assays and partially colocalized with R within cells. The presence of R alleviated IK-1-mediated transcriptional repression, with IK-1 then cooperating with Z and R to enhance lytic gene expression. Thus, we conclude that Ikaros plays distinct roles at different stages of EBV's life cycle: it contributes to maintaining latency via indirect mechanisms, and it may also synergize with Z and R to enhance lytic replication through direct association with R and/or R-induced alterations in Ikaros' functional activities via cellular signaling pathways.

IMPORTANCE

This is the first report showing that the cellular protein Ikaros, a known master regulator of hematopoiesis and critical tumor suppressor in acute lymphoblastic leukemia, also plays important roles in the life cycle of Epstein-Barr virus in B cells.

Ikaros is absolutely required for pre-B cell differentiation by attenuating IL-7 signals

Ikaros is essential for pre-BCR down-regulation, Igκ germline transcription, Ig light chain recombination, and pre-B cell differentiation, in part by antagonizing IL-7–dependent gene regulation.

Pre-B cell receptor (pre-BCR) signaling and migration from IL-7–rich environments cooperate to drive pre-B cell differentiation via transcriptional programs that remain unclear. We show that the Ikaros transcription factor is required for the differentiation of large pre-B to small pre-B cells. Mice deleted for Ikaros in pro/pre-B cells show a complete block of differentiation at the fraction C′ stage, and Ikaros-null pre-B cells cannot differentiate upon withdrawal of IL-7 in vitro. Restoration of Ikaros function rescues pre-B cell differentiation in vitro and in vivo and depends on DNA binding. Ikaros is required for the down-regulation of the pre-BCR, Igκ germline transcription, and Ig L chain recombination. Furthermore, Ikaros antagonizes the IL-7–dependent regulation of >3,000 genes, many of which are up- or down-regulated between fractions C′ and D. Affected genes include those important for survival, metabolism, B cell signaling, and function, as well as transcriptional regulators like Ebf1, Pax5, and the Foxo1 family. Our data thus identify Ikaros as a central regulator of IL-7 signaling and pre-B cell development.

Constitutive function of the Ikaros transcription factor in primary leukemia cells from pediatric newly diagnosed high-risk and relapsed B-precursor ALL patients

We examined the constitutive function of the Ikaros (IK) transcription factor in blast cells from pediatric B-precursor acute lymphoblastic leukemia (BPL) patients using multiple assay platforms and bioinformatics tools. We found no evidence of diminished IK expression or function for primary cells from high-risk BPL patients including a Philadelphia chromosome (Ph)⁺ subset. Relapse clones as well as very aggressive in vivo clonogenic leukemic B-cell precursors isolated from spleens of xenografted NOD/SCID mice that developed overt leukemia after inoculation with primary leukemic cells of patients with BPL invariably and abundantly expressed intact IK protein. These results demonstrate that a lost or diminished IK function is not a characteristic feature of leukemic cells in Ph⁺ or Ph^- high-risk BPL.

Regulatory phosphorylation of Ikaros by Bruton's tyrosine kinase

Diminished Ikaros function has been implicated in the pathogenesis of acute lymphoblastic leukemia (ALL), the most common form of childhood cancer. Therefore, a stringent regulation of Ikaros is of paramount importance for normal lymphocyte ontogeny. Here we provide genetic and biochemical evidence for a previously unknown function of Bruton's tyrosine kinase (BTK) as a partner and posttranslational regulator of Ikaros, a zinc finger-containing DNA-binding protein that plays a pivotal role in immune homeostasis. We demonstrate that BTK phosphorylates Ikaros at unique phosphorylation sites S214 and S215 in the close vicinity of its zinc finger 4 (ZF4) within the DNA binding domain, thereby augmenting its nuclear localization and sequence-specific DNA binding activity. Our results further demonstrate that BTK-induced activating phosphorylation is critical for the optimal transcription factor function of Ikaros.

KU HAPLOINSUFFIENCY CAUSES A LYMPHOPROLIFERATIVE DISORDER OF IMMATURE T-CELL PRECURSORS DUE TO IKAROS MALFUNCTION

Ikaros (IK) malfunction has been implicated in the pathogenesis of acute lymphoblastic leukemia (ALL), the most common form of childhood cancer. Therefore, a stringent regulation of IK activity is very important. Here we provide unique genetic and biochemical evidence that the Ku protein components Ku70 and Ku80 act as positive regulators of IK function via formation of IK-Ku70 and IK-Ku80 heterodimers with augmented sequence-specific DNA binding activity. siRNA-mediated depletion of Ku70 or Ku80 reduced the sequence-specific DNA binding activity of IK in EMSA as well as the RT-PCR measured IK target gene expression levels in human cells. The interaction of Ku components with IK likely contributes to the anti-leukemic effects of IK as a tumor suppressor, because Ku70 as well as Ku80 haploinsuffiency in mice caused development of a lymphoproliferative disorder (LPD) involving CD2+CD4+CD8+CD1+IL7R+ thymic T-cell precursors with functional IK deficiency.

Absence of Genomic Ikaros/IKZF1 Deletions in Pediatric B-Precursor Acute Lymphoblastic Leukemia

Here we report the results of gene expression analyses using multiple probesets aimed at determining the incidence of Ikaros/IKZF1 deletions in pediatric B-precursor acute lymphoblastic leukemia (BPL). Primary leukemia cells from 122 Philadelphia chromosome (Ph)⁺ BPL patients and 237 Ph^- BPL patients as well as normal hematopoietic cells from 74 normal non-leukemic bone marrow specimens were organized according to expression levels of IKZF1 transcripts utilizing two-way hierarchical clustering technique to identify specimens with low IKZF1 expression for the 10 probesets interrogating Exons 1 through 4 and Exon 8. Our analysis demonstrated no changes in expression that would be expected from homozygous or heterozygous deletions of IKZF1 in primary leukemic cells. Similar results were obtained in gene expression analysis of primary leukemic cells from 20 Ph⁺ positive and 155 Ph^- BPL patients in a validation dataset. Taken together, our gene expression analyses in 534 pediatric BPL cases, including 142 cases with Ph⁺ BPL, contradict previous reports that were based on SNP array data and suggested that Ph⁺ pediatric BPL is characterized by a high frequency of homozygous or heterozygous IKZF1 deletions. Further, exon-specific genomic PCR analysis of primary leukemia cells from 21 high-risk pediatric BPL patients and 11 standard-risk pediatric BPL patients, and 8 patients with infant BPL did not show any evidence for homozygous IKZF1 locus deletions. Nor was there any evidence for homozygous or heterozygous intragenic IKZF1 deletions.