RESUMO
The Ikaros zing-finger family transcription factors (IKZF TFs) are important regulators of lymphocyte development and differentiation and are also highly expressed in B cell malignancies, including Multiple Myeloma (MM), where they are required for cancer cell growth and survival. Moreover, IKZF TFs negatively control the functional properties of many immune cells. Thus, the targeting of these proteins has relevant therapeutic implications in cancer. Indeed, accumulating evidence demonstrated that downregulation of Ikaros and Aiolos, two members of the IKZF family, in malignant plasma cells as well as in adaptative and innate lymphocytes, is key for the anti-myeloma activity of Immunomodulatory drugs (IMiDs). This review is focused on IKZF TF-related pathways in MM. In particular, we will address how the depletion of IKZF TFs exerts cytotoxic effects on MM cells, by reducing their survival and proliferation, and concomitantly potentiates the antitumor immune response, thus contributing to therapeutic efficacy of IMiDs, a cornerstone in the treatment of this neoplasia.
Assuntos
Fator de Transcrição Ikaros/fisiologia , Mieloma Múltiplo/tratamento farmacológico , Animais , Antineoplásicos/farmacologia , Apoptose/efeitos dos fármacos , Diferenciação Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Proliferação de Células , Sobrevivência Celular , Humanos , Fator de Transcrição Ikaros/genética , Imunidade/efeitos dos fármacos , Imunomodulação/efeitos dos fármacos , Lenalidomida/farmacologia , Linfócitos/citologia , Camundongos , Mieloma Múltiplo/imunologia , Talidomida/farmacologiaRESUMO
The majority of cases of T-cell acute lymphoblastic leukemia (T-ALL) contain chromosomal abnormalities that drive overexpression of oncogenic transcription factors. However, whether these initiating oncogenes are required for leukemia maintenance is poorly understood. To address this, we developed a tetracycline-regulated mouse model of T-ALL driven by the oncogenic transcription factor Lmo2. This revealed that whilst thymus-resident pre-Leukemic Stem Cells (pre-LSCs) required continuous Lmo2 expression, the majority of leukemias relapsed despite Lmo2 withdrawal. Relapse was associated with a mature phenotype and frequent mutation or loss of tumor suppressor genes including Ikzf1 (Ikaros), with targeted deletion Ikzf1 being sufficient to transform Lmo2-dependent leukemias to Lmo2-independence. Moreover, we found that the related transcription factor TAL1 was dispensable in several human T-ALL cell lines that contain SIL-TAL1 chromosomal deletions driving its overexpression, indicating that evolution to oncogene independence can also occur in human T-ALL. Together these results indicate an evolution of oncogene addiction in murine and human T-ALL and show that loss of Ikaros is a mechanism that can promote self-renewal of T-ALL lymphoblasts in the absence of an initiating oncogenic transcription factor.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Regulação Leucêmica da Expressão Gênica , Fator de Transcrição Ikaros/fisiologia , Proteínas com Domínio LIM/fisiologia , Leucemia-Linfoma Linfoblástico de Células T Precursoras/patologia , Animais , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Oncogenes , Leucemia-Linfoma Linfoblástico de Células T Precursoras/etiologia , Leucemia-Linfoma Linfoblástico de Células T Precursoras/metabolismoRESUMO
BACKGROUND: Leukemia is a heterogeneous disorder, characterized by elevated proliferation of white blood cells. Various genetic studies have assessed the contributory roles of several single nucleotide polymorphisms with the development of leukemia. The role of genetic variation in the ARID5B and IKZF1 genes has previously been identified in various population groups; however, the role of these variants in the north Indian populations of Jammu and Kashmir is unknown. AIM: In this study, we explored the association of the newly identified genetic variants, rs10740055 of ARID5B and rs6964823 of IKZF1, with leukemic patients from Jammu and Kashmir of northern India. METHODS: The variants were genotyped using TaqMan allele discrimination assays for 616 individuals (210 leukemic cases and 406 healthy controls). The association of each SNP with the disease was evaluated using logistic regression. RESULTS: It was observed that the variants rs6964823 (IKZF1) and rs10740055 (ARID5B) showed significant associations with odds ratio (OR) and p-values of 1.5 (1.0-2.3 at 95% confidence interval [CI]) and 0.04; and 2.5 (1.5-4.1 at 95% CI) and 0.0002, respectively. We also evaluated the cumulative effect for both the variants by combining the risk genotypes and obtained and OR of 4.9. DISCUSSION: It was found that the variants rs10740055 of ARID5B and rs6964823 of IKZF1 act individually and additively as risk factors in the development of leukemia in the populations of Jammu and Kashmir in Northern India.
Assuntos
Proteínas de Ligação a DNA/genética , Fator de Transcrição Ikaros/genética , Leucemia/genética , Fatores de Transcrição/genética , Adulto , Alelos , Povo Asiático/genética , Estudos de Casos e Controles , Proteínas de Ligação a DNA/fisiologia , Epistasia Genética , Feminino , Frequência do Gene/genética , Predisposição Genética para Doença/genética , Estudo de Associação Genômica Ampla , Genótipo , Humanos , Fator de Transcrição Ikaros/fisiologia , Índia , Masculino , Pessoa de Meia-Idade , Razão de Chances , Polimorfismo de Nucleotídeo Único/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Fatores de Risco , Fatores de Transcrição/fisiologiaRESUMO
Unveiling the mechanism of the relapse of acute lymphoblastic leukemia (ALL) is the key to improve the prognosis of ALL and remains a huge challenge. Glycan-based interactions play a vital role in immune surveillance, cell-cell adhesion and cell-matrix interaction, contributing to treatment failure in tumor. However, the glycan essential for leukemia development and its upstream regulatory mechanism by oncogenic drivers were rarely reported. Here, we demonstrated that LeX, a well-characterized cancer-related glycan epitope, strengthened the cell-matrix interaction via glycosylating α5ß1 integrin under the control of the driver oncogenic Ikaros isoform (IK6) in ALL. By analyzing the expression profile of Ikaros and the level of FUT4/LeX in clinical samples, we found that FUT4/LeX was positively correlated with dysfunctional Ikaros isoforms. IK1 (Full length Ikaros) regulates the level of FUT4 as a transcription repressor, while IK6 abolished the wild-type Ikaros mediated transcriptional repression and resulted in higher level of FUT4 expression. Moreover, we demonstrated that FUT4 could activate α5ß1-mediated sequential signal transduction and accelerate adhesion and invasion between integrin α5ß1 in leukemia cells and fibronectin in extracellular matrix (ECM) via increasing glycosylation. Together, our study provides a new insight into the mechanisms by which Ikaros mutation induced ALL cells invasion and a potential strategy for drug-resistance ALL by blocking LeX in combination with common chemotherapy.
Assuntos
Processamento Alternativo/fisiologia , Fator de Transcrição Ikaros/fisiologia , Leucemia-Linfoma Linfoblástico de Células Precursoras/metabolismo , Células Cultivadas , Quinase 1 de Adesão Focal/metabolismo , Fucosiltransferases/metabolismo , Glicosilação , Humanos , Fator de Transcrição Ikaros/genética , Integrina alfa5beta1/metabolismo , Antígenos CD15/metabolismo , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Transdução de SinaisRESUMO
Ikaros, encoded by IKZF1 (Ikaros family zinc finger 1), is an important transcription factor in the control of lymphocyte specification and differentiation. Multiple functions of Ikaros have been exerted in almost all hematopoietic cell types, from stem cells to mature lymphoid and myeloid cells. Moreover, nonhematopoietic cells are also functional targets of Ikaros. Ikaros is essential for normal hematopoiesis, autoimmune and tumor suppression. Ikaros mutations were associated with lymphoblastic cells deficiency, autoimmunity and malignancies development, including hematological malignancies (leukemia) and solid tumors. This review focus on discuss the role of Ikaros in hematological malignancies, solid tumors and autoimmune diseases, and highlight the importance of Ikaros in cancer and immune diseases therapy.
Assuntos
Fator de Transcrição Ikaros/genética , Fator de Transcrição Ikaros/metabolismo , Fator de Transcrição Ikaros/fisiologia , Animais , Autoimunidade , Diferenciação Celular , Regulação da Expressão Gênica , Neoplasias Hematológicas , Células-Tronco Hematopoéticas/metabolismo , Humanos , Linfócitos/fisiologia , NeoplasiasRESUMO
Immunotherapies are some of the most promising emergent treatments for several cancers, yet there remains a majority of patients who do not benefit from them due to immune-resistant tumors. One avenue for enhancing treatment for these patients is by converting these tumors to an immunoreactive state, thereby restoring treatment efficacy. By leveraging regulatory networks we previously characterized in autoimmunity, here we show that overexpression of the master regulator IKZF1 leads to enhanced immune infiltrate recruitment and tumor sensitivity to PD1 and CTLA4 inhibitors in several tumors that normally lack IKZF1 expression. This work provides proof of concept that tumors can be rendered susceptible by hijacking immune cell recruitment signals through molecular master regulators. On a broader scale, this work also demonstrates the feasibility of using computational approaches to drive the discovery of novel molecular mechanisms toward treatment.
Assuntos
Anticorpos Monoclonais/farmacologia , Fator de Transcrição Ikaros/metabolismo , Neoplasias/imunologia , Animais , Anticorpos Monoclonais/metabolismo , Antígeno CTLA-4/imunologia , Linhagem Celular Tumoral , Feminino , Humanos , Fator de Transcrição Ikaros/fisiologia , Fatores Imunológicos , Imunoterapia/métodos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Nus , Receptor de Morte Celular Programada 1/imunologia , Biologia de Sistemas/métodosRESUMO
Primary effusion lymphoma (PEL) is an aggressive cancer with few treatment options. The immunomodulatory drugs (IMiDs) lenalidomide and pomalidomide have recently been shown to kill PEL cell lines, and lenalidomide is in clinical trials against PEL. IMiDs bind to the CRL4CRBN E3 ubiquitin ligase complex, leading to the acquisition of the Ikaros family zinc finger proteins 1 and 3 (IKZF1 and IKZF3), casein kinase 1 α (CK1α), and zinc finger protein 91 (ZFP91) as neosubstrates. IMiDs are effective against multiple myeloma because of degradation of IKZF1 and IKZF3 and the consequent loss of interferon regulatory factor 4 (IRF4) and MYC expression. Lenalidomide is also effective in chromosome 5q deletion-associated myelodysplastic syndrome as a result of degradation of CK1α. An essential IKZF1-IRF4-MYC axis has recently been proposed to underlie the toxicity of IMiDs in PEL. Here, we further investigate IMiD effectors in PEL cell lines, based on genome-wide CRISPR/Cas9 screens for essential human genes. These screens and extensive validation experiments show that, of the 4 neosubstrates, only CK1α is essential for the survival of PEL cell lines. In contrast, IKZF1 and IKZF3 are dispensable, individually or in combination. IRF4 was critical in all 8 PEL cell lines tested, and surprisingly, IMiDs triggered downregulation of IRF4 expression independently of both IKZF1 and IKZF3. Reexpression of CK1α and/or IRF4 partially rescued PEL cell lines from IMiD-mediated toxicity. In conclusion, IMiD toxicity in PEL cell lines is independent of IKZF1 and IKZF3 but proceeds through degradation of the neosubstrate CK1α and downregulation of IRF4.
Assuntos
Caseína Quinase Ialfa/fisiologia , Fatores Imunológicos/farmacologia , Fatores Reguladores de Interferon/fisiologia , Lenalidomida/farmacologia , Linfoma de Efusão Primária/tratamento farmacológico , Proteínas de Neoplasias/fisiologia , Talidomida/análogos & derivados , Sistemas CRISPR-Cas , Caseína Quinase Ialfa/genética , Linhagem Celular Tumoral , Regulação para Baixo/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Técnicas de Inativação de Genes , Humanos , Fator de Transcrição Ikaros/fisiologia , Fatores Imunológicos/uso terapêutico , Fatores Reguladores de Interferon/biossíntese , Fatores Reguladores de Interferon/genética , Lenalidomida/uso terapêutico , Linfoma de Efusão Primária/genética , Linfoma de Efusão Primária/metabolismo , Terapia de Alvo Molecular , Proteínas de Neoplasias/biossíntese , Proteínas de Neoplasias/genética , Interferência de RNA , RNA Interferente Pequeno/genética , Transdução de Sinais , Talidomida/farmacologia , Talidomida/uso terapêutico , Ubiquitina-Proteína Ligases/fisiologiaRESUMO
Ikaros family zinc finger 1 (IKZF1) is a haematopoietic transcription factor required for mammalian B-cell development. IKZF1 deficiency also reduces plasmacytoid dendritic cell (pDC) numbers in mice, but its effects on human DC development are unknown. Here we show that heterozygous mutation of IKZF1 in human decreases pDC numbers and expands conventional DC1 (cDC1). Lenalidomide, a drug that induces proteosomal degradation of IKZF1, also decreases pDC numbers in vivo, and reduces the ratio of pDC/cDC1 differentiated from progenitor cells in vitro in a dose-dependent manner. In addition, non-classical monocytes are reduced by IKZF1 deficiency in vivo. DC and monocytes from patients with IKZF1 deficiency or lenalidomide-treated cultures secrete less IFN-α, TNF and IL-12. These results indicate that human DC development and function are regulated by IKZF1, providing further insights into the consequences of IKZF1 mutation on immune function and the mechanism of immunomodulation by lenalidomide.
Assuntos
Células Dendríticas/fisiologia , Fator de Transcrição Ikaros/fisiologia , Haploinsuficiência , Hematopoese , Humanos , Interferon-alfa/metabolismo , Interleucina-12/metabolismo , LenalidomidaRESUMO
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.
Assuntos
Fator de Transcrição Ikaros/genética , Fator de Transcrição Ikaros/fisiologia , Adulto , Adesão Celular/genética , Criança , Resistência a Medicamentos/genética , Deleção de Genes , Humanos , MutaçãoRESUMO
B-lineage and myeloid leukemia cells are often transformed by the same oncogenes, but have different biological and clinical characteristics. Although B-lineage acute lymphoblastic leukemia (B-ALL) cells are characterized by a state of chronic energy deficit, myeloid leukemia cells show abundant energy reserve. Interestingly, fasting has been demonstrated to inhibit selectively the development of B-ALL but not myeloid leukemia, further suggesting that lineage identity may be linked to divergent metabolic states in hematopoietic malignancies. The B-lymphoid transcription factors IKZF1, EBF1, and PAX5 are essential for early B-cell development and commitment to B-cell identity. However, in >80% of human pre-B-ALL cases, the leukemic clones harbor genetic lesions of these transcription factors. The significance of these defects has only recently been investigated. Here, we discuss the unexpected function of a B-lymphoid transcriptional program as a metabolic barrier against malignant transformation of B-cell precursor cells. The metabolic gatekeeper function of B-lymphoid transcription factors may force silent preleukemic clones carrying potentially oncogenic lesions to remain in a latent state. In addition, this program sets the threshold for responses to glucocorticoids in pre-B-ALL. Finally, the link between the tumor-suppressor and metabolic functions of B-lymphoid transcription factors is matched by observations in clinical trials: obesity and hyperglycemia are associated with poor clinical outcome in patients with pre-B-ALL.
Assuntos
Linfócitos B/fisiologia , Transformação Celular Neoplásica , Leucemia-Linfoma Linfoblástico de Células Precursoras B/etiologia , Animais , Linhagem da Célula , Metabolismo Energético , Proteína Forkhead Box O1/fisiologia , Humanos , Fator de Transcrição Ikaros/fisiologia , Camundongos , Obesidade/complicações , Fator de Transcrição PAX5/fisiologia , Fosfatidilinositol 3-Quinases/fisiologia , Proteínas Proto-Oncogênicas c-akt/fisiologia , Receptores para Leptina/fisiologiaRESUMO
Genetic alterations disrupting the transcription factor IKZF1 (encoding IKAROS) are associated with poor outcome in B lineage acute lymphoblastic leukemia (B-ALL) and occur in >70% of the high-risk BCR-ABL1+ (Ph+) and Ph-like disease subtypes. To examine IKAROS function in this context, we have developed novel mouse models allowing reversible RNAi-based control of Ikaros expression in established B-ALL in vivo. Notably, leukemias driven by combined BCR-ABL1 expression and Ikaros suppression rapidly regress when endogenous Ikaros is restored, causing sustained disease remission or ablation. Comparison of transcriptional profiles accompanying dynamic Ikaros perturbation in murine B-ALL in vivo with two independent human B-ALL cohorts identified nine evolutionarily conserved IKAROS-repressed genes. Notably, high expression of six of these genes is associated with inferior event-free survival in both patient cohorts. Among them are EMP1, which was recently implicated in B-ALL proliferation and prednisolone resistance, and the novel target CTNND1, encoding P120-catenin. We demonstrate that elevated Ctnnd1 expression contributes to maintenance of murine B-ALL cells with compromised Ikaros function. These results suggest that IKZF1 alterations in B-ALL leads to induction of multiple genes associated with proliferation and treatment resistance, identifying potential new therapeutic targets for high-risk disease.
Assuntos
Fator de Transcrição Ikaros/fisiologia , Leucemia-Linfoma Linfoblástico de Células Precursoras B/genética , Animais , Cateninas/genética , Linhagem Celular Tumoral , Proteínas de Fusão bcr-abl/análise , Humanos , Proteínas de Membrana/genética , Camundongos , Proteínas de Neoplasias/genética , Proteínas de Ligação a RNA/genética , Receptores de Superfície Celular/genética , delta CateninaRESUMO
Inactivation of the tumor suppressor gene encoding the transcriptional regulator Ikaros (IKZF1) is a hallmark of BCR-ABL1+ precursor B cell acute lymphoblastic leukemia (pre-B ALL). However, the mechanisms by which Ikaros functions as a tumor suppressor in pre-B ALL remain poorly understood. Here, we analyzed a mouse model of BCR-ABL1+ pre-B ALL together with a new model of inducible expression of wild-type Ikaros in IKZF1 mutant human BCR-ABL1+ pre-B ALL. We performed integrated genome-wide chromatin and expression analyses and identified Ikaros target genes in mouse and human BCR-ABL1+ pre-B ALL, revealing novel conserved gene pathways associated with Ikaros tumor suppressor function. Notably, genetic depletion of different Ikaros targets, including CTNND1 and the early hematopoietic cell surface marker CD34, resulted in reduced leukemic growth. Our results suggest that Ikaros mediates tumor suppressor function by enforcing proper developmental stage-specific expression of multiple genes through chromatin compaction at its target genes.
Assuntos
Proteínas de Fusão bcr-abl/análise , Fator de Transcrição Ikaros/fisiologia , Leucemia-Linfoma Linfoblástico de Células Precursoras B/genética , Proteínas Supressoras de Tumor/fisiologia , Animais , Antígenos CD34/análise , Ciclo Celular , Linhagem Celular Tumoral , Regulação Leucêmica da Expressão Gênica , Humanos , Fator de Transcrição Ikaros/genética , Leucossialina/análise , Camundongos , Camundongos Endogâmicos C57BL , Proteínas Proto-Oncogênicas c-kit/genéticaRESUMO
Children with P2RY8-CRLF2-positive acute lymphoblastic leukemia have an increased relapse risk. Their mutational and transcriptional landscape, as well as the respective patterns at relapse remain largely elusive. We, therefore, performed an integrated analysis of whole-exome and RNA sequencing in 41 major clone fusion-positive cases including 19 matched diagnosis/relapse pairs. We detected a variety of frequently subclonal and highly instable JAK/STAT but also RTK/Ras pathway-activating mutations in 76% of cases at diagnosis and virtually all relapses. Unlike P2RY8-CRLF2 that was lost in 32% of relapses, all other genomic alterations affecting lymphoid development (58%) and cell cycle (39%) remained stable. Only IKZF1 alterations predominated in relapsing cases (P=0.001) and increased from initially 36 to 58% in matched cases. IKZF1's critical role is further corroborated by its specific transcriptional signature comprising stem cell features with signs of impaired lymphoid differentiation, enhanced focal adhesion, activated hypoxia pathway, deregulated cell cycle and increased drug resistance. Our findings support the notion that P2RY8-CRLF2 is dispensable for relapse development and instead highlight the prominent rank of IKZF1 for relapse development by mediating self-renewal and homing to the bone marrow niche. Consequently, reverting aberrant IKAROS signaling or its disparate programs emerges as an attractive potential treatment option in these leukemias.
Assuntos
Fusão Gênica , Genômica , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Receptores de Citocinas/genética , Receptores Purinérgicos P2Y/genética , Transcrição Gênica , Adolescente , Criança , Pré-Escolar , Dosagem de Genes , Genes Supressores de Tumor , Humanos , Fator de Transcrição Ikaros/genética , Fator de Transcrição Ikaros/fisiologia , Lactente , Janus Quinases/fisiologia , Polimorfismo de Nucleotídeo Único , Fatores de Transcrição STAT/fisiologiaRESUMO
Aberrant stem cell-like gene regulatory networks are a feature of leukaemogenesis. The ETS-related gene (ERG), an important regulator of normal haematopoiesis, is also highly expressed in T-ALL and acute myeloid leukaemia (AML). However, the transcriptional regulation of ERG in leukaemic cells remains poorly understood. In order to discover transcriptional regulators of ERG, we employed a quantitative mass spectrometry-based method to identify factors binding the 321 bp ERG +85 stem cell enhancer region in MOLT-4 T-ALL and KG-1 AML cells. Using this approach, we identified a number of known binders of the +85 enhancer in leukaemic cells along with previously unknown binders, including ETV6 and IKZF1. We confirmed that ETV6 and IKZF1 were also bound at the +85 enhancer in both leukaemic cells and in healthy human CD34+ haematopoietic stem and progenitor cells. Knockdown experiments confirmed that ETV6 and IKZF1 are transcriptional regulators not just of ERG, but also of a number of genes regulated by a densely interconnected network of seven transcription factors. At last, we show that ETV6 and IKZF1 expression levels are positively correlated with expression of a number of heptad genes in AML and high expression of all nine genes confers poorer overall prognosis.
Assuntos
Fator de Transcrição Ikaros/fisiologia , Proteínas Proto-Oncogênicas c-ets/fisiologia , Proteínas Repressoras/fisiologia , Transcrição Gênica , Sequência de Bases , Sítios de Ligação , Linhagem Celular Tumoral , Sequência Consenso , Elementos Facilitadores Genéticos , Regulação Leucêmica da Expressão Gênica , Redes Reguladoras de Genes , Humanos , Estimativa de Kaplan-Meier , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/metabolismo , Leucemia Mieloide Aguda/mortalidade , Prognóstico , Modelos de Riscos Proporcionais , Ligação Proteica , Proteoma , Proteômica , Regulador Transcricional ERG/fisiologia , Variante 6 da Proteína do Fator de Translocação ETSRESUMO
Transcription factors are important determinants of lineage specification during hematopoiesis. They favor recruitment of cofactors involved in epigenetic regulation, thereby defining patterns of gene expression in a development- and lineage-specific manner. Additionally, transcription factors can facilitate transcription preinitiation complex (PIC) formation and assembly on chromatin. Interestingly, a few lineage-specific transcription factors, including IKAROS, also regulate transcription elongation. IKAROS is a tumor suppressor frequently inactivated in leukemia and associated with a poor prognosis. It forms a complex with the nucleosome remodeling and deacetylase (NuRD) complex and the positive transcription elongation factor b (P-TEFb), which is required for productive transcription elongation. It has also been reported that IKAROS interacts with factors involved in transcription termination. Here we review these and other recent findings that establish IKAROS as the first transcription factor found to act as a multifunctional regulator of the transcription cycle in hematopoietic cells.
Assuntos
Montagem e Desmontagem da Cromatina , DNA Polimerase II/fisiologia , Fator de Transcrição Ikaros/fisiologia , Transcrição Gênica , Animais , Regulação da Expressão Gênica , HumanosRESUMO
Inactivating mutations in IKZF1, the gene that encodes the transcription factor IKAROS, are recurrent in poor-prognosis human B-cell leukemias, in which these mutations co-exist with BCR-ABL1 or other genetic changes that activate similar intracellular signaling pathways. However, little is known about the mechanism(s) by which loss of IKAROS activity may co-operate with BCR-ABL1 to transform lymphoid cells. To investigate this question, we used expression of a dominant-negative isoform of IKAROS (IK6) to suppress endogenous IKAROS activity in the interleukin-3 (IL-3)-dependent mouse pro-B BA/F3 cell line and in an IL-3-independent BCR-ABL1(+) derivative. We then used intracellular phospho-flow cytometry to assess the effects of BCR-ABL1 and IK6, alone and in combination, on the signaling state of the cells before and after their stimulation with IL-3. BCR-ABL1 and IK6 each produced a constitutively activated signaling phenotype and also enhanced the signaling responses of BA/F3 cells to IL-3. These effects, however, were neither equivalent nor additive, and IK6 alone was insufficient to confer the IL-3-independent growth characteristic of BCR-ABL1(+) BA/F3 cells. In addition to its effects on lymphoid cells, IK6 also induced constitutively activated signaling in a subset of myeloid leukemia cell lines. Together, these studies indicate an ability of IK6 to enhance intracellular signaling in both lymphoid and myeloid cells, but not to synergize with BCR-ABL1 in this model system.
Assuntos
Linfócitos B/metabolismo , Fator de Transcrição Ikaros/fisiologia , Interleucina-3/agonistas , Transdução de Sinais/genética , Animais , Linfócitos B/efeitos dos fármacos , Divisão Celular , Linhagem Celular Transformada , Linhagem da Célula , Sobrevivência Celular/efeitos dos fármacos , Transformação Celular Neoplásica , Células Cultivadas , Proteínas de Fusão bcr-abl/genética , Proteínas de Fusão bcr-abl/fisiologia , Genes Dominantes , Humanos , Fator de Transcrição Ikaros/antagonistas & inibidores , Fator de Transcrição Ikaros/genética , Linfócitos/citologia , Linfócitos/metabolismo , Camundongos , Mutação , Células Mieloides/citologia , Células Mieloides/metabolismo , Fenótipo , Proteínas Recombinantes de Fusão/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução GenéticaRESUMO
Recombination activating gene-2 (RAG-2) and NWC are strongly evolutionarily conserved overlapping genes which are convergently transcribed. In non-lymphoid cells the NWC promoter is active whereas in lymphocytes it is inactive due to the DNA methylation. Analysing the mechanism responsible for lymphocyte-specific methylation and inactivation of NWC promoter we found that Ikaros, a lymphocyte-specific transcription factor, acts as a repressor of NWC promoter--thus identifying a new Ikaros target--but is insufficient for inducing its methylation which depends on the antisense transcription driven by RAG-2 promoter. Possible implications of these observations for understanding evolutionary mechanisms leading to lymphocyte specific expression of RAG genes are discussed.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Fator de Transcrição Ikaros/fisiologia , Regiões Promotoras Genéticas , Transcrição Gênica , Sequência de Bases , Metilação de DNA , Primers do DNA , Regulação para Baixo , Ensaio de Desvio de Mobilidade Eletroforética , Células HEK293 , Humanos , Linfócitos/imunologia , Reação em Cadeia da Polimerase em Tempo RealRESUMO
The Notch signaling pathway is activated in many cell types, but its effects are cell type- and stage-specific. In the immune system, Notch activity is required for the differentiation of T cell progenitors, but it is reduced in more mature thymocytes, in which Notch is oncogenic. Studies based on single-gene models have suggested that the tumor suppressor protein Ikaros plays an important role in repressing the transcription of Notch target genes. We used genome-wide analyses, including chromatin immunoprecipitation sequencing, to identify genes controlled by Notch and Ikaros in gain- and loss-of-function experiments. We found that Ikaros bound to and directly repressed the expression of most genes that are activated by Notch. Specific deletion of Ikaros in thymocytes led to the persistent expression of Notch target genes that are essential for T cell maturation, as well as the rapid development of T cell leukemias in mice. Expression of Notch target genes that are normally silent in T cells, but are activated by Notch in other cell types, occurred in T cells of mice genetically deficient in Ikaros. We propose that Ikaros shapes the timing and repertoire of the Notch transcriptional response in T cells through widespread targeting of elements adjacent to Notch regulatory sequences. These results provide a molecular framework for understanding the regulation of tissue-specific and tumor-related Notch responses.