Glucocorticoid receptor knock down reveals a similar apoptotic threshold but differing gene regulation patterns in T-cell and pre-B-cell acute lymphoblastic leukemia

Abstract B-cell acute lymphoblastic leukemia (B-ALL) results from clonal expansion of B-lymphocytes derived at different stage of differentiation. Immunoglobulin (Ig) heavy chain genes (IGH), light chain kappa (IGK) and lambda (IGL) genes rearrange during early B-lymphocyte differentiation. T-cell receptor (TCR) genes are considered to rearrange exclusively in normal T lymphocytes, but malignant B lymphoblasts often contain crosslineage rearranged TCR genes. The clonal leukemic cell population, carrying identical copies of rearranged Ig and/or TCR genes, can be identified above 95% of B-ALL patients. In our study Ig/TCR genes rearrangements were detected by multiplex PCR with heteroduplex analysis according to BIOMED-2 protocol. DNA was isolated by column method from mononuclear cells isolated from the peripheral blood/bone marrow samples obtained at initial diagnosis from 36 B-ALL patients. Monoclonal rearrangements of Ig genes were detected in 100% (36/36) of patients. The most frequent rearrangements were observed in IGH genes (94%), including complete IGHV-IGHJ in 83% (30/36) and incomplete IGHD-IGHJ in 22% (8/36) of patients. Among complete IGH rearrangements 2 biallelic rearrangements in IGHV1-7 and IGHJ genes (FR3) were found. Ig light chain genes rearrangements were identified in 26 patients (72%) (including 64% of IGKV-IGKJ, 47% IGKV/intron-Kde, and 22% IGLV-IGLJ) what indicates active receptor editing occurring during B lymphoblasts leukemogenesis. Crosslineage TCR genes rearrangements were found in 97% (35/36) of patients. TCR beta genes rearrangements were detected in 47% (17/36) of patients (complete TRBV-TRBJ in 25% (9/36), TRBD-TRBJ in 6/36 patients - 17%). TRGV-TRGV in 58% (21/36), TRDV-TRDJ in 58% (21/36); 17 monoallelic and 4 biallelic were found. The inactivation of potentially functional IGKV-IGKJ by secondary rearrangements indicates active receptor editing. Our data describe IGK and IGL genes rearrangements incidence, present allelic exclusion and active receptor editing in B-ALL patients. B-ALL lymphoblast undergoes rearrangement on the same IGK allele before IGL genes rearrangement occur. The data may suggest the possible of antigens in B-ALL immunopathogenesis. The results indicate also rearranged IGK, IGL and TCR genes as stable molecular marker for monitoring MRD in B-ALL.

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Transcriptional Repression of the LMO2 Oncogene By Ikaros in T-Cell Acute Lymphoblastic Leukemia

Blood ◽

10.1182/blood.v128.22.439.439 ◽

2016 ◽

Vol 128 (22) ◽

pp. 439-439

Author(s):

Yali Ding ◽

Chunhua Song ◽

Chandrika S. Gowda ◽

Malika Kapadia ◽

Kimberly Payne ◽

...

Keyword(s):

Acute Lymphoblastic Leukemia ◽

T Cell ◽

Chromatin Immunoprecipitation ◽

Transcriptional Repression ◽

Conflicts Of Interest ◽

Lymphoblastic Leukemia ◽

Transcriptional Level ◽

Knock Down ◽

Cell Acute Lymphoblastic Leukemia ◽

Ck2 Inhibitors

Abstract LIM domain only protein 2 (LMO2) is a regulator of hematopoiesis and an oncogene that is overexpressed in a subset of T-cell acute lymphoblastic leukemia (T-ALL). Overexpression of LMO2 in T-ALL is associated with a poor prognosis. The mechanisms that regulate LMO2 expression in T-ALL are still unknown. Here, we present evidence that expression of LMO2 in T-ALL is regulated at the transcriptional level by Ikaros, a tumor suppressor protein whose deletion is associated with the development T-ALL. Global chromatin immunoprecipitation coupled with next-generation sequencing (ChIP-seq) studies in primary human acute lymphoblastic leukemia cells and in cell lines demonstrated Ikaros occupancy of the LMO2 promoter. Ikaros binding at the LMO2 promoter was confirmed by quantitative chromatin immunoprecipitation (qChIP) in primary T-ALL and B-ALL cells. The role of Ikaros in the regulation of LMO2 transcription in T-ALL was tested using gain-of-function and loss-of-function experiments. Ikaros knock-down with siRNA resulted in increased transcription of LMO2 in T-ALL. Overexpression of Ikaros in human T-ALL was associated with strongly reduced transcription of LMO2. In mice, T-ALL cells that are derived from Ikaros-knockout mice express high levels of LMO2. Transduction of these cells with Ikaros-containing retrovirus, results in a sharp reduction of LMO2 expression. Since Ikaros function in T-ALL is negatively regulated by the pro-oncogenic Casein Kinase II (CK2), we tested whether CK2 inhibition can enhance Ikaros-mediated transcriptional repression of LMO2. Molecular inhibition of CK2 using shRNA, as well as pharmacological inhibition with a specific CK2 inhibitor, resulted in reduced expression of LMO2 in primary human T-ALL. Inhibition of CK2 was associated with increased Ikaros binding at the LMO2 promoter. Ikaros knock-down restored high expression of LMO2 in T-ALL cells that were treated with CK2 inhibitors. These data show that Ikaros is a major regulator of LMO2 transcription in T-ALL and that CK2 inhibition requires Ikaros activity to repress LMO2 transcription. Increased Ikaros binding was associated with reduced histone H3K9ac and H3K4me3 marks at the LMO2 promoter suggesting that Ikaros regulates LMO2 transcription via chromatin remodeling. In conclusion, these results provide evidence that expression of the LMO2 oncogene is regulated by Ikaros and CK2 in T-ALL. Targeting CK2 with specific inhibitors has been used as a therapeutic strategy in a preclinical model of T-ALL. The presented data reveal a novel mechanism of therapeutic action for CK2 inhibitors - repression of LMO2 expression via Ikaros. These results provide a rationale for the use of CK2 inhibitors in T-ALL with LMO2 overexpression. Disclosures No relevant conflicts of interest to declare.

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