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Background: There is growing evidence for the inherited basis of susceptibility to childhood acute lymphoblastic leukemia (ALL). Genome-wide association studies have identified non-coding ALL risk variants at the ARID5B gene locus, but their exact functional effects and the molecular mechanism linking ARID5B to B-cell ALL leukemogenesis remain largely unknown., Methods: We performed targeted sequencing of ARID5B in germline DNA of 5008 children with ALL. Variants were evaluated for association with ALL susceptibility using 3644 patients from the UK10K cohort as non-ALL controls, under an additive model. Cis-regulatory elements in ARID5B were systematically identified using dCas9-KRAB-mediated enhancer interference system enhancer screen in ALL cells. Disruption of transcription factor binding by ARID5B variant was predicted informatically and then confirmed using chromatin immunoprecipitation and coimmunoprecipitation. ARID5B variant association with hematological traits was examined using UK Biobank dataset. All statistical tests were 2-sided., Results: We identified 54 common variants in ARID5B statistically significantly associated with leukemia risk, all of which were noncoding. Six cis-regulatory elements at the ARID5B locus were discovered using CRISPR-based high-throughput enhancer screening. Strikingly, the top ALL risk variant (rs7090445, P = 5.57 × 10-45) is located precisely within the strongest enhancer element, which is also distally tethered to the ARID5B promoter. The variant allele disrupts the MEF2C binding motif sequence, resulting in reduced MEF2C affinity and decreased local chromosome accessibility. MEF2C influences ARID5B expression in ALL, likely via a transcription factor complex with RUNX1. Using the UK Biobank dataset (n = 349 861), we showed that rs7090445 was also associated with lymphocyte percentage and count in the general population (P = 8.6 × 10-22 and 2.1 × 10-18, respectively)., Conclusions: Our results indicate that ALL risk variants in ARID5B function by modulating cis-regulatory elements at this locus., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Hhex encodes a homeodomain transcription factor that is widely expressed in hematopoietic stem and progenitor cell populations. Its enforced expression induces T-cell leukemia and we have implicated it as an important oncogene in early T-cell precursor leukemias where it is immediately downstream of an LMO2-associated protein complex. Conventional Hhex knockouts cause embryonic lethality precluding analysis of adult hematopoiesis. Thus, we induced highly efficient conditional knockout (cKO) using vav-Cre transgenic mice. Hhex cKO mice were viable and born at normal litter sizes. At steady state, we observed a defect in B-cell development that we localized to the earliest B-cell precursor, the pro-B-cell stage. Most remarkably, bone marrow transplantation using Hhex cKO donor cells revealed a more profound defect in all hematopoietic lineages. In contrast, sublethal irradiation resulted in normal myeloid cell repopulation of the bone marrow but markedly impaired repopulation of T- and B-cell compartments. We noted that Hhex cKO stem and progenitor cell populations were skewed in their distribution and showed enhanced proliferation compared to WT cells. Our results implicate Hhex in the maintenance of LT-HSCs and in lineage allocation from multipotent progenitors especially in stress hematopoiesis., (© 2015 AlphaMed Press.)

LIM domain only 2 (Lmo2) is frequently deregulated in sporadic and gene therapy-induced acute T-cell lymphoblastic leukemia (T-ALL) where its overexpression is an important initiating mutational event. In transgenic and retroviral mouse models, Lmo2 expression can be enforced in multiple hematopoietic lineages but leukemia only arises from T cells. These data suggest that Lmo2 confers clonal growth advantage in T-cell progenitors. We analyzed proliferation, differentiation, and cell death in CD2-Lmo2 transgenic thymic progenitor cells to understand the cellular effects of enforced Lmo2 expression. Most impressively, Lmo2 transgenic T-cell progenitor cells were blocked in differentiation, quiescent, and immortalized in vitro on OP9-DL1 stromal cells. These cellular effects were concordant with a transcriptional signature in Lmo2 transgenic T-cell progenitor cells that is also present in hematopoietic stem cells (HSCs) and early T-cell precursor ALL. These results are significant in light of the crucial role of Lmo2 in the maintenance of the HSC. The cellular effects and transcriptional effects have implications for LMO2-dependent leukemogenesis and the treatment of LMO2-induced T-ALL., (Copyright © 2013 AlphaMed Press.)