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Ldb1 is required for Lmo2 oncogene-induced thymocyte self-renewal and T-cell acute lymphoblastic leukemia.

ABSTRACT: Prolonged or enhanced expression of the proto-oncogene Lmo2 is associated with a severe form of T-cell acute lymphoblastic leukemia (T-ALL), designated early T-cell precursor ALL, which is characterized by the aberrant self-renewal and subsequent oncogenic transformation of immature thymocytes. It has been suggested that Lmo2 exerts these effects by functioning as component of a multi-subunit transcription complex that includes the ubiquitous adapter Ldb1 along with b-HLH and/or GATA family transcription factors; however, direct experimental evidence for this mechanism is lacking. In this study, we investigated the importance of Ldb1 for Lmo2-induced T-ALL by conditional deletion of Ldb1 in thymocytes in an Lmo2 transgenic mouse model of T-ALL. Our results identify a critical requirement for Ldb1 in Lmo2-induced thymocyte self-renewal and thymocyte radiation resistance and for the transition of preleukemic thymocytes to overt T-ALL. Moreover, Ldb1 was also required for acquisition of the aberrant preleukemic ETP gene expression signature in immature Lmo2 transgenic thymocytes. Co-binding of Ldb1 and Lmo2 was detected at the promoters of key upregulated T-ALL driver genes (Hhex, Lyl1, and Nfe2) in preleukemic Lmo2 transgenic thymocytes, and binding of both Ldb1 and Lmo2 at these sites was reduced following Cre-mediated deletion of Ldb1. Together, these results identify a key role for Ldb1, a nonproto-oncogene, in T-ALL and support a model in which Lmo2-induced T-ALL results from failure to downregulate Ldb1/Lmo2-nucleated transcription complexes which normally function to enforce self-renewal in bone marrow hematopoietic progenitors.

SUBMITTER: Li L

PROVIDER: S-EPMC7316212 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:T-cell Acute Lymphoblastic Leukaemia (T-ALL) can be classified into a number of subfamilies, including those that overexpress TAL1/LMO, TLX1/3 and HOXA transcription factors. Whilst it has been previously shown in mouse models that TAL1/LMO transcription factors induce thymocyte self-renewal, whether this is the case for other transcription factor subclasses is currently unknown. To address this, we have studied vav-Nup98-HoxD13-transgenic (NHD13-Tg) mice, a model of HOXA-driven T-ALL, which overexpress HOXA transcription factors throughout haematopoiesis and display features of myelodysplastic syndrome in the bone marrow along with T-cell developmental abnormalities in the thymus and subsequent development of T-ALL in approximately 15% of mice. Thymocytes from preleukemic NHD13-Tg mice could engraft long-term in serial transplantation assays, demonstrating that NHD13-Tg thymocytes have acquired self-renewal capacity. Transcriptome analysis showed that NHD13-Tg thymocytes exhibited a Stem Cell like transcriptional program which closely resembled that of Lmo2 transgenic thymocytes, including Lmo2 itself and the critical Lmo2 cofactor Lyl1, suggesting a common mechanism of thymocyte self-renewal in these models. To determine whether Lmo2/Lyl1 are required for NHD13-induced thymocyte self-renewal, NHD13-Tg mice were crossed with Lyl1 knockout mice to generate NHD13-Tg mice lacking Lyl1. This showed that Lyl1 is essential for expression of the stem cell-like gene expression program in NHD13-Tg thymocytes and for thymocyte self-renewal. Surprisingly however, absence of Lyl1 accelerated the onset of T-ALL in NHD13-Tg mice. These studies demonstrate that Lyl1 is essential for self-renewal of NHD13-Tg thymocytes, suggesting that Lmo2 and Lyl1 may mediate thymocyte self-renewal induced by a variety of T-cell oncogenes. However, whilst Lyl1-induced thymocyte self-renewal is essential for Lmo2-driven T-cell leukemia, NHD13 can also promote T-ALL via an alternative pathway.

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Ldb1 is required for Lmo2 oncogene-induced thymocyte self-renewal and T-cell acute lymphoblastic leukemia.

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