The TLX1 oncogene drives aneuploidy in T cell transformation

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Abstract
The oncogenic activation of TLX transcription factors demarcates a specific molecular subtype of T cell acute lymphoblastic leukemia (T-ALL). This study identifies aneuploidy induction as a molecular mechanism by which TLX1 transforms T cell progenitors and reveals new TLX1 transcriptional targets, including Bcl11b, a crucial factor in T cell progenitor differentiation and survival, and Chek1, a mitotic checkpoint regulator. The findings delineate the role of TLX1 in T-ALL initiation and maintenance. The TLX1 oncogene (encoding the transcription factor T cell leukemia homeobox protein-1) has a major role in the pathogenesis of T cell acute lymphoblastic leukemia (T-ALL). However, the specific mechanisms of T cell transformation downstream of TLX1 remain to be elucidated. Here we show that transgenic expression of human TLX1 in mice induces T-ALL with frequent deletions and mutations in Bcl11b (encoding B cell leukemia/lymphoma-11B) and identify the presence of recurrent mutations and deletions in BCL11B in 16% of human T-ALLs. Most notably, mouse TLX1 tumors were typically aneuploid and showed a marked defect in the activation of the mitotic checkpoint. Mechanistically, TLX1 directly downregulates the expression of CHEK1 (encoding CHK1 checkpoint homolog) and additional mitotic control genes and induces loss of the mitotic checkpoint in nontransformed preleukemic thymocytes. These results identify a previously unrecognized mechanism contributing to chromosomal missegregation and aneuploidy active at the earliest stages of tumor development in the pathogenesis of cancer.