The B cell–specific transcription factor BACH2 is required for affinity maturation of B cells. Here we show that Bach2-mediated activation of p53 is required for stringent elimination of pre-B cells that failed to productively rearrange immunoglobulin VH-DJH gene segments. After productive VH-DJH gene rearrangement, pre-B cell receptor signaling ends BACH2-mediated negative selection through B cell lymphoma 6 (BCL6)-mediated repression of p53. In patients with pre-B acute lymphoblastic leukemia, the BACH2-mediated checkpoint control is compromised by deletions, rare somatic mutations and loss of its upstream activator, PAX5. Low levels of BACH2 expression in these patients represent a strong independent predictor of poor clinical outcome. In this study, we demonstrate that Bach2+/+ pre-B cells resist leukemic transformation by Myc through Bach2-dependent upregulation of p53 and do not initiate fatal leukemia in transplant-recipient mice. Chromatin immunoprecipitation sequencing and gene expression analyses carried out by us revealed that BACH2 competes with BCL6 for promoter binding and reverses BCL6-mediated repression of p53 and other cell cycle checkpoint–control genes. These findings identify BACH2 as a crucial mediator of negative selection at the pre-B cell receptor checkpoint and a safeguard against leukemogenesis.
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Gene Expression Omnibus
NCBI Reference Sequence
We would like to thank H. Ye (Albert Einstein College of Medicine) for sharing Bcl6−/− mice and wild-type controls and L. Hennighausen (US National Institute of Diabetes and Digestive and Kidney Diseases) for Stat5flox/flox mice. Samples used in this research include those obtained from the Newcastle Haematology Biobank (http://www.ncl.ac.uk/nbb/collections/nhb/index.htm). We thank D.B. Kohn (University of California Los Angeles) for providing us with the retroviral envelope and packaging vectors used in this study. This work is supported by grants from the US National Institutes of Health National Cancer Institute through R01CA137060, R01CA139032, R01CA157644, R01CA172558, R01CA172558 and R01CA169458 (to M.M.), Translational Research Program grants from the Leukemia and Lymphoma Society (grants 6132-09 and 6097-10), a Leukemia and Lymphoma Society Specialized Center of Research (grant 7005-11, B.J. Druker (principal investigator)), the William Lawrence and Blanche Hughes Foundation and a Stand Up To Cancer–American Association for Cancer Research Innovative Research Grant (IRG00909 to M.M.), the California Institute for Regenerative Medicine (CIRM; TR2-01816 to M.M.) and Leukaemia and Lymphoma Research (V.R. and A.G.H.). A.M. and M.M. are Scholars of the Leukemia and Lymphoma Society. V.R. is a Leukaemia and Lymphoma Research Bennett Fellow.
Supplementary Figures 1–22 and Supplementary Tables 1–8