Metabolic gatekeeper function of B-lymphoid transcription factors

Abstract

B-lymphoid transcription factors (e.g. PAX5, IKZF1) are critical for early B-cell development1–2, yet genetic lesions occur in >80% of cases of B-cell acute lymphoblastic leukemia (ALL)3–4. The significance of these lesions in ALL remained unclear. Combining ChIP-seq and RNA-seq studies, we identified a novel B-lymphoid program for transcriptional repression of glucose and energy supply. Our metabolic analyses revealed that PAX5 and IKZF1 enforce a state of chronic energy deprivation, resulting in constitutive activation of the energy-stress sensor AMPK5–7. Dominant-negative mutants of PAX5 and IKZF1 relieved glucose and energy restriction. Studying a transgenic pre-B ALL mouse model, heterozygous deletion of Pax5 increased glucose uptake and ATP-levels by >25-fold. Reconstitution of PAX5 and IKZF1 in pre-B ALL patient samples restored a non-permissive state and induced energy crisis and cell death. A CRISPR/Cas9-based screen of PAX5- and IKZF1- transcriptional targets identified NR3C1 (glucocorticoid receptor)8, TXNIP (glucose feedback sensor)9 and CNR2 (cannabinoid receptor)10 as central effectors of B-lymphoid restriction of glucose and energy supply. Interestingly, transport-independent lipophilic methyl-conjugates of pyruvate and TCA cycle metabolites bypassed the gatekeeper function of PAX5 and IKZF1 and readily enabled leukemic transformation. Conversely, pharmacological TXNIP- and CNR2-agonists and a small molecule AMPK-inhibitor strongly synergized with glucocorticoids, identifying TXNIP, CNR2 and AMPK as potential therapy-targets. Furthermore, our results provide a mechanistic explanation for the empiric finding that glucocorticoids are effective in the treatment of B-lymphoid but not myeloid malignancies. We conclude that B-lymphoid transcription factors function as metabolic gatekeepers by limiting the amount of cellular ATP to levels that are insufficient for malignant transformation.