The branched-chain amino acid (BCAA) pathway and high levels of BCAA transaminase 1 (BCAT1) have recently been associated with aggressiveness in several cancer entities1,2,3,4,5,6. However, the mechanistic role of BCAT1 in this process remains largely uncertain. Here, by performing high-resolution proteomic analysis of human acute myeloid leukaemia (AML) stem-cell and non-stem-cell populations, we find the BCAA pathway enriched and BCAT1 protein and transcripts overexpressed in leukaemia stem cells. We show that BCAT1, which transfers α-amino groups from BCAAs to α-ketoglutarate (αKG), is a critical regulator of intracellular αKG homeostasis. Further to its role in the tricarboxylic acid cycle, αKG is an essential cofactor for αKG-dependent dioxygenases such as Egl-9 family hypoxia inducible factor 1 (EGLN1) and the ten-eleven translocation (TET) family of DNA demethylases7,8,9,10. Knockdown of BCAT1 in leukaemia cells caused accumulation of αKG, leading to EGLN1-mediated HIF1α protein degradation. This resulted in a growth and survival defect and abrogated leukaemia-initiating potential. By contrast, overexpression of BCAT1 in leukaemia cells decreased intracellular αKG levels and caused DNA hypermethylation through altered TET activity. AML with high levels of BCAT1 (BCAT1high) displayed a DNA hypermethylation phenotype similar to cases carrying a mutant isocitrate dehydrogenase (IDHmut), in which TET2 is inhibited by the oncometabolite 2-hydroxyglutarate11,12. High levels of BCAT1 strongly correlate with shorter overall survival in IDHWTTET2WT, but not IDHmut or TET2mut AML. Gene sets characteristic for IDHmut AML13 were enriched in samples from patients with an IDHWTTET2WTBCAT1high status. BCAT1high AML showed robust enrichment for leukaemia stem-cell signatures14,15, and paired sample analysis showed a significant increase in BCAT1 levels upon disease relapse. In summary, by limiting intracellular αKG, BCAT1 links BCAA catabolism to HIF1α stability and regulation of the epigenomic landscape, mimicking the effects of IDH mutations. Our results suggest the BCAA–BCAT1–αKG pathway as a therapeutic target to compromise leukaemia stem-cell function in patients with IDHWTTET2WT AML.
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Gene Expression Omnibus
We thank all members of HI-STEM for discussions, M. Milsom and S. Haas for reading the manuscript, A. Ehninger for help with AML sample acquisition, the members of the Central Animal Laboratory at DKFZ for animal husbandry, the members of the DKFZ Flow Cytometry Core Facility for expertise and support, R. Delwel, P. Valk and B. Lowenberg for providing patient survival data for the Erasmus GSE14468 dataset, and A. Lenze for processing cord blood samples. We thank the EMBL Proteomics Core Facility for assistance with mass spectrometry analysis, the microarray unit of the DKFZ Genomics and Proteomics Core Facility for support, and the Metabolomics Core Technology Platform of the Excellence Cluster CellNetworks for support with ultra-performance liquid chromatography-based metabolite quantification. This work was supported by the SFB873 funded by the Deutsche Forschungsgemeinschaft (DFG) (C.L., C.S., and A.T.), the SyTASC consortium funded by the Deutsche Krebshilfe (A.T.) and the Dietmar Hopp Foundation (A.T.), by grant ZUK 49/2 from the DFG (G.P.), and the DFG Heisenberg-Professorship BU 1339/8-1 (L.B.).
Extended data figures
This file contains differentially expressed proteins between LSC and non-LSC populations for all six patients used for proteomic analysis.
This file contains GSEA for c2cp and hallmark gene sets comparing LSC to non-LSC populations.
Differentially methylated CpGs comparing IDHmut to IDHwtBCAT1Q4 and IDHwtBCAT1Q1 to IDHwtBCAT1Q4 AML patients in the TCGA dataset and overlap to BCAT1-overexpressing AML cell lines.
This file indicates sampling and labelling strategies and lists all identified proteins and their differential expression in LSC compared to non-LSC.
About this article
Cellular and Molecular Life Sciences (2018)