SummaryReprogrammed cellular metabolism is a common characteristic observed in various cancers1,2. However, whether metabolic changes directly regulate cancer development and progression remains poorly understood. Here we show that BCAT1, a cytosolic aminotransferase for the branched-chain amino acids (BCAAs), is aberrantly activated and functionally required for chronic myeloid leukemia (CML). BCAT1 is up-regulated during CML progression and promotes BCAA production in leukemia cells by aminating the branched-chain keto acids. Blocking BCAT1 expression or enzymatic activity induces cellular differentiation and impairs the propagation of blast crisis CML (BC-CML) both in vitro and in vivo. Stable isotope tracer experiments combined with NMR-based metabolic analysis demonstrate the intracellular production of BCAAs by BCAT1. Direct supplementation with BCAAs ameliorates the defects caused by BCAT1 knockdown, indicating that BCAT1 exerts its oncogenic function via BCAA production in BC-CML cells. Importantly, BCAT1 expression not only is activated in human BC-CML and de novo acute myeloid leukemia but also predicts disease outcome in patients. As an upstream regulator of BCAT1 expression, we identified Musashi2 (MSI2), an oncogenic RNA binding protein that is required for BC-CML. MSI2 is physically associated with the BCAT1 transcript and positively regulates its protein expression in leukemia. Taken together, this work reveals that altered BCAA metabolism activated through the MSI2-BCAT1 axis drives cancer progression in myeloid leukemia.

Plant cell walls are comprised largely of the polysaccharides cellulose, hemicellulose, and pectin, along with ;10% protein and up to 40% lignin. These wall polymers interact covalently and noncovalently to form the functional cell wall. Characterized cross-links in the wall include covalent linkages between wall glycoprotein extensins between rhamnogalacturonan II monomer domains and between polysaccharides and lignin phenolic residues. Here, we show that two isoforms of a purified Arabidopsis thaliana arabinogalactan protein (AGP) encoded by hydroxyproline-rich glycoprotein family protein gene At3g45230 are covalently attached to wall matrix hemicellulosic and pectic polysaccharides, with rhamnogalacturonan I (RG I)/homogalacturonan linked to the rhamnosyl residue in the arabinogalactan (AG) of the AGP and with arabinoxylan attached to either a rhamnosyl residue in the RG I domain or directly to an arabinosyl residue in the AG glycan domain. The existence of this wall structure, named ARABINOXYLAN PECTIN ARABINOGALACTAN PROTEIN1 (APAP1), is contrary to prevailing cell wall models that depict separate protein, pectin, and hemicellulose polysaccharide networks. The modified sugar composition and increased extractability of pectin and xylan immunoreactive epitopes in apap1 mutant aerial biomass support a role for the APAP1 proteoglycan in plant wall architecture and function.

A systematic, efficient means of producing diverse libraries of asymmetrically branched N-glycans is needed to investigate the specificities and biology of glycan binding proteins. To that end, we describe a core pentasaccharide that at potential branching positions is modified by orthogonal protecting groups to allow selective attachment of unique saccharide moieties by chemical glycosylation. The appendages were selected in such a way that the antenna of the resulting deprotected compounds could be selectively extended by glycosyltransferases to give libraries of asymmetrical multi-antennary glycans. The power of the methodology was demonstrated by the preparation of a series of complex oligosaccharides that were printed as microarrays and screened for binding to lectins and influenza-virus hemagglutinins, which showed that recognition is modulated by presentation of minimal epitopes in the context of complex N-glycans.

Rhizobium meliloti produces a family of sulfated lipooligosaccharides exhibiting different degrees of plant host specificity (nod ABSTRACTWe have shown that a Rhizobium meliloi strain overexpressing nodulation genes excreted high amounts of a family of N-acylated and 6-0-sulfated N-acetyl-fi-1,4-Dglucosamine penta-, tetra-, and trisaccharide Nod factors.Either a C16:2 or a C16:3 acyl chain is attached to the nonre-

Significant differences exist between mammals and fungi with respect to glycosphingolipid (GSL) structure and biosynthesis. Thus, these compounds, as well as the cellular machinery regulating their expression, have considerable potential as targets for the diagnosis and treatment of fungal diseases. In this study, the major neutral GSL components extracted from both yeast and mycelium forms of the thermally dimorphic mycopathogen Paracoccidioides brasiliensis were purified and characterized by 1H and 13C NMR spectroscopy, ESI-MS and ESI-MS/CID-MS, and GC-MS. The major GSLs of both forms were identified as beta-glucopyranosylceramides (GlcCer) having (4E, 8E)-9-methyl-4,8-sphingadienine as long chain base in combination with either N-2'-hydroxyoctadecanoate or N-2'-hydroxy-(E)-3'-octadecenoate. The mycelium form GlcCer had both fatty acids in a approximately 1:1 ratio, while that of the yeast form had on average only approximately 15% of the (E)-Delta 3-unsaturated fatty acid. Cerebrosides from two strains of Aspergillus fumigatus (237 and ATCC 9197) expressing both GalCer and GlcCer were also purified and characterized by similar methods. The GalCer fractions were found to have approximately 70% and approximately 90% N-2'-hydroxy-(E)-3'-octadecenoate, respectively, in the two strains. In contrast, the GlcCer fractions had N-2'-hydroxy-(E)-3'-octadecenoate at only approximately 20 and approximately 50%, respectively. The remainder in all cases was the saturated 2-OH fatty acid, which has not been previously reported in cerebrosides from A. fumigatus. The availability of detailed structures of both glycosylinositol phosphorylceramides [Levery, S. B., Toledo, M. S., Straus, A. H., and Takahashi, H. K. (1998) Biochemistry 37, 8764-8775] and cerebrosides from P. brasiliensis revealed parallel quantitative differences in expression between yeast and mycelium forms, as well as a striking general partitioning of ceramide structure between the two classes of GSLs. These results are discussed with respect to possible functional roles for fungal sphingolipids, particularly as they relate to the morphological transitions exhibited by P. brasiliensis.