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The metabolic enzyme branched-chain amino acid transaminase 1 (BCAT1) drives cell proliferation in aggressive cancers such as glioblastoma. Here, we show that BCAT1 localizes to mitotic structures and has a non-metabolic function as a mitotic regulator. Furthermore, BCAT1 is required for chromosome segregation in cancer and induced pluripotent stem cells and tumor growth in human cerebral organoid and mouse syngraft models. Applying gene knockout and rescue strategies, we show that the BCAT1 CXXC redox motif is crucial for controlling cysteine sulfenylation specifically in mitotic cells, promoting Aurora kinase B localization to centromeres, and securing accurate chromosome segregation. These findings offer an explanation for the well-established role of BCAT1 in promoting cancer cell proliferation. In summary, our data establish BCAT1 as a component of the mitotic apparatus that safeguards mitotic fidelity through a moonlighting redox functionality., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Sufficient amino acid supplies are critical for protein synthesis and, thus, cell growth and proliferation. Specialized transporters mediate amino acid exchange across membranes and their regulation is critical for amino acid homeostasis. Here, we report that the DNA- and RNA-binding protein YBX3 regulates the expression of amino acid transporters. To investigate the functions of YBX3, we integrated proteomic and transcriptomic data from cells depleted of YBX3 with analyses of YBX3 RNA binding sites to identify RNAs directly regulated by YBX3. The data implicate YBX3 as a RNA-binding protein that regulates distinct sets of mRNAs by discrete mechanisms, including mRNA abundance. Among direct YBX3 targets, two solute carrier (SLC) amino acid transporters (SLC7A5 and SLC3A2) were identified. We show that YBX3 stabilizes these SLC mRNAs and that YBX3 depletion diminishes the expression of SLC7A5/SLC3A2, which specifically reduces SLC7A5/SLC3A2 amino acid substrates. Thus, YBX3 emerges as a key regulator of amino acid levels., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

RNA functions through the dynamic formation of complexes with RNA-binding proteins (RBPs) in all clades of life. We determined the RBP repertoire of beating cardiomyocytic HL-1 cells by jointly employing two in vivo proteomic methods, mRNA interactome capture and RBDmap. Together, these yielded 1,148 RBPs, 391 of which are shared with all other available mammalian RBP repertoires, while 393 are thus far unique to cardiomyocytes. RBDmap further identified 568 regions of RNA contact within 368 RBPs. The cardiomyocyte mRNA interactome composition reflects their unique biology. Proteins with roles in cardiovascular physiology or disease, mitochondrial function, and intermediary metabolism are all highly represented. Notably, we identified 73 metabolic enzymes as RBPs. RNA-enzyme contacts frequently involve Rossmann fold domains with examples in evidence of both, mutual exclusivity of, or compatibility between RNA binding and enzymatic function. Our findings raise the prospect of previously hidden RNA-mediated regulatory interactions among cardiomyocyte gene expression, physiology, and metabolism., (Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.)

The oocyte-to-embryo transition marks the onset of development. The initial phase of this profound change from the differentiated oocyte to the totipotent embryo occurs in the absence of both transcription and mRNA degradation. Here we combine global polysome profiling, ribosome-footprint profiling, and quantitative mass spectrometry in a comprehensive approach to delineate the translational and proteomic changes that occur during this important transition in Drosophila. Our results show that PNG kinase is a critical regulator of the extensive changes in the translatome, acting uniquely at this developmental window. Analysis of the proteome in png mutants provided insights into the contributions of translation to changes in protein levels, revealing a compensatory dynamic between translation and protein turnover during proteome remodeling at the return to totipotency. The proteome changes additionally suggested regulators of meiosis and early embryogenesis, including the conserved H3K4 demethylase LID, which we demonstrated is required during this period despite transcriptional inactivity., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

Generation of induced pluripotent stem cells (iPSCs) is a process whose mechanistic underpinnings are only beginning to emerge. Here, we applied in-depth quantitative proteomics to monitor proteome changes during the course of reprogramming of fibroblasts to iPSCs. We uncover a two-step resetting of the proteome during the first and last 3 days of reprogramming, with multiple functionally related proteins changing in expression in a highly coordinated fashion. This comprised several biological processes, including changes in the stoichiometry of electron transport-chain complexes, repressed vesicle-mediated transport during the intermediate stage, and an EMT-like process in the late phase. In addition, we demonstrate that the nucleoporin Nup210 is essential for reprogramming by its permitting of rapid cellular proliferation and subsequent progression through MET. Along with the identification of proteins expressed in a stage-specific manner, this study provides a rich resource toward an enhanced mechanistic understanding of cellular reprogramming., (Copyright © 2012 The Authors. Published by Elsevier Inc. All rights reserved.)