By characterizing dynamic changes in yeast protein abundance following osmotic shock, this study shows that the correlation between protein and mRNA differs for transcripts that increase versus decrease in abundance, and reveals physiological reasons for these differences.

The stress-induced attachment of small ubiquitin-like modifier (SUMO) to a diverse collection of nuclear proteins regulating chromatin architecture, transcription, and RNA biology has been implicated in protecting plants and animals against numerous environmental challenges. In order to better understand stress-induced SUMOylation, we combined stringent purification of SUMO conjugates with isobaric tag for relative and absolute quantification mass spectrometry and an advanced method to adjust for sample-to-sample variation so as to study quantitatively the SUMOylation dynamics of intact Arabidopsis seedlings subjected to stress. Inspection of 172 SUMO substrates during and after heat shock (37°C) revealed that stress mostly increases the abundance of existing conjugates, as opposed to modifying new targets. Some of the most robustly up-regulated targets participate in RNA processing and turnover and RNA-directed DNA modification, thus implicating SUMO as a regulator of the transcriptome during stress. Many of these targets were also strongly SUMOylated during ethanol and oxidative stress, suggesting that their modification is crucial for general stress tolerance. Collectively, our quantitative data emphasize the importance of SUMO to RNA-related processes protecting plants from adverse environments. The ability of cellular organisms to cope with environmental challenges requires the detection and immediate initiation of defense responses designed to mitigate the damage inflicted and enhance the organism's ability to tolerate future insults. For sessile organisms such as plants, robust stress responses are fundamental to their survival in a wide range of adverse environments (1, 2). Genetic and biochemical studies have identified a plethora of input pathways and output responses for stress protection in both prokaryotes and eukaryotes. Universally important is the synthesis of heat shock proteins that minimize protein aggregation and stimulate protein refolding through intrinsic chaperone activities (3).The stress-induced modification of intracellular proteins by small ubiquitin-like modifier (SUMO) 1 has recently emerged as an additional line of defense in eukaryotes (4 -6). Attachment of the ϳ100-amino-acid SUMO protein is driven by an ATPdependent, three-step enzyme cascade, which in Arabidopsis thaliana involves the E1 heterodimer (SAE2 together with either of two SAE1 isoforms), a single E2 SCE1, and at least two E3s (SAP, MIZ1 (SIZ1), and MMS21/HYP2) (7-11). The end result is the isopeptide linkage of one or more SUMO moieties to accessible target lysine(s). Most commonly, a consensus ⌿KxE SUMO-binding motif is modified, where ⌿ represents a bulky hydrophobic residue (12, 13). In some cases, the bound SUMOs themselves are also substrates, which results in poly-SUMO chains decorating the target (14, 15). Once generated, SUMO conjugates can be disassembled by a family of deSUMOylating proteases that specifically cleave these isopeptide bonds, thus allowing SUMO to act reversibly (e.g. Refs. 7,[16][17][18].Imp...

Summary Mitochondria are dynamic organelles that play a central role in a diverse array of metabolic processes. Elucidating mitochondrial adaptations to changing metabolic demands and the pathogenic alterations that underlie metabolic disorders represent principal challenges in cell biology. Here, we performed multiplexed quantitative mass spectrometry-based proteomics to chart the remodeling of the mouse liver mitochondrial proteome and phosphoproteome during both acute and chronic physiological transformations in more than 50 mice. Our analyses reveal that reversible phosphorylation is widespread in mitochondria, and is a key mechanism for regulating ketogenesis during the onset of obesity and type 2 diabetes. Specifically, we have demonstrated that phosphorylation of a conserved serine on Hmgcs2 (S456) significantly enhances its catalytic activity in response to increased ketogenic demand. Collectively, our work describes the plasticity of this organelle at high resolution and provides a framework for investigating the roles of proteome restructuring and reversible phosphorylation in mitochondrial adaptation.

SummaryThe rigorous characterization of distinct induced pluripotent stem cells (iPSC) derived from multiple reprogramming technologies, somatic sources, and donors is required to understand potential sources of variability and downstream potential. To achieve this goal, the Progenitor Cell Biology Consortium performed comprehensive experimental and genomic analyses of 58 iPSC from ten laboratories generated using a variety of reprogramming genes, vectors, and cells. Associated global molecular characterization studies identified functionally informative correlations in gene expression, DNA methylation, and/or copy-number variation among key developmental and oncogenic regulators as a result of donor, sex, line stability, reprogramming technology, and cell of origin. Furthermore, X-chromosome inactivation in PSC produced highly correlated differences in teratoma-lineage staining and regulator expression upon differentiation. All experimental results, and raw, processed, and metadata from these analyses, including powerful tools, are interactively accessible from a new online portal at https://www.synapse.org to serve as a reusable resource for the stem cell community.