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1.  The E3 ubiquitin ligase ZNRF2 is a substrate of mTORC1 and regulates its activation by amino acids 
eLife  null;5:e12278.
The mechanistic Target of Rapamycin complex 1 (mTORC1) senses intracellular amino acid levels through an intricate machinery, which includes the Rag GTPases, Ragulator and vacuolar ATPase (V-ATPase). The membrane-associated E3 ubiquitin ligase ZNRF2 is released into the cytosol upon its phosphorylation by Akt. In this study, we show that ZNRF2 interacts with mTOR on membranes, promoting the amino acid-stimulated translocation of mTORC1 to lysosomes and its activation in human cells. ZNRF2 also interacts with the V-ATPase and preserves lysosomal acidity. Moreover, knockdown of ZNRF2 decreases cell size and cell proliferation. Upon growth factor and amino acid stimulation, mTORC1 phosphorylates ZNRF2 on Ser145, and this phosphosite is dephosphorylated by protein phosphatase 6. Ser145 phosphorylation stimulates vesicle-to-cytosol translocation of ZNRF2 and forms a novel negative feedback on mTORC1. Our findings uncover ZNRF2 as a component of the amino acid sensing machinery that acts upstream of Rag-GTPases and the V-ATPase to activate mTORC1.
eLife digest
During digestion, proteins are broken down into their constituent parts called amino acids. Amino acids are transported in the bloodstream and are used to build up new cells and repair old ones. Optimal regulation of the cellular rates of amino acid uptake and protein synthesis is critical to the overall health of our bodies.
Inside each of our cells is a molecule called mammalian target of rapamycin (mTOR for short), which acts as a controller that receives information about amino acid availability. mTOR also senses how much of each amino acid the cell needs and calibrates the cell’s amino acid uptake and protein synthesis machineries accordingly.
When investigating an enzyme named ZNRF2, Hoxhaj et al. discovered that it interacts with mTOR on membranes inside cells. This raised questions about how ZNRF2 might work with mTOR to sense amino acid supplies and regulate cell growth.
Hoxhaj et al. found that when cells are provided with amino acids and growth-stimulating hormones, mTOR is activated and attaches a phosphate group to ZNRF2. This chemical modification promotes the release of ZNRF2 from membranes so that ZNRF2 separates from mTOR. In contrast, when cells are starved of amino acids, this phosphate group is removed from ZNRF2, which then returns to the membranes. On membranes, ZNRF2 also influences the activity of a pump called V-ATPase, which controls the internal acidity of the membrane-enclosed vesicles named lysosomes that help to recycle amino acids inside cells. The action of ZNRF2 on the pump may help to prime mTOR so that it is ready to sense amino acids.
These findings by Hoxhaj et al. suggest that ZNRF2 and mTOR may ‘tune’ each other, making constant to-and-fro adjustments to help ensure that levels of amino acid uptake and cell growth are set just right. However, many questions about ZNRF2 still remain to be addressed. For example, are genetic mutations in ZNRF2 involved in cancers, developmental disorders or growth syndromes? Is ZNRF2 most important in the brain, where it is particularly abundant? And how does ZNRF2 affect acidity within the lysosomes?
PMCID: PMC4889327  PMID: 27244671
ZNRF2; mTORC1; amino acid sensing; V-ATPase; PP6; Ragulator; Human; Mouse
2.  Visualization and Biochemical Analyses of the Emerging Mammalian 14-3-3-Phosphoproteome* 
Molecular & Cellular Proteomics : MCP  2011;10(10):M110.005751.
Hundreds of candidate 14-3-3-binding (phospho)proteins have been reported in publications that describe one interaction at a time, as well as high-throughput 14-3-3-affinity and mass spectrometry-based studies. Here, we transcribed these data into a common format, deposited the collated data from low-throughput studies in MINT (, and compared the low- and high-throughput data in VisANT graphs that are easy to analyze and extend. Exploring the graphs prompted questions about technical and biological specificity, which were addressed experimentally, resulting in identification of phosphorylated 14-3-3-binding sites in the mitochondrial import sequence of the iron-sulfur cluster assembly enzyme (ISCU), cytoplasmic domains of the mitochondrial fission factor (MFF), and endoplasmic reticulum-tethered receptor expression-enhancing protein 4 (REEP4), RNA regulator SMAUG2, and cytoskeletal regulatory proteins, namely debrin-like protein (DBNL) and kinesin light chain (KLC) isoforms. Therefore, 14-3-3s undergo physiological interactions with proteins that are destined for diverse subcellular locations. Graphing and validating interactions underpins efforts to use 14-3-3-phosphoproteomics to identify mechanisms and biomarkers for signaling pathways in health and disease.
PMCID: PMC3205853  PMID: 21725060
3.  Bioinformatic and experimental survey of 14-3-3-binding sites 
Biochemical Journal  2010;427(Pt 1):69-78.
More than 200 phosphorylated 14-3-3-binding sites in the literature were analysed to define 14-3-3 specificities, identify relevant protein kinases, and give insights into how cellular 14-3-3/phosphoprotein networks work. Mode I RXX(pS/pT)XP motifs dominate, although the +2 proline residue occurs in less than half, and LX(R/K)SX(pS/pT)XP is prominent in plant 14-3-3-binding sites. Proline at +1 is rarely reported, and such motifs did not stand up to experimental reanalysis of human Ndel1. Instead, we discovered that 14-3-3 interacts with two residues that are phosphorylated by basophilic kinases and located in the DISC1 (disrupted-in-schizophrenia 1)-interacting region of Ndel1 that is implicated in cognitive disorders. These data conform with the general findings that there are different subtypes of 14-3-3-binding sites that overlap with the specificities of different basophilic AGC (protein kinase A/protein kinase G/protein kinase C family) and CaMK (Ca2+/calmodulin-dependent protein kinase) protein kinases, and a 14-3-3 dimer often engages with two tandem phosphorylated sites, which is a configuration with special signalling, mechanical and evolutionary properties. Thus 14-3-3 dimers can be digital logic gates that integrate more than one input to generate an action, and coincidence detectors when the two binding sites are phosphorylated by different protein kinases. Paired sites are generally located within disordered regions and/or straddle either side of functional domains, indicating how 14-3-3 dimers modulate the conformations and/or interactions of their targets. Finally, 14-3-3 proteins bind to members of several multi-protein families. Two 14-3-3-binding sites are conserved across the class IIa histone deacetylases, whereas other protein families display differential regulation by 14-3-3s. We speculate that 14-3-3 dimers may have contributed to the evolution of such families, tailoring regulatory inputs to different physiological demands.
PMCID: PMC2860806  PMID: 20141511
14-3-3 protein; AGC protein kinase; Ca2+/calmodulin-dependent protein kinase; disrupted-in-schizophrenia 1 (DISC1); evolution; AANAT, serotonin acetyltransferase; AGC, protein kinase A/protein kinase G/protein kinase C family kinase; AMPK, AMP-activated protein kinase; BAD, Bcl-XL/Bcl-2-associated death promoter; CaMK, Ca2+/calmodulin-dependent protein kinase; CDK5, cyclin-dependent kinase 5; DIG, digoxigenin; DISC1, disrupted-in-schizophrenia 1; DSTT, Division of Signal Transduction Therapy; EST, expressed sequence tag; FOXO, Forkhead box O; GLUT4, glucose transporter 4; GST, glutathione transferase; HA, haemagglutinin; HAP1A, Huntingtin-associated protein 1A; HDAC, histone deacetylase; HEK, human embryonic kidney; KLC, kinesin light chain; MARK, microtubule affinity-regulating kinase; PI4K, phosphoinositide 4-kinase; PKB, protein kinase B; PKC, protein kinase C; PP2A, protein phosphatase 2A; RSK, ribosomal S6 kinase; YAP1, yes-associated protein 1

Results 1-3 (3)