Lipid droplets in Arabidopsis thaliana leaves contain myosin-binding proteins and enzymes associated with furan-containing fatty acid biosynthesis.

Lipid droplets (LDs) are lipid storage organelles in plant leaves and seeds. Seed LD proteins are well known, and their functions in lipid metabolism have been characterized; however, many leaf LD proteins remain to be identified. We therefore isolated LDs from leaves of the leaf LD-overaccumulating mutant high sterol ester 1 (hise1) of Arabidopsis thaliana by centrifugation or co-immunoprecipitation. We then performed LD proteomics by mass spectrometry and identified 3,206 candidate leaf LD proteins. In this study, we selected 31 candidate proteins for transient expression assays using a construct encoding the candidate protein fused with green fluorescent protein (GFP). Fluorescence microscopy showed that MYOSIN BINDING PROTEIN14 (MYOB14) and two uncharacterized proteins localized to LDs labeled with the LD marker. Subcellular localization analysis of MYOB family members revealed that MYOB1, MYOB2, MYOB3, and MYOB5 localized to LDs. LDs moved along actin filaments together with the endoplasmic reticulum. Co-immunoprecipitation of myosin XIK with MYOB2-GFP or MYOB14-GFP suggested that LD-localized MYOBs are involved in association with the myosin XIK-LDs. The two uncharacterized proteins were highly similar to enzymes for furan fatty acid biosynthesis in the photosynthetic bacterium Cereibacter sphaeroides, suggesting a relationship between LDs and furan fatty acid biosynthesis. Our findings thus reveal potential molecular functions of LDs and provide a valuable resource for further studies of the leaf LD proteome.

Measurement of the intracellular active metabolites of thiopurine drugs to evaluate the enzymatic activity of nudix hydrolase 15 in human blood samples.

Thiopurine is metabolized to 6-thio-(deoxy) guanosine triphosphate (6-thio-(d) GTP), which is then incorporated into DNA or RNA and causes cytotoxicity. Nudix hydrolase 15 (NUDT15) reduces the cytotoxic effects of thiopurine by converting 6-thio-(d) GTP to 6-thio-(d) guanosine monophosphate (6-thio-(d) GMP). NUDT15 polymorphisms like the Arg139Cys variant are strongly linked to thiopurine-induced severe leukocytopenia and alopecia. Therefore, measurement of NUDT15 enzymatic activity in individual patients can help predict thiopurine tolerability and adjust the dosage. We aimed to develop a quantitative assay for NUDT15 enzymatic activity in human blood samples. Blood samples were collected from donors whose NUDT15 genetic status was determined. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to assess the 6-thio-GTP metabolic activity in cell extracts. Because 6-thio-guanosine diphosphate (6-thio-GDP) and 6-thio-GMP were generated upon incubation of 6-thio-GTP with human blood cell extracts, the method detecting 6-thio-GTP, 6-thio-GDP, and 6-thio-GMP was validated. All three metabolites were linearly detected, and the lower limit of quantification (LLOQ) of 6-thio-GTP, 6-thio-GDP, and 6-thio-GMP were 5 µM, 1 µM, and 2 µM, respectively. Matrix effects of human blood cell extracts to detect 6-thio-GTP, 6-thio-GDP, and 6-thio-GMP were 99.0 %, 100.5 %, and 101.4 %, respectively, relative to the signals in the absence of blood cell extracts. The accuracy and precision of the method and the stability of the samples were also assessed. Using this established method, the genotype-dependent differences in NUDT15 activities were successfully determined using cell extracts derived from human blood cells with NUDT15 wild-type (WT) or Arg139Cys variant and 6-thio-GTP (100 µM) as a substrate (18.1, 14.9, and 6.43 µM/h/106 cells for WT, Arg139Cys heterozygous, and homozygous variant, respectively). We developed a method for quantifying intracellular NUDT15 activity in peripheral blood mononuclear cells (PBMCs), which we defined as the conversion of 6-thio-GTP to 6-thio-GMP. Although PBMCs preparation takes some time, its reproducibility in experiments makes it a promising candidate for clinical application. This method can tell the difference between WT and Arg139Cys homozygous blood samples. Even in patients with WT NUDT15, WT samples showed variations in NUDT15 activity, which may correlate with variations in thiopurine dosage.

TGF-ß signaling promotes desmoid tumor formation via CSRP2 upregulation.

Desmoid tumors (DTs), also called desmoid-type fibromatoses, are locally aggressive tumors of mesenchymal origin. In the present study, we developed a novel mouse model of DTs by inducing a local mutation in the Ctnnb1 gene, encoding ß-catenin in PDGFRA-positive stromal cells, by subcutaneous injection of 4-hydroxy-tamoxifen. Tumors in this model resembled histologically clinical samples from DT patients and showed strong phosphorylation of nuclear SMAD2. Knockout of SMAD4 in the model significantly suppressed tumor growth. Proteomic analysis revealed that SMAD4 knockout reduced the level of Cysteine-and-Glycine-Rich Protein 2 (CSRP2) in DTs, and treatment of DT-derived cells with a TGF-ß receptor inhibitor reduced CSRP2 RNA levels. Knockdown of CSRP2 in DT cells significantly suppressed their proliferation. These results indicate that the TGF-ß/CSRP2 axis is a potential therapeutic target for DTs downstream of TGF-ß signaling.

Decreased liver B vitamin-related enzymes as a metabolic hallmark of cancer cachexia.

Cancer cachexia is a complex metabolic disorder accounting for ~20% of cancer-related deaths, yet its metabolic landscape remains unexplored. Here, we report a decrease in B vitamin-related liver enzymes as a hallmark of systemic metabolic changes occurring in cancer cachexia. Metabolomics of multiple mouse models highlights cachexia-associated reductions of niacin, vitamin B6, and a glycine-related subset of one-carbon (C1) metabolites in the liver. Integration of proteomics and metabolomics reveals that liver enzymes related to niacin, vitamin B6, and glycine-related C1 enzymes dependent on B vitamins decrease linearly with their associated metabolites, likely reflecting stoichiometric cofactor-enzyme interactions. The decrease of B vitamin-related enzymes is also found to depend on protein abundance and cofactor subtype. These metabolic/proteomic changes and decreased protein malonylation, another cachexia feature identified by protein post-translational modification analysis, are reflected in blood samples from mouse models and gastric cancer patients with cachexia, underscoring the clinical relevance of our findings.

Palmitoylation-Dependent Small-Molecule Fluorescent Probes for Live-Cell Golgi Imaging.

Small-molecule fluorescent probes enabling visualization of the Golgi apparatus in living cells are essential tools for studying Golgi-associated biological processes and diseases. So far, several fluorescent Golgi stains have been developed by linking ceramide lipids to fluorophores. However, ceramide-based probes suffer from cumbersome staining procedures and low Golgi specificity. Here, we introduce fluorescent Golgi-staining probes based on the tri-N-methylated myristoyl-Gly-Cys (myrGC3Me) motif. The cell-permeable myrGC3Me motif localizes to the Golgi membrane upon S-palmitoylation. By modularly conjugating the myrGC3Me motif to fluorophores, we developed blue, green, and red fluorescent Golgi probes, all of which allowed simple and rapid staining of the Golgi in living cells with high specificity and no cytotoxicity. The probe was also applicable to the visualization of dynamic changes of the Golgi morphology induced by drug treatments and during cell division. The present work provides an entirely new series of live-cell Golgi probes useful for cell biological and diagnostic applications.

Discovery of 2,6-Dihalopurines as Stomata Opening Inhibitors: Implication of an LRX-Mediated H+-ATPase Phosphorylation Pathway.

Stomata are pores in the leaf epidermis of plants and their opening and closing regulate gas exchange and water transpiration. Stomatal movements play key roles in both plant growth and stress responses. In recent years, small molecules regulating stomatal movements have been used as a powerful tool in mechanistic studies, as well as key players for agricultural applications. Therefore, the development of new molecules regulating stomatal movement and the elucidation of their mechanisms have attracted much attention. We herein describe the discovery of 2,6-dihalopurines, AUs, as a new stomatal opening inhibitor, and their mechanistic study. Based on biological assays, AUs may involve in the pathway related with plasma membrane H+-ATPase phosphorylation. In addition, we identified leucine-rich repeat extensin proteins (LRXs), LRX3, LRX4 and LRX5 as well as RALF, as target protein candidates of AUs by affinity based pull down assay and molecular dynamics simulation. The mechanism of stomatal movement related with the LRXs-RALF is an unexplored pathway, and therefore further studies may lead to the discovery of new signaling pathways and regulatory factors in the stomatal movement.

The cAMP/PKA/CREB and TGFß/SMAD4 Pathways Regulate Stemness and Metastatic Potential in Colorectal Cancer Cells.

SIGNIFICANCE: This study identifies signaling pathways essential for maintaining the stemness and metastatic potential of colorectal cancer cells and proposes CREB as a therapeutic target in metastatic colorectal cancer.

Silencing of SmgGDS, a Novel mTORC1 Inducer That Binds to RHEBs, Inhibits Malignant Mesothelioma Cell Proliferation.

Malignant mesothelioma (MM) is an aggressive tumor that typically develops after a long latency following asbestos exposure. Although mechanistic target of rapamycin complex 1 (mTORC1) activation enhances MM cell growth, the mTORC1 inhibitor everolimus has shown limited efficacy in clinical trials of MM patients. We explored the mechanism underlying mTORC1 activation in MM cells and its effects on cell proliferation and progression. Analysis of the expression profiles of 87 MMs from The Cancer Genome Atlas revealed that 40 samples (46%) displayed altered expression of RPTOR (mTORC1 component) and genes immediately upstream that activate mTORC1. Among them, we focused on RHEB and RHEBL1, which encode direct activators of mTORC1. Exogenous RHEBL1 expression enhanced MM cell growth, indicating that RHEB-mTORC1 signaling acts as a pro-oncogenic cascade. We investigated molecules that directly activate RHEBs, identifying SmgGDS as a novel RHEB-binding protein. SmgGDS knockdown reduced mTORC1 activation and inhibited the proliferation of MM cells with mTORC1 activation. Interestingly, SmgGDS displayed high binding affinity with inactive GDP-bound RHEBL1, and its knockdown reduced cytosolic RHEBL1 without affecting its activation. These findings suggest that SmgGDS retains GDP-bound RHEBs in the cytosol, whereas GTP-bound RHEBs are localized on intracellular membranes to promote mTORC1 activation. We revealed a novel role for SmgGDS in the RHEB-mTORC1 pathway and its potential as a therapeutic target in MM with aberrant mTORC1 activation. IMPLICATIONS: Our data showing that SmgGDS regulates RHEB localization to activate mTORC1 indicate that SmgGDS can be used as a new therapeutic target for MM exhibiting mTORC1 activation.

Stromal iodothyronine deiodinase 2 (DIO2) promotes the growth of intestinal tumors in ApcΔ716 mutant mice.

Iodothyronine deiodinase 2 (DIO2) converts the prohormone thyroxine (T4) to bioactive T3 in peripheral tissues and thereby regulates local thyroid hormone (TH) levels. Although epidemiologic studies suggest the contribution of TH to the progression of colorectal cancer (CRC), the role of DIO2 in CRC remains elusive. Here we show that Dio2 is highly expressed in intestinal polyps of ApcΔ716 mice, a mouse model of familial adenomatous polyposis and early stage sporadic CRC. Laser capture microdissection and in situ hybridization analysis show almost exclusive expression of Dio2 in the stroma of ApcΔ716 polyps in the proximity of the COX-2-positive areas. Treatment with iopanoic acid, a deiodinase inhibitor, or chemical thyroidectomy suppresses tumor formation in ApcΔ716 mice, accompanied by reduced tumor cell proliferation and angiogenesis. Dio2 expression in ApcΔ716 polyps is strongly suppressed by treatment with the COX-2 inhibitor meloxicam. Analysis of The Cancer Genome Atlas data shows upregulation of DIO2 in CRC clinical samples and a close association of its expression pattern with the stromal component, consistently with almost exclusive expression of DIO2 in the stroma of human CRC as revealed by in situ hybridization. These results indicate essential roles of stromal DIO2 and thyroid hormone signaling in promoting the growth of intestinal tumors.

TAZ activation by Hippo pathway dysregulation induces cytokine gene expression and promotes mesothelial cell transformation.

Malignant mesothelioma (MM) constitutes a very aggressive tumor that is caused by asbestos exposure after long latency. The NF2 tumor suppressor gene is mutated in 40-50% of MM; moreover, one of its downstream signaling cascades, the Hippo signaling pathway, is also frequently inactivated in MM cells. Although the YAP transcriptional coactivator, which is regulated by the Hippo pathway, can function as a pro-oncogenic protein, the role of TAZ, a paralog of YAP, in MM cells has not yet been clarified. Here, we show that TAZ is expressed and underphosphorylated (activated) in the majority of MM cells compared to immortalized mesothelial cells. ShRNA-mediated TAZ knockdown highly suppressed cell proliferation, anchorage-independent growth, cell motility, and invasion in MM cells harboring activated TAZ. Conversely, transduction of an activated form of TAZ in immortalized mesothelial cells enhanced these in vitro phenotypes and conferred tumorigenicity in vivo. Microarray analysis determined that activated TAZ most significantly enhanced the transcription of genes related to "cytokine-cytokine receptor interaction." Among selected cytokines, we found that IL-1 signaling activation plays a major role in proliferation in TAZ-activated MM cells. Both IL1B knockdown and an IL-1 receptor antagonist significantly suppressed malignant phenotypes of immortalized mesothelial cells and MM cells with activated TAZ. Overall, these results indicate an oncogenic role for TAZ in MMs via transcriptional induction of distinct pro-oncogenic genes including cytokines. Among these, IL-1 signaling appears as one of the most important cascades, thus potentially serving as a target pathway in MM cells harboring Hippo pathway inactivation.

Crystal structure of human tyrosylprotein sulfotransferase-2 reveals the mechanism of protein tyrosine sulfation reaction.

Post-translational protein modification by tyrosine sulfation has an important role in extracellular protein-protein interactions. The protein tyrosine sulfation reaction is catalysed by the Golgi enzyme called the tyrosylprotein sulfotransferase. To date, no crystal structure is available for tyrosylprotein sulfotransferase. Detailed mechanism of protein tyrosine sulfation reaction has thus remained unclear. Here we present the first crystal structure of the human tyrosylprotein sulfotransferase isoform 2 complexed with a substrate peptide (C4P5Y3) derived from complement C4 and 3'-phosphoadenosine-5'-phosphate at 1.9 Å resolution. Structural and complementary mutational analyses revealed the molecular basis for catalysis being an SN2-like in-line displacement mechanism. Tyrosylprotein sulfotransferase isoform 2 appeared to recognize the C4 peptide in a deep cleft by using a short parallel ß-sheet type interaction, and the bound C4P5Y3 forms an L-shaped structure. Surprisingly, the mode of substrate peptide recognition observed in the tyrosylprotein sulfotransferase isoform 2 structure resembles that observed for the receptor type tyrosine kinases.

Molecular characterization and biological function of neuroendocrine regulatory peptide-3 in the rat.

Neuroendocrine regulatory peptide (NERP)-3, derived from the neurosecretory protein VGF (non-aconymic), is a new biologically active peptide identified through peptidomic analysis of the peptides secreted by an endocrine cell line. Using a specific antibody recognizing the C-terminal region of NERP-3, immunoreactive (ir)-NERP-3 was identified in acid extracts of rat brain and gut as a 30-residue NERP-3 with N-terminal pyroglutamylation. Assessed by radioimmunoassay, ir-NERP-3 was more abundant in the brain, including the posterior pituitary (PP), than in the gut. Immunohistochemistry demonstrated that ir-NERP-3 was significantly increased in the suprachiasmatic nucleus, the magnocellular division of the paraventricular nucleus, and the external layer of the median eminence, but not in the supraoptic nucleus, after dehydration. The immunoreactivity was, however, markedly decreased in all of these locations after chronic salt loading. Intracerebroventricular administration of NERP-3 in conscious rats induced Fos expression in a subset of arginine vasopressin (AVP)-containing neurons in the supraoptic nucleus and the magnocellular division of the paraventricular nucleus. On in vitro isolated rat PP preparations, NERP-3 caused a significant AVP release in a dose-related manner, suggesting that NERP-3 in the PP could be an autocrine activator of AVP release. Taken together, the present results suggest that NERP-3 in the hypothalamo-neurohypophyseal system may be involved in the regulation of body fluid balance.

Distribution of neuroendocrine regulatory peptide-1 and -2, and proteolytic processing of their precursor VGF protein in the rat.

Neuroendocrine regulatory peptide (NERP)-1 and NERP-2 are biologically active peptides recently discovered by peptidomic analysis. NERPs are processed out from the 594-residue VGF protein which contains many prohormone convertase cleavage motifs. VGF-deficient mice exhibit a hypermetabolic and infertile phenotype, for which VGF protein-derived peptides including NERPs are presumably responsible. To provide a solid basis for elucidating physiological roles of NERPs, we investigated rat VGF protein processing by chromatographic and mass spectrometric analysis, and immunoblotting, using antibodies against NERPs and the VGF protein C-terminus (VGF-C). Cellular and tissue distribution of immunoreactive (ir) NERPs were also analyzed in the rat. Both ir-NERP-1 and ir-NERP-2, which occur abundantly in the CNS and pituitary, moderately in the gastrointestinal (GI) tract, were mainly localized in neuronal structures. Major endogenous forms of ir-NERPs in the brain and GI tract were identified as NERP-1, NERP-2, and big NERP-2 (NERP-1 + NERP-2), with NERP-1 and big NERP-2 being predominant. Regarding ir-VGF-C peptides, VGF[588-617], VGF[556-617], and VGF[509-617] were found to be major forms. Immunoblotting with the NERP-2 and VGF-C antibodies revealed processing intermediates of 10-37 kDa. Taken together, we deduce that VGF protein is primarily cleaved at 10 sites through the processing pathway common to the brain and GI tract.