Severe Molecular Defects Exhibited by the R179H Mutation in Human Vascular Smooth Muscle {alpha}-Actin [Protein Structure and Folding]

August 22nd, 2016 by Lu, H., Fagnant, P. M., Krementsova, E. B., Trybus, K. M.

Mutations in vascular smooth muscle α-actin (SM α-actin), encoded by ACTA2, are the most common cause of familial thoracic aortic aneurysms that lead to dissection (TAAD). The R179H mutation has a poor patient prognosis, and is unique in causing multisystemic smooth muscle dysfunction (1). Here we characterize this mutation in expressed human SM α-actin. R179H actin shows severe polymerization defects, with a 40-fold higher critical concentration for assembly than WT SM α-actin, driven by a high disassembly rate. The mutant filaments are more readily severed by cofilin. Both defects are attenuated by copolymerization with WT. The R179H monomer binds more tightly to profilin, and formin binding suppresses nucleation and slows polymerization rates. Linear filaments will thus not be readily formed, and cells expressing R179H actin will likely have increased levels of monomeric G-actin. The co-transcription factor myocardin-related transcription factor-A (MRTF-A), which affects cellular phenotype, binds R179H actin with less cooperativity than WT actin. Smooth muscle myosin moves R179H filaments more slowly than WT, even when copolymerized with equimolar amounts of WT. The marked decrease in the ability to form filaments may contribute to the poor patient prognosis, and explain why R179H disrupts even visceral smooth muscle cell function where the SM α-actin isoform is present in low amounts. The R179H mutation has the potential to affect actin structure and function in both the contractile domain of the cell, and the more dynamic cytoskeletal pool of actin, both of which are required for contraction.

DUSP1 maintains IRF1 and leads to increased expression of IRF1-dependent genes: A mechanism promoting glucocorticoid-insensitivity [Signal Transduction]

August 22nd, 2016 by Shah, S., King, E. M., Mostafa, M. M., Altonsy, M. O., Newton, R.

Although, the mitogen-activated protein kinase (MAPK) phosphatase, DUSP1, mediates dexamethasone-induced repression of MAPKs, 14 out of 46 interleukin-1β (IL1B)-induced mRNAs were significantly enhanced by DUSP1 over-expression in pulmonary A549 cells. These include the interferon regulatory factor, IRF1, and the chemokine, CXCL10. Of these DUSP1-enhanced mRNAs, 10, including CXCL10, were IRF1-dependent. MAPK inhibitors and DUSP1 over-expression prolonged IRF1 expression by elevating transcription, and increasing IRF1 mRNA and protein stability. Conversely, DUSP1 silencing increased IL1B-induced MAPK phosphorylation, while significantly reducing IRF1 protein expression at 4h. This confirms a regulatory network, whereby DUSP1 switches off MAPKs to maintain IRF1 expression. There was no repression of IRF1 expression by dexamethasone in primary human bronchial epithelial cells, and in A549 cells IL1B-induced IRF1 protein was only modestly and transiently repressed. While dexamethasone did not repress IL1B-induced IRF1 protein expression at 4-6h, silencing of IL1B plus dexamethasone-induced DUSP1 significantly reduced IRF1 expression. IL1B-induced expression of CXCL10 was largely insensitive to dexamethasone, whereas other DUSP1-enhanced, IRF1-dependent mRNAs showed various degrees of repression. With IL1B plus dexamethasone, CXCL10 expression was also IRF1-dependent and expression was reduced by DUSP1 silencing. Thus, IL1B plus dexamethasone-induced DUSP1 maintains expression of IRF1 and the IRF1-dependent gene, CXCL10. This is supported by chromatin immunoprecipitation showing IRF1 recruitment to be essentially unaffected by dexamethasone at the CXCL10 promoter or at the promoters of more highly repressed IRF1-dependent genes. Since, IRF1-dependent genes, such as CXCL10, are central to host defence, these data may help explain the reduced effectiveness of glucocorticoids during asthma exacerbations.
  • Posted in Journal of Biological Chemistry, Publications
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Fluorogenic probes reveal a role of GLUT4 N-glycosylation in intracellular trafficking

August 22nd, 2016 by Shinya Hirayama

Nature Chemical Biology 12, 853 (2016). doi:10.1038/nchembio.2156

Authors: Shinya Hirayama, Yuichiro Hori, Zsolt Benedek, Tadashi Suzuki & Kazuya Kikuchi

  • Posted in Nat Chem Biol, Publications
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Divergent biosynthesis yields a cytotoxic aminomalonate-containing precolibactin

August 22nd, 2016 by Zhong-Rui Li

Nature Chemical Biology 12, 773 (2016). doi:10.1038/nchembio.2157

Authors: Zhong-Rui Li, Jie Li, Jin-Ping Gu, Jennifer Y H Lai, Brendan M Duggan, Wei-Peng Zhang, Zhi-Long Li, Yong-Xin Li, Rong-Biao Tong, Ying Xu, Dong-Hai Lin, Bradley S Moore & Pei-Yuan Qian

Colibactin is an as-yet-uncharacterized genotoxic secondary metabolite produced by human gut bacteria. Here we report the biosynthetic discovery of two new precolibactin molecules from Escherichia coli, including precolibactin-886, which uniquely incorporates the highly sought genotoxicity-associated aminomalonate building block into its unprecedented macrocyclic structure. This work provides new insights into the biosynthetic logic and mode of action of this colorectal-cancer-linked microbial chemical.

  • Posted in Nat Chem Biol, Publications
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Discovery of LRE1 as a specific and allosteric inhibitor of soluble adenylyl cyclase

August 22nd, 2016 by Lavoisier Ramos-Espiritu

Nature Chemical Biology 12, 838 (2016). doi:10.1038/nchembio.2151

Authors: Lavoisier Ramos-Espiritu, Silke Kleinboelting, Felipe A Navarrete, Antonio Alvau, Pablo E Visconti, Federica Valsecchi, Anatoly Starkov, Giovanni Manfredi, Hannes Buck, Carolina Adura, Jonathan H Zippin, Joop van den Heuvel, J Fraser Glickman, Clemens Steegborn, Lonny R Levin & Jochen Buck

  • Posted in Nat Chem Biol, Publications
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Biophysical determinants for cellular uptake of hydrocarbon-stapled peptide helices

August 22nd, 2016 by Gregory H Bird

Nature Chemical Biology 12, 845 (2016). doi:10.1038/nchembio.2153

Authors: Gregory H Bird, Emanuele Mazzola, Kwadwo Opoku-Nsiah, Margaret A Lammert, Marina Godes, Donna S Neuberg & Loren D Walensky

  • Posted in Nat Chem Biol, Publications
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Oxidation increases the strength of the methionine-aromatic interaction

August 22nd, 2016 by Andrew K Lewis

Nature Chemical Biology 12, 860 (2016). doi:10.1038/nchembio.2159

Authors: Andrew K Lewis, Katie M Dunleavy, Tiffany L Senkow, Cheng Her, Benjamin T Horn, Mark A Jersett, Ryan Mahling, Megan R McCarthy, Gabriella T Perell, Christopher C Valley, Christine B Karim, Jiali Gao, William C K Pomerantz, David D Thomas, Alessandro Cembran, Anne Hinderliter & Jonathan N Sachs

  • Posted in Nat Chem Biol, Publications
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Nitric Oxide Regulation of H-NOX Signaling Pathways in Bacteria

August 19th, 2016 by Lisa-Marie Nisbett and Elizabeth M. Boon

TOC Graphic

Biochemistry
DOI: 10.1021/acs.biochem.6b00754

Insights into newly discovered marks and readers of epigenetic information

August 18th, 2016 by Forest H Andrews

Nature Chemical Biology 12, 662 (2016). doi:10.1038/nchembio.2149

Authors: Forest H Andrews, Brian D Strahl & Tatiana G Kutateladze

  • Posted in Nat Chem Biol, Publications
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Innate immunity: A sweet switch

August 18th, 2016 by Terry L. Sheppard

Nature Chemical Biology 12, 657 (2016). doi:10.1038/nchembio.2162

Author: Terry L. Sheppard