Reactive nitrogen species regulate autophagy through ATM-AMPK-TSC2–mediated suppression of mTORC1
Durga N. Tripathi, Rajdeep Chowdhury, Laura J. Trudel, Andrew R. Tee, Rebecca S. Slack, Cheryl Lyn Walker, and Gerald N. Wogan
NO exposure triggered an ATM-mediated damage response in breast cancer cells involving activation of the LKB1 and TSC2 tumor suppressors, repression of mTORC1, ULK phosphorylation, and increased autophagic flux. The associated loss of cell viability indicates that autophagy can function as a cytotoxic response to nitrosative stress in tumor cells. Collectively, the data (pp. E2950–E2957) identify a nitrosative-stress signaling pathway that regulates autophagy. A more comprehensive understanding of signaling pathways regulating autophagy holds promise for developing new therapeutic approaches compromising prosurvival autophagic pathways that enable tumor cells to evade therapy, or promoting prodeath autophagic pathways that kill cancer cells.
Crystal structure of a GroEL-ADP complex in the relaxed allosteric state at 2.7 Å resolution
Xue Fei, Dong Yang, Nicole LaRonde-LeBlanc, and George H. Lorimer
Chaperonins GroEL and GroES facilitate the folding of diverse substrate proteins driven by ATP hydrolysis. GroEL subunits cycle through a series of allosteric states in a concerted manner (pp. E2958–E2966), enabling work to be performed on substrate proteins. Removing two salt bridges that ordinarily break during the allosteric transitions of the WT permitted the structure of GroEL in the relaxed R state to be solved. Whereas the equatorial and intermediate domains display almost perfect sevenfold symmetry, the apical domains display remarkable asymmetry. Freed of intersubunit contacts, each subunit adopts a different conformation, suggesting a flexibility that permits interaction with diverse substrate proteins.
Impaired complex IV activity in response to loss of LRPPRC function can be compensated by mitochondrial hyperfusion
Stéphane G. Rolland, Elisa Motori, Nadin Memar, Jürgen Hench, Stephan Frank, Konstanze F. Winklhofer, and Barbara Conradt
Mitochondria, the powerhouses of the cell, constantly change their shape by fusing and dividing. How these two opposite processes are controlled remains unclear. In our study (E2967–E2976), we identified the Caenorhabditis elegans homolog of the human mitochondrial protein LRPPRC (leucine-rich pentatricopeptide repeat containing), which has been previously associated with the neurodegenerative French Canadian Leigh Syndrome. Analysis of this protein revealed an evolutionary conserved pathway that regulates mitochondrial shape. Specifically, we show that mitochondria transiently form a highly connected network to compensate for a decrease of the activity of the complex IV of the electron transport chain.
Activation-induced cytidine deaminase (AID) is necessary for the epithelial–mesenchymal transition in mammary epithelial cells
Denise P. Muñoz, Elbert L. Lee, Sachiko Takayama, Jean-Philippe Coppé, Seok-Jin Heo, Dario Boffelli, Javier M. Di Noia, and David I. K. Martin
The epithelial to mesenchymal transition (EMT) is a driving force behind normal morphogenesis and tumor metastasis. We have found evidence that the EMT in both malignant and nonmalignant mammary epithelial cells requires the enzyme activation-induced cytidine deaminase (AID). AID is induced in mammary epithelial cell lines by inflammatory stimuli that also induce the EMT. Deficiency of AID in these cells blocks morphological and transcriptional changes typical of the EMT and increases promoter cytosine methylation in genes encoding key EMT factors. These findings (pp. E2977–E2986) suggest that AID regulates gene expression in a complex developmental process that involves epigenetic reprogramming.
Monovalent antibody design and mechanism of action of onartuzumab, a MET antagonist with anti-tumor activity as a therapeutic agent
Mark Merchant, Xiaolei Ma, Henry R. Maun, Zhong Zheng, Jing Peng, Mally Romero, Arthur Huang, Nai-ying Yang, Merry Nishimura, Joan Greve, Lydia Santell, Yu-Wen Zhang, Yanli Su, Dafna W. Kaufman, Karen L. Billeci, Elaine Mai, Barbara Moffat, Amy Lim, Eileen T. Duenas, Heidi S. Phillips, Hong Xiang, Judy C. Young, George F. Vande Woude, Mark S. Dennis, Dorothea E. Reilly, Ralph H. Schwall, Melissa A. Starovasnik, Robert A. Lazarus, and Daniel G. Yansura
Therapeutic antibodies have revolutionized the treatment of human disease. Despite these advances, antibody bivalency limits their utility against some targets. Here (pp. E2987–E2996), we describe the development of a one-armed (monovalent) antibody, onartuzumab, targeting the receptor tyrosine kinase MET. While initial screening of bivalent antibodies produced agonists of MET, engineering them into monovalent antibodies produced antagonists instead. We explain the structural basis of the mechanism of action with the crystal structure of onartuzumab antigen-binding fragment in complex with MET and HGF-β. These discoveries have led to an additional antibody-based therapeutic option and shed light on the underpinnings of HGF/MET signaling.
Macrophage migration inhibitory factor (MIF) is a critical mediator of the innate immune response to Mycobacterium tuberculosis
Rituparna Das, Mi-Sun Koo, Bae Hoon Kim, Shevin T. Jacob, Selvakumar Subbian, Jie Yao, Lin Leng, Rebecca Levy, Charles Murchison, William J. Burman, Christopher C. Moore, W. Michael Scheld, John R. David, Gilla Kaplan, John D. MacMicking, and Richard Bucala
Failure of the host immune system to control infection with Mycobacterium tuberculosis is a major determinant of tuberculosis (TB) disease. In this work (pp. E2997–E3006), we examined the role of macrophage migration inhibitory factor (MIF), a cytokine that is encoded in a functionally polymorphic locus in humans, in TB. We found genetic low expressers of MIF to be enriched in a population of patients with HIV and disseminated TB. From our work in cellular and mouse models, we propose a key mechanism by which MIF regulates bacterial recognition as the first step in triggering inflammatory pathways to enable mycobacterial control.
In vivo synaptic recovery following optogenetic hyperstimulation
Maike Kittelmann, Jana F. Liewald, Jan Hegermann, Christian Schultheis, Martin Brauner, Wagner Steuer Costa, Sebastian Wabnig, Stefan Eimer, and Alexander Gottschalk
Chemical synapses are key contact points in the nervous system, where signals are transmitted between neurons. These signals, small chemical molecules, are released from membranous synaptic vesicles by fusion with the neuronal membrane. Synaptic vesicle membrane and proteins need to be recycled to support ongoing transmission. Upon seizure, massive amounts of synaptic vesicles fuse, while neurons become exhausted and need to recover. We used (pp. E3007–E3016) optical stimulation of neurons in live Caenorhabditis elegans nematodes to induce extreme neuronal activity and followed processes underlying the recovery progression at behavioral, genetic, physiological, and ultrastructural levels in an intact animal.
SOX2–LIN28/let-7 pathway regulates proliferation and neurogenesis in neural precursors
Flavio Cimadamore, Alejandro Amador-Arjona, Connie Chen, Chun-Teng Huang, and Alexey V. Terskikh
The transcription factor SOX2 plays a critical role in self-renewal and neuronal differentiation of neural precursors (NPCs); however, the molecular mechanisms underlying its functions are poorly understood. We found that SOX2 regulates the expression of LIN28, a suppressor of let-7 microRNA biogenesis. Exogenous LIN28 rescued the NPC proliferation and some neurogenic deficits in the absence of SOX2. We identified (pp. E3017–E3026) let-7i as a novel and potent inhibitor of neuronal differentiation that represses proneural genes. The discovery of SOX2–LIN28/let-7 pathway that maintains both NPC proliferation and neurogenic potential will enhance our understanding and therapeutic development relevant to neurodegeneration and brain tumors.
Targeting H3K4 trimethylation in Huntington disease
Malini Vashishtha, Christopher W. Ng, Ferah Yildirim, Theresa A. Gipson, Ian H. Kratter, Laszlo Bodai, Wan Song, Alice Lau, Adam Labadorf, Annie Vogel-Ciernia, Juan Troncosco, Christopher A. Ross, Gillian P. Bates, Dimitri Krainc, Ghazaleh Sadri-Vakili, Steven Finkbeiner, J. Lawrence Marsh, David E. Housman, Ernest Fraenkel, and Leslie M. Thompson
Transcriptional dysregulation is an early and reproducible feature of Huntington disease (HD); however, mechanisms underlying this dysregulation are unclear. This article (pp. E3027–E3036) describes a unique pattern of the chromatin mark H3K4me3 at transcriptionally repressed promoters in HD mouse and human brain identified by genome-wide analysis. Reducing the levels of the demethylase SMCX/Jarid1c in primary neurons reversed down-regulation of key neuronal genes caused by mutant Huntingtin expression and was neuroprotective in a Drosophila HD model. These results suggest that targeting epigenetic signatures may be an effective strategy to ameliorate the consequences of HD and other neurodegenerative diseases.
Ion channel-kinase TRPM7 is required for maintaining cardiac automaticity
Rajan Sah, Pietro Mesirca, Marjolein Van den Boogert, Jonathan Rosen, John Mably, Matteo E. Mangoni, and David E. Clapham
Transient Receptor Potential Melastatin 7 (TRPM7) is a divalent-permeant channel-kinase of unknown function expressed in human atrial myocytes and fibroblasts and recently implicated in atrial arrhythmias. We show (pp. E3037–E3046) that TRPM7 is highly expressed in embryonic myocardium and sinoatrial node (SAN). Trpm7 disruption in vitro, in cultured embryonic cardiomyocytes, and in vivo in zebrafish and in mice impairs cardiac automaticity. We show that this occurs via reductions in Hcn4 mRNA and the pacemaker current, If, in SAN. We conclude that TRPM7 influences diastolic membrane depolarization and automaticity in SAN via regulation of Hcn4 expression.