Katie Wang

All Publications

• Kynurenic Acid Is a Nutritional Cue that Enables Behavioral Plasticity. Cell Lemieux, G. A., Cunningham, K. A., Lin, L., Mayer, F., Werb, Z., Ashrafi, K. 2015; 160 (1-2): 119-31

  Abstract

  The kynurenine pathway of tryptophan metabolism is involved in the pathogenesis of several brain diseases, but its physiological functions remain unclear. We report that kynurenic acid, a metabolite in this pathway, functions as a regulator of food-dependent behavioral plasticity in C. elegans. The experience of fasting in C. elegans alters a variety of behaviors, including feeding rate, when food is encountered post-fast. Levels of neurally produced kynurenic acid are depleted by fasting, leading to activation of NMDA-receptor-expressing interneurons and initiation of a neuropeptide-y-like signaling axis that promotes elevated feeding through enhanced serotonin release when animals re-encounter food. Upon refeeding, kynurenic acid levels are eventually replenished, ending the elevated feeding period. Because tryptophan is an essential amino acid, these findings suggest that a physiological role of kynurenic acid is in directly linking metabolism to activity of NMDA and serotonergic circuits, which regulate a broad range of behaviors and physiologies.

  View details for DOI 10.1016/j.cell.2014.12.028

  View details for PubMedID 25594177

• Loss of a Neural AMP-Activated Kinase Mimics the Effects of Elevated Serotonin on Fat, Movement, and Hormonal Secretions PLOS GENETICS Cunningham, K. A., Bouagnon, A. D., Barros, A. G., Lin, L., Malard, L., Romano-Silva, M. A., Ashrafi, K. 2014; 10 (6)

  Abstract

  AMP-activated protein kinase (AMPK) is an evolutionarily conserved master regulator of metabolism and a therapeutic target in type 2 diabetes. As an energy sensor, AMPK activity is responsive to both metabolic inputs, for instance the ratio of AMP to ATP, and numerous hormonal cues. As in mammals, each of two genes, aak-1 and aak-2, encode for the catalytic subunit of AMPK in C. elegans. Here we show that in C. elegans loss of aak-2 mimics the effects of elevated serotonin signaling on fat reduction, slowed movement, and promoting exit from dauer arrest. Reconstitution of aak-2 in only the nervous system restored wild type fat levels and movement rate to aak-2 mutants and reconstitution in only the ASI neurons was sufficient to significantly restore dauer maintenance to the mutant animals. As in elevated serotonin signaling, inactivation of AAK-2 in the ASI neurons caused enhanced secretion of dense core vesicles from these neurons. The ASI neurons are the site of production of the DAF-7 TGF-β ligand and the DAF-28 insulin, both of which are secreted by dense core vesicles and play critical roles in whether animals stay in dauer or undergo reproductive development. These findings show that elevated levels of serotonin promote enhanced secretions of systemic regulators of pro-growth and differentiation pathways through inactivation of AAK-2. As such, AMPK is not only a recipient of hormonal signals but can also be an upstream regulator. Our data suggest that some of the physiological phenotypes previously attributed to peripheral AAK-2 activity on metabolic targets may instead be due to the role of this kinase in neural serotonin signaling.

  View details for DOI 10.1371/journal.pgen.1004394

  View details for Web of Science ID 000338847700015

  View details for PubMedID 24921650

• AMP-Activated Kinase Links Serotonergic Signaling to Glutamate Release for Regulation of Feeding Behavior in C. elegans CELL METABOLISM Cunningham, K. A., Hua, Z., Srinivasan, S., Liu, J., Lee, B. H., Edwards, R. H., Ashrafi, K. 2012; 16 (1): 113-121

  Abstract

  Serotonergic regulation of feeding behavior has been studied intensively, both for an understanding of the basic neurocircuitry of energy balance in various organisms and as a therapeutic target for human obesity. However, its underlying molecular mechanisms remain poorly understood. Here, we show that neural serotonin signaling in C. elegans modulates feeding behavior through inhibition of AMP-activated kinase (AMPK) in interneurons expressing the C. elegans counterpart of human SIM1, a transcription factor associated with obesity. In turn, glutamatergic signaling links these interneurons to pharyngeal neurons implicated in feeding behavior. We show that AMPK-mediated regulation of glutamatergic release is conserved in rat hippocampal neurons. These findings reveal cellular and molecular mediators of serotonergic signaling.

  View details for DOI 10.1016/j.cmet.2012.05.014

  View details for Web of Science ID 000306383200015

  View details for PubMedID 22768843

• Fat Rationing in Dauer Times CELL METABOLISM Cunningham, K. A., Ashrafi, K. 2009; 9 (2): 113-114

  Abstract

  The fundamental task of maintaining energy balance is complex when nutrient levels are plentiful, but it becomes even more challenging when nutrients are dynamic or scarce. A recent Nature report delineates a role of the AMP kinase pathway in rationing energy stores for the long-term survival of Caenorhabditis elegans dauers (Narbonne and Roy, 2009).

  View details for DOI 10.1016/j.cmet.2009.01.008

  View details for Web of Science ID 000263269400002

  View details for PubMedID 19187769

• The histidine kinase inhibitor Sda binds near the site of autophosphorylation and may sterically hinder autophosphorylation and phosphotransfer to Spo0F MOLECULAR MICROBIOLOGY Cunningham, K. A., Burkholder, W. F. 2009; 71 (3): 659-677

  Abstract

  Histidine kinases are widely used by bacteria, fungi and plants to sense and respond to changing environmental conditions. Signals in addition to those directly sensed by the kinase are often integrated by proteins that fine-tune the biological response by modulating the activity of the kinase or its targets. The Bacillus subtilis histidine kinase KinA promotes the initiation of sporulation when nutrients are limiting, but sporulation can be delayed by two inhibitors of KinA, Sda (when DNA replication is perturbed) or KipI (under unknown conditions). We have identified residues in the dimerization/histidine-phosphotransfer (DHp) domain of KinA that are functionally important for inhibition by Sda and KipI and overlapping surface-exposed residues that lie close to or comprise the Sda binding site. Sda inhibits the intermolecular transfer of phosphate from the catalytic ATP-binding (CA) domain of KinA to the autophosphorylation site in the DHp domain when the domains are split into separate polypeptides, either by steric hindrance or by altering the conformation of the DHp domain. Sda also slows the rate of phosphotransfer from KinA approximately P to its target, Spo0F, consistent with our finding that a KinA residue important for Sda function overlaps with the predicted Spo0F binding site on KinA.

  View details for DOI 10.1111/j.1365-2958.2008.06554.x

  View details for Web of Science ID 000262478800009

  View details for PubMedID 19040634

• Histidine Kinase Regulation by a Cyclophilin-like Inhibitor JOURNAL OF MOLECULAR BIOLOGY Jacques, D. A., Langley, D. B., Jeffries, C. M., Cunningham, K. A., Burkholder, W. F., Guss, J. M., Trewhella, J. 2008; 384 (2): 422-435

  Abstract

  The sensor histidine kinase A (KinA) from Bacillus subtilis triggers a phosphorelay that activates sporulation. The antikinase KipI prevents sporulation by binding KinA and inhibiting the autophosphorylation reaction. Using neutron contrast variation, mutagenesis, and fluorescence data, we show that two KipI monomers bind via their C-domains at a conserved proline in the KinA dimerization and histidine-phosphotransfer (DHp) domain. Our crystal structure of the KipI C-domain reveals the binding motif has a distinctive hydrophobic groove formed by a five-stranded antiparallel beta-sheet; a characteristic of the cyclophilin family of proteins that bind prolines and often act as cis-trans peptidyl-prolyl isomerases. We propose that the DHp domain of KinA transmits conformational signals to regulate kinase activity via this proline-mediated interaction. Given that both KinA and KipI homologues are widespread in the bacterial kingdom, this mechanism has broad significance in bacterial signal transduction.

  View details for DOI 10.1016/j.jmb.2008.09.017

  View details for Web of Science ID 000261272500010

  View details for PubMedID 18823995

• Structure and mechanism of action of Sda, an inhibitor of the histidine kinases that regulate initiation of sporulation in Bacillus subtilis MOLECULAR CELL Rowland, S. L., Burkholder, W. F., Cunningham, K. A., Maciejewski, M. W., Grossman, A. D., King, G. F. 2004; 13 (5): 689-701

  Abstract

  Histidine kinases are used extensively in prokaryotes to monitor and respond to changes in cellular and environmental conditions. In Bacillus subtilis, sporulation-specific gene expression is controlled by a histidine kinase phosphorelay that culminates in phosphorylation of the Spo0A transcription factor. Sda provides a developmental checkpoint by inhibiting this phosphorelay in response to DNA damage and replication defects. We show that Sda acts at the first step in the relay by inhibiting autophosphorylation of the histidine kinase KinA. The structure of Sda, which we determined using NMR, comprises a helical hairpin. A cluster of conserved residues on one face of the hairpin mediates an interaction between Sda and the KinA dimerization/phosphotransfer domain. This interaction stabilizes the KinA dimer, and the two proteins form a stable heterotetramer. The data indicate that Sda forms a molecular barricade that inhibits productive interaction between the catalytic and phosphotransfer domains of KinA.

  View details for Web of Science ID 000220209000007

  View details for PubMedID 15023339

• Maize BMS cultured cell lines survive with massive plastid gene loss CURRENT GENETICS Cahoon, A. B., Cunningham, K. A., Bollenbach, T. J., Stern, D. B. 2003; 44 (2): 104-113

  Abstract

  As part of developing an ex planta model system for the study of maize plastid and mitochondrial gene expression, a series of established Black Mexican Sweet (BMS) suspension cell lines was characterized. Although the initial assumption was that their organelle biochemistry would be similar enough to normal in planta cells to facilitate future work, each of the three lines was found to have plastid DNA (ptDNA) differing from control maize plants, in one case lacking as much as 70% of the genome. The other two BMS lines possessed either near-wild-type ptDNA or displayed an intermediate state of gene loss, suggesting that these clonal lines are rapidly evolving. Gene expression profiles of BMS cells varied dramatically from those in maize leaf chloroplasts, but resembled those of albino plants lacking plastid ribosomes. In spite of lacking most plastid gene expression and apparently mature rRNAs, BMS cells appear to import proteins from the cytoplasm in a normal manner. The regions retained in BMS ptDNAs point to a set of tRNA genes universally preserved among even highly reduced plastid genomes, whereas the other preserved regions may illuminate which plastid genes are truly indispensable for plant cell survival.

  View details for DOI 10.1007/s00294-003-0408-1

  View details for Web of Science ID 000186464800005

  View details for PubMedID 12811510

• The plastid clpP gene may not be essential for plant cell viability PLANT AND CELL PHYSIOLOGY Cahoon, A. B., Cunningham, K. A., Stern, D. B. 2003; 44 (1): 93-95

  Abstract

  The plastid gene clpP is widely regarded as essential for chloroplast function and general plant cell survival. In this note we provide evidence that certain lines of non-photosynthetic maize (Zea mays) Black Mexican Sweet (BMS) suspension cells do not carry clpP in their plastid genomes. We also discuss several incidences in the literature where clpP is either missing or not expressed in other non-green cell lines and plants. We conclude that clpP is not required for general plant cell survival but instead may only be essential for the development and/or function of plastids with active gene expression.

  View details for Web of Science ID 000180841900013

  View details for PubMedID 12552152