Publications by authors named "Rebecca A Kohnz"

11 Publications

  • Page 1 of 1

MYC-driven inhibition of the glutamate-cysteine ligase promotes glutathione depletion in liver cancer.

EMBO Rep 2017 04 20;18(4):569-585. Epub 2017 Feb 20.

Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA, USA

How MYC reprograms metabolism in primary tumors remains poorly understood. Using integrated gene expression and metabolite profiling, we identify six pathways that are coordinately deregulated in primary MYC-driven liver tumors: glutathione metabolism; glycine, serine, and threonine metabolism; aminoacyl-tRNA biosynthesis; cysteine and methionine metabolism; ABC transporters; and mineral absorption. We then focus our attention on glutathione (GSH) and glutathione disulfide (GSSG), as they are markedly decreased in MYC-driven tumors. We find that fewer glutamine-derived carbons are incorporated into GSH in tumor tissue relative to non-tumor tissue. Expression of GCLC, the rate-limiting enzyme of GSH synthesis, is attenuated by the MYC-induced microRNA miR-18a. Inhibition of miR-18a leads to increased GCLC protein expression and GSH abundance in tumor tissue. Finally, MYC-driven liver tumors exhibit increased sensitivity to acute oxidative stress. In summary, MYC-dependent attenuation of GCLC by miR-18a contributes to GSH depletion , and low GSH corresponds with increased sensitivity to oxidative stress in tumors. Our results identify new metabolic pathways deregulated in primary MYC tumors and implicate a role for MYC in regulating a major antioxidant pathway downstream of glutamine.
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http://dx.doi.org/10.15252/embr.201643068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5376764PMC
April 2017

Lipid Biosynthesis Coordinates a Mitochondrial-to-Cytosolic Stress Response.

Cell 2016 Sep;166(6):1539-1552.e16

Glenn Center for Research on Aging, Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address:

Defects in mitochondrial metabolism have been increasingly linked with age-onset protein-misfolding diseases such as Alzheimer's, Parkinson's, and Huntington's. In response to protein-folding stress, compartment-specific unfolded protein responses (UPRs) within the ER, mitochondria, and cytosol work in parallel to ensure cellular protein homeostasis. While perturbation of individual compartments can make other compartments more susceptible to protein stress, the cellular conditions that trigger cross-communication between the individual UPRs remain poorly understood. We have uncovered a conserved, robust mechanism linking mitochondrial protein homeostasis and the cytosolic folding environment through changes in lipid homeostasis. Metabolic restructuring caused by mitochondrial stress or small-molecule activators trigger changes in gene expression coordinated uniquely by both the mitochondrial and cytosolic UPRs, protecting the cell from disease-associated proteins. Our data suggest an intricate and unique system of communication between UPRs in response to metabolic changes that could unveil new targets for diseases of protein misfolding.
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http://dx.doi.org/10.1016/j.cell.2016.08.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5922983PMC
September 2016

Protein Sialylation Regulates a Gene Expression Signature that Promotes Breast Cancer Cell Pathogenicity.

ACS Chem Biol 2016 08 22;11(8):2131-9. Epub 2016 Jul 22.

Departments of Chemistry, Molecular and Cell Biology, and Nutritional Sciences and Toxicology, University of California, Berkeley , Berkeley, California 94720, United States.

Many mechanisms have been proposed for how heightened aerobic glycolytic metabolism fuels cancer pathogenicity, but there are still many unexplored pathways. Here, we have performed metabolomic profiling to map glucose incorporation into metabolic pathways upon transformation of mammary epithelial cells by 11 commonly mutated human oncogenes. We show that transformation of mammary epithelial cells by oncogenic stimuli commonly shunts glucose-derived carbons into synthesis of sialic acid, a hexosamine pathway metabolite that is converted to CMP-sialic acid by cytidine monophosphate N-acetylneuraminic acid synthase (CMAS) as a precursor to glycoprotein and glycolipid sialylation. We show that CMAS knockdown leads to elevations in intracellular sialic acid levels, a depletion of cellular sialylation, and alterations in the expression of many cancer-relevant genes to impair breast cancer pathogenicity. Our study reveals the heretofore unrecognized role of sialic acid metabolism and protein sialylation in regulating the expression of genes that maintain breast cancer pathogenicity.
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http://dx.doi.org/10.1021/acschembio.6b00433DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4994060PMC
August 2016

Inhibition of fatty acid oxidation as a therapy for MYC-overexpressing triple-negative breast cancer.

Nat Med 2016 04 7;22(4):427-32. Epub 2016 Mar 7.

Department of Cell and Tissue Biology, University of California, San Francisco (UCSF), San Francisco, California, USA.

Expression of the oncogenic transcription factor MYC is disproportionately elevated in triple-negative breast cancer (TNBC), as compared to estrogen receptor-, progesterone receptor- or human epidermal growth factor 2 receptor-positive (RP) breast cancer. We and others have shown that MYC alters metabolism during tumorigenesis. However, the role of MYC in TNBC metabolism remains mostly unexplored. We hypothesized that MYC-dependent metabolic dysregulation is essential for the growth of MYC-overexpressing TNBC cells and may identify new therapeutic targets for this clinically challenging subset of breast cancer. Using a targeted metabolomics approach, we identified fatty acid oxidation (FAO) intermediates as being dramatically upregulated in a MYC-driven model of TNBC. We also identified a lipid metabolism gene signature in patients with TNBC that were identified from The Cancer Genome Atlas database and from multiple other clinical data sets, implicating FAO as a dysregulated pathway that is critical for TNBC cell metabolism. We found that pharmacologic inhibition of FAO catastrophically decreased energy metabolism in MYC-overexpressing TNBC cells and blocked tumor growth in a MYC-driven transgenic TNBC model and in a MYC-overexpressing TNBC patient-derived xenograft. These findings demonstrate that MYC-overexpressing TNBC shows an increased bioenergetic reliance on FAO and identify the inhibition of FAO as a potential therapeutic strategy for this subset of breast cancer.
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http://dx.doi.org/10.1038/nm.4055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4892846PMC
April 2016

Mitochondrial DNA Replication Defects Disturb Cellular dNTP Pools and Remodel One-Carbon Metabolism.

Cell Metab 2016 Apr 25;23(4):635-48. Epub 2016 Feb 25.

Research Programs Unit, Molecular Neurology, University of Helsinki, 00290 Helsinki, Finland; Department of Neurology, University of Helsinki, Helsinki University Hospital, 00290 Helsinki, Finland; Neuroscience Center, University of Helsinki, 00790 Helsinki, Finland. Electronic address:

Mitochondrial dysfunction affects cellular energy metabolism, but less is known about the consequences for cytoplasmic biosynthetic reactions. We report that mtDNA replication disorders caused by TWINKLE mutations-mitochondrial myopathy (MM) and infantile onset spinocerebellar ataxia (IOSCA)-remodel cellular dNTP pools in mice. MM muscle shows tissue-specific induction of the mitochondrial folate cycle, purine metabolism, and imbalanced and increased dNTP pools, consistent with progressive mtDNA mutagenesis. IOSCA-TWINKLE is predicted to hydrolyze dNTPs, consistent with low dNTP pools and mtDNA depletion in the disease. MM muscle also modifies the cytoplasmic one-carbon cycle, transsulfuration, and methylation, as well as increases glucose uptake and its utilization for de novo serine and glutathione biosynthesis. Our evidence indicates that the mitochondrial replication machinery communicates with cytoplasmic dNTP pools and that upregulation of glutathione synthesis through glucose-driven de novo serine biosynthesis contributes to the metabolic stress response. These results are important for disorders with primary or secondary mtDNA instability and offer targets for metabolic therapy.
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http://dx.doi.org/10.1016/j.cmet.2016.01.019DOI Listing
April 2016

Activity-Based Protein Profiling of Oncogene-Driven Changes in Metabolism Reveals Broad Dysregulation of PAFAH1B2 and 1B3 in Cancer.

ACS Chem Biol 2015 Jul 7;10(7):1624-30. Epub 2015 May 7.

†Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, 127 Morgan Hall, Berkeley, California 94720, United States.

Targeting dysregulated metabolic pathways is a promising therapeutic strategy for eradicating cancer. Understanding how frequently altered oncogenes regulate metabolic enzyme targets would be useful in identifying both broad-spectrum and targeted metabolic therapies for cancer. Here, we used activity-based protein profiling to identify serine hydrolase activities that were consistently upregulated by various human oncogenes. Through this profiling effort, we found oncogenic regulatory mechanisms for several cancer-relevant serine hydrolases and discovered that platelet activating factor acetylhydrolase 1B2 and 1B3 (PAFAH1B2 and PAFAH1B3) activities were consistently upregulated by several oncogenes, alongside previously discovered cancer-relevant hydrolases fatty acid synthase and monoacylglycerol lipase. While we previously showed that PAFAH1B2 and 1B3 were important in breast cancer, our most recent profiling studies have revealed that these enzymes may be dysregulated broadly across many types of cancers. Here, we find that pharmacological blockade of both enzymes impairs cancer pathogenicity across multiple different types of cancer cells, including breast, ovarian, melanoma, and prostate cancer. We also show that pharmacological blockade of PAFAH1B2 and 1B3 causes unique changes in lipid metabolism, including heightened levels of tumor-suppressing lipids. Our results reveal oncogenic regulatory mechanisms of several cancer-relevant serine hydrolases using activity-based protein profiling, and we show that PAFAH1B2 and 1B3 are important in maintaining cancer pathogenicity across a wide spectrum of cancer types.
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http://dx.doi.org/10.1021/acschembio.5b00053DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4702252PMC
July 2015

Monoacylglycerol lipase inhibitor JZL184 improves behavior and neural properties in Ts65Dn mice, a model of down syndrome.

PLoS One 2014 4;9(12):e114521. Epub 2014 Dec 4.

Department of Neurosciences, University of California San Diego, La Jolla, CA, United States of America.

Genetic alterations or pharmacological treatments affecting endocannabinoid signaling have profound effects on synaptic and neuronal properties and, under certain conditions, may improve higher brain functions. Down syndrome (DS), a developmental disorder caused by triplication of chromosome 21, is characterized by deficient cognition and inevitable development of the Alzheimer disease (AD) type pathology during aging. Here we used JZL184, a selective inhibitor of monoacylglycerol lipase (MAGL), to examine the effects of chronic MAGL inhibition on the behavioral, biochemical, and synaptic properties of aged Ts65Dn mice, a genetic model of DS. In both Ts65Dn mice and their normosomic (2N) controls, JZL184-treatment increased brain levels of 2-arachidonoylglycerol (2-AG) and decreased levels of its metabolites such as arachidonic acid, prostaglandins PGD2, PGE2, PGFα, and PGJ2. Enhanced spontaneous locomotor activity of Ts65Dn mice was reduced by the JZL184-treatement to the levels observed in 2N animals. Deficient long-term memory was also improved, while short-term and working types of memory were unaffected. Furthermore, reduced hippocampal long-term potentiation (LTP) was increased in the JZL184-treated Ts65Dn mice to the levels observed in 2N mice. Interestingly, changes in synaptic plasticity and behavior were not observed in the JZL184-treated 2N mice suggesting that the treatment specifically attenuated the defects in the trisomic animals. The JZL184-treatment also reduced the levels of Aβ40 and Aβ42, but had no effect on the levels of full length APP and BACE1 in both Ts65Dn and 2N mice. These data show that chronic MAGL inhibition improves the behavior and brain functions in a DS model suggesting that pharmacological targeting of MAGL may be considered as a perspective new approach for improving cognition in DS.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0114521PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4256450PMC
December 2015

Employing a combinatorial expression approach to characterize xylose utilization in Saccharomyces cerevisiae.

Metab Eng 2014 Sep 13;25:20-9. Epub 2014 Jun 13.

Energy Biosciences Institute, Berkeley, CA 94720, USA; Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address:

Fermentation of xylose, a major constituent of lignocellulose, will be important for expanding sustainable biofuel production. We sought to better understand the effects of intrinsic (genotypic) and extrinsic (growth conditions) variables on optimal gene expression of the Scheffersomyces stipitis xylose utilization pathway in Saccharomyces cerevisiae by using a set of five promoters to simultaneously regulate each gene. Three-gene (xylose reductase, xylitol dehydrogenase (XDH), and xylulokinase) and eight-gene (expanded with non-oxidative pentose phosphate pathway enzymes and pyruvate kinase) promoter libraries were enriched under aerobic and anaerobic conditions or with a mutant XDH with altered cofactor usage. Through characterization of enriched strains, we observed (1) differences in promoter enrichment for the three-gene library depending on whether the pentose phosphate pathway genes were included during the aerobic enrichment; (2) the importance of selection conditions, where some aerobically-enriched strains underperform in anaerobic conditions compared to anaerobically-enriched strains; (3) improved growth rather than improved fermentation product yields for optimized strains carrying the mutant XDH compared to the wild-type XDH.
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http://dx.doi.org/10.1016/j.ymben.2014.06.002DOI Listing
September 2014

Inositol phosphate recycling regulates glycolytic and lipid metabolism that drives cancer aggressiveness.

ACS Chem Biol 2014 Jun 28;9(6):1340-50. Epub 2014 Apr 28.

Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley , Berkeley, California 94720, United States.

Cancer cells possess fundamentally altered metabolism that supports their pathogenic features, which includes a heightened reliance on aerobic glycolysis to provide precursors for synthesis of biomass. We show here that inositol polyphosphate phosphatase 1 (INPP1) is highly expressed in aggressive human cancer cells and primary high-grade human tumors. Inactivation of INPP1 leads to a reduction in glycolytic intermediates that feed into the synthesis of the oncogenic signaling lipid lysophosphatidic acid (LPA), which in turn impairs LPA signaling and further attenuates glycolytic metabolism in a feed-forward mechanism to impair cancer cell motility, invasiveness, and tumorigenicity. Taken together these findings reveal a novel mode of glycolytic control in cancer cells that can serve to promote key oncogenic lipid signaling pathways that drive cancer pathogenicity.
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http://dx.doi.org/10.1021/cb5001907DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4076040PMC
June 2014

Chemical approaches to therapeutically target the metabolism and signaling of the endocannabinoid 2-AG and eicosanoids.

Chem Soc Rev 2014 Oct 28;43(19):6859-69. Epub 2014 Mar 28.

Program in Metabolic Biology, University of California, Berkeley, 127 Morgan Hall, Berkeley, CA 94720, USA.

The endocannabinoid system, most popularly known as the target of the psychoactive component of marijuana, Δ(9)-tetrahydrocannabinol (THC), is a signaling network that modulates a diverse range of physiological processes including nociception, behavior, cognitive function, appetite, metabolism, motor control, memory formation, and inflammation. While THC and its derivatives have garnered notoriety in the eyes of the public, the endocannabinoid system consists of two endogenous signaling lipids, 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide), which activate cannabinoid receptors CB1 and CB2 in the nervous system and peripheral tissues. This review will focus on the recent efforts to chemically manipulate 2-AG signaling through the development of inhibitors of the 2-AG-synthesizing enzyme diacylglycerol lipase (DAGL) or the 2-AG-degrading enzyme monoacylglycerol lipase (MAGL), and assessing the therapeutic potential of DAGL and MAGL inhibitors in pain, inflammation, degenerative diseases, tissue injury, and cancer.
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http://dx.doi.org/10.1039/c4cs00047aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4159426PMC
October 2014

Phosphorylation of ULK1 (hATG1) by AMP-activated protein kinase connects energy sensing to mitophagy.

Science 2011 Jan 23;331(6016):456-61. Epub 2010 Dec 23.

Molecular and Cell Biology Laboratory, Dulbecco Center for Cancer Research, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.

Adenosine monophosphate-activated protein kinase (AMPK) is a conserved sensor of intracellular energy activated in response to low nutrient availability and environmental stress. In a screen for conserved substrates of AMPK, we identified ULK1 and ULK2, mammalian orthologs of the yeast protein kinase Atg1, which is required for autophagy. Genetic analysis of AMPK or ULK1 in mammalian liver and Caenorhabditis elegans revealed a requirement for these kinases in autophagy. In mammals, loss of AMPK or ULK1 resulted in aberrant accumulation of the autophagy adaptor p62 and defective mitophagy. Reconstitution of ULK1-deficient cells with a mutant ULK1 that cannot be phosphorylated by AMPK revealed that such phosphorylation is required for mitochondrial homeostasis and cell survival during starvation. These findings uncover a conserved biochemical mechanism coupling nutrient status with autophagy and cell survival.
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http://dx.doi.org/10.1126/science.1196371DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3030664PMC
January 2011