bims-camemi 2019-07-14 papers

bims-camemi

Biomed News

on Mitochondrial metabolism in cancer

Issue of 2019–07–14
thirty-two papers selected by
Christian Frezza, , University of Cambridge, MRC Cancer Unit

Uremic metabolites impair skeletal muscle mitochondrial energetics through disruption of the electron transport system and matrix dehydrogenase activity.
The Warburg Effect, Lactate, and Nearly a Century of Trying to Cure Cancer.
Incidence of Succinate Dehydrogenase and Fumarate Hydratase-Deficient Renal Cell Carcinoma Based on Immunohistochemical Screening with SDHA/SDHB and FH/2SC.
Mitochondrial DNA: the overlooked oncogenome?
SDHC-related deficiency of SDH complex activity promotes growth and metastasis of hepatocellular carcinoma via ROS/NFκB signaling.
MTHFD2 links RNA methylation to metabolic reprogramming in renal cell carcinoma.
Mitochondria in Health and Disease.
Somatic and germline mutations in the tumor suppressor gene PARK2 impair PINK1/Parkin-mediated mitophagy in lung cancer cells.
Outstanding Questions in Mitophagy: What we Do and Do Not Know.
Acute Iron Deprivation Reprograms Human Macrophage Metabolism and Reduces Inflammation In Vivo.
The strange case of AMPK and cancer: Dr Jekyll or Mr Hyde? †.
Exogenous nicotinamide adenine dinucleotide administration alleviates ischemia/reperfusion-induced oxidative injury in isolated rat hearts via Sirt5-SDH-succinate pathway.
PINK1 Content in Mitochondria is Regulated by ER-Associated Degradation.
Mitochondrial Involvement in Cisplatin Resistance.
SAMHD1 Modulates Early Steps during Human Cytomegalovirus Infection by Limiting NF-κB Activation.
Notum produced by Paneth cells attenuates regeneration of aged intestinal epithelium.
Branched-Chain Amino Acid Metabolic Reprogramming Orchestrates Drug Resistance to EGFR Tyrosine Kinase Inhibitors.
Structure and assembly of the mitochondrial membrane remodelling GTPase Mgm1.
Oncogenic MYC Induces the Impaired Ribosome Biogenesis Checkpoint and Stabilizes p53, Independent of Increased Ribosome Content.
Crucial role for central carbon metabolism in the bacterial L-form switch and killing by β-lactam antibiotics.
Metabolic vulnerabilities of metastasizing cancer cells.
Pan-cancer Convergence to a Small-Cell Neuroendocrine Phenotype that Shares Susceptibilities with Hematological Malignancies.
Blockade of leukemia inhibitory factor as a therapeutic approach to KRAS driven pancreatic cancer.
The Cytoplasmic DNA Sensor cGAS Promotes Mitotic Cell Death.
Diverse Cellular Roles of Autophagy.
Metabolic Regulation of Redox Balance in Cancer.
Covalent targeting of the vacuolar H+-ATPase activates autophagy via mTORC1 inhibition.
Tumour lineage shapes BRCA-mediated phenotypes.
MondoA drives muscle lipid accumulation and insulin resistance.
Mitochondrial ecophysiology: assessing the evolutionary forces that shape mitochondrial variation.
Dimethyl fumarate alters intracellular Ca2+ handling in immune cells by redox-mediated pleiotropic effects.
CRISPR editing of mutant IDH R132H induces a CpG methylation-low state in patient-derived glioma models of G-CIMP.

Am J Physiol Cell Physiol. 2019 Jul 10.

Uremic metabolites impair skeletal muscle mitochondrial energetics through disruption of the electron transport system and matrix dehydrogenase activity.

Trace Thome, Zachary R Salyers, Ravi A Kumar, Dongwoo Hahn, Fabian N Berru, Leonardo F Ferreira, Salvatore T Scali, Terence E Ryan.

  Chronic kidney disease (CKD) leads to increased skeletal muscle fatigue, weakness, and atrophy. Previous work has implicated mitochondria within the skeletal muscle as a mediator of muscle dysfunction in CKD, however the mechanisms underlying mitochondrial dysfunction in CKD are not entirely known.
PURPOSE: To define the impact of uremic metabolites on mitochondrial energetics.
METHODS: Skeletal muscle mitochondria were isolated from C57BL/6N mice and exposed to vehicle (DMSO) or varying concentrations of uremic metabolites: indoxyl sulfate, indole-3-acetic-acid, L-kynurenine, and kynurenic acid. A comprehensive mitochondrial phenotyping platform that included assessments of mitochondrial OXPHOS conductance and respiratory capacity, hydrogen peroxide production (JH2O2), matrix dehydrogenase activity, electron transport system enzyme activity, and ATP synthase activity was employed.
RESULTS: Uremic metabolite exposure resulted in a ~25-40% decrease in OXPHOS conductance across multiple substrate conditions(P<0.05, n = 5-6/condition), as well as decreased ADP-stimulated and uncoupled respiratory capacity. ATP synthase activity was not impacted by uremic metabolites, however, a screen of matrix dehydrogenases indicated that malate and glutamate dehydrogenases were impaired by some, but not all, uremic metabolites. Assessments of electron transport system enzymes indicated that uremic metabolites significantly impair complex III and IV. Uremic metabolites resulted in increased JH2O2under glutamate/malate, pyruvate/malate, and succinate conditions across multiple levels of energy demand (all P<0.05, n=4/group).Disruption of mitochondrial OXPHOS was confirmed by decreased respiratory capacity and elevated superoxide production in cultured myotubes.
CONCLUSION: These findings provide direct evidence that uremic metabolites negatively impact skeletal muscle mitochondrial energetics, resulting in decreased energy transfer, impaired complex III and IV enzyme activity, and elevated oxidant production.

Keywords:  bioenergetics; chronic kidney disease; kidney; oxidative stress; uremia

DOI:  https://doi.org/10.1152/ajpcell.00098.2019
Semin Nephrol. 2019 Jul;pii: S0270-9295(19)30040-3. [Epub ahead of print]39(4): 380-393

The Warburg Effect, Lactate, and Nearly a Century of Trying to Cure Cancer.

Netanya Y Spencer, Robert C Stanton.

  Nearly 100 years ago, Otto Warburg undertook a study of tumor metabolism, and discovered increased lactate caused by increased glycolysis in cancer cells. His experiments were conducted in the presence of excess oxygen, but today tumor tissue is known to be a hypoxic environment. However, an increase of glycolysis and lactate production is still a valid observation. Numerous abnormalities and mutations of metabolic enzymes have been found in many cancers. For example, pyruvate kinase M2 has been associated with many cancers and is a major contributor to directing glycolysis into fermentation, forming lactate. Increases in several enzymes, including glucose 6-phosphate dehydrogenase, pyruvate kinase M2, Rad6, or deficiency of other enzymes such as succinate dehydrogenase, all may contribute directly or indirectly to increases in lactate associated with the Warburg effect. In addition, the increased lactate and acid-base changes are modified further by monocarboxylate transporters and carbonic anhydrase, which contribute to alkalinizing tumor cells while acidifying the tumor extracellular environment. This acidification leads to cancer spread. Fully understanding the mechanisms underlying the Warburg effect should provide new approaches to cancer treatment.

Keywords:  CRISPR; Warburg effect; cancer; glucose 6-phosphate dehydrogenase (G6PD); glycolysis; lactate; metabolism

DOI:  https://doi.org/10.1016/j.semnephrol.2019.04.007
Hum Pathol. 2019 Jul 09. pii: S0046-8177(19)30123-6. [Epub ahead of print]

Incidence of Succinate Dehydrogenase and Fumarate Hydratase-Deficient Renal Cell Carcinoma Based on Immunohistochemical Screening with SDHA/SDHB and FH/2SC.

Sounak Gupta, Amy A Swanson, Ying-Bei Chen, Tilcia Lopez, Dragana Milosevic, Benjamin R Kipp, Bradley C Leibovich, R Houston Thompson, Loren Herrera-Hernandez, John C Cheville, Rafael E Jimenez.

  Mutations of the succinate dehydrogenase (SDHX) enzyme subunits commonly lead to a loss of function of the holoenzyme complex, and germline SDHX mutations lead to a genetic predisposition to SDH-deficient neoplasms, including renal cell carcinomas (RCC). Similarly, loss of function alterations of fumarate hydratase (FH) leads to a genetic predisposition to hereditary leiomyomatosis and renal cell cancer (HLRCC)-associated RCC. Loss of FH leads to an accumulation of fumarate and aberrantly high levels of S-(2-succino)-cysteine (2SC). Subtype-specific consecutively diagnosed renal cell neoplasms were selected for the study and cases were not otherwise selected based on clinicopathologic features. Tissue Microarrays were constructed from 1009 renal cell neoplasms [papillary: 400, clear cell: 203, chromophobe: 87, oncocytomas (original diagnosis): 273, unclassified: 46] and these cases were immunostained for SDHA/SDHB to screen for SDH loss. A smaller subset (n=730; oncocytomas, papillary and unclassified RCCs) were screened for FH-deficiency using immunohistochemistry for FH/2SC. Loss of SDHA/SDHB was seen in three of 273 tumors originally diagnosed as oncocytomas (1.1%). Diffuse nuclear and cytoplasmic 2SC staining, with retained FH expression was seen in one case (suggestive of dysfunctional FH protein), while absent FH was seen in 3 cases (2/400 papillary RCCs, 0.5% and 2/46 unclassified RCCs, 4.35%). No aberrant FH/2SC expression was noted in 273 cases originally diagnosed as oncocytomas. SDH-deficient RCCs were identified only in the cases originally diagnosed as oncocytomas (1.1%), while FH-deficient RCCs were identified in the papillary (0.5%) and unclassified RCC cohorts (4.35%). These results can help guide immunohistochemistry-based screening strategies for these tumors.

Keywords:  2SC; FH; Fumarate Hydratase; Renal Cell Carcinoma; S-(2-succino)-cysteine; SDHA; SDHB; Succinate Dehydrogenase

DOI:  https://doi.org/10.1016/j.humpath.2019.07.004
BMC Biol. 2019 Jul 08. 17(1): 53

Mitochondrial DNA: the overlooked oncogenome?

Payam A Gammage, Christian Frezza.

  Perturbed mitochondrial bioenergetics constitute a core pillar of cancer-associated metabolic dysfunction. While mitochondrial dysfunction in cancer may result from myriad biochemical causes, a historically neglected source is that of the mitochondrial genome. Recent large-scale sequencing efforts and clinical studies have highlighted the prevalence of mutations in mitochondrial DNA (mtDNA) in human tumours and their potential roles in cancer progression. In this review we discuss the biology of the mitochondrial genome, sources of mtDNA mutations, and experimental evidence of a role for mtDNA mutations in cancer. We also propose a 'metabolic licensing' model for mtDNA mutation-derived dysfunction in cancer initiation and progression.

Keywords:  Cancer; Metabolism; Mitochondria; mtDNA

DOI:  https://doi.org/10.1186/s12915-019-0668-y
Cancer Lett. 2019 Jul 03. pii: S0304-3835(19)30389-1. [Epub ahead of print]

SDHC-related deficiency of SDH complex activity promotes growth and metastasis of hepatocellular carcinoma via ROS/NFκB signaling.

Jibin Li, Ning Liang, Xiaoyu Long, Jing Zhao, Jin Yang, Xiaohong Du, Tao Yang, Peng Yuan, Xiaojun Huang, Jiansheng Zhang, Xianli He, Jinliang Xing.

  Succinate dehydrogenase is a heterotetrameric complex comprising four nuclear-encoded subunits, catalyzes the oxidation of succinate to fumarate in the tricarboxylic acid cycle. A subset of cancers have been found to be associated with mutations in the four SDH genes. However, the functional roles of the SDH complex in tumorigenesis remain largely unclear, especially in hepatocellular carcinoma (HCC). Here, we investigated the expression levels of the four SDH subunits and their clinical significance in HCC, followed by systematic exploration of the effects of SDH dysfunction on HCC cell survival and metastasis both in vitro and in vivo, as well as the underlying molecular mechanisms. Our results showed that the expression of the SDHA/B/C/D subunits was significantly downregulated in HCC, associated with poor patient prognosis, and contributed to SDH inactivation. Additionally, attenuated SDH activity following SDHC knockdown promoted HCC-cell growth and metastasis both in vitro and in vivo via elevated reactive oxygen species levels and subsequent activation of nuclear factor-κB signaling. These findings suggest a critical tumor-suppressive role for SDH and provide strong evidence supporting this enzyme as a potential drug target in the treatment of HCC.

Keywords:  HCC; TCA cycle; metabolic enzyme; mitochondrial respiratory chain complex II

DOI:  https://doi.org/10.1016/j.canlet.2019.07.001
Oncogene. 2019 Jul 09.

MTHFD2 links RNA methylation to metabolic reprogramming in renal cell carcinoma.

Nathanael H Green, Daniel L Galvan, Shawn S Badal, Benny H Chang, Valerie S LeBleu, Jianyin Long, Eric Jonasch, Farhad R Danesh.

One-carbon metabolism plays a central role in a broad array of metabolic processes required for the survival and growth of tumor cells. However, the molecular basis of how one-carbon metabolism may influence RNA methylation and tumorigenesis remains largely unknown. Here we show MTHFD2, a mitochondrial enzyme involved in one-carbon metabolism, contributes to the progression of renal cell carcinoma (RCC) via a novel epitranscriptomic mechanism that involves HIF-2α. We found that expression of MTHFD2 was significantly elevated in human RCC tissues, and MTHFD2 knockdown strongly reduced xenograft tumor growth. Mechanistically, using an unbiased methylated RNA immunoprecipitation sequencing (meRIP-Seq) approach, we found that MTHFD2 plays a critical role in controlling global N6-methyladenosine (m6A) methylation levels, including the m6A methylation of HIF-2α mRNA, which results in enhanced translation of HIF-2α. Enhanced HIF-2α translation, in turn, promotes the aerobic glycolysis, linking one-carbon metabolism to HIF-2α-dependent metabolic reprogramming through RNA methylation. Our findings also suggest that MTHFD2 and HIF-2α form a positive feedforward loop in RCC, promoting metabolic reprograming and tumor growth. Taken together, our results suggest that MTHFD2 links RNA methylation status to the metabolic state of tumor cells in RCC.

DOI: https://doi.org/10.1038/s41388-019-0869-4
Cells. 2019 Jul 05. pii: E680. [Epub ahead of print]8(7):

Mitochondria in Health and Disease.

Sarah J Annesley, Paul R Fisher.

  Mitochondria are best known as the sites for production of respiratory ATP and are essential for eukaryotic life. They have their own genome but the great majority of the mitochondrial proteins are encoded by the nuclear genome and are imported into the mitochondria. The mitochondria participate in critical central metabolic pathways and they are fully integrated into the intracellular signalling networks that regulate diverse cellular functions. It is not surprising then that mitochondrial defects or dysregulation have emerged as having key roles in ageing and in the cytopathological mechanisms underlying cancer, neurodegenerative and other diseases. This special issue contains 12 publications-nine review articles and three original research articles. They cover diverse areas of mitochondrial biology and function and how defects in these areas can lead to disease. In addition, the articles in this issue highlight how model organisms have contributed to our understanding of these processes.

Keywords:  ROS; SIRT; mitochondria; mitochondrial dynamics; neurological disease

DOI:  https://doi.org/10.3390/cells8070680
Acta Pharmacol Sin. 2019 Jul 08.

Somatic and germline mutations in the tumor suppressor gene PARK2 impair PINK1/Parkin-mediated mitophagy in lung cancer cells.

Zeng-Li Zhang, Na-Na Wang, Qi-Lian Ma, Yang Chen, Li Yao, Li Zhang, Qiu-Shi Li, Min-Hua Shi, Hong-Feng Wang, Zheng Ying.

  PARK2, which encodes Parkin, is a disease-causing gene for both neurodegenerative disorders and cancer. Parkin can function as a neuroprotector that plays a crucial role in the regulation of mitophagy, and germline mutations in PARK2 are associated with Parkinson's disease (PD). Intriguingly, recent studies suggest that Parkin can also function as a tumor suppressor and that somatic and germline mutations in PARK2 are associated with various human cancers, including lung cancer. However, it is presently unknown how the tumor suppressor activity of Parkin is affected by these mutations and whether it is associated with mitophagy. Herein, we show that wild-type (WT) Parkin can rapidly translocate onto mitochondria following mitochondrial damage and that Parkin promotes mitophagic clearance of mitochondria in lung cancer cells. However, lung cancer-linked mutations inhibit the mitochondrial translocation and ubiquitin-associated activity of Parkin. Among all lung cancer-linked mutants that we tested, A46T Parkin failed to translocate onto mitochondria and could not recruit downstream mitophagic regulators, including optineurin (OPTN) and TFEB, whereas N254S and R275W Parkin displayed slower mitochondrial translocation than WT Parkin. Moreover, we found that deferiprone (DFP), an iron chelator that can induce mitophagy, greatly increased the death of A46T Parkin-expressing lung cancer cells. Taken together, our results reveal a novel mitophagic mechanism in lung cancer, suggesting that lung cancer-linked mutations in PARK2 are associated with impaired mitophagy and identifying DFP as a novel therapeutic agent for PARK2-linked lung cancer and possibly other types of cancers driven by mitophagic dysregulation.

Keywords:  Parkin; autophagy; cancer; mitophagy; ubiquitin

DOI:  https://doi.org/10.1038/s41401-019-0260-6
J Mol Biol. 2019 Jul 09. pii: S0022-2836(19)30429-2. [Epub ahead of print]

Outstanding Questions in Mitophagy: What we Do and Do Not Know.

Lambert Montava-Garriga, Ian G Ganley.

  The elimination of mitochondria via autophagy, termed mitophagy, is an evolutionarily conserved mechanism for mitochondrial quality control and homeostasis. Mitophagy, therefore, has an important contribution to cell function and integrity, which extends to the whole organism for development and survival. Research in mitophagy has boomed in recent years and it is becoming clear that mitophagy is a complex and multi-factorial cellular response that depends on tissue, energetic, stress and signalling contexts. Yet we know very little of its physiological regulation and the direct contribution of mitophagy to pathologies like neurodegenerative diseases. In this review, we aim to discuss the outstanding questions (and questions outstanding) in the field and reflect on our current understanding of mitophagy, the current challenges and the future directions to take.

Keywords:  Autophagosome; Autophagy; Metabolism; Mitochondria; Mitophagy; Neurodegeneration; Parkinson's disease; Ubiquitylation; mito-QC

DOI:  https://doi.org/10.1016/j.jmb.2019.06.032
Cell Rep. 2019 Jul 09. pii: S2211-1247(19)30805-8. [Epub ahead of print]28(2): 498-511.e5

Acute Iron Deprivation Reprograms Human Macrophage Metabolism and Reduces Inflammation In Vivo.

Marie Pereira, Tai-Di Chen, Norzawani Buang, Antoni Olona, Jeong-Hun Ko, Maria Prendecki, Ana S H Costa, Efterpi Nikitopoulou, Laura Tronci, Charles D Pusey, H Terence Cook, Stephen P McAdoo, Christian Frezza, Jacques Behmoaras.

  Iron is an essential metal that fine-tunes the innate immune response by regulating macrophage function, but an integrative view of transcriptional and metabolic responses to iron perturbation in macrophages is lacking. Here, we induced acute iron chelation in primary human macrophages and measured their transcriptional and metabolic responses. Acute iron deprivation causes an anti-proliferative Warburg transcriptome, characterized by an ATF4-dependent signature. Iron-deprived human macrophages show an inhibition of oxidative phosphorylation and a concomitant increase in glycolysis, a large increase in glucose-derived citrate pools associated with lipid droplet accumulation, and modest levels of itaconate production. LPS polarization increases the itaconate:succinate ratio and decreases pro-inflammatory cytokine production. In rats, acute iron deprivation reduces the severity of macrophage-dependent crescentic glomerulonephritis by limiting glomerular cell proliferation and inducing lipid accumulation in the renal cortex. These results suggest that acute iron deprivation has in vivo protective effects mediated by an anti-inflammatory immunometabolic switch in macrophages.

Keywords:  glomerulonephritis; immunometabolism; inflammation; iron; macrophages; mitochondria

DOI:  https://doi.org/10.1016/j.celrep.2019.06.039
Open Biol. 2019 Jul 26. 9(7): 190099

The strange case of AMPK and cancer: Dr Jekyll or Mr Hyde? †.

Diana Vara-Ciruelos, Fiona M Russell, D Grahame Hardie.

  The AMP-activated protein kinase (AMPK) acts as a cellular energy sensor. Once switched on by increases in cellular AMP : ATP ratios, it acts to restore energy homeostasis by switching on catabolic pathways while switching off cell growth and proliferation. The canonical AMP-dependent mechanism of activation requires the upstream kinase LKB1, which was identified genetically to be a tumour suppressor. AMPK can also be switched on by increases in intracellular Ca2+, by glucose starvation and by DNA damage via non-canonical, AMP-independent pathways. Genetic studies of the role of AMPK in mouse cancer suggest that, before disease arises, AMPK acts as a tumour suppressor that protects against cancer, with this protection being further enhanced by AMPK activators such as the biguanide phenformin. However, once cancer has occurred, AMPK switches to being a tumour promoter instead, enhancing cancer cell survival by protecting against metabolic, oxidative and genotoxic stresses. Studies of genetic changes in human cancer also suggest diverging roles for genes encoding subunit isoforms, with some being frequently amplified, while others are mutated.

Keywords:  AMPK; LKB1; cancer; metabolism; tumour promoters; tumour suppressors

DOI:  https://doi.org/10.1098/rsob.190099
Eur J Pharmacol. 2019 Jul 03. pii: S0014-2999(19)30472-8. [Epub ahead of print]858 172520

Exogenous nicotinamide adenine dinucleotide administration alleviates ischemia/reperfusion-induced oxidative injury in isolated rat hearts via Sirt5-SDH-succinate pathway.

Ling Liu, Qunying Wang, Bangshu Zhao, Qian Wu, Ping Wang.

  The metabolic disorder of succinate in myocardial tissue during ischemia-reperfusion can lead to the myocardial oxidative injury. The activation of succinate dehydrogenase (SDH) plays a vital role in the process. Silent information regulator 5 (Sirt5), a nicotinamide adenine dinucleotide (NAD)-dependent desuccinylase, desuccinylates and inactivates SDH thus exerting a protective effect on the myocardium. This research was designed to investigate whether exogenous NAD protects the myocardium from the ischemia-reperfusion-induced oxidative injury through regulating Sirt5-SDH pathway and succinate metabolism. We first found that myocardial total NAD level was remarkably increased with NAD treatment (10 mg/kg) for 14 days. NAD administration significantly decreased the lactate dehydrogenase (LDH) level in coronary leakage, decreased the malondialdehyde (MDA) level and increased the reduced glutathione/oxidized glutathione disulfide ratio (GSH/GSSG) in myocardial tissue. In addition, NAD treatment effectively attenuated the depression of cardiac function in the isolated rat hearts after ischemia-reperfusion. Furthermore, we found that exogenous NAD attenuated the succinate accumulation during ischemia and decreased its depleting rate during reperfusion. We also found that NAD administration had no obvious effects on myocardial Sirt5 and SDH-a expressions. However, the results of immunofluorescence showed that Sirt5 and SDH-a interacted in ischemia-reperfused myocardium. Utilizing co-immunoprecipitation method, we found that NAD administration promoted the Sirt5 and SDH-a interaction and decreased the succinylation level of SDH-a. These results implied that exogenous NAD administration promoted Sirt5-mediated SDH-a desuccinylation and decreased the activity of SDH-a, which attenuated the succinate accumulation during ischemia and its depleting rate during reperfusion and finally alleviated reactive oxygen species generation.

Keywords:  Myocardial ischemia-reperfusion; Nicotinamide adenine dinucleotide; Sirt5; Succinate; Succinate dehydrogenase

DOI:  https://doi.org/10.1016/j.ejphar.2019.172520
J Neurosci. 2019 Jul 12. pii: 1691-18. [Epub ahead of print]

PINK1 Content in Mitochondria is Regulated by ER-Associated Degradation.

Cristina Guardia-Laguarta, Yuhui Liu, Knut H Lauritzen, Hediye Erdjument-Bromage, Brittany Martin, Theresa C Swayne, Xuejun Jiang, Serge Przedborski.

Maintaining a pool of functional mitochondria requires degradation of damaged ones within the cell. PINK1 is critical in this quality-control process: loss of mitochondrial membrane potential causes PINK1 to accumulate on the mitochondrial surface, triggering mitophagy. However, little is known about how PINK1 is regulated. Recently, we showed that PINK1 content is kept low in healthy mitochondria by continuous ubiquitination and proteasomal degradation of its mature form via a mechanism inconsistent with the proposed N-end rule process. Using both human female and monkey cell lines, here, we now demonstrate that once generated within the mitochondria, 52-kDa PINK1 adopts a mitochondrial topology most consistent with it being at the mitochondrial-endoplasmic reticulum (ER) interface. From this particular submitochondrial location, PINK1 interacts with components of the ER-associated degradation pathway, such as the E3 ligases gp78 and HRD1, which cooperate to catalyze PINK1 ubiquitination. The valosin-containing protein and its cofactor, UFD1, then target ubiquitinated PINK1 for proteasomal degradation. Our data show that PINK1 in healthy mitochondria is negatively regulated via an interplay between mitochondria and ER, and shed light on how this mitochondrial protein gains access to the proteasome.SIGNIFICANCE STATEMENTRegulation of mitochondrial content of PINK1, a contributor to mitophagy, is an important area of research. Recently, we found that PINK1 content is kept low in healthy mitochondria by continuous ubiquitination and proteasomal degradation. We now extend and refine this novel finding by showing that PINK1 localizes at the mitochondrial-endoplasmic reticulum (ER) interface, from where it interacts with the ER-associated degradation machinery, which catalyzes its ubiquitination and transfer to the proteasome. Thus, these data show that PINK1 in healthy mitochondria is negatively regulated via a mitochondria and ER interplay, and how this mitochondrial protein gains access to the proteasome.

DOI: https://doi.org/10.1523/JNEUROSCI.1691-18.2019
Int J Mol Sci. 2019 Jul 10. pii: E3384. [Epub ahead of print]20(14):

Mitochondrial Involvement in Cisplatin Resistance.

Veronica Cocetta, Eugenio Ragazzi, Monica Montopoli.

  Cisplatin is one of the worldwide anticancer drugs and, despite its toxicity and frequent recurrence of resistance phenomena, it still remains the only therapeutic option for several tumors. Circumventing cisplatin resistance remains, therefore, a major goal for clinical therapy and represents a challenge for scientific research. Recent studies have brought to light the fundamental role of mitochondria in onset, progression, and metastasis of cancer, as well as its importance in the resistance to chemotherapy. The aim of this review is to give an overview of the current knowledge about the implication of mitochondria in cisplatin resistance and on the recent development in this research field. Recent studies have highlighted the role of mitochondrial DNA alterations in onset of resistance phenomena, being related both to redox balance alterations and to signal crosstalk with the nucleus, allowing a rewiring of cell metabolism. Moreover, an important role of the mitochondrial dynamics in the adaptation mechanism of cancer cells to challenging environment has been revealed. Giving bioenergetic plasticity to tumor cells, mitochondria allow cells to evade death pathways in stressful conditions, including chemotherapy. So far, even if the central role of mitochondria is recognized, little is known about the specific mechanisms implicated in the resistance. Nevertheless, mitochondria appear to be promising pharmacological targets for overcoming cisplatin resistance, but further studies are necessary.

Keywords:  cisplatin; mitochondria; mitochondrial dynamics; mtDNA; resistance

DOI:  https://doi.org/10.3390/ijms20143384
Cell Rep. 2019 Jul 09. pii: S2211-1247(19)30793-4. [Epub ahead of print]28(2): 434-448.e6

SAMHD1 Modulates Early Steps during Human Cytomegalovirus Infection by Limiting NF-κB Activation.

Eui Tae Kim, Kathryn L Roche, Katarzyna Kulej, Lynn A Spruce, Steven H Seeholzer, Donald M Coen, Felipe Diaz-Griffero, Eain A Murphy, Matthew D Weitzman.

  Cellular SAMHD1 inhibits replication of many viruses by limiting intracellular deoxynucleoside triphosphate (dNTP) pools. We investigate the influence of SAMHD1 on human cytomegalovirus (HCMV). During HCMV infection, we observe SAMHD1 induction, accompanied by phosphorylation via viral kinase UL97. SAMHD1 depletion increases HCMV replication in permissive fibroblasts and conditionally permissive myeloid cells. We show this is due to enhanced gene expression from the major immediate-early (MIE) promoter and is independent of dNTP levels. SAMHD1 suppresses innate immune responses by inhibiting nuclear factor κB (NF-κB) activation. We show that SAMHD1 regulates the HCMV MIE promoter through NF-κB activation. Chromatin immunoprecipitation reveals increased RELA and RNA polymerase II on the HCMV MIE promoter in the absence of SAMHD1. Our studies reveal a mechanism of HCMV virus restriction by SAMHD1 and show how SAMHD1 deficiency activates an innate immune pathway that paradoxically results in increased viral replication through transcriptional activation of the HCMV MIE gene promoter.

Keywords:  HCMV; NF-κB; SAMHD1; human cytomegalovirus; virus restriction

DOI:  https://doi.org/10.1016/j.celrep.2019.06.027
Nature. 2019 Jul 10.

Notum produced by Paneth cells attenuates regeneration of aged intestinal epithelium.

Nalle Pentinmikko, Sharif Iqbal, Miyeko Mana, Simon Andersson, Armand B Cognetta, Radu M Suciu, Jatin Roper, Kalle Luopajärvi, Eino Markelin, Swetha Gopalakrishnan, Olli-Pekka Smolander, Santiago Naranjo, Tuure Saarinen, Anne Juuti, Kirsi Pietiläinen, Petri Auvinen, Ari Ristimäki, Nitin Gupta, Tuomas Tammela, Tyler Jacks, David M Sabatini, Benjamin F Cravatt, Ömer H Yilmaz, Pekka Katajisto.

A decline in stem cell function impairs tissue regeneration during ageing, but the role of the stem-cell-supporting niche in ageing is not well understood. The small intestine is maintained by actively cycling intestinal stem cells that are regulated by the Paneth cell niche1,2. Here we show that the regenerative potential of human and mouse intestinal epithelium diminishes with age owing to defects in both stem cells and their niche. The functional decline was caused by a decrease in stemness-maintaining Wnt signalling due to production of Notum, an extracellular Wnt inhibitor, in aged Paneth cells. Mechanistically, high activity of mammalian target of rapamycin complex 1 (mTORC1) in aged Paneth cells inhibits activity of peroxisome proliferator activated receptor α (PPAR-α)3, and lowered PPAR-α activity increased Notum expression. Genetic targeting of Notum or Wnt supplementation restored function of aged intestinal organoids. Moreover, pharmacological inhibition of Notum in mice enhanced the regenerative capacity of aged stem cells and promoted recovery from chemotherapy-induced damage. Our results reveal a role of the stem cell niche in ageing and demonstrate that targeting of Notum can promote regeneration of aged tissues.

DOI: https://doi.org/10.1038/s41586-019-1383-0
Cell Rep. 2019 Jul 09. pii: S2211-1247(19)30792-2. [Epub ahead of print]28(2): 512-525.e6

Branched-Chain Amino Acid Metabolic Reprogramming Orchestrates Drug Resistance to EGFR Tyrosine Kinase Inhibitors.

Yuetong Wang, Jian Zhang, Shengxiang Ren, Dan Sun, Hsin-Yi Huang, Hua Wang, Yujuan Jin, Fuming Li, Chao Zheng, Liu Yang, Lei Deng, Zhonglin Jiang, Tao Jiang, Xiangkun Han, Shenda Hou, Chenchen Guo, Fei Li, Dong Gao, Jun Qin, Daming Gao, Luonan Chen, Shu-Hai Lin, Kwok-Kin Wong, Cheng Li, Liang Hu, Caicun Zhou, Hongbin Ji.

  Drug resistance is a significant hindrance to effective cancer treatment. Although resistance mechanisms of epidermal growth factor receptor (EGFR) mutant cancer cells to lethal EGFR tyrosine kinase inhibitors (TKI) treatment have been investigated intensively, how cancer cells orchestrate adaptive response under sublethal drug challenge remains largely unknown. Here, we find that 2-h sublethal TKI treatment elicits a transient drug-tolerant state in EGFR mutant lung cancer cells. Continuous sublethal treatment reinforces this tolerance and eventually establishes long-term TKI resistance. This adaptive process involves H3K9 demethylation-mediated upregulation of branched-chain amino acid aminotransferase 1 (BCAT1) and subsequent metabolic reprogramming, which promotes TKI resistance through attenuating reactive oxygen species (ROS) accumulation. Combination treatment with TKI- and ROS-inducing reagents overcomes this drug resistance in preclinical mouse models. Clinical information analyses support the correlation of BCAT1 expression with the EGFR TKI response. Our findings reveal the importance of BCAT1-engaged metabolism reprogramming in TKI resistance in lung cancer.

Keywords:  BCAT1; EGFR tyrosine kinase inhibitors; branched-chain amino acids; drug resistance; lung cancer; metabolic reprogramming

DOI:  https://doi.org/10.1016/j.celrep.2019.06.026
Nature. 2019 Jul 10.

Structure and assembly of the mitochondrial membrane remodelling GTPase Mgm1.

Katja Faelber, Lea Dietrich, Jeffrey K Noel, Florian Wollweber, Anna-Katharina Pfitzner, Alexander Mühleip, Ricardo Sánchez, Misha Kudryashev, Nicolas Chiaruttini, Hauke Lilie, Jeanette Schlegel, Eva Rosenbaum, Manuel Hessenberger, Claudia Matthaeus, Séverine Kunz, Alexander von der Malsburg, Frank Noé, Aurélien Roux, Martin van der Laan, Werner Kühlbrandt, Oliver Daumke.

Balanced fusion and fission are key for the proper function and physiology of mitochondria1,2. Remodelling of the mitochondrial inner membrane is mediated by the dynamin-like protein mitochondrial genome maintenance 1 (Mgm1) in fungi or the related protein optic atrophy 1 (OPA1) in animals3-5. Mgm1 is required for the preservation of mitochondrial DNA in yeast6, whereas mutations in the OPA1 gene in humans are a common cause of autosomal dominant optic atrophy-a genetic disorder that affects the optic nerve7,8. Mgm1 and OPA1 are present in mitochondria as a membrane-integral long form and a short form that is soluble in the intermembrane space. Yeast strains that express temperature-sensitive mutants of Mgm19,10 or mammalian cells that lack OPA1 display fragmented mitochondria11,12, which suggests that Mgm1 and OPA1 have an important role in inner-membrane fusion. Consistently, only the mitochondrial outer membrane-not the inner membrane-fuses in the absence of functional Mgm113. Mgm1 and OPA1 have also been shown to maintain proper cristae architecture10,14; for example, OPA1 prevents the release of pro-apoptotic factors by tightening crista junctions15. Finally, the short form of OPA1 localizes to mitochondrial constriction sites, where it presumably promotes mitochondrial fission16. How Mgm1 and OPA1 perform their diverse functions in membrane fusion, scission and cristae organization is at present unknown. Here we present crystal and electron cryo-tomography structures of Mgm1 from Chaetomium thermophilum. Mgm1 consists of a GTPase (G) domain, a bundle signalling element domain, a stalk, and a paddle domain that contains a membrane-binding site. Biochemical and cell-based experiments demonstrate that the Mgm1 stalk mediates the assembly of bent tetramers into helical filaments. Electron cryo-tomography studies of Mgm1-decorated lipid tubes and fluorescence microscopy experiments on reconstituted membrane tubes indicate how the tetramers assemble on positively or negatively curved membranes. Our findings convey how Mgm1 and OPA1 filaments dynamically remodel the mitochondrial inner membrane.

DOI: https://doi.org/10.1038/s41586-019-1372-3
Cancer Res. 2019 Jul 10. pii: canres.2718.2018. [Epub ahead of print]

Oncogenic MYC Induces the Impaired Ribosome Biogenesis Checkpoint and Stabilizes p53, Independent of Increased Ribosome Content.

Carmen Morcelle, Sandra Menoyo, Francisco D Morón-Duran, Albert Tauler, Sara C Kozma, George Thomas, Antonio Gentilella.

The role of MYC in regulating p53 stability as a function of increased ribosome biogenesis is controversial. On one hand, it was suggested that MYC drives the overexpression of ribosomal proteins (RP)L5 and RPL11, which bind and inhibit HDM2, stabilizing p53. On the other, it has been proposed that increased ribosome biogenesis leads the consumption of RPL5/RPL11 into nascent ribosomes, reducing p53 levels and enhancing tumorigenesis. Here we show that the components that make-up the recently described impaired ribosome biogenesis checkpoint (IRBC) complex, RPL5, RPL11 and 5S rRNA, are reduced following MYC silencing. This leads to a rapid reduction in p53 protein half-life, in an HDM2-dependent manner. In contrast, MYC induction leads to increased ribosome biogenesis and p53 protein stabilization. Unexpectedly, there is no change in free RPL5/RPL11 levels, but there is a striking increase in IRBC complex bound to HDM2. Our data supports a cell intrinsic tumor suppressor response to MYC expression, which is presently being exploited to treat cancer.

DOI: https://doi.org/10.1158/0008-5472.CAN-18-2718
Nat Microbiol. 2019 Jul 08.

Crucial role for central carbon metabolism in the bacterial L-form switch and killing by β-lactam antibiotics.

Yoshikazu Kawai, Romain Mercier, Katarzyna Mickiewicz, Agnese Serafini, Luiz Pedro Sório de Carvalho, Jeff Errington.

The peptidoglycan cell wall is an essential structure for the growth of most bacteria. However, many are capable of switching into a wall-deficient L-form state in which they are resistant to antibiotics that target cell wall synthesis under osmoprotective conditions, including host environments. L-form cells may have an important role in chronic or recurrent infections. The cellular pathways involved in switching to and from the L-form state remain poorly understood. This work shows that the lack of a cell wall, or blocking its synthesis with β-lactam antibiotics, results in an increased flux through glycolysis. This leads to the production of reactive oxygen species from the respiratory chain, which prevents L-form growth. Compensating for the metabolic imbalance by slowing down glycolysis, activating gluconeogenesis or depleting oxygen enables L-form growth in Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus. These effects do not occur in Enterococcus faecium, which lacks the respiratory chain pathway. Our results collectively show that when cell wall synthesis is blocked under aerobic and glycolytic conditions, perturbation of cellular metabolism causes cell death. We provide a mechanistic framework for many anecdotal descriptions of the optimal conditions for L-form growth and non-lytic killing by β-lactam antibiotics.

DOI: https://doi.org/10.1038/s41564-019-0497-3
BMC Biol. 2019 Jul 11. 17(1): 54

Metabolic vulnerabilities of metastasizing cancer cells.

Sarah-Maria Fendt.

Most cancer patients die due to metastasis formation. Therefore, understanding, preventing, and treating metastatic cancers is an unmet need. Recent research indicates that cancer cells that undergo metastasis formation have a distinct metabolism that can be targeted. Here, I would like to discuss potential opportunities in exploiting the metabolic vulnerabilities of metastasizing cancer cells.

DOI: https://doi.org/10.1186/s12915-019-0672-2
Cancer Cell. 2019 Jul 08. pii: S1535-6108(19)30296-X. [Epub ahead of print]36(1): 17-34.e7

Pan-cancer Convergence to a Small-Cell Neuroendocrine Phenotype that Shares Susceptibilities with Hematological Malignancies.

Nikolas G Balanis, Katherine M Sheu, Favour N Esedebe, Saahil J Patel, Bryan A Smith, Jung Wook Park, Salwan Alhani, Brigitte N Gomperts, Jiaoti Huang, Owen N Witte, Thomas G Graeber.

  Small-cell neuroendocrine cancers (SCNCs) are an aggressive cancer subtype. Transdifferentiation toward an SCN phenotype has been reported as a resistance route in response to targeted therapies. Here, we identified a convergence to an SCN state that is widespread across epithelial cancers and is associated with poor prognosis. More broadly, non-SCN metastases have higher expression of SCN-associated transcription factors than non-SCN primary tumors. Drug sensitivity and gene dependency screens demonstrate that these convergent SCNCs have shared vulnerabilities. These common vulnerabilities are found across unannotated SCN-like epithelial cases, small-round-blue cell tumors, and unexpectedly in hematological malignancies. The SCN convergent phenotype and common sensitivity profiles with hematological cancers can guide treatment options beyond tissue-specific targeted therapies.

Keywords:  Dependency Map (depmap); RNA interference screen; SCLC; TCGA; blood cancer; drug sensitivity screen; pan-cancer signatures; pharmacogenomics; small-cell neuroendocrine; transdifferentiation

DOI:  https://doi.org/10.1016/j.ccell.2019.06.005
Nat Commun. 2019 Jul 11. 10(1): 3055

Blockade of leukemia inhibitory factor as a therapeutic approach to KRAS driven pancreatic cancer.

Man-Tzu Wang, Nicole Fer, Jacqueline Galeas, Eric A Collisson, Sung Eun Kim, Jeremy Sharib, Frank McCormick.

KRAS mutations are present in over 90% of pancreatic ductal adenocarcinomas (PDAC), and drive their poor outcomes and failure to respond to targeted therapies. Here we show that Leukemia Inhibitory Factor (LIF) expression is induced specifically by oncogenic KRAS in PDAC and that LIF depletion by genetic means or by neutralizing antibodies prevents engraftment in pancreatic xenograft models. Moreover, LIF-neutralizing antibodies synergize with gemcitabine to eradicate established pancreatic tumors in a syngeneic, KrasG12D-driven, PDAC mouse model. The related cytokine IL-6 cannot substitute for LIF, suggesting that LIF mediates KRAS-driven malignancies through a non-STAT-signaling pathway. Unlike IL-6, LIF inhibits the activity of the Hippo-signaling pathway in PDACs. Depletion of YAP inhibits the function of LIF in human PDAC cells. Our data suggest a crucial role of LIF in KRAS-driven pancreatic cancer and that blockade of LIF by neutralizing antibodies represents an attractive approach to improving therapeutic outcomes.

DOI: https://doi.org/10.1038/s41467-019-11044-9
Cell. 2019 Jul 11. pii: S0092-8674(19)30563-X. [Epub ahead of print]178(2): 302-315.e23

The Cytoplasmic DNA Sensor cGAS Promotes Mitotic Cell Death.

Christian Zierhut, Norihiro Yamaguchi, Maria Paredes, Ji-Dung Luo, Thomas Carroll, Hironori Funabiki.

  Pathogenic and other cytoplasmic DNAs activate the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway to induce inflammation via transcriptional activation by IRF3 and nuclear factor κB (NF-κB), but the functional consequences of exposing cGAS to chromosomes upon mitotic nuclear envelope breakdown are unknown. Here, we show that nucleosomes competitively inhibit DNA-dependent cGAS activation and that the cGAS-STING pathway is not effectively activated during normal mitosis. However, during mitotic arrest, low level cGAS-dependent IRF3 phosphorylation slowly accumulates without triggering inflammation. Phosphorylated IRF3, independently of its DNA-binding domain, stimulates apoptosis through alleviating Bcl-xL-dependent suppression of mitochondrial outer membrane permeabilization. We propose that slow accumulation of phosphorylated IRF3, normally not sufficient for inducing inflammation, can trigger transcription-independent induction of apoptosis upon mitotic aberrations. Accordingly, expression of cGAS and IRF3 in cancer cells makes mouse xenograft tumors responsive to the anti-mitotic agent Taxol. The Cancer Genome Atlas (TCGA) datasets for non-small cell lung cancer patients also suggest an effect of cGAS expression on taxane response.

Keywords:  cGAS; cancer; cell death; innate immunity; mitosis; paclitaxel; taxane

DOI:  https://doi.org/10.1016/j.cell.2019.05.035
Annu Rev Cell Dev Biol. 2019 Jul 05.

Diverse Cellular Roles of Autophagy.

Hideaki Morishita, Noboru Mizushima.

Macroautophagy is an intracellular degradation system that delivers diverse cytoplasmic materials to lysosomes via autophagosomes. Recent advances have enabled identification of several selective autophagy substrates and receptors, greatly expanding our understanding of the cellular functions of autophagy. In this review, we describe the diverse cellular functions of macroautophagy, including its essential contribution to metabolic adaptation and cellular homeostasis. We also discuss emerging findings on the mechanisms and functions of various types of selective autophagy. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 35 is October 7, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

DOI: https://doi.org/10.1146/annurev-cellbio-100818-125300
Cancers (Basel). 2019 Jul 08. pii: E955. [Epub ahead of print]11(7):

Metabolic Regulation of Redox Balance in Cancer.

Vinee Purohit, Diane M Simeone, Costas A Lyssiotis.

  Reactive oxygen species (ROS) are chemically active free radicals produced by partial reduction of oxygen that can activate discrete signaling pathways or disrupt redox homeostasis depending on their concentration. ROS interacts with biomolecules, including DNA, and can cause mutations that can transform normal cells into cancer cells. Furthermore, certain cancer-causing mutations trigger alterations in cellular metabolism that can increase ROS production, resulting in genomic instability, additional DNA mutations, and tumor evolution. To prevent excess ROS-mediated toxicity, cancer-causing mutations concurrently activate pathways that manage this oxidative burden. Hence, an understanding of the metabolic pathways that regulate ROS levels is imperative for devising therapies that target tumor cells. In this review, we summarize the dual role of metabolism as a generator and inhibitor of ROS in cancer and discuss current strategies to target the ROS axis.

Keywords:  NADPH; ROS; antioxidants; oxidative stress

DOI:  https://doi.org/10.3390/cancers11070955
Nat Chem Biol. 2019 Jul 08.

Covalent targeting of the vacuolar H+-ATPase activates autophagy via mTORC1 inhibition.

Clive Yik-Sham Chung, Hijai R Shin, Charles A Berdan, Breanna Ford, Carl C Ward, James A Olzmann, Roberto Zoncu, Daniel K Nomura.

Autophagy is a lysosomal degradation pathway that eliminates aggregated proteins and damaged organelles to maintain cellular homeostasis. A major route for activating autophagy involves inhibition of the mTORC1 kinase, but current mTORC1-targeting compounds do not allow complete and selective mTORC1 blockade. Here, we have coupled screening of a covalent ligand library with activity-based protein profiling to discover EN6, a small-molecule in vivo activator of autophagy that covalently targets cysteine 277 in the ATP6V1A subunit of the lysosomal v-ATPase, which activates mTORC1 via the Rag guanosine triphosphatases. EN6-mediated ATP6V1A modification decouples the v-ATPase from the Rags, leading to inhibition of mTORC1 signaling, increased lysosomal acidification and activation of autophagy. Consistently, EN6 clears TDP-43 aggregates, a causative agent in frontotemporal dementia, in a lysosome-dependent manner. Our results provide insight into how the v-ATPase regulates mTORC1, and reveal a unique approach for enhancing cellular clearance based on covalent inhibition of lysosomal mTORC1 signaling.

DOI: https://doi.org/10.1038/s41589-019-0308-4
Nature. 2019 Jul 10.

Tumour lineage shapes BRCA-mediated phenotypes.

Philip Jonsson, Chaitanya Bandlamudi, Michael L Cheng, Preethi Srinivasan, Shweta S Chavan, Noah D Friedman, Ezra Y Rosen, Allison L Richards, Nancy Bouvier, S Duygu Selcuklu, Craig M Bielski, Wassim Abida, Diana Mandelker, Ozge Birsoy, Liying Zhang, Ahmet Zehir, Mark T A Donoghue, José Baselga, Kenneth Offit, Howard I Scher, Eileen M O'Reilly, Zsofia K Stadler, Nikolaus Schultz, Nicholas D Socci, Agnes Viale, Marc Ladanyi, Mark E Robson, David M Hyman, Michael F Berger, David B Solit, Barry S Taylor.

Mutations in BRCA1 and BRCA2 predispose individuals to certain cancers1-3, and disease-specific screening and preventative strategies have reduced cancer mortality in affected patients4,5. These classical tumour-suppressor genes have tumorigenic effects associated with somatic biallelic inactivation, although haploinsufficiency may also promote the formation and progression of tumours6,7. Moreover, BRCA1/2-mutant tumours are often deficient in the repair of double-stranded DNA breaks by homologous recombination8-13, and consequently exhibit increased therapeutic sensitivity to platinum-containing therapy and inhibitors of poly-(ADP-ribose)-polymerase (PARP)14,15. However, the phenotypic and therapeutic relevance of mutations in BRCA1 or BRCA2 remains poorly defined in most cancer types. Here we show that in the 2.7% and 1.8% of patients with advanced-stage cancer and germline pathogenic or somatic loss-of-function alterations in BRCA1/2, respectively, selective pressure for biallelic inactivation, zygosity-dependent phenotype penetrance, and sensitivity to PARP inhibition were observed only in tumour types associated with increased heritable cancer risk in BRCA1/2 carriers (BRCA-associated cancer types). Conversely, among patients with non-BRCA-associated cancer types, most carriers of these BRCA1/2 mutation types had evidence for tumour pathogenesis that was independent of mutant BRCA1/2. Overall, mutant BRCA is an indispensable founding event for some tumours, but in a considerable proportion of other cancers, it appears to be biologically neutral-a difference predominantly conditioned by tumour lineage-with implications for disease pathogenesis, screening, design of clinical trials and therapeutic decision-making.

DOI: https://doi.org/10.1038/s41586-019-1382-1
JCI Insight. 2019 Jul 09. pii: 129119. [Epub ahead of print]5

MondoA drives muscle lipid accumulation and insulin resistance.

Byungyong Ahn, Shibiao Wan, Natasha Jaiswal, Rick B Vega, Donald E Ayer, Paul M Titchenell, Xianlin Han, Kyoung Jae Won, Daniel P Kelly.

  Obesity-related insulin resistance is associated with intramyocellular lipid accumulation in skeletal muscle. We hypothesized that in contrast to current dogma, this linkage is related to an upstream mechanism that coordinately regulates both processes. We demonstrate that the muscle-enriched transcription factor MondoA is glucose/fructose responsive in human skeletal myotubes and directs the transcription of genes in cellular metabolic pathways involved in diversion of energy substrate from a catabolic fate into nutrient storage pathways including fatty acid desaturation and elongation, triacylglyeride (TAG) biosynthesis, glycogen storage, and hexosamine biosynthesis. MondoA also reduces myocyte glucose uptake by suppressing insulin signaling. Mice with muscle-specific MondoA deficiency were partially protected from insulin resistance and muscle TAG accumulation in the context of diet-induced obesity. These results identify MondoA as a nutrient-regulated transcription factor that under normal physiological conditions serves a dynamic checkpoint function to prevent excess energy substrate flux into muscle catabolic pathways when myocyte nutrient balance is positive. However, in conditions of chronic caloric excess, this mechanism becomes persistently activated leading to progressive myocyte lipid storage and insulin resistance.

Keywords:  Glucose metabolism; Insulin signaling; Metabolism; Muscle Biology; Transcription

DOI:  https://doi.org/10.1172/jci.insight.129119
Integr Comp Biol. 2019 Jul 08. pii: icz124. [Epub ahead of print]

Mitochondrial ecophysiology: assessing the evolutionary forces that shape mitochondrial variation.

Jessica L McKenzie, Dillon J Chung, Timothy M Healy, Reid S Brennan, Heather J Bryant, Andrew Whitehead, Patricia M Schulte.

  The mitonuclear species concept hypothesizes that incompatibilities between interacting gene products of the nuclear and mitochondrial genomes are a major factor establishing and maintaining species boundaries. However, most of the data available to test this concept come from studies of genetic variation in mitochondrial DNA, and clines in the mitochondrial genome across contact zones can be produced by a variety of forces. Here, we show that using a combination of population genomic analyses of the nuclear and mitochondrial genomes and studies of mitochondrial function can provide insight into the relative roles of neutral processes, adaptive evolution, and mitonuclear incompatibility in establishing and maintaining mitochondrial clines, using Atlantic killifish (Fundulus heteroclitus) as a case study. There is strong evidence for a role of secondary contact following the last glaciation in shaping a steep mitochondrial cline across a contact zone between northern and southern subspecies of killifish, but there is also evidence for a role of adaptive evolution in driving differentiation between the subspecies in a variety of traits from the level of the whole organism to the level of mitochondrial function. In addition, studies are beginning to address the potential for mitonuclear incompatibilities in admixed populations. However, population genomic studies have failed to detect evidence for a strong and pervasive influence of mitonuclear incompatibilities, and we suggest that polygenic selection may be responsible for the complex patterns observed. This case study demonstrates that multiple forces can act together in shaping mitochondrial clines, and illustrates the challenge of disentangling their relative roles.

Keywords:  Mitochondria; clines; cytonuclear; incompatibility; local adaptation; mitochondrial metabolism

DOI:  https://doi.org/10.1093/icb/icz124
Free Radic Biol Med. 2019 Jul 04. pii: S0891-5849(19)30508-8. [Epub ahead of print]

Dimethyl fumarate alters intracellular Ca2+ handling in immune cells by redox-mediated pleiotropic effects.

Ann-Kathrin Herrmann, Verena Wüllner, Sonja Moos, Jonas Graf, Jialin Chen, Bernd Kieseier, Florian C Kurschus, Philipp Albrecht, Peter Vangheluwe, Axel Methner.

  Dimethyl fumarate (DMF) is widely used to treat the human autoimmune diseases multiple sclerosis (MS) and psoriasis. DMF causes short-term oxidative stress and activates the antioxidant response via the transcription factor Nrf2 but its immunosuppressive effect is not well understood. Immune cell activation depends on calcium signaling which itself is influenced by the cellular redox state. We therefore measured calcium, reactive oxygen species levels and glutathione content in lymphocytes from immunized mice before onset of experimental autoimmune encephalomyelitis, in peripheral blood mononuclear cells from MS patients treated with DMF, and in mouse splenocytes treated ex vivo with DMF. This demonstrated altered redox states and increased lymphocytic calcium levels in all model systems. DMF caused an immediate influx of calcium from the extracellular space, long-term increased cytosolic calcium levels and reduced calcium stored in intracellular stores. The DMF-elicited current had the electrophysiological characteristics of a transient receptor potential channel and the intracellular calcium levels were normalized by antagonists of TRPA1. Interestingly, the sarco/endoplasmic reticulum Ca2+-ATPase SERCA2b was downregulated but more active due to glutathionylation of the redox-sensitive cysteine 674. DMF therefore causes pleiotropic changes in cellular calcium homeostasis which are likely caused by redox-sensitive post-translational modifications. These changes probably contribute to its immunosuppressive effects.

Keywords:  4–6): calcium; DMF; Multiple sclerosis; Redox signaling; SERCA2b; TRPA1

DOI:  https://doi.org/10.1016/j.freeradbiomed.2019.07.005
Mol Cancer Res. 2019 Jul 10. pii: molcanres.0309.2019. [Epub ahead of print]

CRISPR editing of mutant IDH R132H induces a CpG methylation-low state in patient-derived glioma models of G-CIMP.

Casey J Moure, Bill H Diplas, Lee H Chen, Rui Yang, Christopher J Pirozzi, Zhaohui Wang, Ivan Spasojevic, Matthew S Waitkus, Yiping He, Hai Yan.

Mutations in isocitrate dehydrogenases 1 and 2 (IDH) occur in the majority of WHO grade II and III gliomas. IDH1/2 active site mutations confer a neomorphic enzyme activity producing the oncometabolite D-2-hydroxyglutarate (D-2HG), which generates the glioma CpG island methylation phenotype (G-CIMP). While IDH1/2 mutations and G-CIMP are commonly retained during tumor recurrence, recent work has uncovered losses of the IDH1 mutation in a subset of secondary glioblastomas. Co-occurrence of the loss of the mutant allele with extensive methylation changes suggests a possible link between the two phenomena. Here, we utilize patient-derived IDH1R132H/WT glioma cell lines and CRISPR-Cas9 mediated gene knockout to model the genetic loss of IDH1R132H, and characterize the effects of this deletion on DNA methylation. After D-2HG production has been abolished by deletions within the IDH1 alleles, these models show persistent DNA hypermethylation at 7 CpG sites previously used to define G-CIMP-positivity in patient tumor samples. Despite these defining G-CIMP sites showing persistent hypermethylation, we observed a genome-wide pattern of DNA demethylation, enriched for CpG sites located within open sea regions of the genome as well as in CpG-island shores of transcription start sites, after loss of D-2HG production. These results suggest that inhibition of D-2HG from genetic deletion of IDH alleles is not sufficient to reverse hypermethylation of all G-CIMP defining CpG sites, but does result in more demethylation globally and may contribute to the formation of a G-CIMP-low like phenotype. Implications: These findings show that loss of the IDH1 mutation in malignant glioma cells leads to a pattern of DNA methylation alterations, and shows plausibility of IDH1 mutation loss being causally related to the gain of a G-CIMP-low like phenotype.

DOI: https://doi.org/10.1158/1541-7786.MCR-19-0309