Publications by authors named "Othon Iliopoulos"

41 Publications

Belzutifan for Renal Cell Carcinoma in von Hippel-Lindau Disease.

N Engl J Med 2021 11;385(22):2036-2046

From the University of Texas M.D. Anderson Cancer Center, Houston (E.J.); Aarhus University Hospital, Aarhus, Denmark (F.D.); Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston (O.I.); Vanderbilt University Medical Center, Nashville (W.K.R.); University of Pennsylvania, Philadelphia (V.K.N.); the University of Utah, Salt Lake City (B.L.M.); Hôpital Européen Georges-Pompidou, University of Paris, Paris (S.O.); the University of Michigan, Ann Arbor (T.E.); the University of Pittsburgh, Pittsburgh (J.K.M.); Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom (S.J.W.); Merck, Kenilworth, NJ (S.T., E.K.P., R.F.P.); and the Center for Cancer Research, National Cancer Institute, Bethesda, MD (W.M.L., R.S.).

Background: Patients with von Hippel-Lindau (VHL) disease have a high incidence of renal cell carcinoma owing to gene inactivation and constitutive activation of the transcription factor hypoxia-inducible factor 2α (HIF-2α).

Methods: In this phase 2, open-label, single-group trial, we investigated the efficacy and safety of the HIF-2α inhibitor belzutifan (MK-6482, previously called PT2977), administered orally at a dose of 120 mg daily, in patients with renal cell carcinoma associated with VHL disease. The primary end point was objective response (complete or partial response) as measured according to the Response Evaluation Criteria in Solid Tumors, version 1.1, by an independent central radiology review committee. We also assessed responses to belzutifan in patients with non-renal cell carcinoma neoplasms and the safety of belzutifan.

Results: After a median follow-up of 21.8 months (range, 20.2 to 30.1), the percentage of patients with renal cell carcinoma who had an objective response was 49% (95% confidence interval, 36 to 62). Responses were also observed in patients with pancreatic lesions (47 of 61 patients [77%]) and central nervous system hemangioblastomas (15 of 50 patients [30%]). Among the 16 eyes that could be evaluated in 12 patients with retinal hemangioblastomas at baseline, all (100%) were graded as showing improvement. The most common adverse events were anemia (in 90% of the patients) and fatigue (in 66%). Seven patients discontinued treatment: four patients voluntarily discontinued, one discontinued owing to a treatment-related adverse event (grade 1 dizziness), one discontinued because of disease progression as assessed by the investigator, and one patient died (of acute toxic effects of fentanyl).

Conclusions: Belzutifan was associated with predominantly grade 1 and 2 adverse events and showed activity in patients with renal cell carcinomas and non-renal cell carcinoma neoplasms associated with VHL disease. (Funded by Merck Sharp and Dohme and others; MK-6482-004 ClinicalTrials.gov number, NCT03401788.).
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http://dx.doi.org/10.1056/NEJMoa2103425DOI Listing
November 2021

The fission yeast FLCN/FNIP complex augments TORC1 repression or activation in response to amino acid (AA) availability.

iScience 2021 Nov 23;24(11):103338. Epub 2021 Oct 23.

Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA.

The target of Rapamycin complex1 (TORC1) senses and integrates several environmental signals, including amino acid (AA) availability, to regulate cell growth. Folliculin (FLCN) is a tumor suppressor (TS) protein in renal cell carcinoma, which paradoxically activates TORC1 in response to AA supplementation. Few tractable systems for modeling FLCN as a TS are available. Here, we characterize the FLCN-containing complex in (called BFC) and show that BFC augments TORC1 repression and activation in response to AA starvation and supplementation, respectively. BFC co-immunoprecipitates V-ATPase, a TORC1 modulator, and regulates its activity in an AA-dependent manner. BFC genetic and proteomic networks identify the conserved peptide transmembrane transporter Ptr2 and the phosphoribosylformylglycinamidine synthase Ade3 as new AA-dependent regulators of TORC1. Overall, these data ascribe an additional repressive function to Folliculin in TORC1 regulation and reveal as an excellent system for modeling the AA-dependent, FLCN-mediated repression of TORC1 in eukaryotes.
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http://dx.doi.org/10.1016/j.isci.2021.103338DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8590082PMC
November 2021

Genetic risk assessment for hereditary renal cell carcinoma: Clinical consensus statement.

Cancer 2021 Nov 3;127(21):3957-3966. Epub 2021 Aug 3.

Massachusetts General Hospital Cancer Center, Boston, Massachusetts.

Background: Although renal cell carcinoma (RCC) is believed to have a strong hereditary component, there is a paucity of published guidelines for genetic risk assessment. A panel of experts was convened to gauge current opinions.

Methods: A North American multidisciplinary panel with expertise in hereditary RCC, including urologists, medical oncologists, clinical geneticists, genetic counselors, and patient advocates, was convened. Before the summit, a modified Delphi methodology was used to generate, review, and curate a set of consensus questions regarding RCC genetic risk assessment. Uniform consensus was defined as ≥85% agreement on particular questions.

Results: Thirty-three panelists, including urologists (n = 13), medical oncologists (n = 12), genetic counselors and clinical geneticists (n = 6), and patient advocates (n = 2), reviewed 53 curated consensus questions. Uniform consensus was achieved on 30 statements in specific areas that addressed for whom, what, when, and how genetic testing should be performed. Topics of consensus included the family history criteria, which should trigger further assessment, the need for risk assessment in those with bilateral or multifocal disease and/or specific histology, the utility of multigene panel testing, and acceptance of clinician-based counseling and testing by those who have experience with hereditary RCC.

Conclusions: In the first ever consensus panel on RCC genetic risk assessment, 30 consensus statements were reached. Areas that require further research and discussion were also identified, with a second future meeting planned. This consensus statement may provide further guidance for clinicians when considering RCC genetic risk assessment.

Lay Summary: The contribution of germline genetics to the development of renal cell carcinoma (RCC) has long been recognized. However, there is a paucity of guidelines to define how and when genetic risk assessment should be performed for patients with known or suspected hereditary RCC. Without guidelines, clinicians struggle to define who requires further evaluation, when risk assessment or testing should be done, which genes should be considered, and how counseling and/or testing should be performed. To this end, a multidisciplinary panel of national experts was convened to gauge current opinion on genetic risk assessment in RCC and to enumerate a set of recommendations to guide clinicians when evaluating individuals with suspected hereditary kidney cancer.
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http://dx.doi.org/10.1002/cncr.33679DOI Listing
November 2021

NNT mediates redox-dependent pigmentation via a UVB- and MITF-independent mechanism.

Cell 2021 Aug 6;184(16):4268-4283.e20. Epub 2021 Jul 6.

Cutaneous Biology Research Center, Department of Dermatology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.

Ultraviolet (UV) light and incompletely understood genetic and epigenetic variations determine skin color. Here we describe an UV- and microphthalmia-associated transcription factor (MITF)-independent mechanism of skin pigmentation. Targeting the mitochondrial redox-regulating enzyme nicotinamide nucleotide transhydrogenase (NNT) resulted in cellular redox changes that affect tyrosinase degradation. These changes regulate melanosome maturation and, consequently, eumelanin levels and pigmentation. Topical application of small-molecule inhibitors yielded skin darkening in human skin, and mice with decreased NNT function displayed increased pigmentation. Additionally, genetic modification of NNT in zebrafish alters melanocytic pigmentation. Analysis of four diverse human cohorts revealed significant associations of skin color, tanning, and sun protection use with various single-nucleotide polymorphisms within NNT. NNT levels were independent of UVB irradiation and redox modulation. Individuals with postinflammatory hyperpigmentation or lentigines displayed decreased skin NNT levels, suggesting an NNT-driven, redox-dependent pigmentation mechanism that can be targeted with NNT-modifying topical drugs for medical and cosmetic purposes.
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http://dx.doi.org/10.1016/j.cell.2021.06.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8349839PMC
August 2021

Differential substrate use in EGF- and oncogenic KRAS-stimulated human mammary epithelial cells.

FEBS J 2021 10 13;288(19):5629-5649. Epub 2021 May 13.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.

Many metabolic phenotypes in cancer cells are also characteristic of proliferating nontransformed mammalian cells, and attempts to distinguish between phenotypes resulting from oncogenic perturbation from those associated with increased proliferation are limited. Here, we examined the extent to which metabolic changes corresponding to oncogenic KRAS expression differed from those corresponding to epidermal growth factor (EGF)-driven proliferation in human mammary epithelial cells (HMECs). Removal of EGF from culture medium reduced growth rates and glucose/glutamine consumption in control HMECs despite limited changes in respiration and fatty acid synthesis, while the relative contribution of branched-chain amino acids to the TCA cycle and lipogenesis increased in the near-quiescent conditions. Most metabolic phenotypes measured in HMECs expressing mutant KRAS were similar to those observed in EGF-stimulated control HMECs that were growing at comparable rates. However, glucose and glutamine consumption as well as lactate and glutamate production were lower in KRAS-expressing cells cultured in media without added EGF, and these changes correlated with reduced sensitivity to GLUT1 inhibitor and phenformin treatment. Our results demonstrate the strong dependence of metabolic behavior on growth rate and provide a model to distinguish the metabolic influences of oncogenic mutations and nononcogenic growth.
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http://dx.doi.org/10.1111/febs.15858DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8487438PMC
October 2021

Evaluation, diagnosis and surveillance of renal masses in the setting of VHL disease.

World J Urol 2021 Jul 16;39(7):2409-2415. Epub 2020 Sep 16.

Department of Genitourinary Oncology, H. Lee Moffitt Cancer Center, 12902 Magnolia Dr., Tampa, FL, 33612, USA.

This brief report focuses on the evaluation and diagnosis of clinically localized renal masses in children and adults with Von Hippel-Lindau (VHL) disease. Counseling considerations pertinent to the urologists, medical oncologists, and multidisciplinary teams involved in the care of these patients are addressed. As practice patterns regarding the evaluation and management of VHL tumors can vary considerably, this report aims to provide guidance on some of the controversies associated with the diagnostic evaluation and initial management of localized renal masses in VHL patients.
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http://dx.doi.org/10.1007/s00345-020-03441-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8101019PMC
July 2021

Nitrogen Trapping as a Therapeutic Strategy in Tumors with Mitochondrial Dysfunction.

Cancer Res 2020 09 10;80(17):3492-3506. Epub 2020 Jul 10.

Cardiovascular Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts.

Under conditions of inherent or induced mitochondrial dysfunction, cancer cells manifest overlapping metabolic phenotypes, suggesting that they may be targeted via a common approach. Here, we use multiple oxidative phosphorylation (OXPHOS)-competent and incompetent cancer cell pairs to demonstrate that treatment with α-ketoglutarate (aKG) esters elicits rapid death of OXPHOS-deficient cancer cells by elevating intracellular aKG concentrations, thereby sequestering nitrogen from aspartate through glutamic-oxaloacetic transaminase 1 (GOT1). Exhaustion of aspartate in these cells resulted in immediate depletion of adenylates, which plays a central role in mediating mTOR inactivation and inhibition of glycolysis. aKG esters also conferred cytotoxicity in a variety of cancer types if their cell respiration was obstructed by hypoxia or by chemical inhibition of the electron transport chain (ETC), both of which are known to increase aspartate and GOT1 dependencies. Furthermore, preclinical mouse studies suggested that cell-permeable aKG displays a good biosafety profile, eliminates aspartate only in OXPHOS-incompetent tumors, and prevents their growth and metastasis. This study reveals a novel cytotoxic mechanism for the metabolite aKG and identifies cell-permeable aKG, either by itself or in combination with ETC inhibitors, as a potential anticancer approach. SIGNIFICANCE: These findings demonstrate that OXPHOS deficiency caused by either hypoxia or mutations, which can significantly increase cancer virulence, renders tumors sensitive to aKG esters by targeting their dependence upon GOT1 for aspartate synthesis. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/17/3492/F1.large.jpg.
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http://dx.doi.org/10.1158/0008-5472.CAN-20-0246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7484159PMC
September 2020

Case 36-2018: A 29-Year-Old Man with an Incidentally Discovered Renal Mass.

N Engl J Med 2018 11;379(21):2064-2072

From the Departments of Urology (D.M.D.), Radiology (J.F.S.), Medicine (O.I., P.J.S.), and Pathology (C.-L.W.), Massachusetts General Hospital, and the Departments of Surgery (D.M.D.), Radiology (J.F.S.), Medicine (O.I., P.J.S.), and Pathology (C.-L.W.), Harvard Medical School - both in Boston.

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http://dx.doi.org/10.1056/NEJMcpc1802832DOI Listing
November 2018

Negative regulation of EGFR signalling by the human folliculin tumour suppressor protein.

Nat Commun 2017 06 28;8:15866. Epub 2017 Jun 28.

Center for Cancer Research, Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston, Massachusetts 02139, USA.

Germline mutations in the Folliculin (FLCN) tumour suppressor gene result in fibrofolliculomas, lung cysts and renal cancers, but the precise mechanisms of tumour suppression by FLCN remain elusive. Here we identify Rab7A, a small GTPase important for endocytic trafficking, as a novel FLCN interacting protein and demonstrate that FLCN acts as a Rab7A GTPase-activating protein. FLCN cells display slower trafficking of epidermal growth factor receptors (EGFR) from early to late endosomes and enhanced activation of EGFR signalling upon ligand stimulation. Reintroduction of wild-type FLCN, but not tumour-associated FLCN mutants, suppresses EGFR signalling in a Rab7A-dependent manner. EGFR signalling is elevated in FLCN tumours and the EGFR inhibitor afatinib suppresses the growth of human FLCN cells as tumour xenografts. The functional interaction between FLCN and Rab7A appears conserved across species. Our work highlights a mechanism explaining, at least in part, the tumour suppressor function of FLCN.
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http://dx.doi.org/10.1038/ncomms15866DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5493755PMC
June 2017

Early onset renal cell carcinoma in an adolescent girl with germline FLCN exon 5 deletion.

Fam Cancer 2018 01;17(1):135-139

Massachusetts General Hospital Cancer Center, Boston, MA, 02114, USA.

Birt-Hogg-Dube (BHD) disease is an autosomal dominant cancer syndrome characterized by benign skin tumors, renal cancer and spontaneous pneumothorax and is caused by mutations in the Folliculin (FLCN) gene. Benign skin tumors and pneumothorax occur in the majority of patients affected by BHD syndrome, but only 30-45% of them develop renal cell carcinoma (RCC) with a median age of diagnosis at 48. The earliest onset of RCC in a BHD patient has been reported at age 20. Here we report a case of a 14 year-old patient with germline FLCN mutation leading to an early-onset bulky RCC that could not be classified strictly according to existing histological types. Germline genetic testing revealed a deletion at FLCN exon 5. The father of the patient was identified as the asymptomatic carrier. We report the youngest patient with BHD-related RCC. This early onset presentation supports genetic testing of at-risk patients and initiation of imaging surveillance for RCC in early adolescence. In addition, future studies are necessary to understand the determinants of reduced penetrance in BHD disease.
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http://dx.doi.org/10.1007/s10689-017-0008-8DOI Listing
January 2018

Glutaminase and poly(ADP-ribose) polymerase inhibitors suppress pyrimidine synthesis and VHL-deficient renal cancers.

J Clin Invest 2017 May 27;127(5):1631-1645. Epub 2017 Mar 27.

Many cancer-associated mutations that deregulate cellular metabolic responses to hypoxia also reprogram carbon metabolism to promote utilization of glutamine. In renal cell carcinoma (RCC), cells deficient in the von Hippel-Lindau (VHL) tumor suppressor gene use glutamine to generate citrate and lipids through reductive carboxylation (RC) of α-ketoglutarate (αKG). Glutamine can also generate aspartate, the carbon source for pyrimidine biosynthesis, and glutathione for redox balance. Here we have shown that VHL-/- RCC cells rely on RC-derived aspartate to maintain de novo pyrimidine biosynthesis. Glutaminase 1 (GLS1) inhibitors depleted pyrimidines and increased ROS in VHL-/- cells but not in VHL+/+ cells, which utilized glucose oxidation for glutamate and aspartate production. GLS1 inhibitor-induced nucleoside depletion and ROS enhancement led to DNA replication stress and activation of an intra-S phase checkpoint, and suppressed the growth of VHL-/- RCC cells. These effects were rescued by administration of glutamate, αKG, or nucleobases with N-acetylcysteine. Further, we observed that the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib synergizes with GLS1 inhibitors to suppress the growth of VHL-/- cells in vitro and in vivo. This work describes a mechanism that explains the sensitivity of RCC tumor growth to GLS1 inhibitors and supports the development of therapeutic strategies for targeting VHL-deficient RCC.
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http://dx.doi.org/10.1172/JCI87800DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5409089PMC
May 2017

Assessment of Overall Survival, Quality of Life, and Safety Benefits Associated With New Cancer Medicines.

JAMA Oncol 2017 Mar;3(3):382-390

London School of Economics and Political Science, London, England4Institute of Global Health Innovation, Imperial College London, South Kensington Campus, London, England.

Importance: There is a dearth of evidence examining the impact of newly licensed cancer medicines on therapy. This information could otherwise support clinical practice, and promote value-based decision-making in the cancer drug market.

Objective: To evaluate the comparative therapeutic value of all new cancer medicines approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) between 2003 and 2013.

Design, Setting, And Participants: We used a narrative synthesis approach to systematically synthesize and analyze English, French, and Australian health technology assessments (HTAs) of all new cancer medicines licensed in the United States and Europe between 2003 and 2013.

Interventions: Sixty-two new molecular entities with a primary oncology indication.

Main Outcomes And Measures: Overall survival (OS), quality of life (QoL), and safety.

Results: Of the 62 new active cancer molecules approved by the FDA and EMA between 2003 and 2013, 53 were appraised by English, French, or Australian HTA agencies through May 2015. Of these 53 drugs, 23 (43%) increased OS by 3 months or longer, 6 (11%) by less than 3 months, and 8 (15%) by an unknown magnitude; there was no evidence to suggest that the remaining 16 (30%) increased OS over best alternative treatments. Where overall survival gains could be quantified, all new cancer drugs were associated with a mean (SE) total increase in OS of 3.43 (0.63) months over the treatments that were available in 2003. Drug-related improvements in OS were, however, widely distributed across therapeutic targets-ranging between 0 (thyroid, ascites) and 8.48 months (breast cancers)-and were sometimes based on modeled data, indirect or nonactive comparisons, or nonvalidated evidence. Although 22 (42%) of 53 new medicines were associated with an increase in QoL, 24 (45%) were also associated with reduced patient safety. Of the 53 new cancer drugs, 42 (79%) were associated with at least some improvement in OS, QoL, or safety.

Conclusions And Relevance: Although innovation in the oncology drug market has contributed to improvements in therapy, the magnitude and dimension of clinical benefits vary widely, and there may be reasons to doubt that claims of efficacy reflect real-world effectiveness exactly. These findings raise important questions for clinical decision-making and value-based policy.
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http://dx.doi.org/10.1001/jamaoncol.2016.4166DOI Listing
March 2017

Metabolic requirements for cancer cell proliferation.

Cancer Metab 2016 18;4:16. Epub 2016 Aug 18.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.

Background: The study of cancer metabolism has been largely dedicated to exploring the hypothesis that oncogenic transformation rewires cellular metabolism to sustain elevated rates of growth and division. Intense examination of tumors and cancer cell lines has confirmed that many cancer-associated metabolic phenotypes allow robust growth and survival; however, little attention has been given to explicitly identifying the biochemical requirements for cell proliferation in a rigorous manner in the context of cancer metabolism.

Results: Using a well-studied hybridoma line as a model, we comprehensively and quantitatively enumerate the metabolic requirements for generating new biomass in mammalian cells; this indicated a large biosynthetic requirement for ATP, NADPH, NAD(+), acetyl-CoA, and amino acids. Extension of this approach to serine/glycine and glutamine metabolic pathways suggested lower limits on serine and glycine catabolism to supply one-carbon unit synthesis and significant availability of glutamine-derived carbon for biosynthesis resulting from nitrogen demands alone, respectively. We integrated our biomass composition results into a flux balance analysis model, placing upper bounds on mitochondrial NADH oxidation to simulate metformin treatment; these simulations reproduced several empirically observed metabolic phenotypes, including increased reductive isocitrate dehydrogenase flux.

Conclusions: Our analysis clarifies the differential needs for central carbon metabolism precursors, glutamine-derived nitrogen, and cofactors such as ATP, NADPH, and NAD(+), while also providing justification for various extracellular nutrient uptake behaviors observed in tumors. Collectively, these results demonstrate how stoichiometric considerations alone can successfully predict empirically observed phenotypes and provide insight into biochemical dynamics that underlie responses to metabolic perturbations.
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http://dx.doi.org/10.1186/s40170-016-0156-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989334PMC
August 2016

Loss of vhl in the zebrafish pronephros recapitulates early stages of human clear cell renal cell carcinoma.

Dis Model Mech 2016 08;9(8):873-84

Center for Cancer Research, Massachusetts General Hospital, Boston, MA 02114, USA Department of Medicine, Harvard Medical School, Boston, MA 02115, USA Division of Hematology-Oncology, Department of Medicine, Massachusetts General Hospital, Boston, MA 02142, USA

Patients with von Hippel-Lindau (VHL) disease harbor a germline mutation in the VHL gene leading to the development of several tumor types including clear cell renal cell carcinoma (ccRCC). In addition, the VHL gene is inactivated in over 90% of sporadic ccRCC cases. 'Clear cell' tumors contain large, proliferating cells with 'clear cytoplasm', and a reduced number of cilia. VHL inactivation leads to the stabilization of hypoxia inducible factors 1a and 2a [HIF1a and HIF2a (HIF2a is also known as EPAS1)] with consequent up-regulation of specific target genes involved in cell proliferation, angiogenesis and erythropoiesis. A zebrafish model with a homozygous inactivation in the VHL gene (vhl(-/-)) recapitulates several aspects of the human disease, including development of highly vascular lesions in the brain and the retina and erythrocytosis. Here, we characterize for the first time the epithelial abnormalities present in the kidney of the vhl(-/-) zebrafish larvae as a first step in building a model of ccRCC in zebrafish. Our data show that the vhl(-/-) zebrafish kidney is characterized by an increased tubule diameter, disorganized cilia, the dramatic formation of cytoplasmic lipid vesicles, glycogen accumulation, aberrant cell proliferation and abnormal apoptosis. This phenotype of the vhl(-/-) pronephros is reminiscent of clear cell histology, indicating that the vhl(-/-) mutant zebrafish might serve as a model of early stage RCC. Treatment of vhl(-/-) zebrafish embryos with a small-molecule HIF2a inhibitor rescued the pronephric abnormalities, underscoring the value of the zebrafish model in drug discovery for treatment of VHL disease and ccRCC.
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http://dx.doi.org/10.1242/dmm.024380DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5007981PMC
August 2016

HIF2a inhibitors for the treatment of VHL disease.

Oncotarget 2015 Sep;6(27):23036-7

Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, MA, USA.

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http://dx.doi.org/10.18632/oncotarget.4564DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4695098PMC
September 2015

Hypoxia drives transient site-specific copy gain and drug-resistant gene expression.

Genes Dev 2015 May;29(10):1018-31

Massachusetts General Hospital Cancer Center, Department of Medicine, Harvard Medical School, Charlestown, Massachusetts 02129, USA;

Copy number heterogeneity is a prominent feature within tumors. The molecular basis for this heterogeneity remains poorly characterized. Here, we demonstrate that hypoxia induces transient site-specific copy gains (TSSGs) in primary, nontransformed, and transformed human cells. Hypoxia-driven copy gains are not dependent on HIF1α or HIF2α; however, they are dependent on the KDM4A histone demethylase and are blocked by inhibition of KDM4A with a small molecule or the natural metabolite succinate. Furthermore, this response is conserved at a syntenic region in zebrafish cells. Regions with site-specific copy gain are also enriched for amplifications in hypoxic primary tumors. These tumors exhibited amplification and overexpression of the drug resistance gene CKS1B, which we recapitulated in hypoxic breast cancer cells. Our results demonstrate that hypoxia provides a biological stimulus to create transient site-specific copy alterations that could result in heterogeneity within tumors and cell populations. These findings have major implications in our understanding of copy number heterogeneity and the emergence of drug resistance genes in cancer.
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http://dx.doi.org/10.1101/gad.259796.115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4441050PMC
May 2015

Pharmacological HIF2α inhibition improves VHL disease-associated phenotypes in zebrafish model.

J Clin Invest 2015 May 13;125(5):1987-97. Epub 2015 Apr 13.

Patients with a germline mutation in von Hippel-Lindau (VHL) develop renal cell cancers and hypervascular tumors of the brain, adrenal glands, and pancreas as well as erythrocytosis. These phenotypes are driven by aberrant expression of HIF2α, which induces expression of genes involved in cell proliferation, angiogenesis, and red blood cell production. Currently, there are no effective treatments available for VHL disease. Here, using an animal model of VHL, we report a marked improvement of VHL-associated phenotypes following treatment with HIF2α inhibitors. Inactivation of vhl in zebrafish led to constitutive activation of HIF2α orthologs and modeled several aspects of the human disease, including erythrocytosis, pathologic angiogenesis in the brain and retina, and aberrant kidney and liver proliferation. Treatment of vhl(-/-) mutant embryos with HIF2α-specific inhibitors downregulated Hif target gene expression in a dose-dependent manner, improved abnormal hematopoiesis, and substantially suppressed erythrocytosis and angiogenic sprouting. Moreover, pharmacologic inhibition of HIF2α reversed the compromised cardiac contractility of vhl(-/-) embryos and partially rescued early lethality. This study demonstrates that small-molecule targeting of HIF2α improves VHL-related phenotypes in a vertebrate animal model and supports further exploration of this strategy for treating VHL disease.
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http://dx.doi.org/10.1172/JCI73665DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4463187PMC
May 2015

Clusterin glycopeptide variant characterization reveals significant site-specific glycan changes in the plasma of clear cell renal cell carcinoma.

J Proteome Res 2015 Jun 11;14(6):2425-36. Epub 2015 May 11.

⊥Center for Cancer Research at Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, United States.

Cancer-related alterations in protein glycosylation may serve as diagnostic or prognostic biomarkers or may be used for monitoring disease progression. Clusterin is a medium abundance, yet heavily glycosylated, glycoprotein that is upregulated in clear cell renal cell carcinoma (ccRCC) tumors. We recently reported that the N-glycan profile of clusterin is altered in the plasma of ccRCC patients. Here, we characterized the occupancy and the degree of heterogeneity of individual N-glycosylation sites of clusterin in the plasma of patients diagnosed with localized ccRCC, before and after curative nephrectomy (n = 40). To this end, we used tandem mass spectrometry of immunoaffinity-enriched plasma samples to analyze the individual glycosylation sites in clusterin. We determined the levels of targeted clusterin glycoforms containing either a biantennary digalactosylated disialylated (A2G2S2) glycan or a core fucosylated biantennary digalactosylated disialylated (FA2G2S2) glycan at N-glycosite N374. We showed that the presence of these two clusterin glycoforms differed significantly in the plasma of patients prior to and after curative nephrectomy for localized ccRCC. Removal of ccRCC led to a significant increase in the levels of both FA2G2S2 and A2G2S2 glycans in plasma clusterin. These changes were further confirmed by lectin blotting of plasma clusterin. It is envisioned that these identified glycan alterations may provide an additional level of therapeutic or biomarker sensitivity than levels currently achievable by monitoring expression differences alone.
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http://dx.doi.org/10.1021/pr501104jDOI Listing
June 2015

Comparative studies of the proteome, glycoproteome, and N-glycome of clear cell renal cell carcinoma plasma before and after curative nephrectomy.

J Proteome Res 2014 Nov 10;13(11):4889-900. Epub 2014 Sep 10.

Barnett Institute and Department of Chemistry and Chemical Biology, Northeastern University , 360 Huntington Avenue, Boston, Massachusetts 02115, United States.

Clear cell renal cell carcinoma is the most prevalent of all reported kidney cancer cases, and currently there are no markers for early diagnosis. This has stimulated great research interest recently because early detection of the disease can significantly improve the low survival rate. Combining the proteome, glycoproteome, and N-glycome data from clear cell renal cell carcinoma plasma has the potential of identifying candidate markers for early diagnosis and prognosis and/or to monitor disease recurrence. Here, we report on the utilization of a multi-dimensional fractionation approach (12P-M-LAC) and LC-MS/MS to comprehensively investigate clear cell renal cell carcinoma plasma collected before (disease) and after (non-disease) curative nephrectomy (n = 40). Proteins detected in the subproteomes were investigated via label-free quantification. Protein abundance analysis revealed a number of low-level proteins with significant differential expression levels in disease samples, including HSPG2, CD146, ECM1, SELL, SYNE1, and VCAM1. Importantly, we observed a strong correlation between differentially expressed proteins and clinical status of the patient. Investigation of the glycoproteome returned 13 candidate glycoproteins with significant differential M-LAC column binding. Qualitative analysis indicated that 62% of selected candidate glycoproteins showed higher levels (upregulation) in M-LAC bound fraction of disease samples. This observation was further confirmed by released N-glycans data in which 53% of identified N-glycans were present at different levels in plasma in the disease vs non-disease samples. This striking result demonstrates the potential for significant protein glycosylation alterations in clear cell renal cell carcinoma cancer plasma. With future validation in a larger cohort, information derived from this study may lead to the development of clear cell renal cell carcinoma candidate biomarkers.
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http://dx.doi.org/10.1021/pr500591eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4227548PMC
November 2014

Human folliculin delays cell cycle progression through late S and G2/M-phases: effect of phosphorylation and tumor associated mutations.

PLoS One 2013 11;8(7):e66775. Epub 2013 Jul 11.

Center for Cancer Research at The Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts, United States of America.

The Birt-Hogg-Dube disease occurs as a result of germline mutations in the human Folliculin gene (FLCN), and is characterized by clinical features including fibrofolliculomas, lung cysts and multifocal renal neoplasia. Clinical and genetic evidence suggest that FLCN acts as a tumor suppressor gene. The human cell line UOK257, derived from the renal cell carcinoma of a patient with a germline mutation in the FLCN gene, harbors a truncated version of the FLCN protein. Reconstitution of the wild type FLCN protein into UOK257 cells delays cell cycle progression, due to a slower progression through the late S and G2/M-phases. Similarly, Flcn (-/-) mouse embryonic fibroblasts progress more rapidly through the cell cycle than wild type controls (Flcn (flox/flox)). The reintroduction of tumor-associated FLCN mutants (FLCN ΔF157, FLCN 1-469 or FLCN K508R) fails to delay cell cycle progression in UOK257 cells. Additionally, FLCN phosphorylation (on Serines 62 and 73) fluctuates throughout the cell cycle and peaks during the G2/M phase in cells treated with nocodazole. In keeping with this observation, the reintroduction of a FLCN phosphomimetic mutant into the UOK257 cell line results in faster progression through the cell cycle compared to those expressing the wild type FLCN protein. These findings suggest that the tumor suppression function of FLCN may be linked to its impact on the cell cycle and that FLCN phosphorylation is important for this activity. Additionally, these observations describe a novel in vitro assay for testing the functional significance of FLCN mutations and/or genetic polymorphisms.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0066775PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708955PMC
April 2014

Cofactor balance by nicotinamide nucleotide transhydrogenase (NNT) coordinates reductive carboxylation and glucose catabolism in the tricarboxylic acid (TCA) cycle.

J Biol Chem 2013 May 15;288(18):12967-77. Epub 2013 Mar 15.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Cancer and proliferating cells exhibit an increased demand for glutamine-derived carbons to support anabolic processes. In addition, reductive carboxylation of α-ketoglutarate by isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) was recently shown to be a major source of citrate synthesis from glutamine. The role of NAD(P)H/NAD(P)(+) cofactors in coordinating glucose and glutamine utilization in the tricarboxylic acid (TCA) cycle is not well understood, with the source(s) of NADPH for the reductive carboxylation reaction remaining unexplored. Nicotinamide nucleotide transhydrogenase (NNT) is a mitochondrial enzyme that transfers reducing equivalents from NADH to NADPH. Here, we show that knockdown of NNT inhibits the contribution of glutamine to the TCA cycle and activates glucose catabolism in SkMel5 melanoma cells. The increase in glucose oxidation partially occurred through pyruvate carboxylase and rendered NNT knockdown cells more sensitive to glucose deprivation. Importantly, knocking down NNT inhibits reductive carboxylation in SkMel5 and 786-O renal carcinoma cells. Overexpression of NNT is sufficient to stimulate glutamine oxidation and reductive carboxylation, whereas it inhibits glucose catabolism in the TCA cycle. These observations are supported by an impairment of the NAD(P)H/NAD(P)(+) ratios. Our findings underscore the role of NNT in regulating central carbon metabolism via redox balance, calling for other mechanisms that coordinate substrate preference to maintain a functional TCA cycle.
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http://dx.doi.org/10.1074/jbc.M112.396796DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3642339PMC
May 2013

In vivo HIF-mediated reductive carboxylation is regulated by citrate levels and sensitizes VHL-deficient cells to glutamine deprivation.

Cell Metab 2013 Mar;17(3):372-85

Center for Cancer Research, Massachusetts General Hospital Cancer Center, Charlestown, MA 02129, USA.

Hypoxic and VHL-deficient cells use glutamine to generate citrate and lipids through reductive carboxylation (RC) of α-ketoglutarate. To gain insights into the role of HIF and the molecular mechanisms underlying RC, we took advantage of a panel of disease-associated VHL mutants and showed that HIF expression is necessary and sufficient for the induction of RC in human renal cell carcinoma (RCC) cells. HIF expression drastically reduced intracellular citrate levels. Feeding VHL-deficient RCC cells with acetate or citrate or knocking down PDK-1 and ACLY restored citrate levels and suppressed RC. These data suggest that HIF-induced low intracellular citrate levels promote the reductive flux by mass action to maintain lipogenesis. Using [(1-13)C]glutamine, we demonstrated in vivo RC activity in VHL-deficient tumors growing as xenografts in mice. Lastly, HIF rendered VHL-deficient cells sensitive to glutamine deprivation in vitro, and systemic administration of glutaminase inhibitors suppressed the growth of RCC cells as mice xenografts.
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http://dx.doi.org/10.1016/j.cmet.2013.02.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4003458PMC
March 2013

Loss of RBF1 changes glutamine catabolism.

Genes Dev 2013 Jan 15;27(2):182-96. Epub 2013 Jan 15.

Laboratory of Molecular Oncology, Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts 02129, USA.

Inactivation of the retinoblastoma tumor suppressor (pRB) alters the expression of a myriad of genes. To understand the altered cellular environment that these changes create, we took advantage of the Drosophila model system and used targeted liquid chromatography tandem mass spectrometry (LC-MS/MS) to profile the metabolic changes that occur when RBF1, the fly ortholog of pRB, is removed. We show that RBF1-depleted tissues and larvae are sensitive to fasting. Depletion of RBF1 causes major changes in nucleotide synthesis and glutathione metabolism. Under fasting conditions, these changes interconnect, and the increased replication demand of RBF1-depleted larvae is associated with the depletion of glutathione pools. In vivo (13)C isotopic tracer analysis shows that RBF1-depleted larvae increase the flux of glutamine toward glutathione synthesis, presumably to minimize oxidative stress. Concordantly, H(2)O(2) preferentially promoted apoptosis in RBF1-depleted tissues, and the sensitivity of RBF1-depleted animals to fasting was specifically suppressed by either a glutamine supplement or the antioxidant N-acetyl-cysteine. Effects of pRB activation/inactivation on glutamine catabolism were also detected in human cell lines. These results show that the inactivation of RB proteins causes metabolic reprogramming and that these consequences of RBF/RB function are present in both flies and human cell lines.
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http://dx.doi.org/10.1101/gad.206227.112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3566311PMC
January 2013

Multidimensional liquid chromatography platform for profiling alterations of clusterin N-glycosylation in the plasma of patients with renal cell carcinoma.

J Chromatogr A 2012 Sep 28;1256:121-8. Epub 2012 Jul 28.

Department of Chemistry and Chemical Biology, Barnett Institute, Northeastern University, Boston, MA 02115, USA.

Identification of potential changes in the glycosylation of existing cancer biomarkers can result in a higher level of diagnostic sensitivity and specificity. Clusterin (Apolipoprotein J) has been implicated in renal cell carcinoma (RCC) and other types of malignancy as potential biomarker. In the present work, an automated multi-dimensional HPLC platform enabling high throughput affinity enrichment of clusterin from plasma samples was developed. Integrated with two dimensional gel electrophoresis, high purity clusterin in microgram quantities suitable for glycan characterization was isolated. The analytical platform was applied to study clusterin glycosylation in a small group of RCC patients before and after nephrectopy as a pilot study to evaluate the performance of the platform. A statistically significant decrease was observed in the levels of a bi-antennary digalactosyl disialylated (A2G2S(3)2) glycans while the levels of a core fucosylated bi-antennary digalactosyl disialylated glycan (FA2G2S(6)2) and a tri-antennary trigalactosyl disialylated glycan (A3G3S(6)2) were increased in the post-surgery plasma samples.
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http://dx.doi.org/10.1016/j.chroma.2012.07.066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4392643PMC
September 2012

Epithelial cell guidance by self-generated EGF gradients.

Integr Biol (Camb) 2012 Mar 8;4(3):259-69. Epub 2012 Feb 8.

Surgical Services and BioMEMS Resource Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.

Cancer epithelial cells often migrate away from the primary tumor to invade into the surrounding tissues. Their migration is commonly assumed to be directed by pre-existent spatial gradients of chemokines and growth factors in the target tissues. Unexpectedly however, we found that the guided migration of epithelial cells is possible in vitro in the absence of pre-existent chemical gradients. We observed that both normal and cancer epithelial cells can migrate persistently and reach the exit along the shortest path from microscopic mazes filled with uniform concentrations of media. Using microscale engineering techniques and biophysical models, we uncovered a self-guidance strategy during which epithelial cells generate their own guiding cues under conditions of biochemical confinement. The self-guidance strategy depends on the balance between three interdependent processes: epidermal growth factor (EGF) uptake by the cells (U), the restricted transport of EGF through the structured microenvironment (T), and cell chemotaxis toward the resultant EGF gradients (C). The UTC self-guidance strategy can be perturbed by inhibition of signalling through EGF-receptors and appears to be independent from chemokine signalling. Better understanding of the UTC self-guidance strategy could eventually help devise new ways for modulating epithelial cell migration and delaying cancer cell invasion or accelerating wound healing.
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http://dx.doi.org/10.1039/c2ib00106cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3440622PMC
March 2012

Reductive glutamine metabolism by IDH1 mediates lipogenesis under hypoxia.

Nature 2011 Nov 20;481(7381):380-4. Epub 2011 Nov 20.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Acetyl coenzyme A (AcCoA) is the central biosynthetic precursor for fatty-acid synthesis and protein acetylation. In the conventional view of mammalian cell metabolism, AcCoA is primarily generated from glucose-derived pyruvate through the citrate shuttle and ATP citrate lyase in the cytosol. However, proliferating cells that exhibit aerobic glycolysis and those exposed to hypoxia convert glucose to lactate at near-stoichiometric levels, directing glucose carbon away from the tricarboxylic acid cycle and fatty-acid synthesis. Although glutamine is consumed at levels exceeding that required for nitrogen biosynthesis, the regulation and use of glutamine metabolism in hypoxic cells is not well understood. Here we show that human cells use reductive metabolism of α-ketoglutarate to synthesize AcCoA for lipid synthesis. This isocitrate dehydrogenase-1 (IDH1)-dependent pathway is active in most cell lines under normal culture conditions, but cells grown under hypoxia rely almost exclusively on the reductive carboxylation of glutamine-derived α-ketoglutarate for de novo lipogenesis. Furthermore, renal cell lines deficient in the von Hippel-Lindau tumour suppressor protein preferentially use reductive glutamine metabolism for lipid biosynthesis even at normal oxygen levels. These results identify a critical role for oxygen in regulating carbon use to produce AcCoA and support lipid synthesis in mammalian cells.
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http://dx.doi.org/10.1038/nature10602DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3710581PMC
November 2011

Immunoaffinity enrichment and liquid chromatography-selected reaction monitoring mass spectrometry for quantitation of carbonic anhydrase 12 in cultured renal carcinoma cells.

Anal Chem 2010 Nov 11;82(21):8998-9005. Epub 2010 Oct 11.

The Barnett Institute of Chemical and Biological Analysis of Northeastern University, Boston, Massachusetts, United States, Massachusetts General Hospital Cancer Center, Boston, Massachusetts, United States, and Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts, United States.

Liquid chromatography-selected reaction monitoring (LC-SRM) is a highly specific and sensitive mass spectrometry (MS) technique that is widely being applied to selectively qualify and validate candidate markers within complex biological samples. However, in order for LC-SRM methods to take on these attributes, target-specific optimization of sample processing is required, in order to reduce analyte complexity, prior to LC-SRM. In this study, we have developed a targeted platform consisting of protein immunoaffinity enrichment on magnetic beads and LC-SRM for measuring carbonic anhydrase 12 (CA12) protein in a renal cell carcinoma (RCC) cell line (PRC3), a candidate biomarker for RCC whose expression at the protein level has not been previously reported. Sample processing and LC-SRM assay were optimized for signature peptides selected as surrogate markers of CA12 protein. Using LC-SRM coupled with stable isotope dilution, we achieved limits of quantitation in the low fmol range sufficient for measuring clinically relevant biomarkers with good intra- and interassay accuracy and precision (≤17%). Our results show that using a quantitative immunoaffinity capture approach provides specific, accurate, and robust assays amenable to high-throughput verification of potential biomarkers.
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http://dx.doi.org/10.1021/ac101981tDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046293PMC
November 2010

The connectivity map links iron regulatory protein-1-mediated inhibition of hypoxia-inducible factor-2a translation to the anti-inflammatory 15-deoxy-delta12,14-prostaglandin J2.

Cancer Res 2010 Apr 30;70(8):3071-9. Epub 2010 Mar 30.

Center for Cancer Research, Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, USA.

Hypoxia-inducible factors 1 and 2 (HIF1 and HIF2) are heterodimeric transcription factors consisting of alpha regulatory subunits and a constitutively expressed beta subunit. The expression of alpha regulatory subunits is promoted by hypoxia, cancer-associated mutations, and inflammatory cytokines. Thus, HIF1 and HIF2 provide a molecular link between cancer and inflammation. We have recently identified novel small molecules that selectively inhibit translation of the HIF2a message and thereby powerfully inhibit the expression of HIF2a target genes. We report here that Connectivity Map analysis links three of these compounds to the anti-inflammatory cytokine 15-deoxy-Delta(12,14)-prostaglandin J(2) (PGJ(2)). As with our identified compounds, PGJ(2) inhibits translation of the HIF2a message in a mammalian target of rapamycin-independent manner by promoting the binding of iron regulatory protein-1 (IRP1) to a noncanonical iron responsive element (IRE) embedded within the 5'-untranslated region of the HIF2a message. The IRE is necessary and sufficient for mediating the effect. Mutation of the IRE sequence, or downregulation of IRP1 expression, blocks the effect of PGJ(2) on HIF2a translation. This is the first report of an endogenous natural molecule regulating HIF2a translation, and it suggests that part of the anti-inflammatory and putative antineoplastic effects of PGJ(2) may be mediated through inhibition of HIF2a within tumor epithelial cells themselves and/or mesenchymal cells of the tumor microenvironment.
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http://dx.doi.org/10.1158/0008-5472.CAN-09-2877DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2861799PMC
April 2010

The histone deacetylase Sirt6 regulates glucose homeostasis via Hif1alpha.

Cell 2010 Jan;140(2):280-93

The Massachusetts General Hospital Cancer Center, Harvard Medical School, Boston, MA 02114, USA.

SIRT6 is a member of a highly conserved family of NAD(+)-dependent deacetylases with various roles in metabolism, stress resistance, and life span. SIRT6-deficient mice develop normally but succumb to a lethal hypoglycemia early in life; however, the mechanism underlying this hypoglycemia remained unclear. Here, we demonstrate that SIRT6 functions as a histone H3K9 deacetylase to control the expression of multiple glycolytic genes. Specifically, SIRT6 appears to function as a corepressor of the transcription factor Hif1alpha, a critical regulator of nutrient stress responses. Consistent with this notion, SIRT6-deficient cells exhibit increased Hif1alpha activity and show increased glucose uptake with upregulation of glycolysis and diminished mitochondrial respiration. Our studies uncover a role for the chromatin factor SIRT6 as a master regulator of glucose homeostasis and may provide the basis for novel therapeutic approaches against metabolic diseases, such as diabetes and obesity.
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http://dx.doi.org/10.1016/j.cell.2009.12.041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821045PMC
January 2010

Small-molecule inhibitors of HIF-2a translation link its 5'UTR iron-responsive element to oxygen sensing.

Mol Cell 2008 Dec;32(6):838-48

Department of Medicine, Hematology-Oncology Unit, Massachusetts General Hospital, Boston, MA 02114, USA.

Cells transiently adapt to hypoxia by globally decreasing protein translation. However, specific proteins needed to respond to hypoxia evade this translational repression. The mechanisms of this phenomenon remain unclear. We screened for and identified small molecules that selectively decrease HIF-2a translation in an mTOR-independent manner, by enhancing the binding of Iron-Regulatory Protein 1 (IRP1) to a recently reported iron-responsive element (IRE) within the 5'-untranslated region (UTR) of the HIF-2a message. Knocking down the expression of IRP1 by shRNA abolished the effect of the compounds. Hypoxia derepresses HIF-2a translation by disrupting the IRP1-HIF-2a IRE interaction. Thus, this chemical genetic analysis describes a molecular mechanism by which translation of the HIF-2a message is maintained during conditions of cellular hypoxia through inhibition of IRP-1-dependent repression. It also provides the chemical tools for studying this phenomenon.
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http://dx.doi.org/10.1016/j.molcel.2008.12.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978139PMC
December 2008
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