1,721,055 research outputs found
Primary and metastatic tumors exhibit systems-level differences in dependence on mitochondrial respiratory function
No full textThe Warburg effect, aerobic glycolysis, is a hallmark feature of cancer cells grown in culture. However, the relative roles of glycolysis and respiratory metabolism in supporting in vivo tumor growth and processes such as tumor dissemination and metastatic growth remain poorly understood, particularly on a systems level. Using a CRISPRi mini-library enriched for mitochondrial ribosomal protein and respiratory chain genes in multiple human lung cancer cell lines, we analyzed in vivo metabolic requirements in xenograft tumors grown in distinct anatomic contexts. While knockdown of mitochondrial ribosomal protein and respiratory chain genes (mito-respiratory genes) has little impact on growth in vitro, tumor cells depend heavily on these genes when grown in vivo as either flank or primary orthotopic lung tumor xenografts. In contrast, respiratory function is comparatively dispensable for metastatic tumor growth. RNA-Seq and metabolomics analysis of tumor cells expressing individual sgRNAs against mito-respiratory genes indicate overexpression of glycolytic genes and increased sensitivity of glycolytic inhibition compared to control when grown in vitro, but when grown in vivo as primary tumors these cells down-regulate glycolytic mechanisms. These studies demonstrate that discrete perturbations of mitochondrial respiratory chain function impact in vivo tumor growth in a context-specific manner with differential impacts on primary and metastatic tumors
Glutamine deficiency induces DNA alkylation damage and sensitizes cancer cells to alkylating agents through inhibition of ALKBH enzymes.
No full textDriven by oncogenic signaling, glutamine addiction exhibited by cancer cells often leads to severe glutamine depletion in solid tumors. Despite this nutritional environment that tumor cells often experience, the effect of glutamine deficiency on cellular responses to DNA damage and chemotherapeutic treatment remains unclear. Here, we show that glutamine deficiency, through the reduction of alpha-ketoglutarate, inhibits the AlkB homolog (ALKBH) enzymes activity and induces DNA alkylation damage. As a result, glutamine deprivation or glutaminase inhibitor treatment triggers DNA damage accumulation independent of cell death. In addition, low glutamine-induced DNA damage is abolished in ALKBH deficient cells. Importantly, we show that glutaminase inhibitors, 6-Diazo-5-oxo-L-norleucine (DON) or CB-839, hypersensitize cancer cells to alkylating agents both in vitro and in vivo. Together, the crosstalk between glutamine metabolism and the DNA repair pathway identified in this study highlights a potential role of metabolic stress in genomic instability and therapeutic response in cancer
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Viral Reprogramming of Metabolism as an Approach to Identify Metabolic Vulnerabilities in Cancer
Get PDFCancer cells and viruses reprogram cell metabolism towards increased nutrient uptakeand anabolism. Unlike cancer cells, viruses undergo intense selection for efficiency, onlyupregulating metabolic nodes critical for their rapid replication. Viruses are therefore powerfultools to identify essential metabolic pathways in cancer cells. A previous study from our labreported that adenovirus infection increases host cell anabolic glucose metabolism. Specificglycolytic genes are activated by binding of viral protein E4ORF1 with cellular transcriptionfactor MYC, which is upregulated in many cancers. Here, we show that adenovirus infectionalso upregulates glutamine metabolism through E4ORF1-induced MYC activation, leading toincreased levels of glutaminase and glutamine transporters. Inhibition of glutaminase reducesoptimal replication of adenovirus and other diverse viruses, including HSV-1 and influenza.Glutaminase inhibitors are also currently in clinical trials to treat certain types of cancers. Thisstudy serves as a proof-of-principle that metabolic enzymes and pathways important for adenovirus infection converge on critical metabolic enzymes in cancer.The specific compilation of metabolic genes altered by adenovirus infection, that mayalso be critical for cancer cell proliferation, is currently undefined. We find that adenovirusinfection leads to upregulation of an enzyme involved in fructose metabolism, ketohexokinase,which supports optimal virus replication and lung tumor growth. We further show that lungcancer cells can convert glucose via the polyol pathway into fructose, which can then bemetabolized by ketohexokinase. Our model for how ketohexokinase promotes anabolism is byallowing cells to bypass negative feedback on a heavily regulated enzyme in glycolysis,phosphofructokinase, and allowing increased glucose utilization into nucleotides. Since KHKdeficiency is a clinically benign, targeting KHK in lung cancer have limited systemic toxicities in patients.Finally, numerous viruses in addition to adenovirus have been found to reprogram host cell metabolism, but whether the flavivirus Zika virus alters metabolism and whether viruses have unique effects on different host cells remains unclear. We find that Zika virus differentially alters glucose metabolism in both human cells and mosquito cells by increasing glucose use in the TCA cycle in human cells, while increasing glucose utilization into the pentose phosphate pathway in mosquito cells. Zika virus infection of human cells leads to selective depletion of nucleotide triphosphates, leading to AMP-activated protein kinase activation and cell death. Our findings suggest that the differential metabolic reprogramming during Zika virus infection of human versus mosquito cells determines whether or not cell death occurs and demonstrates that viruses can have contrasting effects depending on the host cell. Taken together, this dissertation (i) describes virally induced metabolic changes in both adenovirus and Zika virus and (ii) utilizes the evolutionary efficiency of adenovirus infection as an approach to identify important metabolic enzymes in anabolism and cancer
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Glycolytic Metabolism Plays a Functional Role in Regulating Human Pluripotent Stem Cell State
Get PDFThe rate of glycolytic metabolism changes during differentiation of human embryonic stem cells (hESCs) and reprogramming of somatic cells to pluripotent stem cells. However, the functional contribution of glycolytic metabolism to pluripotency is unclear. Here we show that the degree of pluripotency is associated with glycolytic rate, whereby naive hESCs exhibit increased glycolytic flux, MYC transcriptional activity, and nuclear localization of N-MYC relative to primed hESCs. This is consistent with the inner cell mass of human blastocysts which exhibit increased MYC transcriptional activity relative primed hESCs and elevated nuclear N-MYC levels. Reduction of glycolysis decreases self-renewal of naive hESCs and feeder-free cultured primed hESCs, but not primed hESCs grown in feeder-supported conditions. Reduction of glycolysis in feeder-free primed hESCs also enhances neural specification. These findings reveal associations between glycolytic metabolism and the state of pluripotency, differences in the metabolism of feeder- versus feeder-free cultured hESCs, and identify methods for regulating self-renewal and initial cell fate specification of hESCs
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Hyaluronidase Promotes Glucose Metabolism: Identification of the Extracellular Matrix as a Node of Cell-Extrinsic Metabolic Regulation
Get PDFThe metabolic state of a cell can be determined by cell-extrinsic factors, including nutrient availability and growth factor signaling. Here, we define extracellular matrix (ECM) remodeling as another fundamental node of cell-extrinsic metabolic regulation. Unbiased analysis of glycolytic drivers identified the hyaluronan-mediated motility receptor as among the most highly correlated with glycolysis in cancer. Confirming a mechanistic link between the ECM glycosaminoglycan hyaluronan and metabolism, treatment of cells with hyaluronidase (HAase) triggers a robust increase in glycolysis. This is largely achieved through rapid receptor tyrosine kinase-mediated induction of mRNA decay factor ZFP36, which targets TXNIP transcripts for degradation. Since TXNIP promotes internalization of the glucose transporter GLUT1, its acute decline liberates GLUT1 to the plasma membrane. In fibroblasts, the rapid induction of glycolysis induced by HAase is necessary for a concomitant increase in migration. Both tumor cross-sections and early mammalian embryos exhibit a ZFP36- and TXNIP-mediated interconnection between extracellular matrix remodeling and metabolism in vivo. In a subset of cells, HAase has sustained metabolic effects that track with changes in cell identity. HAase treatment of LiSa-2 liposarcoma cells led to the identification of GLUT1 as a target of sialylation—the addition of a sialic acid residue as the terminal monosaccharide of its N-glycan linkage. Increases in this modification coincide with the transcriptional upregulation of various sialyltransferases. Consistent with previous reports that sialylation is upregulated as part of the epithelial-to-mesenchymal transition (EMT), the gene expression profile of HAase-treated cells closely resembles that of both EMT in breast cancer cells and the dedifferentiated state in melanoma. This change in the transcriptional state of the cell is accompanied by stable metabolic and epigenetic reprogramming
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Monocarboxylate Transporter 1 modulates cancer cell pyruvate export and tumor growth
Get PDFMany cancers rely on glycolytic metabolism to fuel rapid proliferation. This has spurred interest in designing drugs that target tumor glycolysis such as AZD3965, a small molecule inhibitor of Monocarboxylate Transporter 1 (MCT1) currently undergoing Phase I evaluation for cancer treatment. Since MCT1 mediates proton-linked transport of monocarboxylates such as lactate and pyruvate across the plasma membrane (Halestrap and Meredith, 2004), AZD3965 is thought to block tumor growth through disruption of lactate transport and glycolysis. Here we show that MCT1 inhibition impairs proliferation of glycolytic breast cancer cells that express MCT4 via disruption of pyruvate rather than lactate export. We found that MCT1 expression is elevated in glycolytic breast tumors and cell lines as well as in malignant breast and lung tissues. High MCT1 expression predicts poor prognosis in breast and lung cancer patients. Stable knockdown and AZD3965-mediated inhibition of MCT1 promote oxidative metabolism. Acute inhibition of MCT1 reduces pyruvate export rate but does not consistently alter lactate transport or glycolytic flux in breast cancer cells that also express MCT4. Despite the lack of glycolysis impairment, MCT1 loss-of-function decreases breast cancer cell proliferation and blocks growth of mammary fat pad xenograft tumors. Our data suggest that MCT1 expression is elevated in glycolytic cancers to promote pyruvate export, which when inhibited enhances oxidative metabolism and reduces proliferation. This study presents an alternative molecular consequence of MCT1 inhibitors that further supports their use as anti-cancer therapeutics
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Metabolite Signaling Mediates Cellular Homeostasis and Proliferation
Get PDFNutrients and metabolites can both positively and negatively regulate cell signaling and anabolic metabolism. These signaling properties suggest that metabolites can influence both proliferation and cellular homeostasis. Here we describe a role for asparagine as an amino acid exchange factor: intracellular asparagine exchanges with extracellular amino acids. We show that intracellular asparagine levels regulate uptake of amino acids, especially serine, arginine, and histidine. Through its exchange factor role, asparagine promotes mTORC1 activity and downstream anabolic metabolism. In addition, we show that asparagine depletion may be sensed through intracellular lactate accumulation. Asparagine depletion impairs trafficking of lactate transporters MCT1 and MCT4 to decrease lactate export. We also provide evidence that lactate binds to and stabilizes ATF4, the transcription factor responsible for asparagine synthetase expression, suggesting that lactate, as a signal of asparagine depletion, is sensed by ATF4 to restore intracellular asparagine. In addition to stimulating ATF4 activity and ASNS expression, we find that lactate inhibits mTORC1 activity in an ATF4-dependent manner. Given the role of asparagine in amino acid uptake, our data suggest that lactate may be a novel signal to communicate amino acid deficiency to mTORC1. We propose that the cell coordinates anabolism with nutrient availability by linking ATF4 transcriptional activity to mTORC1 inhibition, such that lactate-induced mTORC1 inhibition upon asparagine depletion coincides with ATF4-mediated asparagine regeneration and is relieved upon asparagine restoration. Finally, we hypothesize that lactate signaling may explain why lactate export is a cancer hallmark: cancer cell lactate export both relieves cell-autonomous restrictions on mTORC1-mediated anabolism and enables exploitation of the tumor microenvironment through tumor-generated paracrine lactate signaling
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Deletion of the imprinted gene, Grb10, promotes hematopoietic stem cell self-renewal and regeneration
Get PDFImprinted genes have been shown to be differentially expressed by adult stem cells, but the function of imprinted genes in regulating adult stem cell fate is not well understood. Here, we show that growth factor receptor bound protein 10 (Grb10), a member of the imprinted gene family, regulates hematopoietic stem cell (HSC) self-renewal and regeneration. Deletion of the maternal allele of Grb10 in mice (Grb10m/+ mice) substantially increased HSC long-term repopulating capacity compared to Grb10+/+ mice. Furthermore, following total body irradiation (TBI), Grb10m/+ mice displayed accelerated HSC regeneration and overall hematopoietic reconstitution compared to Grb10+/+ mice. Grb10-deficient HSCs displayed increased migratory capacity and proliferative capacity in vivo following competitive transplantation or irradiation, commensurate with increased activation of the RhoGTPase, Rac1. Inhibition of Rac1 abrogated both the enhanced migratory capacity and the increased proliferative potential of Grb10-deficient HSCs in vivo. Grb10 has a long established role as a negative feedback inhibitor of Akt-mTOR signaling pathway. In accordance with this, our data show that inhibition of Akt-mTOR signaling pathway abolished the early regeneration of long-term HSCs in Grb10m/+ mice following irradiation, compared to Grb10+/+ mice. This study reveals a previously unrecognized role for the imprinted gene, Grb10, in regulating HSC self-renewal and regeneration and suggests that antagonism of Grb10 can promote hematopoietic regeneration in vivo
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