Search

The most frequently mutated oncogene in cancer is KRAS, which uses alternative fourth exons to generate two gene products (KRAS4A and KRAS4B) that differ only in their C-terminal membrane-targeting region1. Because oncogenic mutations occur in exons 2 or 3, two constitutively active KRAS proteins-each capable of transforming cells-are encoded when KRAS is activated by mutation2. No functional distinctions among the splice variants have so far been established. Oncogenic KRAS alters the metabolism of tumour cells3 in several ways, including increased glucose uptake and glycolysis even in the presence of abundant oxygen4 (the Warburg effect). Whereas these metabolic effects of oncogenic KRAS have been explained by transcriptional upregulation of glucose transporters and glycolytic enzymes3-5, it is not known whether there is direct regulation of metabolic enzymes. Here we report a direct, GTP-dependent interaction between KRAS4A and hexokinase 1 (HK1) that alters the activity of the kinase, and thereby establish that HK1 is an effector of KRAS4A. This interaction is unique to KRAS4A because the palmitoylation-depalmitoylation cycle of this RAS isoform enables colocalization with HK1 on the outer mitochondrial membrane. The expression of KRAS4A in cancer may drive unique metabolic vulnerabilities that can be exploited therapeutically.

Objective: The objective for this study was to evaluate the effects of short chain fatty acids (SCFAs) on arthritic bone remodeling. Methods: We treated a recently described preclinical murine model of psoriatic arthritis (PsA), R26STAT3Cstopfl/fl CD4Cre mice, with SCFA‐supplemented water. We also performed in vitro osteoclast differentiation assays in the presence of serum‐level SCFAs to evaluate the direct impact of these microbial metabolites on maturation and function of osteoclasts. We further characterized the molecular mechanism of SCFAs by transcriptional analysis. Results: The osteoporosis condition in R26STAT3Cstopfl/fl CD4Cre animals is attributed primarily to robust osteoclast differentiation driven by an expansion of osteoclast progenitor cells (OCPs), accompanied by impaired osteoblast development. We show that SCFA supplementation can rescue the osteoporosis phenotype in this model of PsA. Our in vitro experiments revealed an inhibitory effect of the SCFAs on osteoclast differentiation, even at very low serum concentrations. This suppression of osteoclast differentiation enabled SCFAs to impede osteoporosis development in R26STAT3Cstopfl/fl CD4Cre mice. Further interrogation revealed that bone marrow–derived OCPs from diseased mice expressed a higher level of SCFA receptors than those of control mice and that the progenitor cells in the bone marrow of SCFA‐treated mice presented a modified transcriptomic landscape, suggesting a direct impact of SCFAs on bone marrow progenitors in the context of osteoporosis. Conclusion: We demonstrated how gut microbiota‐derived SCFAs can regulate distal pathology (ie, osteoporosis) and identified a potential therapeutic option for restoring bone density in rheumatic disease, further highlighting the critical role of the gut–bone axis in these disorders. [ABSTRACT FROM AUTHOR]

Author(s): Samantha W. Alvarez [1, 2]; Vladislav O. Sviderskiy [1, 2]; Erdem M. Terzi [1, 2]; Thales Papagiannakopoulos [1, 2]; Andre L. Moreira [1, 2]; Sylvia Adams [1, 2]; David [...]

Cancer cells adapt their metabolic processes to support rapid proliferation, but less is known about how cancer cells alter metabolism to promote cell survival in a poorly vascularized tumour microenvironment (1-3). Here we identify a key role for serine and glycine metabolism in the survival of brain cancer cells within the ischaemic zones of gliomas. In human glioblastoma multiforme, mitochondrial serine hydroxymethyltransferase (SHMT2) and glycine decarboxylase (GLDC) are highly expressed in the pseudopalisading cells that surround necrotic foci. We find that SHMT2 activity limits that of pyruvate kinase (PKM2) and reduces oxygen consumption, eliciting a metabolic state that confers a profound survival advantage to cells in poorly vascularized tumour regions. GLDC inhibition impairs cells with high SHMT2 levels as the excess glycine not metabolized by GLDC can be converted to the toxic molecules aminoacetone and methylglyoxal. Thus, SHMT2 is required for cancer cells to adapt to the tumour environment, but also renders these cells sensitive to glycine cleavage system inhibition., Many inborn disorders of amino acid metabolism lead to severe impairment of the developing nervous system, at least in part through toxic effects on neural stem cells (4,5). As brain [...]

New apparatus is used to maintain proliferating cancer cells in low-glucose conditions, demonstrating that mitochondrial oxidative phosphorylation (OXPHOS) is essential for optimal proliferation in these conditions; the most sensitive cell lines are defective in OXPHOS upregulation and may therefore be sensitive to current antidiabetic drugs that inhibit OXPHOS. Biguanides active against starved tumour cells Using a new continuous-flow culture apparatus called Nutrostat, designed to ensure constant and controlled extracellular nutrient levels, David Sabatini and colleagues screened cancer cell lines for genes important when cells experience low glucose levels. They found that the ability of cells to increase mitochondrial oxidative phosphorylation under conditions of low glucose was crucial. Cancer cells unable to do so due to impaired glucose utilization or mitochondrial DNA mutations were particularly sensitive to a class of compounds, biguanides, which are in use to treat diabetes. These findings may lead to new therapeutic applications of these drugs to treat tumours displaying such defects. As the concentrations of highly consumed nutrients, particularly glucose, are generally lower in tumours than in normal tissues.sup.1,2, cancer cells must adapt their metabolism to the tumour microenvironment. A better understanding of these adaptations might reveal cancer cell liabilities that can be exploited for therapeutic benefit. Here we developed a continuous-flow culture apparatus (Nutrostat) for maintaining proliferating cells in low-nutrient media for long periods of time, and used it to undertake competitive proliferation assays on a pooled collection of barcoded cancer cell lines cultured in low-glucose conditions. Sensitivity to low glucose varies amongst cell lines, and an RNA interference (RNAi) screen pinpointed mitochondrial oxidative phosphorylation (OXPHOS) as the major pathway required for optimal proliferation in low glucose. We found that cell lines most sensitive to low glucose are defective in the OXPHOS upregulation that is normally caused by glucose limitation as a result of either mitochondrial DNA (mtDNA) mutations in complex I genes or impaired glucose utilization. These defects predict sensitivity to biguanides, antidiabetic drugs that inhibit OXPHOS.sup.3,4, when cancer cells are grown in low glucose or as tumour xenografts. Notably, the biguanide sensitivity of cancer cells with mtDNA mutations was reversed by ectopic expression of yeast NDI1, a ubiquinone oxidoreductase that allows bypass of complex I function.sup.5. Thus, we conclude that mtDNA mutations and impaired glucose utilization are potential biomarkers for identifying tumours with increased sensitivity to OXPHOS inhibitors., Author(s): Kivanç Birsoy [sup.1] [sup.2] [sup.3] [sup.4] , Richard Possemato [sup.1] [sup.2] [sup.3] [sup.4] , Franziska K. Lorbeer [sup.1] , Erol C. Bayraktar [sup.1] , Prathapan Thiru [sup.1] , Burcu [...]

Cancer cells adapt their metabolic processes to drive macromolecular biosynthesis for rapid cell growth and proliferation (1,2). RNA interference (RNAi)-based loss-of-function screening has proven powerful for the identification of new [...]

Constitutive expression of telomerase in human cells prevents the onset of senescence and crisis by maintaining telomere homeostasis. However, accumulating evidence suggests that the human telomerase reverse transcriptase catalytic subunit (TERT) contributes to cell physiology independently of its ability to elongate telomeres. Here we show that TERT interacts with the RNA component of mitochondrial RNA processing endoribonuclease (RMRP), a gene that is mutated in the inherited pleiotropic syndrome cartilage-hair hypoplasia. Human TERT and RMRP form a distinct ribonucleoprotein complex that has RNA-dependent RNA polymerase (RdRP) activity and produces double-stranded RNAs that can be processed into small interfering RNA in a Dicer (also known as DICER1)-dependent manner. These observations identify a mammalian RdRP composed of TERT in complex with RMRP., Telomerase is a ribonucleoprotein complex that elongates telomeres. Although several proteins interact with telomerase (1-4), the minimal components of active telomerase include the catalytic telomerase reverse transcriptase (TERT) and a [...]

IFN-[gamma] is well known as the signature cytokine of CD[4.sup.+] T helper 1, CD[8.sup.+] and natural killer cells, but recent studies demonstrate that antigen-presenting cells, in particular dendritic cells (DCs), are another potent source for this proinflammatory cytokine. T-bet, a transcription factor that controls IFN-[gamma] expression in CD[4.sup.+] T cells, was reported recently to be expressed in human monocytes and myeloid DCs. In this study we investigate the role of T-bet in this important cell type. The development, differentiation, and activation of bone marrow and splenic DCs were unimpaired in mice lacking T-bet. However, T-bet was essential for the optimal production of IFN-[gamma] by both CD8[[alpha].sup.+] and CD8[[alpha].sup.-] DCs. T-bet-deficient DCs were significantly impaired in their capacity to secrete IFN-[gamma] after both stimulation with IL-12 alone or in combination with IL-18. Further, [T-bet.sup.-/-] DCs were impaired in their ability to activate the T helper 1 program of adoptively transferred antigen-specific T cells in vivo. The rapid up-regulation of T-bet by IFN-[gamma] in DCs coupled with a function for DC-derived IFN-[gamma] in T cell activation may constitute a positive feedback loop to maximize type 1 immunity.