Phosphoenolpyruvate Carboxykinase Maintains Glycolysis-driven Growth in Drosophila Tumors

Long-term exposure to polystyrene microplastics induces hepatotoxicity by altering lipid signatures in C57BL/6J mice

It is estimated that the life of plastics is hundreds to thousands of years, their lasting properties making plastic debris absorbing toxic chemicals and degrading into microplastics (MPs). The purpose of this study was to explore the effects of exposure to different size (0.08 and 0.5 μm) polystyrene (PS) in mice. After 16 weeks of exposure, it was found that PS-MPs could be identified in the liver. No effect of PS-MPs treatment on body weight was observed. PS-MPs exposure disturbed lipids and lipid-like molecule metabolisms and perturbed the citrate cycle and oxidative phosphorylation. Meanwhile, isocitrate dehydrogenase (ICDHc), nicotinamide adenine dinucleotide -malate dehydrogenase (NAD-MDH), succinate dehydrogenase (SDH), α ketoglutarate dehydrogenase (α-KGDH) activities and adenosine triphosphate (ATP) level were obviously affected by PS-MPs treatment. In addition, significant differences were recorded in catalase (CAT) and malondialdehyde (MDA) levels, indicating that PS-MPs exposure induced an oxidative stress in the liver. In conclusion, our present study provided the first evidence of: (a) long-term exposure to PS-MPs lead to PS-MPs accumulated in the liver and results in liver injury; (b) long-term exposure to PS-MPs disturbs lipids and lipid-like molecule metabolisms; (c) long-term exposure to PS-MPs perturbs citrate cycle and oxidative phosphorylation and leads to oxidative stress in the liver.

Drosophila as a toolkit to tackle cancer and its metabolism

Cancer is one of the most severe health problems worldwide accounting for the second leading cause of death. Studies have indicated that cancers utilize different metabolic systems as compared with normal cells to produce extra energy and substances required for their survival, which contributes to tumor formation and progression. Recently, the fruit fly Drosophila has been attracting significant attention as a whole-body model for elucidating the cancer mechanisms including metabolism. This tiny organism offers a valuable toolkit with various advantages such as high genetic conservation and similar drug response to mammals. In this review, we introduce flies modeling for cancer patient genotypes which have pinpointed novel therapeutic targets and drug candidates in the salivary gland, thyroid, colon, lung, and brain. Furthermore, we introduce fly models for metabolic diseases such as diabetes mellitus, obesity, and cachexia. Diabetes mellitus and obesity are widely acknowledged risk factors for cancer, while cachexia is a cancer-related metabolic condition. In addition, we specifically focus on two cancer metabolic alterations: the Warburg effect and redox metabolism. Indeed, flies proved useful to reveal the relationship between these metabolic changes and cancer. Such accumulating achievements indicate that Drosophila offers an efficient platform to clarify the mechanisms of cancer as a systemic disease.

Metabolic reprogramming in cancer: mechanistic insights from Drosophila

Cancer cells constantly reprogram their metabolism as the disease progresses. However, our understanding of the metabolic complexity of cancer remains incomplete. Extensive research in the fruit fly Drosophila has established numerous tumor models ranging from hyperplasia to neoplasia. These fly tumor models exhibit a broad range of metabolic profiles and varying nutrient sensitivity. Genetic studies show that fly tumors can use various alternative strategies, such as feedback circuits and nutrient-sensing machinery, to acquire and consolidate distinct metabolic profiles. These studies not only provide fresh insights into the causes and functional relevance of metabolic reprogramming but also identify metabolic vulnerabilities as potential targets for cancer therapy. Here, we review the conceptual advances in cancer metabolism derived from comparing and contrasting the metabolic profiles of fly tumor models, with a particular focus on the Warburg effect, mitochondrial metabolism, and the links between diet and cancer.

Summary: Recent research in fruit flies has demonstrated that tumors rewire their metabolism by using diverse strategies that involve feedback regulation, nutrient sensing, intercellular or even inter-organ interactions, yielding new molecules as potential cancer markers or drug targets.

Flexibility and Adaptation of Cancer Cells in a Heterogenous Metabolic Microenvironment

The metabolic microenvironment, comprising all soluble and insoluble nutrients and co-factors in the extracellular milieu, has a major impact on cancer cell proliferation and survival. A large body of evidence from recent studies suggests that tumor cells show a high degree of metabolic flexibility and adapt to variations in nutrient availability. Insufficient vascular networks and an imbalance of supply and demand shape the metabolic tumor microenvironment, which typically contains a lower concentration of glucose compared to normal tissues. The present review sheds light on the recent literature on adaptive responses in cancer cells to nutrient deprivation. It focuses on the utilization of alternative nutrients in anabolic metabolic pathways in cancer cells, including soluble metabolites and macromolecules and outlines the role of central metabolic enzymes conferring metabolic flexibility, like gluconeogenesis enzymes. Moreover, a conceptual framework for potential therapies targeting metabolically flexible cancer cells is presented.

The insulin signaling pathway in Drosophila melanogaster: A nexus revealing an "Achilles' heel" in DDT resistance

Insecticide resistance is an ongoing challenge in agriculture and disease vector control. Here, we demonstrate a novel strategy to attenuate resistance. We used genomics tools to target fundamental energy-associated pathways and identified a potential "Achilles' heel" for resistance, a resistance-associated protein that, upon inhibition, results in a substantial loss in the resistance phenotype. Specifically, we compared the gene expression profiles and structural variations of the insulin/insulin-like growth factor signaling (IIS) pathway genes in DDT-susceptible (91-C) and -resistant (91-R) Drosophila melanogaster (Drosophila) strains. A total of eight and seven IIS transcripts were up- and down-regulated, respectively, in 91-R compared to 91-C. A total of 114 nonsynonymous mutations were observed between 91-C and 91-R, of which 51.8% were fixed. Among the differentially expressed transcripts, phosphoenolpyruvate carboxykinase (PEPCK), down-regulated in 91-R, encoded the greatest number of amino acid changes, prompting us to perform PEPCK inhibitor-pesticide exposure bioassays. The inhibitor of PEPCK, hydrazine sulfate, resulted in a 161- to 218-fold decrease in the DDT resistance phenotype (91-R) and more than a 4- to 5-fold increase in susceptibility in 91-C. A second target protein, Glycogen synthase kinase 3β (GSK3β-PO), had one amino acid difference between 91-C and 91-R, and the corresponding transcript was also down-regulated in 91-R. A GSK3β-PO inhibitor, lithium chloride, likewise reduced the resistance but to a lesser extent than did hydrazine sulfate for PEPCK. We demonstrate the potential role of IIS genes in DDT resistance and the potential discovery of an "Achilles' heel" against pesticide resistance in this pathway.

Gluconeogenesis in cancer cells - Repurposing of a starvation-induced metabolic pathway?

Cancer cells constantly face a fluctuating nutrient supply and interference with adaptive responses might be an effective therapeutic approach. It has been discovered that in the absence of glucose, cancer cells can synthesize crucial metabolites by expressing phosphoenolpyruvate carboxykinase (PEPCK, PCK1 or PCK2) using abbreviated forms of gluconeogenesis. Gluconeogenesis, which in essence is the reverse pathway of glycolysis, uses lactate or amino acids to feed biosynthetic pathways branching from glycolysis. PCK1 and PCK2 have been shown to be critical for the growth of certain cancers. In contrast, fructose-1,6-bisphosphatase 1 (FBP1), a downstream gluconeogenesis enzyme, inhibits glycolysis and tumor growth, partly by non-enzymatic mechanisms. This review sheds light on the current knowledge of cancer cell gluconeogenesis and its role in metabolic reprogramming, cancer cell plasticity, and tumor growth.

Chromosomal instability causes sensitivity to protein folding stress and ATP depletion

Aneuploidy _­– having an unbalanced genome – is poorly tolerated at the cellular and organismal level. It gives rise to proteotoxic stress as well as a stereotypical oxidative shift which makes these cells sensitive to internal and environmental stresses. Using Drosophila as a model, we found that protein folding stress is exacerbated by redox stress that occurs in response to ongoing changes to ploidy (chromosomal instability, CIN). We also found that if de novo nucleotide synthesis is blocked, CIN cells are dependent on a high level of lysosome function to survive. Depletion of adenosine monophosphate (AMP) synthesis enzymes led to DNA damage in CIN cells, which showed elevated activity of the DNA repair enzyme activated poly(ADP ribose) polymerase (PARP). PARP activation causes depletion of its substrate, nicotinamide adenine dinucleotide (NAD+) and subsequent loss of Adenosine Tri-Phosphate (ATP), and we found that adding ATP or nicotinamide (a precursor in the synthesis of NAD+) could rescue the observed phenotypes. These findings provide ways to interpret, target and exploit aneuploidy, which has the potential to offer tumour-specific therapies.

Summary: Cells that gain or lose chromosomes during cell division are shown to be sensitive to ATP levels and protein folding stress.