Cancer & Metabolism最新文献

Background: Glycolytic flux is regulated by the energy demands of the cell. Upregulated glycolysis in cancer cells may therefore result from increased demand for adenosine triphosphate (ATP), however it is unknown what this extra ATP turnover is used for. We hypothesise that an important contribution to the increased glycolytic flux in cancer cells results from the ATP demand of Na⁺/K⁺-ATPase (NKA) due to altered sodium ion homeostasis in cancer cells.

Methods: Live whole-cell measurements of intracellular sodium [Na⁺]_i were performed in three human breast cancer cells (MDA-MB-231, HCC1954, MCF-7), in murine breast cancer cells (4T1), and control human epithelial cells MCF-10A using triple quantum filtered ²³Na nuclear magnetic resonance (NMR) spectroscopy. Glycolytic flux was measured by ²H NMR to monitor conversion of [6,6-²H₂]D-glucose to [²H]-labelled L-lactate at baseline and in response to NKA inhibition with ouabain. Intracellular [Na⁺]_i was titrated using isotonic buffers with varying [Na⁺] and [K⁺] and introducing an artificial Na⁺ plasma membrane leak using the ionophore gramicidin-A. Experiments were carried out in parallel with cell viability assays, ¹H NMR metabolomics of intracellular and extracellular metabolites, extracellular flux analyses and in vivo measurements in a MDA-MB-231 human-xenograft mouse model using 2-deoxy-2-[¹⁸F]fluoroglucose (¹⁸F-FDG) positron emission tomography (PET).

Results: Intracellular [Na⁺]_i was elevated in human and murine breast cancer cells compared to control MCF-10A cells. Acute inhibition of NKA by ouabain resulted in elevated [Na⁺]_i and inhibition of glycolytic flux in all three human cancer cells which are ouabain sensitive, but not in the murine cells which are ouabain resistant. Permeabilization of cell membranes with gramicidin-A led to a titratable increase of [Na⁺]_i in MDA-MB-231 and 4T1 cells and a Na⁺-dependent increase in glycolytic flux. This was attenuated with ouabain in the human cells but not in the murine cells. ¹⁸FDG PET imaging in an MDA-MB-231 human-xenograft mouse model recorded lower ¹⁸FDG tumour uptake when treated with ouabain while murine tissue uptake was unaffected.

Conclusions: Glycolytic flux correlates with Na⁺-driven NKA activity in breast cancer cells, providing evidence for the 'centrality of the [Na⁺]_i-NKA nexus' in the mechanistic basis of the Warburg effect.

Background: It is well established that hypercholesterolemia increases the risk of atherosclerosis, especially because it reduces the availability of nitric oxide (NO). However, the relationship between hypercholesterolemia and NO in regulating colorectal cancer development and progression remains unknown.

Methods: We conducted bioinformatics analysis, qRT-PCR, ChIP-qPCR assays, luciferase report assays, clonogenic survival assays, and multiple mouse models to investigate the function and mechanism of hypercholesterolemia in regulating NO signaling. Additionally, NOS inhibitors were used to evaluate the potential of therapeutic strategy in anti-tumor response.

Results: Here, we show that oxidized low-density lipoprotein (oxLDL) cholesterol and its receptor LOX-1 are essential for hypercholesterolemia-induced colorectal tumorigenesis. Mechanically, the oxLDL promotes the oxidant stress-dependent induction of hypoxia signaling to transcriptionally up-regulate NO synthase (NOS) especially NOS1 expression in colorectal cancer (CRC) cells. More importantly, our results suggested that selective inhibition of NOS1 with its specific inhibitor Nω-Propyl-L-arginine is a suitable therapeutic strategy for hypercholesterolemia-related CRC with both efficacy and toxicity reduction.

Conclusions: Our findings established that hypercholesterolemia induces the oxidant stress-dependent induction of hypoxia signaling to transcriptionally up-regulate NOS1 expression in CRC cells, and the clinically applicable NOS1 inhibitor Nω-Propyl-L-arginine represents an effective therapeutic strategy for hypercholesterolemia-related CRC.

Background: Pancreatic ductal adenocarcinoma (PDAC) has been associated with the host dysmetabolism of branched-chain amino acids (BCAAs), however, the implications for the role of BCAA metabolism in PDAC development or progression are not clear. The mitochondrial catabolism of valine, leucine, and isoleucine is a multistep process leading to the production of short-chain R-CoA species. They can be subsequently exported from mitochondria as short-chain carnitines (SC-CARs), utilized in anabolic pathways, or released from the cells.

Methods: We examined the specificities of BCAA catabolism and cellular adaptation strategies to BCAA starvation in PDAC cells in vitro. We used metabolomics and lipidomics to quantify major metabolic changes in response to BCAA withdrawal. Using confocal microscopy and flow cytometry we quantified the fluorescence of BODIPY probe and the level of lipid droplets (LDs). We used BODIPY-conjugated palmitate to evaluate transport of fatty acids (FAs) into mitochondria. Also, we have developed a protocol for quantification of SC-CARs, BCAA-derived metabolites.

Results: Using metabolic profiling, we found that BCAA starvation leads to massive triglyceride (TG) synthesis and LD accumulation. This was associated with the suppression of activated FA transport into the mitochondrial matrix. The suppression of FA import into mitochondria was rescued with the inhibitor of the acetyl-CoA carboxylase (ACC) and the activator of AMP kinase (AMPK), which both regulate carnitine palmitoyltransferase 1A (CPT1) activation status.

Conclusions: Our data suggest that BCAA catabolism is required for the import of long chain carnitines (LC-CARs) into mitochondria, whereas the disruption of this link results in the redirection of activated FAs into TG synthesis and its deposition into LDs. We propose that this mechanism protects cells against mitochondrial overload with LC-CARs and it might be part of the universal reaction to amino acid perturbations during cancer growth, regulating FA handling and storage.

Serine and glycine give rise to important building blocks in proliferating cells. Both amino acids are either synthesized de novo or taken up from the extracellular space. In lung cancer, serine synthesis gene expression is variable, yet, expression of the initial enzyme, phosphoglycerate dehydrogenase (PHGDH), was found to be associated with poor prognosis. While the contribution of de novo synthesis to serine pools has been shown to be enhanced by serine starvation, the impact of glucose deprivation, a commonly found condition in solid cancers is poorly understood. Here, we utilized a stable isotopic tracing approach to assess serine and glycine de novo synthesis and uptake in different lung cancer cell lines and normal bronchial epithelial cells in variable serine, glycine, and glucose conditions. Under low glucose supplementation (0.2 mM, 3-5% of normal plasma levels), serine de novo synthesis was maintained or even activated. As previously reported, also gluconeogenesis supplied carbons from glutamine to serine and glycine under these conditions. Unexpectedly, low glucose treatment consistently enhanced serine to glycine conversion, along with an up-regulation of the mitochondrial one-carbon metabolism enzymes, serine hydroxymethyltransferase (SHMT2) and methylenetetrahydrofolate dehydrogenase (MTHFD2). The relative contribution of de novo synthesis greatly increased in low serine/glycine conditions. In bronchial epithelial cells, adaptations occurred in a similar fashion as in cancer cells, but serine synthesis and serine to glycine conversion, as assessed by label enrichments and gene expression levels, were generally lower than in (PHGDH positive) cancer cells. In summary, we found a variable contribution of glucose or non-glucose carbon sources to serine and glycine and a high adaptability of the downstream one-carbon metabolism pathway to variable glucose supply.

Background: Hypoxia contributes to cancer progression through various molecular mechanisms and hepatocellular carcinoma (HCC) is one of the most hypoxic malignancies. Hypoxia-inducible gene domain protein-1a (HIGD1A) is typically induced via epigenetic regulation and promotes tumor cell survival during hypoxia. However, the role of HIGD1A in HCC remains unknown.

Methods: HIGD1A expression was determined in 24 pairs of human HCC samples and para-tumorous tissues. Loss-of-function experiments were conducted both in vivo and in vitro to explore the role of HIGD1A in HCC proliferation and metastasis.

Results: Increased HIGD1A expression was found in HCC tissues and cell lines, which was induced by hypoxia or low-glucose condition. Moreover, HIGD1A knockdown in HCC cells arrested the cell cycle at the G2/M phase and promoted hypoxia-induced cell apoptosis, resulting in great inhibition of cell proliferation, migration, and invasion, as well as tumor xenograft formation. Interestingly, these anti-tumor effects were not observed in normal hepatocyte cell line L02. Further, HIGD1A knockdown suppressed the expression of ornithine decarboxylase 1 (ODC1), a rate-limiting enzyme of polyamine metabolism under c-Myc regulation. HIGD1A was found to bind with the c-Myc promoter region, and its knockdown decreased the levels of polyamine metabolites. Consistently, the inhibitory effect on HCC phenotype by HIGD1A silencing could be reversed by overexpression of c-Myc or supplementation of polyamines.

Conclusions: Our results demonstrated that HIGD1A activated c-Myc-ODC1 nexus to regulate polyamine synthesis and to promote HCC survival and malignant phenotype, implying that HIGD1A might represent a novel therapeutic target for HCC.

Background: Metastasis is the leading cause of death among prostate cancer (PCa) patients. Obesity is associated with both PCa-specific and all-cause mortality. High-fat diet (HFD) is a risk factor contributing to obesity. However, the association of HFD with PCa metastasis and its underlying mechanisms are unclear.

Methods: Tumor xenografts were conducted by intrasplenic injections. The ability of migration or invasion was detected by transwell assay. The expression levels of RPS27 were detected by QRT-PCR and western blot.

Results: The present study verified the increase in PCa metastasis caused by HFD in mice. Bioinformatics analysis demonstrated increased RPS27 in the experimentally induced PCa in HFD mice, indicating that it is an unfavorable prognostic factor. Intrasplenic injections were used to demonstrate that RPS27 overexpression promotes, while RPS27 knockdown significantly reduces, PCa liver metastasis. Moreover, RPS27 inhibition suppresses the effects of HFD on PCa metastasis. Further mRNA sequencing analysis revealed that RPS27 promotes PCa metastasis by selectively enhancing the expression of various genes.

Conclusion: Our findings indicate that HFD increases the risk of PCa metastasis by elevating RPS27 expression and, subsequently, the expression of genes involved in PRAD progression. Therefore, RPS27 may serve as a novel target for the diagnosis and treatment of metastatic PCa.