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Depletion of pyruvate kinase (PK) activity causes glycolytic intermediate imbalances and reveals a PK-TXNIP regulatory axis [RNA-seq]

ABSTRACT: Objective Cancer cells convert more glucose into lactate than healthy cells, what results in their growth advantage. Pyruvate kinase (PK) is a key rate limiting enzyme in this process, what makes it a promising potential therapeutic target. However, currently it is still unclear what consequences the inhibition of PK has on cellular processes. Here, we systematically investigate the consequences of PK depletion for gene expression, histone modifications and metabolism. Methods Epigenetic, transcriptional and metabolic targets were analysed in different cellular and animal models with stable knockdown or knockout of PK. Results Depleting PK activity reduces the glycolytic flux and causes accumulation of glucose-6-phosphate (G6P). Such metabolic perturbation results in stimulation of the activity of a heterodimeric pair of transcription factors MondoA and MLX but not in a major reprogramming of the global H3K9ac and H3K4me3 histone modification landscape. The MondoA:MLX heterodimer upregulates expression of thioredoxin-interacting protein (TXNIP) – a tumour suppressor with multifaceted anticancer activity. This effect of TXNIP upregulation extends beyond immortalised cancer cell lines and is applicable to multiple cellular and animal models. Conclusions Our work shows that actions of often pro-tumorigenic PK and anti-tumorigenic TXNIP are tightly linked via a glycolytic intermediate. We suggest that PK depletion stimulates the activity of MondoA:MLX transcription factor heterodimers and subsequently, increases cellular TXNIP levels. TXNIP-mediated inhibition of thioredoxin (TXN) can reduce the ability of cells to scavenge reactive oxygen species (ROS) leading to the oxidative damage of cellular structures including DNA. These findings highlight an important regulatory axis affecting tumour suppression mechanisms and provide an attractive opportunity for combination cancer therapies targeting glycolytic activity and ROS-generating pathways

ORGANISM(S): Homo sapiens

PROVIDER: GSE235387 | GEO | 2023/07/06

REPOSITORIES: GEO

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Project description:BACKGROUND: Protein synthesis is regulated by the availability of amino acids, the engagement of growth factor signaling pathways and ATP levels sufficient to support translation. Crosstalk between these inputs is extensive, yet other regulatory mechanisms remain to be characterized. For example, the translation initiation inhibitor Rocaglamide A (RocA) induces Thioredoxin Interacting Protein (TXNIP). TXNIP is a negative regulator of glucose uptake, thus its induction by RocA links translation to the availability of glucose. MondoA is the principal regulator of glucose-induced transcription and its activity is triggered by the glycolytic intermediate, glucose 6-phosphate (G6P). MondoA responds to G6P generated by cytoplasmic glucose and mitochondrial ATP (mtATP), suggesting a critical role in the cellular response to these energy sources. TXNIP expression is entirely dependent on MondoA, therefore, we investigated how protein synthesis inhibitors impact its transcriptional activity. METHODS: We investigated how translation regulates MondoA activity using cell line models and loss-of-function approaches. We examined how protein synthesis inhibitors effect gene expression and metabolism using RNA-sequencing and metabolomics, respectively. The biological impact of RocA was evaluated using both cell line models and Patient-Derived Xenograft Organoid models. RESULTS: We discovered that multiple protein synthesis inhibitors, including RocA, increase TXNIP expression in a manner that depends on MondoA, a functional electron transport chain and mtATP synthesis. Furthermore, RocA increases mtATP and G6P levels and TXNIP induction depends on interactions between the Voltage-Dependent Anion Channel (VDAC) and hexokinase, which generates G6P. RocA treatment impacts the regulation of ~1200 genes and ~250 of those genes are MondoA-dependent. RocA treatment is cytotoxic to Triple Negative Breast Cancer cell lines and shows preferential cytotoxicity against ER- patient-derived breast cancer models. Finally, RocA-driven cytotoxicity is partially-dependent on MondoA or TXNIP. CONCLUSION: Our data suggest that protein synthesis inhibitors rewire metabolism, resulting in an increase in mtATP and G6P, the latter driving MondoA-dependent transcriptional activity. Further, MondoA is a critical component of the cellular transcriptional response to RocA. Our functional assays suggest that RocA or similar translation inhibitors may show efficacy against ER- tumors and that the levels of MondoA and TXNIP should be considered when exploring these potential treatment options.

Project description:We hypothesized that the potential ability of the 18 kDa mitochondrial translocator protein (TSPO) to regulate gene expression may underlie its numerous reported functions, ranging from mitochondrial activity till mental disorders. Therefore, we applied microarray analysis of gene expression to U118MG glioblastoma cells. Within 1 hr the TSPO ligand PK 11195 induced changes in expression of immediate early genes and transcription factors. After 24 hrs primarily gene expression for enzymes and other proteins is changed. The associated gene products are known to affect various cellular functions: programmed cell death, cell cycle, viability, proliferation, migration, differentiation, development, tumorigenesis, and inflammatory / immune responses. Our microscopic studies showed intense TSPO mitochondrial labeling but no TSPO signal in the cell nuclei. Thus, it appears that the TSPO is part of the retrograde mitochondrial-nuclear signaling pathway for modulation of gene expression and thereby may exert its numerous effects on cell function, phenotype, and disease. U118MG cells (1.255 Ã 106) were seeded in Petri dishes (i.e. 28.5 Ã 103 cells / cm2) and allowed to proliferate for 3 days in full medium. Experiments for gene expression assayed with microarray typically consisted of three experimental groups and a vehicle control group (n = 3 for each group). Serum deprived medium was applied for 24 hrs, in the experimental groups ending with the inclusion a choice of various PK 11195 exposures i.e. either 1 hr, 3 hrs, or 24 hrs. Exposure to PK 11195 implies serum deprived medium with 1% alcohol (vehicle) and PK 11195 (25 ÂµM final concentration) for the required time period. 25 ÂµM of PK 11195 is the optimal concentration for these types of experiments with U118MG cells (Kugler et al., 2008). The cells were collected by trypsinization, washed by centrifugation in phosphate buffered saline (PBS) (400 Ã g, 5 min), and lysed [RLT lysis buffer provided with the RNeasy Mini Kit diluted with Î²-mercaptoethanol (1 : 100)], according to the manufacturer's instructions. Lysates were stored at -70oC.

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Depletion of pyruvate kinase (PK) activity causes glycolytic intermediate imbalances and reveals a PK-TXNIP regulatory axis [RNA-seq]

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