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Lactate-mediated mitoribosomal defects impair mitochondrial oxidative phosphorylation and promote hepatoma cell invasiveness.

ABSTRACT: Impaired mitochondrial oxidative phosphorylation (OXPHOS) capacity, accompanied by enhanced glycolysis, is a key metabolic feature of cancer cells, but its underlying mechanism remains unclear. Previously, we reported that human hepatoma cells that harbor OXPHOS defects exhibit high tumor cell invasiveness via elevated claudin-1 (CLN1). In the present study, we show that OXPHOS-defective hepatoma cells (SNU354 and SNU423 cell lines) exhibit reduced expression of mitochondrial ribosomal protein L13 (MRPL13), a mitochondrial ribosome (mitoribosome) subunit, suggesting a ribosomal defect. Specific inhibition of mitoribosomal translation by doxycycline, chloramphenicol, or siRNA-mediated MRPL13 knockdown decreased mitochondrial protein expression, reduced oxygen consumption rate, and increased CLN1-mediated tumor cell invasiveness in SNU387 cells, which have active mitochondria. Interestingly, we also found that exogenous lactate treatment suppressed MRPL13 expression and oxygen consumption rate and induced CLN1 expression. A bioinformatic analysis of the open RNA-Seq database from The Cancer Genome Atlas (TCGA) liver hepatocellular carcinoma (LIHC) cohort revealed a significant negative correlation between MRPL13 and CLN1 expression. Moreover, in patients with low MRPL13 expression, two oxidative metabolic indicators, pyruvate dehydrogenase B expression and the ratio of lactate dehydrogenase type B to type A, significantly and negatively correlated with CLN1 expression, indicating that the combination of elevated glycolysis and deficient MRPL13 activity was closely linked to CLN1-mediated tumor activity in LIHC. These results suggest that OXPHOS defects may be initiated and propagated by lactate-mediated mitoribosomal deficiencies and that these deficiencies are critically involved in LIHC development.

SUBMITTER: Lee YK

PROVIDER: S-EPMC5724007 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Lactate-mediated mitoribosomal defects impair mitochondrial oxidative phosphorylation and promote hepatoma cell invasiveness.

Lee Young-Kyoung YK Lim Jin J JJ Jeoun Un-Woo UW Min Seongki S Lee Eun-Beom EB Kwon So Mee SM Lee Changhan C Yoon Gyesoon G

The Journal of biological chemistry 20171004 49

Impaired mitochondrial oxidative phosphorylation (OXPHOS) capacity, accompanied by enhanced glycolysis, is a key metabolic feature of cancer cells, but its underlying mechanism remains unclear. Previously, we reported that human hepatoma cells that harbor OXPHOS defects exhibit high tumor cell invasiveness via elevated claudin-1 (CLN1). In the present study, we show that OXPHOS-defective hepatoma cells (SNU354 and SNU423 cell lines) exhibit reduced expression of mitochondrial ribosomal protein L ...[more]

PMID: 28978646

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Project description:BackgroundIntervertebral disc degeneration contributes to low back pain. The avascular intervertebral disc consists of a central hypoxic nucleus pulpous (NP) surrounded by the more oxygenated annulus fibrosus (AF). Lactic acid, an abundant end-product of NP glycolysis, has long been viewed as a harmful waste that acidifies disc tissue and decreases cell viability and function. As lactic acid is readily converted into lactate in disc tissue, the objective of this study was to determine whether lactate could be used by AF cells as a carbon source rather than being removed from disc tissue as a waste byproduct.MethodsImport and conversion of lactate to tricarboxylic acid (TCA) cycle intermediates and amino acids in rabbit AF cells were measured by heavy-isotope (13C-lactate) tracing experiments using mass spectrometry. Levels of protein expression of lactate converting enzymes, lactate importer and exporter in NP and AF tissues were quantified by Western blots. Effects of lactate on proteoglycan (35S-sulfate) and collagen (3H-proline) matrix protein synthesis and oxidative phosphorylation (Seahorse XFe96 Extracellular Flux Analyzer) in AF cells were assessed.ResultsHeavy-isotope tracing experiments revealed that AF cells imported and converted lactate into TCA cycle intermediates and amino acids using in vitro cell culture and in vivo models. Addition of exogenous lactate (4 mM) in culture media induced expression of the lactate importer MCT1 and increased oxygen consumption rate by 50%, mitochondrial ATP-linked respiration by 30%, and collagen synthesis by 50% in AF cell cultures grown under physiologic oxygen (2-5% O2) and glucose concentration (1-5 mM). AF tissue highly expresses MCT1, LDH-H, an enzyme that preferentially converts lactate to pyruvate, and PDH, an enzyme that converts pyruvate to acetyl-coA. In contrast, NP tissue highly expresses MCT4, a lactate exporter, and LDH-M, an enzyme that preferentially converts pyruvate to lactate.ConclusionsThese findings support disc lactate-dependent metabolic symbiosis in which lactate produced by the hypoxic, glycolytic NP cells is utilized by the more oxygenated AF cells via oxidative phosphorylation for energy and matrix production, thus shifting the current research paradigm of viewing disc lactate as a waste product to considering it as an important biofuel. These scientifically impactful results suggest novel therapeutic targets in disc metabolism and degeneration.

Dataset Information

Lactate-mediated mitoribosomal defects impair mitochondrial oxidative phosphorylation and promote hepatoma cell invasiveness.

Publications

Lactate-mediated mitoribosomal defects impair mitochondrial oxidative phosphorylation and promote hepatoma cell invasiveness.

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