Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Bluemel, G.
Regulation of the TCA cycle, respiration and redox balance by the gluconeogenesis enzyme PCK2 in starved lung cancer cells
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medizinische Universität Graz; 2021. pp. 76
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Höfler Gerald
- Leithner Katharina
- Olschewski Horst
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- Abstract:
- Cancer cells often face starvation and fluctuating nutrient concentration, due to inadequate supply and high consumption, requiring metabolic adaptions. Gluconeogenesis, largely the inverse pathway of glycolysis, is a metabolic pathway activated by starvation. The key enzyme, initiating gluconeogenesis is phosphoenolpyruvate carboxykinase (PEPCK, PCK) which converts the tricarboxylic acid (TCA) cycle intermediate oxaloacetate to phosphoenolpyruvate. PCK2 (PEPCK-M), the mitochondrial isoform of PEPCK, is expressed by different tumors, including lung cancer. Expression of PCK2 has been shown to be beneficial for tumor growth in vitro and in vivo in diverse models and enables biosynthesis of gluconeogenic intermediates in glucose starved cancer cells. In this thesis, it was identified that in two different lung cancer cell lines PCK2 silencing increased the abundance and interconversion of TCA cycle intermediates upon treatment with glucose and serum starvation media. This effect was reversed by PCK2 re-expression. Glucose and serum starvation enhanced the mitochondrial respiration compared to non-starvation conditions and it was additionally augmented by PCK2 silencing. Mitochondrial respiration induces oxidative stress. Superoxide and H2O2 levels were not affected but glutathione oxidation was increased by PCK2 inhibition. Furthermore, PCK2 silencing significantly impaired colony formation upon starvation treatment, and was rescued by addition of antioxidants. Importantly, these findings could be linked to the enhancement of TCA cycle activity by PCK2 silencing, as the effects were phenocopied by supplementing media with the TCA cycle intermediate dimethylmalate. In summary, the cataplerotic activity of PCK2 limits mitochondrial respiration and balances the glutathione redox equilibrium upon glucose and serum starvation. In this thesis, gluconeogenesis, as an adaptive response of tumor cells to nutrient starvation is examined and the role of PCK2 expression to limit respiration-induced oxidative stress is identified.