Abstract
Genetic up-regulation of mitochondrial 2-oxoglutarate dehydrogenase is known to increase reactive oxygen species, being detrimental for cancer cells. Thiamine diphosphate (ThDP, cocarboxylase) is an essential activator of the enzyme and inhibits p53–DNA binding in cancer cells. We hypothesize that the pleiotropic regulator ThDP may be of importance for anticancer therapies. The hypothesis is tested in the present work on lung adenocarcinoma cells A549 possessing the p53–p21 pathway as fully functional or perturbed by p21 knockdown. Molecular mechanisms of ThDP action on cellular viability and their interplay with the cisplatin and p53–p21 pathways are characterized. Despite the well-known antioxidant properties of thiamine, A549 cells exhibit decreases in their reducing power and glutathione level after incubation with 5 mM ThDP, not observed in non-cancer epithelial cells Vero. Moreover, thiamine deficiency elevates glutathione in A549 cells. Viability of the thiamine deficient A549 cells is increased at a low (0.05 mM) ThDP. However, the increase is attenuated by 5 mM ThDP, p21 knockdown, specific inhibitor of the 2-oxoglutarate dehydrogenase complex (OGDHC), or cisplatin. Cellular levels of the catalytically competent ThDP·OGDHC holoenzyme are dysregulated by p21 knockdown and correlate negatively with the A549 viability. The inverse relationship between cellular glutathione and holo-OGDHC is corroborated by their comparison in the A549 and Vero cells. The similarity, non-additivity, and p21 dependence of the dual actions of ThDP and cisplatin on A549 cells manifest a common OGDHC-mediated mechanism of the viability decrease. High ThDP saturation of OGDHC compromises the redox state of A549 cells under the control of p53–p21 axes.
Highlights
Mitochondrial multienzyme complexes of dehydrogenases of 2-oxo acids catalyze irreversible reactions in highly regulated metabolic checkpoints [1,2,3], demonstrating cell-specific expression and functional significance in cancer [4,5,6,7]
Using the oxoglutarate dehydrogenase complex (OGDHC) activity as an indicator of intracellular thiamine diphosphate (ThDP) levels, we show that viability of the A549 cells with the fully functional or partly disabled p53–p21 pathway exhibits different response to the ThDP exposure
We show that ThDP effects on viability of A549 cells depend on the functions of cellular OGDHC and p53–p21 pathway
Summary
Mitochondrial multienzyme complexes of dehydrogenases of 2-oxo acids catalyze irreversible reactions in highly regulated metabolic checkpoints [1,2,3], demonstrating cell-specific expression and functional significance in cancer [4,5,6,7]. Unlike the OGDHL protein, the ubiquitous OGDH-encoded 2-oxoglutarate dehydrogenase is important for A549 cells viability [6,7]. This isoenzyme is known to actively produce mitochondrial ROS under metabolic dysbalance [3]. In view of these data, we hypothesize that pharmacological over-activation of the 2-oxoglutarate dehydrogenase reaction, catalysed by the multienzyme 2-oxoglutarate dehydrogenase complex (OGDHC), may be detrimental for the cancer cells with functional OGDHC. The goal of this work was to study potential antiproliferative action of the ThDP-dependent activation of the 2-oxoglutarate dehydrogenase reaction in cancer cells and its interaction with the p53 pathway
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