Abstract
The energy metabolism of most tumor cells relies on aerobic glycolysis (Warburg effect) characterized by an increased glycolytic flux that is accompanied by the increased formation of the cytotoxic metabolite methylglyoxal (MGO). Consequently, the rate of detoxification of this reactive glycolytic byproduct needs to be increased in order to prevent deleterious effects to the cells. This is brought about by an increased expression of glyoxalase 1 (GLO1) that is the rate-limiting enzyme of the MGO-detoxifying glyoxalase system. Here, we overexpressed GLO1 in HEK 293 cells and silenced it in MCF-7 cells using shRNA. Tumor-related properties of wild type and transformed cells were compared and key glycolytic enzyme activities assessed. Furthermore, the cells were subjected to hypoxic conditions to analyze the impact on cell proliferation and enzyme activities. Our results demonstrate that knockdown of GLO1 in the cancer cells significantly reduced tumor-associated properties such as migration and proliferation, whereas no functional alterations where found by overexpression of GLO1 in HEK 293 cells. In contrast, hypoxia caused inhibition of cell growth of all cells except of those overexpressing GLO1. Altogether, we conclude that GLO1 on one hand is crucial to maintaining tumor characteristics of malignant cells, and, on the other hand, supports malignant transformation of cells in a hypoxic environment when overexpressed.
Highlights
Glyoxalase 1 (GLO1; S-D-lactoylglutathione lyase, EC 4.4.1.5) is part of the glyoxalase system, which, in addition to glyoxalase 1 (GLO1), consists of GLO2 and of catalytic amounts of reduced glutathione (GSH)
In o2r9d3e-GrLtOo 1acseslelsss(Faiguproes1sBib,Dle). influence of GLO1 on glycolysis, we determined the activities of the three keyIngolyrdceorlytotiacsseensszya mpoessibhleexinofkluinenacseeo(fHGKLO),1pohnogslpychoolyfrsuisc, twoekdinetaesrem(inPeFdKth) eaancdtivpityiersuovfattheekinase (PK) [23t]h. reIenkeaydgdlyitcioolnyt,icwenezyamnaelsyhzeexdokitnhaesee(nHzKy)m, pehoaspcthiovfirtuyctookfingalsuec(oPsFeK-)6a-npdhpoysrpuhvaatteekdineahsey(dPrKo)genase (G6PDH[)2,3w]
We found that pyruvate kinase (PK) was the only enzyme whose activity was significantly reduced as a consequence of GLO1-knockdown in MCF-7 tumor cells
Summary
Glyoxalase 1 (GLO1; S-D-lactoylglutathione lyase, EC 4.4.1.5) is part of the glyoxalase system, which, in addition to GLO1, consists of GLO2 (hydroxyacyl glutathione hydrolase, EC 3.1.2.6) and of catalytic amounts of reduced glutathione (GSH). It is expressed at early stages of embryogenesis [1], and it is responsible for the conversion of reactive oxo-aldehydes such as methylglyoxal (MGO) to D-lactate. 0.1%–0.4% of the glucose consumed by the cells and shuttled through glycolysis is transformed to MGO [2]. Under conditions of high glycolytic flux, such as aerobic glycolysis, the formation of MGO is increased [4]
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