Modulation of GLO1 Expression Affects Malignant Properties of Cells

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.

Effect of Hypoxia on the Expression of a Subset of Proliferation Related Genes in IRE1 Knockdown U87 Glioma Cells

“…In this study, we have shown that inhibition of the IRE1 signaling enzyme leads to strong down-regulation of GLO1 gene expression in U87 glioma cells. Our results agree well with data Hutschenreuther et al [43] that knockdown of GLO1 in the cancer cells significantly reduced tumor-associated properties such as migration and proliferation, whereas hypoxia …”

“…Results of this investigation clearly demonstrated that hypoxia affects different plained by over-expression of GLO1 enzyme, which is implicated in the progression of human malignancies and is up-regulated in tumor tissues with high metabolic rate [40] [41] [43]. In this study, we have shown that inhibition of the IRE1 signaling enzyme leads to strong down-regulation of GLO1 gene expression in U87 glioma cells.…”

“…[42]. Furthermore, knockdown of GLO1 in the cancer cells significantly reduced tumor-associated properties such as migration and proliferation, whereas hypoxia caused inhibition of cell growth of all cells except of those over-expressing GLO1 [43]. It is possible that over-expression of GLO1 supports malignant transformation and proliferation of cells in a hypoxic environment.…”

Multiple roles of glyoxalase 1-mediated suppression of methylglyoxal glycation in cancer biology—Involvement in tumour suppression, tumour growth, multidrug resistance and target for chemotherapy

“…Indeed, in the non-malignant state, Glo1 is a tumour suppressor gene -see above. Rather, increase Glo1 expression contributes to robust growth -particularly in conditions of high glycolytic activity and adaptation to hypoxia [35,36]. Increased Glo1 expression is likely due to an increased requirement to protect the tumour proteome against a local, relatively high flux of MG formation.…”

“…Bcr-Abl+ leukaemia-derived stem cells exhibited a counter response -increased Glo1 expression in response to hypoxia [36]. This is a growth advantage: evidenced by transfection of the HEK293 tumour cell line to overexpress Glo1 gave improving adaptation to growth in hypoxic conditions [35]. The dependence of Glo1 for hypoxia adaptation is a metabolic weakness or "Achilles heel" to exploit since hypoxiaadapted tumour stem cells were vulnerable to cytotoxicity induced by cell permeable Glo1 inhibitors [36].…”