Role and regulation of catalase and NAD(P)H : quinone oxidoreductase 1 in cancer cells

The aim of this thesis was to understand the role of antioxidant enzymes (catalase and NQO1) in the sensitivity to chemotherapeutic compounds and to identify the transcription factors involved in the repression of catalase in tumor cells. Because the expression of the antioxidant enzyme catalase was modified in several models of cell lines resistant to chemotherapeutic drugs (doxorubicin, cisplatin, etc.) and that catalase has an oxidase activity which is susceptible to detoxifying them, we decided to investigate the effect of a catalase overexpression in breast cancer MCF-7 cells. We demonstrated that catalase could not be involved in the resistance to classical chemotherapeutic compounds and radiotherapy but rather to pro-oxidant compounds. Moreover, an overexpression of catalase in MCF-7 cells leads to a less aggressive phenotype because their growth and migration capacities are reduced. In this way, we also investigated also the role of another antioxidant enzyme, the NADPH quinone oxidoreductase 1 (NQO1), in the sensitivity to quinonic compounds (doxorubicin, menadione, beta-lapachone). NQO1 has the capacity to detoxify menadione, doxorubicin and to activate beta-lapachone. The polymorphism of the NQO1 gene (NQO1wt or NQO1 C609T, both present in MCF-7 cells) is very important for the activity of the enzyme. Moreover, cells with a higher NQO1 expression are correlated with a gain of NQO1 gene copies. The second part of the study comprised of identifying the factors involved in the repression of catalase in tumor cells. Indeed, the expression of this antioxidant enzyme is generally reduced in the majority of cancers. Transcription factors such as NF-Y, Sp1, FoxM1, Oct-1 and PPARγ can bind to the promoter of human catalase and upregulate its expression. A member of the Forkhead box family, FoxO3a, was a good target to regulate catalase expression in cancer cells. We demonstrated that PI3K/Akt/mTOR signalling represses catalase expression in MCF-7 cells but FoxO3a, regulated by this pathway, does not appear to play a critical role in the regulation of the enzyme expression. Therefore, we analysed the promoter of the human catalase and our results demonstrated that a particular region of the promoter is responsible for the regulation. Furthermore, we identified key factors which bind and regulate catalase expression in cancer cell lines by purifying proteins bound to this sequence, followed by their identification via mass spectrometry.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201