(b) Hybridization of catalase (crimson spots) and control (green spots) FISH probes in metaphases of 250 MK cells. proteins level in MCF-7 and its own level of resistance to prooxidant medications. Consistent with our prior report, chromatin Enecadin redecorating appears as the primary regulator of catalase appearance in breast cancers after chronic contact with an oxidative tension. 1. Launch Catalase generally catalyzes the dismutation of hydrogen peroxide (H2O2) into drinking water and molecular oxygen. This antioxidant enzyme Enecadin is expressed in all major body organs especially in the liver, kidney, and erythrocytes. In these organs, catalase plays an essential role in cell defense against oxidative stress [1, 2]. A decrease in catalase activity is thus frequently associated with several diseases. For instance, some polymorphisms into the promoter or introns of the gene are involved in diabetes, hypertension, vitiligo, Alzheimer’s disease, Enecadin and acatalasemia [3, 4]. Interestingly, catalase is also frequently downregulated in tumor tissues compared to normal tissues of the same origin [5C7]. In this context, when compared to their normal healthy counterparts, we have reported a severe decrease of catalase activity in TLT cells, a murine hepatocarcinoma cell line [8]; in K562 cells, a human chronic myeloid leukemia cell line [9]; and in MCF-7 cells, a human breast carcinoma cell line [10]. These observations are consistent with the study of Sun et al., who showed that immortalization and transformation of mouse liver cells with SV40 virus results in a decrease in catalase activity, which contributes to oncogenesis by increasing reactive oxygen species (ROS) level in transformed cells [11]. The mechanisms controlling the transcription of gene are poorly understood, and diverse mechanisms have also been proposed to regulate catalase expression [3]. We explored a potential role of catalase during the acquisition of cancer cell resistance to chemotherapeutic agents. To this end, we overexpressed human catalase in MCF-7 breast cancer cells. No particular resistance against conventional chemotherapies like doxorubicin, cisplatin, and paclitaxel was observed in cells overexpressing catalase, but they were more resistant to prooxidant therapies [12]. Furthermore, we generated a resistant cell line by chronic exposure of MCF-7 cells to an H2O2-generating system, namely, the ascorbate/menadione (Asc/Men) combination. Catalase was overexpressed in resistant-Resox cells when compared to parental MCF-7 cells [13, 14]. Fli1 In these cells, transcription factors (i.e., RARand JunB) and other proteins belonging to coactivator or corepressor complexes (i.e., HDACs) affect chromatin remodelling and lead to the activation or repression of gene [10]. Additional regulatory levels clarifying this altered catalase expression in cancer cells were also explored. Since ROS induce DNA lesions, we were interested to know whether a potential role of DNA repair pathways may have an impact on the regulation of catalase expression. Genetic alterations such as loss of heterozygosity or amplification of the gene locus, although very rare, were investigated. Both posttranscriptional and posttranslational catalase modifications were also analysed regarding putative alterations of protein stability. Finally, since gene transcription is also regulated by chromatin modulation due to histone acetylation or DNA methylation, these epigenetic marks were also investigated as potential modulators of altered catalase expression in breast cancer cells. 2. Materials and Methods 2.1. Cell Lines and Chemicals MCF-7 cells were purchased at ATCC (Manassas, VA, United States). An MCF-7 cell line resistant to oxidative stress (namely Resox cells) was generated by chronic exposure of cells to increasing concentrations of the prooxidant combination of ascorbate/menadione (Asc/Men) for 6 months, starting with 0.5?mM ascorbate/5? 0.05. 3. Results and Discussion 3.1. Is a Genomic Enecadin Gain of Locus in Breast Cancer Cell Lines Responsible for Catalase Overexpression.