Rémi Klotz

Manganese superoxide dismutase in breast cancer: From molecular mechanisms of gene regulation to biological and clinical significance

Breast cancer is one of the most common malignancies of all cancers in women worldwide. Many difficulties reside in the prediction of tumor metastatic progression because of the lack of sufficiently reliable predictive biological markers, and this is a permanent preoccupation for clinicians. Manganese superoxide dismutase (MnSOD) may represent a rational candidate as a predictive biomarker of breast tumor metastatic progression, because its gene expression is profoundly altered between early and advanced breast cancer, in contrast to expression in the normal mammary gland. In this review, we report the characterization of some gene polymorphisms and molecular mechanisms of SOD2 gene regulation, which allows a better understanding of how MnSOD is decreased in early breast cancer and increased in advanced breast cancer. Several studies display the biological significance of MnSOD level in proliferation as well as in invasive and angiogenic abilities of breast tumor cells by controlling superoxide anion radical (O2(•-)) and hydrogen peroxide (H2O2). Particularly, they report how these reactive oxygen species may activate some signaling pathways involved in breast tumor growth. Emerging understanding of these findings provides an interesting framework for guiding translational research and suggests a way to define precisely the clinical interest of MnSOD as a prognostic and/or predicting marker in breast cancer, by associating with some regulators involved in SOD2 gene regulation and other well-known biomarkers, in addition to the typical clinical parameters.

DDB2: A Novel Regulator of NF-κB and Breast Tumor Invasion

The DNA repair protein damaged DNA-binding 2 (DDB2) has been implicated in promoting cell-cycle progression by regulating gene expression. DDB2 is selectively overexpressed in breast tumor cells that are noninvasive, but not in those that are invasive. We found that its overexpression in invasive human breast tumor cells limited their motility and invasiveness in vitro and blocked their ability to colonize lungs in vivo, defining a new function for DDB2 in malignant progression. DDB2 overexpression attenuated the activity of NF-κB and the expression of its target matrix metalloprotease 9 (MMP9). Mechanistic investigations indicated that DDB2 decreased NF-κB activity by upregulating expression of IκBα by binding the proximal promoter of this gene. This effect was causally linked to invasive capacity. Indeed, knockdown of DDB2-induced IκBα gene expression restored NF-κB activity and MMP9 expression, along with the invasive properties of breast tumor cells overexpressing DDB2. Taken together, our findings enlighten understanding of how breast cancer cells progress to an invasive phenotype and underscore potential clinical interest in DDB2 as a prognostic marker or therapeutic target in this setting.

The Damaged DNA Binding 2 protein: a new modulator of TGFβ1 signaling pathway and membrane nanomechanics in breast cancer cells

Posttranslational modification (PTM) of proteins is a versatile cellular process to regulate the activities of proteins. The high regioselectivity and catalysis rate of posttranslationally modifying ...Dynamic modeling showed that the topology of fatty-acid betaoxidation makes this pathway intrinsically vulnerable to substrate overload: at a high influx of palmitoyl-CoA into the pathway the flux dropped and intermediate CoA-esters accumulated extremely(Van Eunen et al., 2013 PLoS Comput Biol). We show here that inborn errors in fatty-acid metabolism aggravate the risk of amitochondrial catastrophe.We applied the previously constructed dynamic model to study the impact of multiple acyl-CoA dehydrogenase deficiency(MADD) and medium-chain acyl-CoA dehydrogenase deficiency(MCADD) on the kinetics of fatty acid oxidation. We explored the relation between the deficiencies and metabolite profiles and calculated which profiles might enhance the risk of pathway overload. MADD patients show accumulation of acylcarnitines acrossall chain lengths. In contrast, MCADD patients accumulate the medium-chain acylcarnitines. A linear non-competition model could not explain this, as it predicted exclusive accumulation of longer chain-length metabolites in MADD. This provides the first experimental evidence that molecular competition at the enzyme level is physiologically relevant for fatty-acid oxidation. Subsequently,this more realistic competition model was fitted to either mouse liver data or to disease-specific patient plasma data. When the substrate concentration was varied, both MADD and MCADD enhanced the accumulation of intermediate metabolite sand the flux declined already at lower substrate concentrations compared to the model without enzyme deficiencies.We hypothesize that the pathway structure of the beta-oxidationin which substrates compete for enzymes, is at the basis of the disease phenotypes associated with enzyme deficiencies.

DDB2, a new regulator of metabolism and cell death in human breast tumor cells

The protein Damaged DNA Binding-2 (DDB2) is well known for its role in DNA repair by nucleotide excision repair. Interestingly, DDB2 is differentially expressed in breast cancer expressing the estrogen receptor alpha or not. Recent works performed in our laboratory showed a new role of DDB2 in the control of proliferation and invasive abilities in different breast tumor cells through its involvement in the transcriptional regulation of target genes. Two genes involved in tumorigenic processes, MnSOD (manganese superoxide dismutase) and IκBα (inhibitor alpha of Nuclear Factor-kappa B), have been found to be regulated by DDB2. In addition, transcriptomic analyses on cells that differentially express DDB2 showed that several genes involved in the regulation of cellular metabolism are modulated. Our aim is now to focus on the effects of DDB2 expression on cellular metabolism and glycolysis. The results indicated that the overexpression of DDB2 leads to a respiratory chain dysfunction and an increase of the glycolytic pathway. Moreover, we observed an increased production of reactive oxygen species in these cells, compared to parental cells. As mitochondria are involved in cell death, we performed different experiments to evaluate the impact of DDB2 in the response to anticancer agents (Doxorubicin, and 5-fluorouracile (5-FU)) commonly used in the treatment of breast cancer. Interestingly, the cells exhibit a greater sensitivity to anticancer drugs when DDB2 is overexpressed. As these two agents are related to DNA damaged, we have also used other molecules, the apoptotic inducer, TNFα (Tumor Necrosis Factor alpha), and the Paclitaxel (an antimicrotubule agent) to precise the role of DDB2 on cell death. Similar results were obtained, thus demonstrating the influence of DDB2 overexpression in the response to cell death. The identification of molecular mechanisms responsible for these cellular modifications could place DDB2 and these target genes as predictive markers of sensitivity to anticancer drugs in breast cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-01-04.