Invasive Potential Induced under Long-Term Oxidative Stress in Mammary Epithelial Cells

Abstract

Although the causal relationship between chronic inflammation and carcinogenesis has long been discussed, the molecular basis of the relation is poorly understood. In the present study, we focused on reactive oxygen species (ROS) and their signals under inflammatory conditions leading to the carcinogenesis of epithelial cells and found that repeated treatment with a low dose of H 2 O 2 (0.2 mmol/L) for periods of 2 to 4 days caused a phenotypic conversion of mouse NMuMG mammary epithelial cells from epithelial to fibroblast-like as in malignant transformation. The phenotypic conversion included the dissolution of cell-cell contacts, redistribution of E-cadherin in the cytoplasm, and up-regulation of a set of integrin family members (integrin ␣2, ␣6, and ␤3) and matrix metalloproteinases (MMPs; MMP-3, -10, and -13), as analyzed using Northern blot analysis and quantitative reverse transcription-PCR. Gelatin zymography indicated post-transcriptional activation of gelatinases, including MMP-2 and -9. In parallel, p38 mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 were activated, which contributed to the induction of MMP-13, and a glutathione S-transferase pull-down assay showed the activation of a small GTPase, Rac1. Surprisingly, the prolonged oxidative treatment was sufficient to induce all of the aforementioned events. Most importantly, depending on the MMP activities, the epithelial cells exposed to oxidative conditions eventually acquired invasiveness in a reconstituted model system with a Matrigel invasion chamber containing normal fibroblasts at the bottom, providing the first substantial evidence supporting the direct role of ROS signals in the malignant transformation of epithelial cells.

Cancer Associated Fibroblasts Exploit Reactive Oxygen Species Through a Proinflammatory Signature Leading to Epithelial Mesenchymal Transition and Stemness

“…They cause oxidative damage to DNA and genomic instability or alter gene expression through modulation of transcription factors. In addition, repeated treatment with H 2 O 2 caused a phenotypic conversion from mammary epithelial to fibroblast-like as in malignant transformation (27). In mammary carcinoma cells, ROS have also been correlated with EMT, through a Rac1b-mediated delivery of mitochondrial ROS (36).…”

Translationally controlled tumor protein induces human breast epithelial cell transformation through the activation of Src

“…Abnormal expression of MMPs contributes to tumor growth, invasion and metastasis (Rowe and Weiss, 2008). Recent reports suggest that chronic stimulation of ROS upregulates at least four MMPs (MMP-2, MMP-3 and MMP-9, MMP-13), causing tumor initiation and dissemination (Mori et al, 2004). It has also been reported that MMP-3 and MMP-13 serve as tumor promoters (Sternlicht et al, 2000;Impola et al, 2005).…”

Mitochondrial pyrimidine nucleotide carrier (PNC1) regulates mitochondrial biogenesis and the invasive phenotype of cancer cells

“…However, damaged mitochondria may also directly participate in increasing metastatic potential by activating a reactive oxygen species (ROS)-mediated retrograde signalling pathway (Ferraro et al, 2006;Owusu-Ansah et al, 2008). Earlier studies have correlated elevated levels of ROS in cancer cells with carcinogenesis (Klaunig et al, 1998;Mori et al, 2004). Numerous studies have implicated ROS in DNA mutation and apoptosis, low levels of ROS produced in response to growth factor signalling may also function as a secondary messenger to activate signalling pathways (Finkel, 2000).…”