Redox mechanisms switch on hypoxia-dependent epithelial–mesenchymal transition in cancer cells

Abstract

Epithelial-mesenchymal transition (EMT) and hypoxia are considered as crucial events favouring invasion and metastasis of many cancer cells. In this study, different human neoplastic cell lines of epithelial origin were exposed to hypoxic conditions in order to investigate whether hypoxia per se may trigger EMT programme as well as to mechanistically elucidate signal transduction mechanisms involved. The following human cancer cell lines were used: HepG2 (from human hepatoblastoma), PANC-1 (from pancreatic carcinoma), HT-29 (from colon carcinoma) and MCF-7 (from breast carcinoma). Cancer cells were exposed to carefully controlled hypoxic conditions and investigated for EMT changes and signal transduction by using morphological, cell and molecular biology techniques. All cancer cells responded to hypoxia within 72 h by classic EMT changes (fibroblastoid phenotype, SNAIL and beta-catenin nuclear translocation and changes in E-cadherin) and by increased migration and invasiveness. This was involving very early inhibition of glycogen synthase kinase-3beta (GSK-3beta), early SNAIL translocation as well as later and long-lasting activation of Wnt/beta-catenin-signalling machinery. Experimental manipulation, including silencing of hypoxia-inducible factor (HIF)-1alpha and the specific inhibition of mitochondrial generation of reactive oxygen species (ROS), revealed that early EMT-related events induced by hypoxia (GSK-3beta inhibition and SNAIL translocation) were dependent on transient intracellular increased generation of ROS whereas late migration and invasiveness were sustained by HIF-1alpha- and vascular endothelial growth factor (VEGF)-dependent mechanisms. These findings indicate that in cancer cells, early redox mechanisms can switch on hypoxia-dependent EMT programme whereas increased invasiveness is sustained by late and HIF-1alpha-dependent release of VEGF.

Anoikis: an emerging hallmark in health and diseases

“…This hypothesis is supported by the ability of hypoxia to induce EMT in a redox-dependent manner [141]. Furthermore, hypoxia has been linked to mitochondrial oxidative stress, leading to HIF1α stabilization [141,142]. Owing to the acknowledged pro-survival role of both the EMT programme and oxidative stress, we therefore speculate that an hypoxic environment may act on tumour cells, stimulating their resistance to anoikis cell death.…”

“…This hypothesis is supported by the ability of hypoxia to induce EMT in a redox-dependent manner [141]. Furthermore, hypoxia has been linked to mitochondrial oxidative stress, leading to HIF1α stabilization [141,142].…”

Hydrogen Peroxide Promotes Epithelial to Mesenchymal Transition and Stemness in Human Malignant Mesothelioma Cells

“…As epithelial cells are adherent to each other via E-cadherin, loss of the E-cadherin may be associated with detachment of individual cells from neighboring cells (Cannito et al, 2008), stimulating migration and metastasis. Induction of EMT confers resistance to apoptosis and promotes anchorage-independent growth in epithelial cell lines (Robson et al, 2006;Yang et al, 2006).…”

“…EMT program is controlled by various growth and differentiation factors including transforming growth factor β1 (TGF-β1) and hypoxia inducible factor 1 (HIF-1α) (Xu et al, 2009), mediated through EMT transcription factors such as SNAIL, SLUG, and TWIST1 (Cannito et al, 2008;Yang et al, 2008a). Stabilization of RESEARCH ARTICLE…”

A microfluidic device to study cancer metastasis under chronic and intermittent hypoxia

“…The observation of increased migration in the device with cells maintained under 1% oxygen is consistent with an extensive literature, suggesting that hypoxia generates a more aggressive phenotype 53,54 and was found in traditional transwell chamber assays for the PANC-1 cell line. [55][56][57] It should be noted that in these earlier studies, cells were trypsinized and resuspended in low-serum medium and a chemoattractant was used in each invasion assay. [55][56][57] In this communication, trypsinization, which may affect viability and invasiveness, was not necessary for the invasion assay nor was a chemoattractant (other than oxygen) added to induce migration.…”