Chronic oxidative stress leads to malignant transformation along with acquisition of stem cell characteristics, and epithelial to mesenchymal transition in human renal epithelial cells

Oxidative injury to cellular macromolecules has been suggested as a common pathway shared by multiple etiological factors for kidney cancer. Whether the chronic oxidative stress alone is sufficient to induce malignant transformation in human kidney cells is not clear. Therefore, the objective of this study was to evaluate the effect of H₂O₂-induced chronic oxidative stress on growth, and malignant transformation of HK-2 normal kidney epithelial cells. This study revealed that chronic oxidative stress causes increased growth and neoplastic transformation in normal kidney epithelial cells at non-cytotoxic dose and increased adaptation to cytotoxic level. This was confirmed by gene expression changes, cell cycle analysis, anchorage independent growth assay and in vivo tumorigenicity in nude mice. Stem cells characteristics as revealed by up-regulation of stem cell marker genes, and morphological changes indicative of EMT with up regulation of mesenchymal markers were also observed in cells exposed to chronic oxidative stress. Antioxidant NAC did not reverse the chronic oxidative stress-induced growth, and adaptation suggesting that perturbed biological function in these cells are permanent. Partial reversal of oxidative stress-induced growth, and adaptation by silencing of Oct 4 and Snail1, respectively, suggest that these changes are mediated by acquisition of stem cell and EMT characteristics. In summary, this study for the first time suggests that chronic exposure to elevated levels of oxidative stress is sufficient to induce malignant transformation in kidney epithelial cells through acquisition of stem cell characteristics. Additionally, the EMT plays an important role in increased adaptive response of renal cells to oxidative stress. J. Cell. Physiol. 230: 1916-1928, 2015.