APE1/Ref-1 with reducing activity induces mesenchymal-to-epithelial transition in TNF-α-stimulated breast cancer cells

Metastasis is the leading cause of breast cancer-related mortality and involves cells from a primary tumor invading into adjacent tissue by using the circulatory system.During the process of metastasis, several dynamic and reciprocal interactions between cancer cells and inflammatory cells occur in the surrounding tumor microenvironment via the secretion of several cytokines, including tumor necrosis factor-α, and transforming growth factor-β.The present study aimed to investigate the functional role of recombinant apurinic apyrimidinic endonuclease 1(APE1)/Redox factor-1 (Ref-1) with reducing activity, [APE1/Ref-1-(SH)2] in the regulation of metastatic migration in cytokine-stimulated MDA-MB-231 breast cancer cells.The results reveal that [APE1/Ref-1-(SH)2], but not the oxidized form of recombinant APE1/Ref-1, attenuated migration, and invasion of cytokines-stimulated MDA-MB-231 cells.These effects were induced by the oxidative conformational changes due to the thiol-disulfide exchange reaction targeting disulfide bonds in extracellular domain of the cytokine receptors.Blocking of the binding of the cytokines to the corresponding receptors also reversed epithelial-to-mesenchymal transition (EMT) in cytokine-stimulated MDA-MB-231 cells.The reversal of EMT was accompanied by changes in the expression levels of representative EMT markers, E-cadherin, N-cadherin, vimentin, and snail.Remarkable phenotypic changes were also observed in MDA-MB-231 cells, as the cells adopted an epithelial like globular shape, with regular dimension, a reorganized cytoskeleton, and collapsing filopodia and lamellipodia.In conclusion, although devising a stable form of recombinant [APE1/Ref-1-(SH)2] requires further study, its ability to target cytokine receptors and to inhibit their intracellular signaling suggests the use of [APE1/Ref-1-(SH)2] as a promising agent for regulating metastatic cancer cells.