EFFECTS OF ZINC ION ON EPITHELIAL TO MESENCHYMAL TRANSITION AND CANCER STEMNESS OF LUNG CANCER CELLS

Abstract

Epithelial-to-mesenchymal transition (EMT) as well as cancer stem cells (CSCs) play critical roles in cancer progression and metastasis. Although these two events have distinct characteristics and molecular pathways, CSCs could be trigger during EMT process and CSCs were frequently found to possess EMT characteristics. Collective evidence showed that plasma level of zinc ion in the patients with lung cancer has significantly lower than that of normal subjects, suggesting the impact of zinc ion on the disease. Zinc ion implicates in many cellular processes and signaling of the cells; however, the regulatory role of zinc ion on EMT and CSCs are unknown. Herein, the present study has shown for the first time that zinc ion has converse effects on EMT and CSCs of lung cancer cells. While zinc ion enhances EMT phenotypes, it was shown to suppresses CSC program. For EMT, an increase in EMT markers including N-cadherin, vimentin, snail and slug and decrease of E-cadherin was observed in zinc ion-treated cells, indicating the induction of EMT with mesenchymal-like morphology and increased cancer cell motility. In contrast, zinc ion reduced tumor spheroid forming with the decreased expression of CSC markers (CD133 and ALDH1A1) and CSC transcription factors (Oct4, Nanog, and Sox2). For mechanistic approaches, zinc ion generated intracellular superoxide anion that increased the EMT proteins and promoted cell motility. Treatment with the specific superoxide anion inhibitor (MnTBAP) could reverse the effect of zinc ion on superoxide anion and EMT phenotypes. The decrease in tumor sphere formation and CSC markers in zinc ion-treated cells were also reversed by MnTBAP treatment. Moreover, this study found that superoxide anion generated by zinc ion suppressed CSCs through the PKCα/ß-catenin dependent mechanism by activating PKCα which subsequently phosphorylated and mediated ß-catenin degradation via the ubiquitin-proteasomal mechanism. Zinc ion has a capability to increase the ß-catenin-ubiquitin complex which can be blocked by bisindolylmaleimide I (PKC inhibitor). In conclusion, this current study has addressed the novel important regulatory roles of zinc ion and underlying mechanisms in regulation of EMT and CSCs, two major factors facilitating cancer aggressiveness. These findings lead to the better understanding of cancer cell biology regarding this essential endogenous element on cancer aggressive behaviors.