CircLRP6 Regulation of ZEB1 via miR-455 Is Involved in the Epithelial-Mesenchymal Transition During Arsenite-Induced Malignant Transformation of Human Keratinocytes

Circular RNAs (circRNAs), a class of noncoding RNAs generated from pre-mRNAs, participate in the regulation of tumorigenesis. The mechanism for regulation, however, is unclear. Here, to determine whether circRNAs are involved in arsenite-induced epithelial-mesenchymal transition (EMT) and malignant transformation in human keratinocyte (HaCaT) cells, the up-regulation of circLRP6 was confirmed in arsenite-transformed HaCaT (T-HaCaT) cells. In HaCaT cells, circLRP6 acted as an microRNA (miR)-455 sponge. For these cells, chronic exposure to arsenite caused an increase of circLRP6 and the transcription factor ZEB1, which induced the EMT. miR-455 suppressed the expression of ZEB1. Further, in T-HaCaT cells, knockdown of circLRP6 with siRNA inhibited ZEB1 expression, but cotransfection with circLRP6 siRNA and an miR-455 inhibitor reversed this inhibition. These results suggest that, in HaCaT cells, arsenite increases circLRP6 levels, which act as a sponge for miR-455 and up-regulate the miR-455 target, ZEB1, which subsequently induces the EMT, thus promoting malignant transformation. Thus, for HaCaT cells chronically exposed to arsenite, circLRP6 via miR-455 regulation of ZEB1 is involved in the EMT during malignant transformation. The results establish a previously unknown mechanism for arsenite-induced carcinogenesis.