The mechanisms by which miRNAs critically contribute to differential roles of Nrf1 and Nrf2 in modulating the epithelial-mesenchymal transformation of hepatocellular carcinoma

Accumulation of various genetics and epigenetics alterations are accepted to result in the initiation and progression of hepatocellular carcinoma (HCC), and its high metastasis is viewed as a critical bottleneck leading to its treatment failure. Amongst them, the abnormal expression of several microRNAs arising from lack of antioxidant transcription factor Nrf2 (encoded by Nfe2l2) leads to cancer metastasis. However, much less known is about regulation of microRNAs by Nrf1 (encoded by Nfe2l1), even though it acts as an essential determinon of cell homeostasis by governing the transcriptional expression of those driver genes contributing to the epithelial-mesenchymal transition (EMT) involved in its metastasis. In this study, distinctive EMT phenotypes were unveiled to result from specific knockout of Nrf1 and Nrf2 in HepG2 cells, as accompanied by differential migratory and invasive capabilities. The Nrf1-/--leading EMT results from a significantly decrease in the epithelial CDH1 expression, plus another increased expression of the mesenchymal CDH2. Such distinct phenotypes of Nrf1-/- from Nrf2-/- cell lines were also attributable to differential regulation of two key microRNAs, i.e., miR3187-3P and miR1247-5p. Further experiments unraveled that Nrf1 activates the expression of miR-3187-3p, directly targeting for the inhibition of SNAI1, leading to CDH1 activation but CDH2 inhibition insomuch as to prevent the process of EMT. By contrast, Nrf2 inhibits the expression of miR1247-5p, relieving its inhibitory effect on MMP15 and MMP17 to promote the EMT. Collectively, these demonstrate that the EMT of liver cancer cells is likely prevented by Nrf1 via the miR3187-3P signaling to the SNAI1-CDH1/2 axis, but conversely promoted by Nrf2 through the miR1247-5p-MMP15/17 signaling axis.