Nuclear factor (erythroid-derived 2)-like 2 promotes tumor-initiating cell lineage and drug resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common malignancy worldwide. The long-term prognosis of HCC remains unsatisfactory due to high recurrence rates and chemoresistance. The efficacy of sorafenib, the only FDA-approved molecularly targeted drug in advanced hepatocellular carcinoma (HCC) is limited by acquired resistance. Increasing evidences showed that liver tumor-initiating cells (T-ICs) is the source of acquired resistance and metastasis. We have previously established sorafenib-resistant HCC cells both in vitro and PDTX models and demonstrated that these cells are endowed with enhanced T-IC properties. Interestingly, nuclear factor (erythroid-derived 2)-like 2 (NRF2) expression was elevated in these resistant cells. The transcription factor NRF2 has long been considered as a tumour suppressor, as it can regulate cellular antioxidant response to protect cells from oxidative stress, chemotherapeutic agents and radiotherapy. In HCC, NRF2 level was up-regulated, and its expression was correlated with tumor differentiation, metastasis, and tumor size, revealing its oncogenic role. By lentiviral based knockdown approach, we found that NRF2 repression suppressed liver T-IC properties including self-renewal, in vivo tumorigenicity, HCC invasiveness and expression of liver T-IC markers. In addition, we found that NRF2 repression not only sensitized HCC cells to sorafenib but also to other chemotherapeutic drugs including doxorubicin and fluorouracil. Mechanistically, the signaling cascade related to sonic hedgehog pathway was greatly suppressed in NRF2 knockdown HCC cells, when compared with control counterparts. Collectively, NRF2 was involved in drug resistance, invasion and migration, tumorigenicity and self-renewal via regulating T-IC properties at least in part through direct regulation of sonic hedgehog pathway in HCC. Targeting NRF2 mediated signaling cascade alone or in combination with other treatment modalities may be a new a potential therapeutic approach for treatment of HCC.