Decoupling of Nrf2 Expression Promotes Mesenchymal State Maintenance in Non-Small Cell Lung Cancer

Abstract

Epithelial mesenchymal transition is a common mechanism leading to metastatic dissemination and cancer progression. In an effort to better understand this process we found an intersection of Nrf2/NLE2F2 (Nrf2), epithelial mesenchymal transition (EMT), and metabolic alterations using multiple in vitro and in vivo approaches. Nrf2 is a key transcription factor controlling the expression of redox regulators to establish cellular redox homeostasis. Nrf2 has been shown to exert both cancer inhibitory and stimulatory activities. Using multiple isogenic non-small cell lung cancer (NSCLC) cell lines, we observed a reduction of Nrf2 protein and activity in a prometastatic mesenchymal cell state and increased reactive oxygen species. Knockdown of Nrf2 promoted a mesenchymal phenotype and reduced glycolytic, TCA cycle and lipogenic output from both glucose and glutamine in the isogenic cell models; while overexpression of Nrf2 promoted a more epithelial phenotype and metabolic reactivation. In both Nrf2 knockout mice and in NSCLC patient samples, Nrf2low was co-correlated with markedly decreased expression of glycolytic, lipogenic, and mesenchymal RNAs. Conversely, Nrf2high was associated with partial mesenchymal epithelial transition and increased expression of metabolic RNAs. The impact of Nrf2 on epithelial and mesenchymal cancer cell states and metabolic output provide an additional context to Nrf2 function in cancer initiation and progression, with implications for therapeutic inhibition of Nrf2 in cancer treatment.

Oxidative Stress in Cancer

“…Whilst ROS are necessary to initiate EMT, it is unclear to what extent they are required to maintain a mesenchymal phenotype. Consistent with ROS playing a role in initiation of EMT, treatment with the antioxidant NAC can antagonise stimulation of EMT by TGF-β in various cells types, including murine AML12 hepatocytes (Kim et al, 2019), human ARPE-19 adult retinal pigment epithelial cells (Yang et al, 2020) and human HCC4006 lung epithelial cells (Haley et al, 2019). Possibly more surprising is that in a stably gefitinib-resistant human PC-9 non-small cell lung cancer cell line, treatment with NAC has been reported to increase an epithelial-phenotype and decrease the mesenchymal-phenotype (Li et al, 2020), suggesting a relative absence of ROS may stimulate mesenchymal-to-epithelial transition (MET).…”

“…Comparisons between epithelial-like human MCF-7 breast cancer cells and mesenchymal-like human MDA-MB-231 breast cancer cells revealed that the latter produce substantially higher levels of H 2 O 2 than the former (Lunetti et al, 2019). Moreover, HCC4006, A549 and H538 non-small cell lung cancer cell lines treated with TGF-β to induce a mesenchymal phenotype produce substantially higher levels of ROS than their non-treated epithelial counterparts (Haley et al, 2019). By contrast, breast cancer stem cells (BCSCs) with an epithelial-type morphology (i.e., E-BCSCs) have been reported to generate high levels of ROS, exhibit metabolic flexibility and possess heightened NRF2-regulated antioxidant defences necessary for survival, whereas BCSCs with a mesenchymal-type morphology (i.e., M-BCSCs) have low ROS levels, are dependent on glycolysis for energy, do not have high antioxidant defences, and do not require NRF2 for survival (Luo et al, 2018).…”

The Epithelial–Mesenchymal Transition at the Crossroads between Metabolism and Tumor Progression

“…Researchers have raised an interesting consideration regarding the changes in metabolism from primary tumor, migrating cells, and cells that colonize the metastatic niche, in which a sort of EMT-MET occurs. EMT and MET in metastasis formation is a theme that has been deeply discussed [ 187 ] and a deeper comprehension of the associated metabolic alterations could hopefully provide important insight to counteract cancer cell dissemination [ 188 ].…”

Epithelial–mesenchymal transition: The history, regulatory mechanism, and cancer therapeutic opportunities

“…390 In consistence with these, treatment of antioxidants, such as N-acetylcysteine (NAC), curcumin, resveratrol, has been shown to inhibit EMT in a variety of tumor cells. [391][392][393] It is worth noting that ROS also promote MET in cancer cells. For example, 2-deoxyglucose-induced ROS accumulation promotes the phenotype transition of mesenchymal breast cancer stem cells (CSCs) into epithelial breast CSCs.…”