Targeted Deletion of Nrf2 Reduces Urethane-Induced Lung Tumor Development in Mice

Abstract

Nrf2 is a key transcription factor that regulates cellular redox and defense responses. However, permanent Nrf2 activation in human lung carcinomas promotes pulmonary malignancy and chemoresistance. We tested the hypothesis that Nrf2 has cell survival properties and lack of Nrf2 suppresses chemically-induced pulmonary neoplasia by treating Nrf2 +/+ and Nrf2 -/- mice with urethane. Airway inflammation and injury were assessed by bronchoalveolar lavage analyses and histopathology, and lung tumors were analyzed by gross and histologic analysis. We used transcriptomics to assess Nrf2-dependent changes in pulmonary gene transcripts at multiple stages of neoplasia. Lung hyperpermeability, cell death and apoptosis, and inflammatory cell infiltration were significantly higher in Nrf2 -/- mice compared to Nrf2 +/+ mice 9 and 11 wk after urethane. Significantly fewer lung adenomas were found in Nrf2 -/- mice than in Nrf2 +/+ mice at 12 and 22 wk. Nrf2 modulated expression of genes involved cell-cell signaling, glutathione metabolism and oxidative stress response, and immune responses during early stage neoplasia. In lung tumors, Nrf2-altered genes had roles in transcriptional regulation of cell cycle and proliferation, carcinogenesis, organismal injury and abnormalities, xenobiotic metabolism, and cell-cell signaling genes. Collectively, Nrf2 deficiency decreased susceptibility to urethane-induced lung tumorigenesis in mice. Cell survival properties of Nrf2 were supported, at least in part, by reduced early death of initiated cells and heightened advantage for tumor cell expansion in Nrf2 +/+ mice relative to Nrf2 -/- mice. Our results were consistent with the concept that Nrf2 over-activation is an adaptive response of cancer conferring resistance to anti-cancer drugs and promoting malignancy.

Gene expression analysis in the lung of the rasH2 transgenic mouse at week 4 prior to induction of malignant tumor formation by urethane and N-methylolacrylamide

“…The bioinformatics analysis demonstrated disturbances in the expressions of cell-cycle related genes in the lungs of the UR-treated animal groups. Similar changes were also reported from analyses at weeks 12 and 22 of whole lung tissues of BALB/cCR mice containing tumors induced by UR (Bauer et al, 2011) and from analysis at week 10 of lung adenoma induced by UR in the rasH2 Tg mice (Okamura et al, 2006). On the other hand, these studies also demonstrated changes in the expressions of other categories of gene sets, no remarkable changes of which were found in our study, including genes related to cellular growth and proliferation, cell and tissue development, and metabolism (Bauer et al, 2011;Okamura et al, 2006).…”

“…Similar changes were also reported from analyses at weeks 12 and 22 of whole lung tissues of BALB/cCR mice containing tumors induced by UR (Bauer et al, 2011) and from analysis at week 10 of lung adenoma induced by UR in the rasH2 Tg mice (Okamura et al, 2006). On the other hand, these studies also demonstrated changes in the expressions of other categories of gene sets, no remarkable changes of which were found in our study, including genes related to cellular growth and proliferation, cell and tissue development, and metabolism (Bauer et al, 2011;Okamura et al, 2006). Considering that we used the non-neoplastic regions of the lung at earlier time-points for this analysis, these differences between the studies may suggest that the changes in the expressions of the cell cycle-related genes may be the initial event in UR-induced tumorigenesis.…”

“…Ereg is known to be expressed in cancers of the lung (Zhang et al, 2008), colon (Khambata-Ford et al, 2007), prostate (Sauer et al, 2010) and ovary (Amsterdam et al, 2011) in humans. In the mice, increased expressions of Ereg mRNA have been reported in lung tumors induced by vinyl carbamate (Alyaqoub et al, 2008) or UR (Bauer et al, 2011). Increased expression of Ereg has also been reported in lung tumors of Tg mice that express the K-ras proto-oncogene (Sunaga et al, 2013).…”

“…Cyclin B1 expression has been reported in cancers of the lung (Soria et al, 2000), breast (Kawamoto et al, 1997), colon (Wang et al, 1997) and prostate (Mashal et al, 1996) in humans. Another study reported an increased expression of cyclin B1 in UR-induced lung tumors in mice (Bauer et al, 2011). In addition to the genotypically differential increase in cyclin B1 gene expression, we also observed increased expressions of other cyclin genes, cyclin D1 and cyclin G1, in the UR-treated groups (mean log2 intensity value, cyclin D1, non-Tg/Control: Tg/Control: non-Tg/UR: Tg/UR = 8.8: 9.0: 10.7: 10.8; Cyclin G1, non-Tg/Control: Tg/Control: non-Tg/UR: Tg/UR = 6.7: 6.5: 10.7: 10.8), although no differences in the expression levels were observed between the Tg and non-Tg mice.…”

Nuclear Factor–Erythroid-2–Related Factor 2 in Aging and Lung Fibrosis

“…133 Targeted deletion of Nrf2 reduced urethaneinduced tumorigenesis in lungs of mice by minimizing the expression of ARE-responsive genes. 134 In addition, the tumor stroma has been reported to express high levels of Nrf2 and Nrf2 inhibitors proposed as an anticancer strategy. 135 Hence, Nrf2 may represent double-edged sword, and this must be considered when administering Nrf2 activators as interventional drugs.…”