Abstract
Purpose: Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is transcription factor that regulates expression of antioxidant and phase II detoxifying genes and that promotes tumor growth and chemoresistance. Nuclear import and export of Nrf2 controls the cellular oxidoreduction homeostasis. In the current study, we explored whether expression of Nrf2 in the cytoplasm could promote tumor progression and subsequent poor survival in colorectal cancer patients.
Experimental Design: One hundred and fifty tumors from colorectal cancer patients were enrolled to evaluate Nrf2 expression by immunohistochemistry. The prognostic value of Nrf2 was analyzed by Kaplan-Meier and multivariate Cox regression models. The nuclear localization sequence (NLS) of Nrf2 was mutated by site-directed mutagenesis for transfection into Nrf2-knockdown HCT116 stable clones. HCT116 and HCT116 p53 null cells were also treated with a NO scavenger (carboxy-PTIO) and donor (GSNO), respectively. The effects of cytoplasmic Nrf2 on cell growth and migration capability were evaluated by colony formation and Boyden chamber assays.
Results: Fifty percent of the tumors displayed only cytoplasmic Nrf2, 32% of the tumors displayed cytoplasmic/nuclear Nrf2, and 18% of the tumors showed no Nrf2 expression by immunohistochemistry. Kaplan-Meier and Cox regression models showed that cytoplasmic Nrf2 may independently predict poor survival in colorectal cancer patients. Mechanistically, the elevation of cytoplasmic Nrf2 expression in the HCT116 shNrf2 stable clone by NLS-mutated Nrf2 transfection or NO scavenger treatment was responsible for the increase in colony formation and migration capability in these colon cells.
Conclusion: Cytoplasmic Nrf2 promotes tumor progression and subsequent poor survival in colorectal cancer patients.
