Estrogen increases Nrf2 activity through activation of the PI3K pathway in MCF-7 breast cancer cells

• Published in: Experimental cell research Vol. 328; no. 2; pp. 351 - 360
• Main Authors: Wu, Juanjuan, Williams, Devin, Walter, Grant A., Thompson, Winston E., Sidell, Neil
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2014; Elsevier BV
• Subjects: 60 APPLIED LIFE SCIENCES; Breast cancer; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Cell Line, Tumor; Cellular biology; Estrogen; ESTROGENS; Estrogens - genetics; Estrogens - metabolism; Female; GENES; Glycogen Synthase Kinase 3 - genetics; Glycogen Synthase Kinase 3 - metabolism; Glycogen Synthase Kinase 3 beta; HEME; Heme Oxygenase-1 - genetics; Heme Oxygenase-1 - metabolism; Humans; LUCIFERASE; MAMMARY GLANDS; MCF-7 Cells; MESSENGER-RNA; NEOPLASMS; NF-E2-Related Factor 2 - genetics; Nrf2 activation; Phosphatidylinositol 3-Kinase - genetics; Phosphatidylinositol 3-Kinase - metabolism; PHOSPHORYLATION; Phosphorylation - genetics; PROGESTERONE; Progesterone - genetics; Progesterone - metabolism; Proteins; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; RECEPTORS; Receptors, Estrogen - genetics; Receptors, Estrogen - metabolism; Signal transduction; Signal Transduction - genetics; TRANSCRIPTION FACTORS; Up-Regulation - genetics; Breast cancer; Nrf2 activation; Estrogen
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/j.yexcr.2014.08.030

The actions of the transcription factor Nuclear factor erythroid 2-related factor (Nrf2) in breast cancer have been shown to include both pro-oncogenic and anti-oncogenic activities which is influenced, at least in part, by the hormonal environment. However, direct regulation of Nrf2 by steroid hormones (estrogen and progesterone) has received only scant attention. Nrf2 is known to be regulated by its cytosolic binding protein, Kelch-like ECH-associated protein 1 (Keap1), and by a Keap1-independent mechanism involving a series of phosphorylation steps mediated by phosphatidylinositol 3-kinase (PI3K) and glycogen synthase kinase 3 beta (GSK3β). Here, we report that estrogen (E2) increases Nrf2 activity in MCF7 breast cancer cells through activation of the PI3K/GSK3β pathway. Utilizing antioxidant response element (ARE)-containing luciferase reporter constructs as read-outs for Nrf2 activity, our data indicated that E2 increased ARE activity >14-fold and enhanced the action of the Nrf2 activators, tertiary butylhydroquinone (tBHQ) and sulforaphane (Sul) 4 to 9 fold compared with cells treated with tBHQ or Sul as single agents. This activity was shown to be an estrogen receptor-mediated phenomenon and was antagonized by progesterone. In addition to its action on the reporter constructs, mRNA and protein levels of heme oxygenase 1, an endogenous target gene of Nrf2, was markedly upregulated by E2 both alone and in combination with tBHQ. Importantly, E2-induced Nrf2 activation was completely suppressed by the PI3K inhibitors LY294002 and Wortmannin while the GSK3β inhibitor CT99021 upregulated Nrf2 activity. Confirmation that E2 was, at least partly, acting through the PI3K/GSK3β pathway was indicated by our finding that E2 increased the phosphorylation status of both GSK3β and Akt, a well-characterized downstream target of PI3K. Together, these results demonstrate a novel mechanism by which E2 can regulate Nrf2 activity in estrogen receptor-positive breast cancer cells and suggest that patients׳ hormonal status through this activity may play a significant role in some therapeutic outcomes. •Estrogen (E2) increases Nrf2 activity in E2-responsive breast cancer cells.•ERα, but not ERβ is essential for E2-mediated stimulation of Nrf2 in MCF7 cells.•The PI3K/Akt/GSK3β pathway is involved in E2 stimulation of Nrf2.•E2 stimulates phosphorylation of Akt and GSK3β.