Docosahexaenoic Acid Induces Expression of Heme Oxygenase-1 and NAD(P)H: quinone Oxidoreductase through Activation of Nrf2 in Human Mammary Epithelial Cells

Docosahexaenoic acid (DHA), an omega-3 fatty acid abundant in fish oils, has diverse health beneficial effects, such as anti-oxidative, anti-inflammatory, neuroprotective, and chemopreventive activities. In this study, we found that DHA induced expression of two representative antioxidant/ cytoprotective enzymes, heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase (NQO1), in human mammary epithealial (MCF-10A) cells. DHA-induced upregulation of these enzymes was accompanied by enhanced translocation of the redox-sensitive transcription factor Nrf2 into the nucleus and its binding to antioxidant response element. Nrf2 gene silencing by siRNA abolished the DHA-induced expression of HO-1 and NQO1 proteins. When MCF-10A cells were transfected with mutant constructs in which the cysteine 151 or 288 residue of Keap1 was replaced by serine, DHA-induced expression of HO-1 and NQO1 was markedly reduced. Moreover, DHA activated protein kinase C (PKC)delta and induced Nrf2 phosphorylation. DHA-induced phosphorylation of Nrf2 was abrogated by the pharmacological PKC delta inhibitor rottlerin or siRNA knockdown of its gene expression. The antioxidants N-acetyl-L-cysteine and Trolox attenuated DHA-induced activation of PKC delta, phosphorylation of Nrf2, and and its target protein expression. In conclusion, DHA activates Nrf2, possibly through modification of critical Keap1 cysteine 288 residue and PKC delta-mediated phosphorylation of Nrf2, leading to upregulation of HO-1 and NQO1 expression.