Abstract #16: Piceatannol induces heme oxygenase-1 expression in human mammary epithelial cells through activation of ARE-driven Nrf2 signaling

Piceatannol (3,4,3\#8217;,5\#8217;-tetrahydroxy-trans-stilbene), derived from the seeds of Euphorbia lagascae, has been reported to have anti-proliferative, anti-inflammatory, and anti-oxidant properties. However, the mechanisms underlying its chemoprotective effects remain largely unresolved. In the present study, we found that piceatannol treatment (30 \#956;M) significantly upregulated the expression of the antioxidant enzyme heme oxygenase-1 (HO-1) and its mRNA transcript at 6 h and 3 h, respectively in human breast epithelial (MCF10A) cells. A redox-sensitive transcription factor NF-E2-related factor (Nrf2) plays a pivotal role in induced expression of many antioxidant and phase-2 detoxifying enzymes. Piceatannol induced translocation of Nrf2 into the nucleus and its transcriptional activities when treated to the MCF10A cells for 6 h. Up-regulation of HO-1 expression by piceatannol through direct binding of Nrf2 to antioxidant response element (ARE) was verified by the chromatin immunoprecipitation (ChIP) assay. siRNA knock down of Nrf2 gene abolished piceatannol-induced HO-1 expression. In addition, piceatannol-induced activation of Nrf2 was abrogated by the pharmacological inhibitor (LY294002) as well as the kinase dead form of Akt. HO-1 upregulation and Nrf2 activation induced by piceatannol were more prominent than those afforded by the same concentration of resveratrol (3,4\#8217;,5-trihydroxy-trans-stilbene) and oxyresveratrol (2,\#8217;,4,5\#8217;-tetrahydroxy-trans-stilbene), stilbene analogs structurally related to piceatannol. In an attempt to explain the cytoprotective or chemoprotective activity exerted by piceatannol, we examined its effect on the expression of HO-1 and the signaling pathways responsible for induction of this antioxidant enzyme. We hypothesize that an electrophilic quinone formed as a consequence of oxidation of piceatannol bearing the catechol moiety may bind covalently to Kelch-like ECH-associated protein 1 (Keap1), an inhibitory protein that sequesters Nrf2 in the cytoplasm. This will diminish the affinity of Keap1 for Nrf2. The thiol reducing agent dithiothreitol (100 \#956;M) attenuated piceatannol-induced Nrf2 activation and HO-1 expression. It is hence likely that piceatannol modifies specific cysteine residues of Keap1, which allows Nrf2 to translocate into the nucleus and bind to ARE, leading to enhancement of the expression of HO-1. The characteristic catechol moiety of piceatannol appears to be critical for the induction of Nrf2 activation and subsequent upregulation of HO-1. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 16.