Heme oxygenase-1 (HO-1) is a stress-responsive enzyme that has antioxidant and cytoprotective functions. 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), an endogenous ligand of peroxisome proliferator-activated receptor γ (PPARγ), has been reported to induce HO-1 and other antioxidant enzymes in certain cell lines. In the present work, we investigated the effects of HO-1 on the expression of p53 and p21 induced by 15d-PGJ2 in human breast cancer (MCF-7) cells. Treatment of MCF-7 cells with 15d-PGJ2 (30 μM) led to time-dependent increases in the expression of p53 and p21 as well as HO-1. The up-regulation of p53 and p21 expression by 15d-PGJ2 was abrogated by pharmacological inhibition with zinc protophophyrin (10 μM) or si-RNA knock down of HO-1. Nrf2, a basic-leucine zipper transcription factor, plays a key role in regulating the up-regulation of many antioxidant enzymes including HO-1. In MCF-7 cells transfected with NRF2 si-RNA, 15d-PGJ2 failed to induce expression of p53, p21 and HO-1. In addition, HO-1 inducers, such as cobalt protoporphyrin (25 μM) and hemin (10 μM), upregulated the expression of p53 and p21 without eliciting any apparent cytotoxicity. HO-1 degrades heme to produce iron, biliverdin, and carbon monoxide. We hypothesize that iron, a by-product of HO-1-catalyzed reactions, could mediate 15d-PGJ2-induced expression p53 and p21. Up-regulation of p53 and p21 expression by 15d-PGJ2 was abrogated by the iron chelator desferrioxamine (25 μM) in MCF-7 cells. Iron released from heme by HO-1 activity is mostly in the ferrous (Fe2+) form. When MCF-7 cells were treated with the iron-specific chelator phenanathroline (10 μM), 15d-PGJ2-induced expression of p53 and p21 was attenuated. However, p53 induction by 15d-PGJ2 was not affected by GW9662, a PPARγ antagonist. In addition, levels of the iron-sequestering protein H-ferritin were induced by 15d-PGJ2 in MCF-7 cells. Addition of the antioxidant N-acetylcysteine lowered the 15d-PGJ2-mediated H-ferritin levels. Recently, it has been reported that p21 as a positive regulator of Nrf2 extends the prosurvival function of p53 through recruitment of stress-response genes. Up-regulation of p53 and p21 expression via Nrf2-driven HO-1 induction and subsequent release of iron together with elevated expression of H-ferritin may confer resistance to oxidative damage in MCF-7 cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1470.