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Elevated expression or activity of heme oxygenase-1 (HO-1), a ubiquitous stress-responsive enzyme, has been reported to stimulate proliferation and to accelerate angiogenesis in several types of tumor cells. 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), an endogenous ligand of peroxisome proliferator-activated receptor γ, has been known to induce HO-1 in certain cell lines. In the present work, we found that treatment of human breast cancer (MCF-7) cells with nontoxic doses of 15d-PGJ2 led to concentration- and time-dependent increases in the expression and activity of HO-1. The induction of HO-1 expression preceded the upregulation of vascular endothelial growth factor (VEGF) in MCF-7 cells stimulated with 15d-PGJ2. To determine whether the induction of HO-1 is responsible for VEGF production, a specific inhibitor of HO-1 was utilized. The upregulation of VEGF production by 15d-PGJ2 was abrogated by the HO-1 inhibitor, ZnPP. Moreover, ZnPP decreased the in vitro capillary formation induced by 15d-PGJ2 in human umbilical vein endothelial cells. Likewise, ZnPP treatment inhibited the migrative phenotype of 15d-PGJ2-treated MCF-7 cells as determined by the wound migration assay. Nrf2, a basic-leucine zipper transcription factor, plays a key role in regulating the antioxidant response element (ARE)-mediated expression of antioxidant enzymes including HO-1. 15d-PGJ2 induced increased nuclear translocation and subsequent ARE binding of Nrf2. MCF-7 cells transfected with dominant negative Nrf2 exhibited reduced expression of HO-1 and VEGF in response to 15d-PGJ2 treatment. Taken together, these results suggest that 15d-PGJ2-induced expression of HO-1 via the Nrf2 signaling is implicated in angiogenesis in human breast cancer. To the best of our knowledge, this is the first demonstration of involvement of Nrf2 in VEGF induction and angiogenesis.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]