15-Deoxy-Δ^12,14-prostaglandin J₂ stabilizes hypoxia inducible factor-1α through induction of heme oxygenase-1 and direct modification ofprolyl-4-hydroxylase 2

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), a representative J-series cyclopentenone prostaglandin, has biphasic roles in cell proliferation and apoptosis. Hypoxia inducible factor-1 (HIF-1) regulates expression of various genes involved in tumor growth and angiogenesis. In the present study, treatment of human breast cancer (MCF-7) cells with 15d-PGJ₂ resulted in the accumulation of the α-subunit of HIF-1. Pretreatment with zinc protoporphyrin IX, a pharmacological inhibitor of heme oxygenase-1 (HO-1), as well as siRNA knockdown of HO-1 gene in MCF-7 cells attenuated 15d-PGJ₂-mediated HIF-1α accumulation. 15d-PGJ₂ treatment increased intracellular production of reactive oxygen species (ROS), which was mediated by HO-1 induction. Preincubation of MCF-7 cells with trolox, a water-soluble form of vitamin E, attenuated 15d-PGJ₂-induced HIF-1α expression although HO-1 expression was unchanged. This finding suggests that ROS accumulated as a consequence of HO-1 up-regulation can enhance HIF-1α expression in MCF-7 cells treated with 15d-PGJ₂. Alternatively, 15d-PGJ₂ was found to covalently bind to HIF-1α prolyl-4-hydroxylase 2 (PHD2) in MCF-7 cells, which hampers the proline hydroxylation of HIF-1α, thereby disrupting ubiquitin-dependent proteasomal degradation of this transcription factor. Pretreatment with thiol reducing agents blunted 15d-PGJ₂-induced HIF-1α stabilization, indicative of a cysteine residue as a direct target of 15d-PGJ₂. Molecular docking analysis suggests that 15d-PGJ₂ preferentially binds to PHD2 in the vicinity of the Cys²⁰¹ residue based on binding energies and carbon–sulfur distances. In summary, 15d-PGJ₂ stabilizes HIF-1α in MCF-7 cells through HO-1 induction with subsequent ROS generation and also through direct modification of PHD2.