15-Deoxy-Delta(12,14)-prostaglandin J(2) stabilizes hypoxia inducible factor-1 alpha through induction of heme oxygenase-1 and direct modification ofprolyl-4-hydroxylase 2

Abstract

15-Deoxy-(12,14)-prostaglandin J(2) (15d-PGJ(2)), 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-PGJ(2) resulted in the accumulation of the -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-PGJ(2)-mediated HIF-1 accumulation. 15d-PGJ(2) 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-PGJ(2)-induced HIF-1 expression although HO-1 expression was unchanged. This finding suggests that ROS accumulated as a consequence of HO-1 up-regulation can enhance HIF-1 expression in MCF-7 cells treated with 15d-PGJ(2). Alternatively, 15d-PGJ(2) was found to covalently bind to HIF-1 prolyl-4-hydroxylase 2 (PHD2) in MCF-7 cells, which hampers the proline hydroxylation of HIF-1, thereby disrupting ubiquitin-dependent proteasomal degradation of this transcription factor. Pretreatment with thiol reducing agents blunted 15d-PGJ(2)-induced HIF-1 stabilization, indicative of a cysteine residue as a direct target of 15d-PGJ(2). Molecular docking analysis suggests that 15d-PGJ(2) preferentially binds to PHD2 in the vicinity of the Cys(201) residue based on binding energies and carbon-sulfur distances. In summary, 15d-PGJ(2) stabilizes HIF-1 in MCF-7 cells through HO-1 induction with subsequent ROS generation and also through direct modification of PHD2.