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    Research Paper
    15-Keto prostaglandin E2 suppresses STAT3 signaling and inhibits breast cancer cell growth and progression
    Eun Ji Leea,b, Su-Jung Kimb, Young-Il Hahna,b, Hyo-Jin Yoonb, Bitnara Hane, Kyeojin Kimg, Seungbeom Leeh, Kwang Pyo Kime,f, Young Ger Suhg,h, Hye-Kyung Nad,∗∗, Young-Joon Surha,b,c,∗ a Department of Molecular Medicine and Biopharmaceutical Science, Seoul National University, Seoul 08826, South Korea b Tumor Microenvironment Global Core Research Center, College of Pharmacy, Seoul National University, Seoul 08826, South Korea c Cancer Research Institute, Seoul National University, Seoul 03080, South Korea d Department of Food Science and Biotechnology, Sungshin Women's University, College of Knowledge-Based Services Engineering, Seoul 01133, South Korea e Department of Applied Chemistry, Institute of Natural Science, Global Center for Pharmaceutical Ingredient Materials, Kyung Hee University, Yongin 17104, South Korea f Department of Biomedical Science and Technology, Kyung Hee Medical Science Research Institute, Kyung Hee University, Seoul 02453, South Korea g College of Pharmacy, Seoul National University, Seoul 08826, Republic of Korea h College of Pharmacy, CHA University, Gyeonggi-do 11160, South Korea
    Breast cancer
    15-Hydroxyprostaglandin dehydrogenase
    15-Keto-prostaglandin E2
    Thiol modification
    MCF10A-ras cells
    Overproduction of prostaglandin E2 (PGE2) has been linked to enhanced tumor cell proliferation, invasiveness and metastasis as well as resistance to apoptosis. 15-Keto prostaglandin E2 (15-keto PGE2), a product formed from 15-hydroxyprostaglandin dehydrogenase-catalyzed oxidation of PGE2, has recently been shown to have anti-inflammatory and anticarcinogenic activities. In this study, we observed that 15-keto PGE2 suppressed the phosphorylation, dimerization and nuclear translocation of signal transducer and activator of transcription 3 (STAT3) in human mammary epithelial Acetylcysteine transfected with H-ras (MCF10A-ras). 15-Keto PGE2 inhibited the migration and clonogenicity of MCF10A-ras cells. In addition, subcutaneous injection of 15-keto PGE2 attenuated xenograft tumor growth and phosphorylation of STAT3 induced by breast cancer MDA-MB-231 cells. However, a non-electrophilic analogue, 13,14-dihydro-15-keto PGE2 failed to inhibit STAT3 signaling and was unable to suppress the growth and transformation of MCF10A-ras cells. These findings suggest that the α,β-unsaturated carbonyl moiety of 15-keto PGE2 is essential for its suppression of STAT3 signaling. We observed that the thiol reducing agent, dithiothreitol abrogated 15-keto PGE2-induced STAT3 inactivation and disrupted the direct interaction between 15-keto PGE2 and STAT3. Furthermore, a molecular docking analysis suggested that Cys251 and Cys259 residues of STAT3 could be preferential binding sites for this lipid mediator. Mass spectral analysis revealed the covalent modification of recombinant STAT3 by 15-keto PGE2 at Cys259. Taken together, thiol modification of STAT3 by 15-keto PGE2 inactivates STAT3 which may account for its suppression of breast cancer cell proliferation and progression.
    1. Introduction
    An inflammatory lipid mediator prostaglandin E2 (PGE2) is formed from arachidonic acid by cyclooxygenase-2 (COX-2) [1]. Over-production of PGE2 is constitutively elevated in various human malig-nancies, such as colon, gastric, lung and breast cancer [2–4]. COX-2-derived PGE2 plays an important role in inflammation and cancer progression through modulation of several intracellular signaling pathways [5–7].
    The intracellular level of PGE2 is regulated not only by its bio-synthesis but also by degradation. The key enzyme involved in cata-bolism of PGE2 is 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Expression of 15-PGDH is low in various cancers, including those of colon, stomach, bladder, and breast [8–11]. 15-PGDH knockout mice are susceptible to colon tumor induction [12]. Down regulation of 15-PGDH in breast cancer cells is associated with its gene silencing via hypermethylation of its promoter [11]. Overexpression and activity of 15-PGDH in various cancer cells have been shown to suppress their