title: Lipocalin 2 attenuates iron-related oxidative stress and prolongs the survival of ovarian clear cell carcinoma cells by up-regulating the CD44 variant.
abstract: Ovarian clear cell carcinoma (CCC) arises from ovarian endometriosis. Intra-cystic fluid contains abundant amounts of free iron, which causes persistent oxidative stress, a factor that has been suggested to induce malignant transformation. However, the mechanisms linking oxidative stress and carcinogenesis in CCC currently remain unclear. Lipocalin 2 (LCN2), a multifunctional secretory protein, functions as an iron transporter as well as an antioxidant. Therefore, we herein examined the roles of LCN2 in the regulation of intracellular iron concentrations, oxidative stress, DNA damage, and antioxidative functions using LCN2-overexpressing (ES2), and LCN2-silenced (RMG-1) CCC cell lines. The results of calcein staining indicated that the up-regulated expression of LCN2 correlated with increases in intracellular iron concentrations. However, a DCFH-DA assay and 8OHdG staining revealed that LCN2 reduced intracellular levels of reactive oxygen species and DNA damage. Furthermore, the expression of LCN2 suppressed hydrogen peroxide-induced apoptosis and prolonged cell survival, suggesting an antioxidative role for LCN2. The expression of mRNAs and proteins for various oxidative stress-catalyzing enzymes, such as heme oxygenase (HO), superoxide dismutase (SOD), and glutathione peroxidase, was not affected by LCN2, whereas the intracellular concentration of the potent antioxidant, glutathione (GSH), was increased by LCN2. Furthermore, the expression of xCT, a cystine transporter protein, and CD44 variant 8-10 (CD44v), a stem cell marker, was up-regulated by LCN2. Although LCN2 increased intracellular iron concentrations, LCN2-induced GSH may catalyze and override oxidative stress via CD44v and xCT, and subsequently enhance the survival of CCC cells in oxidative stress-rich endometriosis.
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamada
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Miyamoto
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kashima
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Kobara
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Asaka
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Ando
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Shotaro
authors.initials: S
authors.lastname: Higuchi
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Ida
authors.affiliation: a Department of Obstetrics and Gynecology , Shinshu University School of Medicine , Matsumoto , Japan.
authors.forename: Tanri
authors.initials: T
authors.lastname: Shiozawa
mesh_terms: D027182:Amino Acid Transport System y+ / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D004847:Epithelial Cells / Q000378:metabolism* / Q000473:pathology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics* / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D000071068:Lipocalin-2 / Q000235:genetics* / Q000378:metabolism; D010053:Ovary / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism
chemical_list: D027182:Amino Acid Transport System y+; C497483:CD44 protein, human; D018960:Hyaluronan Receptors; C489506:LCN2 protein, human; D000071068:Lipocalin-2; C118895:SLC7A11 protein, human; D007501:Iron; D005979:Glutathione Peroxidase; D006419:Heme Oxygenase (Decyclizing); D013482:Superoxide Dismutase; D005978:Glutathione
keywords: Cystine transporter; lipocalin 2; ovarian clear cell carcinoma; ovarian endometriosis; oxidative stress; reactive oxygen species (ROS)