title: Iron modulates cell survival in a Ras- and MAPK-dependent manner in ovarian cells.
abstract: Ovarian cancer is a leading cause of cancer death in women in the United States. While the majority of ovarian cancers are serous, some rarer subtypes (i.e. clear cell) are often associated with endometriosis, a benign gynecological disease. Iron is rich in the cyst fluid of endometriosis-associated ovarian cancers and induces persistent oxidative stress. The role of iron, an essential nutrient involved in multiple cellular functions, in normal ovarian cell survival and ovarian cancer remains unclear. Iron, presented as ferric ammonium citrate (FAC), dramatically inhibits cell survival in ovarian cancer cell types associated with Ras mutations, while it is without effect in immortalized normal ovarian surface epithelial (T80) and endometriotic epithelial cells (lacking Ras mutations). Interestingly, FAC induced changes in cytoplasmic vacuolation concurrently with increases in LC3-II levels (an autophagy marker); these changes occurred in an ATG5/ATG7-dependent, beclin-1/hVps34-independent, and Ras-independent manner. Knockdown of autophagy mediators in HEY ovarian cancer cells reversed FAC-induced LC3-II levels, but there was little effect on reversing the cell death response. Intriguingly, transmission electron microscopy of FAC-treated T80 cells demonstrated abundant lysosomes (confirmed using Lysotracker) rich in iron particles, which occurred in a Ras-independent manner. Although the mitogen-activated protein kinase (MAPK) inhibitor, U0126, reversed FAC-induced LC3-II/autophagic punctae and lysosomes in a Ras-independent manner, it was remarkable that U0126 reversed cell death in malignant ovarian cells associated with Ras mutations. Moreover, FAC increased heme oxygenase-1 expression in H-Ras-overexpressing T80 cells, which was associated with increased cell death when overexpressed in T80 cells. Disruption of intracellular iron levels, via chelation of intracellular iron (deferoxamine), was also detrimental to malignant ovarian cell survival; thus, homeostatic intracellular iron levels are essential for cell survival. Collectively, our results implicate iron in modulating cell death in a Ras- and MAPK-dependent manner in ovarian cancer cells.
authors.affiliation: Moffitt Cancer Center and Research Institute, Cancer Biology Program, Tampa, FL, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Bauckman
authors.forename: E
authors.initials: E
authors.lastname: Haller
authors.forename: I
authors.initials: I
authors.lastname: Flores
authors.forename: M
authors.initials: M
authors.lastname: Nanjundan
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D000071193:Autophagy-Related Protein 7; D000071186:Beclin-1; D002070:Butadienes / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D058546:Class III Phosphatidylinositol 3-Kinases / Q000378:metabolism; D005260:Female; D005290:Ferric Compounds / Q000494:pharmacology*; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000473:pathology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C502778:ATG5 protein, human; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; D002070:Butadienes; D005290:Ferric Compounds; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D009570:Nitriles; D000644:Quaternary Ammonium Compounds; C113580:U 0126; D051547:Heme Oxygenase-1; D058546:Class III Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes; C013531:ferric ammonium citrate