title: Reactive oxygen species via redox signaling to PI3K/AKT pathway contribute to the malignant growth of 4-hydroxy estradiol-transformed mammary epithelial cells.
abstract: The purpose of this study was to investigate the effects of 17-β-estradiol (E2)-induced reactive oxygen species (ROS) on the induction of mammary tumorigenesis. We found that ROS-induced by repeated exposures to 4-hydroxy-estradiol (4-OH-E2), a predominant catechol metabolite of E2, caused transformation of normal human mammary epithelial MCF-10A cells with malignant growth in nude mice. This was evident from inhibition of estrogen-induced breast tumor formation in the xenograft model by both overexpression of catalase as well as by co-treatment with Ebselen. To understand how 4-OH-E2 induces this malignant phenotype through ROS, we investigated the effects of 4-OH-E2 on redox-sensitive signal transduction pathways. During the malignant transformation process we observed that 4-OH-E2 treatment increased AKT phosphorylation through PI3K activation. The PI3K-mediated phosphorylation of AKT in 4-OH-E2-treated cells was inhibited by ROS modifiers as well as by silencing of AKT expression. RNA interference of AKT markedly inhibited 4-OH-E2-induced in vitro tumor formation. The expression of cell cycle genes, cdc2, PRC1 and PCNA and one of transcription factors that control the expression of these genes - nuclear respiratory factor-1 (NRF-1) was significantly up-regulated during the 4-OH-E2-mediated malignant transformation process. The increased expression of these genes was inhibited by ROS modifiers as well as by silencing of AKT expression. These results indicate that 4-OH-E2-induced cell transformation may be mediated, in part, through redox-sensitive AKT signal transduction pathways by up-regulating the expression of cell cycle genes cdc2, PRC1 and PCNA, and the transcription factor - NRF-1. In summary, our study has demonstrated that: (i) 4-OH-E2 is one of the main estrogen metabolites that induce mammary tumorigenesis and (ii) ROS-mediated signaling leading to the activation of PI3K/AKT pathway plays an important role in the generation of 4-OH-E2-induced malignant phenotype of breast epithelial cells. In conclusion, ROS are important signaling molecules in the development of estrogen-induced malignant breast lesions.
authors: Department of Environmental and Occupational Health, Florida International University, Miami, Florida, USA.
authors: Victor O
authors: VO
authors: Okoh
authors: Quentin
authors: Q
authors: Felty
authors: Jai
authors: J
authors: Parkash
authors: Robert
authors: R
authors: Poppiti
authors: Deodutta
authors: D
authors: Roy
mesh_terms: D000818:Animals; D001393:Azoles / Q000494:pharmacology; D002374:Catalase / Q000378:metabolism; D002396:Catechols / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000473:pathology*; D003094:Collagen / Q000494:pharmacology; D003114:Colony-Forming Units Assay; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000201:enzymology* / Q000473:pathology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D002393:Estrogens, Catechol / Q000494:pharmacology*; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D054833:Isoindoles; D042361:Mammary Glands, Human / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D051379:Mice; D008954:Models, Biological; D009361:Neoplasm Invasiveness; D016566:Organoselenium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D018874:Spheroids, Cellular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
chemical_list: D001393:Azoles; D002374:Catalase; D002396:Catechols; D018797:Cell Cycle Proteins; D003094:Collagen; D004958:Estradiol; D002393:Estrogens, Catechol; D000077267:Fulvestrant; D054833:Isoindoles; D016566:Organoselenium Compounds; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D017382:Reactive Oxygen Species; C042986:ebselen; C014036:4-hydroxyestradiol