Estrogen in ovarian cancer cell metastasis

Benign ovarian tumors and majority of epithelial ovarian cancers possess steroid receptors including estrogen receptors (ERs). However, the estrogen-ER signaling in ovarian carcinomas is not completely understood. Tumorigenesis is a multiple-step process involving dysregulated cell growth and metastasis. Tumor cells acquire the capacity of migration and invasion by temporal phenotypical and genotypical changes termed epithelial-mesenchymal transition (EMT). Considerable evidence implicates a mitogenic action of estrogen in early ovarian carcinogenesis. In contrast, its influence in the metastatic cascade of ovarian tumor cells remains obscure. In this study, I have focused on the role of 17β-estradiol (E2) in ovarian tumorigenesis. EMT related genes including E-cadherin, Snail, Slug, and Twist were examined. E2 treatment led to clear morphological changes and an enhanced cell migratory propensity. These morphologic and functional alterations were associated with changes in the abundance of EMT-related genes. Upon E2 stimulation, expression and promoter activity of the epithelial marker E-cadherin was strikingly suppressed, whereas EMT-associated transcription factors Snail and Slug were significantly up-regulated. This up-regulation was attributed to the increase in gene transcription activated by E2. Depletion of the endogenous Snail or Slug using small interfering RNA (siRNA) attenuated E2-mediated control in E-cadherin. In addition, the E2-induced cell migration was neutralized by Snail and Slug siRNAs, implying that both transcription factors are indispensable for the pro-metastatic actions of E2. Importantly, by using selective ER agonists as well as over-expression and siRNA approaches, it was identified that E2 triggered the metastatic behaviors exclusively through an ER⍺-dependent pathway. In contrast, overexpression of ERβ opposed the phenotypic changes and down-regulation of E-cadherin induced by ER⍺. In addition, microarray analysis was performed to characterize more putative downstream mediators of E2. Expression levels of 486 genes were found to be altered by at least 50% upon E2 treatment, and included several genes involved in oncogenesis, cell cycle control, apoptosis, signal transduction and the gene expression machinery. These candidate genes may be valuable for better delineating the ER pathways and functions. In summary, this study provides compelling arguments that estrogen can potentiate tumor progression by EMT induction, and highlight the crucial role of ER⍺ in ovarian tumorigenesis.Medicine, Faculty ofObstetrics and Gynaecology, Department ofGraduat