Ovarian serous carcinoma is a highly aggressive neoplastic disease in women. Our previous studies have demonstrated Notch3 gene amplification and upregulation in many ovarian serous carcinomas and Notch pathway activity contributed to drug resistance. Among different Notch3 ligands, Jagged1 is most dominant in ovarian cancer, and Notch3 pathway activity correlated with Jagged1 expression level in ovarian carcinoma tissues. In this study, we found that Jagged1 expression depended on Notch3 pathway activation. Knockdown of either Notch3 or RBPjk, a Notch-interacting transcription factor critical in Notch signaling, suppressed Jagged1 expression in ovarian cancer cells. Moreover, Jagged1 expression was upregulated in human ovarian surface epithelial cells after ectopic expression of Notch3 intracellular domain and was upregulated in mouse epithelial cells isolated from Notch3-inducible mice after induction. We also found that inhibition of Wnt/β-catenin signaling reduced Jagged1 expression, and co-administration of shRNAs targeting both Notch3 and β-catenin reduced Jagged1 expression much more than targeting either individual gene. Taken together, our data suggested a positive regulatory loop between Notch3 and its ligand, Jagged1, in ovarian cancer cells. In addition, Wnt/β-catenin pathway activation also up-regulated Jagged1. Both mechanisms may sustain Notch3 signaling in ovarian cancer cells and contribute to the pathogenesis of ovarian carcinoma.
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