Dysregulated expression and function of Plexin-β1 in ovarian cancers

Abstract

BACKGROUND: Ovarian cancer has a tendency to spread within the peritoneal cavity early in the disease course. Understanding the metastatic pathways of ovarian cancer is thus of high importance for devising ovarian cancer treatment. Plexin-B1 is a cognate receptor of Semaphorin 4D (Sema4D). This study aims at investigating the role of Plexin-B1 in ovarian cancer. MATERIALS AND METHODS: Expression of Plexin-B1 and its ligand in ovarian epithelial cell lines was examined by western blot and qPCR. Their expression in benign, borderline, and malignant tumors was revealed by immunohistochemistrty of paraffin embedded tissues. High-resolution melting (HRM) curve analysis was used to screen for mutation in Rac binding region of PLXNB1. Recombinant Sema4D was purified and used to treat OVCA420 cells which express high level of Plexin-B1. siRNA was used to knock-down Plexin-B1 in OVCA420. Cell migration and invasion ability was assayed by transwell migration and invasion assay. RESULTS: Plexin-B1 was most highly overexpressed in serous ovarian cancer cell lines OVCA420, OVCA429, and SW626, whereas Sema4D was overexpressed in OVCAR3, TOV21G, and PAI. In contrast, Plexin-B1 and Sema4D were not expressed in immortalized normal ovarian epithelial cell lines. Immunohistochemical studies also revealed high Plexin B1 expression in ovarian borderline tumors and invasive cancers while no Plexin B1 expression was detectable in benign tumor. On the other hand, downregulation of Plexin-B1 was observed in the metastatic foci compared with their corresponding primary tumors. There is also a tendency of higher Plexin-B1 expression in serous histotype than in other histotypes. A preliminary HRM screening of Plexin-B1 cDNA from 28 ovarian cancers detected no mutation in the Rac binding region. Knock-down of Plexin-B1 by siRNA caused increased migration and invasion of ovarian cancer cells. In contrast to Sema4D, treatment of ovarian cancer cells OVCA420 by follicle-stimulating hormone which enhances ovarian cancer growth, led to Plexin-B1 downregulation. CONCLUSION: Our study suggested that Plexin-B1 may contribute to early ovarian carcinogenesis. Its dyregulation in ovarian cancers is paradoxically associated with altered cancer cell invasion and migration. The role of Plexin B1 in ovarian cancer progression is complex.