Ye et al. BMC Cancer 2010, 10:611 http://www.biomedcentral.com/1471-2407/10/611 R E S E A R C H A R T I C L E Open Access Plexin-B1 silencing inhibits ovarian cancer cell migration and invasion Shuangmei Ye1†, Xing Hao1†, Ting Zhou1, Mingfu Wu1, Juncheng Wei1, Yongjun Wang1,2, Li Zhou1, Xuefeng Jiang1, Li Ji1, Yin Chen1, Lanying You1, Yiqun Zhang1, Gang Xu1, Jianfeng Zhou1, Ding Ma1*, Shixuan Wang1* Abstract Background: Elevated Plexin-B1 expression has been found in diverse human cancers and in non-neoplastic tissues, and it mediates diverse biological and pathological activities. However, whether or not Plexin-B1 expression is involved in human ovarian tumors remains unclear. In the present study, Plexin-B1 expression was explored in benign and malignant human ovarian tumor tissues. In addition, the impact of Plexin-B1 expression on ovarian cancer cell proliferation, migration and invasion were investigated in vitro. Methods: Plexin-B1 expression was analyzed in normal and benign ovarian tissues and serous ovarian tumors (both borderline and malignant) by immunohistochemical staining, as well as in four human ovarian cancer cell lines (A2780, C13*, SKOV3, and OV2008) by RT-PCR and western blot analyses. Furthermore, endogenous Plexin-B1 expression was suppressed by Plexin-B1 siRNA in SKOV3 cells, which overexpress Plexin-B1. Protein levels of Plexin-B1, AKT and AKTSer473 were examined by western blot analysis. Cell proliferation, migration and invasion were measured with MTT, wound healing and boyden chamber assays, respectively, and the cytoskeleton was monitored via F-actin staining. Results: Expression levels of Plexin-B1 protein were significantly higher in serous ovarian carcinomas than in normal ovaries or benign ovarian neoplasms, and in the former, Plexin-B1 expression was positively correlated with lymphatic metastasis, and the membrane and cytoplasm of cancer cells stained positively. SKOV3 cells displayed the highest Plexin-B1 expression at both the mRNA and protein levels among the four tested human ovarian cancer cell lines and was selected as a cell model for further in vitro experiments. Plexin-B1 siRNA significantly suppressed phosphorylation of AKT at Ser473 in SKOV3 cells, but it did not alter total AKT expression. In addition, silencing of Plexin-B1 in SKOV3 cells inhibited cell migration and invasion and reorganized the cytoskeleton, whereas cell proliferation was not affected. Conclusion: Plexin-B1 expression correlates with malignant phenotypes of serous ovarian tumors, probably via phosphorylation of AKT at Ser473, suggesting that Plexin-B1 might be a useful biomarker and/or a novel therapeutic target. Background Plexin proteins comprise a large family of trans-mem- brane receptors for semaphorins, which are secreted, membrane-associated or GPI-anchored proteins origin- ally identified for their role in axon guidance repulsion * Correspondence: dma@tjh.tjmu.edu.cn; sxwang@tjh.tjmu.edul.cn † Contributed equally 1Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China Full list of author information is available at the end of the article [1]. In vertebrates, nine plexins are divided into four subfamilies according to their different structures: plex- inA1-4, plexinB1-3, plexin-C1 and plexin-D1 [1]. All the plexins share significant homology in their extracellular region with the scatter factor receptors c-Met and RON, whereas the highly conserved cytoplasmic region of plexins fails to show homology with any other trans- membrane receptor protein [2]. Plexin-A subgroup members bind secreted class III semaphorins by asso- ciating with neuropilin-1 and neuropilin-2, and plexin-B © 2010 Ye et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.