Ye et al. BMC Cancer 2010, 10:611 http://www.biomedcentral.com/1471-2407/10/611 Page 8 of 11 Figure 3 Effect of Plexin-B1 inhibition on SKOV3 cell proliferation, migration and invasion in vitro. (A) Cell migration capability was determined with a wound healing assay. A confluent monolayer of untransfected SKOV3 cells or SKOV3 cells at 24 h after a 5-h exposure to Plexin-B1 siRNA2, Plexin-B1 siRNA3 or negative control siRNA (Blank control) was wounded. Photographs were taken immediately (0 h) and at 24 h and 48 h after wounding. (B) Quantification of wound closure. The data present the mean distance of cell migration to the wound area at 24 h and 48 h after wounding in three independent wound sites per group. Values are means ± SD from at least three independent experiments. (C) Analysis of the proliferation of untransfected (Blank control) SKOV3 cells and SKOV3 cells 72 h after treatment with Plexin-B1 siRNA2, Plexin-B1 siRNA3 or negative control siRNA. The data present the mean proliferation rate ± SD from three independent assays. (D) Cell invasion capability was assessed with a transwell assay. Untransfected (Blank control) SKOV3 cells and SKOV3 cells at 24 h after a 5-h exposure to Plexin-B1 siRNA2, Plexin-B1 siRNA3 or negative control siRNA were trypsinized and then plated in the upper chamber and allowed to grow for 48 h in serum-free medium. Cells that invaded the underside of the filter were fixed and stained. (D) Quantification of the transwell assay. The data present the mean number of cells on the bottom surface of the membrane from independent assays performed in triplicate. There were fewer invaded cells in the Plexin-B1 siRNA2 group (100 ± 52) and the siRNA3 group (42 ± 36) than in the blank control group (825 ± 32) or the negative control siRNA group (848 ± 41). * indicates P < 0.01 when compared to the blank control. might be an early factor in ovarian serous tumor devel- opment. Furthermore, the tumors with lymph node metastasis expressed higher levels of Plexin-B1 than those without lymph node metastasis. Indeed, Plexin-B1 expression in precursor lesions suggested a certain role of this protein in early ovarian carcinogenesis before invasion or metastasis. It has been reported that Sema 4D might exert its proangiogenic effect via Plexin-B1 to promote tumor growth and survival and thereby facilitate tumor metastasis in head and neck squamous cell carcinomas and other epithelial-derived tumors [37]. However, Plexin-B1 protein may have additional roles in different types of tumors. For example, Plexin-B1 is absent in more than 80% of renal cell carcinomas but present in all kinds of renal tubules [28]. A possible mechanism underlying this expression status is that the Plexin-B1 gene is located in 3p21, which is a frequently deleted region in renal cell carcinomas.