Abstract. The semaphorin and plexin family of ligands and receptor proteins provides important axon growth and guidance cues required for development. In recent years, studies have expanded their role in the regulation of cardiac morphogenesis and tumorigenesis. However, the mechanism responsible for their role in regulating cancer development and progression has not been clarified. In the present study, semaphorin 6D (Sema6D) and its receptor plexin-A1 were identified to be expressed at high levels in vascular epithelial cells within gastric cancer, and were positively correlated with vascular endothelial growth factor receptor 2 (VEGFR2). These findings verify our hypothesis that Sema6D and plexin-A1 may be closely associated with tumor angiogenesis. Combined with experimental observations in the MGC803 gastric cancer cell line, it was observed that knocking down plexin-A1 signaling led to a decreased expression of VEGFR2 at the messenger RNA and protein levels. Sema6D recognized and activated plexin-A1, which subsequently activated its downstream target, VEGFR2. The activation of VEGFR2 functioned as a positive regulator of tumor angiogenesis. Our data provided an understanding of the complex signaling cascades involved in the angiogenesis-related pathway in tumor cells. In light of our observations, pharmacological interventions targeting Sema6D/plexin-A1/VEGFR2 signaling may potentially be used as a target for the development of novel anti-angiogenic drugs in gastric cancer. IntroductionThe semaphor in fam ily is a la rge super-protei n fa m ily cont a in ing secreted, t ra nsmembra ne a nd glycosylphosphatidylinositol-linked proteins, and it has been divided into eight hypotypes based on their structures and amino acid sequence similarity: Invertebrate semaphorins consist of classes 1 and 2, while classes 3-7 are vertebrate semaphorins (with the exception of class 5C semaphorins, which are encoded by viral genomes) (1). The semaphorin family was initially identified to be involved in mediating axonal guidance in the developing nervous system (2). Certain members of the semaphorin family have been also shown to exert diverse and important functions in other physiological processes, including heart morphogenesis (3,4), vascular growth (5), immune cell regulation (6) and tumor progression (7,8). Important regulatory functions of certain members of the semaphorin family within tumor angiogenesis have been reported. For example, semaphorin 3A (Sema3A) inhibits angiogenesis through competition for vascular endothelial growth factor (VEGF) (9), and Sema3B has also been indicated as a putative tumor suppressor that inhibits tumor growth and angiogenesis (10). By contrast, Sema3C presumably may promote angiogenesis by stimulating integrin phosphorylation and VEGF120 secretion (11), and Sema4D has been demonstrated to serve a role in tumor-induced angiogenesis (12).Sema6D, mapped on chromosome 2, is the best characterized factor of the class 6 semaphorins, which are single-pass membrane-bound semaphorins (13). It wa...

Transforming growth factor-β1 (TGF-β1) is involved in the regulation of trophoblast cell proliferation and invasion. However, the mechanism underlying this process remains unknown, which is predominantly due to the difficulty in obtaining and maintaining primary trophoblast cells in culture over a long period of time. The HTR-8/SVneo cell line is an immortalized trophoblast cell line, which has been reported to exhibit a number of similar characteristics to those of parental trophoblast cells. Therefore, the cell line has been a useful tool for the investigation of placental function and tumor progression. In the present study, the HTR-8/SVneo cell line was used as a model to investigate the TGF-β1/SMAD signaling pathway in the proliferation and invasion of trophoblast cells. The proliferation and invasion ability of HTR-8/SVneo cells was determined using the MTT and Transwell assays, respectively. In addition, reverse transcription polymerase chain reactions were performed to detect the mRNA expression of a panel of known downstream mediators of TGF-β1, including TGF-β receptor I (TβRI), SMAD4, SMAD3, SMAD7 and tissue inhibitor of metalloproteinases-1 (TIMP-1). The results indicated that TGF-β1 promotes the proliferation and invasion of the HTR-8/SVneo cell line at passage 90. Furthermore, the expression of TβRI, SMAD3 and SMAD4 were reduced following treatment with TGF-β1, while the expression of SMAD7 was increased and the expression of TIMP-1 remained unchanged following TGF-β1 treatment. These observations indicated that the effects of TGF-β1 on the proliferation and invasion of the HTR-8/SVneo cell line at passage 90 were different from those of parental trophoblasts, which is in contrast to the results of previous studies. It was concluded that the HTR-8/SVneo cell lines, which have been grown for over 90 passages, do not accurately represent parental trophoblast cells in studies of the TGF-β/SMAD signaling pathway.