HGF/MET signaling in ovarian cancer.

Ovarian cancer is the leading cause of death from gynecological cancers in North America and Europe. Despite its clinical significance, the factors that regulate the development and progression of ovarian cancer are among the least understood of all major human malignancies. A growth factor with pleiotropic effects, which has attracted increasing attention in recent years, is the hepatocyte growth factor (HGF) and its receptor MET. While deregulated HGF/MET signaling is observed in many tumors, the consequences of MET activation are complex and context dependent. Recent observations have demonstrated a cross-talk of other signaling pathways with MET signaling. This review summarizes the key findings and recent advances in our understanding of HGF and MET in the transformation and progression of ovarian cancer. We will begin with a brief discussion on the role of HGF and MET in the physiology of normal ovarian surface epithelium (OSE) and ovarian cancer development. In particular, the coexpression of HGF and MET in OSE of women with hereditary ovarian cancer syndromes emphasizes their importance in neoplastic transformation of OSE. The involvement of HGF in other aspects of tumor progression, such as invasion and metastasis, and novel downstream target genes activated by HGF is summarized next. The therapeutic potential of HGF to treat ovarian cancer and to improve response to conventional chemotherapy is also described. Finally, the most recent progress in drug development and future areas of research in terms of their potential clinical implications are discussed.

Novel RNA aptamers targeting gastrointestinal cancer biomarkers CEA, CA50 and CA72-4 with superior affinity and specificity.

Gastric cancer is the third most common cause of death from cancer in the world and it remains difficult to cure in Western countries, primarily because most patients present with advanced disease. Currently, CEA, CA50 and CA72-4 are commonly used as tumor markers for gastric cancer by immunoassays. However, the drawback and conundrum of immunoassay are the unceasing problem in standardization of quality of antibodies and time/effort for the intensive production. Therefore, there is an urgent need for the development of a standardized assay to detect gastric cancer at the early stage. Aptamers are DNA or RNA oligonucleotides with structural domain which recognize ligands such as proteins with superior affinity and specificity when compared to antibodies. In this study, SELEX (Systematic Evolution of Ligands by Exponential enrichment) technique was adopted to screen a random 30mer RNA library for aptamers targeting CEA, CA50 and CA72-4 respectively. Combined with high-throughput sequencing, we identified 6 aptamers which specifically target for these three biomarkers of gastrointestinal cancer. Intriguingly, the predicted secondary structures of RNA aptamers from each antigen showed significant structural similarity, suggesting the structural recognition between the aptamers and the antigens. Moreover, we determined the dissociation constants of all the aptamers to their corresponding antigens by fluorescence spectroscopy, which further demonstrated high affinities between the aptamers and the antigens. In addition, immunostaining of gastric adenocarcinoma cell line AGS using CEA Aptamer probe showed positive fluorescent signal which proves the potential of the aptamer as a detection tool for gastric cancer. Furthermore, substantially decreased cell viability and growth were observed when human colorectal cell line LS-174T was transfected with each individual aptamers. Taking together, these novel RNA aptamers targeting gastrointestinal cancer biomarker CEA, CA50 and CA72-4 will aid further development and standardization of clinical diagnostic method with better sensitivity and specificity, and potentially future therapeutics development of gastric cancer.

Gonadotropin-induced apoptosis in human ovarian surface epithelial cells is associated with cyclooxygenase-2 up-regulation via the beta-catenin/T-cell factor signaling pathway.

Gonadotropins play a prominent role in ovarian function and pathology. We have shown that treatment with gonadotropins (FSH and LH/human chorionic gonadotropin) reduces the amount of N-cadherin with a concomitant induction of apoptosis in human ovarian surface epithelial (OSE) cells, but precise molecular mechanisms remain to be elucidated. Here, we demonstrated activation of beta-catenin/T-cell factor (TCF) signaling by gonadotropins. We further showed that ectopic expression of N-cadherin was sufficient to recruit beta-catenin to the plasma membrane, thereby blocking beta-catenin/TCF-mediated transactivation in gonadotropin-treated cells. Transfection with beta-catenin small interfering RNA or expression of dominant negative TCF inhibited apoptosis, whereas expression of dominant stable beta-catenin (S37A) caused significant apoptosis, thus supporting a proapoptotic role for beta-catenin/TCF in human OSE. In addition, we showed that gonadotropins enhanced beta-catenin/TCF transcriptional activity through inactivation of glycogen synthase kinase-3beta in a phosphatidylinositol 3-kinase/Akt-dependent manner, indicating cross talk between the phosphatidylinositol 3-kinase/Akt and beta-catenin signaling pathways through glycogen synthase kinase-3beta. Furthermore, gonadotropins increased cyclooxygenase-2 (COX-2) expression via the beta-catenin/TCF pathway. COX-2 also played a role in gonadotropin-induced apoptosis, as treatment with the COX-2-specific inhibitor NS-398 or COX-2 small interfering RNA blocked gonadotropin-dependent apoptotic activity. These findings suggest that the participation of beta-catenin in adhesion and signaling may represent a novel mechanism through which gonadotropins may regulate the cellular fate of human OSE.

Gonadotropin and its role in the ß-catenin/T-cell factor signaling pathway.

Gonadotropins, follicle-stimulating hormone and luteinizing hormone are key regulators in ovarian function, acting in an endocrine manner to regulate gametogenesis and steroidogenesis. In addition to normal tissue, gonadotropin receptors have also been demonstrated in ovarian carcinoma cell lines and primary tumors, suggesting that the gonadotropins may play a role in the pathophysiology of ovarian cancer. Thus, understanding mechanisms involved in signaling transduction by the gonadotropin receptors are of considerable interest and potential significance. In the ovary, gonadotropins initiate their cellular responses by binding to their G-protein-coupled receptors and activation of specific downstream intracellular effectors and signal pathways, including those of protein kinases A and C and mitogen-activated protein kinase. Recently, gonadotropins were shown to stimulate nuclear accumulation of ß-catenin, which controls lymphoid-enhancing factor/T-cell factor family-sensitive gene expression. ß-catenin has a pivotal function in the control of cell fate. The ability of gonadotropins to regulate ß-catenin provides a new dimension of knowledge linking pituitary hormones to the ß-catenin signaling in normal ovarian physiology and demonstrating how its dysregulation can contribute to the development of ovarian cancer.

Ginsenoside-Rg1 induces vascular endothelial growth factor expression through the glucocorticoid receptor-related phosphatidylinositol 3-kinase/Akt and beta-catenin/T-cell factor-dependent pathway in human endothelial cells.

Ginsenoside-Rg1, the most prevalent active constituent of ginseng, is a potent proangiogenic factor of vascular endothelial cells. This suggests that Rg1 may be a new modality for angiotherapy. Rg1 can activate the glucocorticoid receptor (GR). However, the regulatory steps downstream from GR that promote Rg1-induced angiogenesis have not been elucidated. Here we showed for the first time that Rg1 was a potent stimulator of vascular endothelial growth factor (VEGF) expression in human umbilical vein endothelial cells, and importantly this induction was mediated through a phosphatidylinositol 3-kinase (PI3K)/Akt and beta-catenin/T-cell factor-dependent pathway via the GR. Rg1 stimulation resulted in an increase in the level of beta-catenin, culminating its nuclear accumulation, and subsequent activation of VEGF expression. Transfection of a stable form of beta-catenin (S37A) or the use of a glycogen synthase kinase 3beta inhibitor to stabilize beta-catenin induced VEGF synthesis, whereas small interfering RNA-mediated down-regulation of beta-catenin did not, confirming that the effect was beta-catenin-specific. Using a luciferase reporter gene assay, we observed that Rg1 increased T-cell factor/lymphoid enhancer factor transcriptional activity. These events were mediated via a PI3K-dependent phosphorylation of the inhibitory Ser9 residue of glycogen synthase kinase 3beta. In addition, the GR antagonist RU486 was able to inhibit Rg1-induced PI3K/Akt and beta-catenin activation. These findings provide new insights into the mechanism responsible for Rg1 functions.

Gonadotropins regulate N-cadherin-mediated human ovarian surface epithelial cell survival at both post-translational and transcriptional levels through a cyclic AMP/protein kinase A pathway.

Gonadotropins are the major regulators of ovarian function and may be involved in the etiology of ovarian cancer. In this study, we report a new mechanism whereby gonadotropins regulate the survival of human ovarian surface epithelium (OSE), the tissue of origin of epithelial ovarian carcinomas. Our results indicate that disruption of N-cadherin-mediated cell-cell adhesion is an important molecular event in the apoptosis of human OSE. Treatment with surge serum concentrations of gonadotropins reduced the amount of N-cadherin with a concomitant induction of apoptosis, and this effect was mediated by a cAMP/protein kinase A pathway but not the ERK1/2 and protein kinase C cascades. We further demonstrated that activation of the gonadotropins/cAMP signaling pathway in human OSE led to a rapid down-regulation of N-cadherin protein level followed by a reduction at the level of N-cadherin mRNA, indicating that expression of N-cadherin was regulated by post-translational and transcriptional mechanisms. The former mechanism was mediated by increased turnover of N-cadherin protein and could be reversed by inhibition of proteasomal or matrix metalloproteinase (MMP-2) activity. On the other hand, at the transcriptional level, the addition of actinomycin D abolished the cAMP-mediated decrease in N-cadherin mRNA but did not change its stability. Inhibition of protein kinase A or expressing a dominant negative mutant of cAMP-response element-binding protein blocked this decrease of N-cadherin mRNA. Together, the combined operation of post-translational and transcriptional mechanisms suggests that regulation of N-cadherin is a crucial event and emphasizes the important role that N-cadherin has in controlling the survival capability of human OSE.