Neomorphic mutations create therapeutic challenges in cancer.

Oncogenesis is a pathologic process driven by genomic aberrations, including changes in nucleotide sequences. The majority of these mutational events fall into two broad categories: inactivation of tumor suppressor genes (hypomorph, antimorph or amorph) or activation of oncogenes (hypermorph). The recent surge in genome sequence data and functional genomics research has ushered in the discovery of aberrations in a third category: gain-of-novel-function mutation (neomorph). These neomorphic mutations, which can be found in both tumor suppressor genes and oncogenes, produce proteins with entirely different functions from their respective wild-type (WT) proteins and the other morphs. The unanticipated phenotypic outcomes elicited by neomorphic mutations imply that tumors with the neomorphic mutations may not respond to therapies designed to target the WT protein. Therefore, understanding the functional activities of each genomic aberration to be targeted is crucial in devising effective treatment strategies that will benefit specific cancer patients.

P-cadherin cooperates with insulin-like growth factor-1 receptor to promote metastatic signaling of gonadotropin-releasing hormone in ovarian cancer via p120 catenin.

Gonadotropin-releasing hormone (GnRH) is a potent prometastatic factor in ovarian cancer, but the intracellular signaling events are not well understood. The classical Gα(q)-phospholipase C signal transduction pathway known to operate in the pituitary is not involved in GnRH actions at non-pituitary targets. Here we showed that GnRH treatment of ovarian cancer cells led to a rapid and remarkable tyrosine phosphorylation of p120 catenin (p120(ctn)), which was mediated by P-cadherin. The use of P-cadherin small interfering RNA or neutralizing antibodies to inhibit P-cadherin expression and function resulted in diminished p120(ctn) activation, confirming that the effect was P-cadherin specific. On exploring how P-cadherin, which lacks intrinsic kinase activity, might regulate the activation of p120(ctn), we found that P-cadherin could induce the ligand-independent activation of insulin-like growth factor-1 receptor (IGF-1R). Inhibition of IGF-1R expression or its activity significantly inhibited GnRH-induced p120(ctn) activation, and the subsequent cell migration and invasion. In addition, we showed that IGF-1R regulation by P-cadherin was associated with complex formation between IGF-1R and P-cadherin, and this regulation was also observed to be in vivo correlated with metastasis. Furthermore, using a mouse model of ovarian cancer metastasis, GnRH receptor knockdown was shown to diminish peritoneal dissemination of tumors and ascites formation. These findings suggest for the first time that GnRH can initiate an outside-in p120(ctn) signal transduction through the cross-talk between P-cadherin and IGF-1R, thus providing a novel molecular mechanism by which GnRH may control the high level of aggressiveness and invasion and metastasis potential that are characteristic of ovarian cancer.

Cadherin switching and activation of p120 catenin signaling are mediators of gonadotropin-releasing hormone to promote tumor cell migration and invasion in ovarian cancer.

Gonadotropin-releasing hormone (GnRH) receptor expression is often elevated in ovarian cancer, but its potential role in ovarian cancer metastasis has just begun to be revealed. Cadherin switching is a crucial step during tumorigenesis, particularly in metastasis. Here, we showed that GnRH is an inducer of E- to P-cadherin switching, which is reminiscent of that seen during ovarian tumor progression. Overexpression of P-cadherin significantly enhanced, whereas knockdown of P-cadherin reduced migration and invasion regardless of E-cadherin expression, suggesting that inappropriate expression of P-cadherin contributes to the invasive phenotype. These effects of P-cadherin were mediated by activation of the Rho GTPases, Rac1, and Cdc42, through accumulation of p120 catenin (p120(ctn)) in the cytoplasm. The use of p120(ctn) small interfering RNA or chimeric cadherin construct to inhibit p120(ctn) expression and cytoplasmic localization, respectively, resulted in significant inhibition of cell migration and invasion, with a concomitant reduction in Rac1 and Cdc42 activation, confirming that the effect was p120(ctn) specific. Similarly, the migratory/invasive phenotype could be reversed by expression of dominant-negative Rac1 and Cdc42. These results identify for the first time cadherin switching and p120(ctn) signaling as important targets of GnRH function and as novel mediators of invasiveness and tumor progression in ovarian cancer.

Ginsenoside Rb1 inhibits tube-like structure formation of endothelial cells by regulating pigment epithelium-derived factor through the oestrogen beta receptor.

BACKGROUND AND PURPOSE: Angiogenesis is a crucial step in tumour growth and metastasis. Ginsenoside-Rb1 (Rb1), the major active constituent of ginseng, potently inhibits angiogenesis in vivo and in vitro. However, the underlying mechanism remains unknown. We hypothesized that the potent anti-angiogenic protein, pigment epithelium-derived factor (PEDF), is involved in regulating the anti-angiogenic effects of Rb1. EXPERIMENTAL APPROACHES: Rb1-induced PEDF was determined by real-time PCR and western blot analysis. The anti-angiogenic effects of Rb1 were demonstrated using endothelial cell tube formation assay. Competitive ligand-binding and reporter gene assays were employed to indicate the interaction between Rb1 and the oestrogen receptor (ER). KEY RESULTS: Rb1 significantly increased the transcription, protein expression and secretion of PEDF. Targeted inhibition of PEDF completely prevented Rb1-induced inhibition of endothelial tube formation, suggesting that the anti-angiogenic effect of Rb1 was PEDF specific. Interestingly, the activation of PEDF occurred via a genomic pathway of ERbeta. Competitive ligand-binding assays indicated that Rb1 is a specific agonist of ERbeta, but not ERalpha. Rb1 effectively recruited transcriptional activators and activated an oestrogen-responsive reporter gene. Furthermore, Rb1-mediated PEDF activation and the subsequent inhibition of tube formation were blocked by the ER antagonist ICI 182,780 or transfection of ERbeta siRNA, indicating ERbeta dependence. CONCLUSIONS AND IMPLICATIONS: Here we show for the first time that the Rb1 suppressed the formation of endothelial tube-like structures through modulation of PEDF via ERbeta. These findings demonstrate a novel mechanism of the action of this ginsenoside that may have value in anti-cancer and anti-angiogenesis therapy.