Modulation of protein S and growth arrest specific 6 protein signaling inhibits pancreatic cancer cell survival and proliferation.

Thrombotic complications and hypercoagulopathies are commonly associated with the progression of pancreatic ductal adenocarcinoma (PDAC). Although the mechanistic link between the two phenomena is uncertain, there is evidently an increase in procoagulant proteins and a decrease in anticoagulants in PDAC patients. For example, the anticoagulant protein S (PS) is decreased during the progression of PDAC, a condition that possibly contributes to the hypercoagulopathies. PS is also an important signaling molecule that binds a family of tyrosine kinase receptors known as TAM (Tyro3, Axl and Mer) receptors; TAM receptors are often upregulated in different cancers. Growth Arrest Specific 6 or GAS6 protein, a homolog of PS, is also a TAM receptor family ligand. The downstream signaling pathways triggered by this ligand­receptor interaction perform diverse functions, such as cell survival, proliferation, efferocytosis, and apoptosis. Targeting the TAM receptors to treat cancer has had limited success; side effects are a significant obstacle due to the widespread numerous functions of TAM receptors. In the present study, it was revealed that PS­TAM interaction was pro­apoptotic, whereas GAS6­mediated TAM signaling promoted proliferation and survival in select PDAC cell lines. Furthermore, by regulating the balance between these two signaling pathways (by overexpressing PS or knocking down GAS6), the proliferative potential of the cells was decreased. Both long­term and short­term effects of natural PS overexpression were comparable to the treatment of the cells with the drug UNC2025, which inhibits the Mer­receptor. The present study lays the foundation for investigation of PS as a therapeutic agent to control cancer progression and to concurrently arrest thrombotic events.

Padua FIXa resistance to Protein S and a potential therapy for hyperactive FIXa.

INTRODUCTION: Abnormalities in the levels and functions of proteins that maintain hemostasis can cause thrombosis. Factor IX (FIX) R338L, i.e., Factor IX Padua, is a hyperactive clotting factor that promotes thrombosis. The R338L mutation increases the clotting rate by 8-fold despite increasing the Factor IXa enzymatic activity by only 2-fold. Protein S (PS) is a natural anticoagulant that directly inhibits FIXa. Because individuals affected by the R338L mutation have normal concentrations of PS, we speculated that the Padua hypercoagulation phenotype is due to decreased inhibition of FIXa R338L by PS. METHODS: We measured the ability of PS to inhibit FIX R338L, and we assessed the ability of PS to mitigate the prothrombotic effect FIX R338L. RESULTS: Plasma clotting assays demonstrated that 3-fold more PS was required to inhibit FIXa R338L compared with inhibition of wild type FIXa. Thrombin generation assays with Padua patient plasma recapitulated this biochemical consequence of the R338L mutation. Importantly, the less efficient inhibition of FIXa R338L was reversed by increasing PS concentration. Binding and co-immunoprecipitation studies revealed that the decrease in the inhibition of FIXa R338L by PS was caused by a 3- to 4-fold reduction in FIXa R338L affinity for PS. CONCLUSION: In summary, the resistance of FIXa R338L to inhibition by PS likely contributes to the unexpectedly high clotting rate in Padua individuals. Moreover, PS-mediated reversal of the pathological properties of FIXa R338L suggests that PS administration may be a novel and effective means to mitigate thrombophilia caused by any source of elevated FIXa activity.

Snail-mediated Cripto-1 repression regulates the cell cycle and epithelial-mesenchymal transition-related gene expression.

Transcription factor Snail mediates epithelial to mesenchymal transitions (EMT) by coordinate repression of epithelial markers, facilitating mass cell movement during germ layer formation. Aberrant reprogramming in its signaling pathways causes metastatic cancer. Snail's involvement in "fate-changing" decisions is however not understood. Cripto-1 shares a common temporal expression pattern with Snail during development. While Cripto-1 is required for mammary morphogenesis and hematopoietic stem cell renewal, its unregulated expression causes metastatic cancers. Therefore, we suspected that Snail regulates the expression of Cripto-1 controlling decisions such as motility, transformation and differentiation. We demonstrate that Snail represses Cripto-1 gene by direct transcriptional interaction and propose a novel mechanism by which it co-ordinately regulates cell fate decisions during development and could be causal of cancers.