Identifying Functional Differences Between Protein S and Gas-6 in Pancreatic Cancer

Introduction: Procoagulants such as Factor IX and thrombin play major roles in cancer cell proliferation and migration; however, a role for anticoagulant proteins in cancer biology has not been elucidated. The anticoagulant Protein S (PS), its homologous protein Growth Arrest Specific protein-6 (GAS-6), and the receptors for these proteins, Tyro-3, Axl and Mertk (TAM), are over expressed in many cancer cells. TAM family receptors regulate functions such as cell survival, proliferation, migration, and apoptosis. The consequences of activation of each of these receptors varies, although the mechanism that leads to different outcomes is unknown. We hypothesized that the PS and GAS-6 ligands are responsible for the variations in the functions of these signaling cascades.

Methods: We used qPCR to analyze the pancreatic cancer cell lines Miapaca-2 and Panc-1 for variations in the expression of GAS-6 and PS. We sequestered PS and GAS-6 with antibodies and used FACS analysis to detect effects on the cell cycle and on cell cycle regulators.

Results: GAS-6 was observed to be highly expressed in proliferating Miapaca-2 cells compared with Panc-1 cells, whereas there was no significant difference in PS mRNA levels between these cell lines. For the cell line Miapaca-2, antibody sequestration of GAS-6 arrested the cell cycle in S-phase and increased p53 phosphorylation; conversely, inhibition of PS reduced p53 phosphorylation.

Conclusion: Our results indicate that PS and GAS-6 act antagonistically in controlling pancreatic cancer cell proliferation, and we hypothesize that the ratio of GAS-6 to PS expression is key to this regulation. We will further confirm our hypothesis by overexpressing and knocking down PS and GAS-6 in the pancreatic cancer cell lines.