Characterization of functional thrombin receptors in human pancreatic tumor cells (MIA PACA-2)

In this article, the "tethered ligand" thrombin receptor was identified on human pancreatic tumor cells, MIA PaCa-2, using immunofluorescence studies with a monoclonal anti-thrombin receptor antibody. Pharmacological characterization, using H-3-labeled thrombin receptor activating peptide-6 (TRAP-6) as radioligand, demonstrated a single class of high-affinity binding sites (K-D = 9.1 +/- 1.8 x 10(-7) M) and a binding capacity of 13.9 +/- 0.7 fmol/mg protein. These binding sites represent functional thrombin receptors, as shown by alpha-thrombin-and TRAP-6-induced mobilization of free intracellular calcium, protein kinase C translocation from cytosol to the cell membrane, and stimulation of DNA synthesis in MIA PaCa-2 cells. These results provide the first identification of tethered ligand thrombin receptor in human pancreatic cancer cells and suggest thrombin receptor involvement in mechanisms of human pancreatic tumor progression.