CHARACTERIZATION OF FUNCTIONAL THROMBIN RECEPTORS IN HUMAN PANCREATICTUMOR-CELLS (MIA PACA-2)

In this article, the ''tethered ligand'' thrombin receptor was identif ied on human pancreatic tumor cells, MIA PaCa-2, using immunofluoresce nce studies with a monoclonal anti-thrombin receptor antibody. Pharmac ological characterization, using H-3-labeled thrombin receptor activat ing 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 bindi ng capacity of 13.9 +/- 0.7 fmol/mg protein. These binding sites repre sent functional thrombin receptors, as shown by alpha-thrombin-and TRA P-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 id entification of tethered ligand thrombin receptor in human pancreatic cancer cells and suggest thrombin receptor involvement in mechanisms o f human pancreatic tumor progression.