THROMBIN STIMULATES EXPRESSION OF THE RECEPTOR FOR UROKINASE-TYPE PLASMINOGEN-ACTIVATOR IN DU-145 PROSTATE-CANCER CELLS

Coagulants, including thrombin, have been found in many tissues, inclu ding tumor cells, but their significance is not fully understood. Rece ntly, the expression of the receptor (uPAR) for urokinase-type plasmin ogen activator (uPA) and of uPA by many cells has been found to regula te pericellular proteolysis which is essential for cell migration, it is well correlated with tumor invasiveness. We studied the effect of t hrombin on the expression of uPAR in the human prostate cancer cell li ne, DU-145. Human a-thrombin added to a confluent cultures caused a do se-dependent increase in [I-125]-pro-uPA binding capacity of DU-145 ce lls. Incubation with 2 U/ml thrombin for 16 h resulted in an increase in the number of uPAR from 10.3 +/- 1.6 x 10(4) to 25.4 +/- 3.3 x 10(4 )/cell, and in an increase in Kd of 0.4 +/- 0.17 nM to 1.0 +/- 0.32 nM . Northern blot analysis showed an increase in the level of uPAR mRNA, which reached a maximum of 5-fold. Thrombin treated with phenylalanyl -prolyl-arginylchloromethylketone and hirudin did not produce the effe ct on uPAR expression, nor did Factor Xa. This thrombin effect can als o be produced by a thrombin receptor activating peptide, indicating th at DU-145 cells have specific thrombin receptors and thrombin acts thr ough its activation. Thrombin had no detectable effect on the expressi on of uPA and plasminogen activator inhibitor type-1. An acceleration of the activation of plasminogen was observed in the presence of throm bin-stimulated DU-145 cells, indicating a functional consequence of th rombin stimulation. These findings suggest an important role of thromb in in the regulation of invasive ability of tumor cells through the in duction of uPAR expression.