Effects of thrombin and thrombin peptide activating receptor (SFLLRN) on proteoglycan synthesis and distribution in human endothelial cells.

In the present study we compared the effect of alpha-thrombin and the active receptor peptide (SFLLRN) on proteoglycan (PG) release from human endothelial cells (HUVEC) exposed for 24 h in the presence of 35S-sulfate and 3H-glucosamine. The effect of thrombin (5U/ml) and receptor peptide (100 microM) was evaluated on the distribution of PGs in the conditioned medium, cellular extract and extracellular matrix. In the conditioned medium, thrombin increased the amount of PGs. In extracellular matrix thrombin decreased radioactive PGs measured by both isotopes; no difference was observed in cell extracts. SFLLRN peptide showed a consistent increase in PG content in the medium. At variance with thrombin, in cell extracts the peptide increased the amount of PGs. No relevant differences were observed in PG content of extracellular matrix. These results indicate that thrombin and the peptide act differently on PG distribution and underline the different role of the serine protease and of the receptor binding activities of thrombin.