Thrombin and S1P synergistically induce NF-κB binding activity. NF-κB DNA binding activity was measured by EMSA in nuclear extracts of ECs that were exposed to 10 nM thrombin, 4 μM S1P, or 10 nM thrombin plus 4 μM S1P for 30 or 60 minutes. Similar results were observed in 2 independent experiments.