PMA-mediated, but not TNF- or VEGF-mediated soluble tie-1 release is regulated by protein kinase C activation. HUVECs were incubated with 200 nmol/L GF109203X or 20 μmol/L PD098059 for 10 minutes before the addition of 10 ng/mL PMA, TNF, or 20 ng/mL VEGF for 2 hours. Supernatants were collected and assayed for soluble tie-1 release by sandwich ELISA as described in Materials and Methods. Results are expressed as the mean percentage of control ± SD, where 100% control represents soluble tie release in the absence of inhibitor.