PROTEIN-KINASE-C MEDIATES BASIC FIBROBLAST GROWTH-FACTOR PROTECTION OF ENDOTHELIAL-CELLS AGAINST RADIATION-INDUCED APOPTOSIS

Basic fibroblast growth factor (bFGF) was found to protect bovine aort ic endothelial cells against the lethal effects of ionizing radiation by inhibiting the programmed cell death (apoptosis) induced in these c ells by radiation exposure. The involvement of the bFGF receptor tyros ine kinase in this function was demonstrated by abrogation of the radi oprotective effect of bFGF by a specific inhibitor of the bFGF recepto r tyrosine kinase, the tyrphostin AG213. The downstream signaling afte r stimulation of the bFGF receptor tyrosine kinase in bovine aortic en dothelial cells involved translocation of the alpha isotype of cytopla smic protein kinase C (PKC) into the membrane and its activation withi n 30 s after bFGF stimulation. The involvement of PKC in the radioprot ective effect conferred by bFGF was suggested by the demonstration tha t nonspecific PKC activation by short-term exposure (30 min) to the ph orbol ester, 12-O-tetradecanoylphorbol- 13-acetate (TPA; 30 ng/ml) mim icked the radioprotective effect of bFGF. Furthermore, treatment of th e cells with the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpipe razine (20 mu M) abrogated the radioprotective effect of bFGF, as was observed after the depletion of cellular PKC by overnight preincubatio n with high-dose TPA (200 nM). Agarose gel electrophoresis of DNA extr acted from irradiated bovine aortic endothelial cells showed that both TPA (30 ng/ml; 30 min) and bFGF (1 ng/ml) inhibited the apoptotic deg radation of DNA induced in these cells by radiation exposure (500 cGy) . Both the bFGF- and the TPA-mediated inhibition of apoptosis could be reversed by the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpipe razine (20 mu M). These data demonstrate the involvement of PKC in the inhibition of radiation-induced apoptosis by bFGF and the rescue of e ndothelial cells from this mode of radiation-induced cell death.