Gu, Q., Wang, D., Wang, X., Peng, R., Liu, J., Deng, H., Wang, Z. and Jiang, T. Basic Fibroblast Growth Factor Inhibits Radiation-Induced Apoptosis of HUVECs. II. The RAS/ MAPK Pathway and Phosphorylation of BAD at Serine 112. Radiat. Res. 161, 703–711 (2004).

Radiation-induced endothelial cell apoptosis is involved in the development of many radiation injuries, including radiation-induced skin ulcers. The proangiogenic growth factor basic fibroblast growth factor (bFGF, NUDT6) enhances endothelial cell survival. In the present study, we set up a model of apoptosis in which primary cultured human umbilical vein endothelial cells (HUVECs) were irradiated with 60Co γ rays to explore the effects of bFGF on radiation-induced apoptosis of HUVECs and the signaling pathways involved. We found that bFGF inhibited radiation-induced apoptosis of HUVECs, and that the effect was mediated in part by the RAS/MEK/ MAPK/RSK (p90 ribosomal S6 kinase)/BAD pathway. This pathway was activated by exposure of irradiated HUVECs to bFGF, involving phosphorylation of FGFR, MEK and p44/42 MAPK. The survival-enhancing effect of bFGF was partly inhibited by U0126 and PD98059. The fact that the anti-apoptosis effect of bFGF on irradiated HUVECs was not completely abrogated by U0126 and PD98059 suggests that other survival signaling pathways may exist. Transfection of a dominant-negative form of RSK2 (DN RSK2) partly blocked the anti-apoptosis effect of bFGF in irradiated HUVECs. Moreover, we provide evidence for the first time that bFGF induced BAD phosphorylation (at serine 112) and CREB (cAMP response element-binding protein) activation (phosphorylation at serine 133) in γ-irradiated HUVECs. In our model, inhibition of MAPK signaling-dependent phosphorylation of BAD at serine 112 promoted increased association with BCL-XL, suggesting that MAPK pathway-dependent serine 112 phosphorylation of BAD is critical for the effect of bFGF on cell survival. These results showed that RAS/MAPK/BAD pathway participated in the bFGF-induced effect on survival of HUVECs exposed to radiation. It is suggested that RAS/ MAPK pathway in tumor vascular endothelium could be a potential therapeutic target to enhance the efficacy of ionizing radiation.

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