. . . . . . . . . "bp(GO:\"response to UV-B\") -> bp(MESHPP:Apoptosis)" . "Approximately 61,000 statements." . "Copyright (c) 2011-2012, Selventa. All rights reserved." . "BEL Framework Large Corpus Document" . . "1.4" . "Ultraviolet radiation is a potent inducer of apoptosis, whereas autocrine nerve growth factor protects human keratinocytes from programmed cell death. To evaluate the role of nerve growth factor in the mechanisms of ultraviolet B-induced apoptosis, cultured human keratinocytes were ultraviolet B irradiated following pretreatment with K252, a specific inhibitor of the tyrosine kinase high-affinity nerve growth factor receptor. Here we report that the addition of K252 significantly enhanced keratinocyte apoptosis. We then transfected normal human keratinocytes with pNUT-hNGF. Nerve growth factor overexpressing keratinocytes secreted the highest amounts of nerve growth factor in culture supernatants, were more viable, and had a higher rate of proliferation than mock-transfected cells. Whereas ultraviolet B radiation downregulated nerve growth factor mRNA and protein as well as the tyrosine kinase high-affinity nerve growth factor receptor in normal keratinocytes, it failed to do so in nerve growth factor-transfected cells. Moreover, nerve growth factor overexpressing keratinocytes were partially resistant to apoptosis induced by increasing doses of ultraviolet B at 24 and 48 h. These results indicate that downregulation of nerve growth factor function plays an important part in the mechanisms of ultraviolet B-induced apoptosis in human keratinocytes. In addition, ultraviolet B caused a decrease in BCL-2 and BCL-xL expression in mock-transfected keratinocytes, but not in nerve growth factor overexpressing cells. Finally, nerve growth factor prevented the cleavage of the enzyme poly(ADP-ribose) polymerase induced in human keratinocytes by ultraviolet B. These results are consistent with a model whereby the autocrine nerve growth factor protects human keratinocytes from ultraviolet B-induced apoptosis by maintaining constant levels of BCL-2 and BCL-xL, which in turn might block caspase activation." . . "Selventa" . . . . "2014-07-03T14:29:49.473+02:00"^^ . . .