Nerve growth factor protects human keratinocytes from ultraviolet-B-induced apoptosis.
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.
Marconi
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A
Department of Neuropsychosensorial Pathology, Section of Dermatology, University of Modena and Reggion Emilia, Modena, Italy.
Vaschieri
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C
Zanoli
S
S
Giannetti
A
A
Pincelli
C
C
D017209:Apoptosis / Q000528:radiation effects*; D002455:Cell Division / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000528:radiation effects*; D020932:Nerve Growth Factor / Q000032:analysis / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D020917:Receptor, trkA / Q000032:analysis; D014162:Transfection; D014466:Ultraviolet Rays; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D020932:Nerve Growth Factor; D020917:Receptor, trkA