Objective: The exposure of mammalian cells to extracellular stress induces the expression of immediate early genes such as c-fos and c-jun and activates transcription factor activator protein-1 (AP-1). The purpose of the current study was to investigate the role of c-Fos and JunD in stress-induced cell death.
Materials and methods: We exposed cultured primary mouse embryonic fibroblasts (MEF) to ultraviolet light (UV-C) or hydrogen peroxide (H(2)O(2)). Induction of c-Fos and JunD and activation of MAPK/ERK1/2 signalling in the presence or absence of a MAPK inhibitor were analyzed by western blotting. Activation of AP-1 transcription factors was detected by the electrophoretic mobility shift assay and immunoprecipitation. Cell death was measured by changes in caspase 3 activities and nuclear morphology. Effects of c-Fos and JunD expression on cell death were investigated by transfection.
Results: We found that the exposure of cultured primary MEF cells to UV or H(2)O(2) caused a significant increase in c-Fos and JunD protein levels. In addition, these two proteins formed complexes with each other and contributed to activation of AP-1 transcription complexes. More importantly, under both stress conditions, overexpression of JunD alone or overexpression of both c-Fos and JunD reduced caspase 3 activity and cell death. At the same time, UV irradiation activated the MAPK/ERK1/2 signalling pathway. The suppression of MEK1/ERK1/2 activation inhibited UV-induced expression of c-Fos and JunD and increased caspase 3 activity and cell death.
Conclusion: Our results suggest that both UV and H(2)O(2 )induce the activation of c-Fos/JunD AP-1 complexes resulting in the prevention of cell death. Moreover, UV irradiation-induced increases in c-Fos/JunD expression in primary MEF cells are mediated through the activation of the MAPK/ERK1/2 signalling pathway.