A pathway from JNK through decreased ERK and Akt activities for FOXO3a nuclear translocation in response to UV irradiation.

Forkhead box O (FOXO) transcription factors play an important role in physiological and pathological processes. Extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) can phosphorylate FOXO and cause its degradation or cytoplasmic retention, respectively, leading to tumorigenesis. In addition, C-Jun N-terminal protein kinase (JNK) can promote FOXO nuclear localization, leading to apoptosis. Using confocal imaging of cells transfected with GFP-FOXO3a, we visualized the dynamic translocation of GFP-FOXO3a from the cytoplasm to the nucleus after UV irradiation in a time- and dose-dependent manner. We also found that UV irradiation caused activation of JNK, which in turn inactivated ERK and Akt, leading to FOXO3a translocation and Bim expression. Our results indicate that nuclear translocation of FOXO3a can be regulated by UV irradiation through the JNK-ERK/Akt pathway.