E3 ubiquitin/ISG15 ligase TRIM25
protein K48-linked ubiquitination
FOXO4 mediates resistance to oxidative stress in lens epithelial cells by modulating the TRIM25/Nrf2 signaling.
Oxidative stress damage to the lens is a key factor in most cataracts. Forkhead box O 4 (FOXO4), a member of the forkhead box O family, plays a pivotal role in oxidative stress. FOXO4 is upregulated in lens of age-related cataract patients, but its role in cataract has not been elucidated. Herein, we investigated the role and mechanism of FOXO4 during oxidative stress damage in lens epithelial cells. H<sub>2</sub>O<sub>2</sub> treatment enhanced FOXO4 expression in HLEpiC cells. Short hairpin RNAs mediated FOXO4 silence aggravated H<sub>2</sub>O<sub>2</sub>-induced cell apoptosis. In addition, upon H<sub>2</sub>O<sub>2</sub> exposure, silencing of FOXO4 reduced SOD and CAT activities, as well as increased intracellular MDA and ROS levels. FOXO4 silencing also inhibited Nrf2 nuclear translocation, followed by reducing the expressions of Nrf2-governed antioxidant genes HO-1 and NOQ-1. Exogenous overexpression of FOXO4 was also involved in this study and exhibited opposite effects of FOXO4-silencing. Mechanistically, FOXO4 directly bound the promoter of TRIM25 and regulated its transcription, thereby activating the Nrf2 signaling. Taken together, in the condition of oxidative stress, the expression of FOXO4 showed a compensatory upregulation and it exhibited an anti-oxidative effect by modulating the transcription of TRIM25, thus activating the Nrf2 signaling. The FOXO4/TRIM25/Nrf2 axis may be associated with the pathological mechanisms of cataract.