H 2O 2-mediated oxidative stress activates NF-κB in lens epithelial cells

Abstract

In the mammalian lens, intracellular oxidants produced by photo-oxidative processes and exposure to toxic chemicals constitute stresses that produce cellular oxidative damage, result in changes in gene expression, and are causally related to cataract formation. Currently, it is believed that H 2O 2 is the major oxidant to which the lens is exposed. In this report, we examine the activation and regulation of the oxidant-sensitive transcription factor, NF-κB, by H 2O 2-mediated oxidative stress in lens epithelial cells. Lens epithelial cells treated with H 2O 2 demonstrated at 1 h a strong activation of NF-κB which returned to basal levels by 2 h. Under proteasome inhibition using both MG132 and lactacystin, H 2O 2-mediated activation of NF-κB was prevented, implicating the involvement of proteasome degradation of IκB proteins as being necessary for this activation. However, Western blot analysis demonstrated no degradation of IκB-α, -β, or -ε associated with H 2O 2-mediated NF-κB activation. In comparison, when cells were treated with the cytokine TNF-α, NF-κB was strongly activated and degradation of both IκB-α and -β was observed. These results clearly demonstrate that H 2O 2-mediated oxidative stress activates NF-κB in lens epithelial cells, which may subsequently lead to changes in gene expression. The results also reveal that different signaling pathways in the activation of NF-κB in lens epithelial cells are utilized by H 2O 2 and TNF-α. These different pathways of NF-κB activation may be required to effect specific NF-κB-dependent gene expression in response to these different stimuli.