Over-expression of JunB inhibits mitochondrial stress and cytotoxicity in human lymphoma cells exposed to chronic oxidative stress

Activator protein-1 can induce either cell survival or death, which is controlled by opposing effects of different Jun members. It is generally accepted that c-Jun is pro-apoptotic, but that JunD is anti-apoptotic in stress-exposed cells. Additionally, although there are reports suggesting that JunB plays a protective role, its role in stress-induced apoptosis remains unclear. Here, we investigated the role of JunB in H₂O₂-induced cell death using cells that over-expressed the protein or were transfected with si-JunB. Inhibition of JunB expression accelerated H₂O₂-mediated loss of mitochondrial membrane potential (MMP) and cytotoxicity. Conversely, over-expression of JunB protein led to significant inhibition of the MMP loss and cell death. The increase in JunB expression also attenuated nuclear relocation of apoptosis-inducing factor and mitochondrial Bcl-2 reduction that occurred following H₂O₂ exposure. These results suggest that JunB can signal survival against oxidant-mediated cell death by suppressing mitochondrial stress.