Exportin 1 inhibition attenuates nuclear factor-kappaB-dependent gene expression.

Activation of nuclear factor (NF)-kappa B is mediated by signal-induced phosphorylation of I kappa B alpha, subsequent I kappa B alpha degradation, and then translocation of unbound NF-kappa B to the nucleus. Termination of gene expression occurs when I kappa B alpha binds NF-kappa B subunits (Rel A) in the nucleus. Leptomycin B specifically inhibits export of I kappa B alpha and the inactive I kappa B alpha/ Rel A complex via the nuclear export protein exportin 1. We hypothesized that inhibition of I kappa B alpha nuclear export would increase nuclear I kappa B alpha and attenuate NF-KB inflammatory gene expression in pulmonary microvascular endothelial cells. We found that inhibition of exportin 1 causes nuclear accumulation of both endogenous NF-KB (Rel A) and I kappa B alpha. IL-1 beta causes nuclear accumulation of NF-kappa B (Rel A) but does not increase nuclear I kappa B alpha. Inhibition of exportin 1 before IL-1/beta prevented an increase in the nuclear ratio of NF-KB (Rel A) to I kappa B alpha and decreases NF-KB DNA binding. Furthermore, inhibition of exportin 1 attenuates IL-1 beta-induced phosphorylation Of I kappa B alpha without affecting I kappa B kinase phosphorylation. Lastly, inhibition of exportin 1 attenuates monocyte chemoattractant protein, IL-8, and intercellular adhesion molecule expression in response to IL-1/beta stimulation. We suggest that the decrease in cell activation due to exportin 1 inhibition is a result of termination of NF-kappa B DNA binding due to increased concentration Of I kappa B alpha in the nucleus.