IκBα and IκBβ possess injury context-specific functions that uniquely influence hepatic NF-κB induction and inflammation

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Abstract
IκB proteins play an important role in regulating NF-κB induction following a diverse range of environmental injuries. Studies evaluating IκBβ knock-in mice (AKBI), in which the IκBα gene is replaced by the IκBβ cDNA, have uncovered divergent properties of IκBα and IκBβ that influence their ability to activate hepatic NF-κB and subsequent downstream proinflammatory processes in a stimulus-specific manner. While AKBI mice demonstrated identical levels of hepatic NF-κB activation in response to endotoxin, a significantly reduced level of hepatic NF-κB activation was observed in AKBI mice after liver ischemia/reperfusion (I/R) injury. This reduced level of NF-κB activation in AKBI mice after liver I/R also correlated with decreased induction of serum TNF-α, reduced hepatic inflammation, and increased survival. In contrast, no differences in any of these indicators were observed between AKBI mice and WT littermates after a lethal injection of LPS. Molecular studies suggest that the specificity of IκBα, but not IκBβ, to properly regulate NF-κB induction during the acute phase of I/R injury is due to injury context–specific activation of c-Src and subsequent tyrosine phosphorylation of IκBα on Tyr42. These results demonstrate that IκBα and IκBβ play unique injury context–specific roles in activating NF-κB–mediated proinflammatory responses and suggest that strategies aimed at inhibiting IκBα gene expression may be of potential therapeutic benefit in hepatic I/R injury.