Functions of IκB proteins in inflammatory responses to Escherichia coli LPS in mouse lungs

Acute inflammation induced by intrapulmonary LPS requires nuclear factor (NF)-kappaB RelA. This study elucidates the effects of intrapulmonary LPS on IkappaB proteins, endogenous inhibitors of RelA, and the effects of deficiency of IkappaB-beta. IkappaB-alpha, IkappaB-beta, and IkappaB- each complexed with RelA in uninfected murine lungs. Intratracheal instillation of LPS induced the degradation of IkappaB-alpha and IkappaB-beta, as measured by the loss of immunoreactive proteins in non-nuclear fractions. Degradation was apparent by 2 h and sustained through 6 h. In contrast, net IkappaB-beta content increased over this period. The small amounts of IkappaB-alpha and IkappaB-beta that were detected in nuclear fractions from the lungs also decreased over this time frame, whereas intranuclear NF-kappaB content (including both RelA and p50) increased. The hypophosphorylated form of IkappaB-beta, which facilitates transcription induced by NF-kappaB, was not detected. Neutrophil recruitment and edema accumulation did not differ between wild type mice and gene-targeted mice deficient in IkappaB-beta, suggesting that IkappaB-beta is not specifically required for these responses. Altogether, these data suggest that RelA is liberated during LPS-induced pulmonary inflammation by the regulated degradation of both IkappaB-alpha and IkappaB-beta. In the absence of IkappaB-beta, IkappaB-alpha or other inhibitory proteins can regulate NF-kappaB functions essential to acute neutrophil emigration in the lungs.