IL-1β-specific up-regulation of neutrophil gelatinase-associated lipocalin is controlled by IκB-ξ

Neutrophil gelatinase-associated lipocalin (NGAL) is a siderophore-binding protein that exerts a bacteriostatic effect by sequestering iron. Strong induction of NGAL synthesis has been observed in inflamed epithelium of the lungs and colon. Expression of NGAL is up-regulated in the lung epithelial cell line A549 by IL-1 beta, but not by TNF-alpha, despite an induction of NF-kappa B binding to the NGAL promoter by both cytokines. In this study, we present evidence that the IL-1 beta specificity is caused by a requirement of the NGAL promoter for the NF-kappa B-binding cofactor I kappa B-zeta for transcriptional activation. Up-regulation of NGAL expression in A549 cells following IL-1 beta stimulation was dependent on de novo protein synthesis and was greatly diminished by a small interfering against I kappa B-zeta mRNA. Cotransfection of A549 cells with a plasmid expressing I kappa B-zeta made TNF-alpha capable of inducing NGAL transcription, indicating that IKB-zeta induction is the only factor discriminating between IL-1 beta and TNF-alpha in their ability to induce NGAL expression. Coexpression of the cofactor Bcl-3, which is closely related to IKB-zeta, did not enable TNF-alpha to induce NGAL transcription. A functional NF-kappa B site of the NGAL promoter was required for IKB-zeta to exert its effect. The human beta defensin 2 gene also required IKB-zeta for its IL-1 beta-specific induction in A549 cells. Our findings indicate that a common regulatory mechanism has evolved to control expression of a subset of antimicrobial proteins expressed in epithelial cells.