Selective up-regulation of cytokine-induced RANTES gene expression in lung epithelial cells by overexpression of IkappaBR.

We previously reported the cloning of a cDNA for IkappaBR (for IkappaB-related) from human lung alveolar epithelial cells. IkappaBR is related to the IkappaB proteins that function as regulators of the NF-kappaB family of transcription factors. Here, we investigated the consequence of IkappaBR overexpression on the expression of NF-kappaB-regulated chemokine genes in lung alveolar epithelial cells. Chemokines play an important role in many inflammatory diseases such as asthma and AIDS. Overexpression of IkappaBR in the lung cells resulted in a rapid 50-100-fold greater production of the RANTES (regulated upon activation, normal T expressed and presumably secreted) protein upon cytokine-induction compared with control cells. IkappaBR overexpression, however, did not enhance interleukin-8 or MIP-1alpha gene expression, despite the fact that the expression of all three chemokine genes are regulated by NF-kappaB. The up-regulation of RANTES gene expression resulting from overexpression of IkappaBR correlated with increased amounts of a unique RANTES-kappaB binding activity and decreased binding of p50 homodimers. Previous studies have shown that p50 homodimers function as repressors of certain kappaB sites. Our studies suggest that IkappaBR can aid activation of select NF-kappaB-regulated genes by sequestering p50 homodimers.