Regulation of Elastin Gene Transcription by Interleukin-1β- Induced C/ebpβ Isoforms

We previously showed that interleukin-1β (IL-1β) decreased elastin gene transcription through activation of the NF-κB subunit p65 in neonatal rat lung fibroblasts. The present study was undertaken to further explore the molecular mechanisms responsible for the inhibitory effect of IL-1β on elastin gene transcription. We found that cycloheximide blocked IL-1β-induced down-regulation of elastin mRNA but did not inhibit IL-1β-induced translocation of p65 into the nucleus. IL-1β treatment increased CCAAT/enhancer-binding protein-β (C/EBPβ) mRNA and protein levels including LAP (liver-enriched activating protein) and LIP (liver-enriched inhibitory protein) that was cycloheximide sensitive. C/EBPβ isoforms bound a GCAAT containing sequence in the proximal elastin promoter as determined by electrophoretic gel shift studies and confirmed by using specific anti-C/EBPβ antibodies and by competition studies with oligonucleotides. Transient transfection of LIP expression vectors strongly decreased the transcriptional activity of the co-transfected elastin promoter and decreased levels of endogenous elastin mRNA. We demonstrated IL-1β induced down-regulation of elastin mRNA was dependent on NF-κB activation and C/EBPβ expression. These results indicate that IL-1β treatment activates NF-κB that subsequently induces LIP expression and inhibition of elastin gene transcription.