Serum amyloid A activates NF-κB and proinflammatory gene expression in human and murine intestinal epithelial cells

Serum amyloid A (SAA) is an acute-phase protein whose levels positively correlate with disease activity in inflammatory bowel diseases. In this study we investigated the impact of SAA on NF-kappa B signaling and proinflammatory gene expression in intestinal epithelial cells (IEC). Human HT-29 and Caco-2 monolayers were stimulated with recombinant SAA and NF-kappa B activation/NF-kappa B-dependent gene expression measured. Adenoviral dominant negative mutants I kappa B-alpha (Ad5I kappa BAA) were utilized to determine the contribution of NF-kappa B signaling pathway to SAA-dependent gene expression. Intestinal explant and primary IEC derived from kappa B-EGFP transgenic mice were exposed to SAA and NF-kappa B-dependent enhanced green fluorescent protein (EGFP) fluorescence measured. SAA induced I kappa B-alpha degradation, Re1A serine 536 (S536) phosphorylation, NF-kappa B transcriptional activity, RelA recruitment to the IL-8 gene promoter and endogenous gene expression (IL-8, COX-2) in HT-29 cells. Further, Ad5I kappa BAA abrogated SAA-induced Re1A nuclear translocation, NF-kappa B transcriptional activity and IL-8 gene expression. SAA-dependent IL-8 gene expression required activation of the MAPK ERK, p38 and JNK in HT-29 cells. Finally, SAA induced EGFP expression in intestinal explants isolated from kappa B-EGFP transgenic mice and enhanced Re1A and I kappa B alpha phosphorylation in primary IEC. This indicates that SAA potentially participate in the inflammatory process by virtue of its ability to activate proinflammatory signaling in IEC.