Involvement of NF-κB in the regulation of S100A6 gene expression in human hepatoblastoma cell line HepG2

Abstract

S100A6 (calcyclin) is an acidic calcium binding protein with two EF-hand motifs and overexpressed in several tumors including intrahepatic carcinoma. TNFα, a strong NF-κB activator required for hepatocyte proliferation during liver regeneration, triggered the expression of S100A6 mRNA in human hepatoblastoma cell line HepG2. Transient expression of NF-κB (p65) increased S100A6 promoter activity and expression of inhibitor of NF-κB (IκBα) decreased TNFα-induced S100A6 promoter activity. To confirm the involvement of NF-κB in S100A6 promoter activation, we analyzed serially deleted promoter constructs of the S100A6 gene by luciferase reporter assay and found a NF-κB-responsive DNA fragment at the position between -584 and -361. Electrophoretic mobility shift assays showed that TNFα induced p65 binding to a potential NF-κB binding site at -460/-451. Furthermore, treatment of cells with CAPE (caffeic acid phenethyl ester), a specific NF-κB (p65) inhibitor, decreased NF-κB binding and promoter activity. These results suggest that NF-κB transcription factor contributes to the activation of S100A6 gene expression in response to TNFα in HepG2 cells.