Enhanced DNA binding and activation of transcription factors NF-κB and AP-1 by acetaldehyde in HEPG2 cells

Because transcription factors NF-kappa B and activator protein-1 (AP-1) are known to regulate gene expression, we have analyzed the role of acetaldehyde in the activation of NF-kappa B and AP-1 in HepG2 cells. Binding activity and transactivation of NF-kappa B and AP-1 were determined by gel retardation assays and transfection of a luciferase reporter construct controlled by kappa B and AP-1 binding sites, respectively. Acetaldehyde enhanced the DNA binding of NF-kappa B and AP-1 by 1 and 4 h, respectively, increasing the kappa B- and AP-1-dependent luciferase expression. Supershift assays revealed the presence of NF-kappa B heterodimers p65/p50 and p50/p52, whereas nuclear c-Jun levels correlated with the DNA binding of AP-1. The enhanced binding of NF-kappa B to DNA by acetaldehyde in intact cells was accompanied by the proteolytic degradation of I kappa B-alpha. However, the addition of acetaldehyde to cytostolic extracts from untreated Hep G2 cells did not affect the DNA binding of AP-1 but activated the NF-kappa B heterodimer p65/p50 in the absence of I kappa B-alpha degradation. Preincubation of HepG2 cells with protein kinase C inhibitors abolished the enhanced DNA binding of NF-kappa B and AP-1 caused by acetaldehyde. Hence, these findings uncover a previously unrecognized role for acetaldehyde in the activation of NF-kappa B and AP-1, which may be of relevance in the alcohol-induced liver disease.