NF-κB is Involved in the Induction of the Rat Hepatic α1-Acid Glycoprotein Gene by Phenobarbital ☆

Abstract Phenobarbital, a classical inducer of the drug-metabolizing cytochrome P450 genes, induces α1-acid glycoprotein gene expression through a PB-responsive element (PBRE) located at position −142 to −126 from the transcriptional start site. The aim of this study was to investigate nuclear protein binding to the PBRE sequence after PB treatment. Cycloheximide treatment showed that de novo protein synthesis was not required for PB to induce AGP gene expression, pointing to post-translational modifications. Studies of the DNA–protein complex with the PBRE showed that phosphorylation status is a key regulator of the binding capacity of transactivating proteins involved in PB transcriptional activation. This DNA–protein complex, analyzed by southwestern blotting and UV cross-linking, involves three nuclear factors with molecular weights of 43, 52, and 65 kDa. Supershift and competition experiments showed that the 43-kDa factor can be related to C/EBPα and the 52- and 65-kDa factors to the two subunits of NF-κB.