Expression of the chloramphenicol acetyltransferase (CAT) reporter gene by the murine [formula omitted] (cytochrome P 3450) promoter in hepatoma cell cultures

Abstract

In C57BL 6 mouse liver, both murine Cyp1a-1 (cytochrome P 1450) and Cyp1a-2 (P 3450) genes are inducible by 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD; dioxin), and Cyp1a-2 is constitutively expressed at high levels. Although the Cyp1a-1 gene is constitutively expressed and TCDD-inducible in mouse hepatoma Hepa-1 cell cultures, Cyp1a-2 gene expression is absent in these cultures. We show here that the 5′ flanking region of Cyp1a-2 from −1843 to +52 (base pairs relative to the transcription initiation site) linked to the chloramphenicol acetyltransferase ( CAT ) reporter gene in stable Hepa-1 transformants produces no basal or TCDD-or cycloheximide-inducible CAT activity. On the other hand, the Cyp1a-2 promoter from −63 to +52 driving the CAT gene is inducible by cycloheximide. A chimeric plasmid containing the Cyp1a-1 TCDD-responsive enhancer (−1646 to −245) ligated to a Cyp1a-2 promoter region (−129 to +52) supports TCDD-inducible CAT expression in Hepa-1 cells and in rat 7777 cells. These data suggest that, although sequences between −1843 and +52 are not sufficient for Cyp1a-2 gene expression, the murine Cyp1a-2 promoter is functional in cell cultures.