Inducer-dependent transcriptional activation of the P4501A2 gene in vivo and in isolated hepatocytes.

In vitro nuclear run-on transcription analysis using probes directed against different regions of CYP1A2 revealed that the 70-100-fold induction of CYP1A2 mRNA by polycyclic aromatic compounds is associated with a corresponding increase in the transcriptional activation of this gene in rat liver. Probes from regions of the 1st, 2nd, and 4th introns detected approximately 50-100-fold higher CYP1A2 run-on transcription in liver nuclei from inducer-treated animals than in nuclei from untreated animals. The run-on signals from untreated rats were 3-5-fold above background signals. Additional experiments using single-stranded DNA probes and a probe from a region 5' to the CYP1A2 transcription start site revealed that the inducer-dependent transcripts were colinear with the CYP1A2 mRNA and that they did not result from read through of an initiation event 5' to CYP1A2. Run-on transcription analyses were also carried out with nuclei from isolated hepatocytes using the same series of probes spanning CYP1A2. These analyses indicated that the inducer-dependent accumulation of CYP1A2 mRNA in hepatocytes is associated with at least a 20-fold increase in CYP1A2 transcription. In contrast to liver and hepatocytes, these probes failed to detect run-on transcripts from kidney nuclei, indicating that the lack of CYP1A2 mRNA in this tissue is due to the lack of transcriptional activation of this gene by polycyclic aromatic compounds.