Effect of dexamethasone and phenobarbital on run-on transcription rate and CYP3A mRNA concentration in rat liver: changes during development.
Modulation of CYP3A1 and CYP3A2 mRNA expression by dexamethasone and by phenobarbital has been studied in immature (21-day-old) and adult (90-day-old) rat liver. Positive modulation of these forms by both agents markedly declines with the age of the animals. However, CYP3A2 mRNA, although physiologically extinguished in the adult females, still responds to dexamethasone stimulation. The regulatory mechanisms underlying the differential behavior of CYP3A1 in the immature and adult animals have been further investigated by analyzing the early changes in the run-on transcription rates and the subsequent mRNA accumulation in the liver in response to the inducer agents. CYP3A genomic clones were constructed and characterized for this purpose. The use of a unique cosCYP/3A1 intronic sequence, identified in this work, made possible the selective determination of the transcription rate of this gene by run-on assay, as a function of ontological development and inducer treatment. Parallel determination of the mRNA concentration in the liver by dot blot analysis demonstrated that dexamethasone induces CYP3A1 essentially through transcription regulation in immature animals, while in adults it is suggested to act mainly at a post-transcriptional level.
Telhada
M B
MB
Laboratory of Biochemistry, Instituto Gulbenkian de Ciência, Oeiras, Portugal.
Pereira
T M
TM
Lechner
M C
MC
D000375:Aging / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D015698:Genomic Library; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development; D008297:Male; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010634:Phenobarbital / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D012727:Sex Characteristics; D014158:Transcription, Genetic / Q000187:drug effects*
D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D003907:Dexamethasone; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C465138:Cyp3a23-3a1 protein, rat; D051544:Cytochrome P-450 CYP3A; D010634:Phenobarbital