Differential expression of two CYP1A genes in rainbow trout (Oncorhynchys mykiss)

Differential expression of two rainbow trout CYP1A genes was measured in vi vo and in vitro in response to treatment with the model CYP1A inducers beta -naphthoflavone (BNF), 3-methylcholanthrene (3-MC), isosafrole (ISF), and 2 ,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, only in vitro). Originally descri bed by Berndtson and Chen (Arch. Biochem. Biophys. 310, 187-195, 1994) as C YP1A1 and CYP1A2, these genes were renamed CYP1A3 and CYP1A1, respectively, by the P450 nomenclature committee. A significant, differential, inducer-d ependent induction of the two CYP1A mRNAs, as measured by RNase protection assay, was observed in vivo. CYP1A3 and CYP1A1 mRNA levels in liver were si gnificantly induced 50- and 18-fold, respectively, following ip injection w ith BNF. Conversely, CYP1A3 and CYP1A1 mRNA levels were significantly induc ed 5- and 66-fold, respectively, following ip injection with 3-MC. Isosafro le had no significant effect on in vivo induction of CYP1A mRNA levels. In primary cultures of hepatocytes, BNF, 3-MC, ISF, as well as TCDD all signif icantly induced CYP1A3 and CYP1A1 mRNA levels compared to controls. The dif ferential induction of the two CYP1A genes was not as evident in vitro as i n vivo. In addition, reanalysis and sequence comparison of the these two tr out CYP1A genes with the first trout CYP1A cDNA described by Heilmann et al . (DNA 7, 379-387, 1988) indicate that the Heilmann cDNA is a hybrid of the two trout genes. The 5' portion of the cDNA sequence (212 bp) was determin ed by sequencing of a genomic clone and is 100% identical to the trout CYP1 A3 gene. The majority of the cDNA sequence (2377 bp), however, was sequence d from a partial cDNA clone and is 99.2% identical to trout CYP1A1. Althoug h the nomenclature of these two trout CYP1A genes is undergoing revision, t hese results demonstrate a differential, inducer-dependent response to mode l mammalian CYP1A inducers. (C) 2000 Academic Press.