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Interferon-mediated changes in the expression of CYP1A1 in human B lymphoblastoid (AHH-1 TK +/-) cells
E Delaporte1, A E Cribb, K W Renton
1Department of Pharmacology, Dalhousie University, Halifax, NS, Canada.
Abstract:
The expression of constitutive and inducible cytochrome P450s has been shown to be downregulated by interferon through an unknown pretranslational mechanism that depresses the mRNA encoding P450 apoproteins. To establish an association between gene transcription and P450 apoprotein downregulation by interferon, we studied the effect of recombinant interferon (IFN-alpha 2a) on CYP1A1 in human B lymphoblastoid cell lines. The cHoI cell line expresses inducible native CYP1A1, while the genetically engineered derivative h1A1 v2 expresses a noninducible extrachromosomal vector-derived human CYP1A1 cDNA lacking the CYP1A1 promoter region. We characterized CYP1A1 activity, apoprotein, and mRNA by ethoxyresorufin O-deethylase activity, Western immunoblotting, and Northern blot analysis, respectively. In cHoI cells, following induction with dibenz[a,h]anthracene, interferon depressed CYP1A1 apoprotein and mRNA levels by 55 and 76%, respectively, with no detectable changes in enzyme activity. In h1A1 v2, however, interferon increased CYP1A1 activity, apoprotein, and mRNA. The depression of CYP1A1 mRNA and apoprotein levels incHoI cells, in contrast with the increase observed in h1A1 v2 cells, suggests that nuclear mechanisms are essential for interferon-mediated depression of inducible P450s. From our preliminary results we propose that interferon-mediated downregulation of CYP1A1 may result from inhibition of gene transcription.
Insights
Interferon (IFN-alpha 2a) downregulates inducible cytochrome P450 (CYP1A1) expression by inhibiting gene transcription, not affecting enzyme activity. This suggests nuclear mechanisms are key to interferon
Area of Science:
- Biochemistry
- Molecular Biology
- Immunology
Background:
- Interferons (IFNs) are known to downregulate cytochrome P450 (CYP) expression via pretranslational mechanisms.
- The precise mechanism, particularly the role of gene transcription, in interferon-mediated CYP downregulation remains unclear.
Purpose of the Study:
- To investigate the association between gene transcription and interferon-induced P450 apoprotein downregulation.
- To determine the effect of recombinant interferon (IFN-alpha 2a) on CYP1A1 expression and activity in human B lymphoblastoid cell lines.
Main Methods:
- Utilized cHoI (inducible CYP1A1) and h1A1 v2 (noninducible CYP1A1 cDNA) cell lines.
- Assessed CYP1A1 activity (ethoxyresorufin O-deethylase), apoprotein (Western immunoblotting), and mRNA (Northern blot analysis).
- Administered dibenz[a,h]anthracene for induction and IFN-alpha 2a for treatment.
Main Results:
- In cHoI cells, IFN-alpha 2a significantly depressed CYP1A1 apoprotein (55%) and mRNA (76%) levels after induction, with no change in enzyme activity.
- Conversely, in h1A1 v2 cells, IFN-alpha 2a increased CYP1A1 activity, apoprotein, and mRNA levels.
- The contrasting effects in the two cell lines highlight the importance of the CYP1A1 promoter region.
Conclusions:
- Interferon-mediated downregulation of inducible CYP1A1 involves nuclear mechanisms, likely through inhibition of gene transcription.
- These findings suggest that interferon's effect on CYP450 expression is dependent on the transcriptional regulation of the gene.