Received for publication September 20, 2006.
Revised November 12, 2006.
Accepted for publication December 5, 2006.

Transcriptional Regulation of Human CYP2A13 Expression in the Respiratory Tract by C/EBP and Epigenetic Modulation

Abstract

CYP2A13, which is highly active in the metabolic activation of tobacco-specific nitrosamines, is selectively expressed in the respiratory tract, where it is believed to play an important role in chemical carcinogenesis. The aim of this study was to determine the basis for tissue-specific regulation of CYP2A13 gene expression. Previously, we showed that expression of CYP2A3, the rat homolog of CYP2A13, is regulated by nuclear factor I (NFI) in a tissue-specific manner. In the present study, we find that the transcriptional regulation of human CYP2A13 gene involves C/EBP transcription factors, instead of NFI. DNase I footprinting and gel-shift assays with human lung nuclear extract identified two DNA elements bound by C/EBP. Reporter gene assays using a 216-bp CYP2A13 promoter fragment confirmed activation of CYP2A13 by transfected C/EBP factors, and results from chromatin immunoprecipitation assays indicated that C/EBP is associated with CYP2A13 promoter in vivo in the olfactory mucosa of CYP2A13-transgenic mice. In NCI-H441 human lung cancer cells, we discovered that CYP2A13 expression can be induced by a combined treatment with 5-aza-2'-deoxycytosine, a DNA demethylation agent, and trichostatin, a histone deacetylation inhibitor. In 5-aza-2'-deoxycytosine/trichostatin treated NCI-H441 cells, over-expression of C/EBP, a lung-enriched C/EBP, led to additional increases in CYP2A13 expression, whereas C/EBP knockdown by siRNA suppressed CYP2A13 expression, findings that confirm a role for C/EBP in CYP2A13 regulation. Our findings pave the way for further studies of the regulation of the CYP2A13 gene, particularly the gene's potential suppression by airway inflammation, and the role of epigenetic modulation in the gene's tissue-selective expression.

Key words: Promoter analysis, Cytochrome P450, Regulation - transcriptional

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