Transcriptional regulation of cytochrome P450 2A genes

CYP2A enzymes in the respiratory tract play a critical role in the metabolic activation of inhaled toxicants. However, little is known about how these respiratory-tract P450s are regulated, a fact that hinders us from fully understanding the adverse responses of the body to inhaled toxicants. Here I present our studies on the transcriptional regulation of rat CYP2A3 and human CYP2A13, both of which are respiratory-tract specific P450s.; Previously we showed that a DNA element in rat CYP2A3 promoter, named NPTA (Nasal Predominant Transcriptional Activation) element, may play an important role in CYP2A3 gene transcription. In this study, the NPTA-binding proteins were purified and identified as nuclear factor 1 (NF1) proteins. Functional analysis showed that NFIA transactivated CYP2A3 promoter. This activation can be modulated by a novel, alternatively spliced NFI isoform, NFIA_short. NFI proteins interact with CYP2A3 promoter in vivo in the nasal mucosa, but not in the liver, where the CYP2A3 gene is silent. We further demonstrated that methylation of the CYP2A3 promoter in rat liver is extensive, a finding indicative of a nonpermissive chromatin structure for NFI binding, which strengthens our view of NFI as an important regulator in tissue-specific CYP2A3 expression.; NFI proteins may also be important in CYP2A13 gene regulation. DNase I footprinting assays using human lung nuclear extract identified an NPTA-like region in the CYP2A13 promoter. Gel shift assays indicated that multiple proteins, some of which NFI-related, bind to this region. In addition, footprinting assays reveal another element in the CYP2A13 promoter that interacts with transcription factors. Some of these factors seem to be lung-specific. Further characterization of these factors is now underway.; In summary, we have obtained comprehensive and conclusive evidence to establish NFI proteins as transcriptional regulators of CYP2A3 and CYP2A13 gene expression. Our findings, as well as our approaches, pave the way for further exploration of the mechanisms of respiratory tract-specific CYP gene regulation, a quest that will ultimately contribute to a better understanding of adverse human responses to inhaled toxicants.