Identification of a Novel Dioxin-Inducible Cytochrome P450

Abstract

Representational difference analysis was used to isolate cDNAs corresponding to 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin)-inducible genes from mouse Hepa-1 cells. One cDNA encoded a novel cytochrome P450. The human homolog was also isolated and later proved to be human CYP2S1. The induction of mouse CYP2S1 mRNA by dioxin represents a primary response and required the aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator proteins. The induction of CYP2S1 also occurred in mouse liver and lung, with the highest expression found in lung. CYP2S1 was also inducible in a human lung epithelial cell line. The dioxin-inducibility of CY2S1 is exceptional, because all previously well-characterized cases of the induction of cytochromes P450 by dioxin involve members of the CYP1 family.The cytochrome P450 (P450) superfamily of proteins is involved in the metabolism of a vast array of carcinogens, drugs, and endogenous metabolites. The three members of the CYP1 cytochrome P450 family are inducible by ligands for the aryl hydrocarbon receptor, which include important classes of chemical carcinogens such as PAHs, aromatic amines, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin). All three CYP1 family members also play important roles in the metabolic activation of a number of these same compounds to carcinogenic derivatives. CYP1A1 and CYP1B1 both activate PAHs to carcinogenic intermediates, whereas CYP1A2 activates aromatic amines. Dioxin is the most carcinogenic substance evaluated (Hankinson, 1995). In contrast to PAHs and aromatic amines, dioxin is refractory to biotransformation, and the parent compound itself acts as a carcinogen. The induction of CYP1A1 has been well-studied. After binding the ligand, the AHR translocates to the nucleus, where it dimerizes with the ARNT protein. The AHR/ARNT dimer then binds to xenobiotic-responsive elements in the 5Ј flanking region of the CYP1A1 gene, leading to stimulation of transcription of the gene (Whitlock, 1999). Transcriptional activation of the CYP1A2 and CYP1B1 genes seems to occur in a similar fashion. Induction of CYP1A2 is restricted to the liver, whereas CYP1A1 and CYP1B1 are both inducible in many tissues (Savas et al., 1994;Dey et al., 1999).The aim of this study was to identify novel dioxin-inducible genes, with the notion that such genes might be involved in carcinogenesis by PAHs, dioxin, and related compounds. Using representational difference analysis (RDA) on the mouse hepatoma cell line Hepa-1, we identified several genes not known previously to be inducible by dioxin. This report focuses on one of these genes, a novel cytochrome P450 that belongs to the CYP2 family rather than to the CYP1 family, which includes all other previously well-characterized, dioxin-inducible cytochromes P450.

CYP2A13 in Human Respiratory Tissues and Lung Cancers: An Immunohistochemical Study with A New Peptide-Specific Antibody

“…Immunoblot analysis clearly demonstrated that our CYP2A13 peptide antibody does not cross-react with CYP2A6 protein (expressed either heterologously or in human liver microsomes) or any of the P450 proteins that are mainly expressed in human liver, that include CYP1A1, CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A4 (Parkinson, 2001). Moreover, the anti-CYP2A13 antibody does not cross-react with CYP2S1, which is a nonhepatic P450 with high expression in human respiratory tract (Rylander et al, 2001;Rivera et al, 2002;Saarikoski et al, 2005), or mouse CYP2A5, which also shares a high degree of amino acid sequence similarity with both human CYP2A13 and CYP2A6. To our knowledge, this is the first specific antibody that can distinguish CYP2A13 from CYP2A6.…”

Cytochrome P450 Profile of Colorectal Cancer: Identification of Markers of Prognosis

“…This P450 has only recently been cloned and although assigned to the CYP2 family on the basis of nucleic acid and amino acid sequence homology, it is dioxin inducible (31,32). All other dioxininducible P450s are members of the CYP1 family and this suggests that CYP2S1 may have similar functional characteristics and metabolic substrates as CYP1 P450s (31,32). The immunohistochemical localization of CYP2S1 protein in normal colon is a novel finding although a high level of CYP2S1 mRNA has previously been identified by real-time quantitative PCR in this tissue (33).…”

Characterization of a Human Keratinocyte HaCaT Cell Line Model to Study the Regulation of CYP2S1

“…For example, 2,3,7,8-tetrachlorodibenzo-p-dioxin, a well characterized Family 1 P450 inducer, induces CYP2S1 (Rivera et al, 2002), and ␣-naphthalene, an active component of coal tar, is oxidized by CYP2S1 (Karlgren et al, 2005). However, there are conflicting reports on the role of CYP2S1 in carcinogen metabolism.…”