Expression of CYP1B1 in human adult and fetal tissues and differential inducibility of CYP1B1 and CYP1A1 by Ah receptor ligands in human placenta and cultured cells.

tetrachlorodibenzo-p-dioxin (TCDD) and was found to also beExpression of the Ah receptor-regulated cytochrome inducible in primary cultures of human epidermal keratinocytesP4501B1 (CYP1B1) gene was studied in human adult and (1). CYP1B1 mRNA was detected in several human tissuesfetal tissues and cells in culture by reverse transcriptase- by RNA blotting (1). Metabolic activity and immunoreactivitycoupled polymerase chain reaction (RT-PCR). In adults, with anti-murine CYP1B1 antibody suggest that CYP1B1 isCYP1B1 mRNA was detected in liver, lymphocytes, cells of constitutively expressed in the human breast cancer cell linebronchoalveolar lavage samples and uterine endometrium, MCF-7 and in uterine myometrium and myoma tissues (7,8).but not in lung. The level of expression was very low in In a recent study CYP1B1 was also identified in human breastadult liver and only three out of six fetal livers expressed tumors (9).CYP1B1. Extrahepatic fetal tissues, especially brains and Endocrine glands have been shown to be the major sites ofkidneys, expressed high levels of CYP1B1. CYP1B1 mRNA CYP1B1 expression in experimental animals (10). Humanwas constitutively detected at a low level in first trimester placenta is an important endocrine organ during pregnancyand full-term placental samples. A competitive RT-PCR and produces notable amounts of estrogens. In placenta,assay was developed to assess the regulation of CYP1B1. estradiol is hydroxylated predominantly at C-2 by aromataseCYP1B1 mRNA was not induced in placenta by maternal (CYP19) (11), while constitutive 4-hydroxylation is only acigarette smoking. Inducibility of CYP1B1 in cells in culture minor pathway (7). Maternal smoking, however, preferentiallyby the Ah receptor ligand 2,3,7,8-tetrachlorodibenzo-p- increases placental 4-hydroxylation, concomitantly withdioxin was studied in primary fibroblasts and chorion increased aryl hydrocarbon hydroxylase (AHH) activity (12).carcinoma cell line JEG-3 having different CYP1A1 induc- Cigarette smoke strongly induces CYP1A1 in human placenta.tion properties. Inducibility of CYP1B1 was found to be This enzyme mainly 2-hydroxylates estradiol and has veryregulated independently from CYP1A1. In JEG-3 cells little 4-hydroxylase activity (13). Several lines of evidenceCYP1A1 mRNA was induced up to 9000-fold, while the suggest that CYP1B1 mediates estradiol 4-hydroxylation (6,7).expression of CYP1B1 was not affected. Expression of Ah CYP1B1 could therefore potentially be the inducible placentalreceptor and Ah receptor nuclear translocator (regulators estradiol 4-hydroxylase.of the CYP1 family) was determined in human placenta Induction of members in the CYP1 family is controlled byand in the JEG-3 cell line. Expression of these transcription the aryl hydrocarbon receptor (Ah receptor) and Ah receptorfactors was found neither to be co-regulated nor affected nuclear translocator (ARNT). The Ah receptor has been shownby Ah receptor ligands. This study provides evidence that to be expressed abundantly in human placenta (14,15). How-in addition to the Ah receptor complex, other cell-specific ever, individual variations in the expression level of placentalfactors modulate the response of CYP1B1 and CYP1A1 to Ah receptor and its relation to ARNT has not been elucidated.Ah receptor ligands. In the present study we have characterized, using qualitativeand quantitative reverse transcriptase-polymerase chain reac-tion (RT-PCR): (i) constitutive expression of theCYP1B1 geneIntroduction in human adult and fetal tissues; (ii) the relationship betweenA new member of human cytochrome P450 (CYP*) family 1 CYP1A1 and CYP1B1 induction; (iii) CYP1B1 induction bywas recently identified (1) and designated CYP1B1 according cigarette smoke in placenta in vivo; (iv) placental expressionand regulation of the CYP1 family regulating factors Ahreceptor and ARNT.