Ah receptor regulation of CYP1B1 expression in primary mouse embryo-derived cells

Area of Science:

• Biochemistry
• Molecular Biology
• Toxicology

Background:

• Cytochrome P450 1B1 (CYP1B1) is crucial for metabolizing polycyclic aromatic hydrocarbons (PAHs) into mutagenic compounds.
• Mouse embryo fibroblasts (MEFs) and the C3H10T1/2 cell line express CYP1B1 as a primary P450 form.
• CYP1B1 is constitutively expressed and inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and PAHs.

Purpose of the Study:

• To investigate the role of the aryl hydrocarbon receptor (AhR) in mediating CYP1B1 induction by PAHs and TCDD in MEFs.
• To determine how AhR phenotype (b-1 vs. d-type) influences CYP1B1 expression and induction responses.
• To assess the impact of cell passage number and proliferative state on CYP1B1 expression in MEFs.

Main Methods:

• Primary MEFs from congenic C57b/6 mice with differing AhR loci (b-1 and d-type) were utilized.
• CYP1B1 expression was quantified via mRNA, protein levels, and metabolic activity (PAH metabolism).
• Reverse transcriptase-PCR was used to detect CYP1A1 mRNA expression.

Main Results:

• Constitutive CYP1B1 expression was similar in both AhR phenotype MEFs.
• AhR-dependent induction of CYP1B1 by TCDD showed a 5-fold lower EC50 in b-1 MEFs compared to d-type MEFs.
• CYP1B1 expression decreased with increasing passage number, correlating with reduced proliferation and differentiation, but was regained in non-senescent, proliferating colonies.

Conclusions:

• CYP1B1 induction by TCDD and PAHs is mediated by the AhR in MEFs.
• The proliferative state of MEFs is a critical factor for CYP1B1 expression, including AhR-dependent induction.
• These findings highlight the interplay between AhR signaling, xenobiotic metabolism, and cellular senescence in primary fibroblast cultures.