Correlation between alterations in nucleosomal organization of LINEs in the promoter of cytochrome p450 2B1/2 gene and induction of CYP2B1/2B2 mRNA expression by phenobarbitone in rat liver

Mammalian genome contains a high proportion of repetitive DNA with a sizeable fraction of Long Interspersed Nuclear Elements (LINEs). LINEs have been functionally implicated in the organization and evolution of mammalian genome. However, functions of LINEs in the promoter region and gene expression are poorly understood. Here, we report two small, conserved LINE sequences (3P and 5P) that occur as multiple copies of inverted repeats in the rat Cytochrome P450 2B1/2B2 (CYP 2B1/2) gene promoter. Using 3P or 5P as a single primer, the CYP 2B1/2 promoter DNA was amplified by PCR from the rat genome. Phenobarbitone (PB), a prototype xenobiotic drug, strongly induced CYP 2B1/2 mRNA expression in the rat liver. 3P and 5P LINE sequences showed an alteration in the nucleosomal organization in the CYP 2B1/2 promoter after 2, 4, and 6 h of PB induction, and the promoter was mostly devoid of nucleosomes during the induction. Reorganization of nucleosomes associated with these LINE sequences were strongly correlated with induction of CYP 2B1/2 mRNA expression by PB in vivo. Our results strongly suggest that these LINE sequences in CYP 2B1/2 gene promoter(s) may facilitate transcriptional activation of the gene(s) by PB through retention and reorganization of nucleosomes. This might be a novel function of LINEs in the mammalian genome that correlates the chromatin structure with gene expression during drug metabolism.