The effect of endotoxin on hepatocyte nuclear factor 1 nuclear protein binding: potential implications on CYP2E1 expression in the rat

The purpose of this study was to determine if changes in nuclear protein binding of hepatocyte nuclear factor 1 (HNF‐1) occur after lipopolysaccharide (LPS) administration. In addition, the time‐course of alterations in CYP2E1 regulation were evaluated. Rats were injected with 2.0 mg LPS and euthanized over a 72‐h period. Nuclear protein binding to a consensus HNF‐1 oligonucleotide was assessed by the electrophoretic mobility shift assay. CYP2E1 activity was analysed using chlorzoxazone as a substrate (6OH‐CLZ), and CYP2E1 protein concentration was determined by enzyme‐linked immunosorbent assay. Endotoxin treatment resulted in decreased nuclear protein binding to an HNF‐1 element as early as 1 h after treatment and returned to control levels by 72 h. This reduced binding persisted for 24 h and returned to control values 48 h after LPS administration. In addition, the reduction in binding was primarily attributable to a HNF‐1α immunoreactive protein. The observed reduction in HNF‐1 binding was followed in the time‐course by decreases in CYP2E1 activity and protein content with maximal decreases to 50 and 67% of control, respectively, at 48 h after LPS administration. Endotoxin is a potent inducer of the acute phase response (APR). The APR stimulation by endotoxin administration reduced HNF‐1α binding and decreased the expression of CYP2E1 in the rat liver. The time‐course of alterations in HNF‐1 and CYP2E1 lend support to the possibility that HNF‐1α may play a role in the down‐regulation of genes that require HNF‐1α for their constitutive expression. These data serve as an important precedent for future studies evaluating the direct association of decreased HNF‐1α binding and reduced gene expression after LPS administration.