Gene expression profiling of murine hepatic steatosis induced by tamoxifen

Abstract

Tamoxifen is an antiestrogenic agent used widely in the treatment of estrogen receptor-positive breast cancer. However, hepatic steatosis has been reported during clinical trials of tamoxifen. To explore the mechanism responsible for this tamoxifen-induced hepatic steatosis, we used microarray analysis to profile the gene expression pattern of mouse liver after tamoxifen treatment. Tamoxifen was administered orally as a single dose of 10 mg/kg (low dose), 50 mg/kg (medium dose), or 100 mg/kg (high dose) to C57BL/6 mice, and the livers were removed 2 h, 4 h, 8 h, and 24 h later. From microarray data obtained from the liver samples, 414 genes were selected as tamoxifen-responsive genes (P < 0.05, two-way ANOVA: cutoff >= 1.5-fold response). These genes were classified into three groups: 308 of the 414 genes showed a time-dependent response, nine genes showed a dose-dependent response, and 97 genes showed a time- and dose-dependent response. Most of the 308 time-dependent-responsive genes were associated predominantly with the biological processes involved in lipid metabolism. Overrepresented transcription factor binding site analysis showed that the following nuclear receptors that are important in lipid and carbohydrate metabolism were overrepresented: the androgen receptor (AR), nuclear receptor subfamily 2 group F member 1 (NR2F1), hepatocyte nuclear factor 4 alpha (HNF4 alpha), and retinoic acid receptor-related orphan receptor alpha 1 (ROR alpha l). Reporter gene analysis further revealed that tamoxifen repressed the 5 alpha-dihydrotestosterone-induced activation of the AR and the intrinsic transactivation function of ROR alpha l, HNF4 alpha, and NR2F1. Taken together, these data provide a better understanding of the molecular mechanism underlying tamoxifen-induced steatogenic hepatotoxicity and useful information for predicting steatogenic hepatotoxicity.