Butein Up-Regulates the Expression of the π Class of Glutathione S-Transferase in Rat Primary Hepatocytes through the ERK/AP-1 Pathway

Induction of phase II enzymes is an important mechanism of chemoprevention. Here we compared the effects of chalcones on the expression of the pi class of glutathione S-transferase (GSTP) in rat primary hepatocytes. Hepatocytes were treated with 10 or 25 mu M of phloretin or butein for 24 h. Both butein and phloretin dose-dependently increased GSTP protein expression, and the induction potency of butein was stronger than that of phloretin. The increase in GSTP mRNA in cells treated with 25 mu M of phloretin and butein was 107% and 211%, respectively (P < 0.05). Butein increased GST enzyme activity by 27% compared with that in the control cells (P < 0.05). In contrast, phloretin had no significant effect on GST enzyme activity. The pTA-luciferase reporter construct with the rat -2.7 kb GSTP promoter region was transiently transfected into Clone 9 liver cells, and the luciferase activity in butein-treated cells was 1.1-fold higher than that in control cells (P < 0.05). GSTP enhancer 1 (GPE1) deletion abolished the induction of reporter activity by butein. The phosphorylation of extracellular signal-regulated kinase (ERK), but not of c-Jun NH2-terminal kinase (JNK) and p38, was stimulated in the presence of butein. Pretreatment with PD98059, an ERK inhibitor, alleviated the increase in activator protein-1 (AP-1)-DNA binding activity and also the activation of GSTP protein expression by butein. Moreover, c-Jun is likely to bind to the GPE1. Silencing of ERK2 by siRNA gene knockdown reduced the butein-induced expression of GSTP. In conclusion, the increased GSTP expression by butein is likely related to the ERK-AP-1 pathway.