"Induction of phase II enzymes is an important mechanism of chemoprevention. Here we compared the
effects of chalcones on the expression of the π class of glutathione S-transferase (GSTP) in rat primary
hepatocytes. Hepatocytes were treated with 10 or 25 μM 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 μM 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."
