IGF-I plus E2 induces proliferation via activation of ROS-Dependent ERKs and JNKs in human breast carcinoma cells

Induction of 17 beta-estradiol (E2) and insulin-like growth factor-I (IGF-1) has been detected in breast carcinoma, however the interaction between E2 and IGF-I in the proliferation of breast carcinorna cells is still unclear. In the present study, we found that IGF-I enhances the E2induced proliferation in MCF-7 human breast carcinoma cells in accordance with stimulation of colony formation via a soft agar assay. Activation of insulin receptor substrate- I (IRS- 1) protein and extracellular signal-related kinases (ERKs) and c-Jun N-terminal kinases JNKs), but not p38 mitogen -activated protein kinase (MAPK), via phosphorylation induction was detected in MCF-7 cells i treated with IGF-I plus E2 (E2/IGF-1). E2/IG F-I -induced proliferation was blocked by chemical inhibitors of ERKs (PD98059) and JNKs (SP600125). An increase in the expression of c-Jun protein was detected in E2/IGF-I-treated MCF-7 cells, and this was inhibited by PD98059 and SP600125. Transfection of the dominant negative MEKK and JNK plasmids significantly reduced E2/IG F-I -induced proliferation with suppression of cJun protein expression. An increase in peroxide production was detected in E2/IGF-1-treated cells, and N-acetyl-L-cysteine (NAC) and Tiron (TIR) addition significantly inhibited E2/1 G F-I -induced cell proliferation with blocking of the phosphorylation of ERKs and JNKs, and the expression of c-Jun protein. Additionally, 3-OH flavone, baicalein, and quercetin showed effective inhibitory activities against E2/IGF-1induced proliferation through suppressing proliferative events such as phosphorylation of IRS- 1, ERKs, and JNKs proteins, and induction of c-Jun protein and colony formation. These results indicate that IGF-I interacts with E2 to promote the proliferation of breast carcinoma cells via RCS-dependent MAPK activation and c-Jun protein expression. The structure-related inhibition of E2/IGF-1-induced proliferative events by flavonoids is elucidated.