The proliferative role of insulin and the mechanism underlying this action in human breast cancer cell line MCF-7.

Purpose: To explore the proliferative role of insulin and the potential mechanism in human breast cancer cell line MCF-7. Methods: MCF-7 cells were treated with different concentrations of insulin. Morphological observation and methylthiazolyltetrazolium (MTT) assay were used to detect the proliferation of MCF-7 cells. The expression of insulin receptor mRNA was detected by RT-PCR, with or without mitogen activated kinase (MAPK) signals blocked by their inhibitors: SP600125, the inhibitor of Jun N-terminal kinase (JNK), and PD98059, the inhibitor of extracellular signal-regulated (ERK1/2). Results: Insulin increased the proliferation of MCF-7 cells in a concentration-independent manner. Western blotting implicated that 100 nM insulin induced activation of JNK and ERK. The expression of phosphorylated JNK was detected within 5 min after insulin treatment and sustained for an hour, while ERK was activated later than JNK, at the 30th min after insulin treatment. Then we reevaluated the proliferative effect promoted by insulin after MAPK signaling pathway was blocked by its inhibitors. The results showed that after inhibiting the activities of JNK and ERK, the proliferative effect of insulin was also attenuated. Western blot results showed that, while blocking the MAPK signaling pathway, 10 mu M (ERK pathway inhibitor) could significantly inhibit phosphorylated activation of ERK1/2 with 200 nM insulin at 30 min, while no obvious inhibition with 20 mu M SP600125 (JNK pathway inhibitor) of phosphorylated activation of ERK1/2 was noticed. Conclusion: It seems that insulin can stimulate the proliferation of MCF-7 cells in vitro. MAPK signal transduction pathway involves the proliferative effect, which also regulates the expression of insulin receptor, mediates and amplifies the insulin signaling pathway.