miR-126-mediated activation of IGF2/IGF1R/IRS1 signaling promotes the Herceptin resistance in ErbB2 positive breast cancer cells

Objective To explore the role of insulin-like growth factor-2/insulin-like growth factor-1 receptor/insulin receptor substrate-1 (IGF2/IGF1R/IRS1) signal pathway inducing the chemoresistance of epidermal growth factor receptor 2 (ErbB2) positive breast cancer cells to Herceptin. Methods Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot assay were used to determine the expression levels of IGF2, IGF1R, and IRS1. The direct targets of miR-126 were validated by dual-luciferase reporter gene assay. In SKBR3/pool2 cells, IGF1R activity was reduced by an inhibitor of IGF1R, and IRS1 was knocked-down by shRNAs. Furthermore, 3-(4, 5-dimenthylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay was performed to evaluate the sensitivity of these treated cells to Herceptin. Results IGF2, IGF1R, and IRS1 were significantly higher expressed in SKBR3/pool2 cell compared to that in SKBR3 cell. Western blot assay showed that IGF2/IGF1R/IRS1 was activated in SKBR3/pool2 cells. Bioinformatics analysis combined with luciferase activity suggested that miR-126 directly targeted IRS1. MTS results demonstrated that the chemosensitivity to Herceptin of SKBR3/pool2 cells with inhibitor of IGF1R or shRNAs targeting IRS1 or overexpressing miR-126 was significantly reduced. Conclusions IGF2/IGF1R/IRS1 signal pathway confers to the chemoresistance of ErbB2 positive breast cancer cells to Herceptin. Key words: MicroRNAs; Insulin-like growth factor II; Receptor, IGF type 1; Receptor, insulin; Breast neoplasms/DT/ME; Drug tolerance; Antibodies, monoclonal/TU