The microRNA-141-3p/ CDK8 pathway regulates the chemosensitivity of breast cancer cells to trastuzumab

Aims: This study was conducted to explore the function of microRNA-141-3p/cyclin-dependent kinase 8 (miR-141-3p/CDK8) in regulating trastuzumab resistance of breast Cancer cells.

Materials and methods: Microarray analysis was performed to screen MicroRNAs that are differentially expressed in wild type and trastuzumab-resistant (TR) breast Cancer cell lines. TargetScan helped predict the target gene of miR-141-3p. The regulatory relationship was confirmed through a luciferase reporter assay, quantitative Reverse Transcriptase polymerase chain reaction, and Western blot analysis. The MTT assay, transwell invasion assay, and wound scratch assay were performed to measure the proliferative, invasive, and migratory ability of breast Cancer cells, respectively. Tumor cell xenografts in nude mice were conducted to observe the effect of miR-141-3p on trastuzumab resistance in breast Cancer cells in vivo. The enzyme-linked immunosorbent assay was used to detect protein secretion.

Results: miR-141-3p was downregulated in the drug-resistant cell lines. CDK8 was proved to be a target gene of miR-141-3p. Transfection of miR-141-3p or CDK8 small interfering RNA (siRNA) reversed the resistance to trastuzumab in TR cell lines and suppressed cell invasion and migration. Dysregulation of transforming growth factor beta (TGF-β) was detected when the expression of CDK8 was silenced by CDK8 siRNA, and downregulation of TGF-β had a notable effect on reducing the phosphorylation of SMAD2/SMAD3.

Conclusion: miR-141-3p could restore the sensitivity to trastuzumab in breast Cancer cells by repressing CDK8, which might regulate the phosphorylation levels of SMAD2/SMAD3 via TGF-β.