Amyloid precursor protein promotes the migration and invasion of breast cancer cells by regulating the MAPK signaling pathway

Abstract

To verify whether amyloid precursor protein (APP) affects the migration and invasion of breast cancer cell lines, and to understand its underlying mechanisms, epithelial-mesenchymal transition (EMT), the mitogen-activated protein kinase (MAPK) signaling pathway and the matrix metalloproteinase (MMP) family were investigated in MDA-MB-231, MCF-7 and BT474 human breast cancer cells. Breast cancer cell lines were transfected with plasmids containing APP coding sequences (pEGFP-n1-APP) and APP short hairpin RNA (pENTR APP shRNA). APP overexpression efficiency, knockout efficiency and the expression levels of related genes were tested using reverse transcription-quantitative PCR (RT-qPCR) and western blot analyses. The effects of APP and mitogen-activated protein kinase kinase (MEK) inhibitor on cell migration and invasion were examined using Transwell assays. The results demonstrated that APP was significantly upregulated in the pEGFP-n1-APP group (P<0.05), and significantly downregulated in the pENTR APP shRNA group (P<0.05), compared with the control group. APP overexpression increased the migratory and invasive ability of human breast cancer cells (P<0.05), whereas APP silencing significantly inhibited cell migration and invasion (P<0.05). RT-qPCR and western blot analysis results suggested that APP overexpression significantly increased the expression of MMP-9, MMP-2, MMP-3, N-cadherin and vimentin (P<0.05). In addition, the enhanced expression of APP markedly affected the phosphorylation of mitogen-activated protein kinase kinase kinase 11 (MLK3), mitogen-activated protein kinase kinase 4 (MEK4) and mitogen-activated protein kinase 10 (JNK3; P<0.05). Additionally, APP overexpression had no effect on the total expression levels of MLK3, MEK4, and JNK3; however, APP overexpression significantly decreased the expression levels of E-cadherin and cytokeratin (P<0.05). Conversely, APP silencing had the opposite effects. When cells were treated with the MEK inhibitor PD0325901, the expression of APP was not altered, nor was the expression levels of MEK and its upstream signaling molecules. Taken together, the present findings suggested that APP could affect the migration and invasion of human breast cancer cells by mediating the activation of the MAPK signaling pathway, thereby promoting the EMT process.