Up-regulation of NGEF by ERK/AP1 signaling pathway in BRAFV600E-mutant thyroid cancer promotes cancer metastasis

Abstract

Background The BRAFV600E mutation is the most frequent genetic mutation in thyroid tumors, and is therefore a key therapeutic target. However, intrinsic feedback mechanisms impact the clinical use of BRAFV600E-specific inhibitors. Further investigations into the specific roles and molecular mechanisms underlying BRAFV600E in thyroid cancer progression are required.Methods In the present study, Gene Expression Omnibus and The Cancer Genome Atlas datasets were used to identify NGEF (Neuronal Guanine Nucleotide Exchange Factor ) gene expression patterns and the corresponding clinical relevance. NGEF expression levels were determined in tissues and cells using reverse transcription-quantitative (RT-q) PCR, western blotting and immunohistochemical analyses. Moreover, potential associations between the BRAFV600E mutation and NGEF were verified using bioinformatics, RT-qPCR and western blot analysis. In vitro experiments were conducted to investigate the cytological role of NGEF. Results of the present study demonstrated that the transcription factor AP-1 (c-fos/c-jun) was upstream of NGEF by the bioinformatics, qRT-PCR, WB, and dual luciferase reporter assays.Results NGEF mRNA and protein expression levels were significantly elevated in thyroid malignant specimens, compared with adjacent non-tumor tissues. In addition, increased NGEF expression was associated with TNM stage in patients with thyroid cancer. Results of the present study also demonstrated that NGEF expression was significantly enhanced in BRAFV600E-mutant thyroid cancer, and NGEF knockdown in BRAFV600E-mutant thyroid cancer cells inhibited migration and invasion, through impacting epithelial-mesenchymal transition. On the other hand, the reverse effects were observed following NGEF overexpression. Results of the present study further demonstrated that the BRAFV600E-mediated MAPK/ERK cascade upregulated NGEF expression, and NGEF was subsequently identified as a target of AP-1.Conclusions NGEF is expressed by the ERK/AP-1 pathway in BRAFV600E-mutant thyroid cancer, and is associated with tumor metastasis. These results indicated that NGEF may exhibit potential as a therapeutic target in BRAFV600E-mutant thyroid cancer.