COPB2 promotes cell proliferation and tumorigenesis through up-regulating YAP1 expression in lung adenocarcinoma cells

Lung adenocarcinoma is the most common subtype of non-small cell lung cancer and responsible for more than 500,000 deaths per year worldwide. In this study, we aimed to explore the effects of COPB2 in the progression of lung adenocarcinoma and its underlying mechanism. The mRNA and protein levels of COPB2 in tumor tissues and cell lines were determined by qRT-PCR and western blotting analysis. siRNAs and over-expressed vector targeting COPB2 were used to down-regulate and up-regulate COPB2 expression in lung adenocarcinoma cell lines H1975. Cell apoptosis rate, proliferation and tumorigenesis of H1975 cells were determined by flow cytometry analysis, MTT assay and in vivo xenotransplantation assay, respectively. Western blotting and immunofluorescence assays were performed to evaluate the effects of COPB on the expression and subcellular location of YAP. Results showed COPB2 was significantly up-regulated in lung adenocarcinoma tissues and cell lines, which showed a close correlation with advanced clinical symptoms, such as tumor differentiation, TNM stage and the occurrence of lymph node metastasis and distance metastasis. Besides, the overall survival time of patients with high expression of COPB2 was shorter than that of patients with low COPB2 expression. After knockdown of COPB2, cell apoptosis rate was increased, whereas cell proliferation was decreased. Compared with that in the normal lung cell line H1688 cells, YAP1 expression was obviously increased in H1975, and overexpression of COPB2 translocated YAP1 from cytoplasm to nuclear, whereas knockdown of COPB2 showed the opposite effect. Overexpression of COPB2 enhanced cell proliferation, tumorigenesis and inhibited cell apoptosis. However, these effects were abolished when down-regulated YAP1 expression on the base of COPB2 overexpression. In conclusion, the increased expression of COPB2 was significantly correlated with the progression of lung adenocarcinoma. Up-regulation of COPB2 inhibited cell apoptosis and promoted cell growth and tumorigenesis through up-regulating YAP1 expression in lung adenocarcinoma.