Expression of RAP1B is associated with poor prognosis and promotes an aggressive phenotype in gastric cancer.

Metastasis is the major cause of death among gastric cancer (GC) patients, and altered expression of Ras-related protein RAP1B is associated with cancer development. The present study assessed RAP1B expression ex vivo and the effect of hypoxia‑induced RAP1B overexpression on the promotion of the metastatic potential of GC cells in vitro. Immunohistochemistry was used to detect the expression of RAP1B and hypoxia‑inducible factor-1α (HIF-1α) in 178 GC tissue specimens. GC cell lines were used to assess the effects of hypoxia and RAP1B knockdown with RAP1B small interfering RNA (siRNA). Tumor cell viability was detected by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, invasion capacity was evaluated by a Transwell assay, and gene expression was determined by qRT-PCR and western blotting. The data showed that expression levels of RAP1B and HIF-1α proteins were high in the GC tissue specimens, and RAP1B expression was significantly associated with tumor-node-metastasis (TNM) stage and tumor size, while HIF-1α expression was significantly associated with TNM stage, Borrmann type and tumor differentiation. Moreover, RAP1B expression was associated with HIF-1α expression (r=0.547, P<0.001). The expression of RAP1B and HIF-1α proteins was associated with a shorter overall survival of patients according to the univariate analysis (log-rank test, P<0.01), and RAP1B expression and TNM stage were independent prognostic predictors in patients using a multivariate analysis (P<0.001). In vitro, hypoxia induced the invasion of GC cells and the expression of RAP1B and HIF-1α (P<0.05); whereas knockdown of RAP1B expression using siRNA inhibited the tumor cell invasion capacity even under hypoxic culture conditions (P<0.05). In conclusion, the protein expression of RAP1B and HIF-1α contributed to GC malignant behavior and poor prognosis. Future studies will evaluate whether targeting RAP1B expression can be used as a novel strategy to control GC or as a biomarker for prognosis prediction.