CXCR6 predicts poor prognosis in gastric cancer and promotes tumor metastasis through epithelial-mesenchymal transition

Chemokines and their receptors have been confirmed to be involved in several types of cancer. However, little is known concerning the role of CXCL16 and its receptor CXCR6 in gastric cancer (GC) progression and metastasis. In the present study, expression of CXCL16 and CXCR6 in GC tumor and peritumoral tissues was detected by immunohistochemistry (IHC) in a cohort of 352 GC patients who underwent gastrectomy, and the correlation between CXCL16/CXCR6 expression and clinicopathological characteristics was further analyzed. To evaluate the function of CXCR6, we overexpressed and knocked down CXCR6 in GC cell lines. Results showed that expression of CXCR6, but not CXCL16, was significantly upregulated in GC tumor tissues, and was significantly correlated with lymph node and distant metastases, and advanced clinical stage in the GC patients. Survival analysis showed that large tumor size (>5 cm), elevated preoperative serum carcinoembryonic antigen (CEA) level, advanced TNM stage and high CXCR6 expression indicated worse overall survival (OS) and disease-free survival (DFS) in GC, and CXCR6 was an independent predictor for both OS and DFS in GC. In vitro experiments showed that CXCR6 overexpression induced cell migration and invasion ability, and promoted epithelial-mesenchymal transition of GC cells by upregulation of mesenchymal markers and inhibition of epithelial markers. In contrast, knockdown of CXCR6 in GC cells resulted in inhibition of cell proliferation, migration and invasion ability, and reversal of epithelial-mesenchymal transition (EMT) phenomenon. Our results demonstrated that CXCR6 is an independent prognostic factor for poor survival in GC patients, and may promote GC metastasis through EMT.