Platelet-activating factor receptor-mediated PI3K/AKT activation contributes to the malignant development of esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide and occurs at a relatively high frequency in China, yet the mechanisms underlying its devastating outcome remain unclear. Here we report that platelet-activating factor receptor (PAFR), a type of G-protein-coupled receptor, was upregulated in ESCC tumors and cell lines, compared with controls; PAFR levels were positively correlated with ESCC clinical stages and survival time. Overexpression of PAFR promoted the malignant development of ESCC in vitro and in vivo, whereas depletion of PAFR suppressed these effects. Interestingly, PAFR was observed to activate PI3K/AKT (phosphatidylinositol 3-kinase/AKT) through the upregulation of FAK kinase activity. AKT-triggered nuclear factor-kappa B transcriptionally activated PAFR expression. This mutual positive regulation between PAFR and AKT was required for the aggressiveness of ESCC cells both in vitro and in vivo. Furthermore, treating mice bearing ESCC tumors with cholesterolconjugated PAFR small interfering RNA effectively inhibited tumor progression and the expression of AKT-mediated oncogenic proteins. Taken together, we made the first demonstration that dysregulation of PAFR and the positive regulatory loop between PAFR and pAKT contribute to malignant progression of ESCC.