Quantitative Proteomics Identify the Possible Tumor Suppressive Role of Protease-Activated Receptor-4 in Esophageal Squamous Cell Carcinoma Cells

Exposure to carcinogens of tobacco smoke may result in methylation of protease-activated receptors-4 (PAR4) gene and further induces the loss of PAR4 expression, which is considered to be involved in carcinogenesis of esophageal squamous cell carcinoma (ESCC). Here we employed a TMT-based quantitative proteomic approach to identify PAR4-regulated changes of proteomic profiles in ESCC cells and to identify potentially therapeutic value. A total of 33 proteins were found significantly changed with 15 up-regulated and 18 down-regulated in PAR4-activating peptide (PAR4-AP) treated ESCC cells compared with controls. Bioinformatics analysis showed that key higher expressed proteins included those associated with apoptosis and tumor suppressor (e.g. CASP9), and lower expressed proteins included those associated with anti-apoptosis, autophagy and promoting cell proliferation (e.g. CHMP1B, PURA, PARG and HIST1H2AH). Western blot verified changes in five representative proteins including CASP9, CHMP1B, PURA, PARG and HIST1H2AH. Immunohistochemistry analysis showed that CHMP1B, PURA, PARG and HIST1H2AH expression in ESCC tissues were significantly higher than those in adjacent nontumorous tissues. Our findings will be helpful in further investigations into the functions and molecular mechanisms of PAR4 in ESCC.