Identification of differential proteins in colorectal cancer cells treated with caffeic acid phenethyl ester

AIM: To investigate the molecular mechanisms of the anti-cancer activity of caffeic acid phenethyl ester(CAPE).METHODS: Protein profiles of human colorectal cancer SW480 cells treated with or without CAPE were analysed using a two-dimensional(2D) electrophoresis gelbased proteomics approach. After electrophoresis, the gels were stained with Coomassie brilliant blue R-250. Digital images were taken with a GS-800 Calibrated Densitometer, and image analysis was performed using PDQuest 2-D Analysis software. The altered proteins following CAPE treatment were further identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry following a database search. The identified proteins were validated by Western blot and immunofluorescence assay.RESULTS: CAPE induced human colorectal cancer cell apoptosis. Four up-regulated proteins and seven down-regulated proteins in colorectal cancer cells treated with CAPE were found. The identified downregulated proteins in CAPE-treated colorectal cancer cells were Triosephosphate Isomerase(Tim), Proteasome subunit alpha 4(PSMA4) protein, Guanine nucleotide binding protein beta, Phosphoserine aminotransferase 1(PSAT1), PSMA1, Myosin XVIIIB and Tryptophanyl-tRNA synthetase. Notably, CAPE treatment led to the down-regulation of PSAT1 and PSMA1, two proteins that have been implicated in tumorigenesis. The identified up-regulated proteins were Annexin A4, glyceraldehyde-3-phosphate dehydrogenase, Glucosamine-6-phosphate deaminase 1(GNPDA1), and Glutathione peroxidase(GPX-1). Based on high match scores and potential role in cell growth control, PSMA1, PSAT1, GNPDA1 and GPX-1 were further validated by Western blotting and immunofluorescence assay. PSMA1 and PSAT1 were down-regulated, while GNPDA1 and GPX-1 were up-regulated in CAPE-treated colorectal cancer cells. CONCLUSION: These differentiated proteins in colorectal cancer cells following CAPE treatment, may be potential molecular targets of CAPE and involved in the anti-cancer effect of CAPE.