Inhibitory effects of curcumin on gastric cancer cells: a proteomic study of molecular targets.

ABSTRACT

Curcumin, a natural anticancer agent, has been shown to inhibit cell growth in a number of tumor cell lines and animal models. We examined the inhibition of curcumin on cell viability and its induction of apoptosis using different gastric cancer cell lines (BGC-823, MKN-45 and SCG-7901). 3-(4,5-dimethyl-thiazol-2-yl)-2-5-diphenyltetrazolium-bromide (MTT) assay showed that curcumin inhibited cell growth in a dose- (1, 5, 10 and 30 µM) and time- (24, 48, 72 and 96 h) dependent manner; analysis of Annexin V binding showed that curcumin induced apoptosis at the dose of 10 and 30 µM when the cells were treated for 24 and 48 h. As cancers are caused by dysregulation of various proteins, we investigated target proteins associated with curcumin by two-dimensional gel electrophoresis (2-DE) and MALDI-TOF-TOF mass spectrometer. BGC-823 cells were treated with 30 µM curcumin for 24 h and total protein was extracted for the 2-DE. In the first dimension of the 2-DE, protein samples (800 µg) were applied to immobilized pH gradient (IPG) strips (24 cm, pH 3-10, NL) and the isoelectric focusing (IEF) was performed using a step-wise voltage ramp; the second dimension was performed using 12.5% SDS-PAGE gel at 1 W constant power per gel. In total, 75 proteins showed significant changes over 1.5-fold in curcumin-treated cells compared to control cells (Student's t-test, p<0.05). Among them, 33 proteins were upregulated and 42 proteins downregulated by curcumin as determined by spot densitometry. 52 proteins with significant mascot scores were identified and implicated in cancer development and progression. Their biological function included cell proliferation, cycle and apoptosis (20%), metabolism (16%), nucleic acid processing (15%), cytoskeleton organization and movement (11%), signal transduction (11%), protein folding, proteolysis and translation (20%), and immune response (2%). Furthermore, protein-protein interacting analysis demonstrated the interaction networks affected by curcumin in gastric cancer cells. These data provide some clues for explaining the anticancer mechanisms of curcumin and explore more potent molecular targets of the drug expected to be helpful for the development of new drugs.