Overexpression of Dickkopf-3 induces apoptosis through mitochondrial pathway in human colon cancer

AIM：To investigate the mechanisms of the biological roles of Dickkopf-3（Dkk-3） in cell invasion,survival and apoptosis in colon cancer cells.METHODS：Three human colon cancer cell lines,i.e.,HT-29,LoVo and SW480,were used.Overexpression of Dkk-3 induced by pEGFP-N1-Dkk-3-GFP plasmid in LoVo cells was performed using Lipofectamine 2000 reagent.Reverse transcription polymerase chain reaction and Western blotting were performed to determine the mRNA and protein expression levels of Dkk-3,respectively.Cell proliferation assay,cell cycle analysis,hoechst 33258 assay and Matrigel invasion assay were performed on Dkk-3 overexpressing transfectants.RESULTS：The mRNA and protein expressions of Dkk-3 in HT-29（mRNA：0.06 ± 0.02,protein：0.06 ± 0.01） and LoVo（mRNA：0.07 ± 0.02,protein：0.07 ± 0.02） cells were significantly lower than that in SW480 cells（mRNA：0.92 ± 0.04,protein：0.69 ± 0.13;all P 0.05）,and the greatest levels of invasiveness wasin LoVo cells.Dkk-3 overexpression inhibited the proliferation and invasion of LoVo cells and induced cell cycle arrest at G0/G1 phase and subsequent apoptosis,as indicated by increased chromatin condensation and fragments,upregulated Bax and cytochrome c protein,downregulated survivin and Bcl-2 protein,and the activation of caspase-3 and caspase-9.Furthermore,Dkk-3 overexpression reduced the accumulation of cytosolic fraction of β-catenin.CONCLUSION：Dkk-3 overexpression induced apoptosis in human colon cancer possibly through the mitochondrial pathway.Dkk-3 may be involved in the Wnt/β-catenin signaling pathways in colon cancer.