Abstract: Objective To explore the inhibitory effect and mechanism of 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃]on β-catenin transcriptional activity in human colon cancer cells. Methods Colon cancer cell line SW480 was treated with either 1,25(OH)₂D₃ (100 nmol/L) or vehicle (control) for 48 hours, then several parameters were measured: the transcriptional activity of β-catenin by Dual-Luciferase? Reporter Assay System; the nuclear protein expression level of β-catenin by Western blot; mRNA coding for β-catenin and forkhead box M1 (FOXM1) and the protein expression by RT-qPCR and Western blot. SW480 cells were subjected to transfecting siRNA to knock down FOXM1, followed by 1,25(OH)₂D₃ treatment and measurement of the transcriptional activity of β-catenin by Dual-Luciferase? Reporter Assay System. Results 1) 1,25(OH)₂D₃ significantly repressed the transcriptional activity of β-catenin in SW480 cells (P＜0.05), while did not affect its mRNA and protein expression; 2)1,25(OH)₂D₃ increased the protein expression of FOXM1(P＜0.05); 3)The inhibitory effect of the transcriptional activity of β-catenin by 1,25(OH)₂D₃ in SW480 cells was decreased when FOXM1 was knocked down(P＜0.05). Conclusions 1,25(OH)₂D₃ represses the transcriptional activity of β-catenin via increasing FOXM1 expression.

Key words: 1,25(OH)₂D₃, colon cancer, β-catenin, FOXM1