Upregulation of 25-hydroxyvitamin D(3)-1(alpha)-hydroxylase by butyrate in Caco-2 cells

To investigate the possible involvement of 25-hydroxyvitamin D(3)-1(alpha)-hydroxylase [1alpha-25(OH) (2) D(3)] in butyrate-induced differentiation in human intestinal cell line Caco-2 cells.

Caco-2 cells were incubated either with 3 mmol/L butyrate and 1 micromol/L 25(OH) (2) D(3) or with 1 micromol/L 1alpha-25(OH) (2) D(3) for various time intervals ranging from 0 to 72 h. Additionally, cells were co-incubated with butyrate and either 25(OH) (2) D(3) or 1alpha-25(OH) (2) D(3). 1alpha-25(OH) (2) D(3) mRNA was determined semi-quantitatively using the fluorescent dye PicoGreen. Immunoblotting was used for the detection of 1alpha-25(OH) (2) D(3) protein. Finally, enzymatic activity was measured by ELISA.

Both butyrate and 1alpha-25(OH) (2) D(3) stimulated differentiation of Caco-2 cells after a 48 h incubation period, while 25(OH) (2) D(3) had no impact on cell differentiation. Synergistic effects on differentiation were observed when cells were co-incubated with butyrate and vitamin D metabolite. Butyrate transiently upregulated 1alpha-25(OH) (2) D(3) mRNA followed by a timely delayed protein upregulation. Coincidently, enzymatic activity was enhanced significantly. The induction of the enzyme allowed for comparable differentiating effects of both vitamin D metabolites.

Our experimental data provide a further mechanism for the involvement of the vitamin D signaling pathway in colonic epithelial cell differentiation by butyrate. The enhancement of 1alpha-25(OH) (2) D(3) followed by antiproliferative effects of the vitamin D prohormone in the Caco-2 cell line suggest that 25(OH) (2) D(3) in combination with butyrate may offer a new therapeutic approach for the treatment of colon cancer.