Vitamin D-24-hydroxylase in benign and malignant breast tissue and cell lines.

Tissue-specific expression of 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-OHase) and vitamin D-hydroxylase (24-OHase) may act as the pivotal link between 25-hydroxyvitamin D3 (25(OH)D3) serum levels and the anticancer effects of 1,25-dihydoxyvitamin D3 (1,25(OH)2D3) and alternative splicing of the enzymes may regulate their biological function. The expression of 24-OHase in cells and breast tissue was investigated and its splice variants were detected. The expression of 24-OHase RNA and protein was assessed by RT-PCR followed by Western blot. The expression of 24-OHase was reduced by about 57% in MCF-7 breast cancer cells, compared to MCF-10F benign breast cells. In the Western blot, a signal at 56 kDa was found and further bands were detected at 42 and 44 kDa. In the breast cancer tissue, the expression of 24-OHase was reduced by about 58% compared to benign tissue. However, in the Western blot, only one signal was found in the benign tissue at 56 kDa, while in malignant tissue, a further band was detected at 40 kDa. Alternative splicing of 24-OHase may lead to a catalytically dysfunctional enzyme and may lead to less reduction of the target protein.