Background: The presence of extra-renal 25-hydroxyvitamin D3 [25(OH)D3]-1alpha-hydroxylase (1alpha-OHase) has been reported in several cell types including prostate and colon cancer cells. Additionally, alterations in the local production of 1alpha,25-dihydroxyvitamin D [1alpha,25(OH)2D3] have been implicated in the tumorigenesis of these malignancies. The aim of this study was to analyze whether normal breast tissue or breast cancer cells expressed 1alpha-OHase and to evaluate whether breast tissue possessed the capacity to produce 1alpha,25(OH)2D3 from 25(OH)D3.
Materials and methods: Total RNA was extracted from normal breast tissue (n = 11), breast carcinomas (n = 12) and cultured MCF-7 breast cancer cells for real-time (LightCycler using specific hybridization probes) and conventional PCR analysis.
Results: mRNA for 1alpha-OHase was detected in breast cancer tissue and in MCF-7 breast cancer cells. Interestingly, the mRNA levels for 1alpha-OHase were significantly increased in breast cancer compared to normal breast tissue. When the MCF-7 cells were treated with 1alpha,25(OH)2D3, cell proliferation was inhibited in a dose-dependent manner. Incubation of the MCF-7 cells with [3H]-25(OH)D3 resulted in its conversion to [3H]-1,25(OH)2D3. The 1alpha-OHase activity in the MCF-7 cells was blocked by a specific cytochrome P450 inhibitor, clotrimazole.
Conclusion: The data suggest that at least breast cancer cells expressed 1alpha-OHase mRNA and, therefore, might have the ability to synthesize 1alpha,25(OH)2D3 within the cells. The local production of 1alpha,25(OH)2D3 might play an important role in regulating the proliferation and differentiation of breast cells. We hypothesize that alterations in the local production of 1alpha,25(OH)2D3 may be involved in the tumorigenesis of breast cancer. Additionally, breast cancer may be a target for treatment with precursors of biologically-active vitamin D analogs.