Analysis of 25-hydroxyvitamin D3–1alpha-hydroxylase in normal and malignant breast tissue

Abstract

806 Background: The presence of extrarenal 25-hydroxyvitamin D3 [25(OH)D3]-1alpha-hydroxylase (1a-OHase) has been reported in several malignant cell types. Additionally, alterations in the local production of 1alpha,25-dihydroxyvitamin D [1a,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 express 1a-OHase and to evaluate whether breast tissue possesses the capacity to produce 1a,25(OH)2D3 from 25(OH)D3. 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 and conventional PCR analysis. Results: We detected mRNA for 1a-OHase in normal breast tissue and breast cancer tissue as well as in MCF-7 breast cancer cell line. mRNA for 1a-OHase was increased in breast cancer cells as compared to normal tissue. In MCF-7 cells 1a,25(OH)2D3 inhibited cell proliferation in a dose-dependent manner. Incubation of MCF-7 cells with [3H]-25(OH)D3 resulted in conversion to [3H]-1,25(OH)2D3. 1a-OHase activity in MCF-7 cells was blocked by a specific cytochrome P450 inhibitor, clotrimazole. Conclusion: Our data suggest that normal and breast cancer tissues express 1a-OHase mRNA and therefore, may have the ability to synthesize 1a,25(OH)2D3. The local production of 1a,25(OH)2D3 in normal and cancerous breast tissue may play an important role in regulating proliferation and differentiation of breast cells. We hypothesize that alterations in the local production of 1a,25(OH)2D3 may be involved in the tumorigenesis of breast cancer. Thus, breast cancer may be a target for treatment with precursors of biologically active vitamin D analogues. No significant financial relationships to disclose.