Expression of prostaglandin metabolizing enzymes in correlation with vitamin D receptor in benign and malignant breast cell lines and breast tissue and regulation of prostaglandin metabolism by calcitriol.

Abstract

Abstract Abstract #6028 Backround: The antiproliferative effects of calcitriol [1,25(OH)2D3] make the biologically active form of vitamin D to a promising target in breast cancer therapy. It is well known, that these effects are mediated via the vitamin D3 receptor (VDR). Furthermore breast cancer is associated with inflammatory processes based on an upregulation of cyclooxygenase-2 (COX-2) expression, the prostaglandin E2 (PGE2) synthesizing enzyme. The PGE2 metabolizing enzyme, 15 hydroxyprostaglandin dehydrogenase (15 PGDH) is described as a tumor suppressor in cancer. First references suggest a correlation between vitamin D and prostaglandin metabolism through the impact of 1,25(OH)2D3 on the expression of COX-2 and 15 PGDH. Thus we evaluated the expression of COX-2 and 15 PGDH with VDR and the influence of calcitriol on COX-2 and 15 PGDH.
 Materials and methods: The Expression of VDR, COX-2 and 15 PGDH in MCF10F, a human benign epithelial cell line and the breast cancer cell line MCF-7 was determined by real time PCR and western blot analysis. Furthermore, we determined mRNA level of COX-2 and 15 PGDH and VDR in healthy and malignant breast sample tissues. In addition we examined the effect of calcitriol on COX-2 and 15 PGDH mRNA levels.
 Results: Although our data from real time pCR were divergent from those obtained from the western blot analysis, we showed, that COX-2 protein expression is increased in MCF-7 2-fold compared to MCF10F. These data were confirmed in breast cancer tissue samples, where COX-2 mRNA level increased to 1,44 in comparison to healthy tissues. No correlation of 15 PGDH was detected in both cell lines, but in malignant tissues 15 PGDH expression increase dramatically compared to healthy tissue samples. The expression of VDR we found differs in protein and mRNA level in benign and malign cell lines. VDR protein levels were inverse correlated to 15 PGDH expression and reveal that the benign tissue as well as the MCF10F cells have the highest VDR expression. Furthermore we demonstrated a downregulation of cyclooxygenase and an up-regulation of 15 PGDH by calcitriol.
 Conclusion: We found a basically inverse correlation between VDR and 15 PGDH protein level expression. These findings suggest a possible link between VDR, associated target genes and the prostaglandin metabolism. The influence of calcitriol on COX-2 and 15 PGDH might lead to an additional novel pathway of calcitriol action mediating its antiproliferative effects in breast cancer and might open new therapeutic approaches in breast cancer therapy. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6028.