Human CYP24 Catalyzing the Inactivation of Calcitriol Is Post-Transcriptionally Regulated by miR-125b

Human vitamin D 3 hydroxylase (CYP24) catalyzes the inactivation of 1α,25-dihydroxyvitamin D 3 (calcitriol), which exerts antiproliferative effects. CYP24 has been reported to be overexpressed in various cancers in which microRNA levels are dysregulated. In silico analysis identified a potential miR-125b recognition element (MRE125b) in the 3′-untranslated region of human CYP24 mRNA. We investigated whether CYP24 is regulated by miR-125b. In luciferase assays using a reporter plasmid containing MRE125b, transfection of the antisense oligonucleotide (AsO) for miR-125b increased the reporter activity in KGN cells, and transfection of precursor miR-125b decreased the reporter activity in MCF-7 cells. The endogenous CYP24 protein level was also increased by AsO for miR-125b in KGN cells and was decreased by precursor miR-125b in MCF-7 cells. These results suggested that human CYP24 is regulated by miR-125b. Immunohistochemical analysis revealed that the CYP24 protein levels in human breast cancer were higher than in adjacent normal tissues, without an accompanying CYP24 mRNA increase. On the other hand, the expression levels of miR-125b in cancer tissues were significantly ( P