Abstract 4944: Regulation of vitamin D 24-hydroxylase gene expression in human prostate cancer by epigenetic mechanisms

Abstract

Abstract 1,25-dihydroxycholecalciferol (calcitriol), the active form of vitamin D3, plays a major role in regulating calcium homeostasis and bone mineralization. Calcitriol also modulates cellular proliferation and differentiation in a variety of cell types. Furthermore, calcitriol has an anti-tumor effect in several tumor models. 1,25-(OH)2D-hydroxylase (24-hydroxylase), encoded by the CYP24A1 gene, plays a key role in attenuation of calcitriol effects by degrading calcitriol to a much less active vitamin D metabolite. CYP24A1 is dysregulated in wide range of tumors. The over-expression of CYP24A1 is associated with poor prognosis of some human cancers. Interestingly, CYP24A1 is down-regulated in human prostate cancer. Little is known about the mechanism(s) underlying the regulation of CYP24A1 expression in human prostate cancer. We have analyzed 3 prostate cancer cell lines (LNCaP, DU-145 and PC3) which express variable levels of CYP24A1. We have found that CYP24A1 gene expression is inversely correlated with promoter DNA methylation in human prostate cell lines. Treatment with the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine (DAC), activates CYP24A1 gene expression in prostate cancer cells. In vitro methylation of the CYP24A1 promoter by methylases SssI, HpaII and HhaI represses its promoter activity. Furthermore, inhibition of histone deacetylases by trichostatin A (TSA) enhances the expression of CYP24A1 in prostate cancer cells. ChIP-qPCR reveals that histone modifications are associated with the CYP24A1 promoter region. Treatment with TSA increases acetylated H3K9 and dimethylated H3K4 and simultaneously decreases dimethylated H3K9 at the CYP24A1 promoter. ChIP-qPCR assay also shows that treatment of prostate cancer cells with DAC and TSA increases the recruitment of VDR to the CYP24A1 promoter. We have also collected paired samples of benign and malignant tissue from 30 human prostatectomy samples. RT-PCR analysis of paired human prostate samples reveals that CYP24A1 expression is down-regulated in prostate malignant lesions compared to matched benign lesions (p<0.001). Bisulfite DNA pyrosequencing reveals that CYP24A1 gene is hypermethylated in malignant lesions compared to matched benign lesions. Taken together, these data indicate that the repression of CYP24A1 gene expression in human prostate cancer cells is mediated in part by promoter DNA methylation and repressive histone modifications. Epigenetic repression of CYP24A1 may involve blocked recruitment of VDR to CYP24A1 regulatory regions, and nucleation of repressive chromatin structures at the CYP24A1 promoter. This study was supported by NIH/NCI grants CA067267, CA095045 and CA085142. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4944.