title: Epigenetic regulation of the 1,25-dihydroxyvitamin D3 24-hydroxylase (CYP24A1) in colon cancer cells.
abstract: Calcitriol is the hormonally active form of vitamin D and has anti-proliferative and pro-apoptotic effects. Calcitriol and its precursor calcidiol (25(OH)D3) are degraded by the 1,25-dihydroxyvitamin D3 24-hydroxylase (CYP24A1). This enzyme is overexpressed in colorectal tumors, however, the mechanisms of this overexpression remain to be elucidated. CYP24A1 mRNA level differs among colorectal cancer cell lines and range from almost undetectable to high. Since DNA methylation and histone acetylation regulate CYP24A1 gene expression in prostate cancer cell lines, we investigated whether epigenetic mechanisms could explain the differences in basal expression of CYP24A1 in colon cancer cells. Methyltransferase inhibitor 5-aza-2'-deoxycytidine (DAC) treatment resulted in an over 50-fold induction of CYP24A1 mRNA expression in Coga1A and HT-29 cells but in no response in Caco2/AQ and Coga13 cells. This finding is supported by a strong increase in CYP24A1 activity after DAC treatment in Coga1A (35%). In addition, calcitriol and DAC had synergistic effects on CYP24A1 gene transcription. Interestingly, the CYP24A1 promoter was not methylated in Coga1A and HT-29 (<5%), while in Caco2/AQ it was 62% methylated. This suggests that DNA demethylation must activate genes upstream of CYP24A1 rather than act on the gene itself. However, transcriptional regulators of CYP24A1 such as vitamin D receptor (VDR), retinoid X receptor (RXR), specificity protein 1 (SP1), or mediator complex subunit 1 (MED1) were not upregulated. We conclude that in colon cancer cells, CYP24A1 gene expression is inducible by methyltransferase and some histone deacetylase inhibitors in a cell line-dependent manner. This effect does not correlate with the methylation state of the promoter and therefore must affect genes upstream of CYP24A1. This article is part of a Special Issue 'Vitamin D Workshop'.
authors.affiliation: Department of Pathophysiology and Allergy Research, Medical University of Vienna, Austria. julia.hoebaus@meduniwien.ac.at
authors.forename: Julia
authors.initials: J
authors.lastname: Höbaus
authors.forename: Irfete Sh
authors.initials: ISh
authors.lastname: Fetahu
authors.forename: Maya
authors.initials: M
authors.lastname: Khorchide
authors.forename: Teresa
authors.initials: T
authors.lastname: Manhardt
authors.forename: Enikö
authors.initials: E
authors.lastname: Kallay
mesh_terms: D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000201:enzymology* / Q000235:genetics*; D019175:DNA Methylation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors; D000077209:Decitabine; D044127:Epigenesis, Genetic / Q000187:drug effects / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D019073:HT29 Cells; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D056572:Histone Deacetylase Inhibitors; D000077209:Decitabine; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D015254:DNA Modification Methylases; D001374:Azacitidine