Extensive methylation of CpG island of CYP24 gene in osteoblastic ROS17/2.8 cells.

CYP24 is a target gene of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and is induced in the cells expressing vitamin D receptor (VDR) in response to 1,25-(OH)2D3. The osteoblastic ROS17/2.8 cells abundantly express VDR and have been used for the promoter analysis of many of vitamin D3 target genes. However, unlike other cells, ROS cells did not induce CYP24 expression upon 1,25-(OH)2D3 treatment. It has been reported that the methylation of CpG islands of a promoter region is involved in gene silencing. Methylation analysis of the CYP24 gene revealed that the CpG island in 5' part of the transcription unit is extensively methylated. This result suggests that unresponsiveness of the CYP24 gene to 1,25-(OH)2D3 would result from the methylation of the promoter region.