title: Increased copy-number and not DNA hypomethylation causes overexpression of the candidate proto-oncogene CYP24A1 in colorectal cancer.
abstract: In colorectal cancer (CRC) the vitamin D catabolizing enzyme 1,25-dihydroxyvitamin D 24-hydroxylase (CYP24A1) is overexpressed with a potentially significant, positive impact on the catabolism of 1,25-dihydroxyvitamin D3 (1,25-D3 ). However, the underlying mechanism of CYP24A1 overexpression is poorly understood. In the present study, we investigated possible causes including hypomethylation of the CYP24A1 promoter, amplification of the CYP24A1 gene locus (20q13.2), and altered expression of CYP24A1-specific transcription factors. We quantified CYP24A1 gene copy-number, performed bisulfite sequencing of the CYP24A1 promoter to assess DNA methylation, and measured mRNA expression of CYP24A1, 25-hydroxyvitamin D 1α-hydroxylase (CYP27B1), vitamin D receptor (VDR) and retinoid X receptor (RXR). We found that 77 (60%) out of 127 colorectal tumors showed increased CYP24A1 gene copy-number and that more than 6 copies of CYP24A1 correlated positively with CYP24A1 mRNA expression suggestive of a causal relationship. No differences in CYP24A1 promoter methylation were found between tumor tissue and adjacent mucosa from the same patient or between tissues with high or low mRNA expression, thus excluding DNA hypomethylation as a possible cause of CYP24A1 overexpression in CRC. Furthermore, mRNA expression of several factors involved in replication licensing positively correlated with CYP24A1 mRNA expression, raising the possibility that CYP24A1 overexpression might favor increased proliferation in tumors by suppressing local 1,25-D3 levels. We conclude that high copy-number gain is a key determinant of CYP24A1 overexpression in CRC. Other postulated causes of CYP24A1 overexpression including promoter hypomethylation and enhanced VDR and/or RXR expression do not appear to be involved.
authors: Department of Pathophysiology, Medical University of Vienna, Vienna, 1090, Austria.
authors: Julia
authors: J
authors: Höbaus
authors: Doris M
authors: DM
authors: Hummel
authors: Ursula
authors: U
authors: Thiem
authors: Irfete S
authors: IS
authors: Fetahu
authors: Abhishek
authors: A
authors: Aggarwal
authors: Leonhard
authors: L
authors: Müllauer
authors: Gerwin
authors: G
authors: Heller
authors: Gerda
authors: G
authors: Egger
authors: Ildiko
authors: I
authors: Mesteri
authors: Sabina
authors: S
authors: Baumgartner-Parzer
authors: Enikö
authors: E
authors: Kallay
mesh_terms: D000328:Adult; D000368:Aged; D002112:Calcifediol / Q000378:metabolism; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D005260:Female; D018628:Gene Dosage; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D008875:Middle Aged; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000032:analysis; D013250:Steroid Hydroxylases / Q000235:genetics*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D002112:Calcifediol
keywords: 20q13.2; CYP24A1; colorectal cancer; methylation; proliferation