Epigenetic and transcriptional dysregulation of VWA2 associated with a MYC-driven oncogenic program in colorectal cancer

Abstract

VWA2 encodes AMACO, a secreted protein up-regulated in most colorectal carcinomas (CRC), constituting a promising biomarker. The mechanism responsible for its aberrant up-regulation has not been previously described. In this work, we analyzed VWA2 DNA methylation in over 400 primary CRCs. No epigenetic alterations were found in its promoter-associated CpG island. However, the region located downstream of the transcriptional start site was hypomethylated in most CRCs. ChIP-Seq revealed increased levels of the active mark H3K4me3 and reduction of the repressive mark H3K27me3. In contrast, several CRC cell lines exhibited hypermethylation of VWA2. 5-AZA-2-deoxycitidine treatment led to transcriptional activation of VWA2, supporting a functional link between DNA methylation and transcription. VWA2 expression in primary CRCs correlated with that of Myc and Myc-target genes. Transcriptional up-regulation of VWA2 is extremely frequent (78%) and strong (average fold change >15) in CRC, but not in other types of cancer. VWA2 undergoes hypomethylation in the majority of CRCs. This alteration could partly underlie the previously reported over-expression of AMACO. Co-expression profiling suggests that VWA2 might be a constituent of a larger oncogenic transcriptional program regulated by c-Myc. Up-regulation of VWA2 is virtually exclusive of CRC, reinforcing its potential as a specific biomarker.