Down-regulation of RBM47 due to diminished activation by forkhead box A1 (FOXA1) and silencing by CpG methylation is associated with epithelial-mesenchymal transition and metastasis of colorectal cancer

The gene encoding the RNA-binding motif protein 47 (RBM47) is highly expressed in epithelial cells and its down-regulation is characteristic for many types of cancer, among them colorectal cancer (CRC). However, the underlying mechanisms for this differential expression of RBM47 and its functional consequences during CRC progression have remained unknown. Here we found that RBM47 expression progressively decreases during CRC progression and is associated with poor prognosis and the metastatic CRC subtypes CMS4 and CRIS-B. In mice and humans RBM47 expression was highest in endoderm-derived tissues. The expression of forkhead box A1 (FOXA1), a transcription factor essential for the development of endoderm-derived epithelial tissues, showed a positive correlation with RBM47 expression in human tissues, as well as in primary CRCs and derived cell lines. Like RBM47, FOXA1 showed a down-regulation during CRC progression that is associated with poor prognosis and CMS4/CRIS-B. Ectopic FOXA1 induced RBM47 via directly binding to FOXA1 binding sites within the RBM47 promoter region. Up-regulation of RBM47 was necessary for FOXA1-mediated mesenchymal-to-epithelial transition (MET) and inhibition of CRC cell migration and invasion. RBM47 expression was silenced by CpG methylation in mesenchymal-like CRC cell lines. Moreover, epigenetic silencing of RBM47 in primary CRCs was associated with liver metastases. Therefore, the down-regulation of RBM47 is presumably initially mediated by loss of FOXA1 expression and subsequently fixed by CpG methylation of the RBM47 promoter. This down-regulation of RBM47 facilitates EMT and thereby promotes CRC metastasis. Finally, our results show that CpG hypermethylation of the RBM47 promoter represents a potential biomarker for metastatic CRC.