Loss of discoidin domain receptor 1 (DDR1) via CpG methylation during EMT in epithelial ovarian cancer.

Epithelial ovarian cancer (EOC) can be stratified according to the stages of epithelial-mesenchymal transition (EMT). Here, we aim to identify tyrosine kinases (TKs) in EOC that correlate with the EMT subtypes. By gene expression microarray, we analyzed the expression levels of tyrosine kinases in EOC cell lines in correlation with EMT. Among the candidate TKs identified, DDR1 was expressed mainly in EOC cells with an Epithelial phenotype. Its expression was validated by qPCR, ELISA and western blotting. Using Infinium HumanMethylation27K BeadChip array and pyrosequencing, we further analyzed the CpG methylation levels at the DDR1 promoter in EOC cells and found that the CpG methylation levels of DDR1 promoter correlated negatively with the expression of DDR1 along the EMT spectrum. Therefore, EMT stratification could be a potential biomarker to predict patient response to DDR1-targeting drugs.