Elevated MGAT3 expression in ovarian cancer cells is epigenetically regulated by DNA hypomethylation

Introduction: We have identified by mass spectrometry complex glycan structures comprising a unique bisecting GlcNAc (N-acetylgucosamine) motif exclusively on serous ovarian cancer cells. Bisecting GlcNAc on N-glycosylated proteins is a unique product of the beta-1,4-N-acetylglucosaminyltransferase 3, MGAT3. The function of MGAT3 and bisecting GlcNAc in tumorigenesis is unclear, since both oncogenic and tumor suppressive functions have been described. Our aim is to investigate the molecular basis of dysregulated MGAT3 expression in ovarian cancer cells.

Material and methods: DNA methylation of the MGAT3 promoter was addressed by bisulfite sequencing. Gene expression was analyzed by (semi-) quantitative RT-PCR, protein levels by Western blotting. Flow cytometry was used to sort human ovarian surface epithelial (HOSE) cells.

Results: Gene and protein expression analysis of MGAT3 further support the observed elevated bisecting GlcNAc expression on ovarian cancer cell lines when compared to normal human ovarian surface epithelial (HOSE) cells. Bisulfite sequencing showed that DNA hypomethylation of the MGAT3 promoter at the transcription start site (TSS) correlates with increased expression in ovarian cancer cells. Treatment of HOSE cells with the DNA-methyltransferase inhibitor 5-Aza increased MGAT3 expression associated with reduced DNA methylation at TSS. We also observed elevated MGAT3 expression in stem cell-like pools of HOSE cells. Protein level analysis suggests that MGAT3 is differentially expressed in matched primary and metastatic samples of human ovarian cancer.

Conclusion: Elevated MGAT3 expression in ovarian cancer cells is epigenetically regulated by DNA hypomethylation. Further studies are required to understand whether this mechanism contributes to ovarian cancer development.