Comparative N-glycan profiling of colorectal cancer cell lines reveals unique bisecting GlcNAc and α-2,3-linked sialic acid determinants are associated with membrane proteins of the more metastatic/aggressive cell lines.

ABSTRACT

Advances in colorectal cancer (CRC) diagnosis will be enhanced by development of more sensitive and reliable methods for early detection of the disease when treatment is more effective. Because many known disease biomarkers are membrane-bound glycoproteins with important biological functions, we chose to compare N-glycan profiles of membrane proteins from three phenotypically different CRC cell lines, LIM1215, LIM1899, and LIM2405, representing moderately differentiated metastatic, moderately differentiated primary, and poorly differentiated (aggressive) primary CRC cell lines, respectively. The N-glycan structures and their relative abundances were determined as their underivatized reduced forms, using porous graphitized carbon LC-ESI-MS/MS. A key observation was the similar N-glycan landscape in these cells with the dominance of high mannose type glycan structures (70-90%) in all three cell lines, suggesting an incomplete glycan processing. Importantly, unique glycan determinants such as bisecting N-acetylglucosamine were observed at a high level in the metastatic LIM1215 cells, with some expressed in the moderately differentiated LIM1899, while none were detected in the poorly differentiated LIM2405 cells. Conversely, α-2,3-sialylation was completely absent in LIM1215 and LIM1899 and present only in LIM2405. RNA-Seq and lectin immunofluorescence data correlated well with these data, showing the highest upregulation of Mgat3 and binding with PHA-E in LIM1215. Downregulation of Man1α1 and Mgat1 in LIM1215 also coincided with the higher degree of incomplete N-glycan processing and accumulation of high mannose type structures as well as bisecting N-glycans when compared to the other two cell lines. This study provides a comprehensive analysis of the membrane N-glycome in three CRC cell lines and identifies N-glycosylation differences that correlate with the histological and pathological features of the cell lines. The unique glycosylation phenotypes may therefore serve as a molecular feature to differentiate CRC disease stages.