Aberrant O-GlcNAc-modified proteins expressed in primary colorectal cancer

Abstract

O-GlcNAcylation is a post-translational modification of serine and threonine residues which is dynamically regulated by 2 enzymes; O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) that catalyze the addition and removal of a single N-acetylglucosamine (GlcNAc) molecule, respectively. This modification is thought to be a nutrient sensor in highly proliferating cells via the hexosamine biosynthesis pathway, a minor branch of glycolysis. Although emerging evidence suggests that O-GlcNAc modification is associated with many types of cancer, identification of O-GlcNAc-modified proteins and their role in cancer remain unexplored. In the present study, we demonstrated that O-GlcNAcylation is increased in primary colorectal cancer tissues, and that this augmentation is associated with an increased expression of OGT levels. Using 2-dimensional O-GlcNAc immunoblotting and LC-MS/MS analysis, 16 proteins were successfully identified and 8 proteins showed an increase in O-GlcNAcylation, including cytokeratin 18, heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1), hnRNP H, annexin A2, annexin A7, laminin-binding protein, α-tubulin and protein DJ-1. Among these identified proteins, annexin A2 was further confirmed to show overexpression of O-GlcNAc in all cancer samples. The results, therefore, indicate that aberrant O-GlcNAcylation of proteins is associated with colorectal cancer and that identification of O-GlcNAc-modified proteins may provide novel biomarkers of cancer.

Aberrant O-GlcNAcylated Proteins: New Perspectives in Breast and Colorectal Cancer

“…However, OGA level was not significantly enhanced in such cancer tissue samples (47). Consistent with this finding, Phueaouan et al also reported that, in primary CRC patients (grade II), the upregulation of O -GlcNAcylation and OGT enzyme was found in CRC tissues, but the expression of OGA did not differ in CRC tissue extracts compared to normal samples (40). …”

“…Accumulating evidence reveals that the levels of O -GlcNAcylation and its cycling enzymes in malignant tissues are altered in various cancers. Recently, we showed that O -GlcNAcylation and OGT expression levels are increased in both breast and CRC (25, 40). As mentioned above, the O -GlcNAc cycling enzymes OGT and OGA tightly regulate the level of O -GlcNAcylation.…”

“…Gel based proteomics was used by our group to study the O -GlcNAc profile in CRC tissues (40). Eight O -GlcNAc modified proteins showed an increase in O -GlcNAcylation including cytokeratin 18 (CK18), α-tubulin, heterogeneous nuclear ribonucleoproteins (hnRNPs) A2/B1 (hnRNPA2/B1), hnRNPH, annexin A2, annexin A7, laminin-binding protein, and protein DJ-1 (40).…”

“…Eight O -GlcNAc modified proteins showed an increase in O -GlcNAcylation including cytokeratin 18 (CK18), α-tubulin, heterogeneous nuclear ribonucleoproteins (hnRNPs) A2/B1 (hnRNPA2/B1), hnRNPH, annexin A2, annexin A7, laminin-binding protein, and protein DJ-1 (40). CK18 was reported to be modified by O -GlcNAc in at least three sites (Ser-30/Ser-31/Ser-49) (79).…”

“…Annexin A2 and A7 play important roles in cytoskeletal formation and cell matrix interaction. O -GlcNAcylation of annexin A2 was found to be overexpressed in all cancer samples (7/7) (40). HnRNPA2/B1 and H are a group of RNA-binding proteins involved in various processes in RNA metabolism including pre-mRNA splicing, mRNA transport, and translation.…”