O-linked N-acetylglucosamine and cancer: messages from the glycosylation of c-Myc.

Altered protein glycosylation is known to correlate with tumorigenesis, but its role remains enigmatic. Cells transformed by altered oncogene or tumor suppressor gene expression often also show changes of carbohydrate on cell surface glycoconjugates which correlate with the potential for tumor invasion and metastasis. In recent years, many oncogene and tumor suppressor gene products, such as c-Myc, SV40 large T antigen, and p53, were shown to be modified by O-GlcNAc. O-GlcNAc is a form of protein glycosylation found almost exclusively in the nucleus and cytoplasm of eukaryotic cells. The known O-GlcNAc-bearing proteins are phosphoproteins and form reversible multimeric complexes. O-GlcNAc modification is dynamic and appears to have a reciprocal relationship with protein phosphorylation. The enzymes which catalyze O-GlcNAc addition and removal have been characterized and used as effective tools in O-GlcNAc studies. It is of great interest in the future to investigate the alteration of O-GlcNAc in different cancers since addition/removal of O-GlcNAc on oncoproteins, tumor suppressor proteins, and other tumor-related proteins very likely plays a key role in the pathogenesis of tumors.