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O‐GlcNAc Causes Increased levels of Tumor Suppressor Protein p53 in Human Breast Cancer MCF‐7 Cells

The tumor suppressor protein p53 may play an anti‐cancer role by activating DNA repair proteins, inducing growth arrest, and initiating apoptosis. The concentration of p53 is controlled by proteasomal degradation. Hence, the proteasome controls important cellular functions such as cell cycle and apoptosis. O‐GlcNAcylation is a dynamic protein post‐translational modification that adds the monosaccharide N‐acetylglucosamine (GlcNAc) to specific serine or threonine residues on target proteins. We have previously found that O‐GlcNAc modification is an endogenous inhibitor of the proteasome. In this study, we tested the hypothesis that O‐GlcNAc modification can cause increased levels of p53 through proteasomal inhibition. Human breast cancer MCF‐7 cells were treated with 5 mM glucosamine (GlcN) for 2, 4, 6, 12, 24 hours. At 24 hours of GlcN treatment, O‐GlcNAc modification was increased 5.3‐fold and p53 levels increased 2.3‐fold compared to vehicle controls. We found that the proteasome had 18.7% decreased activity after 24 hours of GlcN treatment compared to the cells without GlcN treatment. These observations suggest that O‐GlcNAc modification may participate in the apoptosis of cancer cells and be a novel therapeutic target for cancer therapy.