Elevated O-GlcNAcylation Promotes Malignant Phenotypes of Hypopharyngeal Squamous Cell Carcinoma by Stabilizing Nrf2 through Regulation of the PI3K/Akt Pathway.

BACKGROUND AND PURPOSE O-GlcNAcylation is a significant protein posttranslational modification with O-linked β-N-acetylglucosamine (GlcNAc) for intracellular signaling. Elevated O-GlcNAcylation contributes to cell proliferation, cell migration, cell apoptosis and signal transduction in various cancers. However, the expression level and functional role of O-GlcNAcylation in Hypopharyngeal Squamous Cell Carcinoma (HSCC) is not clearly elucidated. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a master transcriptional factor that has been found aberrant activated in HSCC. Here, we provide a molecular rationale between O-GlcNAcylation and Nrf2 in HSCC patients. METHODS The protein levels of O-GlcNAcylation and Nrf2 in HSCC tissues were detected by immunohistochemistry technique and western blot analysis. Then, O-GlcNAcylation knockdown HSCC cells were applied in this study. Cell proliferation was detected by CCK8, colony-forming analysis, and cell cycle assays. Cell migration and invasion ability was evaluated by transwell assays. Cell apoptosis was measured by TUNEL analysis. RESULTS O-GlcNAcylation was obviously up-regulated in HSCC tissues, which correlated with tumor size and lymph node metastasis. In addition, the protein level of Nrf2 was found to positively correlate with the expression of O-GlcNAcylation both in vivo and in vitro. Knockdown of O-GlcNAcylation significantly inhibited HSCC cell growth, suppressed cell migration, and promoted cell apoptosis, whereas overexpression of Nrf2 reversed these phenotypes. Mechanismly, upregulation of O-GlcNAcylation promoted the phosphorylation of Akt, leading to the stabilization of Nrf2; this could be attenuated by inhibition of the PI3K/Akt signaling pathway. CONCLUSION Here, we provide a molecular association between O-GlcNAcylation and Nrf2 in HSCC patients, thus providing valuable therapeutic targets for the disease.