High-Glucose Microenvironment Accelerates Malignant Progression Via O-GlcNAcylation in Oral Squamous Cell Carcinoma.

BACKGROUND: Diabetes mellitus (DM) is a risk factor for oral squamous cell carcinoma (OSCC). O-GlcNAcylation is a specific form of glycosylation modification sensitive to glucose levels and implicated in tumour progression. However, the association between the high-glucose environment, O-GlcNAcylation, and OSCC needs further exploration. METHODS: The relationship between DM status and clinicopathological factors was analysed. The Kaplan-Meier analysis was performed to evaluate the effect of DM on OSCC prognosis. The proliferation, migration, invasion, and apoptosis of OSCC cell lines (SCC25 and CAL27) in the high-glucose microenvironment were analysed using CCK8, colony formation, wound healing, transwell assays, flow cytometry, and western blots (WB). Immunohistochemical staining and WB were used to detect O-GlcNAc transferase (OGT) and O-GlcNAcylation levels in OSCC tissues and cells. Changes in cell proliferation, migration, invasion, and apoptosis were analysed in OSCC cells after OGT-shRNA knockdown or adding the OGT inhibitor OSMI-1. The effect of O-GlcNAcylation on the expression of phosphorylated proteins of the PI3K/AKT/mammalian target of rapamycin signalling pathway was analysed by WB. RESULTS: DM status was associated with the clinical T stage, lymph node metastasis, Ki-67, and depth of invasion in OSCC. DM status was significantly associated with prognosis in patients with OSCC. In vitro experiments showed that the high-glucose microenvironment promoted the malignant progression of OSCC cells. OSCC tissues from patients with DM and OSCC cells cultured in high-glucose medium exhibited high O-GlcNAcylation levels. Decreases in hyper-O-GlcNAcylation by knocking down or inhibiting OGT inhibited proliferation and metastasis and promoted the apoptosis of OSCC cells in a high-glucose environment. The hyper-O-GlcNAcylation-mediated protumoural properties partially depended on the PI3K/AKT/mammalian target of rapamycin pathway. CONCLUSIONS: The findings highlight the elevated expression of O-GlcNAcylation in OSCC in a high-glucose microenvironment and its involvement in tumour malignant progression. The study findings have significant implications for the treatment of patients with OSCC who also have DM.