N-glycosylation signaling pathways in oral squamous cell carcinoma

Abstract

Oral squamous cell carcinoma (OSCC) accounts for majority of head and neck cancers and ranks as the sixth most common cancer in the world. OSCC belongs to the most understudied cancers and little is known about molecular mechanisms underlying its etiology and progression to metastasis. A hallmark of cancer is the enhanced posttranslational modification of cell surface proteins with complex N-glycans. Our studies have shown that induced protein N-glycosylation via activation of the core N-glycosylation-regulating gene, DPAGT1, is associated with reduced E-cadherin adhesion, as well as deregulation of several oncogenic signaling pathways, including Wnt/β-catenin and Hippo. Modest increases in DPAGT1 expression are associated with dramatic amplification of Wnt/β-catenin activity and increased expression and nuclear localization of the Hippo pathway effectors TAZ /YAP. The goal of this study was to align the expression and localization of DPAGT1, complex N-glycans, β-catenin, and TAZ/YAP with the progression of oral cancer in vivo from dysplasia to OSCC. Human oral tissues from different stages of OSCC pathogenesis were characterized for DPAGT1/β-catenin/α-catenin/YAP/TAZ expression and localization and correlated with cell surface expression of complex N-glycans by PHA lectin staining and with expression of primitive cell surface markers, CD44, CD24 and CD29. Results showed that high DPAGT1 expression and nuclear TAZ became increasingly associated with disorganized E-cadherin junctions as oral epithelium progressed from mild to severe dysplasia to OSCC. This correlated with increasing expression of cell surface complex N-glycans and CD44. These studies suggest that DPAGT1/β-catenin/TAZ and high PHA staining represent novel signatures for OSCC pathogenesis.