Identification of new targets for the treatment of head and neck cancer: N-glycosylation gene DPAGT1 and β-catenin/CBP signaling
Alamoud, Khalid Abdulrahman M.
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Head and neck squamous cell carcinoma (HNSCC) is pernicious disease with majority of cases presenting as oral squamous cell carcinoma (OSCC). OSCC is characterized by tumor heterogeneity, locoregional metastases and resistance to existing treatments. OSCC five-year overall survival rates are currently ~ 50 % with few therapeutic options available. Cancers are typically associated with dysregulated signaling pathways that normally have vital roles in embryonic development and hemostasis. We have focused on two homeostatic pathways, protein N-glycosylation and the canonical Wnt/β-catenin signaling, which have been shown to converge on each other’s activities. These pathways, when left unchecked, drive early pathogenesis and/or metastasis of a range of cancers, including OSCC. Aberrant activation of the DPAGT1 gene, encoding a key regulatory enzyme that functions at the first committed step in the protein N-glycosylation pathway, has been shown to be associated with OSCC. In OSCC, high DPAGT1 expression drives hyper-glycosylation of E-cadherin and loss of intercellular adhesion. Here, we provide evidence that ectopic expression of DPAGT1 in indolent OSCC CAL27 cells induced epithelial-to-mesenchymal transition (EMT) by upregulation of a key transcription factor, ZEB1, and mesenchymal protein, vimentin, coincident with increased cell migration. In contrast, partial knockdown of DPAGT1 in metastatic OSCC HSC-3 cells reduced expression of the EMT markers, diminished cell migration and enhanced intercellular adhesion. Further, inhibition of the DPAGT1 enzyme, GPT, with tunicamycin interfered with orthotopic tongue tumor growth and metastasis in nude mice coincident with diminished expression of vimentin- positive cells invading the tongue stroma. One mechanism responsible for increased DPAGT1 expression in OSCC is transcriptional activation by β-catenin. We now show that blocking transcriptional activity of β-catenin by interfering with its interaction with the cAMP-responsive element binding (CREB)-binding protein (CBP) using a small molecule inhibitor, ICG-001, inhibited cell proliferation and mesenchymal cell phenotypes in cellular models. In addition, ICG-001 abrogated tumor growth and metastases in zebrafish and murine models. Microarray analyses of ICG-001 gene expression signature revealed inhibition of genes involved in cell proliferation, survival, stemness, as well as N-glycosylation, but upregulation of genes functioning in cell adhesion and cell polarity. Importantly, the ICG-001 inhibition-associated transcriptional signature tracked with advanced tumor grade and poor survival in human patients. Our studies provide the first evidence that aberrant activation of DPAGT1 and β-catenin signaling promotes aggressive traits of OSCC cells and suggest that targeting the β-catenin/CBP interaction in the nucleus may provide an effective novel strategy for OSCC therapy.