N-glycosylation of E-cadherin regulates cytoskeletal dynamics and oral squamous cell carcinoma migration
Date
2011
DOI
Authors
Jamal, Basim T.
Version
OA Version
Citation
Abstract
N-glycosylation of E-cadherin has been shown to inhibit cell-cell adhesion. Specifically, reduction of E-cadherin N-glycosylation have been shown to promote the recruitment of stabilizing components such as [gamma]-catenin, [alpha]-catenin, vinculin and serine/threonine protein phosphatase 2A (PP2A) to adherens junctions (AJs) and to enhance the association of AJs with the actin cytoskeleton. In the first paper, I examined the details of how N-glycosylation of E-cadherin affected AJ remodeling and cytoskeletal interactions. My studies showed that the hypoglycosylated E-cadherin variant, V13, formed distinct junctional complexes: V13/[beta]-catenin complexes that preferentially interacted with PP2A and with the microtubule motor protein dynein. This correlated with de-phosphorylation of the microtubule-associated protein tau, suggesting that increased association of PP2A with V13-containing AJs promoted their tethering to microtubules. On the other hand, V13/[gamma]-catenin complexes associated more with vinculin, suggesting that they mediated the interaction of AJs with the actin cytoskeleton. These studies provided the first mechanistic insights into how N glycosylation of E-cadherin drives changes in AJ composition and how molecular reorganization of AJs impacts cytoskeletal dynamics.
N-glycosylation of E-cadherin, among other cell surface glycoproteins, is frequently altered in cancer, with tumor progression linked to increases in the abundance of complex N-glycans. Our previous studies have shown that oral squamous cell carcinoma (OSCC) tumor spread is promoted, in part, by the loss of E-cadherin adhesion due to its excessive N-glycosylation. The latter is driven by overexpression of the DPAGT1 gene that initiates the metabolic pathway of protein N-glycosylation. Previous studies revealed that DPAGT1 was a downstream target of the canonical Wnt signaling pathway and that canonical Wnt signaling and DPAGT1 functioned in a positive feedback loop. In the second paper, I examined the role of DPAGT1 in OSCC, specifically as it pertained to its interaction with the canonical Wnt pathway. My studies showed that overexpression of DPAGT1 in OSCC was associated with an aberrant upregulation of the canonical Wnt signaling pathway. Accordingly, OSCC tumor specimens and oral cancer cell lines exhibited elevated cytoplasmic levels of [beta]- and [gamma]-catenins and dramatically increased abundance of these catenins at the TCF binding region of the DPAGT1 promoter. This aberrant activation of canonical Wnt signaling in OSCC was due, at least in part, to a significant loss of Dickkopf-1 (Dkk-1), a Wnt inhibitor. In addition, I show that transfection of the hypoglycosylated E-cadherin variant, V13, into human tongue OSCC (CAL27) cells diminished DPAGT1 expression and canonical Wnt signaling. This involved depletion of [beta]- and [gamma]-catenins from the DPAGT1 promoter. Similarly, partial downregulation of DPAGT1 expression with siRNA in oral cancer cells reduced canonical Wnt signaling and cellular N-glycosylation. Therefore, another reason for aberrant upregulation of canonical Wnt signaling-DPAGT1 expression in OSCC is due to the loss of mature hypglycosylated E-cadherin-containing AJs, which themselves negatively feedback these pathways by sequestering nuclear [beta]- and [gamma]-catenins. These studies show that dysregulation of the canonical Wnt/DPAGT1/E-cadherin axis is an underlying mechanism for OSCC tumor spread and suggest that inhibition of DPAGT1 and/or E-cadherin N-glycosylation may represent a useful anticancer strategy.
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Dissertation (DScD) --Boston University, Goldman School of Dental Medicine, 2011 (Department of Oral and Maxillofacial Surgery, in collaboration with the Department of Molecular and Cell Biology).
Includes bibliographic references: leaves 102-115.
Dissertation (DScD) --Boston University, Goldman School of Dental Medicine, 2011 (Department of Oral and Maxillofacial Surgery, in collaboration with the Department of Molecular and Cell Biology).
Includes bibliographic references: leaves 102-115.
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This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.