Stabilization of plakoglobin and enhanced keratinocyte cell-cell adhesion by intracellular O-glycosylation
ABSTRACT O-Glycosylation modifies and regulates a variety of intracellular proteins. Plakoglobin, which functions in both cell-cell adhesion and signal transduction, is modified by O-glycosylation; however, the significance is unknown. To investigate the functional consequence of plakoglobin O-glycosylation, we cloned and overexpressed in keratinocytes murine O-GlcNAc transferase (mOGT). Over expression of mOGT in murine keratinocytes resulted in (i) glycosylation of plakoglobin and (ii) increased levels of plakoglobin due to post-translational stabilization of plakoglobin. Additionally, overexpression of mOGT in keratinocytes correlated with increased staining for cell-cell adhesion proteins and greater cell-cell adhesion. These observations suggest that O-glycosylation functions to regulate the post-translational stability of plakoglobin and keratinocyte cell-cell adhesion.
SourceAvailable from: Leonardo Freire de Lima[Show abstract] [Hide abstract]
ABSTRACT: Glycosylation changes are a feature of disease states. One clear example is cancer cells, which commonly express glycans at atypical levels or with different structural attributes than those found in normal cells. Epithelial-mesenchymal transition (EMT) was initially recognized as an important step for morphogenesis during embryonic development, and is now shown to be one of the key steps promoting tumor metastasis. Cancer cells undergoing EMT are characterized by significant changes in glycosylation of the extracellular matrix (ECM) components and cell-surface glycoconjugates. Current scientific methodology enables all hallmarks of EMT to be monitored in vitro and this experimental model has been extensively used in oncology research during the last 10 years. Several studies have shown that cell-surface carbohydrates attached to proteins through the amino acids, serine, or threonine (O-glycans), are involved in tumor progression and metastasis, however, the impact of O-glycans on EMT is poorly understood. Recent studies have demonstrated that transforming growth factor-beta (TGF-β), a known EMT inducer, has the ability to promote the up-regulation of a site-specific O-glycosylation in the IIICS domain of human oncofetal fibronectin, a major ECM component expressed by cancer cells and embryonic tissues. Armed with the knowledge that cell-surface glycoconjugates play a major role in the maintenance of cell homeostasis and that EMT is closely associated with glycosylation changes, we may benefit from understanding how unusual glycans can govern the molecular pathways associated with cancer progression. This review initially focuses on some well-known changes found in O-glycans expressed by cancer cells, and then discusses how these alterations may modulate the EMT process.Frontiers in Oncology 03/2014; 4:59. DOI:10.3389/fonc.2014.00059
Developmental Biology 06/2007; 306(1):432-432. DOI:10.1016/j.ydbio.2007.03.466 · 3.64 Impact Factor
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ABSTRACT: Non-healing wounds are a significant source of morbidity. This is particularly true for diabetic patients, who tend to develop chronic skin wounds. O-GlcNAc modification of serine and threonine residues is a common regulatory post-translational modification analogous to protein phosphorylation; increased intracellular protein O-GlcNAc modification has been observed in diabetic and hyperglycemic states. Two intracellular enzymes, UDP-N-acetylglucosamine-polypeptide β-N-acetylglucosaminyl transferase (OGT) and O-GlcNAc-selective N-acetyl-β-D-glucosaminidase (OGA), mediate addition and removal, respectively, of N-acetylglucosamine (GlcNAc) from intracellular protein substrates. Alterations in O-GlcNAc modification of intracellular proteins is linked to diabetes and the increased levels of protein O-GlcNAc modification observed in diabetic tissues may in part explain some of the observed underlying pathophysiology that contributes to delayed wound healing. We have previously shown that increasing protein O-GlcNAc modification by over-expression of OGT in murine keratinocytes results in elevated protein O-GlcNAc modification and a hyper-adhesive phenotype. This study was undertaken to explore the hypothesis that increased O-GlcNAc modification of cellular proteins in diabetic skin could contribute to the delayed wound healing observed in patients with diabetic skin ulcers. In the present study, we show human keratinocytes cultured under hyperglycemic conditions display increased levels of O-GlcNAc modification as well as a delay in the rate of wound closure in vitro. We further show that specific knock-down of OGT by RNA interference (RNAi) reverses this effect, thereby opening up the opportunity for OGT-targeted therapies to promote wound healing in diabetic patients.Journal of Biological Chemistry 01/2014; 289(9). DOI:10.1074/jbc.M113.513952 · 4.60 Impact Factor