Abstract
Glycosylation is one of the most abundant post-translational modifications that occur within the cell. Under normal physiological conditions, O-linked glycosylation of extracellular proteins is critical for both structure and function. During the progression of cancer, however, the expression of aberrant and truncated glycans is commonly observed. Mucins are high molecular weight glycoproteins that contain numerous sites of O-glycosylation within their extracellular domains. Transmembrane mucins also play a functional role in monitoring the surrounding microenvironment and transducing these signals into the cell. In cancer, these mucins often take on an oncogenic role and promote a number of pro-tumorigenic effects, including pro-survival, migratory, and invasive behaviors. Within this review, we highlight both the processes involved in the expression of aberrant glycan structures on mucins, as well as the potential downstream impacts on cellular signaling.
Highlights
Glycosylation is one of the most abundant post-translational modifications that occur within the cell
MUC1 consists of two distinct subunits: a large N-terminal extracellular domain that contains a variable number tandem repeat (VNTR) domain and a shorter C-terminal fragment consisting of a short extracellular domain, a transmembrane domain, and a cytoplasmic tail (MUC1.CT)
Galectin-3, whose binding affinity is altered depending on the structural glycans on MUC1, regulates the association between both MUC1 and epidermal growth factor receptor (EGFR) [108,109,110,111]. These results suggest that altered MUC1 glycosylation may readily promote the association of MUC1 and EGFR and integrate morphogenetic signals from the Wnt pathway
Summary
A large family of glycoproteins, are expressed by epithelia of the respiratory, gastrointestinal, and reproductive tracts [1]. Membrane bound mucins are generally localized to the apical surface of epithelial cells by a transmembrane domain and cytoplasmic tail, which is known to engage in signal transduction events [1,2]. O-glycosylation is critical for multiple mucin function, as O-linked rich in serine, threonine, and proline residues that form potential sites for. The initiating step involves the of N-acetylgalactosamine (GalNAc) to(GalNAc) serine ortothreonine residues present the mucin addition of N‐acetylgalactosamine serine or threonine residuesin present in thebackbone mucin to formbackbone the Tn-epitope, stepTn‐epitope, that is catalyzed family by of polypeptide. Initiation occurs through addition of N-acetylgalactosamine (GalNAc) to serine or threonine residues present in the mucin backbone. These structures are extended into Core 1, Core 2, Core 3, and. Gal: galactose; GalNAc-T: GalNAc-transferase; C1GalT: Core 1 Gal-transferase; C2GnT: Core 2 N-acetylglucosamine transferase; C3GnT: Core 3 N-acetylglucosamine transferase; C4GnT: Core 4 N-acetylglucosamine transferase
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