Regulation of Cytokine Receptors by Golgi N-Glycan Processing and Endocytosis

Abstract

The Golgi enzyme beta1,6 N-acetylglucosaminyltransferase V (Mgat5) is up-regulated in carcinomas and promotes the substitution of N-glycan with poly N-acetyllactosamine, the preferred ligand for galectin-3 (Gal-3). Here, we report that expression of Mgat5 sensitized mouse cells to multiple cytokines. Gal-3 cross-linked Mgat5-modified N-glycans on epidermal growth factor and transforming growth factor-beta receptors at the cell surface and delayed their removal by constitutive endocytosis. Mgat5 expression in mammary carcinoma was rate limiting for cytokine signaling and consequently for epithelial-mesenchymal transition, cell motility, and tumor metastasis. Mgat5 also promoted cytokine-mediated leukocyte signaling, phagocytosis, and extravasation in vivo. Thus, conditional regulation of N-glycan processing drives synchronous modification of cytokine receptors, which balances their surface retention against loss via endocytosis.

Loss of expression of N‐acetylglucosaminyltransferase Va results in altered gene expression of glycosyltransferases and galectins

“…Decreased expression of PSA caused by down-regulation of ST8Sia II/STX transcripts after deletion of GnT-Va may, therefore, lead to a phenotype with increased cell adhesive properties and decreased cell motility. This hypothesis is consistent with inhibited cell growth and supportive of previous findings that GnT-Va null MEFs and tumor cells showed decreased cell motility [7,10].…”

“…We showed that deletion of GnT-Va had marked effects on MEFs growth on plastic and cell survival. Supporting these observation, the phosphorylation of both ERK and PKB was significantly inhibited in GnT-Va null mammary tumor cells and MEFs [5,7], suggesting a possible role of GnT-Va in regulating cell growth and apoptosis.…”

Variation in Carbohydrates between Cancer and Normal Cell Membranes Revealed by Super‐Resolution Fluorescence Imaging

“…Polyvalent interactions generally occur throughout biology, with the following functional advantages:27 it can provide a strong binding of ligands with modest or low surface area; it provides a graduated (graded) response to a biological signal via generating a broad range of signal strengths; it is able to obtain a great strength and specificity by heteromeric polyvalency of a mixture of ligand–receptor pairs; it can also induce macroscopic reorganizations of molecules or conformation of one or both of the interacting species; it has an ability to multiply an existing interaction or constructe a new one for biological evolution; it also serves as natural polyvalent inhibitors to prevent undesired interaction. Thus, according to the detailed functions of changed glycosylations in various cancer processes, including decreasing contact inhibition and substratum adhesion,28 increasing immigration,7 promoting the homotypic aggregation of cancer cells and the docking of tumor cells to endothelial cells,11 as well as the functional advantages of polyvalent interactions, we infer that the carbohydrates on cancer cell membranes could be reorganized to form larger clusters or more new clusters via polyvalent interactions with endogenetic lectins (i.e., galectins). In this way, carbohydrate ligands concentrate into large cluster to increase the regional density, which makes themselves easier to participate in interactions with extracellular matrix, homologous or heterogeneous cells, with higher affinity and specificity for CBPs.…”

“…Thus, previous studies have primarily focused on a limited type of glycosylation events that impart tumor cell properties. Some common alterations of glycosylation have shown to generally accompany with tumorigenesis and metastasis, such as, increase in branches of N‐linked oligoaccharides,7, 8 changed sialylation on certain proteins or antigens,5, 9, 10 abnormal biosynthesis of O‐linked oligosaccharides 11, 12. Owing to the complexity and variability of carbohydrate structures, the cancer‐associated carbohydrate chains have no general changed feature.…”

Potential roles of N-glycosylation in cell adhesion

“…For example, it could also be explained that the bisecting GlcNAc might be recognized by an unidentified endogenous lectin, which is similar to E4-PHA, to regulate cell behavior of animal cells. Alterations of N-glycans on integrins could also regulate their cis-interactions with membrane-associated proteins including the epidermal growth factor receptor (EGFR) [22,23], and the tetraspanin family of proteins in microdomain [24,25] as well as endocytosis [10,26,27]. In addition, GnT-III also contributes to suppress some other important glycoproteins, such as EGFR.…”