T Cell Receptor Signaling Co-regulates Multiple Golgi Genes to Enhance N-Glycan Branching

Abstract

T cell receptor (TCR) signaling enhances ␤1,6GlcNAc-branching in N-glycans, a phenotype that promotes growth arrest and inhibits autoimmunity by increasing surface retention of cytotoxic T lymphocyte antigen-4 (CTLA-4) via interactions with galectins. N-Acetylglucosaminyltransferase V (MGAT5) mediates ␤1,6GlcNAc-branching by transferring N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to N-glycan substrates produced by the sequential action of Golgi ␣1,2-mannosidase I (MIa,b,c), MGAT1, ␣1,2-mannosidase II (MII, IIx), and MGAT2. Here we report that TCR signaling enhances mRNA levels of MIa,b,c and MII,IIx in parallel with MGAT5, whereas limiting levels of MGAT1 and MGAT2. Blocking the increase in MI or MII enzyme activity induced by TCR signaling with deoxymannojirimycin or swainsonine, respectively, limits ␤1,6GlcNAc-branching, suggesting that enhanced MI and MII activity are both required for this phenotype. MGAT1 and MGAT2 have an ϳ250-and ϳ20-fold higher affinity for UDP-GlcNAc than MGAT5, respectively, and increasing MGAT1 expression paradoxically inhibits ␤1,6GlcNAc branching by limiting UDP-GlcNAc supply to MGAT5, suggesting that restricted changes in MGAT1 and MGAT2 mRNA levels in TCR-stimulated cells serves to enhance availability of UDP-GlcNAc to MGAT5. Together, these data suggest that TCR signaling differentially regulates multiple N-glycan-processing enzymes at the mRNA level to cooperatively promote ␤1,6GlcNAc branching, and by extension, CTLA-4 surface expression, T cell growth arrest, and self-tolerance.

Galectin 3 as a guardian of the tumor microenvironment

“…Galectin 3 is a key player in modulating the adaptive immune response of T cells by regulating T cell receptor (TCR) activation (123,125,(130)(131)(132). The TCR is glycosylated by MGAT5 in the Golgi which promotes binding to Galectin 3 resulting in reduced activation of the receptor (125,130). As TCR activation has been shown to induce MGAT5, a possible negative feedback loop exists where increased glycosylation of the TCR will dampen activity of subsequent TCR molecules produced (123,130).…”

“…The glycoprotein and glycolipid content of immune or inflammatory cells as well as their targets will modulate response and lectins such as Galectin 3 are critical in these processes (123,124). Galectin 3 has a broad range of effects on T cells, NK cells, macrophages, neutrophils, and other immune cells (125)(126)(127)(128)(129)(130)(131)(132)(133)(134). Galectin 3 can suppress cell function or even induce apoptosis of T cells by binding to CD45 (125,126).…”

“…The effect of Galectin 3 on CD45 is dependent on the type of glycans present; while Galectin 3 binds Nglycans on CD45 interaction with O-glycans is required for apoptotic induction (126). Galectin 3 is a key player in modulating the adaptive immune response of T cells by regulating T cell receptor (TCR) activation (123,125,(130)(131)(132). The TCR is glycosylated by MGAT5 in the Golgi which promotes binding to Galectin 3 resulting in reduced activation of the receptor (125,130).…”

N-Acetylglucosamine Inhibits T-helper 1 (Th1)/T-helper 17 (Th17) Cell Responses and Treats Experimental Autoimmune Encephalomyelitis

“…Multivalent binding of galectins to N-glycans attached to surface glycoproteins forms a molecular lattice at the cell surface that regulates the clustering and endocytosis of transmembrane receptors and transporters to control cell growth and differentiation (12,(17)(18)(19)(20)(21)(22). In T cells, N-glycan branching inhibits basal and activation signaling through the T cell receptor (TCR) and CD45, promotes growth arrest by cytotoxic T lymphocyte antigen-4 (CTLA-4), and enhances T-helper 2 (Th2) over T-helper 1 (Th1) differentiation (12,21,(23)(24)(25)(26)(27)(28). Metabolically increasing availability of substrate (i.e.…”

Human T Cell Activation Results in Extracellular Signal-regulated Kinase (ERK)-Calcineurin-dependent Exposure of Tn Antigen on the Cell Surface and Binding of the Macrophage Galactose-type Lectin (MGL)*

“…Noticeably, expression of the sialyltransferase ST6Gal-I and the UDP-N-acetylglucosamine:␣-6-d-mannoside ␤1,6 N-acetylglucosaminyltransferases II and V (GnT-II and GnT-V are also controlled by the ERK pathway in both tumor cells and immune cells (37,38). GnT-V, which facilitates ␤1,6-branching on N-glycan intermediates, is overexpressed during malignant transformation and is associated with enhanced onset of mammary tumor formation (39).…”