Tumor necrosis factor-alpha up-regulates the expression of beta1,4-galactosyltransferase I in primary human endothelial cells by mRNA stabilization

Sweet Rules: Linking Glycosylation to Antibody Function

Antibodies produced upon infections with pathogenic microorganisms are essential for clearing primary infections and for providing the host with long-lasting immunity. Moreover, antibodies have become the most widely used platform for developing novel therapies against cancer and autoimmunity, requiring an in-depth understanding of how antibodies mediate their activity in vivo and which factors modulate pro- or anti-inflammatory antibody activities. Since the discovery that select residues present in the sugar domain attached to the immunoglobulin G (IgG) fragment crystallizable (Fc) region can modulate both, pro- and anti-inflammatory effector functions, a wealth of studies has focused on understanding how IgG glycosylation is regulated and how this knowledge can be used to optimize therapeutic antibody activity. With the introduction of glycoengineered afucosylated antibodies in cancer therapy and the initiation of clinical testing of highly sialylated anti-inflammatory antibodies the proof-of-concept that understanding antibody glycosylation can lead to clinical innovation has been provided. The focus of this review is to summarize recent insights into how antibody glycosylation is regulated in vivo and how select sugar residues impact IgG function.

Glycosylation in the Tumor Microenvironment: Implications for Tumor Angiogenesis and Metastasis

Just as oncogene activation and tumor suppressor loss are hallmarks of tumor development, emerging evidence indicates that tumor microenvironment-mediated changes in glycosylation play a crucial functional role in tumor progression and metastasis. Hypoxia and inflammatory events regulate protein glycosylation in tumor cells and associated stromal cells in the tumor microenvironment, which facilitates tumor progression and also modulates a patient's response to anti-cancer therapeutics. In this review, we highlight the impact of altered glycosylation on angiogenic signaling and endothelial cell adhesion, and the critical consequences of these changes in tumor behavior.

The β4GalT1 affects the fibroblast-like synoviocytes invasion in rheumatoid arthritis by modifying N-linked glycosylation of CXCR3

OBJECTIVE

The level of β-1,4-galactosyltransferase 1 (β4GalT1) is up-regulated in collagen-induced arthritis (CIA) mice. It is reported that CXC chemokine receptor 3 (CXCR3) can enhance the invasiveness of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA). This study aims to investigate the specific mechanism of β4GalT1 and relationship between β4GalT1 and CXCR3 in RA.

METHODS

The model of CIA mice was established to explore the role of β4GalT1. The N-glycosylation of CXCR3 was detected by mass spectrometry and western-blot. The interaction between β4GalT1 and CXCR3 was tested by immunoprecipitation. The truncted MMP-1 was detected by ELISA. Flow cytometry analysis was applied to measure ligand-receptor interaction between CXCR3 and CXCL10.

RESULTS

β4GalT1 can promote the inflammatory process of arthritis. CXCR3 was N-glycosylated and its glycosylation regulated by β4GalT1. β4GalT1 can enhance the invasiveness of FLS by modifying CXCR3. N-glycosylation of CXCR3 influences the ligand-receptor interaction between CXCR3 and CXCL10.

CONCLUSIONS

β4GalT1 can regulate N-glycans of CXCR3 in RA. N-glycans of CXCR3 affects CXCL10/CXCR3 ligand-binding which enhancing FLS invasion.

Expression of SRC suppressed C kinase substrate in rat neural tissues during inflammation

Src-suppressed C kinase substrate (SSeCKS), an in vivo and in vitro protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein which markedly upregulated in several organs, including brain, lung, heart, kidney etc., indicating a possible role of SSeCKS in inflammatory process. However, the expression and biological function of SSeCKS during neuronal inflammation remains to be elucidated, so we established an inflammatory model injected with LPS to investigate the gene expression patterns of SSeCKS in neural tissues by using TaqMan quantitative real-time PCR and immunohistochemistry in rat. Real-time PCR showed that LPS stimulated the expression of SSeCKS mRNA in a dose- and time-dependent manner in sciatic nerves, spinal cords and dorsal root ganglions. Immunohistochemistry showed that SSeCKS colocalized with nerve fibers in sciatic nerve after LPS administration, but there was no colocalization between SSeCKS and Schwann cells. In addition, SSeCKS colocalized with neurons which existed in dorsal root ganglions and spinal cords. These findings indicated that SSeCKS might play some important roles in sciatic nerve fibers and neurons in spinal cords and dorsal root ganglions after LPS injection.

Analytical tools for the study of cellular glycosylation in the immune system

It is becoming increasingly clear that glycosylation plays important role in intercellular communication within the immune system. Glycosylation-dependent interactions are crucial for the innate and adaptive immune system and regulate immune cell trafficking, synapse formation, activation, and survival. These functions take place by the cis or trans interaction of lectins with glycans. Classical immunological and biochemical methods have been used for the study of lectin function; however, the investigation of their counterparts, glycans, requires very specialized methodologies that have been extensively developed in the past decade within the Glycobiology scientific community. This mini-review intends to summarize the available technology for the study of glycan biosynthesis, its regulation and characterization for their application to the study of glycans in immunology.

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)

The C-type lectin macrophage galactose-type lectin (MGL) exerts an immunosuppressive role reflected by its interaction with terminal GalNAc moieties, such as the Tn antigen, on CD45 of effector T cells, thereby down-regulating T cell receptor signaling, cytokine responses, and induction of T cell death. Here, we provide evidence for the pathways that control the specific expression of GalNAc moieties on human CD4(+) T cells. GalNAc epitopes were readily detectable on the cell surface after T cell activation and required de novo protein synthesis. Expression of GalNAc-containing MGL ligands was completely dependent on PKC and did not involve NF-κB. Instead, activation of the downstream ERK MAPK pathway led to decreased mRNA levels and activity of the core 1 β3GalT enzyme and its chaperone Cosmc, favoring the expression of Tn antigen. In conclusion, expression of GalNAc moieties mirrors the T cell activation status, and thus only highly stimulated T cells are prone to the suppressive action of MGL.

Estrogen induced β-1,4-galactosyltransferase 1 expression regulates proliferation of human breast cancer MCF-7 cells

Beta 1,4-galactosyltransferase 1 (B4GALT1) synthesizes galactose β-1,4-N-acetylglucosamine (Galβ1-4GlcNAc) groups on N-linked sugar chains of glycoproteins, which play important roles in many biological events, including the proliferation and migration of cancer cells. A previous microarray study reported that this gene is expressed by estrogen treatment in breast cancer. In this study, we examined the regulatory mechanisms and biological functions of estrogen-induced B4GALT1 expression. Our data showed that estrogen-induced expression of B4GALT1 is localized in intracellular compartments and in the plasma membrane. In addition, B4GALT1 has an enzyme activity involved in the production of the Galβ1-4GlcNAc structure. The result from a promoter assay and chromatin immunoprecipitation revealed that 3 different estrogen response elements (EREs) in the B4GALT1 promoter are critical for responsiveness to estrogen. In addition, the estrogen antagonists ICI 182,780 and ER-α-ERE binding blocker TPBM inhibit the expression of estrogen-induced B4GALT1. However, the inhibition of signal molecules relating to the extra-nuclear pathway, including the G-protein coupled receptors, Ras, and mitogen-activated protein kinases, had no inhibitory effects on B4GALT1 expression. The knock-down of the B4GALT1 gene and the inhibition of membrane B4GALT1 function resulted in the significant inhibition of estrogen-induced proliferation of MCF-7 cells. Considering these results, we propose that estrogen regulates the expression of B4GALT1 through the direct binding of ER-α to ERE and that the expressed B4GALT1 plays a crucial role in the proliferation of MCF-7 cells through its activity as a membrane receptor.

Tumor necrosis factor-α up-regulates the expression of β1,4-galactosyltransferase-I in human fibroblast-like synoviocytes

β1,4-Galactosyltransferase-I (β1,4-GalT-I), which transfers galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a β1,4-linkage, is considered to be the major galactosyltransferase among the seven members of the subfamily responsible for β4 galactosylation. We previously reported, for the first time, that β1,4-GalT-I may play an important role in the inflammatory processes in synovial tissue of patients with rheumatoid arthritis (RA). In this study, we analyzed whether β1,4-GalT-I expression correlates with the expression of tumor necrosis factor-α (TNF-α) in RA. We show firstly the overexpression and co-localization of β1,4-GalT-I and TNF-α in synovial tissue of RA patients. Then, lipopolysaccharide (LPS) induces β1,4-GalT-I mRNA up-regulation in fibroblast-like synoviocytes (FLSs) through endogenous TNF-α overexpression. In addition, we observed that not only endogenous TNF-α but also exogenous TNF-α induced β1,4-GalT-I mRNA production in FLSs, and TNF-α-knockdown reverses the up-regulation of β1,4-GalT-I in FLSs induced by LPS or TNF-α. These results suggest that TNF-α contributes to the up-regulation of β1,4-GalT-I mRNA in human FLSs.

β-1,4-Galactosyltransferase I involved in Schwann cells proliferation and apoptosis induced by tumor necrosis factor-alpha via the activation of MAP kinases signal pathways

β-1,4-galactosyltransferase-I (β-1,4-GalT-I) plays a critical role in the initiation and maintenance of peripheral nervous system inflammatory reaction. However, the exact function of β-1,4-GalT-I in the regulation of SCs proliferation and apoptosis remains unclear. In this study, we found that low concentration of tumor necrosis factor-alpha (TNF-α) induced SCs proliferation, while high concentration of TNF-α induced SCs apoptosis. Meanwhile, the expressions of β-1,4-GalT-I, TNFR1, and TNFR2 were changed following. When β-1,4-GalT I overexpression, low concentration of TNF-α-induced SCs proliferation was partially repressed. Concurrently, the activity of ERK1/2 was decreased. While knocking down β-1,4-GalT I expression, high concentration of TNF-α-induced SCs apoptosis was partially rescued. Consistent with this, the activity of P38 and JNK were decreased. We also found anti-TNFR2 antibody suppressed low concentration of TNF-α-induced SCs proliferation, while anti-TNFR1 antibody inhibited high concentration of TNF-α-induced SCs apoptosis. Thus, present data show that β-1,4-GalT I may play an important role in SCs proliferation and apoptosis induced by TNF-α via different signal pathways and TNFR.

MS-based glycomic strategies for probing the structural details of polylactosaminoglycan chain on N-glycans and glycoproteomic identification of its protein carriers

Most MS-based glycomic and glycoproteomic analyses focus on identifying changes in terminal glyco-epitopes represented by sialylation and fucosylation at specific positions of the terminal N-acetyllactosamine units. Much less attention was accorded to the underlying linear or branched poly-N-acetyllactosamine extension from the N-glycan trimannosyl core other than a simple inference of its presence due to mass data and hence glycosyl compositional assignment. Using the EA.hy926 cell line derived from human umbilical vein endothelial cells (HUVEC), we have systematically investigated the MALDI- and ESI-MS-based methodologies for probing the structural details of endothelial polylactosaminoglycans at both MS and MS(2) levels in conjunction with the use of endo-β-galactosidase to identify branching motifs and initiation sites. We showed that the polylactosaminoglycan chains on the N-glycans of EA.hy926 were less sialylated and fucosylated but more extended and branched than those of human umbilical vein endothelial cells, thus demonstrating a fundamental glycomic difference. For EA.hy926 that was investigated in more details, its polylactosaminoglycan chains were shown to be not restricted to extending from a specific antenna including the biologically important 6-arm position. Finally, experimental conditions for glycopeptide enrichment by tomato lectin were further optimized, which led to identification of over 40 candidate endothelial membrane protein carriers of polylactosaminoglycans by proteomic analysis.

β-1,4-galactosyltransferase I promotes tumor necrosis factor-α autocrine via the activation of MAP kinase signal pathways in Schwann cells

Recent studies have demonstrated that aberrant galactosylation is associated with some inflammation diseases. β-1,4-Galactosyltransferase-I (β-1,4-GalT I), which transferred galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a β-1,4-linkage, was considered to be the major galactosyltransferase among the seven members of the subfamily responsible for β4 galactosylation. To elucidate the expression and possible function of β-1,4-GalT I in the peripheral nervous system (PNS) inflammatory diseases, we performed a tumor necrosis factor-alpha (TNF-α) autocrine inflammatory model in Schwann cells (SCs). In this study, we found that silencing of β-1,4-GalT I suppressed TNF-α autocrine, while overexpression of β-1,4-GalT I promoted TNF-α autocrine in TNF-α-treated SCs. Meanwhile, anti-TNFR1 antibody suppressed the expression of β-1,4-GalT I, and TNF-α autocrine. β-1,4-GalT I conferred its effect by promoting ERK, JNK, and P38 MAP kinase signal pathways activation in TNF-α-induced SCs. Thus, the present data shows that during SCs activation, β-1,4-GalT I may play an important role in the release of inflammatory mediators.

Specificity of β1,4-galactosyltransferase inhibition by 2-naphthyl 2-butanamido-2-deoxy-1-thio-β-D-glucopyranoside

Inhibitors of Galactosyltransferase (GalT) have the potential of reducing the amounts of adhesive carbohydrates on secreted and cell surface-bound glycoproteins. We recently found a potent inhibitor of β4GalT, 2-naphthyl 2-butanamido-2-deoxy-1-thio-β-D-glucopyranoside (compound 612). In this work, we have tested compound 612 for the specificity of its inhibition and examined its effect on GalT, and on GlcNAc- and GalNAc-transferases in homogenates of different cell lines, as well as on recombinant glycosyltransferases. Compound 612 was found to be a specific inhibitor of β4GalT. The specificity of recombinant human β3GalT5 that also acts on GlcNAc-R substrates, revealed similarities to bovine milk β4GalT. However, 612 was a poor substrate and not an inhibitor for β3GalT5. To further determine the specific structures responsible for the inhibitory property of 612, we synthesized (2-naphthyl)-2-butanamido-2-deoxy-β-D-glucopyranosylamine (compound 629) containing nitrogen in the glycosidic linkage, and compared it to other naphthyl and quinolinyl derivatives of GlcNAc as substrates and inhibitors. Compound 629 was a substrate for both β4GalT and β3GalT5. This suggests that properties of 612 other than the presence of the naphthyl ring alone were responsible for its inhibitory action. The results suggest a usefulness of 612 in specifically blocking the synthesis of type 2 chains and thus epitopes attached to type 2 chains. In addition, 612 potently inhibits β4GalT in cell homogenates and thus allows assaying β3GalT activity in the presence of β4GalT.

Transcriptional regulation of the vascular endothelial glycome by angiogenic and inflammatory signalling

Vascular endothelial cells undergo many molecular changes during pathological processes such as inflammation and tumour development. Tumours such as malignant lymphomas affecting bone marrow are dependent on interactions with endothelial cells for (1) site-specific homing and (2) tumour-induced angiogenesis. Modifications in glycosylation are responsible for fine-tuning of distinct endothelial surface receptors. In order to gain a comprehensive insight into the regulation of the endothelial glycome, comprising genes encoding for sugar transporters (sugar s/t), glycosyltransferases (GT), glycan-degrading enzymes (GD) and lectins (GBP), we performed gene profiling analysis of the human bone marrow-derived microvascular endothelial cell line HBMEC-60 that resembles closely in its biological behaviour primary bone marrow endothelial cells. HBMEC were activated by either angiogenic VEGF or the inflammatory cytokine TNF. Approximately 48% (207 genes) of the 432 glycome genes tested were found to be expressed in HBMEC-60 cells. Inflammatory and angiogenic signals produce different profiles of up- or down-regulated glycome genes, most prominent changes were seen under TNF stimulation in terms of signal intensity and number of alterations. Stimulation by VEGF and TNF affected primarily genes encoding for glycosyltransferases and in particular those important for terminal modulation. For instance, an enhanced alpha2,6 sialylation was observed after TNF stimulation at the transcriptional and glycan expression level whereas transcription of ST3Gal1 sialylating in alpha2,3 position was enhanced after VEGF stimulation. Transcriptional analysis of the glycome gives insights into the differential regulation of glycosylation pathways and may help to understand the functional impact of endothelial glycosylation.

Endogenous ligands for C-type lectin receptors: the true regulators of immune homeostasis

C-type lectin receptors (CLRs) have long been known as pattern-recognition receptors implicated in the recognition of pathogens by the innate immune system. However, evidence is accumulating that many CLRs are also able to recognize endogenous 'self' ligands and that this recognition event often plays an important role in immune homeostasis. In the present review, we focus on the human and mouse CLRs for which endogenous ligands have been described. Special attention is given to the signaling events initiated upon recognition of the self ligand and the regulation of glycosylation as a switch modulating CLR recognition, and therefore, immune homeostasis.

The role of beta-1,4-galactosyltransferase-I in the skin wound-healing process

Cell-surface carbohydrate chains are known to contribute to cell migration, interaction, and proliferation. beta-1,4-galactosyltransferase-I (beta-1,4-GalT-I), which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of type 2 chains in N-glycans and the core 2 branch in O-glycans. Recently, it has been reported that skin wound healing is significantly delayed in beta-1,4-GalT-I mice. However, the expression of beta-1,4-GalT-I and its biological function in the skin wound-healing process remain to be elucidated. We used real-time polymerase chain reaction to demonstrate that the expression of beta-1,4-GalT-I mRNA reached plateau values at 12 hours after skin was injured and remained elevated until 11 days after the injury. Furthermore, lectin blotting showed that beta-1,4-galactosylated carbohydrate chains were also increased after skin injury. A double-staining method combining lectin-fluorescent staining with RCA-I and immunofluorescence was first used to determine the cellular localization of beta-1,4-galactosylated carbohydrate chains. Morphological analysis showed that the chains were primarily expressed in neutrophils and partially expressed in macrophages, endothelial cells, and collagen. Our results suggest that beta-1,4-GalT-I and beta-1,4-galactosylated carbohydrate chains participate in leukocyte recruitment, angiogenesis, and collagen deposition in the skin wound-healing process.

The role of TNF-alpha and its receptors in the production of beta-1,4-galactosyltransferase I mRNA by rat primary type-2 astrocytes

beta-1,4-galactosyltransferase I (beta-1,4-GalT I) plays an important role in the synthesis of the backbone structure of adhesion molecules involved in leukocyte-endothelial cell interaction. The expression of beta-1,4-GalT I mRNA increased in primary human endothelial cells after exposure to tumor necrosis factor-alpha (TNF-alpha). In the central nervous system (CNS), astrocytes play a pivotal role in immunity as immunocompetent cells by secreting cytokines and inflammatory mediators, there are two types of astrocytes. Type-1 astrocytes can secrete TNF-alpha when stimulated with Lipopolysaccharide (LPS), while the responses of type-2 astrocytes during inflammation are unknown. So we examined the expression change of beta-1,4-GalT I mRNA in type-2 astrocytes after exposure to TNF-alpha and LPS. Real-time PCR showed that TNF-alpha or LPS affected beta-1,4-GalT I mRNA expression in a time- and dose-dependent manner. RT-PCR analysis revealed that TNFR1 and TNFR2 were present in normal untreated type-2 astrocytes, and that TNF-alpha, TNFR1 and TNFR2 increased in type-2 astrocytes after exposure to TNF-alpha or LPS. Immunocytochemistry showed that TNFR1 was expressed in the cytoplasm, nucleus and processes of normal untreated type-2 astrocytes, and distributed mainly in the cytoplasm and processes after exposure to LPS. TNFR2 was mainly expressed in the nucleus of normal untreated type-2 astrocytes, and distributed mainly in the processes of type-2 astrocytes after exposure to LPS. Both anti-TNFR1 and anti-TNFR2 antibodies suppressed beta-1,4-GalT I mRNA expression induced by TNF-alpha or LPS. From these results, we conclude that TNF-alpha signaling via both TNFR1 and TNFR2 translocated from nucleus to cytoplasm or processes is sufficient to induce beta-1,4-GalT I mRNA. In addition, we observed that not only exogenous TNF-alpha but also TNF-alpha produced by type-2 astrocytes affected beta-1,4-GalT I mRNA production in type-2 astrocytes. These results suggest that an autocrine loop involving TNF-alpha contributes to the production of beta-1,4-GalT I mRNA in response to inflammation.

Age Effect on Human Aortic Valvular Glycoproteins

BACKGROUND

The aortic valve has been the subject of many hemodynamic studies but, to our knowledge, posttranslational modification of human valve proteins has not yet been studied. Thus, the aim of this study was to determine whether any age-related changes in the protein composition of normal human aortic valves and their glycosylation pattern could be observed.

METHODS

Aortic valves harvested from male cadaveric donors free of cardiovascular diseases were divided into four age groups: I, mean age 21 years; II, 30 years; III, 41 years; IV, 51 years. Proteins were separated by SDS-PAGE and transferred to PVDF membranes. Identification of monosaccharide moieties or oligosaccharide units was performed with the use of eight lectins of narrow specificity: Galantus nivalis agglutinin, Sambucus nigra agglutinin, Maackia amurensis agglutinin, Datura stramonium agglutinin, Aleuria aurantia agglutinin, Arachis hypogeae agglutinin, Phaseolus vulgaris agglutinin, and Lycopersicon esculentum agglutinin.

RESULTS

Isolated proteins showed no age-related changes in SDS-PAGE protein profile, contrary to their glycosylation. Protein sialylation, number of tri/tetraantennary complex glycans, proteins having terminal galactose and polylactosaminyl units increased with age, whereas protein fucosylation showed the opposite relationship. Moreover, groups III and IV possessed a larger number of proteins bearing high-mannose and/or hybrid-type glycans, and the quantity of these structures seemed to change, in particular proteins, with the age of donors.

CONCLUSIONS

Our results clearly demonstrate that glycosylation profile in human aortic proteins is associated with the age of the donor.

Expression of beta-1,4-galactosyltransferase-I in rat during inflammation

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of selectin ligands such as sialy Lewis (sLe( x )) and sulfated sLe( x ). Previous studies showed that inflammatory responses of beta-1,4-GalT-I-deficient mice were impaired because of the defect in selectin-ligand biosynthesis. However, the expression of beta-1,4-GalT-I during inflammation and its biological function remains to be elucidated. Real-time PCR showed that intraperitoneal administration of LPS strongly induced beta-1,4-GalT-I mRNA expression in the lung, heart, liver, spleen, kidney, lymph node, hippocampus, and testis, as well as in the cerebral cortex. In the rat lung, liver and testis, LPS stimulation of beta-1,4-GalT-I mRNA expression is time-dependent and biphasic. Lectin-fluorescent staining with RCA-I showed that LPS induced expression of galactose-containing glycans in rat lung and liver to the higher lever. Morphology analysis observed that galactose-containing glycans and beta-1,4-GalT-I mRNA was mostly expressed in neutrophils, macrophages and endothelial cells. These findings indicated that beta-1,4-GalT-I may play an important role in the inflammation reaction.

N-glycan structures and N-glycosylation sites of mouse soluble intercellular adhesion molecule-1 revealed by MALDI-TOF and FTICR mass spectrometry

Intercellular adhesion molecule-1 (ICAM-1) is a heavily N-glycosylated transmembrane protein comprising five extracellular Ig-like domains. The soluble isoform of ICAM-1 (sICAM-1), consisting of its extracellular part, is elevated in the cerebrospinal fluid of patients with severe brain trauma. In mouse astrocytes, recombinant mouse sICAM-1 induces the production of the CXC chemokine macrophage inflammatory protein-2 (MIP-2). MIP-2 induction is glycosylation dependent, as it is strongly enhanced when sICAM-1 carries sialylated, complex-type N-glycans as synthesized by wild-type Chinese hamster ovary (CHO) cells. The present study was aimed at elucidating the N-glycosylation of mouse sICAM-1 expressed in wild-type CHO cells with regard to sialylation, N-glycan profile, and N-glycosylation sites. Ion-exchange chromatography and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) of the released N-glycans showed that sICAM-1 mostly carried di- and trisialylated complex-type N-glycans with or without one fucose. In some sialylated N-glycans, one N-acetylneuraminic acid was replaced by N-glycolylneuraminic acid, and approximately 4% carried a higher number of sialic acid residues than of antennae. The N-glycosylation sites of mouse sICAM-1 were analyzed by MALDI-Fourier transform ion cyclotron resonance (FTICR)-MS and nanoLC-ESI-FTICR-MS of tryptic digests of mouse sICAM-1 expressed in the Lec1 mutant of CHO cells. All nine consensus sequences for N-glycosylation were found to be glycosylated. These results show that the N-glycans that enhance the MIP-2-inducing activity of mouse sICAM-1 are mostly di- and trisialylated complex-type N-glycans including a small fraction carrying more sialic acid residues than antennae and that the nine N-glycosylation sites of mouse sICAM-1 are all glycosylated.

Convergent actions of I kappa B kinase beta and protein kinase C delta modulate mRNA stability through phosphorylation of 14-3-3 beta complexed with tristetraprolin

Regulation of gene expression at the level of mRNA stability is a major topic of research; however, knowledge about the regulatory mechanisms affecting the binding and function of AU-rich element (ARE)-binding proteins (AUBPs) in response to extracellular signals is minimal. The beta1,4-galactosyltransferase 1 (beta4GalT1) gene enabled us to study the mechanisms involved in binding of tristetraprolin (TTP) as the stability of its mRNA is regulated solely through one ARE bound by TTP in resting human umbilical vein endothelial cells. Here, we provide evidence that the complex formation of TTP with 14-3-3beta is required to bind beta4GalT1 mRNA and promote its decay. Furthermore, upon tumor necrosis factor alpha stimulation, the activation of both Ikappabeta kinase and protein kinase Cdelta is involved in the phosphorylation of 14-3-3beta on two serine residues, paralleled by release of binding of TTP and 14-3-3beta from beta4GalT1 mRNA, nuclear sequestration of TTP, and beta4GalT1 mRNA stabilization. Thus, a key mechanism regulating mRNA binding and function of the destabilizing AUBP TTP involves the phosphorylation status of 14-3-3beta.