Collagen Fragments Produced in Cancer Mediate T Cell Suppression Through Leukocyte-Associated Immunoglobulin-Like Receptor 1.

The tumor microenvironment (TME) is a complex structure comprised of tumor, immune and stromal cells, vasculature, and extracellular matrix (ECM). During tumor development, ECM homeostasis is dysregulated. Collagen remodeling by matrix metalloproteinases (MMPs) generates specific collagen fragments, that can be detected in the circulation of cancer patients and correlate with poor disease outcome. Leukocyte-Associated Immunoglobulin-like Receptor-1 (LAIR-1) is an inhibitory collagen receptor expressed on immune cells in the TME and in the circulation. We hypothesized that in addition to ECM collagen, collagen fragments produced in cancer can mediate T cell immunosuppression through LAIR-1. Our analyses of TCGA datasets show that cancer patients with high tumor mRNA expression of MMPs, collagen I and LAIR-1 have worse overall survival. We show that in vitro generated MMP1 or MMP9 collagen I fragments bind to and trigger LAIR-1. Importantly, LAIR-1 triggering by collagen I fragments inhibits CD3 signaling and IFN-γ secretion in a T cell line. LAIR-2 is a soluble homologue of LAIR-1 with higher affinity for collagen and thereby acts as a decoy receptor. Fc fusion proteins of LAIR-2 have potential as cancer immunotherapeutic agents and are currently being tested in clinical trials. We demonstrate that collagen fragment-induced inhibition of T cell function could be reversed by LAIR-2 fusion proteins. Overall, we show that collagen fragments produced in cancer can mediate T cell suppression through LAIR-1, potentially contributing to systemic immune suppression. Blocking the interaction of LAIR-1 with collagen fragments could be an added benefit of LAIR-1-directed immunotherapy.

B7-H4 Modulates Regulatory CD4+ T Cell Induction and Function via Ligation of a Semaphorin 3a/Plexin A4/Neuropilin-1 Complex.

The potent immune regulatory function of an agonistic B7-H4-Ig fusion protein (B7-H4Ig) has been demonstrated in multiple experimental autoimmune models; however, the identity of a functional B7-H4 receptor remained unknown. The biological activity of B7-H4 is associated with decreased inflammatory CD4+ T cell responses as supported by a correlation between B7-H4-expressing tumor-associated macrophages and Foxp3+ T cells within the tumor microenvironment. Recent data indicate that members of the semaphorin (Sema)/plexin/neuropilin (Nrp) family of proteins both positively and negatively modulate immune cell function. In this study, we show that B7-H4 binds the soluble Sema family member Sema3a. Additionally, B7-H4Ig-induced inhibition of inflammatory CD4+ T cell responses is lost in both Sema3a functional mutant mice and mice lacking Nrp-1 expression in Foxp3+ T cells. These findings indicate that B7-H4Ig binds to Sema3a, which acts as a functional bridge to stimulate an Nrp-1/Plexin A4 heterodimer to form a functional immunoregulatory receptor complex resulting in increased levels of phosphorylated PTEN and enhanced regulatory CD4+ T cell number and function.

Diabetic hyperglycaemia activates CaMKII and arrhythmias by O-linked glycosylation.

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is an enzyme with important regulatory functions in the heart and brain, and its chronic activation can be pathological. CaMKII activation is seen in heart failure, and can directly induce pathological changes in ion channels, Ca(2+) handling and gene transcription. Here, in human, rat and mouse, we identify a novel mechanism linking CaMKII and hyperglycaemic signalling in diabetes mellitus, which is a key risk factor for heart and neurodegenerative diseases. Acute hyperglycaemia causes covalent modification of CaMKII by O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAc modification of CaMKII at Ser 279 activates CaMKII autonomously, creating molecular memory even after Ca(2+) concentration declines. O-GlcNAc-modified CaMKII is increased in the heart and brain of diabetic humans and rats. In cardiomyocytes, increased glucose concentration significantly enhances CaMKII-dependent activation of spontaneous sarcoplasmic reticulum Ca(2+) release events that can contribute to cardiac mechanical dysfunction and arrhythmias. These effects were prevented by pharmacological inhibition of O-GlcNAc signalling or genetic ablation of CaMKIIδ. In intact perfused hearts, arrhythmias were aggravated by increased glucose concentration through O-GlcNAc- and CaMKII-dependent pathways. In diabetic animals, acute blockade of O-GlcNAc inhibited arrhythmogenesis. Thus, O-GlcNAc modification of CaMKII is a novel signalling event in pathways that may contribute critically to cardiac and neuronal pathophysiology in diabetes and other diseases.

O-GlcNAcomics--Revealing roles of O-GlcNAcylation in disease mechanisms and development of potential diagnostics.

O-linked-ß-N-acetylglucosamine (O-GlcNAc) is a dynamic PTM of the 3'-hydroxyl groups of serine or threonine residues of nuclear, cytoplasmic, and mitochondrial proteins. The cycling of this modification is regulated in response to nutrients, stress, and other extracellular stimuli by the catalytic activities of O-GlcNAc transferase and O-GlcNAcase. O-GlcNAc is functionally similar to phosphorylation and has been demonstrated to play critical roles in numerous biological processes, including cell signaling, transcription, and disease etiology. Since its discovery nearly 30 years ago, studies have demonstrated that the O-GlcNAc is highly abundant and widespread, like phosphorylation however, the development of methodologies to study O-GlcNAc at the site level has been challenging. Recently, a number of studies have overcome these challenges and describe new tagging, enrichment, and mass spectrometric-based approaches to study O-GlcNAc in terms of its site identification, stoichiometry, and dynamics on proteins. The development of these methods are key for elucidation of O-GlcNAc's functional crosstalk with phosphorylation and other PTMs, and will serve to provide the necessary information for the development of site-specific antibodies, which will aid in the determination of a particular protein's site-specific function. In this review, we describe these methods and summarize results obtained from them demonstrating the roles of O-GlcNAc in diabetes, cancer, Alzheimer's, and in learning and memory, while also describing how these new strategies have implicated O-GlcNAc as a potential diagnostic for the screening of patients for prediabetes.

Glycomics hits the big time.

Cells run on carbohydrates. Glycans, sequences of carbohydrates conjugated to proteins and lipids, are arguably the most abundant and structurally diverse class of molecules in nature. Recent advances in glycomics reveal the scope and scale of their functional roles and their impact on human disease.

Cross-talk between GlcNAcylation and phosphorylation: roles in insulin resistance and glucose toxicity.

O-linked beta-N-acetylglucosamine (O-GlcNAc) is a dynamic posttranslational modification that, analogous to phosphorylation, cycles on and off serine and/or threonine hydroxyl groups. Cycling of O-GlcNAc is regulated by the concerted actions of O-GlcNAc transferase and O-GlcNAcase. GlcNAcylation is a nutrient/stress-sensitive modification that regulates proteins involved in a wide array of biological processes, including transcription, signaling, and metabolism. GlcNAcylation is involved in the etiology of glucose toxicity and chronic hyperglycemia-induced insulin resistance, a major hallmark of type 2 diabetes. Several reports demonstrate a strong positive correlation between GlcNAcylation and the development of insulin resistance. However, recent studies suggest that inhibiting GlcNAcylation does not prevent hyperglycemia-induced insulin resistance, suggesting that other mechanisms must also be involved. To date, proteomic analyses have identified more than 600 GlcNAcylated proteins in diverse functional classes. However, O-GlcNAc sites have been mapped on only a small percentage (<15%) of these proteins, most of which were isolated from brain or spinal cord tissue and not from other metabolically relevant tissues. Mapping the sites of GlcNAcylation is not only necessary to elucidate the complex cross-talk between GlcNAcylation and phosphorylation but is also key to the design of site-specific mutational studies and necessary for the generation of site-specific antibodies, both of which will help further decipher O-GlcNAc's functional roles. Recent technical advances in O-GlcNAc site-mapping methods should now finally allow for a much-needed increase in site-specific analyses to address the functional significance of O-GlcNAc in insulin resistance and glucose toxicity as well as other major biological processes.

Using a 3-O-sulfated heparin octasaccharide to inhibit the entry of herpes simplex virus type 1.

Heparan sulfate (HS) is a highly sulfated polysaccharide and is present in large quantities on the cell surface and in the extracellular matrix. Herpes simplex virus type 1 (HSV-1) utilizes a specialized cell surface HS, known as 3-O-sulfated HS, as an entry receptor to establish infection. Here, we exploit an approach to inhibiting HSV-1 infection by using a 3-O-sulfated octasaccharide, mimicking the active domain of the entry receptor. The 3-O-sulfated octasaccharide was synthesized by incubating a heparin octasaccharide (3-OH octasaccharide) with HS 3-O-sulfotransferase isoform 3. The resultant 3-O-sulfated octasaccharide has a structure of Delta UA2S-GlcNS6S-IdoUA2S-GlcNS6S-IdoUA2S-GlcNS3S6S-IdoUA2S-GlcNS6S (where Delta UA is 4-deoxy-alpha-L-threo-hex-4-enopyranosyluronic acid, GlcN is D-glucosamine, and IdoUA is L-iduronic acid). Results from cell-based assays revealed that the 3-O-sulfated octasaccharide has stronger activity in blocking HSV-1 infection than that of the 3-OH octasaccharide, suggesting that the inhibition of HSV-1 infection requires a unique sulfation moiety. Our results suggest the feasibility of inhibiting HSV-1 infection by blocking viral entry with a specific oligosaccharide.

Soluble 3-O-sulfated heparan sulfate can trigger herpes simplex virus type 1 entry into resistant Chinese hamster ovary (CHO-K1) cells.

Herpes simplex virus type 1 (HSV-1) interaction with glycoprotein D (gD) receptors facilitates virus entry into cells. Chinese hamster ovary (CHO-K1) cells lacking cellular receptors allow virus to attach, but not to enter, implying a role for receptors during the post-attachment (entry) phase of HSV-1 infection. Here, it is shown that the presence of soluble heparan sulfate (HS) modified by 3-O-sulfotransferase-3 (3-OST-3), but not by 3-OST-1, triggered HSV-1 entry into resistant CHO-K1 cells. It was further demonstrated that a CHO-K1 mutant deficient in glycosaminoglycan synthesis became susceptible to entry when spinoculated in the presence of 3-OST-3-modified soluble HS, indicating that the role of the gD receptor is to trigger entry rather than cell attachment. In separate experiments, 3-OST-3-modified soluble HS also triggered fusion of HSV-1 glycoprotein-expressing cells with CHO-K1 cells. Taken together, these results show that association of gD with cell surface-bound receptor is not essential for HSV-1 entry and spread.

Characterization of a heparan sulfate octasaccharide that binds to herpes simplex virus type 1 glycoprotein D.

Herpes simplex virus type 1 utilizes cell surface heparan sulfate as receptors to infect target cells. The unique heparan sulfate saccharide sequence offers the binding site for viral envelope proteins and plays critical roles in assisting viral infections. A specific 3-O-sulfated heparan sulfate is known to facilitate the entry of herpes simplex virus 1 into cells. The 3-O-sulfated heparan sulfate is generated by the heparan sulfate d-glucosaminyl-3-O-sulfotransferase isoform 3 (3-OST-3), and it provides binding sites for viral glycoprotein D (gD). Here, we report the purification and structural characterization of an oligosaccharide that binds to gD. The isolated gD-binding site is an octasaccharide, and has a binding affinity to gD around 18 microm, as determined by affinity coelectrophoresis. The octasaccharide was prepared and purified from a heparan sulfate oligosaccharide library that was modified by purified 3-OST-3 enzyme. The molecular mass of the isolated octasaccharide was determined using both nanoelectrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry. The results from the sequence analysis suggest that the structure of the octasaccharide is a heptasulfated octasaccharide. The proposed structure of the octasaccharide is DeltaUA-GlcNS-IdoUA2S-GlcNAc-UA2S-GlcNS-IdoUA2S-GlcNH(2)3S6S. Given that the binding of 3-O-sulfated heparan sulfate to gD can mediate viral entry, our results provide structural information about heparan sulfate-assisted viral entry.