Ameliorating skin-homing receptors on malignant T cells with a fluorosugar analog of N-acetylglucosamine: P-selectin ligand is a more sensitive target than E-selectin ligand

sLeX Expression Delineates Distinct Functional Subsets of Human Blood Central and Effector Memory T Cells

Sialyl Lewis X (sLeX) regulates T cell trafficking from the vasculature into skin and sites of inflammation, thereby playing a critical role in immunity. In healthy persons, only a small proportion of human blood T cells express sLeX, and their function is not fully defined. Using a combination of biochemical and functional studies, we find that human blood sLeX+CD4+T cells comprise a subpopulation expressing high levels of Th2 and Th17 cytokines, chemokine receptors CCR4 and CCR6, and the transcription factors GATA-3 and RORγT. Additionally, sLeX+CD4+T cells exclusively contain the regulatory T cell population (CD127lowCD25high and FOXP3+) and characteristically display immune-suppressive molecules, including the coinhibitor receptors PD-1 and CTLA-4. Among CD8+T cells, sLeX expression distinguishes a subset displaying low expression of cytotoxic effector molecules, perforin and granzyme β, with reduced degranulation and CD57 expression and, consistently, marginal cytolytic capacity after TCR engagement. Furthermore, sLeX+CD8+T cells present a pattern of features consistent with Th cell-like phenotype, including release of pertinent Tc2 cytokines and elevated expression of CD40L. Together, these findings reveal that sLeX display is associated with unique functional specialization of both CD4+ and CD8+T cells and indicate that circulating T cells that are primed to migrate to lesional sites at onset of inflammation are not poised for cytotoxic function.

Cancer immunotherapy needs to learn how to stick to its guns

Cancer immunotherapy and its budding effectiveness at improving patient outcomes has revitalized our hope to fight cancer in a logical and safe manner. Immunotherapeutic approaches to reengage the immune system have largely focused on reversing immune checkpoint inhibitor pathways, which suppress the antitumor response. Although these approaches have generated much excitement, they still lack absolute success. Interestingly, newly described host-tumor sugar chains (glycosylations) and glycosylation-binding proteins (lectins) play key roles in evading the immune system to determine cancer progression. In this issue of the JCI, Nambiar et al. used patient head and neck tumors and a mouse model system to investigate the role of galactose-binding lectin 1 (Gal1) in immunotherapy resistance. The authors demonstrated that Gal1 can affect immune checkpoint inhibitor therapy by increasing immune checkpoint molecules and immunosuppressive signaling in the tumor. Notably, these results suggest that targeting a tumor's glycobiological state will improve treatment efficacy.

Fluorescent Multiplex Cell Rolling Assay: Simultaneous Capturing up to Seven Samples in Real-Time Using Spectral Confocal Microscopy

The parallel plate flow chamber assay is widely utilized to study physiological cell-cell adhesive interactions under dynamic flow that mimics the bloodstream. In this technique, the cells are perfused under defined shear stresses over a monolayer of endothelial cells (expressing homing molecules, e.g., selectins) or a surface (expressing recombinant homing molecules). However, with the need to study multiple samples and multiple parameters per sample, using a traditional bright-field microscope-based flow assay allows only one sample at a time to be analyzed, resulting in high interexperiment variability, the need for normalization, waste of materials, and significant consumption of time. We developed a multiplexing approach using a three-color fluorescence staining method, which allowed for up to seven different combination signatures to be run at one time. Using this fluorescent multiplex cell rolling (FMCR) assay, each sample is labeled with a different signature of emission wavelengths and mixed with other samples just minutes before the flow run. Subsequently, real-time images are acquired in a single pass using a line-scanning spectral confocal microscope. To illustrate the glycan-dependent binding of E-selectin, a central molecule in cell migration, to its glycosylated ligands expressed on myeloid-leukemic cells in flow, the FMCR assay was used to analyze E-selectin-ligand interactions following the addition (fucosyltransferase-treatment) or removal (deglycosylation) of key glycans on the flowing cells. The FMCR assay allowed us to analyze the cell-adhesion events from these different treatment conditions simultaneously in a competitive manner and to calculate differences in rolling frequency, velocity, and tethering capability of cells under study.

Inhibition of Delta-induced Notch signaling using fucose analogs

Notch is a cell-surface receptor that controls cell-fate decisions and is regulated by O-glycans attached to epidermal growth factor-like (EGF) repeats in its extracellular domain. Protein O-fucosyltransferase 1 (Pofut1) modifies EGF repeats with O-fucose and is essential for Notch signaling. Constitutive activation of Notch signaling has been associated with a variety of human malignancies. Therefore, tools that inhibit Notch activity are being developed as cancer therapeutics. To this end, we screened L-fucose analogs for their effects on Notch signaling. Two analogs, 6-alkynyl and 6-alkenyl fucose, were substrates of Pofut1 and were incorporated directly into Notch EGF repeats in cells. Both analogs were potent inhibitors of binding to and activation of Notch1 by Notch ligands Dll1 and Dll4, but not by Jag1. Mutagenesis and modeling studies suggest that incorporation of the analogs into EGF8 of Notch1 markedly reduces the ability of Delta ligands to bind and activate Notch1.

Recent advances toward the development of inhibitors to attenuate tumor metastasis via the interruption of lectin-ligand interactions

Aberrant glycosylation is a well-recognized phenomenon that occurs on the surface of tumor cells, and the overexpression of a number of ligands (such as TF, sialyl Tn, and sialyl Lewis X) has been correlated to a worse prognosis for the patient. These unique carbohydrate structures play an integral role in cell-cell communication and have also been associated with more metastatic cancer phenotypes, which can result from binding to lectins present on cell surfaces. The most well studied metastasis-associated lectins are the galectins and selectins, which have been correlated to adhesion, neoangiogenesis, and immune-cell evasion processes. In order to slow the rate of metastatic lesion formation, a number of approaches have been successfully developed which involve interfering with the tumor lectin-substrate binding event. Through the generation of inhibitors, or by attenuating lectin and/or carbohydrate expression, promising results have been observed both in vitro and in vivo. This article briefly summarizes the involvement of lectins in the metastatic process and also describes different approaches used to prevent these undesirable carbohydrate-lectin binding events, which should ultimately lead to improvement in current cancer therapies.

Leveraging fluorinated glucosamine action to boost antitumor immunity

N-acetyllactosaminyl glycans are key regulators of the vitality and effector function of antitumor T cells. When galectin-1 (Gal-1) binds N-acetyllactosamines on select membrane glycoproteins on antitumor T cells, these cells either undergo apoptosis or become immunoregulatory. Methods designed to antagonize expression or function of these N-acetyllactosamines on N-glycans and O-glycans have thus intensified. Since tumors can produce an abundance of Gal-1, Gal-1 is considered a critical factor for protecting tumor cells from T cell-mediated antitumor activity. Recent efforts have capitalized on the anti-N-acetyllactosamine action of fluorinated glucosamines to treat antitumor T cells, resulting in diminished Gal-1-binding and higher antitumor T cell levels. In this perspective, the prospect of fluorinated glucosamines in eliminating N-acetyllactosamines on antitumor T cells to boost antitumor immunity is presented.

Global metabolic inhibitors of sialyl- and fucosyltransferases remodel the glycome

Despite the fundamental roles of sialyl- and fucosyltransferases in mammalian physiology, there are few pharmacological tools to manipulate their function in a cellular setting. Although fluorinated analogs of the donor substrates are well-established transition state inhibitors of these enzymes, they are not membrane permeable. By exploiting promiscuous monosaccharide salvage pathways, we show that fluorinated analogs of sialic acid and fucose can be taken up and metabolized to the desired donor substrate-based inhibitors inside the cell. Because of the existence of metabolic feedback loops, they also act to prevent the de novo synthesis of the natural substrates, resulting in a global, family-wide shutdown of sialyl- and/or fucosyltransferases and remodeling of cell-surface glycans. As an example of the functional consequences, the inhibitors substantially reduce expression of the sialylated and fucosylated ligand sialyl Lewis X on myeloid cells, resulting in loss of selectin binding and impaired leukocyte rolling.

Evaluation of analogues of GalNAc as substrates for enzymes of the mammalian GalNAc salvage pathway

Changes in glycosylation are correlated to disease and associated with differentiation processes. Experimental tools are needed to investigate the physiological implications of these changes either by labeling of the modified glycans or by blocking their biosynthesis. N-Acetylgalactosamine (GalNAc) is a monosaccharide widely encountered in glycolipids, proteoglycans, and glycoproteins; once taken up by cells it can be converted through a salvage pathway to UDP-GalNAc, which is further used by glycosyltransferases to build glycans. In order to find new reporter molecules able to integrate into cellular glycans, synthetic analogues of GalNAc were prepared and tested as substrates of both enzymes acting sequentially in the GalNAc salvage pathway, galactokinase 2 (GK2) and uridylpyrophosphorylase AGX1. Detailed in vitro assays identified the GalNAc analogues that can be transformed into sugar nucleotides and revealed several bottlenecks in the pathway: a modification on C6 is not tolerated by GK2; AGX1 can use all products of GK2 although with various efficiencies; and all analogues transformed into UDP-GalNAc analogues except those with alterations on C4 are substrates for the polypeptide GalNAc transferase T1. Besides, all analogues that could be incorporated in vitro into O-glycans were also integrated into cellular O-glycans as attested by their detection on the cell surface of CHO-ldlD cells. Altogether our results show that GalNAc analogues can help to better define structural requirements of the donor substrates for the enzymes involved in GalNAc metabolism, and those that are incorporated into cells will prove valuable for the development of novel diagnostic and therapeutic tools.

Metabolic inhibition of galectin-1-binding carbohydrates accentuates antitumor immunity

Galectin-1 (Gal-1) has been shown to play a major role in tumor immune escape by inducing apoptosis of effector leukocytes and correlating with tumor aggressiveness and disease progression. Thus, targeting the Gal-1/Gal-1 ligand axis represents a promising cancer therapeutic approach. Here, to test the Gal-1-mediated tumor immune evasion hypothesis and demonstrate the importance of Gal-1-binding N-acetyllactosamines in controlling the fate and function of antitumor immune cells, we treated melanoma- or lymphoma-bearing mice with peracetylated 4-fluoro-glucosamine (4-F-GlcNAc), a metabolic inhibitor of N-acetyllactosamine biosynthesis, and analyzed tumor growth and immune profiles. We found that 4-F-GlcNAc spared Gal-1-mediated apoptosis of T cells and natural killer (NK) cells by decreasing their expression of Gal-1-binding determinants. 4-F-GlcNAc enhanced tumor lymphocytic infiltration and promoted elevations in tumor-specific cytotoxic T cells and IFN-γ levels, while lowering IL-10 production. Collectively, our data suggest that metabolic lowering of Gal-1-binding N-acetyllactosamines may attenuate tumor growth by boosting antitumor immune cell levels, representing a promising approach for cancer immunotherapy.

Metabolic oligosaccharide engineering: implications for selectin-mediated adhesion and leukocyte extravasation

Metabolic oligosaccharide engineering is an emerging technology wherein non-natural monosaccharide analogs are exogenously supplied to living cells and are biosynthetically incorporated into cell surface glycans. A recently reported application of this methodology employs fluorinated analogs of ManNAc, GlcNAc, and GalNAc to modulate selectin-mediated adhesion associated with leukocyte extravasation and cancer cell metastasis. This monograph outlines possible mechanisms underlying the altered adhesion observed in analog-treated cells; these range from the most straightforward explanation (e.g., structural changes to the selectin ligands ablate interaction with their receptors) to the alternative mechanism where the analogs inhibit or otherwise perturb ligand production to more indirect mechanisms (e.g., changes to the biophysical properties of the selectin binding partner, the nanoenviroment of the binding partners, or the entire cell surface).

Peracetylated 4-fluoro-glucosamine reduces the content and repertoire of N- and O-glycans without direct incorporation

Prior studies have shown that treatment with the peracetylated 4-fluorinated analog of glucosamine (4-F-GlcNAc) elicits anti-skin inflammatory activity by ablating N-acetyllactosamine (LacNAc), sialyl Lewis X (sLe(X)), and related lectin ligands on effector leukocytes. Based on anti-sLe(X) antibody and lectin probing experiments on 4-F-GlcNAc-treated leukocytes, it was hypothesized that 4-F-GlcNAc inhibited sLe(X) formation by incorporating into LacNAc and blocking the addition of galactose or fucose at the carbon 4-position of 4-F-GlcNAc. To test this hypothesis, we determined whether 4-F-GlcNAc is directly incorporated into N- and O-glycans released from 4-F-GlcNAc-treated human sLe(X) (+) T cells and leukemic KG1a cells. At concentrations that abrogated galectin-1 (Gal-1) ligand and E-selectin ligand expression and related LacNAc and sLe(X) structures, MALDI-TOF and MALDI-TOF/TOF mass spectrometry analyses showed that 4-F-GlcNAc 1) reduced content and structural diversity of tri- and tetra-antennary N-glycans and of O-glycans, 2) increased biantennary N-glycans, and 3) reduced LacNAc and sLe(X) on N-glycans and on core 2 O-glycans. Moreover, MALDI-TOF MS did not reveal any m/z ratios relating to the presence of fluorine atoms, indicating that 4-F-GlcNAc did not incorporate into glycans. Further analysis showed that 4-F-GlcNAc treatment had minimal effect on expression of 1200 glycome-related genes and did not alter the activity of LacNAc-synthesizing enzymes. However, 4-F-GlcNAc dramatically reduced intracellular levels of uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc), a key precursor of LacNAc synthesis. These data show that Gal-1 and E-selectin ligand reduction by 4-F-GlcNAc is not caused by direct 4-F-GlcNAc glycan incorporation and consequent chain termination but rather by interference with UDP-GlcNAc synthesis.

C2-O-sLeX glycoproteins are E-selectin ligands that regulate invasion of human colon and hepatic carcinoma cells

Similar to mechanisms of recruitment of activated leukocytes to inflamed tissues, selectins mediate adhesion and extravasation of circulating cancer cells. Our objective was to determine whether sialyl Lewis X modified core 2 O-glycans (C2-O-sLe^X) present on colon and hepatic carcinoma cells promote their adhesion and invasion. We examined membrane expression of C2-O-sLe^X, selectin binding, invasion of human colon and hepatic carcinoma cell lines, and mRNA levels of alpha-2,3 fucosyltransferase (FucT-III) and core 2 beta-1,6 N-acetylglucosaminyltransferase (C2GnT1) genes, necessary for C2-O-sLe^X synthesis, by quantitative reverse-transcriptase (RT) PCR. Synthesis of core 2 branched O-glycans decorated by sLe^X is dependent on C2GnT1 function and thus we determined enzyme activity of C2GnT1. The cell lines that expressed C2GnT1 and FucT-III mRNA by quantitative RT-PCR were highly positive for C2-O-sLe^X by flow cytometry, and colon carcinoma cells possessed highly active C2GnT1 enzyme. Cells bound avidly to E-selection but not to P- and L-selectin. Gene knock-down of C2GnT1 in colon and hepatic carcinoma cells using short hairpin RNAs (shRNA) resulted in a 40–90% decrease in C2-O-sLe^X and a 30–50% decrease in E-selectin binding compared to control cells. Invasion of hepatic and colon carcinoma cells containing C2GnT1 shRNA was significantly reduced compared to control cells in Matrigel assays and C2GnT1 activity was down-regulated in the latter cells. The sLe^X epitope was predominantly distributed on core 2 O-glycans on colon and hepatic carcinoma cells. Our findings indicate that C2GnT1 gene expression and the resulting C2-O-sLe^X carbohydrates produced mediate the adhesive and invasive behaviors of human carcinomas which may influence their metastatic potential.

Hill CA. The Novel Carbohydrate Tumor Antigen C2-O-sLex Is Upregulated in Canine Gastric Carcinomas

Sialyl Lewis x–modified core 2 branched O-glycans (C2-O-sLex) on human leukocytes mediate much higher-affinity adhesion to selectins on activated vascular endothelium than does sialyl Lewis x on other structures. In some canine and human carcinomas, high expression of sLex-decorated carbohydrates has been associated with metastasis and, in humans, a poor prognosis, but detection in canine gastric carcinomas is unreported. The authors hypothesized that these carbohydrates are highly expressed in more malignant types of canine gastric carcinomas, they promote metastasis, and they are associated with a poorer prognosis for dogs. The objectives were to determine the presence and importance of C2-O-sLex expression in canine gastric carcinomas. Routine histological sections of 16 canine gastric carcinomas were categorized on the basis of 3 classification schemes: World Health Organization, Lauren, and Goseki. Serial sections were stained with antibodies directed against C2-O-sLex (CHO-131 monoclonal antibody), cytokeratin (Lu-5 monoclonal antibody), and stains to detect neutral and acid mucins (periodic acid–Schiff and alcian blue). Whereas normal gastric mucosal epithelial cells were negative for C2-O-sLex, 56% of the tumors examined were positive for C2-O-sLex. Importantly, the majority of more poorly differentiated tumor types had more numerous and larger intensely stained areas of C2-O-sLex expression compared with moderate to well-differentiated tumor types. Signet ring–type carcinomas had markedly higher distribution and intensity of periodic acid–Schiff and alcian blue staining than did tubular carcinomas. These findings suggest that C2-O-sLex is a tumor-associated antigen that may play a role in the invasiveness and metastatic potential of certain types of canine gastric carcinomas.

Fluorinated per-acetylated GalNAc metabolically alters glycan structures on leukocyte PSGL-1 and reduces cell binding to selectins

Novel strategies to control the binding of adhesion molecules belonging to the selectin family are required for the treatment of inflammatory diseases. We tested the possibility that synthetic monosaccharide analogs can compete with naturally occurring sugars to alter the O-glycan content on human leukocyte cell surface selectin-ligand, P-selectin glycoprotein ligand-1 (PSGL-1). Resulting reduction in the sialyl Lewis-X-bearing epitopes on this ligand may reduce cell adhesion. Consistent with this hypothesis, 50muM per-acetylated 4F-GalNAc added to the growth media of promyelocytic HL-60 cells reduced the expression of the cutaneous lymphocyte associated-antigen (HECA-452 epitope) by 82% within 2 cell doubling cycles. Cell binding to all 3 selectins (L-, E-, and P-selectin) was reduced in vitro. 4F-GalNAc was metabolically incorporated into PSGL-1, and this was accompanied by an approximately 20% reduction in PSGL-1 glycan content. A 70% to 85% reduction in HECA-452 binding epitope and N-acetyl lactosamine content in PSGL-1 was also noted on 4F-GalNAc addition. Intravenous 4F-GalNAc infusion reduced leukocyte migration to the peritoneum in a murine model of thioglycolate-induced peritonitis. Thus, the compound has pharmacologic activity. Overall, the data suggest that 4F-GalNAc may be applied as a metabolic inhibitor to reduce O-linked glycosylation, sialyl Lewis-X formation, and leukocyte adhesion via the selectins.

Cutaneous lymphocyte-associated antigen (CLA) T cells up-regulate P-selectin ligand expression upon their activation

Memory T cells expressing CLA occur in humans and accumulate in normal and inflamed skin. These cells uniformly bind to the vascular adhesion molecule E-selectin, yet only a subset binds to P-selectin. The latter cells are distinguished by the mAb CHO-131, and are enriched in psoriasis lesions. Activated T cells up-regulate CLA expression, but little is currently known about their binding to P-selectin. We observed that CLA(+) CD4(+) T cells derived from stimulated naive T cells uniformly express the CHO-131 epitope. This occurred as well upon the restimulation of memory CLA(+) CD4(+) T cells. The latter cells also expressed higher levels of PSGL-1 modified by P-selectin glycan ligands; C2GlcNAcT-1 mRNA, a glycosyltransferase critical for such glycan synthesis; and more uniformly bound to P-selectin. Our findings thus indicate that unlike memory CLA(+) CD4(+) T cells, when activated these cells can broadly bind to P-selectin, suggesting a more diverse tissue trafficking capacity.

Chemical approaches to perturb, profile, and perceive glycans

Glycosylation is an essential form of post-translational modification that regulates intracellular and extracellular processes. Regrettably, conventional biochemical and genetic methods often fall short for the study of glycans, because their structures are often not precisely defined at the genetic level. To address this deficiency, chemists have developed technologies to perturb glycan biosynthesis, profile their presentation at the systems level, and perceive their spatial distribution. These tools have identified potential disease biomarkers and ways to monitor dynamic changes to the glycome in living organisms. Still, glycosylation remains the underexplored frontier of many biological systems. In this Account, we focus on research in our laboratory that seeks to transform the study of glycan function from a challenge to routine practice.

In studies of proteins and nucleic acids, functional studies have often relied on genetic manipulations to perturb structure. Though not directly subject to mutation, we can determine glycan structure−function relationships by synthesizing defined glycoconjugates or by altering natural glycosylation pathways. Chemical syntheses of uniform glycoproteins and polymeric glycoprotein mimics have facilitated the study of individual glycoconjugates in the absence of glycan microheterogeneity. Alternatively, selective inhibition or activation of glycosyltransferases or glycosidases can define the biological roles of the corresponding glycans. Investigators have developed tools including small molecule inhibitors, decoy substrates, and engineered proteins to modify cellular glycans. Current approaches offer a precision approaching that of genetic control.

Genomic and proteomic profiling form a basis for biological discovery. Glycans also present a rich matrix of information that adapts rapidly to changing environs. Glycomic and glycoproteomic analyses via microarrays and mass spectrometry are beginning to characterize alterations in glycans that correlate with disease. These approaches have already identified several cancer biomarkers. Metabolic labeling can identify recently synthesized glycans and thus directly track glycan dynamics. This approach can highlight changes in physiology or environment and may be more informative than steady-state analyses. Together, glycomic and metabolic labeling techniques provide a comprehensive description of glycosylation as a foundation for hypothesis generation.

Direct visualization of proteins via the green fluorescent protein (GFP) and its congeners has revolutionized the field of protein dynamics. Similarly, the ability to perceive the spatial organization of glycans could transform our understanding of their role in development, infection, and disease progression. Fluorescent tagging in cultured cells and developing organisms has revealed important insights into the dynamics of these structures during growth and development. These results have highlighted the need for additional imaging probes.

The high affinity selectin glycan ligand C2-O-sLex and mRNA transcripts of the core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT1) gene are highly expressed in human colorectal adenocarcinomas

Background

The metastasis of cancer cells and leukocyte extravasation into inflamed tissues share common features. Specialized carbohydrates modified with sialyl Lewis x (sLe^x) antigens on leukocyte membranes are ligands for selectin adhesion molecules on activated vascular endothelial cells at inflammatory sites. The activity of the enzyme core 2 β1,6 N-acetylglucosaminyltransferase (C2GnT1) in leukocytes greatly increases their ability to bind to endothelial selectins. C2GnT1 is essential for the synthesis of core 2-branched O-linked carbohydrates terminated with sLe^x (C2-O-sLe^x). Our goal was to determine the expression profiles of C2-O-sLe^x in the malignant progression and metastasis of colorectal adenocarcinomas. The well characterized CHO-131 monoclonal antibody (mAb) specifically recognizes C2-O-sLe^x present in human leukocytes and carcinoma cells. Using CHO-131 mAb, we investigated whether C2-O-sLe^x was present in 113 human primary colorectal adenocarcinomas, 10 colorectal adenomas, 46 metastatic liver tumors, 28 normal colorectal tissues, and 5 normal liver tissues by immunohistochemistry. We also examined mRNA levels of the enzyme core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT1) in 20 well, 15 moderately, and 2 poorly differentiated colorectal adenocarcinomas, and in 5 normal colorectal tissues by using quantitative real-time polymerase chain reactions (RT-PCR).

Results

We observed high reactivity with CHO-131 mAb in approximately 70% of colorectal carcinomas and 87% of metastatic liver tumors but a lack of reactivity in colorectal adenomas and normal colonic and liver tissues. Positive reactivity with CHO-131 mAb was very prominent in neoplastic colorectal glands of well to moderately differentiated adenocarcinomas. The most intense staining with CHO-131 mAb was observed at the advancing edge of tumors with the deepest invasive components.

Finally, we analyzed C2GnT1 mRNA levels in 37 colorectal adenocarcinomas and 5 normal colorectal tissues by RT-PCR. Significantly, we observed a greater than 15-fold increase in C2GnT1 mRNA levels in colorectal adenocarcinomas compared to normal colorectal tissues.

Conclusion

C2-O-sLe^x, detected by the CHO-131 mAb, is a tumor associated antigen whose expression is highly upregulated in colorectal adenocarcinomas and metastatic liver tumors compared to normal tissues. C2-O-sLe^x is a potentially useful early predictor of metastasis.

Analysis of physiologic E-selectin-mediated leukocyte rolling on microvascular endothelium

E-selectin is a type-1 membrane protein on microvascular endothelial cells that helps initiate recruitment of circulating leukocytes to cutaneous, bone and inflamed tissues. E-selectin expression is constitutive on dermal and bone microvessels and is inducible by pro-inflammatory cytokines, such as IL-1α/ and TNF-α, on microvessels in inflamed tissues. This lectin receptor mediates weak binding interactions with carbohydrate counter-receptor ligands on circulating leukocytes, which results in a characteristic rolling behavior. Because these interactions precede more stable adhesive events and diapedesis activity, characterization of leukocyte rolling activity and identification of leukocyte E-selectin ligands have been major goals in studies of leukocyte trafficking and inflammation and in the development of anti-inflammatory therapeutics (1-5). The intent of this report is to provide a visual, comprehensive description of the most widely-used technology for studying E-selectin E-selectin ligand interactions under physiologic blood flow conditions. Our laboratory in conjunction with the Harvard Skin Disease Research Center uses a state-of-the-art parallel-plate flow chamber apparatus accompanied by digital visualization and new recording software, NIS-Elements. This technology allows us to analyze adhesion events in real time for onscreen visualization as well as record rolling activity in a video format. Cell adhesion parameters, such as rolling frequency, shear resistance and binding/tethering efficiency, are calculated with NIS-Elements software, exported to an Excel spreadsheet and subjected to statistical analysis. In the demonstration presented here, we employed the parallel-plate flow chamber to investigate E-selectin-dependent leukocyte rolling activity on live human bone marrow endothelial cells (hBMEC). Human hematopoietic progenitor KG1a cells, which express a high level of E-selectin ligand, were used as our leukocyte model, while an immortalized hBMEC cell line, HBMEC-60 cells, was used as our endothelial cell model (6). To induce and simulate native E-selectin expression in the flow chamber, HBMEC-60 cells were first activated with IL-1 . Our video presentation showed that parallel-plate flow analysis is a suitable method for studying physiologic E-selectin-mediated leukocyte rolling activities and that functional characterization of leukocyte E-selectin ligand(s) in the flow chamber can be ascertained by implementing protease or glycosidase digestions.

Glycan antagonists and inhibitors: a fount for drug discovery

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.

Skin-homing receptors on effector leukocytes are differentially sensitive to glyco-metabolic antagonism in allergic contact dermatitis

T cell recruitment into inflamed skin is dependent on skin-homing receptor binding to endothelial (E)- and platelet (P)-selectin. These T cell receptors, or E- and P-selectin ligands, can be targeted by the metabolic fluorosugar inhibitor, 4-F-GlcNAc, to blunt cutaneous inflammation. Compelling new data indicate that, in addition to T cells, NK cells are also recruited to inflamed skin in allergic contact hypersensitivity (CHS) contingent on E- and P-selectin-binding. Using a model of allergic CHS, we evaluated the identity and impact of NK cell E-selectin ligand(s) on inflammatory responses and examined the oral efficacy of 4-F-GlcNAc. We demonstrated that the predominant E-selectin ligands on NK cells are P-selectin glycoprotein ligand-1 and protease-resistant glycolipids. We showed that, unlike the induced E-selectin ligand expression on activated T cells upon exposure to Ag, ligand expression on NK cells was constitutive. CHS responses were significantly lowered by orally administered 4-F-GlcNAc treatment. Although E-selectin ligand on activated T cells was suppressed, ligand expression on NK cells was insensitive to 4-F-GlcNAc treatment. These findings indicate that downregulating effector T cell E- and P-selectin ligand expression directly correlates with anti-inflammatory efficacy and provides new insight on metabolic discrepancies of E-selectin ligand biosynthesis in effector leukocytes in vivo.

Targeting selectins and selectin ligands in inflammation and cancer

Inflammation and cancer metastasis are associated with extravasation of leukocytes or tumor cells from blood into tissue. Such movement is believed to follow a coordinated and sequential molecular cascade initiated, in part, by the three members of the selectin family of carbohydrate-binding proteins: E-selectin (CD62E), L-selectin (CD62L) and P-selectin (CD62P). E-selectin is particularly noteworthy in disease by virtue of its expression on activated endothelium and on bone-skin microvascular linings and for its role in cell rolling, cell signaling and chemotaxis. E-selectin, along with L- or P-selectin, mediates cell tethering and rolling interactions through the recognition of sialo-fucosylated Lewis carbohydrates expressed on structurally diverse protein-lipid ligands on circulating leukocytes or tumor cells. Major advances in understanding the role of E-selectin in inflammation and cancer have been advanced by experiments assaying E-selectin-mediated rolling of leukocytes and tumor cells under hydrodynamic shear flow, by clinical models of E-selectin-dependent inflammation, by mice deficient in E-selectin and by mice deficient in glycosyltransferases that regulate the binding activity of E-selectin ligands. Here, the authors elaborate on how E-selectin and its ligands may facilitate leukocyte or tumor cell recruitment in inflammatory and metastatic settings. Antagonists that target cellular interactions with E-selectin and other members of the selectin family, including neutralizing monoclonal antibodies, competitive ligand inhibitors or metabolic carbohydrate mimetics, exemplify a growing arsenal of potentially effective therapeutics in controlling inflammation and the metastatic behavior of cancer.

Synthesis and glycosylation of a series of 6-mono-, di-, and trifluoro S-phenyl 2,3,4-tri-O-benzyl-thiorhamnopyranosides. Effect of the fluorine substituents on glycosylation stereoselectivity

A series of 6-mono-, di-, and trifluoro analogs of S-phenyl 2,3,4-tri-O-benzyl-D- or L-thiorhamnopyranoside has been synthesized and used as donors in glycosylation reactions, with activation by the 1-benzenesulfinyl piperidine/triflic anhydride system. The stereochemical outcome of the glycosylation reactions was found to depend on the electron-withdrawing capability of the disarming substituent at the 6-position, i.e., on the number of fluorine atoms present. The results are explained with regard to the increased stability of the glycosyl triflates, shown to be intermediates in the reaction by low-temperature 1H NMR experiments, with increased fluorine content.