L-Selectin ligands that are O-glycoprotease resistant and distinct from MECA-79 antigen are sufficient for tethering and rolling of lymphocytes on human high endothelial venules

The Role of L-Selectin in HIV Infection

HIV envelope glycoprotein is the most heavily glycosylated viral protein complex identified with over 20 glycans on its surface. This glycan canopy is thought to primarily shield the virus from host immune recognition as glycans are poor immunogens in general, however rare HIV neutralizing antibodies nevertheless potently recognize the glycan epitopes. While CD4 and chemokine receptors have been known as viral entry receptor and coreceptor, for many years the role of viral glycans in HIV entry was controversial. Recently, we showed that HIV envelope glycan binds to L-selectin in solution and on CD4 T lymphocytes. The viral glycan and L-selectin interaction functions to facilitate the viral adhesion and entry. Upon entry, infected CD4 T lymphocytes are stimulated to progressively shed L-selectin and suppressing this lectin receptor shedding greatly reduced HIV viral release and caused aggregation of diminutive virus-like particles within experimental infections and from infected primary T lymphocytes derived from both viremic and aviremic individuals. As shedding of L-selectin is mediated by ADAM metalloproteinases downstream of host-cell stimulation, these findings showed a novel mechanism for HIV viral release and offer a potential new class of anti-HIV compounds.

Nucleolin mediates the binding of cancer cells to L-selectin under conditions of lymphodynamic shear stress

Head and neck squamous cell carcinoma (HNSCC) cells bind to lymphocytes via L-selectin in a shear-dependent manner. This interaction takes place exclusively under low-shear stress conditions, such as those found within the lymph node parenchyma. This represents a novel functional role for L-selectin-selectin ligand interactions. Our previous work has characterized as-of-yet unidentified L-selectin ligands expressed by HNSCC cells that are specifically active under conditions of low shear stress consistent with lymph flow. Using an affinity purification approach, we now show that nucleolin expressed on the surface of HNSCC cells is an active ligand for L-selectin. Parallel plate chamber flow-based experiments and atomic force microscopy (AFM) experiments show that nucleolin is the main functional ligand under these low-force conditions. Furthermore, AFM shows a clear relationship between work of deadhesion and physiological loading rates. Our results reveal nucleolin as the first major ligand reported for L-selectin that operates under low-shear stress conditions.

HIV-1 targets L-selectin for adhesion and induces its shedding for viral release

CD4 and chemokine receptors mediate HIV-1 attachment and entry. They are, however, insufficient to explain the preferential viral infection of central memory T cells. Here, we identify L-selectin (CD62L) as a viral adhesion receptor on CD4⁺ T cells. The binding of viral envelope glycans to L-selectin facilitates HIV entry and infection, and L-selectin expression on central memory CD4⁺ T cells supports their preferential infection by HIV. Upon infection, the virus downregulates L-selectin expression through shedding, resulting in an apparent loss of central memory CD4⁺ T cells. Infected effector memory CD4⁺ T cells, however, remain competent in cytokine production. Surprisingly, inhibition of L-selectin shedding markedly reduces HIV-1 infection and suppresses viral release, suggesting that L-selectin shedding is required for HIV-1 release. These findings highlight a critical role for cell surface sheddase in HIV-1 pathogenesis and reveal new antiretroviral strategies based on small molecular inhibitors targeted at metalloproteinases for viral release.

HIV binding is mediated via CD4 and chemokine co-receptors, but this does not explain the preferential infection of central memory CD4+ T cells. Here the authors show HIV targets L-selectin, induces shedding from the infected cell, and inhibition of L-selectin reduces HIV infection and release.

A monoclonal antibody against a novel Sialomucin CD300LG

CD300LG is a novel O-glycosylated member of the CD300 antigen-like family. Besides a classical mucin-like domain, it contains a V-type Ig domain. CD300LG binds lymphocyte L-selectin via its Ig domain and supports lymphocyte rolling via its mucin-like domain. The unique structure and function of CD300LG suggest it may play an important role in inflammation. For preparation of a monoclonal antibody (MAb) against human CD300LG, prokaryotic and eukaryotic expressing human CD300LG proteins were used as immunogen and detection antigen, respectively. One stable strain of hybridomas (3C7C5A6) was successfully established using the hybridoma technique. The Western blot and immunohistochemistry analyses demonstrated that the MAb was directed against human CD300LG with high specificity. This antibody could possibly facilitate studies on the pathomechanism of inflammation and may have the potential to be a means of effective anti-inflammation.

Identification of mono- and disulfated N-acetyl-lactosaminyl Oligosaccharide structures as epitopes specifically recognized by humanized monoclonal antibody HMOCC-1 raised against ovarian cancer

A humanized monoclonal antibody raised against human ovarian cancer RMG-I cells and designated as HMOCC-1 (Suzuki, N., Aoki, D., Tamada, Y., Susumu, N., Orikawa, K., Tsukazaki, K., Sakayori, M., Suzuki, A., Fukuchi, T., Mukai, M., Kojima-Aikawa, K., Ishida, I., and Nozawa, S. (2004) Gynecol. Oncol. 95, 290-298) was characterized for its carbohydrate epitope structure. Specifically, a series of co-transfections was performed using mammalian expression vectors encoding specific glycosyltransferases and sulfotransferases. These experiments identified one sulfotransferase, GAL3ST3, and one glycosyltransferase, B3GNT7, as required for HMOCC-1 antigen formation. They also suggested that the sulfotransferase CHST1 regulates the abundance and intensity of HMOCC-1 antigen. When HEK293T cells were co-transfected with GAL3ST3 and B3GNT7 expression vectors, transfected cells weakly expressed HMOCC-1 antigen. When cells were first co-transfected with GAL3ST3 and B3GNT7 and then with CHST1, the resulting cells strongly expressed HMOCC-1 antigen. However, when cells were transfected with a mixture of GAL3ST3 and CHST1 before or after transfection with B3GNT7, the number of antigen-positive cells decreased relative to the number seen with only GAL3ST3 and B3GNT7, suggesting that CHST1 plays a regulatory role in HMOCC-1 antigen formation. Because these results predicted that HMOCC-1 antigens are SO(3) → 3Galβ1 → 4GlcNAcβ1 → 3(±SO(3) → 6)Galβ1 → 4GlcNAc, we chemically synthesized mono- and disulfated and unsulfated oligosaccharides. Immunoassays using these oligosaccharides as inhibitors showed the strongest activity by disulfated tetrasaccharide, weak but positive activity by monosulfated tetrasaccharide at the terminal galactose, and no activity by nonsulfated tetrasaccharides. These results establish the HMOCC-1 epitope, which should serve as a useful reagent to further characterize ovarian cancer.

Novel anti-carbohydrate antibodies reveal the cooperative function of sulfated N- and O-glycans in lymphocyte homing

Cell surface glycans play pivotal roles in immune cell trafficking and immunity. Here we present an efficient method for generating anti-carbohydrate monoclonal antibodies (mAbs) using gene-targeted mice and describe critical glycans in lymphocyte homing. We immunized sulfotransferase GlcNAc6ST-1 and GlcNAc6ST-2 doubly deficient mice with sulfotransferase-overexpressing Chinese hamster ovary cells and generated two mAbs, termed S1 and S2. Both S1 and S2 bound high endothelial venules (HEVs) in the lymphoid organs of humans and wild-type mice, but not in those of doubly deficient mice. Glycan array analysis indicated that both S1 and S2 specifically bound 6-sulfo sialyl Lewis X and its defucosylated structure. Interestingly, S2 inhibited lymphocyte homing to peripheral lymph nodes by 95%, whereas S1 inhibited it by only 25%. S2 also significantly inhibited contact hypersensitivity responses and L-selectin-dependent leukocyte adhesion to HEVs. Immunohistochemical and Western blot analyses indicated that S1 preferentially bound sulfated O-glycans, whereas S2 bound both sulfated N- and O-glycans in HEVs. Furthermore, S2 strongly inhibited the N-glycan-dependent residual lymphocyte homing in mutant mice lacking sulfated O-glycans, indicating the importance of both sulfated N- and O-glycans in lymphocyte homing. Thus, the two mAbs generated by a novel method revealed the cooperative function of sulfated N- and O-glycans in lymphocyte homing and immune surveillance.

Functional contributions of N- and O-glycans to L-selectin ligands in murine and human lymphoid organs

L-selectin initiates lymphocyte interactions with high endothelial venules (HEVs) of lymphoid organs through binding to ligands with specific glycosylation modifications. 6-Sulfo sLe(x), a sulfated carbohydrate determinant for L-selectin, is carried on core 2 and extended core 1 O-glycans of HEV-expressed glycoproteins. The MECA-79 monoclonal antibody recognizes sulfated extended core 1 O-glycans and partially blocks lymphocyte-HEV interactions in lymphoid organs. Recent evidence has identified the contribution of 6-sulfo sLe(x) carried on N-glycans to lymphocyte homing in mice. Here, we characterize CL40, a novel IgG monoclonal antibody. CL40 equaled or surpassed MECA-79 as a histochemical staining reagent for HEVs and HEV-like vessels in mouse and human. Using synthetic carbohydrates, we found that CL40 bound to 6-sulfo sLe(x) structures, on both core 2 and extended core 1 structures, with an absolute dependency on 6-O-sulfation. Using transfected CHO cells and gene-targeted mice, we observed that CL40 bound its epitope on both N-glycans and O-glycans. Consistent with its broader glycan-binding, CL40 was superior to MECA-79 in blocking lymphocyte-HEV interactions in both wild-type mice and mice deficient in forming O-glycans. This superiority was more marked in human, as CL40 completely blocked lymphocyte binding to tonsillar HEVs, whereas MECA-79 inhibited only 60%. These findings extend the evidence for the importance of N-glycans in lymphocyte homing in mouse and indicate that this dependency also applies to human lymphoid organs.

Human L-selectin preferentially binds synthetic glycosulfopeptides modeled after endoglycan and containing tyrosine sulfate residues and sialyl Lewis x in core 2 O-glycans

Endoglycan is a mucin-like glycoprotein expressed by endothelial cells and some leukocytes and is recognized by L-selectin, a C-type lectin important in leukocyte trafficking and extravasation during inflammation. Here, we show that recombinant L-selectin and human T lymphocytes expressing L-selectin bind to synthetic glycosulfopeptides (GSPs). These synthetic glycosulfopeptides contain 37 amino acid residues modeled after the N-terminus of human endoglycan and contain one or two tyrosine sulfates (TyrSO(3)) along with a nearby core-2-based Thr-linked O-glycan with sialyl Lewis x (C2-SLe(x)). TyrSO(3) at position Y118 was more critical for binding than at Y97. C2-SLe(x) at T124 was required for L-selectin recognition. Interestingly, under similar conditions, neither L-selectin nor T lymphocytes showed appreciable binding to the sulfated carbohydrate epitope 6-sulfo-SLe(x). P-selectin also bound to endoglycan-based GSPs but with lower affinity than toward GSPs modeled after PSGL-1, the physiological ligand for P- and L-selectin that is expressed on leukocytes. These results demonstrate that TyrSO(3) residues in association with a C2-SLe(x) moiety within endoglycan and PSGL-1 are preferentially recognized by L-selectin.

Glycoforms of human endothelial CD34 that bind L-selectin carry sulfated sialyl Lewis x capped O- and N-glycans

Endothelial sialomucin CD34 functions as an L-selectin ligand mediating lymphocyte extravasation only when properly glycosylated to express a sulfated carbohydrate epitope, 6-sulfo sialyl Lewis x (6-sulfo SLe(x)). It is thought that multivalent 6-sulfo SLe(x) expression promotes high-affinity binding to L-selectin by enhancing avidity. However, the reported low amount of 6-sulfo SLe(x) in total human CD34 is inconsistent with this model and prompted us to re-evaluate CD34 glycosylation. We separated CD34 into 2 glycoforms, the L-selectin-binding and nonbinding glycoforms, L-B-CD34 and L-NB-CD34, respectively, and analyzed released O- and N-glycans from both forms. L-B-CD34 is relatively minor compared with L-NB-CD34 and represented less than 10% of total tonsillar CD34. MECA-79, a mAb to sulfated core-1 O-glycans, bound exclusively to L-B-CD34 and this form contained all sulfated and fucosylated O-glycans. 6-Sulfo SLe(x) epitopes occur on core-2 and extended core-1 O-glycans with approximately 20% of total L-B-CD34 O-glycans expressing 6-sulfo SLe(x). N-glycans containing potential 6-sulfo SLe(x) epitopes were also present in L-B-CD34, but their removal did not abolish binding to L-selectin. Thus, a minor glycoform of CD34 carries relatively abundant 6-sulfo SLe(x) epitopes on O-glycans that are important for its recognition by L-selectin.

Human noroviruses recognize sialyl Lewis x neoglycoprotein

The carbohydrate binding characteristics of a norovirus GII.3 (Chron1) and a GII.4 (Dijon) strain were investigated using virus-like particles (VLPs) and saliva samples from 81 individuals genotyped for FUT2 (secretor) and FUT3 (Lewis) and phenotyped for ABO and Lewis blood groups. The two VLPs showed a typical secretor-gene-dependent binding and bound significantly stronger to saliva from A, B, and AB than from O individuals (P < 0.0001 and P < 0.001) but did not bind to any samples from secretor-negative individuals. The GII.3 strain showed larger interindividual variation and bound stronger to saliva from B than from A(2) secretors (P < 0.01). When assaying for binding to neoglycoproteins, the GII.3 and GII.4 strains were compared with the Norwalk GI.1 prototype strain. Although all three strains bound to Lewis b (and H type 1 chain) glycoconjugates, only the two GII strains showed an additional binding to sialyl Lewis x. This novel binding was specific since the VLPs did not bind to structural analogs, e.g., Lewis x or sialyl Lewis a, but only to sialyl Lewis x, sialyl diLewis x and sialylated type 2 chain conjugates. In inhibition experiments, the sialyl Lewis x conjugate was the most potent inhibitor. The minimal requirement for this potential receptor structure is Neu5Ac alpha 3Gal beta 4(Fuc alpha 3)GlcNAc beta 3Gal beta- where Fuc is not absolutely necessary for binding. Our study shows that some human norovirus GII strains have at least two binding specificities: one secretor-gene-dependent related to alpha1,2-fucosylated carbohydrates and another related to alpha2,3-sialylated carbohydrates of the type 2 chain, e.g., sialyl Lewis x.

Critical functions of N-glycans in L-selectin-mediated lymphocyte homing and recruitment

Lymphocyte homing is mediated by specific interaction between L-selectin on lymphocytes and the carbohydrate ligand 6-sulfo sialyl Lewis X on high endothelial venules. Here we generated mice lacking both core 1 extension and core 2 branching enzymes to assess the functions of O-glycan-borne L-selectin ligands in vivo. Mutant mice maintained robust lymphocyte homing, yet they lacked O-glycan L-selectin ligands. Biochemical analyses identified a class of N-glycans bearing the 6-sulfo sialyl Lewis X L-selectin ligand in high endothelial venules. These N-glycans supported the binding of L-selectin to high endothelial venules in vitro and contributed in vivo to O-glycan-independent lymphocyte homing in wild-type and mutant mice. Our results demonstrate the critical function of N-glycan-linked 6-sulfo sialyl Lewis X in L-selectin-dependent lymphocyte homing and recruitment.

Rapid plasma membrane-endosomal trafficking of the lymph node sinus and high endothelial venule scavenger receptor/homing receptor stabilin-1 (FEEL-1/CLEVER-1)

The sinusoidal endothelia of liver, spleen, and lymph node are major sites for uptake and recycling of waste macromolecules through promiscuous binding to a disparate family of scavenger receptors. Among the most complex is stabilin-1, a large multidomain protein containing tandem fasciclin domains, epidermal growth factor-like repeats, and a C-type lectin-like hyaluronan-binding Link module, which functions as an endocytic receptor for acetylated low density lipoprotein and advanced glycation end products. Intriguingly, stabilin-1 has also been reported to mediate both homing of leukocytes across lymph node high endothelial venules and adhesion of metastatic tumor cells to peritumoral lymphatic vessels. Currently, however, it is not clear how stabilin-1 mediates these distinct functions. To address the issue, we have investigated the tissue and subcellular localization of stabilin-1 in detail and assessed the functional status of its Link module. We show that stabilin-1 is almost entirely intracellular in lymph node high endothelial venules, lymphatic sinus endothelium, and cultured endothelial cells but that a finite population, detectable only by fluorescent antibody or fluorescein-labeled (Fl)-acetylated low density lipoprotein uptake, cycles rapidly between the plasma membrane and EEA-1+ve (early endosome antigen 1) early endosomes. In addition, we show using full-length stabilin-1 cDNA and a stabilin-1/CD44 chimera in HeLa cells that intracellular targeting is influenced by the transmembrane domain/cytoplasmic tail, which contains a putative dileucine (DXXLL) Golgi to endosomal sorting signal. Finally, we provide evidence that the stabilin-1 Link domain binds neither hyaluronan nor other glycosaminoglycans. These properties support a role for stabilin-1 as a rapidly recycling scavenger receptor and argue against a role in cell adhesion or lymphocyte homing.

Ligands for L-selectin: homing, inflammation, and beyond

Understanding the molecular basis of lymphocyte homing to lymphoid organs was originally a problem of concern only to immunologists. With the discovery of L-selectin and its ligands, interested scientists have expanded to include glycobiologists, immunopathologists, cancer biologists, and developmental biologists. Going beyond its first discovered role in homing to lymph nodes, the L-selectin system is implicated in such diverse processes as inflammatory leukocyte trafficking in both acute and chronic settings, hematogenous metastasis of carcinoma cells, effector mechanisms for inflammatory demyelination of axons, and implantation of the early mammalian embryo. This review focuses on the ligands for L-selectin that are found on vascular endothelium, leukocytes, carcinoma cells, and at various extravascular sites. The discovery of selectins and their ligands has validated the long-predicted hypothesis that carbohydrate-directed cell adhesion is relevant in eukaryotic systems. Emphasis will be given to the carbohydrate and sulfation modifications of the ligands, which enable recognition by L-selectin. The rapid "homing" of labeled cells into the lymph nodes presumably had its basis in the special affinity of small lymphocytes for the endothelium of the postcapillary venules.

Molecular Targeting of Lymph Nodes with L-Selectin Ligand-specific US Contrast Agent: A Feasibility Study in Mice and Dogs

PURPOSE

To evaluate the feasibility of using intravenously administered L-selectin ligand-specific polymer-stabilized air-filled microparticles (MPs) for active targeting of peripheral lymph nodes under normal conditions in animal models.

MATERIALS AND METHODS

L-selectin ligand-specific MPs and two control substances (immunoglobulin M-isotype MPs and native MPs) were each administered in three conscious mice as a single intravenous bolus injection (1.4 x 10(7) MPs/kg). All mice were sacrificed 30 minutes after administration. Lymph nodes (cervical, inguinal, axillary, popliteal, mesenteric), spleen (positive control), and kidney (blood pool control) were removed and examined for MP-related stimulated acoustic emission (SAE) signals by using harmonic color Doppler ultrasonography (US) in a tank containing degassed water. A second experiment was performed in six anesthetized beagle dogs by using the same MP formulation. Each of the MP formulations was administered in two anesthetized dogs as a single intravenous bolus injection (1 x 10(7) MPs/kg). The popliteal lymph nodes, spleen (positive control), and kidney (blood pool control) were examined in vivo with US for MP-related SAE signals 30 minutes after administration. Fisher exact test for the one-side alternative was used for mouse data analysis.

RESULTS

The lymph nodes of all mice (P =.05) and the popliteal lymph nodes of both dogs treated with L-selectin ligand-specific MPs showed clear MP-related SAE signals, whereas the lymph nodes of all mice and the popliteal lymph nodes of four dogs that received the control substances did not show any SAE signals.

CONCLUSION

Use of an intravenously administered L-selectin ligand-specific US contrast agent is feasible for active lymph node targeting in mice and dogs.

Trafficking of Th1 cells to lung: a role for selectins and a P-selectin glycoprotein-1-independent ligand

Trafficking of lymphocytes to lung is a critical component of pulmonary immune defense and surveillance. Selectins, expressed on vascular endothelium, regulate T lymphocyte emigration into tissues, such as skin, but the role of the selectins in trafficking of T cells to lung has not been well characterized. Here, we used a model of lung inflammation induced by adoptive transfer of alloreactive Th1 cells to analyze the role of P- and E-selectin in Th1 cell trafficking to lung in vivo. We found that both P- and E-selectin play an important role in Th1 lymphocyte migration to lung. We confirmed that the Th1 cells express P-selectin glycoprotein ligand-1, which was functional in binding to P- and E-selectin in vitro. However, our studies reveal that a ligand distinct from P-selectin glycoprotein-1 also binds these selectins in vitro and appears to play a physiologic role in in vivo emigration of Th1 lymphocytes into the lung.

Core 2 Branching β1,6-N-Acetylglucosaminyltransferase and High Endothelial Venule-restricted Sulfotransferase Collaboratively Control Lymphocyte Homing

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to carbohydrate ligands expressed on high endothelial venules (HEV) of the secondary lymphoid organs. Previous studies demonstrated that L-selectin ligand sulfotransferase (LSST) forms 6-sulfo sialyl Lewis x (sLe(x)) on both core 2 branch and MECA-79-positive extended core 1 O-glycans, but the chemical nature and roles of HEV ligands elaborated by LSST and core 2 beta1,6-N-acetylglucosaminyltransferase-1 (Core2GlcNAcT) have been undefined. In the present study, we have generated mutant mice with deficient LSST and show that inactivation of LSST gene alone leads to only partial impairment of lymphocyte homing to peripheral lymph nodes and moderate reduction in lymphocyte counts in the peripheral lymph nodes, despite the fact that L-selectin ligands that contain 6-sulfo sLe(x) are reduced at HEV. By contrast, LSST/Core2GlcNAcT double null mice exhibited a markedly reduced lymphocyte homing and reduced lymphocyte counts as a result of significantly decreased 6-sulfo sLe(x) on HEV L-selectin counterreceptors, relative to LSST- or Core2GlcNAcT-single null mice. Moreover, induction of LSST and Core2GlcNAcT transcripts was observed in HEV-like structure formed in the salivary gland of the non-obese diabetic mouse, which displays chronic inflammation. These results indicate that LSST and Core2GlcNAcT cooperatively synthesize HEV-specific L-selectin ligands required for lymphocyte homing and suggest that LSST and Core2GlcNAcT play a critical role in lymphocyte trafficking during chronic inflammation.

A novel endothelial L-selectin ligand activity in lymph node medulla that is regulated by alpha(1,3)-fucosyltransferase-IV

Lymphocytes home to peripheral lymph nodes (PLNs) via high endothelial venules (HEVs) in the subcortex and incrementally larger collecting venules in the medulla. HEVs express ligands for L-selectin, which mediates lymphocyte rolling. L-selectin counterreceptors in HEVs are recognized by mAb MECA-79, a surrogate marker for molecularly heterogeneous glycans termed peripheral node addressin. By contrast, we find that medullary venules express L-selectin ligands not recognized by MECA-79. Both L-selectin ligands must be fucosylated by α(1,3)-fucosyltransferase (FucT)-IV or FucT-VII as rolling is absent in FucT-IV+VII^−/− mice. Intravital microscopy experiments revealed that MECA-79–reactive ligands depend primarily on FucT-VII, whereas MECA-79–independent medullary L-selectin ligands are regulated by FucT-IV. Expression levels of both enzymes paralleled these anatomical distinctions. The relative mRNA level of FucT-IV was higher in medullary venules than in HEVs, whereas FucT-VII was most prominent in HEVs and weak in medullary venules. Thus, two distinct L-selectin ligands are segmentally confined to contiguous microvascular domains in PLNs. Although MECA-79–reactive species predominate in HEVs, medullary venules express another ligand that is spatially, antigenically, and biosynthetically unique. Physiologic relevance for this novel activity in medullary microvessels is suggested by the finding that L-selectin–dependent T cell homing to PLNs was partly insensitive to MECA-79 inhibition.

Lymphocyte-HEV interactions in lymph nodes of a sulfotransferase-deficient mouse

The interaction of L-selectin expressed on lymphocytes with sulfated sialomucin ligands such as CD34 and GlyCAM-1 on high endothelial venules (HEV) of lymph nodes results in lymphocyte rolling and is essential for lymphocyte recruitment. HEC-GlcNAc6ST-deficient mice lack an HEV-restricted sulfotransferase with selectivity for the C-6 position of N-acetylglucosamine (GlcNAc). HEC-GlcNAc6ST-/- animals exhibit faster lymphocyte rolling and reduced lymphocyte sticking in HEV, accounting for the diminished lymphocyte homing. Isolated CD34 and GlyCAM-1 from HEC-GlcNAc6ST-/- animals incorporate approximately 70% less sulfate than ligands from wild-type animals. Furthermore, these ligands exhibit a comparable reduction of the epitope recognized by MECA79, a function-blocking antibody that reacts with L-selectin ligands in a GlcNAc-6-sulfate-dependent manner. Whereas MECA79 dramatically inhibits lymphocyte rolling and homing to lymph nodes in wild-type mice, it has no effect on HEC-GlcNAc6ST-/- mice. In contrast, in vitro rolling on purified GlyCAM-1 from HEC-GlcNAc6ST-/- mice, although greatly diminished compared with that on the wild-type ligand, is inhibited by MECA79. Our results demonstrate that HEC-GlcNAc6ST contributes predominantly, but not exclusively, to the sulfation of HEV ligands for L-selectin and that alternative, non-MECA79-reactive ligands are present in the absence of HEC-GlcNAc6ST.

Endoglycan, a member of the CD34 family, functions as an L-selectin ligand through modification with tyrosine sulfation and sialyl Lewis x

During lymphocyte homing to secondary lymphoid organs and instances of inflammatory trafficking, the rolling of leukocytes on vascular endothelium is mediated by transient interactions between L-selectin on leukocytes and several carbohydrate-modified ligands on the endothelium. Most L-selectin ligands such as CD34 and podocalyxin present sulfated carbohydrate structures (6-sulfated sialyl Lewis x or 6-sulfo-sLex) as a recognition determinant within their heavily glycosylated mucin domains. We recently identified endoglycan as a new member of the CD34 family. We report here that endoglycan, like the two other members of this family (CD34 and podocalyxin) can function as a L-selectin ligand. However, endoglycan employs a different binding mechanism, interacting with L-selectin through sulfation on two tyrosine residues and O-linked sLex structures that are presented within its highly acidic amino-terminal region. Our analysis establishes striking parallels with PSGL-1, a leukocyte ligand that interacts with all three selectins, mediating leukocyte-endothelial, leukocyte-leukocyte, and platelet-leukocyte interactions. Since the distribution of endoglycan includes hematopoietic precursors and leukocyte subpopulations, in addition to endothelial cells, our findings suggest several potential settings for endoglycan-mediated adhesion events.

Sulfotransferases and sulfated oligosaccharides

Structural diversity of the sugar chains attached to proteins and lipids that arises from the variety of combinations of different monosaccharides, different types of linkages, branch formation and secondary modifications, such as sulfation, possesses a large amount of biological information. A number of proteoglycans, glycoproteins, and glycolipids contain sulfated carbohydrates. Their sulfate groups provide a negative charge and play a role in a specific molecular recognition process. The sulfation of oligosaccharides is catalyzed by the Golgi-associated sulfotransferases. Recent success in molecular cloning of these sulfotransferases has brought a breakthrough in the understanding of biological function of sulfated oligosaccharides in a variety of contexts. Investigations on the relationship of sulfated oligosaccharides to human diseases including hereditary deficiency, cancer, inflammation, and infection may provide hints for curing disastrous diseases.

P-, E-, and L-selectin mediate migration of activated CD8+ T lymphocytes into inflamed skin

P- and E-selectin mediate CD4+ Th1 cell migration into the inflamed skin in a murine contact hypersensitivity model. In this model, not only CD4+ T cells but also CD8+ T cells infiltrate the inflamed skin, and the role of CD8+ type 1 cytotoxic T (Tc1) cells as effector cells has been demonstrated. Here we show that in mice deficient in both P- and E-selectin, the infiltration of CD8+ T cells in the inflamed skin is reduced, suggesting the role of these selectins in CD8+ T cell migration. We directly studied the role of selectins using in vitro-generated Tc1 cells. These cells are able to migrate into the inflamed skin of wild-type mice. This migration is partially mediated by P- and E-selectin, as shown by the reduced Tc1 cell migration into the inflamed skin of mice deficient in both P- and E-selectin or wild-type mice treated with the combination of anti-P-selectin and anti-E-selectin Abs. During P- and E-selectin-mediated migration of Tc1 cells, P-selectin glycoprotein ligand-1 appears to be the sole ligand for P-selectin and one of the ligands for E-selectin. P- and E-selectin-independent migration of Tc1 cells into the inflamed skin was predominantly mediated by L-selectin. These observations indicate that all three selectins can mediate Tc1 cell migration into the inflamed skin.

Distinct sulfation requirements of selectins disclosed using cells that support rolling mediated by all three selectins under shear flow. L-selectin prefers carbohydrate 6-sulfation totyrosine sulfation, whereas p-selectin does not

l- and P-selectin are known to require sulfation in their ligand molecules. We investigated the significance of carbohydrate 6-sulfation and tyrosine sulfation in selectin-mediated cell adhesion. COS-7 cells were genetically engineered to express P-selectin glycoprotein ligand-1 (PSGL-1) or its mutant in various combinations with 6-O-sulfotransferase (6-Sul-T) and/or alpha1-->3fucosyltransferase VII (Fuc-T VII). The cells transfected with PSGL-1, 6-Sul-T, and Fuc-T VII cDNAs supported rolling mediated by all three selectins and provided the best experimental system so far to estimate kinetic parameters in selectin-mediated cell adhesion for all three selectins using the identical rolling substrate and to compare the ligand specificity of each selectin. L-selectin-mediated rolling was drastically impaired if the cells lacked carbohydrate 6-sulfation elaborated by 6-Sul-T, but not affected when PSGL-1 was replaced with a mutant lacking three tyrosine residues at its NH(2) terminus. L-selectin-mediated adhesion was also hardly affected by mocarhagin treatment of the cells, which cleaved a short peptide containing sulfated tyrosine residues from PSGL-1. In contrast, P-selectin-mediated rolling was abolished when PSGL-1 was either mutated or cleaved by mocarhagin at its NH(2) terminus, whereas the cells expressing PSGL-1 and Fuc-T VII but not 6-Sul-T showed only a modest decrease in P-selectin-mediated adhesion. These results indicate that L-selectin prefers carbohydrate 6-sulfation much more than tyrosine sulfation, whereas P-selectin favors tyrosine sulfation in the PSGL-1 molecule far more than carbohydrate 6-sulfation. E-selectin-mediated adhesion was sulfation-independent requiring only Fuc-T VII, and thus the three members of the selectin family have distinct requirements for ligand sulfation.

Identification of the functional elements in the bidirectional promoter of the mouse O-sialoglycoprotein endopeptidase and APEX nuclease genes

The gene for mammalian O-sialoglycoprotein endopeptidase (Osgep) lies immediately adjacent to the gene for the APEX nuclease (Apex), a multifunctional DNA repair enzyme, in a head-to-head orientation. To clarify the regulation of these divergent genes, we studied their promoter regions with luciferase reporters. Deletion analysis of a fragment containing the entire mouse Apex gene suggested that cis-acting elements driving in the direction of Osgep are widely distributed in the mApex gene, in the antisense orientation. We investigated in detail cis-acting elements near the transcription initiation site of mOsgep. The spacer sequence between mOsgep and mApex was shown to have bidirectional promoter activity and it has been reported that two CCAAT boxes promote basal transcription in the direction of mApex. However, only one of the CCAAT boxes proximal to the transcription initiation site of mOsgep was important for transcription towards mOsgep. An Sp1-binding sequence was found to be involved in bidirectional transcription and a CRE/ATF-like sequence was shown to function as a repressor of mOsgep transcription. Quantitative RT-PCR showed that the mApex and mOsgep genes were expressed in all tissues examined and that expression of mOsgep was low compared with mApex.

Identification and characterization of L-selectin ligands in porcine lymphoid tissues

A human L-selectin-ZZ fusion protein was used to screen porcine inguinal lymph nodes for the presence of monoclonal antibody (mAb) MECA 79-negative ligands. Fractionation of lymph node-conditioned medium by anion-exchange chromatography revealed two distinct L-selectin-binding fractions, one containing a MECA 79 non-reactive species and the second containing two MECA 79 reactive species of approximately 84 000 and 210 000 molecular weight. The MECA 79 non-reactive species exhibited Ca2+- and lectin-dependent binding to L-selectin-ZZ in a solid-phase capture enzyme-linked immunosorbent assay (ELISA), and this was specifically disrupted by the addition of EDTA, mannose-6-phosphate and the blocking anti-L-selectin mAb, DREG-56. Enzymatic characterization of the ligand by trypsin, O-sialoglycoprotease endopeptidase, heparinases I and III, or chondroitinase ABC lyase digestion indicated that L-selectin binding was predominantly dependent upon a chondroitin sulphate-modified glycoprotein determinant. Although Coomassie Blue staining of sodium dodecyl sulphate (SDS) polyacrylamide gels did not reveal a detectable protein species, carbohydrate-specific staining using GlycoTrack revealed a single, heavily glycosylated protein of high molecular weight (> 220 000). These studies have revealed the existence of a MECA 79 non-reactive, chondroitin sulphate glycosaminoglycan-modified ligand, termed csgp>220, which is secreted by peripheral lymph nodes and may play a role in leucocyte trafficking to the lymph node.

Sequencing analysis of a putative human O-sialoglycoprotein endopeptidase gene (OSGEP) and analysis of a bidirectional promoter between the OSGEP and APEX genes

We performed cDNA and genomic cloning, sequencing and promoter analysis of the putative human O-sialoglycoprotein endopeptidase gene OSGEP (a homologue of gcp, a Pasteurella haemolytica A1 glycoprotease). The cloned OSGEP cDNA is 1311 nucleotides long, and encodes a protein consisting of 335 amino acids with predicted molecular mass of 36.4 kDa. The amino acid sequence of OSGEP showed 29.7% identity with that of P. haemolytica glycoprotease. The OSGEP gene is 7.75 kb long, consists of 11 exons and 10 introns, and lies immediately adjacent to the APEX gene (which encodes APEX nuclease, a multifunctional DNA repair enzyme) in 5'-to-5' orientation. The promoter region of the OSGEP gene lacks the typical TATA box, but has putative regulatory elements in the CpG island. Northern blot analysis showed ubiquitous expression of the OSGEP gene in several tissues, and we observed similarities in expression patterns between OSGEP and APEX. In order to study the regulation of OSGEP gene expression, we analyzed the OSGEP promoter region by luciferase assay using HeLa cells. A functional region required for full transcription activity was narrowed down to a 23 bp region containing a CCAAT box. It has been reported that this CCAAT box promotes basal transcription in the APEX direction. We thus conclude that a bidirectional promoter containing a CCAAT box regulates transcription of both the OSGEP and APEX genes.

Route of lymphocyte migration through the high endothelial venule (HEV) in human palatine tonsil

Eleven palatine tonsils were collected from subjects who underwent tonsillectomy in Christian Medical College Hospital and the route of migration of lymphocytes through the high endothelial vessel was studied under EM. In the interendothelial route, migration of a lymphocyte through HEV wall began with the adhesion of a lymphocyte to the surface of endothelial cells by means of a short cytoplasmic projection in the vicinity of intercellular space. The projection extended into the cleft between adjacent endothelial cells. The lymphocyte migrated through HEV by diapedesis. After the lymphocyte had traversed the interendothelial space, it occupied the subendothelial space. In the transendothelial route, migration of a lymphocyte through HEV was initiated by adherence of the lymphocyte to the endothelial cell. The adherent lymphocyte compressed or invaginated into the cytoplasm of the endothelial cell, entered the endothelial cell, was completely enclosed within the endothelial cell cytoplasm, and emerged from the endothelial cell to occupy the subendothelial space. Evidence is presented from static transmission electron microscopic pictures for the migration of lymphocytes by both interendothelial and transendothelial routes through the high endothelial venule.

Identification of a role for the sialomucin CD164 in myogenic differentiation by signal sequence trapping in yeast

Determination and differentiation of skeletal muscle precursors requires cell-cell contact, but the full range of cell surface proteins that mediate this requirement and the mechanisms by which they work are not known. To identify participants in cell contact-mediated regulation of myogenesis, genes that encode secreted proteins specifically upregulated during differentiation of C2C12 myoblasts were identified by the yeast signal sequence trap method (K. A. Jacobs, L. A. Collins-Racie, M. Colbert, M. Duckett, M. Golden-Fleet, K. Kelleher, R. Kriz, E. R. La Vallie, D. Merberg, V. Spaulding, J. Stover, M. J. Williamson, and J. M. McCoy, Gene 198:289-296, 1997), followed by RNA expression analysis. We report here the identification of CD164 as a gene expressed in proliferating C2C12 cells that is upregulated during differentiation. CD164 encodes a widely expressed cell surface sialomucin that has been implicated in regulation of cell proliferation and adhesion during hematopoiesis. Stable overexpression of CD164 in C2C12 and F3 myoblasts enhanced their differentiation, as assessed by both morphological and biochemical criteria. Furthermore, expression of antisense CD164 or soluble extracellular regions of CD164 inhibited myogenic differentiation. Treatment of C2C12 cells with sialidase or O-sialoglycoprotease, two enzymes previously reported to destroy functional epitopes on CD164, also inhibited differentiation. These data indicate that (i) CD164 may play a rate-limiting role in differentiation of cultured myoblasts, (ii) sialomucins represent a class of potential effectors of cell contact-mediated regulation of myogenesis, and (iii) carbohydrate-based cell recognition may play a role in mediating this phenomenon.

Functional characterization of Pactolus, a beta-integrin-like protein preferentially expressed by neutrophils

Murine Pactolus is a beta-integrin-like molecule expressed exclusively on the surface of granulocytes. Cell surface expression of Pactolus is dramatically increased following activation of bone marrow neutrophils with known agonists, and cross-linking of cell surface Pactolus, suggesting the bulk of the protein is in intracellular stores. The mature protein is found in two forms depending upon the extent of N-linked glycosylation. There is no evidence to suggest that Pactolus requires an associated alpha chain for expression. In some mouse strains, a truncated form of the protein is predicted based upon alternative splicing: this form, however, is unstable and rapidly degraded after synthesis. Differences in the quantities of these Pactolus mRNA isoforms have defined two alleles. BALB/c and C3H/HeJ mice possess allele B and preferentially express the truncated, unstable product, whereas C57BL/6 mice possess allele A and only produce the membrane-bound form. Sequence analysis has shown the difference between these two alleles is due to a single base pair difference at the splice acceptor site for the truncated product. The increased expression of the membrane form of Pactolus by granulocytes of C57BL/6 mice suggests a compensatory adhesion function that is reduced in cells from the low producing strains.

Sulfation of L-selectin ligands by an HEV-restricted sulfotransferase regulates lymphocyte homing to lymph nodes

Lymphocytes home to lymph nodes, using L-selectin to bind specific ligands on high endothelial venules (HEV). In vitro studies implicate GlcNAc-6-sulfate as an essential posttranslational modification for ligand activity. Here, we show that genetic deletion of HEC-GlcNAc6ST, a sulfotransferase that is highly restricted to HEV, results in the loss of the binding of recombinant L-selectin to the luminal aspect of HEV, elimination of lymphocyte binding in vitro, and markedly reduced in vivo homing. Reactivity with MECA 79, an adhesion-blocking mAb that stains HEV in lymph nodes and vessels in chronic inflammatory sites, is also lost from the luminal aspects of HEV. These results establish a critical role for HEC-GlcNAc6ST in lymphocyte trafficking and suggest it as an important therapeutic target.

Novel sulfated lymphocyte homing receptors and their control by a Core1 extension beta 1,3-N-acetylglucosaminyltransferase

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to addressins expressed in the high endothelial venules (HEV) of secondary lymphoid organs. Peripheral node addressin recognized by the MECA-79 antibody is apparently part of the L-selectin ligand, but its chemical nature has been undefined. We now identify a sulfated extended core1 mucin-type O-glycan, Gal beta 1-->4(sulfo-->6)GlcNAc beta 1-->3Gal beta 1-->3GalNAc, as the MECA-79 epitope. Molecular cloning of a HEV-expressed core1-beta 1,3-N-acetylglucosaminyltransferase (Core1-beta 3GlcNAcT) enabled the construction of the 6-sulfo sialyl Lewis x on extended core1 O-glycans, recapitulating the potent L-selectin-mediated, shear-dependent adhesion observed with novel L-selectin ligands derived from core2 beta1,6-N-acetylglucosaminyltransferase-I null mice. These results identify Core1-beta 3GlcNAcT and its cognate extended core1 O-glycans as essential participants in the expression of the MECA-79-positive, HEV-specific L-selectin ligands required for lymphocyte homing.

Cutaneous angiolymphoid hyperplasia with high endothelial venules is characterized by endothelial expression of cutaneous lymphocyte antigen

Two cases in which the presence of cutaneous lesions with a characteristic admixture of lymphoid hyperplasia and vascular proliferation lead to the diagnosis of so-called acral pseudolymphomatous angiokeratoma (APA) of children are reported. Owing to the prominence of its blood vessels, so striking as to be reminiscent of high endothelial venules (HEVs), APA was initially interpreted as a vascular lesion rather than a pseudolymphoma. This resemblance is further compounded by our finding that cutaneous lymphocyte antigen (CLA), an HEV marker, is also expressed in APA epithelioid blood vessels. Consequently, we believe that "cutaneous angiolymphoid hyperplasia with high endothelial venules" (ALH-HEV), which alludes to the dual nature of proliferating elements and the HEV-like phenotype of the vascular component, would be a better denomination for this entity. Additionally, we speculate that ALH-HEV lymphoid hyperplasia self-perpetuates through the transformation of dermal capillaries into HEVs, which would bind non-skin homing lymphocytes expressing L-selectin and promote their local recruitment and recirculation.

Minimal sulfated carbohydrates for recognition by L-selectin and the MECA-79 antibody

Sulfated forms of sialyl-Le(X) containing Gal-6-SO(4) or GlcNAc-6-SO(4) have been implicated as potential recognition determinants on high endothelial venule ligands for L-selectin. The optimal configuration of sulfate esters on the N-acetyllactosamine (Galbeta1-->4GlcNAc) core of sulfosialyl-Le(X), however, remains unsettled. Using a panel of sulfated lactose (Galbeta1-->4Glc) neoglycolipids as substrates in direct binding assays, we found that 6',6-disulfolactose was the preferred structure for L-selectin, although significant binding to 6'- and 6-sulfolactose was observed as well. Binding was EDTA-sensitive and blocked by L-selectin-specific monoclonal antibodies. Surprisingly, 6', 6-disulfolactose was poorly recognized by MECA-79, a carbohydrate- and sulfate-dependent monoclonal antibody that binds competitively to L-selectin ligands. Instead, MECA-79 bound preferentially to 6-sulfolactose. The difference in preferred substrates between L-selectin and MECA-79 may explain the variable activity of MECA-79 as an inhibitor of lymphocyte adhesion to high endothelial venules in lymphoid organs. Our results suggest that both Gal-6-SO(4) and GlcNAc-6-SO(4) may contribute to L-selectin recognition, either as components of sulfosialyl-Le(X) capping groups or in internal structures. By contrast, only GlcNAc-6-SO(4) appears to contribute to MECA-79 binding.

Animal lectins as cell adhesion molecules

Protein-carbohydrate interaction is exploited in cell adhesion mechanisms besides the recognition of peptide motifs. The sugar code thus significantly contributes to the intriguing specificity of cellular selection of binding partners. Focusing on two classes of lectins (selectins and galectins), it is evident that their functionality for mediation of adhesive contacts is becoming increasingly appreciated, as is the integration of this type of interaction with other recognition modes to yield the noted specificity. The initial contact formation between leukocytes and activated endothelium makes use of selectins to guide lymphocyte trafficking. In addition to the three selectins which bind a distinct array of ligands, galectin-1 and galectin-3 and possibly other members of this family are involved in cell-cell or cell-matrix interactions. This review summarizes structural and functional aspects of these two classes of endogenous lectins relevant for cell adhesion.

Carbohydrate sulfotransferases in lymphocyte homing

Sulfation is a critical modification in many instances of biological recognition. Early work in lymphocyte homing indicated that the endothelial ligands for L-selectin depended upon sulfation modifications. Subsequent studies showed that the two specific modifications, Gal-6-SO4 and GlcNAc-6-SO4, were present on actual biological ligands. Recently, a family of carbohydrate sulfotransferases capable of generating these modifications has been identified at the molecular level. Reconstitution experiments implicate members of this family as critical participants in lymphocyte homing.

CD164 monoclonal antibodies that block hemopoietic progenitor cell adhesion and proliferation interact with the first mucin domain of the CD164 receptor

The novel sialomucin, CD164, functions as both an adhesion receptor on human CD34+ cell subsets in bone marrow and as a potent negative regulator of CD34+ hemopoietic progenitor cell proliferation. These diverse effects are mediated by at least two functional epitopes defined by the mAbs, 103B2/9E10 and 105A5. We report here the precise epitope mapping of these mAbs together with that of two other CD164 mAbs, N6B6 and 67D2. Using newly defined CD164 splice variants and a set of soluble recombinant chimeric proteins encoded by exons 1-6 of the CD164 gene, we demonstrate that the 105A5 and 103B2/9E10 functional epitopes map to distinct glycosylated regions within the first mucin domain of CD164. The N6B6 and 67D2 mAbs, in contrast, recognize closely associated and complex epitopes that rely on the conformational integrity of the CD164 molecule and encompass the cysteine-rich regions encoded by exons 2 and 3. On the basis of their sensitivities to reducing agents and to sialidase, O-sialoglycoprotease, and N-glycanase treatments, we have characterized CD164 epitopes and grouped them into three classes by analogy with CD34 epitope classification. The class I 105A5 epitope is sialidase, O-glycosidase, and O-sialoglycoprotease sensitive; the class II 103B2/9E10 epitope is N-glycanase, O-glycosidase, and O-sialoglycoprotease sensitive; and the class III N6B6 and 67D2 epitopes are not removed by such enzyme treatments. Collectively, this study indicates that the previously observed differential expression of CD164 epitopes in adult tissues is linked with cell type specific post-translational modifications and suggests a role for epitope-associated carbohydrate structures in CD164 function.

An activated L-selectin mutant with conserved equilibrium binding properties but enhanced ligand recognition under shear flow

Selectins mediate the initial tethering and rolling of leukocytes on vessel walls. Adhesion by selectins is a function of both ligand recognition at equilibrium and mechanical properties of the selectin-ligand bond under applied force. We describe an EGF domain mutant of L-selectin with profoundly augmented adhesiveness over that of native L-selectin but conserved ligand specificity. This mutant, termed LPL, was derived by a substitution of the EGF-like domain of L-selectin with the homologous domain from P-selectin. The mutant bound soluble carbohydrate L-selectin ligand with affinity comparable with that of native L-selectin but interacted with all surface-bound ligands much more readily than native L-selectin, in particular under elevated shear flow. Tethers mediated by both native and mutant L-selectin exhibited similar lifetimes under a range of shear stresses, but the rate of bond formation by the mutant was at least 10-fold higher than that of native L-selectin toward distinct L-selectin ligands. Enhanced rate of bond formation by the mutant was associated with profoundly stronger rolling interactions and reduced dependence of rolling on a threshold of shear stress. This is the first demonstration that the EGF domain can modulate the binding of the lectin domain of a selectin to surface-immobilized ligands under shear flow without affecting the equilibrium properties of the selectin toward soluble ligands.

CD164--a novel sialomucin on CD34+ cells

Hematopoiesis in adult bone marrow is a tightly regulated process involving interactions between cytokine and adhesion receptors on hematopoietic progenitor cells and their cognate ligands in the immediate microenvironment. These interactions control hematopoietic stem cell self-renewal, quiescence, commitment and migration. Recently, sialomucins have assumed some importance in hematopoiesis, with six of these receptors, CD34, PSGL-1, CD43, PCLP, CD45RA and CD164, having been identified on primitive hematopoietic precursor cells and/or their associated stromal/endothelial elements. This article reviews the cloning, expression and function of the recently identified sialomucin, CD164, which is highly expressed by primitive hematopoietic progenitor cells. The CD164 receptor is implicated in mediating or regulating hematopoietic precursor cell adhesion to stroma, and may serve as a potent negative regulator of hematopoietic progenitor cell proliferation.

Mouse vascular adhesion protein 1 is a sialoglycoprotein with enzymatic activity and is induced in diabetic insulitis

The continuous recirculation of lymphocytes requires an adequate expression and function of the molecules mediating the cellular interactions between endothelium and lymphocytes. Human vascular adhesion protein 1 (hVAP-1) is an endothelial cell adhesion molecule that mediates the binding of lymphocytes to venules in peripheral lymph nodes as well as at sites of inflammation. Recently the mouse homologue of hVAP-1 has been cloned. It is a previously unknown molecule with a significant sequence identity to copper-containing amine oxidases. Besides the sequence, very little is known about the expression, structure, and function of mouse VAP-1 (mVAP-1). In this study we demonstrate that mVAP-1 is prominently expressed in endothelial and smooth muscle (but not in other types of muscle cells), as well as in adipocytes. mVAP-1 is a 220-kd homodimeric sialoglycoprotein that displays cell-type-specific differences in glycosylation. The expression of mVAP-1 is induced on inflammation in the vessels of the endocrine pancreas during the development of insulitis, and the up-regulation correlates with the extent of the lymphocytic infiltrate. In general, different mouse strains displayed very similar VAP-1 expression, but the small differences seen in liver and gut suggest that immunostimulation may modulate VAP-1 synthesis in extrapancreatic organs as well. Finally, we show that mVAP-1 has a monoamine oxidase activity against naturally occurring substrates, implying a role in the development of vasculopathies. These data show that mVAP-1 and hVAP-1 are very similar molecules that nevertheless have certain marked differences in expression, biochemical structure, and substrate specificity. Thus mVAP-1 is a novel inflammation-inducible mouse molecule that has a dual adhesive and enzymatic function.

Peripheral lymph node addressins are expressed on skin endothelial cells

The term "peripheral node addressins" describes a set of several endothelial adhesion molecules, which collectively bind to L-selectin and react with monoclonal antibody MECA-79. They regulate lymphocyte recirculation through peripheral nodes. Their expression is thought to be restricted to a specialized vascular segment within the node, called the high endothelial venule. In certain chronic skin diseases, however, postcapillary venules of the skin may also acquire a high endothelial venule-like morphology. Employing immunohistochemistry on cryostat sections, we found these skin endothelial cells - like peripheral node high endothelial venules - to be reactive with monoclonal antibody MECA-79. Tissue lysates from the same specimens were then analyzed by immunoprecipitation using recombinant human L-selectin Fc-chimeras followed by immunoblotting using monoclonal antibody MECA-79. In contrast to peripheral node endothelium, which mainly expressed peripheral node addressin moieties of molecular sizes 90-110 kDa and 160 kDa, endothelial cells in cutaneous T cell lymphoma skin lesions expressed an additional and not yet defined 220 kDa peripheral node addressin-like molecule. Most surprisingly, even in normal skin specimens, we found a distinct subset of endothelial cells located around hair follicles constitutively expressing 90-110 kDa peripheral node addressin-like moieties. It is intriguing to speculate that - in analogy to the role of peripheral node addressins in peripheral nodes - the induced expression of peripheral node addressins in chronic T cell mediated skin diseases is responsible for a sustained lymphocyte recruitment. The constitutive expression of peripheral node addressins on perifollicular endothelium may serve for a continuous lymphocyte recirculation through normal skin.

A novel, high endothelial venule-specific sulfotransferase expresses 6-sulfo sialyl Lewis(x), an L-selectin ligand displayed by CD34

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to unique carbohydrate ligands, sulfated sialyl Lewis(x), which are expressed on high endothelial venules (HEV) in secondary lymphoid organs. The nature of the sulfotransferase(s) that contribute to sulfation of such L-selectin counterreceptors has been uncertain. We herein describe a novel L-selectin ligand sulfotransferase, termed LSST, that directs the synthesis of the 6-sulfo sialyl Lewis(x) on L-selectin counterreceptors CD34, GlyCAM-1, and MAdCAM-1. LSST is predominantly expressed in HEV and exhibits striking catalytic preference for core 2-branched mucin-type O-glycans as found in natural L-selectin counterreceptors. LSST enhances L-selectin-mediated adhesion under shear compared to nonsulfated controls. LSST therefore corresponds to an HEV-specific sulfotransferase that contributes to the biosynthesis of L-selectin ligands required for lymphocyte homing.

Sulfotransferases of two specificities function in the reconstitution of high endothelial cell ligands for L-selectin

L-selectin, a lectin-like receptor, mediates rolling of lymphocytes on high endothelial venules (HEVs) in secondary lymphoid organs by interacting with HEV ligands. These ligands consist of a complex of sialomucins, candidates for which are glycosylation- dependent cell adhesion molecule 1 (GlyCAM-1), CD34, and podocalyxin. The ligands must be sialylated, fucosylated, and sulfated for optimal recognition by L-selectin. Our previous structural characterization of GlyCAM-1 has demonstrated two sulfation modifications, Gal-6-sulfate and GlcNAc-6-sulfate in the context of sialyl Lewis x. We now report the cloning of a Gal-6-sulfotransferase and a GlcNAc-6-sulfotransferase, which can modify GlyCAM-1 and CD34. The Gal-6-sulfotransferase shows a wide tissue distribution. In contrast, the GlcNAc-6-sulfotransferase is highly restricted to HEVs, as revealed by Northern analysis and in situ hybridization. Expression of either enzyme in Chinese hamster ovary cells, along with CD34 and fucosyltransferase VII, results in ligand activity, as detected by binding of an L-selectin/IgM chimera. When coexpressed, the two sulfotransferases synergize to produce strongly enhanced chimera binding.

Reconstitution of functional L-selectin ligands on a cultured human endothelial cell line by cotransfection of alpha1-->3 fucosyltransferase VII and newly cloned GlcNAcbeta:6-sulfotransferase cDNA

Recently, we proposed sialyl 6-sulfo Lewis X as a major carbohydrate-capping group of the L-selectin ligands on high endothelial venules in human lymph nodes. In this study we succeeded in reconstituting functional L-selectin ligands on a cultured human endothelial cell line, ECV304, by transfecting the alpha1-->3fucosyltranseferase VII (Fuc-T VII) and newly cloned GlcNAcbeta:6-sulfotransferase (6-Sul-T) cDNAs. The ECV304 cells transfected with Fuc-T VII cDNA expressed conventional sialyl Lewis X detected with specific antibodies including 2H5, whereas the cells transfected with 6-Sul-T cDNA expressed sialyl 6-sulfo lactosamine as well as MECA-79-defined carbohydrate determinants, but these singly transfected cells failed to express sialyl 6-sulfo Lewis X, as detected with the antisialyl 6-sulfo Lewis X mAb G152. Sialyl 6-sulfo Lewis X appeared only on the cells that were cotransfected with both 6-Sul-T and Fuc-T VII cDNAs. Significant adhesion of L-selectin-expressing cells was seen only to the doubly transfected ECV304 cells and was inhibited by G152. No adhesion was observed to the cells transfected either with 6-Sul-T or with Fuc-T VII cDNA alone. The mRNAs of the two enzymes were expressed or were inducible upon interleukin 1 stimulation in human endothelial cells. These results indicate that a set of carbohydrate determinants synthesized by the concerted action of the two enzymes, as typically represented by the sialyl 6-sulfo Lewis X-capping group, serves as an essential component of the ligand for L-selectin and that the reagents 2H5 and MECA-79, utilized in earlier studies to detect L-selectin ligand on high endothelial venules, recognize two different aspects of the same set of synthetic products.

The cutaneous lymphocyte antigen is an essential component of the L-selectin ligand induced on human vascular endothelial cells

L-selectin mediates leukocyte rolling on vascular endothelium during inflammation. Although vascular endothelium can be activated with inflammatory cytokines to express functional L-selectin ligands, these ligands have not been well characterized. In this study, fucosyltransferase VII cDNA (Fuc-TVII) transfection of the EA.hy926 human vascular endothelial cell line (926-FtVII) induced functional L-selectin ligand expression and expression of sialyl Lewisx (sLex), as defined by HECA-452 (cutaneous lymphocyte antigen; CLA) and CSLEX-1 mAbs. Cytokine activation of human umbilical vein endothelial cells (HUVEC) also induced functional L-selectin ligand expression, with increased CLA expression and Fuc-TVII transcription. The majority of L-selectin-dependent lymphocyte attachment to activated HUVEC and 926-FtVII cells was blocked specifically by treating the endothelial cells with the HECA-452 mAb, but not the CSLEX-1 mAb. CLA-bearing ligands on vascular endothelium also required sulfation and appropriate molecular scaffolds for functional activity, but were distinct from the L-selectin ligands previously identified by the MECA-79 mAb. These findings demonstrate that the HECA-452- defined antigen, CLA, is an essential carbohydrate component of vascular L-selectin ligands.

Core 2 oligosaccharide biosynthesis distinguishes between selectin ligands essential for leukocyte homing and inflammation

Mammalian serine/threonine-linked oligosaccharides (O-glycans) are commonly synthesized with the Golgi enzyme core 2 beta-1,6-N-acetylglucosaminyltransferase (C2 GlcNAcT). Core 2 O-glycans have been hypothesized to be essential for mucin production and selectin ligand biosynthesis. We report that mice lacking C2 GlcNAcT exhibit a restricted phenotype with neutrophilia and a partial deficiency of selectin ligands. Loss of core 2 oligosaccharides reduces neutrophil rolling on substrata bearing E-, L-, and P-selectins and neutrophil recruitment to sites of inflammation. However, the diminished presence of L-selectin ligands on lymph node high endothelial venules does not affect lymphocyte homing. These studies indicate that core 2 oligosaccharide biosynthesis segregates the physiologic roles of selectins and reveal a function for the C2 GlcNAcT in myeloid homeostasis and inflammation.