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J Biol Chem, Vol. 273, Issue 18, 11225-11233, May 1, 1998
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From the We investigated the molecular species of sulfated
sialyl Lewis X determinants, the putative L-selectin ligand, expressed
on high endothelial venules (HEV) in human lymph nodes. Comparison of
the reactivity pattern of HEV with the reactivity of the pure 6-sulfo,
6'-sulfo, or 6,6'-bissulfo sialyl Lewis X determinant with hitherto
known anti-sialyl Lewis X antibodies strongly suggested 6-sulfo sialyl
Lewis X to be the best candidate for the major sulfated sialyl Lewis X
determinant on HEV, followed by 6,6'-bissulfo sialyl Lewis X, whereas
6'-sulfo sialyl Lewis X was unlikely. We newly generated monoclonal
antibodies (mAbs) G152 and G72 directed against 6-sulfo sialyl Lewis X,
which intensely labeled HEV in immunohistochemical examination and
inhibited binding of recombinant L-selectin-IgG to HEV, suggesting that
the determinant serves as a ligand for L-selectin. To test the
concomitant expression of 6,6'-bissulfo sialyl Lewis X, specific mAbs
(G2706, G27011, G27037, and G27039) were generated, but all antibodies
failed to react to HEV. Next, we established mAbs (AG97 and AG273)
directed against 6-sulfo Lewis X, the asialo form of 6-sulfo sialyl
Lewis X. The antibodies were not reactive to untreated HEV, but
strongly reacted to sialidase-treated HEV. This indicated the
predominance of the sialylated form of 6-sulfo sialyl Lewis X and
minimal expression of its asialo form, corroborating that it was
synthesized by fucosyltransferase VII, the isoenzyme that
preferentially produces the sialylated form of the determinant.
L-selectin (leukocyte endothelial cell adhesion molecule-1,
leukocyte adhesion molecule-1, Mel-14 antigen) is expressed on human
peripheral lymphocytes and is proposed to be involved in the homing of
lymphocytes into peripheral lymph nodes (1-3). The high endothelial
venules (HEV)1 in peripheral
lymph nodes are thought to express a carbohydrate ligand that binds to
L-selectin. However, the nature of the L-selectin ligand expressed at
the surface of HEV endothelial cells is not yet clear. Some sulfated
carbohydrate determinants are known to bind to L-selectin or inhibit
L-selectin-mediated cell adhesion. On the other hand, it was suggested
that sialyl Lewis X and sialyl Lewis A have a significant capacity to
bind L-selectin, despite the lack of a sulfate residue in their
carbohydrate structures (4, 5), right after they had first been shown
to serve as ligands for E-selectin (6-10). However, most of the known
anti-sialyl Lewis X antibodies as well as anti-sialyl Lewis A
antibodies did not react efficiently to HEV endothelial cells. In an
earlier report, we showed that one of the anti-sialyl Lewis X
antibodies (2H5) specifically detected a sialyl Lewis X-like
determinant on human HEV, and the antigenic determinant served as a
ligand for L-selectin since the antibody inhibited the binding of
lymphoid cells to human HEV endothelial cells in Stamper-Woodruff
assays (11). We suggested that the antigenic determinant detected by the antibody was closely related, but not exactly identical, to genuine
sialyl Lewis X and called it a complex-type sialyl Lewis X determinant,
which was defined by the 2H5 antibody at that time (11).
In studying the specificity of the known anti-sialyl Lewis X
antibodies, we noticed that they can be classified into two groups according to their cross-reactivity to sialyl Lewis X-related structures. One group consists of antibodies that recognize mainly sialic acid and fucose residues, but do not recognize the type 2 chain
core Gal In a previous study, we investigated the reactivity of a few
anti-sialyl Lewis X antibodies against human HEV and compared it with
the reactivity pattern of the antibodies against a series of pure
sulfated sialyl Lewis X determinants (15). Our unexpected conclusion
was that the best candidate for the molecular species carried by HEV is
6-sulfo sialyl Lewis X (15), a conclusion quite different from those of
preceding researchers, who suggested the 6'-sulfo sialyl Lewis X
species to be a major determinant (13, 14). In this paper, we expanded
our studies and generated a series of new monoclonal antibodies
directed against 6-sulfo sialyl Lewis X, 6,6'-bissulfo sialyl Lewis X,
and 6-sulfo Lewis X. By using these new reagents, we tried to establish
6-sulfo sialyl Lewis X as the major sialyl Lewis X-like carbohydrate
determinant carried by HEV endothelial cells, and the ligand carrying
this capping structure serves as a ligand for L-selectin in human
HEV.
Monoclonal Antibodies Directed against Sialyl Lewis X-related
Carbohydrate Determinants--
The anti-sialyl Lewis X antibodies 2H5
(established against a mixture of complex sialyl Lewis X-active
determinants prepared from human cancer cells) and 2F3 (established
against the synthetic sialyl Lewis X glycolipid) were prepared as
described previously (11, 16). The antibody HECA-452 was a kind gift
from Dr. T. K. Kishimoto (Department of Pathology, Stanford
University School of Medicine, Stanford, CA) (17). SNH-3 and FH-6 were
gifts from Dr. S. Hakomori (Pacific Northwest Research Foundation,
Seattle, WA) (7, 18, 19). CSLEX-1 was obtained from American Type Culture Collection (Bethesda, MD) (20). The anti-Lewis X antibody LeuM1
was purchased from Becton Dickinson Labware (Franklin Lakes, NJ); FH-2
was also a gift from Dr. S. Hakomori; and 73-30 and Tx-17 were
established in our laboratory. The antibody SU59 directed against
3'-sulfo Lewis X was a gift from Dr. Akihiro Hino (Nisshin Shokuhin Co.
Ltd., Otsu, Japan). These antibodies are all murine IgM, except for
HECA-452, which is rat IgM.
Program of Experimental Pathology,
Department of Applied Bio-organic Chemistry,
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ABSTRACT
Top
Abstract
Introduction
Procedures
Results
Discussion
References
![]()
INTRODUCTION
Top
Abstract
Introduction
Procedures
Results
Discussion
References
1
4GlcNAc
, whereas the other group contains antibodies
that unerringly recognize sialic acid residues and type 2 chain core
Gal
1
4GlcNAc
structure, but only weakly recognize fucose
residues (12). The anti-sialyl Lewis X antibodies that reacted to HEV
were all found to belong to the former group, and the antibodies in the
latter group lacked reactivity to HEV endothelial cells. These findings
led us to assume that the complex sialyl Lewis X on HEV could be a
sialyl Lewis X determinant that was somehow modified at the type 2 chain core structure. This modification would not affect the reactivity
of the antibodies in the former group, but would seriously affect the
reactivity of the antibodies in the latter group. The sulfated sialyl
Lewis X determinants, proposed by Hemmerich et al. (13, 14)
to be expressed on HEV in murine lymph nodes, were the sialyl Lewis X
determinants modified by sulfate residues at the type 2 chain core
structure. We thought one of these might be the complex sialyl Lewis X
determinant that had been detected by our antibody on human HEV
endothelial cells.
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EXPERIMENTAL PROCEDURES
Top
Abstract
Introduction
Procedures
Results
Discussion
References
Preparation of Carbohydrate Determinants, ELISA, and TLC Immunostaining-- ELISA was performed using glycolipid antigens immobilized at the bottom of 96-well culture plates by a standard method described previously (23). Peroxidase-conjugated rabbit anti-rat IgM (µ-chain-specific; Zymed Laboratories Inc., South San Francisco, CA) was used for HECA-452, and peroxidase-conjugated goat anti-mouse IgM (µ-chain-specific; Cappel Inc., Malvern, PA) was used for the other antibodies. TLC immunostaining was performed according to the method described previously (23, 24), except that peroxidase-conjugated antibody was used as the second antibody, and ECL Western blotting detection reagents (Amersham International, Buckinghamshire, United Kingdom) were used to detect positive reactions instead of 125I-protein A.
The pure synthetic sialyl Lewis X glycolipid and the synthetic sulfated glycolipids (6-sulfo sialyl Lewis X, 6'-sulfo sialyl Lewis X, 6,6'-bissulfo sialyl Lewis X, and and 3'-sulfo Lewis X) used in this study were synthesized as described previously (25-27). For the structures of these glycolipids, see Table I. The asialo compounds (6-sulfo Lewis X, 6'-sulfo Lewis X, and 6,6'-bissulfo Lewis X) were prepared by sialidase treatment of the corresponding synthetic glycolipids using sialidase from Arthrobacter ureafaciens (Nakarai Chemicals Co. Ltd., Kyoto, Japan).
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Immunohistochemical Examination and Binding Assay of L-selectin-IgG Chimera on Frozen Lymph Node Sections-- Consecutive frozen sections of 10-µm thickness were prepared from human axillary and mesenteric lymph nodes and other tissues and organs for immunohistochemical examination using anti-sialyl Lewis X and newly generated anti-sulfo sialyl Lewis X antibodies. The avidin-biotin complex technique for immunohistochemical study was performed as described in the instructions for the kits (Vectastain) provided by Vector Labs, Inc. (Burlingame, CA). When indicated, the sections were pretreated with sialidase from A. ureafaciens.
For the binding assay of recombinant L-selectin-IgG chimera, frozen sections prepared from freshly obtained human lymph nodes were fixed with 0.5% paraformaldehyde at 4 °C for 10 min. The sections were pretreated for 30 min at room temperature with phosphate-buffered saline containing 20% goat serum. To this, a mixture (1:1:1, v/v/v) of the recombinant human L-selectin-IgG chimera (20 µg/ml; kindly provided by Drs. H. Kondo and Y. Inoue, New Drug Research Labs, Kanebo Ltd., Osaka, Japan), affinity-purified biotinylated goat anti-human IgG antibody (30 µg/ml), and peroxidase-labeled avidin (30 µg/ml) was overlaid and incubated for 60 min at 4 °C. The reaction was visualized with 3,3'-diaminobenzidine tetrahydrochloride, followed by after-staining with 1% methyl green. For the inhibition study, sections were incubated with anti-carbohydrate antibodies (50-100 µg/ml) for 120 min at 4 °C prior to the addition of the recombinant human L-selectin-IgG chimera/peroxidase mixture.Adhesion of L-selectin-transfected Cells to 6-Sulfo Sialyl Lewis X-- A 96-well plate was coated with 6-sulfo sialyl Lewis X by adding ethanol solution containing glycolipid (200 ng/well), egg yolk phosphatidylcholine (1 µg/well), and cholesterol (500 ng/well), followed by air-drying at 37 °C. After blocking with 5% bovine serum albumin in phosphate-buffered saline overnight at 4 °C, the plate was incubated with appropriate inhibitor antibodies (40 µg/well) for 30 min at room temperature. BCECF-AM (Molecular Probes, Inc., Eugene, OR)-labeled HULT-7 cells (2 × 105/well), the human L-selectin-transfected cells (15), were added and incubated for 60 min at 37 °C. The number of adherent cells was estimated by measuring fluorescence at 490 nm excitation and 530 nm emission on a fluorometer (Fluoroscan II, Labosystems, Tokyo).
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RESULTS |
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Detection of the Sialyl Lewis X-like Determinant on HEV Endothelial Cells Using Anti-sialyl Lewis X and Anti-Lewis X Antibodies-- Endothelial cells of HEV in human peripheral lymph nodes were reactive to only a part of anti-sialyl Lewis X antibodies as shown in Fig. 1 (a-f). The antibodies 2F3 and HECA-452 were strongly reactive to the HEV endothelial cells as well as the 2H5 antibody as reported previously (11). The same pattern of staining was observed consistently with 14 different lymph node samples prepared from different individuals. This indicated that there are two groups of anti-sialyl Lewis X antibodies: one group (2F3, 2H5, and HECA-452) of antibodies that stain HEV endothelial cells and another group (SNH-3, FH-6, and CSLEX-1) that are unable to do so. Reactivity of the 2F3, 2H5, and HECA-452 antibodies was eliminated when the sections were pretreated with sialidase (data not shown). These results suggest that the carbohydrate determinant(s) carried by HEV endothelial cells have sialylated structures closely related to sialyl Lewis X, but not genuine sialyl Lewis X, which would have been readily detected by all six anti-sialyl Lewis X antibodies.
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Reactivity of Anti-sialyl Lewis X Antibodies to Synthetic Sulfated
Sialyl Lewis X Determinants and Other Related Compounds--
The six
anti-sialyl Lewis X antibodies reacted equally well to the genuine
sialyl Lewis X glycolipid in ELISA (Fig.
2a), and we thought the
difference in the reactivity of anti-sialyl Lewis X antibodies
against HEV endothelial cells stemmed from the different cross-reactivity of the antibodies. To determine whether the
determinants detected by these anti-sialyl Lewis X antibodies were
sulfated sialyl Lewis X determinants, which Hemmerich et al.
(13, 14) proposed were carried by GlyCAM-1 in murine lymph nodes, we
tested the reactivity of the six anti-sialyl Lewis X antibodies against synthetic sulfo sialyl Lewis X determinants. As shown in Fig. 2b, the sialyl Lewis X sulfated at
-Gal (6'-sulfo
sialyl Lewis X) was reactive to an unexpectedly wide variety of
antibodies, including CSLEX-1, SNH-3, 2F3, 2H5, and HECA-452. Only the
antibody FH-6 lost its binding activity upon 6-sulfation at the
-Gal
moiety of the sialyl Lewis X structure.
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-GlcNAc moiety
(6-sulfo sialyl Lewis X) was detected by antibodies 2F3, 2H5, and
HECA-452, but not by antibodies CSLEX-1, SNH-3, and FH-6 (Fig.
2c). This reaction profile was exactly the same as that of
human HEV endothelial cells against these six antibodies, as indicated
in Fig. 1, and suggested that 6-sulfo sialyl Lewis X would be a good
candidate for the sialyl Lewis X-like determinant expressed on HEV
endothelial cells.
The reactivity of disulfated sialyl Lewis X (6,6'-bissulfo sialyl Lewis
X) was essentially the same as that of GlcNAc-sulfated sialyl Lewis X
(6-sulfo sialyl Lewis X). The antibodies 2F3, 2H5, and HECA-452 were
reactive to 6,6'-bissulfo sialyl Lewis X, whereas FH-6 and CSLEX-1 were
not (Fig. 2d). This led us to assume that 6,6'-bissulfo
sialyl Lewis X is another good candidate for the determinant carried by
human HEV endothelial cells. The only difference between 6-sulfo sialyl
Lewis X and 6,6'-bissulfo sialyl Lewis X was that the latter
determinant was weakly reactive to SNH-3.
Next, we tested the reactivity of four anti-Lewis X antibodies,
all of which recognize the Lewis X determinant (Fig. 2e), against the asialo derivatives of the above sulfated sialyl Lewis X
determinants (Fig. 2, f-h). Three out of the four
anti-Lewis X antibodies were found to react to 6'-sulfo Lewis X (Fig.
2f), whereas all of them failed to react to 6-sulfo Lewis X
(Fig. 2g). Since sialidase-treated HEV endothelial cells
were not stained with any of the anti-Lewis X antibodies in
immunohistochemical examination, these findings again suggest that
6-sulfo sialyl Lewis X is actually the sialyl Lewis X-like determinant
expressed on HEV endothelial cells, but 6'-sulfo sialyl Lewis X is not. Only one anti-Lewis X antibody (FH-2) showed a weak cross-reactivity, and the others were not reactive to 6,6'-bissulfo Lewis X (Fig. 2h). None of the 10 antibodies tested was reactive to the
3'-sulfo Lewis X determinant, which had been reported to be present in mucin side chains of human meconium (28) and later found to bind to
recombinant L-selectin (27).
Generation of Monoclonal Antibodies Specific to 6-Sulfo Sialyl Lewis X-- Since analysis of the reactivity pattern of known anti-sialyl Lewis X and anti-Lewis X antibodies strongly suggested 6-sulfo sialyl Lewis X is most probably the sulfated sialyl Lewis X determinant carried by HEV endothelial cells, we generated two monoclonal antibodies (G152 and G72) by immunizing synthetic 6-sulfo sialyl Lewis X. The specificity of these new antibodies against pure carbohydrate determinants in ELISA is shown in Fig. 3. Both antibodies were strongly reactive to 6-sulfo sialyl Lewis X, but were not reactive to other related structures, including genuine sialyl Lewis X and 6'-sulfo sialyl Lewis X, and were only slightly cross-reactive to 6,6'-bissulfo sialyl Lewis X in ELISA (Fig. 3). They did not react to asialo derivatives such as 6-sulfo Lewis X, 6'-sulfo Lewis X, 6,6'-bissulfo Lewis X, and 3'-sulfo Lewis X. G152 was not at all reactive, whereas G72 showed significant reactivity against the SL2L4 determinant, which does not contain a fucose residue (Fig. 3).
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Characterization of the 6-Sulfo Sialyl Lewis X Determinant on HEV Endothelial Cells-- Both G152 and G72 antibodies strongly stained HEV endothelial cells in human peripheral lymph nodes in immunohistochemical examination (Fig. 5). Frozen sections had to be used in the immunohistochemical detection of the antigen by these two antibodies, and virtually no positive staining was obtained when Formalin-fixed sections were used. As summarized in Table II, these antibodies stained HEV endothelial cells in peripheral lymph nodes, tonsils, Peyer's patches, and appendices. The staining of HEV in Peyer's patches and appendices was significantly weaker than in lymph nodes and tonsils. No blood vessels in other organs including the spleen, thymus, gastrointestinal tract, lung, and kidney were stained by the two antibodies, which is in line with the distribution of L-selectin ligands. This distribution of the antigen also coincides with that detected by the 2H5 antibody as reported earlier (11).
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Detection of 6,6'-Bissulfo sialyl Lewis X Using Newly Generated Specific Monoclonal Antibodies-- Next, we generated antibodies directed against 6,6'-bissulfo sialyl Lewis X since the determinant seemed to be another candidate for the sulfated L-selectin ligand expressed in human lymph nodes. Four monoclonal antibodies (G2706, G27011, G27037, and G27039) were obtained by the immunization of the synthetic 6,6'-bissulfo sialyl Lewis X glycolipid. These antibodies showed strong reactivity to the immunogen 6,6'-bissulfo sialyl Lewis X and were moderately cross-reactive to its desialylated structure, 6,6'-bissulfo Lewis X, in ELISA (Fig. 8, a-d). None of these antibodies reacted to 6-sulfo sialyl Lewis X, genuine sialyl Lewis X, or other related structures, including SL2L4-cholesterylaniline, but some of them showed a weak cross-reactivity to 6'-sulfo sialyl Lewis X.
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Detection of 6-Sulfo Lewis X in Sialidase-treated HEV Endothelial Cells-- By immunizing sialidase-treated 6-sulfo sialyl Lewis X, we further established two monoclonal antibodies directed against the corresponding asialo compound, 6-sulfo Lewis X. The antibodies (AG97 and AG273) thus generated had a strong reactivity to 6-sulfo Lewis X in ELISA, but were not reactive to other related asialo structures, including Lewis X, 6'-sulfo Lewis X, and 3'-sulfo Lewis X (Fig. 8, e and f). Of course, these antibodies lacked reactivity to the sialylated determinants such as 6-sulfo, 6'-sulfo, 6,6'-bissulfo, and genuine sialyl Lewis X. Weak reactivity was noted against 6,6'-bissulfo Lewis X in ELISA, but this reactivity was not detected in TLC immunostaining (Fig. 9b, lane 4), suggesting that it was only a weak cross-reactivity.
These two antibodies did not stain intact HEV endothelial cells in human lymph nodes in immunohistochemical examination, but strongly labeled the cells when the sections were pretreated with sialidase (Fig. 10, i-l). This was in a striking contrast to the strong staining of intact HEV by G152 and G72 antibodies, which was nearly completely eliminated after sialidase treatment (Fig. 10, a-d). These findings indicate that 6-sulfo sialyl Lewis X was abundantly present, whereas there was little or none of its asialo form (6-sulfo Lewis X) on intact HEV endothelial cells. The latter determinant was produced only when 6-sulfo sialyl Lewis X in the frozen sections was hydrolyzed with sialidase.| |
DISCUSSION |
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The aberrant reaction of anti-sialyl Lewis X antibodies against HEV endothelial cells in human lymph nodes has long puzzled researchers (11, 29). Some anti-sialyl Lewis X antibodies react to HEV and inhibit the binding of L-selectin to HEV, yet others do not. Our preliminary study (Ref. 15 and this study), using a series of hitherto known anti-sialyl Lewis X and anti-Lewis X antibodies, suggested that 6-sulfo sialyl Lewis X and 6,6'-bissulfo sialyl Lewis X, but not 6'-sulfo sialyl Lewis X, are possible candidates for the complex sialyl Lewis X-like determinants present on HEV endothelial cells. 6-Sulfo sialyl Lewis X seemed to be the most predominant molecular species of sulfated sialyl Lewis X-related determinants on human HEV endothelial cells, judging from their reactivity pattern to hitherto known anti-sialyl Lewis X and anti-Lewis X antibodies. The results of this study using a series of new monoclonal antibodies directed against the respective sulfated determinants provided strong evidence corroborating the predominant expression of 6-sulfo sialyl Lewis X on HEV endothelial cells. The anti-6-sulfo sialyl Lewis X antibodies G152 and G72 strongly labeled HEV in immunochemical examination, and the anti-6-sulfo Lewis X antibodies AG97 and AG273 intensely stained HEV after sialidase treatment.
If a significant amount of conventional sialyl Lewis X were expressed
on HEV, the reactivity of HEV against anti-sialyl Lewis X antibodies
should have been
CSLEX-1+SNH-3+FH-6+2H5+2F3+HECA-452+
instead of
CSLEX-1
SNH-3
FH-6
2H5+2F3+HECA-452+.
Moreover, the Lewis X determinant should have been detected by all
conventional anti-Lewis X antibodies after an appropriate sialidase
treatment, but it was not. Similarly, if a considerable amount of
6'-sulfo sialyl Lewis X were present on HEV, the reactivity of HEV
against anti-sialyl Lewis X antibodies should have been CSLEX-1+SNH-3+FH-6
2H5+2F3+HECA-452+,
and its asialo form determinant (6'-sulfo Lewis X), which is detectable
by a majority of conventional anti-Lewis X antibodies (Fig. 2), should
have been detected after sialidase treatment. Concerning the disulfated
determinant, we could not obtain any positive evidence to support the
presence of 6,6'-bissulfo sialyl Lewis X in HEV of human peripheral
lymph nodes, although we generated as many as four monoclonal
antibodies specific to the determinant.
Our results also indicated that 6-sulfo sialyl Lewis X accounts for the majority of the carbohydrate capping group of the L-selectin ligand on HEV endothelial cells as far as human HEVs are concerned, judging from the nearly complete inhibition of recombinant L-selectin binding to HEV endothelial cells. These results are at variance with the previous notion that nearly equal amounts of 6'-sulfo and 6-sulfo sialyl Lewis X are expressed on murine HEV (13, 14). This might be partly due to the species difference since we could not detect any significant reactivity of our anti-6-sulfo sialyl Lewis X antibodies (G152 and G72) against HEV endothelial cells in murine and rat lymph nodes.2 It is well known that sialyl Lewis X, the putative ligand for E- and P-selectins, is barely detectable on murine and rat leukocytes using most of the conventional anti-sialyl Lewis X antibodies that readily detect the determinant on human leukocytes, and the carbohydrate ligand on HEV for L-selectin in mice and rats could well be different from that in humans.
An isoenzyme of
1
3-fucosyltransferase (fucosyltransferase VII)
has been shown to be present on HEV and is suggested to be mainly
involved in the synthesis of the L-selectin ligand on HEV (30). In line
with this, we found only a disproportionally small amount of the asialo
species of the 6-sulfo sialyl Lewis X determinant (i.e.
6-sulfo Lewis X) on human HEV in this study. This implies the
contribution of fucosyltransferase VII in the synthesis of the
determinant since fucosyltransferase VII is the only
1
3-fucosyltransferase isoenzyme that lacks the synthetic ability
of the asialo species of the corresponding determinant (31, 32).
Malý et al. (33) studied the substrate specificity of
fucosyltransferase VII and concluded that the enzyme has an ability to
transfer fucose residues onto 6-sulfated lactosamine, but not onto
6'-sulfated lactosamine. Habuchi et al. (34) recently
studied the substrate specificity of a cloned 6'-sulfotransferase and
reported that the enzyme preferred Gal
moieties in partially
sulfated polylactosamine much more than those in non-sulfated
polylactosamine as an acceptor of sulfate residues. On the other hand,
6-sulfation has recently been suggested to occur on the terminal
GlcNAc
moiety even before the transfer of the Gal
moiety, and
6-sulfolactosamine has been suggested to be formed afterward by the
action of
1
4-galactosyltransferase on 6-sulfo-GlcNAc
(35).
These findings imply that sulfation at the 6'-position occurs mainly
after the formation of 6-sulfolactosamine and may not proceed without
6-sulfo-GlcNAc
during the synthesis of sulfated substrates for
fucosyltransferases. This could explain our results showing that
6-sulfo sialyl Lewis X is strongly expressed, whereas the 6'-sulfo
species is virtually undetectable in human HEV endothelial cells.
P-selectin glycoprotein ligand-1 (PSGL-1) has been reported to be necessary for the high affinity binding of sialyl Lewis X-positive leukocytes not only to P-selectin, but also to L-selectin (36-39). This finding was reproducible in our laboratory regarding the leukocyte-leukocyte interaction. The sulfated tyrosine residue near the N terminus of PSGL-1 was proposed to be responsible for the observed high affinity binding to L-selectin. The problem with the lymphocyte-HEV interaction was that we could not detect PSGL-1 in human HEV endothelial cells using well characterized specific antibodies in our preliminary experiments. When tested in the binding assay using recombinant soluble human L-selectin (40) and in the cell adhesion assay using human L-selectin-transfected cells (Fig. 6a), the synthetic 6-sulfo sialyl Lewis X glycolipid exhibited a 30-60% increase in L-selectin binding when compared with the genuine sialyl Lewis X glycolipid. It is not clear if this increase is comparable to the enhancing effect of PSGL-1 on L-selectin-mediated cell adhesion. Sanders et al. (41) recently studied the binding activity of several synthetic sulfated Lewis X determinants and suggested that even a subtle difference in the binding activity of the 6-sulfo species observed in the monovalent binding assay would possibly exert a profound effect on the polyvalent binding in intercellular adhesion.
Although this would provide one possible explanation, the sulfate residue at the penultimate GlcNAc in 6-sulfo sialyl Lewis X nevertheless may not substitute for the sulfate residue near the N terminus of PSGL-1 in the high affinity binding to L-selectin. An alternative explanation would be the presence of an amount of PSGL-1 too small to be detected by immunohistochemical examination or the presence of PSGL-1-like molecule(s) on HEV endothelial cells. Although we failed to detect it on normal human HEV endothelial cells, PSGL-1 is reportedly expressed on microvascular endothelial cells in some pathologic tissues (42).
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ACKNOWLEDGEMENTS |
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We thank Drs. T. K. Kishimoto, S. Hakomori, A. Hino, K. Yoshida, H. Kondo, and Y. Inoue for the gifts of monoclonal antibodies, oligosaccharides, and recombinant selectins.
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FOOTNOTES |
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* This work was supported in part by a grant-in-aid for the second term comprehensive ten-year strategy for cancer control from the Ministry of Health and Welfare, Japan, and by Grants-in-aid for Scientific Research 09281238 and 09672371 from the Ministry of Education, Science, Sports, and Culture, Japan.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
** To whom correspondence should be addressed: Program of Experimental Pathology, Research Inst., Aichi Cancer Center, 1-1 Kanokoden, Chikusaku, Nagoya 464-8681, Japan. Fax: 81-52-763-5233; E-mail: rkannagi{at}aichi-cc.pref.aichi.jp.
1 The abbreviations used are: HEV, high endothelial venule(s); ELISA, enzyme-linked immunosorbent assay; BCECF-AM, 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; PSGL-1, P-selectin glycoprotein ligand-1.
2 M. Sawada-Kasugai, C. Mitsuoka, M. Izawa, and R. Kannagi, unpublished observation.
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REFERENCES |
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S. Kamiyama, N. Sasaki, E. Goda, K. Ui-Tei, K. Saigo, H. Narimatsu, Y. Jigami, R. Kannagi, T. Irimura, and S. Nishihara Molecular Cloning and Characterization of a Novel 3'-Phosphoadenosine 5'-Phosphosulfate Transporter, PAPST2 J. Biol. Chem., April 21, 2006; 281(16): 10945 - 10953. [Abstract] [Full Text] [PDF] |
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K. Ohmori, F. Fukui, M. Kiso, T. Imai, O. Yoshie, H. Hasegawa, K. Matsushima, and R. Kannagi Identification of cutaneous lymphocyte-associated antigen as sialyl 6-sulfo Lewis X, a selectin ligand expressed on a subset of skin-homing helper memory T cells Blood, April 15, 2006; 107(8): 3197 - 3204. [Abstract] [Full Text] [PDF] |
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T. Yamaguchi, K. Kitaya, N. Daikoku, T. Yasuo, S. Fushiki, and H. Honjo Potential Selectin L Ligands Involved in Selective Recruitment of Peripheral Blood CD16(-) Natural Killer Cells into Human Endometrium Biol Reprod, |