1 Agnès Mambole1,2, Dominique Baruch2,3, Patrick Nusbaum1,2, Sylvain Bigot1,2, Misa Suzuki4

20 Pages·2008·0.71 MB·English

JBC Papers in Press. Published on June 27, 2008 as Manuscript M710286200
The latest version is at http://www.jbc.org/cgi/doi/10.1074/jbc.M710286200

THE CLEAVAGE OF NEUTROPHIL LEUKOSIALIN (CD43) BY CATHEPSIN G
RELEASES ITS EXTRACELLULAR DOMAIN AND TRIGGERS ITS INTRAMEMBRANE
PROTEOLYSIS BY PRESENILIN/γ-SECRETASE*
Agnès Mambole1,2, Dominique Baruch2,3, Patrick Nusbaum1,2, Sylvain Bigot1,2, Misa
Suzuki4, Philippe Lesavre1,2, Minoru Fukuda4 and Lise Halbwachs-Mecarelli1,2
From INSERM U8451, Université René Descartes 2, INSERM U7653, Paris, France,
Cancer Research Center, Burnham Institute for Medical Research, La Jolla CA , USA4
Running head: CD43 processing by cathepsin G and γ-secretase
Address correspondence to: Lise Halbwachs-Mecarelli, INSERM U 845, Hôpital Necker, 161 rue de
Sèvres, 75015 Paris, France; Fax [phone]; e-mail: [email protected];

The highly negatively charged membrane The regulated proteolysis of transmembrane
sialoglycoprotein leukosialin, CD43, is shed proteins represents an important mechanism of cell
during neutrophil activation. This is generally functions modulation. The inflammation resolution
thought to enhance cell adhesion. We here involves, for example, the shedding of cytokine
describe two novel consequences of this receptors and adhesion molecules, which down-
shedding, during neutrophil activation by regulates leukocyte adhesion to endothelium. These
phorbol esters or by chemoattractants after regulations result from a decreased membrane
TNF-α priming. CD43 proteolysis was expression of receptors and/or from the release of D
o
investigated by western blotting, using a soluble fragments, competing with their membrane w
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polyclonal antibody to CD43 intracellular counterparts. The majority of shed proteins loa
d
domain. Our data emphasize the importance of a identified to date are cleaved by metalloproteinases ed
juxtamembranous cleavage of about 50% of or by neutrophil-derived serine proteases (1). from
membrane CD43 moleculesof CD43 by cathepsin Leukosialin, CD43 is the predominant cell surface http
G. Indeed, its is inhibited by α1- sialoprotein of leukocytes (2) and has both anti- ://w
antichymotrypsin and and cathepsin G inhibitor adhesive and adhesive properties. Its function has ww
I and is reproduced by exogenous purified been mainly studied on lymphocytes, where CD43 .jb
c
cathepsin G. The resulting membrane-anchored behaves both as a negative-regulator of T cell .org
C-Terminal Fragment, CD43-CTF, becomes proliferation and adhesion and as a positive by/
susceptible to presenilin/γ-secretase, which regulator of memory T cells trafficking (3,4). gu
e
releases CD43 intracytoplasmic domain: Although its expression is normally restricted to st o
n
preincubation with 3 different γ-secretase leukocytes, CD43 is present on colon carcinomas D
e
inhibitors, before PMN treatment by agonists or and on several nonhematopoietic cell lines (5 ,6). In cem
these cell lines, CD43 is processed by a b
by purified cathepsin G, results in the e
accumulation of CD43-CTF. Since CD43 binds presenilin/γ-secretase-mediated Regulated Intra- r 11
E-selectin, we also investigated the effect of the membrane Proteolysis (RIP)1 (7). RIP refers to a , 201
8
soluble extracellular domain CD43s, released by sequential proteolysis of various type I membrane
cathepsin G juxtamembranous cleavage, on

neutrophil adhesion to endothelial cells. A 1 Abbreviations used are : α1PI, α1-proteinase
recombinant CD43s-Fc fusion protein inhibited
inhibitor (α1-antitrypsin) ; α1-CT , α1 anti-
neutrophil E selectin-dependent adhesion to
chymotrypsin ; BSA, bovine serum albumin ;
endothelial cells under flow conditions, while it
CD43-CTF, CD43 C-Terminal Fragment ; CD43s,
had no effect on neutrophil static adhesion.
soluble CD43 ; fMLP, N-formyl-L-methionyl-L-
We thus propose that, in addition to its potential
leucyl-L-phenylalanine ; Galgp,
pro-adhesive role, CD43 proteolysis results in: i)
galactoglycoprotein ; HBSS, Hanks balanced
the release, by cathepsin G, of CD43
solution ; HUVEC, human umbilical vein
extracellular domain, able to inhibit the
endothelial cells ; MMP, matrix metalloproteinase ;
adhesion of flowing neutrophils on endothelial
NE, neutrophil elastase; PBS, phosphate buffered
cells and thus to participate to the natural
saline ; PMA, phorbol myristate acetate ; PMN,
control of inflammation; ii) the release and/or
polymorphonuclear neutrophil ; PMSF, phenyl-
the clearance, by presenilin/γ-secretase, of CD43
methyl-sulfonyl-fluoride; PR3, proteinase 3 ; RIP,
intracellular domain, thereby regulating CD43-
Regulated Intra-membrane Proteolysis ; TNF,
mediated signaling.
Tumor necrosis factor

1
Copyright 2008 by The American Society for Biochemistry and Molecular Biology, Inc.
proteins, including the amyloid precursor protein of also purchased from Calbiochem (Darmstadt,
Alzheimer’s disease, the Notch receptor, CD44, E- Germany) and Athens Technology (Athens,
cadherin…(8). RIP is initiated usually by a Georgia). Human IgGs were purified on protein A-
metalloproteinase, which induces the shedding of sepharose from an AB blood group normal human
the receptor ectodomain, followed by an serum. The CD43s-Fc fusion protein was produced
intramembrane processing of the cell bound in COS cells, as described (22) and purified on
fragment by a PS/γ secretase. This releases the protein A-sepharose. Tumor necrosis factor alpha,
receptor intracellular domain in the cytoplasm. In TNF-α, was from PeproTech (Rocky Hill, NJ).
the case of CD43 in cancer cell lines, this domain Recombinant human VCAM-1-Fc was from R&D
translocates in the nucleus and causes the (Abingdon, UK). α1 anti-chymotrypsin (α1-CT),
upregulation of various genes (9). Cathepsin G inhibitor I, and MG-132 were from
CD43 has been recently described as a ligand for E- Calbiochem, Compound E from Alexis (Lausanne,
selectin (10,11). Its expression on Switzerland), Tapi-0 and Tapi-1 from Peptides
polymorphonuclear neutrophils (PMN) is ten fold International (Louisville, Kentucky), while
higher than P-selectin glycoprotein ligand-1, PSGL- Marimastat, CH46644 and CH6631 were a kind gift
12 the main leukocyte ligand for P-selectin, which from Dr John Bird (Celltech Chiroscience,
also binds E-selectin. In spite of CD43 abundance, Cambridge, UK). All other inhibitors and reagents
data on its precise role in PMN responses are were from Sigma-Aldrich (St Louis, Missouri).
scarce. CD43 is shed during PMN activation (12- Cells: Human neutrophils and endothelial cells
D
15) and during adhesion and spreading (2 ,16), HUVEC were isolated as described (20,23) from ow
n
together with other E-selectin ligands PSGL-1 and platelet-depleted blood and umbilical vein, lo
a
CD44 (17,18). A soluble form of CD43, CD43s, respectively, from healthy volunteers. Neutrophils de
d
representing the entire extracellular domain, has were suspended in Hanks balanced solution with fro
m
been described in plasma and identified to Ca++ and Mg++ containing bovine serum albumin h
goanl aPcMtogNl ywcoapsr octleaiinm (eGd atlog pi)n (v1o9l)v.e C sDer4i3n ep rportoetoelaysseiss 0co.1n%ce n(trHaBtioSnS +h+-aBs SnAo) . efIfne cto uorn hCaDnd4s3, ptrhoitse oBlySsAis ttp://ww
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and metalloproteinases. The precise analysis of the (2). HUVECs were cultured on gelatin coated flasks .jb
proteolysis mechanism was hampered by the fact (Costar Corporation, Cambrige, MA) in M199 c.o
rg
that CD43 soluble fragments do not transfer on supplemented with penicillin, streptomycin, L- b/
y
blotting membranes (15) and required an Glutamine, Hepes (10mM), heparin (50µg/ml), g
u
immunoprecipitation of radiolabelled neutrophil endothelial cell growth supplement ECGS (20 est o
membranes. We produced a polyclonal antibody µg/ml) and 20% fetal calf serum. 3rd- and 4th- n D
against a recombinant CD43 intracellular domain, passage cells were used exclusively. CHO cells ece
in order to re-assess the molecule proteolysis in the m
were either transiently transfected with CD43 b
e
light of recent data on: i) the γ-secretase processing cDNA or stably transfected with cDNAs encoding r 1
1
of CD43 in cancer cells; ii) the description of CD43 both CD43 and core 2 beta-1,6-N- , 20
1
as a leukocyte ligand for endothelial E-selectin. We acetylglucosaminyl transferase (C2GnT), as 8
here describe for the first time, in human PMN described (24), then further transiently transfected
activated by pro-inflammatory stimuli, a cathepsin to enhance protein expression.
G and γ-secretase mediated processing of CD43 Neutrophil activation, flow cytometry and western
with putative important functional consequences. blotting: Freshly isolated neutrophils were
distributed in BSA-coated tubes and gently tumbled
Experimental Procedures every 5 min during their activation at 37°C either
Antibodies and reagents: FITC-anti-CD43 mAb with phorbol-myristate acetate (PMA) or with
(1G10) and IgG1 were from BD Pharmingen (San TNF-α and N-Formyl-L-methionyl-L-leucyl-L-
Diego, CA), anti-CD18 clone IB-4 from Ancell
phenylalanine (fMLP), as described in the figure
(Bayport, MN), anti-CD62E, FITC-anti-CD62L
legends. The reaction was stopped by adding ice-
mAbs and PE-anti-CD146 from Beckman Coulter
cold PBS containing phenyl-methyl-sulfonyl-
(Roissy, France). The rabbit anti-CD43cyto pAb
fluoride (PMSF) 1 mM and 1,10-phenanthroline 1
was obtained as described (20). Human neutrophil
mM, to prevent any further CD43 cleavage. PMN
elastase (NE), cathepsin G and proteinase 3 were
were centrifuged at 4°C for 30 sec at 3,800 g and
purified as described (21). Purified cathepsin G was
submitted to western-blotting or flow cytometry as
described (20).

Assays for PMN adhesion to HUVEC :
2 L Halbwachs-Mecarelli, unpublished observation
2
Static adhesion: Confluent HUVECs, sub-cultured in size to the reported soluble CD43 fragments
in 48-well 0.5% gelatin coated plates, were pre- observed by immunoprecipitation of 125I-labeled
treated for 4 hours with 10 ng/ml TNF-α and rinsed neutrophils (15,27): i) a cell-bound 90 kD doublet,
with medium. PMN were then added (2x106 per ml resulting from clip A (Fig 1C) and complementary
of M199 with 0.1% BSA) and allowed to adhere for to the reported soluble 50 kD doublet; ii) a cell-
30 min at 37°C. Non-adherent cells were removed bound CD43 C-Terminal Fragment, CD43-CTF, of
by rinsing and adherent PMN and HUVEC were 25 kD, resulting from clip B and complementary to
detached with 0.5 mg/ml collagenase for 15 min at the reported soluble 120 kD fragment.
37°C. They were then labeled with PE-anti-CD146, The intensity of the 90kD doublet was variable and
to distinguish CD146 negative PMN from CD146 appeared to be related to the “spontaneous”
positive endothelial cells. PMN were counted by activation of PMN during the isolation procedure:
flow cytometry with a constant time setting. As we had observed with the soluble 50 kD doublet
- Flow assay: Cell adhesion was analyzed, as (27), it was often observed on freshly isolated
described (25), by real-time videomicroscopy with PMN, appeared upon incubation at cell
a 10X objective, in a flow chamber containing a concentration above 106/ml without any stimuli and
0.5% gelatin-precoated glass coverslip with was significantly prevented by avoiding the lysis of
confluent HUVECs, which had been stimulated for contaminating erythrocytes and by the presence of 1
4h with 0.2 ng/ml TNF-α and washed to remove the mg/ml BSA in incubation media. It is not known
TNF-α. Controlled flow rates, generating a wall whether the doublet represents two very close split
D
shear rate of 100 s-1, were applied alternatively to sites, or a single split resulting in fragments that ow
two syringes, resulting in sequential perfusion of differ by post-translational modifications such as nlo
a
37°C warmed HBSS++-BSA and PMN suspension glycosylation. Kinetic studies showed that the small de
d
(2x106/ml), for 4 min each, over the endothelial 25 kD CD43-CTF appeared later than the 90kD fro
m
cells layer. This was followed by a period of doublet and was the main fragment after 30 min h
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described (26). The Histolab software (Microvision CD43, as mentioned previously (14), while priming .jb
Instruments, Evry, France) allowed quantifying the with 5 ng/ml TNF-α for 30 min, followed by 30 c.o
number of adherent cell visible in at least three min activation with fMLP 10-6M resulted in CD43 brg/
y
fields. cleavage similar to PMA, but the 25kD CD43-CTF g
u
Statistical analysis: was either weakly present or not detected (Fig. 1B). est o
Data were compared using a paired t test analysis. CD43 proteolysis in plasma: Western blot n D
Statistical significance was defined as follows: *, p analysis confirmed that plasma inhibits CD43 ec
e
m
< 0.05; **, p<0.01 and ***, p<0.001. proteolysis (Fig. 2A). It significantly prevented the b
e
decrease of CD43 full length band and the r 1
1
RESULTS appearance of CD43 fragments promoted by high , 2
0
1
Cell-associated CD43 fragments, analyzed by PMA concentrations (100 ng/ml) or, to a lesser 8
western blotting: Confirming a previous report (15), extent, by TNF-α 5ng/ml with fMLP 10-6M. This
we observed that extracellular soluble CD43 inhibition, not modified by plasma heat-inactivation
fragments fail to transfer onto blotting membranes, (30 min 56°C), was impressive but not complete.
whatever membrane (nitrocellulose, PVDF, Although neutrophil activation in plasma resulted in
positively charged PALL membranes), blotting little or no increase of the 90kD doublet, as
buffer (pH 4 to 11) or anti-CD43 mAb clones (L60, compared to control cells in buffer, some 25 kD
MEM59, 1G10) were used. We thus raised an anti- CD43-CTF appeared with plasma/PMA-activated
CD43intra polyclonal antibody to analyze by cells (Fig. 2A). This suggests that plasma efficiently
western blotting the fragments containing CD43 protects the extended extracellular domain of CD43
intracellular domains and remaining membrane- from proteolysis, while the juxtamembranous
anchored after proteolysis. The antibody specificity cleavage site is less accessible to plasma inhibitors.
was analyzed by western blot with CHO cell lines Sample loads of Fig 2A blots, aimed to detect the
transfected with CD43 without and with Core2GnT, 25kD CD43-CTF fragment, resulted in saturating
resulting in bands corresponding to the previously signals for the full length CD43 band. However,
reported 115 and 130 kD glycosylated forms of serial dilutions of PMN lysates showed a significant
CD43 (24) (Fig 1A). Analysis of PMA-activated decrease of full length CD43 band intensities, upon
PMN (Fig.1B) confirmed previous data, since it activation in plasma with PMA and TNF/fMLP,
revealed cell-associated fragments complementary respectively (Fig. 2B).
3
Role of neutrophil serine proteases in CD43 individualize, either because they translocate to the
shedding: Inhibition of CD43 proteolysis may nucleus or because they are degraded by the
involve plasma protease inhibitors. Since the main proteasome. PS/γ-secretase activity is thus
plasma serpins are α1-proteinase inhibitor α1-PI indirectly measured by the accumulation of
and α1 anti-chymotrypsin α1-CT, we analyzed the membrane CTF in the presence of γ-secretase
effects of these inhibitors on CD43 proteolysis. inhibitors. The presence of three different inhibitors
Western blotting analysis revealed that, while α1-PI of γ-secretase, L685,458, MG132 or compound E,
does not seem to prevent any cleavage, α1-CT during neutrophil activation by PMA (Fig. 4A),
inhibits the degradation of a newly appearing 70 kD significantly increased the amount of the 25kD
fragment and decreases the intensity of the 25 kD CD43-CTF observed on western blots. Moreover,
CD43-CTF (Fig. 3A). α1-PI is known to inhibit all in the presence of γ-secretase inhibitors, the 25kD
the serine proteases released by PMN upon PMA- CD43-CTF now appeared on western blots from
triggered degranulation, namely elastase, cathepsin neutrophils activated by TNF/fMLP (Fig. 4B).
G and proteinase 3, PR3, with a highest affinity for Neutrophil incubation with γ-secretase inhibitors in
elastase. By contrast, α1-CT inhibits cathepsin G the absence of agonist did not produce any CD43-
but neither elastase nor PR3 (28). These results thus CTF fragment (data not shown). γ-secretase
proposed cathepsin G as a candidate for the inhibition thus reveals the occurrence of a
cleavage of the 70 kD fragment into a 25 kD cell- juxtamembranous cleavage, upon PMN activation
bound CTF. Flow cytometry analysis of CD43 by TNF/fMLP, which was not detected normally, D
o
membrane expression, after neutrophil incubation due to CD43-CTF rapid degradation by γ-secretase. w
n
with exogenous purified serine proteases, showed We did not detect smaller putative intracytoplasmic loa
d
e
no significant cleavage by PR3, while elastase and fragments resulting from this further degradation, d
cathepsin G resulted in up to 80% and 40% CD43 even when cell pellets were immediately boiled in from
down-regulation respectively (Fig. 3B). As shown Laemli buffer to solubilize nuclear proteins before http
in figure 3A and in agreement with previous data western blot analysis (data not shown). ://w
(29), western blot analysis of PMN incubated with Absence of metalloproteinase involvement in w
w
purified elastase resulted in a 90 kD doublet, similar CD43 shedding: RIP intramembranous proteolysis .jb
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to that observed with PMA. Elastase also produced is usually triggered by matrix metalloproteinases, .org
a 70 kD fragment. Interestingly, cathepsin G MMPs. We thus tested the effects of various MMP b/
y
promoted a juxtamembranous cleavage, leaving a inhibitors on CD43 shedding. PMA-induced CD43 gu
e
s
25kD cell-associated fragment analogous to the cleavage was not inhibited by metalloproteinase t o
n
CD43-CTF observed after PMN activation by PMA inhibitors, such as TAPI-0, TAPI-1 and CH4644 D
e
(Fig. 3A). Data shown in figure 3A were obtained and CH6631, that block various MMPs, including ce
m
with our homemade cathepsin G preparation but MMP8 and MMP9 (data not shown) and the broad be
identical results were obtained with two commercial MMP and TACE inhibitor marimastat (BB 2516) r 11
cathepsin G (data not shown). Finally, the specific (Fig.5 A,D). In parallel experiments, marimastat , 20
1
cathepsin G inhibitor 1 (10 µM) partially inhibited efficiently blocked the shedding of L-selectin 8
the appearance of the 25kD CD43-CTF resulting (CD62L) on the same cells (Fig. 5B). CD43 down-
from PMA activation Fig.3C). regulation was inhibited by 1,10 phenanthroline
We thus propose (Fig. 3D) that PMA-induced (Fig. 5C, D), but also by the inactive analogue 1,7
CD43 proteolysis includes: i) clips A and C, phenanthroline (Fig. 5C), confirming previous data
mediated by elastase-like enzyme(s) and resulting (17) and suggesting an effect unrelated to
in 90KD and 70KD membrane spanning fragments, metalloproteinase inhibition. Metalloproteinases
respectively; ii) a juxtamembranous clip B, thus do not seem to be involved in PMA-induced
presumably mediated by cathepsin G, producing the cleavage.
25 kD CD43-CTF. Our results also show that clip C CD43 is processed by presinilin/γ-secretase as a
appears to be followed immediately by clip B and consequence of cathepsin G cleavage: We thus
thus only detected if clip B is prevented by α1-CT. wondered if cathepsin G could fulfill the function of
Role of presenilin/γ-secretase (PS/γ-secretase) : MMPs in the RIP processing and prepare CD43 for
In cancer cells an intramembrane cleavage of CD43 γ-secretase processing. As shown in figure 6A,
by PS/γ-secretase has been described (7). We thus exogenous purified cathepsin G resulted in a CD43-
investigated a possible role of γ-secretase in CD43 CTF fragment, which was further degraded by γ-
processing in neutrophils. In most instances, RIP- secretase. Indeed, the intensity of the CD43-CTF
induced intracytoplasmic fragments are difficult to fragment, resulting from increasing doses of
4
cathepsin G, was further enhanced by PMN pre- this adhesion is β2 integrin-dependent but E-
incubation with γ-secretase inhibitor compound E selectin-independent.
(97.3 ± 64.6 % increase, n = 7, p = 0.007). To By contrast, PMN adhesion to TNF-activated
exclude the effects of putative enzymes HUVECs under flow conditions, partially prevented
contaminating our cathepsin G preparations, we by anti-E-selectin antibodies, was also significantly
repeated these experiments with two commercial inhibited by 10 µg/ml Fc-CD43s, when compared
cathepsin G sources and obtained the same results to human IgGs purified from an AB normal serum,
(data not shown). By contrast, the intensities of as a control for the Fc portion (Fig. 8B). The
CD43 fragments released by exogenous elastase inhibition level was the same with 10 µg/ml and 30
were not modified by compound E (Fig 6A). µg/ml CD43s (data not shown). In similar
Finally, CD43-CTF fragments appearing upon
conditions, 10 µg/ml recombinant Fc-VCAM-1 had
PMN treatment by cathepsin G, in the presence of
no effect on PMN adhesion (Fig. 8B). These results
the γ-secretase inhibitor, disappeared completely in suggest that CD43s interferes with the E-selectin-
the presence of the specific cathepsin G inhibitor I, dependent adhesion of PMN to endothelial cells
but were not affected by the MMP inhibitor under flow.
marimastat (Fig. 6B). This result shows that the
cleavage of CD43 by purified cathepsin G, in the DISCUSSION
absence of any PMN agonist, is sufficient to allow Our analysis of CD43 proteolysis, resulting from
CD43 further processing by PS/γ-secretase. neutrophil activation, confirms several points D
Role of presinilin/γ-secretase in the regulation of proposed previously (15). Indeed, the size of ow
n
neutrophil functions. γ-secretase inhibitors had no membrane-anchored C-terminal fragments, detected loa
d
effect on neutrophil degranulation, promoted by with our anti-CD43cyto antibody, are mostly ed
PMA or TNF/fMLP, reflected by CD11b up- complementary of those previously described for fro
m
regulation, as measured by flow cytometry (n = 5, soluble N-terminal fragments. We demonstrate that h
ttp
data not shown). They had no effect either on the CD43 proteolysis includes three simultaneous or ://w
oxidative burst, measured with the fluorescent sequential proteolytic steps, schematized in figure w
w
probe 2’-7’-dichlorofluorescein hydrodiacetate (n = 1C and 3D: Clips A and C, distant from the .jb
c
5, data not shown). By contrast, all three γ-secretase membrane and a juxtamembranous clip B. .org
inhibitors significantly inhibited neutrophil The double clip A, previously described as a b/
y
adhesion to gelatin, promoted either by TNF/fMLP «spontaneous » cleavage (15) indeed corresponds to gu
e
or by PMA (Fig. 7). a protein domain very sensitive to proteolysis. This st o
n
Modulation of PMN adhesion to endothelial cleavage was observed upon PMN incubation D
e
cells by CD43s, the soluble ectodomain of CD43 without stimuli, particularly in buffers devoid of ce
m
released after cell activation. We tested the effect BSA and it increased with the cell concentration. b
e
of a recombinant chimeric Fc-CD43s molecule on This suggests that it is mediated by proteases either r 11
neutrophil adhesion to endothelial cells. To constitutively present on neutrophils, but normally , 20
1
preserve the function of the natural molecule, blocked by plasma inhibitors or albumin, or induced 8
CD43s was expressed in COS cells, which contain on PMN membrane by the isolation procedure. This
the enzymatic machinery required for a cleavage was enhanced by PMA or by TNF/fMLP
posttranslational glycosylation similar to and we confirm that it results in CD43 fragments
neutrophils (24). We used 10 to 30 µg/ml Fc- similar to those observed with exogenous elastase
CD43s, based on normal plasma CD43s (Galgp) (27,29 ). In addition, purified elastase results in a
concentration, previously estimated at 10 µg/ml minor cleavage C, closer to the membrane and
(19). Moreover, an home-made sandwich ELISA, leaving a 70kD membrane-spanning fragment. A
using anti-CD43-coated plates and biotinylated similar 70 kD fragment was produced during PMN
wheat-germ-agglutinin and standardized with the activation, but was only detected in the presence of
recombinant Fc-CD43s protein, resulted in a mean α1-antichymotrypsin α1-CT, which prevents its
of 7 ± 6.7 µg/ml of CD43s in normal plasma (n = 7, further degradation. These results stongly suggest
data not shown). Our results show that Fc-CD43s that, during PMN activation, (an) elastase-like
has no effect on PMN static adhesion to enzyme(s) cleave(s) CD43 at clip A and C sites,
extracellular matrix (gelatin, fibronectin, data not distant from the cell membrane and resulting in cell
shown) or to TNF-activated endothelial cells (Fig. bound 90kD doublet and 70kD fragments. The clip
8A). We confirmed with blocking antibodies that A site is more exposed and preferentially cleaved.
The minor 70 kD fragment seems to be immediately
5
further processed by the α1CT-sensitive clip B the analysis of CD43 sequence (30) reveals a
enzyme (as schematized in Fig. 3C) . putative cathepsin G site, Val-Pro-Phe, P -P (31),
3 1
The identification of plasma Galgp as the entire 10 aminoacids away from the transmembrane
extracellular CD43 domain released in the fluid sequence. Such a cleavage would release an
phase (19) makes it likely that the extracellular soluble fragment with the same C
juxtamembranous clip B is involved in the terminal Phe 226 as galactoglycoprotein (Galgp),
physiologic ectodomain shedding of CD43. This the soluble CD43 form described in normal plasma
clip had been suggested by the down-regulation of a (19). The clip B cleavage of CD43, resulting from
T305 epitope and claimed to be exclusively induced neutrophil activation, is thus likely to be mediated
by PMA (15). Our anti-CD43cyto pAb allowed to by cathepsin G.
clearly demonstrate, for the first time, the The lack of inhibition of PMA-induced CD43
occurrence of such juxtamembranous clip, which proteolysis by DFP, aprotinin or α1-PI, known
results in a 25kD membrane inserted C-terminal inhibitors of elastase and cathepsin G, remains
fragment CD43-CTF fragment. We also show that puzzling and different hypothesis have been
this cleavage is not only triggered by PMA but also discussed previously (2,15). The large quantities of
by pro-inflammatory stimuli, such as TNF-α proteases released by PMA-activated neutrophils
priming followed by chemoattractant activation. In may overwhelm and inactivate protease inhibitors.
the latter condition, the resulting CD43-CTF is only α1PI is known to be inactivated by PMN
detected in the presence of γ-secretase inhibitors, as membrane-bound MMPs, MMP8 and MT6-
D
discussed below. Clip B also occurs during PMN MMP/MMP25 (32,33) and may not be functional at ow
n
apoptosis, since we previously described a 25kD sites close to PMN membrane, particularly during lo
a
d
membrane-anchored CD43 fragment on apoptosis- cell adhesion. Moreover, a competition between e
d
induced membrane-derived microparticles (20). neutrophil elastase and cathepsin G for binding fro
m
The juxtamembranous Clip B had been proposed alpha1-PI has been described, resulting in a lack of h
to result from an unknown “CD43-ase” insensitive control of cathepsin G by this inhibitor when ttp://w
to serine protease or metalloproteinase inhibitors elastase is present(34). Finally the lack of effect of w
w
(15). We here show that, unlike clip A, which some inhibitors may be related to their accessibility .jb
c
occurs “spontaneously” upon incubation of isolated to the immediate membrane surrounding. Indeed, .o
rg
PMN, clip B requires a strong activation induced by degranulation releases endogenous proteases at the b/
y
PMA or by TNF together with fMLP, while it is not immediate proximity of CD43 juxtamembranous g
u
e
observed with TNF-α or fMLP alone. This is cleavage site. The charge or size of some but not st o
reminiscent of the mobilization of azurophilic other protease inhibitors may limit their access, n D
granules, which requires PMN priming together through the cell glycocalyx, to this cleavage site. ec
e
m
with chemoattractants. Azurophilic granule serine This would also explain the partial inhibition b
e
proteases, which are then released, are elastase, promoted by the specific cathepsin G inhibitor I. r 1
1
cathepsin G and PR3. All are strongly cationic Following the description of a γ-secretase- , 2
0
1
enzymes, likely to spontaneously interact with such mediated RIP of CD43 in cancer cell lines (7), we 8
a negatively-charged preeminent membrane protein investigated a similar cleavage of CD43 during
as CD43. Our flow cytometry data confirm that neutrophil activation. The γ-secretase component
elastase and cathepsin G result in CD43 shedding, presenilin-1 has been described in neutrophil
while PR3 has no significant effect (29). azurophilic granules (35). A functional presenilin/γ-
Western blot analysis of CD43 proteolysis by secretase complex could then result from
cathepsin G, which had not been investigated until azurophilic granule fusion with the plasma
now, reveals that cathepsin G could be a good membrane. Interestingly, γ-secretase inhibitors have
candidate for the juxtamembranous clip B. Indeed: recently been shown to accelerate neutrophil
i) both α1-CT, which inhibits cathepsin G but apoptosis (36), suggesting that some of the γ-
neither elastase nor PR3, and a specific cathepsin G secretase products may be anti-apoptotic. Upon
inhibitor peptide partially inhibited PMA-induced PMN activation by PMA or by TNF-α/fMLP, we
CD43 proteolysis and prevented the appearance of
indeed observed a significant accumulation of the
the 25 kD CD43-CTF fragment; ii) PMN treatment
25 kD CD43-CTF, when cells were pre-incubated
with purified cathepsin G from three different
with three different γ-secretase inhibitors. This
sources resulted in a juxtamembranous cleavage,
effect of γ-secretase inhibitors was also observed on
producing a 25kD CD43-CTF similar to that
the 25 kD CD43-CTF, resulting from PMN
observed after PMN activation by PMA. Moreover,
treatment by exogenous cathepsin G. The
6
juxtamembranous clip promoted by cathepsin G shedding of their extracellular region (39). Finally,
could thus be sufficient to render CD43 susceptible PS/γ-secretase processing may also release CD43
to γ-secretase cleavage. This role of cathepsin G is intracellular fragments endowed with nuclear
unexpected, since in most cases it is performed by localization and transcription properties. Indeed, a
metalloproteinases. nuclear localization sequence has been described in
A role for MMPs in CD43 shedding had been CD43 cytoplasmic tail and, in carcinoma cell lines,
proposed, since PMA-induced CD43 shedding was CD43 intracellular domain was shown to
inhibited by 1,10 orthophenanthroline. We tested translocate in the nucleus and cause an up
here various broad metalloproteinase inhibitors, regulation of target genes (9). Gene transcription is
able to inhibit MMPs and/or membrane sheddases known to be triggered in neutrophils upon
such as TACE: None of them had significant effect stimulation by pro-inflammatory agonists, which
on CD43 down-regulation by PMA, except for 1,10 also induce CD43 shedding. CD43 intracytoplasmic
orthophenanthroline, but a similar inhibition was fragments could regulate these transcriptions, if
observed with the inactive analogue 1,7 they localize in the nucleus. Genes that would be
orthophenanthroline, as previously mentioned (15). differentially expressed in neutrophils in the
Metalloproteinases thus do not appear to be absence or presence of γ-secretase inhibitors
involved in CD43 proteolysis on PMN. deserve investigation.
We addressed the question of the role of the γ- We here show that clip A is mostly prevented by
secretase-mediated release of CD43 intracellular plasma, presumably due to high levels of plasma
D
fragments, by preventing this release with PS/γ- serpins. However, CD43 shedding has been shown ow
n
secretase inhibitors. Our results show that γ- to occur in vivo on circulating PMN during lo
a
d
secretase inhibitors have no effect on neutrophil hemodialysis (42) and during PMN migration to ed
degranulation or oxidative burst, but significantly inflammation sites (43). Our data suggest that the fro
m
inhibit neutrophil adhesion. Although this inhibition juxtamembranous clip B partially escapes plasma h
may extend beyond CD43, to other putative inhibition. This cleavage was only weakly detected ttp://w
membrane receptors processed by γ-secretase, these by western blotting, presumably because of the w
w
results suggest that neutrophil adhesion requires the immediate degradation of CD43-CTF by PS/γ- .jb
c
release of intracellular domains from shed secretase. Interestingly, the decrease of native .o
rg
transmembrane molecules. CD43, induced either by PMA or TNF/fMLP in b/
y
PMN activation by inflammatory stimuli results plasma or by increasing concentrations of gu
e
in the shedding of half of membrane exposed exogenous cathepsin G, reached a plateau of about st o
CD43. The full-length unshed CD43 molecules 50% of the initial PMN CD43 expression. This n D
interact with cytoskeletal linker proteins ezrin, level is reminiscent of the 50% down-regulation of ece
m
radixin and moesin (ERM), are redistributed in the CD43 observed in vitro during PMN adhesion and b
e
uropod and participate to cell motility (37,38). The migration across activated endothelium (16) or in r 1
1
proteolysis by PS/γ-secretase of CD43-CTF vivo during PMN migration to inflamed rheumatoid , 20
1
fragments, remaining in the membrane after CD43 synovial fluids (43). This could reflect an 8
shedding, may be seen as the simple clearing of heterogeneity among CD43 molecules expressed on
useless fragments by a "membrane proteasome" PMN, half of them being less exposed to cathepsin
G cleavage, possibly due to steric hindrance by cis-
(39). By analogy with the E-cadherin cleavage by γ-
interacting membrane molecules.
secretase, that dissociates catenins from the
If PMN activation in whole blood only allows
cytoskeleton (40), γ-secretase effect on CD43 could
CD43 juxtamembranous cleavage by cathepsin G,
be the release of CD43CTF-bound ERM, so that
while preventing cleavages distant from the
actin bundles would only interact with full-length
membrane, this would release the entire
CD43 molecules. Similarly, the removal of CD43-
extracellular domain of CD43, CD43s. CD43s has
CTF cytoplasmic domains, endowed with signaling
indeed been described in human plasma and
functions (4,41) may be crucial to concentrate this
identified to the Galgp protein (19). We addressed
signaling on CD43 molecules with entire functional
the question of a possible function for CD43s, by
ectodomains. Indeed, lymphocyte migration has
analogy with soluble PSGL-1, which has been
been shown to require both the ectodomain and the
shown to have anti-inflammatory functions (49,51).
intracellular domain of CD43 (4). Intramembrane
Interestingly, soluble leukosialin has been reported
proteolysis, such as γ-secretase-mediated RIP, may
to inhibit the adhesion of colon carcinoma cells to
represent a general way of switching off all signals
endothelial cells (22). We postulated that CD43s,
transmitted by transmembrane molecules after the
acting as an E-selectin ligand (10,11), could
7
compete with cell surface selectin ligands to reduce adhesion regulatory functions. The inhibition of
leukocyte rolling. Our data confirm this hypothesis, PMN adhesion to endothelium by local high
since we show that CD43s inhibits the E-selectin- concentrations of CD43s may participate to the
dependent adhesion of neutrophils to endothelium decrease of PMN recruitment required for the
under flow conditions, while it does not interfere resolution of inflammation, as was proposed for
with their integrin-mediated static adhesion. CD43s selectins ectodomain shedding (1). This has to be
effects were observed at a concentration compatible added to the numerous roles of O-glycosylated
with normal plasma concentrations (see results). membrane receptors in immune responses (45).
Moreover, CD43s levels may be enhanced locally Neutrophil cathepsin G participates, together
in inflamed microvessels, where cytokine-activated with elastase, to the shedding of various adhesion
neutrophils adhere to the endothelium, a situation molecules or cytokine receptors and has been
known to result in CD43 shedding(2,16). The effect shown to interfere with neutrophil migration by
of CD43s is reminiscent of the reported partial several ways (reviewed in (46)). Our data
inhibition of leukocyte rolling by recombinant Fc- demonstrate a new function for cathepsin G, CD43
PSGL-1, a complete inhibition being only obtained processing, which may be important for leukocyte
with a mixture of PSGL-1 and L-selectin blocking migration, in view of CD43 known participation to
antibodies(44). leukocyte motility and trafficking (4,37,38 ).
Therefore, CD43 shedding during neutrophil
activation results in fluid phase CD43s with
D
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w
nlo
a
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9
FOOTNOTES

* Authors wish to thank John Bird and Martyn Robinson, from Celltech Chiroscience Ltd,
Cambridge, UK, for providing metalloproteinase inhibitors. AM was supported successively by a
grant from the Association pour La Recherche sur la Polyarthrite and a grant from the Société
Française d’Hématologie. We acknowledge support from the Association pour l’Utilisation du Rein
Artificiel AURA, from Baxter and from Amgen.

FIGURE LEGENDS

Figure 1: Analysis of CD43 proteolysis by western blot with the anti-CD43cyto pAb, showing the
D
remaining membrane-associated CD43 fragments. A: The specificity of the anti-CD43cyto pAb was o
w
tested by western blotting of lysates from native CHO cells (0) and CHO transfected with CD43 nlo
a
without and with the Core2 GnT. Blotted membranes were analyzed with the anti-CD43cyto (right), de
d
while total proteins were detected with ponceau red (left). B: Kinetic analysis of PMA-induced fro
proteolysis of CD43, analyzed by western blotting: Freshly isolated neutrophils (2 x 106/ml in hm
HBSS++/0,1 % BSA) were incubated at 37°C with 3 ng/ml PMA and stopped at increasing incubation ttp
time points (left panel) or with TNF-α 5 ng/ml for 30 min then with fMLP 10-6M for a further 30 ://ww
w
min-incubation, or with TNF-α or fMLP alone (right panel) and compared to cells incubated with .jb
c
buffer (0). Neutrophil lysates, submitted to gel electrophoresis on 7-15% gradient acrylamide, were .o
rg
analyzed by western blotting with the anti-CD43cyto antibody and an HRP-labeled secondary anti- b/
y
rabbit IgG antibody and revealed by chemiluminescence. C: Schematic representation of soluble and g
u
membrane CD43 fragments. es
t o
n
D
Figure 2: CD43 proteolysis in plasma. 2 x 106/ml PMN, suspended in HBSS++-BSA or in undiluted ec
e
m
autologous heparinated plasma, were incubated with PMA 100 ng/ml for 30 min at 37°C or with b
e
TNF-α 5 ng/ml for 30 min, followed by the addition of fMLP 10-6M and a further 30 min incubation. r 1
1
Cells lysates were analyzed by western blotting, as in figure 1. A: Western blot of one representative , 2
0
1
experiment and mean ± SD of the intensities of the 90 kD doublet and 25 kD scanned bands from 4 8
similar experiments. Results are expressed as percent of the maximal level observed with TNF/fMLP
(90 kD doublet) or PMA (25 kD). B: Native CD43 bands shown in the blot A resulted in saturating
signals. Quantitative evaluation of residual full length CD43 was then calculated from western blot
analysis of serial dilutions of PMN lysates, after activation with or without plasma as above. Scanned
band intensities, normalized with the scanned actin bands, are expressed as percent of the initial level
of full length CD43 of PMN incubated in HBSS (n = 4).

Figure 3: Role of neutrophil serine proteases in CD43 shedding. A. Left Pannel: CD43 fragments
resulting from PMA activation in the presence of plasma serpins (left panel). 2 x106/ml PMN were
pre-incubated for 15 min with α1-PI 500 µg/ml or α1-CT 100 µg/ml and activated for 30 min with 3
ng/ml PMA in HBSS++-BSA. Right panel: CD43 fragments resulting from the addition of exogenous
purified serine proteases to resting PMN. 10 x106/ml PMN in PBS were treated with human purified
elastase (NE) 15 µg/ml or cathepsin G (Cat G) 25 µg/ml for 20 min at 37°C. Cell lysates were
analyzed by western blotting revealed by anti-CD43cyto pAb. B: Dose response effect of purified
elastase, cathepsin G and PR3 on CD43 expression. PMN were incubated as described above with
increasing concentrations of serine proteases, then labeled with FITC-anti-CD43 and analyzed by
flow cytometry. C: Inhibition, by cathepsin G inhibitor 1, of the cleavage resulting in 25kD CD43-
1 0