key: cord-0039168-rdv5o8yz
authors: Bauvois, B.; Laouar, A.
title: Distinct cellular functions mediated by haemopoietic cell-surface proteases
date: 2007-03-06
journal: Adv Neuroimmunol
DOI: 10.1016/s0960-5428(05)80019-1
sha: aa83298cc281df566bd27eb2c1863a80620e04f0
doc_id: 39168
cord_uid: rdv5o8yz

nan

The presence of proteolytic activities on cellular surfaces initiates a variety of essential biological responses. Likewise, haemopoietic cell-surface proteases appear to have multiple effects in a wide variety of physiological and pathophysiological processes. Protein turnover, ontogeny, inflammation, cell migration and tissue invasion are among the many systems which depend upon cellsurface protease control mechanisms.

It is possible to discern two classes of enzymes at the surface of haemopoietic cells: the cell-associated protease family and the integral protease family. The cellassociated proteases are bound to the membrane either through ionic interactions or specific binding sites and they include serine elastase, cathepsin G and the plasminogen activators (PAs). The integral proteases are transmembrane type I or type II molecules and they include a growing number of members with various and partly overlapping specificities.

The structural features and degradative properties of these two classes of haemopoietic cell-surface proteases are summarized in this review. Recently, there has been an increase in the information available about extended functions of ectoproteases and we have tried to provide some insight into the way haemopoietic cell-surface proteases, through multifunctional mechanisms, may influence physiological and pathological events.

As summarized in Table 1 , some wellcharacterized proteases are present on the surface of haemopoietic cells. Although initially described as being found in granulocytes, monocytes and alveolar macrophages, serine elastase and cathepsin G are also present on promonocytic cells (Maison et al., 1991; Villiers and Bauvois, unpublished results) . Both proteases are the primary enzymes responsible for extracellular matrix (ECM) degradation (reviewed in Janusz and Doherty, 1991) . Alpha l-protease inhibitor (c~l-PI) synthesized by myeloid cells blocks the activity of both elastase and cathepsin G (Remold O'Donnell et al., 1989) and the complex formed following the interaction of ~I-PI with elastase is chemoattractant for granulocytes (Banda et al., 1988) . Monocytes/macrophages synthesize both urokinase [u-PA] and tissue plasminogen activator [t-PAl as well as inhibitors of plasminogen activators (Vassalli et al., 1984; Chapman and Stone, 1985; Hart et al., 1989) . In addition, monocytes, macrophages and monocytic cell lines express both u-PA and plasminogen receptors and several agonists, including interferon-gamma (IFN-7), tumor necrosis factor-alpha (TNF-o 0 and urokinase itself, have the capacity to modulate the expression of u-PA receptors (Kirchheimer et al., 1988; Felez et al., 1990) . PAs are chemotactic for granulocytes in vivo (Boyle et al., 1987) and they catalyze the proteolytic remodelling and such physiological processes as inflammation and metastasis. Secreted u-PA does not significantly contribute to the invasive process unless it is receptor-bound and cell-surface-associated (Ossowski, 1988) . Moreover, the receptor for u-PA polarizes expression of the protease to the leading edge of migrating monocytes suggesting that this receptor is a key determinant in the control of u-PA-catalysed extracellular proteolysis (Estreicher et al., 1990) . CD10 antigen [CALLA (common acute lymphoblastic leukaemia antigen)] is a type II integral membrane protein that is identical to neutral endopeptidase (NEP, EC 3.4.24.11) (Letarte et al., 1988) . Originally identified as associated with 80% of cases of childhood acute lymphoblastic leukaemia with a pre-B cell phenotype, CD10/NEP is now identified on B lymphocyte progenitors in bone marrow and foetal liver, suggesting it may play a role in the early stages of B cell development. It is also found on culture bone marrow stromal cells, mature granulocytes and Jurkat T cells (reviewed in Bowes and Kenny, 1987; Kee et al., 1992; Marl et al., 1992) as well as in a large number of nonhaemopoietic tissues. CD10/NEP is a zinc-containing endopeptidase which can hydrolyze numerous small biological peptides such as enkephalins, endothelins, substance P, bradykinin, the pleiotropic cytokines IL-l[3 and IL-6 (reviewed in Turner et al., 1985; Bauvois et al., 19911) . NEP, present on the surface of granulocytes cleaves the chemotactic peptide N-formyl-Met-Leu-Phe (f-M-L-P), suggesting that this enzyme can modulate chemotactic responses (Painter et al., 1988) . CD13/aminopeptidase-N (AP-N, EC 3.4.11.2) is a zinccontaining exopeptidase expressed by acute B lymphoid and myeloid leukaemic cells and cells of the granulocyte-macrophage lineage at all stages of differentiation (Look et al., 1989; reviewed in Bauvois et al., 1991; Naquet and Pierres, 1991) . Although CD13 specific antibodies do not bind normal B and T cells, an aminopeptidase-N activity which is enhanced upon mitogenic stimulation, is described on human T lymphocytes and differentiating murine thymocytes (Amos-cato et al., 1989; Bauvois, 1990) . As for CD10, the natural substrates for CD13/AP-N appear to be regulatory peptides including enkephalins and other opioid peptides (reviewed in Turner et al., 1985; Checler, 1991) . Both CD10/NEP and CD13/AP-N are found to be increased on myeloid cells stimulated with C5a in vitro or obtained from patients undergoing activation of C during haemodialysis (Werfel et al., 1991) . CD26/dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5) is a type II serine protease widely distributed in mammalian tissues and in the immune system is expressed by activated B cells, cells of T and granulocytemacrophage lineages (Sch6n et al., 1987; Bauvois et al., 1992; Laouar et al., 1993; Bristol et al., 1992) . By removing dipeptides of the X-Pro-type from peptides and proteins, DPP IV is involved in the processing of bioactive peptide precursors including cecropins and melittin (Kreil et al., 1980; Boman et al., 1989) as well as in the degradation of bioactive peptides ([3-casomorphin, substance P and growth hormone-releasing factor) (Bongers et al., 1992) and denatured collagen I (Bauvois et al., 1991) . In our laboratory, we have recently shown that DPP IV of U937 cells participates in the degradation and inactivation of TNF-o~ . Dipeptidyl carboxypeptidase A (ACE or angiotensin converting enzyme, kininase II, EC 3.4.15.1) is a widely distributed membrane-bound metallopeptidase present on pre-B derived leukaemia cells and cells of T and monocyte-macrophage lineages (reviewed in Checler, 1991; Costerousse et al., 1993) . ACE inactivates enkephalins, substance P and bradykinin and converts angiotensin I into angiotensin II (reviewed in Checler, 1991) . Inside the haemopoietic system, aminopeptidase A (AP-A) is expressed on a subpopulation of cortical thymic epithelial cells and on pre-B and immature B lineage cells (Witlock et al., 1987; Wu et al., 1991) . Such selective expression on pre-B lymphocytes may reflect a requirement for these cells to hydrolyze (a) regulatory peptide(s) at the stage of lymphopoiesis. Outside the haemopoietic system, AP-A can degrade angiotensins I and II. Moreover, IL-7 preferentially induces AP-A expression together with pre-B cell proliferation (Wu et al., 1991) .

A few other cell-surface proteases have been less thoroughly characterized. Among them, a trypsin-like serine protease (TSP-1) on effector T cells is capable of cleaving casein and releasing high-molecular weight products from sulphated proteoglycans (Kramer and Simon, 1987) . A membrane-bound arginine-specific serine enzyme detected on B routine spleen cells is synthesized to a higher level following mitogenic stimulation (Ku et al., 1983) . Human lymphoid T and B cells possess a trypsin-like protease and a neutral endopeptidase on their surface that both participate in the degradation of the vasoactive intestinal peptide (VIP) released by eosinophils and are shown to inhibit the proliferative responses for murine lymphocytes to mitogens (Goetzl et al., 1989) . A neutral serine protease on activated neutrophils may be in part responsible for cytolysis of target cells (Pontremoli et al., 1986) . Finally, the low affinity IgE receptor FceRII/CD23 present on B cells and inducible on monocytes and T cells could be cleaved according to an autocatalytic mechanism (Letellier et al., 1989) .

It is readily apparent from Table 1 that the scope of haemopoietic cell-surface proteases is remarkable. This diversity encompasses virtually all types of peptides and proteins grouped by functional criteria. Most of the proteins listed include pleiotropic cytokines (IL-113, IL-6 and TNF-o~), vasodilatory peptides (VIP and substance P) and neuroendocrine hormones such as endor-phins, enkephalins, somatostatin and angiotensin, all implicated in many functions of the immune system and the inflammatory responses (Lotz et al., 1988; Metcalf, 1989; Gijbels and Billiau, 1992; Van Den Bergh et al., 1992) . Likewise, immunoregulatory properties of substance P (SP) after interaction with specific SP receptors include in vitro stimulation of T cell proliferation, the augmentation of Ig synthesis, macrophage and neutrophil activation and the modulation of lymphocyte traffic (reviewed in Calvo et al., 1992) . As seen in Table 1 , there is therefore much interest in the role of cell-surface proteases such as NEP, ACE and DPP IV in inactivating SP.

Many integral membrane proteins lead to a dual existence as both membrane-bound and soluble isoforms (Ehlers and Riordan, 1991) . Such a proteolytic mechanism leads to the release of a large variety of proteins, including growth factors and cytokines (TGF-o~, TNF-c~, CSF-] (colony stimulating factor), EGF (epidermal growth factor) and S-CGF (stem cell growth factor), growth factor and cytokine receptors (TNF-c~, NGF (nerve growth factor), CSF-1, IL-1, IL-2 and IFN-~/), leukocyte antigens (FcRIII/CD16, FcRII/CD23, CD8, Mel14) and ectoenzymes themselves (cholinesterase, sialyltransferase/CD75, NEP, DPP IV, AP-N and ACE). An endogenous EDTAsensitive membrane-associated protease from pig kidney has been shown to release ACE in a soluble form (Hooper et al., 1987) . This example lends support to the concept that the proteolytic release of membrane proteins can be a specific event regulated by cell-surface proteases themselves.

Besides the CD3/TCR complex which activates T cells and leads to the biological expression of the T cell functional programme, other non-TCR structures including CD2, CD4, CD8, CD28, Thy-1, LFA-1, CD49d/CD29 (VLA-4), CD49e/CD29 (VLA-5) can induce or modulate cell activation. Recently, monoclonal antibodies (mAbs) against the human CD26/DPP IV have been shown to co-stimulate T cell proliferation, IL-2 secretion and cytoxicity (Fleisher, 1987; Dang et al., 1990 Dang et al., , 1991 Hegen et al., 1990) . In the mouse and in the rat, mAbs anti-CD26 have similar effects on immature and mature T cell proliferation (Naquet et al., 1989; Vivier et al., 1991; Bristol et al., 1992) . Moreover, mAb against rat CD26 can also mediate a co-stimulatory signal for granulocyte and macrophage colony formation (Bristol et al., 1992) .

There is current evidence that leukocyte integrins are signal transducers. Indeed, collagen-dependent CD4 T cell activation is found to involve the integrin VLA-3 (CD49c/CD29) but also a second collagen receptor represented by CD26/DPP IV, indicating that cell adhesion via two different families of antigens i.e. integrins and proteases can contribute to cell activation (Dang et al., 1990) .

How does CD26/DPP IV signal? The biochemical signals delivered by CD26 are distinct from signals derived from an increased intracellular calcium level (Bristol et al., 1992) but seem to require protein kinase C activation (Dang et al., 1990; Vivier et al., 1991; Bristol et al., 1992) . CD26 on human T cells is physically associated to CD45RO, one form of the tyrosine phosphatase leukocyte common antigen . Anti-CD26 mAb treatment down-modulates both CD26 and CD45RO expression and results in increased tyrosine phosphorylation of two proteins critical in T cell activation i.e. the TCR~ chain and p561ok kinase . Likewise, similar activation signal transducing properties are now reported with two other cell-surface proteases CD13/AP-N and CD10/NEP. Anti-CD13 mAb is shown to inhibit rosette formation by neutrophils and erythrocyte-antibody complement (O'Connell et al., 1989) , whereas anti-CD10 mAb significantly decreased IL-2 production in activated Jurkat T cells (Mari et al., 1992) . Outside of the haemopoietic system, specific binding of enzymatically active uPA with its receptor is mitogenic in malignant cells (Kirchheimer et al., 1989) . Altogether, these results emphasize the emerging theme of signal transduction by haemopoietic cell-surface proteases.

Other roles?

Outside of the haemopoietic system, CD26/ DPP IV has been shown to have a binding affinity for collagen and fibronectin (Hanski et al., 1988; Bauvois, 1988; Piazza et al., 1989) and was strongly suggested to participate in adhesion of rat hepatocytes and murine fibroblasts to collagen (Hanski et al., 1988; Bauvois, 1988) . Since then, DPP IV on human T cells has been demonstrated to be a functional collagen receptor leading to cell activation (Dang et al., 1990) . Thus, ectoproteases can directly serve as cell adhesion molecules that further modulate intracellular activation signals. Figure 1 depicts a highly speculative hypothesis regarding the potential role of ectoproteases such as DPP IV in regulation of haemopoietic cell adhesion: in a first step, cells may contact the ECM protein (fibronectin/collagen) via specific cell-surface proteases and resulting adhesion could result in signal transduction and cell activation. In a second step, activated cells no longer could bind to ECM, consistent with the detachment of cells and concomitant degradation or not of ECM. Such flexibility provided by cell-surface proteases could be important in attachment and migration of haemopoietic cells occurring in various physiological (development) and pathological processes (inflammation, cancer). 

It is known that viruses make use of cell-surface proteins as cellular receptors to enter and infect cells. Two recent reports provide strong evidence that epithelial cell CD13/AP-N serves as a receptor for at least two viruses i.e. TGEV (transmissible gastroenteritis virus) and HCV-229E human coronavirus (Delmas et al., 1992; Yeager et al., 1992) . Interestingly, very recent data have reported that human immunodeficiency virus (HIV) can bind an integral type II protein which shares close homology with CD23/FcRII (Curtis et al., 1992) suggesting that non-CD4 HIV receptors with structural features of some integral proteases can be important in HIV infection.

Proteases are found to be strong catalysts for transpeptidation reactions (reviewed in Kasche, 1989) . Indeed, CD26/DPP IV in vitro expresses both peptidase and acyl transferase activity (Yoshimoto et al., 1978) . In our laboratory, we have recently shown that cells of the granulocyte-macrophage lineage degrade IL-6 into active 8 kDa peptides. Further inactivation involves formation of a 16 kDa complex due to dimerization of the 8 kDa-derived IL-6 peptides resulting from a peptidyl transferase-catalysed reaction occurring at the cell surface (Laouar et al., 1993) . Our data may explain the origin of high molecular weight IL-6 species (45-85 kDa) detected in human serum (May et al., 1991) .

As summarized here, the structural features of cell-surface proteases in the haemopoietic system are becoming well understood. What has become clear in the last few years is that haemopoietic cell-surface proteases are not simply proteolytic enzymes but they can be considered as receptors in the sense of transmitting signals both into and out of the cells.

Primary function of such enzymes is to activate/inactivate via degradation a variety of molecules including hormones, neuropeptides, cytokines and ECM proteins. Apart from their degradation role, the second major property of cell-surface proteases is their role as signal transducing molecules: (perhaps all) cell-surface proteases mediate information transfer into cells by acting as coreceptors with more traditional receptors. It is reasonable to propose that interaction of these enzymes with their biological substrate(s) can trigger signalling events. One of the unanswered questions is how proteases signal and a rapidly advancing area is presently the dissection of the molecular basis of signal transduction through proteases.

Studies on the role of cell-surface proteases outside the haemopoietic system led to the surprising finding that enzymes such as DPP IV/CD26 may be receptors by which cells attach to ECM. This is an attractive model in which leukocytes via cell-surface proteases could exhibit combined adhesion and migration activities through lymphoid areas and peripheral tissues. This hypothesis will surely benefit from progress in studies of cell adhesion.

A current speculation concerns cell-surface proteases and their contribution in the conversion of peptides and proteins. Further studies are needed to improve the 'planning' of efficient and selective cellsurface protease-catalyzed reactions in biological processes.

Through these activities above, there is emerging evidence that haemopoietic cellsurface proteases may play a dynamic role in development and in adult organisms by regulating cell proliferation and differentiation, secretion, cell-mediated cytotoxicity and cell migration. Cell-surface proteases are subject to fine control such that their expression at any point in time is being regulated by a variety of factors including the immediate microenvironment (cytokines, ECM, inhibitors), the state of cell activation and maturation and in turn they can modulate cell functions.

Definitive evidence for the physiological relevance of a given action of a haemopoietic cell~surface protease requires tests in the intact organism. Obviously, such tests are difficult to carry out and an alternative strategy is the association of modified states of cell-surface proteases with diseases as diverse as thrombosis, inflammation and leukaemias. A number of pathologic conditions are already shown to be associated with up and/or down regulation of cell-surface proteases and they therefore may serve as independent diagnostic predictors. For example, the clinical course of pre-B and T acute lymphoid leukaemias are associated with high content of CD10/NEP (Foon and Todd, 1986 ). Both an increase or decrease in CD6/DPP IV activity has been used as a marker of lymphoid leukaemias (Scott et al., 1988) and HIV infections (De Pasquale et al., 1989) . Thus, the subsequent elucidation of the role(s) of these cell-surface enzymes on leukocytes that possess modified properties should contribute to our understanding of the multifunctional roles of cell-surface proteases.

Finally, one intriguing question is how cell-surface protease molecules can contribute to the infectious process. As promising candidates for receptors of a large variety of mammalian viruses, they may represent a novel area for antiviral research and therapy.

In all of these aspects, we expect considerable progress in the next few years; however, haemopoietic cell-surface proteases already appear as flexible molecules with varied mechanisms directing a multiplicity of cell functions.

Surface aminopeptidase activity on human lymphocytes

The inhibitory complex of human alpha-1 proteinase inhibitor and human leukocyte elastase is a neutrophil chemoattractant

A collagen-binding glycoprotein on the surface of murine fibroblasts is identified as DPP IV

Murine thymocytes possess specific cell-surface-associated exoaminopeptidase activities

Localizations and potential roles of leukocyte proteases

Human U937 cell surface peptidase activities: characterization and degradative effect on tumor necrosis factor-c~

Chemical synthesis and enzymic processing of precursor forms of cecropins A and B

Kinetics of dipeptidyl peptidase IV proteolysis of growth hormonereleasing factor and analogs

An immunohistological study of endopeptidase 24.ll and aminopeptidase N in lymphoid tissues

Urokinase: a chemotactic factor for polymorphonuclear leukocytes in vivo

Thymocyte costimulating antigen is CD26 (dipeptidyl peptidase IV): costimulation of granulocyte, macrophage and T lineage cell proliferation via CD26

Substance P enhances IL-2 expression in activated human T cells

Characterization of a macrophage-derived plasminogen inhibitor

Peptidase and neuropeptideinactivating mechanisms in the circulation and in the gastrointestinal tract

Angiotensin I converting enzyme in human circulating mononuclear cells: genetic polymorphism of expression in T lymphocytes

Sequence and expression of a membrane-associated C-type lectin that exhibits CD4-independent binding of human immunodeficiency virus envelope glycoprotein gp120

Human CD4 helper T cell activation: functional involvement of two distinct collagen receptors, 1F7 and VLA integrin family

1F7 (CD26): a marker of thymic maturation involved in the differential regulation of the CD3 and CD2 pathways of human thymocyte activation

Aminopeptidase N is a major receptor for the entero-pathogenic coronavirus TGEV

Dipeptidyl aminopeptidase IV cytochemistry in circulating lymphocytes from HIV-I seropositive subjects

Membrane proteins with soluble counterparts: role of proteolysis in the release of transmembrane proteins

The receptor for urokinase type plasminogen activator polarizes expression of the protease to the leading edge of migrating monocytes and promotes degradation of enzyme inhibitor complexes

Regulation of plasminogen receptor expression on human monocytes and monocytoid cell lines

A novel pathway of human T cell activation via a 103 kD T cell activation antigen

Immunologic classification of leukaemia and lymphoma

Interleukin 6: general biological properties and possible role in the neural and endocrine systems

Unique pattern of cleavage of vasoactive intestinal peptide by human lymphocytes

Direct evidence for the binding of rat liver DPP IV to collagen in vitro

Human monocytes can produce tissue-type plasminogen activator

The T cell triggering molecule TP103 (CD26) is associated with dipeptidyl aminopeptidase IV activity

Pig kidney angiotensin converting enzyme

Degradation of cartilage matrix proteoglycan by human neutrophils involves both elastase and cathepsin G

Proteases in peptide synthesis

Characterization of murine CD10, an endopeptidase expressed on bone marrow adherent cells

IFN-% tumor necrosis factor-c~ and urokinase regulate the expression of urokinase receptors on human monocytes

Functional inhibition of endogenously produced urokinase decreases cell proliferation in a human melanoma cell line

Are proteinases functional molecules of T lymphocytes? bnmunol

Stepwise cleavage of the Pro part of promelittin by dipeptidylpeptidase IV. Evidence for a new type of precursor product conversion

The inhibition of the mitogenic stimulation of B lymphocytes by a serine protease inhibitor: commitment to proliferation correlates with an enhanced expression of a cellassociated arginine-specific serine enzyme

Characterization and modulation of cell-surface proteases on human myeloblastic (HL-60) cells and comparison to normal myeloid cells

Inactivation of interleukin-6 in vitro by monoblastic U937 cell plasma membranes involves both protease and peptidyl-transferase activities

Commor acute lymphocytic leukaemia antigen is identical to neutral endopeptidase

Mechanisms of formation of IgE binding factors (soluble CD23)

Human myeloid plasma membrane glycoprotein CD13 is identical to aminopeptidase N

Effect of neuropeptides on production of inflammatory cytokines by human monocytes

Proteolysis of C3 on U937 cell plasma membranes; purification of cathepsin G

Jurkat T cells express a functional neutral endopeptidase activity (CALLA) involved in T cell activation

On the multimeric nature of natural human interleukin-6

The molecular control of cell division, differentiation commitment and maturation in haemopoietic cells

Cell-surface enzymes and lymphocyte functions

Activation of mouse T lymphocytes by a monoclonal antibody to a developmentally-regulated surface aminopeptidase (THAM)

CD13: a signal transduction molecule on myeloid cells?

In vivo invasion of modified chorioallantoic membrane by tumor cells

Function of neutral endopeptidase on the cell membrane of human neutrophils

Evidence for a role of dipeptidyl peptidase IV in fibronectin-mediated interactions of hepatocytes with extracellular matrix

Cytolytic effects of neutrophils: role for a membrane-bound neutral proteinase

Elastase inhibitor: characterization of the human elastase inhibitor molecule associated with monocytes, macrophages and neutrophils

The role of dipeptidyl peptidase IV in human T lymphocyte activation. Inhibitors and antibodies against dipeptidyl peptidase IV suppress lymphocyte proliferation and immunoglobulin synthesis in vitro

Quantitative and qualitative studies of leukaemic cell dipeptidyl peptidases II and IV

Coassociation of CD26 (dipeptidyl peptidase IV) with CD45 on the surface of human T lymphocytes

Are there neuropeptide-specific peptidases?

Opioid peptides as cytokines in T cell activation

Concomitant secretion of prourokinase and a plasminogen activator specific inhibitor by cultured human monocytesmacrophages

Evidence that thymocyte activating molecule is mouse CD26 (dipeptidyl peptidase IV)

Rapid increase in the membrane expression of neutral endopeptidase (CD10), aminopeptidase N (CD13), tyrosine phosphatase (CD45) and Fcg-RIII (CDI6) upon stimulation of human peripheral leukocytes with human C5a

Bone marrow stromal cell lines with lymphopoietic activity express high levels of a pre-B neoplasia-associated molecule

Aminopeptidase A activity in the murine B-lymphocyte differentiation antigen BP-1/6C3

Human aminopeptidase N is a receptor for human coronavirus 229E

Post-proline cleaving enzyme and post-proline dipeptidyl aminopeptidase: comparison of two peptidases with high specificity for proline residues

This work was supported by grants from the Institut National de la Sant6 et de la Recherche M6dicale and the Association pour la Recherche sur le Cancer. A. Laouar is the recipient of a French-Algerian fellowship.