Ectopeptidases in pathophysiology

Ectopeptidases are transmembrane proteins present in a wide variety of tissues and cell types. Dysregulated expression of certain ectopeptidases in human malignancies suggests their value as clinical markers. Ectopeptidase interaction with agonistic antibodies or their inhibitors has revealed that these ectoenzymes are able to modulate bioactive peptide responses and to influence growth, apoptosis and differentiation, as well as adhesion and motility, all functions involved in normal and tumoral processes. There is evidence that ectopeptidase-mediated signal transduction frequently involves tyrosine phosphorylation. Combined analyses of gene organization and regulation of ectopeptidases by various physiological factors have provided insights into their structure-function relationships. Understanding the roles of ectopeptidases in pathophysiology may have implications in considering them as therapeutic targets.

Regulation of CD26/DPPIV gene expression by interferons and retinoic acid in tumor B cells

Interferons (IFNs alpha, beta and gamma) and all trans retinoic acid (RA) have the ability to activate genes with GAS sites. We have found that the promoter of CD26/dipeptidylpeptidase IV (DPPIV) contains a consensus GAS site TTCnnnGAA located at bp-35 to -27, and computer analysis confirmed this sequence to be a putative Stat binding site. Consistent with this finding, we show that IFNs and RA rapidly enhanced CD26 gene and protein expression in chronic B lymphocytic leukemia (B-CLL) cells. Immunoblot analyses revealed that unstimulated B-CLL cells expressed detectable levels of serine/tyrosine-phosphorylated Stat1alpha, and RA and IFN-gamma treatment led to increased levels of tyrosine phosphorylation of Stat1alpha and its nuclear accumulation. As shown by electrophoretic mobility shift assay, RA and IFN-gamma increased the binding of a nuclear protein to the GAS-CD26 element. Shift-Western blotting identified Stat1alpha as the GAS-CD26 binding factor. Augmented levels of CD26 protein in malignant B cells cultured with IFNs or RA coincided with the enhancement of DPPIV activity. Taken together, our results are in favor of the IFN-/RA-mediated upregulation of CD26/DPPIV in B-CLL through the signaling pathway involving Stat1alpha and the GAS response element of CD26 promoter.

Upregulation of CD38 gene expression in leukemic B cells by interferon types I and II

The activation antigen CD38, which has NAD+ glycohydrolase activity in its extracellular domain, is expressed by a large variety of cell types. Few investigations into the regulation of CD38 expression by physiologic stimuli have been reported. As the CD38 promoter contains potential binding sites for interferon (IFN) regulatory factor-1 (IRF-1), we investigated the influence of IFN type I (alpha and beta) and type II (gamma) on CD38 gene expression of leukemic B cells. Using the IFN-responsive B cell line Eskol, we found by RT-PCR analysis a rapid time-dependent induction in CD38 mRNA (starting at 6 h) with each type of IFN. This induction was independent of protein synthesis, suggesting that CD38 gene activation does not require IRF-1 but is merely under direct transcriptional regulation by latent IFN-inducible factors. mRNA stimulation was followed within 24 h by induction of membrane CD38, which coincided with rises of CD38-specific ectoenzymatic activities, that is, NAD+ glycohydrolase, (A/G)DP-ribosyl cyclase, and cyclic ADP ribose hydrolase activities. IFN failed to induce or upregulate the other CD38-related ectoenzymes analyzed, that is, CD39, CD73, CD157, and PC-1. Similarly, treatment of leukemic cells of patients with B chronic lymphocytic leukemia (B-CLL) with IFN resulted in an increase in CD38 mRNA mirrored by plasma membrane upregulation of CD38 and NAD+ glycohydrolase activity. Further investigation in relation to CD38 gene activation and B-CLL behavior remains to be defined.

Constitutive expression of CD26/dipeptidylpeptidase IV on peripheral blood B lymphocytes of patients with B chronic lymphocytic leukaemia

We have investigated the expression of the ectoenzyme dipeptidylpeptidase IV (DPP IV)/CD26 on lymphocytes obtained from patients with B chronic lymphocytic leukaemia (B-CLL) and compared it with healthy subjects. Using two-colour immunofluorescence analysis with CD26 and CD20 or CD23 monoclonal antibodies, CD26 was found undetectable on peripheral resting B-cells (CD20+ CD23-) from normal donors whereas it was expressed on B-cells activated in vitro with interleukin (IL)-4 and Staphylococcus aureus strain cowan I (CD20+ CD23+). The expression of CD26 on leukaemic B-cells (CD20+ CD23+) was clearly induced in 22 out of 25 patients examined. Consequently, induced levels of CD26 cell surface expression on either normal activated and malignant B-cells coincided with the enhancement of DPP IV activity detected on the surface of these cells. Reverse transcription polymerase chain reaction analyses showed that the transcript levels of the CD26 gene was higher in normal activated B-cells and B-CLL cells than in resting B-cells, suggesting that CD26 was expressed at the level of transcriptional activation. These observations provide evidence of the abnormal expression of DPPIV/CD26 in B-CLL which, therefore, may be considered as a novel marker for B-CLL. Further investigation in relation to CD26 expression and other B malignancies needs to be defined.

Production of nitric oxide (NO) in human hydatidosis: relationship between nitrite production and interferon-gamma levels

Human hydatidosis is characterized by a prolonged coexistence of parasite (Echinococcus granulosus) and host without effective rejection. The basis of the immune response of the patient is poorly understood. Previously, we reported the presence of IFN, TNF-alpha and IL-6 activities in the serum of patients with liver and lung hydatidosis. In the present work, we have investigated the production of nitrite (NO2-) in the serum of hydatidic patients carrying hepatic and pulmonary cysts (range 36-300 microM). Our present data show a correlation between the production of nitrite + nitrate (NO2- + NO3-) and that of circulating cytokines IFN and IL-6. In relapsing patients who did not produce IFN and IL-6, the observed serum NO2- concentrations were low (range 10-37.2 microM), as compared to those detected in patients before surgery. Induction of NO synthase in leukocytes from hydatidic patients was induced by stimulating these cells with a specific parasitic antigen, Antigen-5, as assessed by the increased levels of NO3- + NO2- in the range of 60-85 microM for patients with liver hydatidosis, as compared to the 20-25 microM detected in healthy controls. Collectively, our data indicate that NO2- + NO3- levels correlate with IFN levels and immunoreactivity, and overall suggest that IFN-gamma and nitric oxide production together play a role in the host defense mechanisms in human hydatidosis.

Induction of macrophagic differentiation and cytokine secretion by IgG1 molecules in human normal monocytes and myelogenous leukemia cells

A role for IgG molecules in the activation of human myelogenous leukemia cells was examined. When added to monoblastic (U937) leukemia cells, mouse (m)IgG1 produced a dose- and time-dependent inhibitory growth effect associated with the induction of morphological features characteristic of macrophage maturation, and enhanced surface expression of Mac-1/CD11b characteristic of monocyte development. A study of isotype dependency of mig indicated that the effect was specific for Ig molecules of the IgG1 and IgG2b subclasses, whereas IgG2a or IgM had no effect. In parallel to U937 cell maturation, a marked production of latent TGF-beta was observed in supernatants of leukemia cells cultured with mIgG1. Myeloblastic (HL-60) leukemia cell line similarly responded to mIgG1 or mIgG2b in induction of macrophage differentiation and in the absence of neutrophil differentiation. Human blood monocytes cultured in the presence of mIgG1, exhibited higher levels of IL-1 beta and IL-6 mRNAs associated with an increase in protein extracellular release, suggesting that the effect of mIgG1 on IL-1 beta and IL-6 production in human monocytes was mediated at both transcriptional and post-transcriptional levels. Monocyte activation by mIgG1 and mIgG2b was associated with increased cell surface expression of HLA-DR class II molecules. Human IgG1 (and to a lesser degree hIgG2), was also capable of inducing leukemia cell growth arrest and macrophage maturation whereas F(ab')2 fragments of mIgG1 were not as efficient as intact mIgG1 in blocking cell growth. Most importantly, mAbs reactive with Fc gamma RII (CD32-specific Abs 2E.1 and IV.3) blocked the effects of mIgG1 on leukemia cell proliferation. Taken together, these data indicate that binding of IgG1 molecules, possibly through Fc gamma RII, may generate an activation signal towards myelogenous leukemia cells and normal counterpart cells, ie monocytes, leading to induction of macrophage maturation and cytokine secretion.

Synergistic effect of prolactin on IFN-gamma-mediated growth arrest in human monoblastic cells: correlation with the up-regulation of IFN-gamma receptor gene expression

Interferon-gamma (IFN-gamma) stimulates the development of monocytic features in human myeloid precursors. Because transcriptional regulation of IFN-gamma and the pituitary hormone prolactin (PRL) has been described to involve common Jak-STAT pathways, we addressed here the question of whether PRL plays a role in monoblastic (U937) cell growth and macrophage maturation. In contrast to IFN-gamma, PRL did not affect U937 cell growth nor induction of differentiation as assessed by the unchanged cell surface expression of maturation markers CD11b and HLA-DR class II. However, PRL in synergy with IFN-gamma inhibited, in a time- and dose-dependence, proliferation of U937 cells without influencing their maturation induced by IFN-gamma. IFN-gamma and PRL both affected the expression of the IFN-gamma receptor (IFN-gamma R) gene by increasing IFN-gamma R mRNA levels. The rise in IFN-gamma R transcripts was accompanied by a low but significant release of IL-6 which has previously been shown to stabilize IFN-gamma R mRNA. Moreover, a transient increase in surface expression of IFN-gamma R was observed in U937 cells treated by IFN-gamma alone or in combination with PRL, whereas no apparent modulation of cell surface IFN-gamma R was observed in cells treated with PRL. Lastly, PRL did not induce transcriptional activation in IFN-gamma inducible IRF-1 and Fc gamma RI genes in U937 cells. Together, our data indicate that IL-6 secretion and increased expression of the IFN-gamma R gene correlate with U937 cell growth arrest induced by IFN-gamma and PRL, probably through a signaling mechanism which does not involve the Stat 1/IRF-1 pathway.

TGF-beta 1-stimulated adhesion of human mononuclear phagocytes to fibronectin and laminin is abolished by IFN-gamma: dependence on alpha 5 beta 1 and beta 2 integrins

Monocyte migration within the extravascular space of inflamed tissues is controlled by adhesion molecules and inflammatory cytokines. In this study, we analyzed the capacity of TGF-beta 1 and IFN-gamma to regulate adhesion of human activated monocytes to fibronectin (FN) and to laminin (LM), two components of the extracellular matrix. When cultured in the absence of any of these two stimuli, human monocytes underwent "spontaneous activation" and adhered to both FN and LM. Adhesion to FN was inhibited in the presence of alpha 5 and beta 1 integrin blocking antibodies, whereas beta 2 blocking antibody blocked attachment to LM. Exogenous TGF-beta 1 increased the adhesive ability of monocytes to FN and to LM, respectively, linked to the increase of alpha 5 and beta 2 mRNA and protein synthesis levels. Moreover, an increase in alpha 5 expression at the monocyte cell surface was observed. In contrast, monocytes stimulated with exogenous IFN-gamma lost their capacity to bind to FN and this coincided with the down-regulation of surface alpha 5 expression which occurred at the posttranscriptional level of alpha 5 synthesis. Although IFN-gamma-treated monocytes also showed a decreased ability to adhere to LM, no alteration of beta 2 mRNA levels, beta 2 protein synthesis, and beta 2 cell surface expression was detectable, thus suggesting a modification of the functional state of surface beta 2 integrins. Furthermore, when stimulated with TGF-beta 1, IFN-gamma-pretreated monocytes reacquired the ability to bind to FN and LM. Conversely, IFN-gamma reduced adhesiveness to FN and LM of monocytes initially stimulated with TGF-beta 1. These in vitro adhesive-deadhesive responses of monocytes to TGF-beta 1 and IFN-gamma modulation may reflect mononuclear phagocyte motility within sites of inflammation.

Inhibition of gamma-glutamyl transpeptidase activity at the surface of human myeloid cells is correlated with macrophage maturation and transforming growth factor beta production

The protease gamma-glutamyl transpeptidase (gamma-GT) activity was detected at the surface of human blood granulocytes and monocytes and myeloblastic HL-60 and monoblastic U937 leukemia cell lines using an enzymatic assay (cleavage of gamma-glu-p-nitroanilide and inhibition by the specific irreversible inhibitor of gamma-GT, i.e., acivicin). Flow cytometric analysis of gamma-GT expression and detection of a 2.4-kb gamma-GT mRNA species by Northern blot analysis confirmed the presence of gamma-GT in cells of the monocytic-granulocytic lineage. Differentiation of HL-60, U937 cells, and blood monocytes along the macrophage pathway or granulocytic maturation of HL-60 cells was accompanied by an increase in gamma-GT mRNA levels without modulation of cell surface gamma-GT activity and protein. When added to leukemic cell cultures, acivicin produced a dose- and time-dependent inhibitory growth effect associated with the induction of morphological features characteristic of macrophage maturation and enhanced surface expression of phenotypic markers CD11b and CD71 characteristic of monocyte development. When cultured in the presence of acivicin, freshly isolated monocytes also underwent characteristic changes in morphology and antigenic phenotype (increase in CD71 and HLA-DR class II) consistent with their differentiation into macrophages. In parallel, a marked production of latent transforming growth factor (TGF)-beta was observed in supernatants of cells cultured with acivicin, although TGF-beta 1 mRNA species were expressed in these cells at a level almost similar to that in unstimulated cell cultures. Moreover, acivicin-treated cells still differentiated into macrophages in the presence of a neutralizing antibody to TGF-beta 1/beta 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Protease-catalyzed conversion of insulin-like growth factor-1 and interleukin-6 into high-molecular-mass species through the sequential action of hematopoietic surface-associated cathepsin G and gamma-glutamyl transpeptidase-related activities

Interleukin-6 (IL-6) and insulin-like growth-factor-1 (IGF-1) are cytokines produced by a variety of cells that act on a wide range of tissues, influencing cell growth and differentiation. Purified plasma membranes from human U937 monoblastic cells produced in vitro dimeric species of IL-6- and IGF-1-derived peptides through the sequential actions of surface-associated enzymes cathepsin G and transpeptidase activities. Cathepsin G degraded native unglycosylated IL-6 and IGF-1 molecules into 8-kDa and 7-kDa peptides respectively. Subsequent dimerisation of these intermediate forms into 16-kDa IL-6- and 14-kDa IGF-1-derived peptides was inhibited by acivicin and glutathione which are specific inhibitors of the standard cell-surface gamma-glutamyl transpeptidase (gamma-GT). However U937 plasma membranes, cleared of gamma-GT activity by immunoprecipitation with anti-gamma-GT and adsorption on protein-G-Sepharose, were still able to convert the intermediate forms of IL-6 and IGF-1 into dimers. Together, these observations indicate that the transpeptidase involved in the formation of the dimeric species of IL-6 and IGF-1 was related to, but distinct from, standard cell-surface gamma-GT. Cells of all hematopoietic lineages expressed gamma-GT-related activity. In contrast to the 16-kDa IL-6-derived peptide that did not retain growth-stimulating activity, the 14-kDa IGF-1 peptide was at least equipotent with native IGF-1 in the BALB/c 3T3 fibroblast DNA synthesis response. The N/O-glycosylated IL-6 was clearly as sensitive to cathepsin-G- and gamma-GT-related activities as the unglycosylated IL-6 from Escherichia coli, thus indicating that the sugar chains did not protect the cleavage sites of the two proteases on the IL-6 molecule. Our in vitro findings raise the possibility that similar proteases participate in the regulation of the catabolism of IL-6 and IGF-1 in vivo.

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

Human promonocytic U937 cells have previously been shown to possess at their cell surface specific transmembrane serine proteases and N-terminal amino acid proteases as well as associated enzymes including elastase and cathepsin G. In this study, purified plasma membranes from U937 cells are reported to degrade the recombinant 21-kDa 125I-interleukin-6 (125I-IL-6) into 8-kDa products with loss of biological activity, as monitored by polyacrylamide gel electrophoresis and a cell-proliferation bioassay. Degradation of 125I-IL-6 by plasma membranes was completely prevented by the serine-protease inhibitor diisopropyl fluorophosphate, but was only partially impaired by alpha 1-protease inhibitor and antibody against cathepsin G. A similar incubation of 125I-IL-6 with cathepsin G purified from U937 cells caused hydrolysis of the cytokine into similar inactive 8-kDa fragments, whereas incubation with purified U937 cell elastase failed to degrade the peptide. These findings indicate that U937 cells hydrolyze IL-6 using cell-associated serine-protease activity and that cathepsin G partially participates in this degradation. Prolonged incubation of 8-kDa 125I-IL-6 fragments with purified U937 plasma membranes, led to a complete loss of IL-6 activity related to the transformation of the 8-kDa forms into a higher-molecular-mass complex (16 kDa). This complex was stable in SDS and 2-mercaptoethanol at 100 degrees C and was not dissociated by hydroxylamine treatment, indicating the formation of a covalent non-ester bond between the 8-kDa 125I-IL-6-derived peptide and an undetermined acceptor. An initial oxidative treatment of 125I-IL-6 partially prevented complex formation, suggesting the presence of one or more oxidizable methionine residues at the binding site of 8-kDa 125I-IL-6 peptide. The kinetics of complex formation (time dependence and plasma-membrane-concentration dependence), as well as its inhibition by a specific inhibitor of N-amino-peptidase activity, bestatin, suggest the participation of peptidyl-transferase activity in complex formation. Finally, a plasma-membrane fraction, corresponding to a molecular mass > or = 30 kDa, was able to convert the 8-kDa 125I-IL-6 forms into the 125I-labeled 16-kDa complex, suggesting that a > or = 30-kDa peptidyl-transferase enzyme catalyzes the reaction and provides the 125I-labeled 16-kDa peptide by dimerization of 8-kDa 125I-IL-6-derived intermediates. Further identification of the plasma-membrane-associated peptidyl transferase as a regulator of IL-6 proteolysis may be of physiological relevance for the control of IL-6 biological activity.

Divergent regulation of cell surface protease expression in HL-60 cells differentiated into macrophages with granulocyte macrophage colony stimulating factor or neutrophils with retinoic acid

Taking advantage of the recently demonstrated presence of N-aminopeptidases and the serine protease dipeptidyl aminopeptidase IV (DPP IV) at the surface of human myeloblastic HL-60 cells, the regulation of these protease activities in HL-60 cell differentiation has been assessed using combined spectrophotometric and flow cytometric assays. Addition of human recombinant granulocyte macrophage colony stimulating factor (rHu-GM-CSF) to HL-60 cells to induce differentiation into macrophages led to a time- and dose-dependent increase in both cell surface N-aminopeptidase and DPP IV activities. Protease up-regulation was due to an enhancement in cell surface protease number, associated with a slight rise in apparent affinities of the enzymes for their substrates. In contrast, in HL-60 cells induced to differentiate into neutrophils in the presence of retinoic acid, expression of cell surface N-aminopeptidases was almost completely abolished in a time- and dose-dependent fashion, and this down-regulation was accompanied by a weak but significant decrease in affinity. However, no noticeable difference was seen in serine DPP IV expression between retinoic acid-treated and untreated HL-60 cells. Retinoic acid treatment also reduced soluble protease activity in vitro indicating that down-regulation of membrane aminopeptidases was not due to their proteolytic clip. No modulation in the activity of any of the enzymes tested was seen with human recombinant tumor necrosis factor-alpha or retinol which do not induce HL-60 cell differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Human myeloblastic HL-60 cells were probed for cell surface protease activity. A class of bestatin sensitive N-exoaminopeptidases and a dipeptidyl aminopeptidase IV-like enzyme specifically inhibited by DFP and diprotin A were detected at the surface of intact cells, as well as in highly purified HL-60 cell membranes. Cell surface proteolytic activities were investigated in HL-60 cells induced to differentiate into granulocytes or macrophages as well as on normal human myeloid cells. It was found that membrane expression of serine and N-aminopeptidases significantly increased following maturation of the HL-60 cell line and normal monocytes toward the macrophage pathway. In contrast, N-aminopeptidase expression was mainly down-regulated on HL-60 cells differentiated into granulocytes and low activity was paralleled with that expressed by normal blood granulocytes. HL-60 maturation into the granulocyte lineage however did not cause any modulation in membrane DPP IV-like enzyme. Thus, selective expression of cell surface proteases along the myeloid lineage provides a useful model system for determining the possible influence of such enzymes on normal and malignant myeloid cells.

IFN-gamma and transforming growth factor-beta 1 differently regulate fibronectin and laminin receptors of human differentiating monocytic cells

The regulation of extracellular matrix (ECM) protein receptor expression was followed in the human promonocytic cell line U937 before and after stimulation either with PMA or various cytokines implicated in monocytopoiesis. On undifferentiated U937 cells, alpha-chains of very late Ag (VLA)-4, VLA-5, and VLA-6 were constitutively expressed whereas alpha-chains of VLA-2 (alpha 2) and vitronectin receptor (alpha V) were not. Maturation of U937 cells with PMA resulted in a marked decrease in alpha 4 expression (25% of control by day 5), and a small but significant increase in the expression of alpha 2 and alpha v over 4 days of stimulation. Unstimulated U937 cells attached to fibronectin (FN) but not to laminin (LM), collagens I/IV-coated surfaces. After PMA stimulation, U937 cells exhibited enhanced adherence on FN and expressed the ability to adhere to LM. PMA stimulation also promoted U937 spreading both on FN and LM. Adhesion on FN all along the maturation pathway was specifically and totally inhibited by anti-alpha 5 mAb but not by anti-alpha 4 mAb. Anti-beta 1, anti-alpha 6, anti-alpha 2, and anti-alpha v mAb, as well as Tyr-Ile-Gly-Ser-Arg and Arg-Gly-Asp synthetic peptides from LM, had no effect on adhesion of PMA-stimulated cells on LM, implying that U937 cell adherence to LM is mediated through hitherto distinct receptors. In the presence of rIFN-gamma, differentiating U937 cells did not adhere to LM and lost the capacity to bind to FN. Loss of adhesion to FN was correlated with the concomitant decrease in the expression of alpha 4 and alpha 5 integrin subunits. In contrast, TGF-beta 1 mimicked most of the effects of PMA by enhancing the attachment of maturating U937 cells on FN through alpha 5 receptors and by promoting adherence to LM. TGF-beta 1 stimulation also promoted U937 cell spreading on both FN- and LM-coated surfaces. The data suggest that inflammatory cytokines such as IFN-gamma and TGF-beta 1 may be critically important in the homing of monocytic cells at sites of inflammation by modulating cell-surface expression of ECM receptors.

IFN-gamma and transforming growth factor-beta 1 differently regulate fibronectin and laminin receptors of human differentiating monocytic cells

The regulation of extracellular matrix (ECM) protein receptor expression was followed in the human promonocytic cell line U937 before and after stimulation either with PMA or various cytokines implicated in monocytopoiesis. On undifferentiated U937 cells, alpha-chains of very late Ag (VLA)-4, VLA-5, and VLA-6 were constitutively expressed whereas alpha-chains of VLA-2 (alpha 2) and vitronectin receptor (alpha V) were not. Maturation of U937 cells with PMA resulted in a marked decrease in alpha 4 expression (25% of control by day 5), and a small but significant increase in the expression of alpha 2 and alpha v over 4 days of stimulation. Unstimulated U937 cells attached to fibronectin (FN) but not to laminin (LM), collagens I/IV-coated surfaces. After PMA stimulation, U937 cells exhibited enhanced adherence on FN and expressed the ability to adhere to LM. PMA stimulation also promoted U937 spreading both on FN and LM. Adhesion on FN all along the maturation pathway was specifically and totally inhibited by anti-alpha 5 mAb but not by anti-alpha 4 mAb. Anti-beta 1, anti-alpha 6, anti-alpha 2, and anti-alpha v mAb, as well as Tyr-Ile-Gly-Ser-Arg and Arg-Gly-Asp synthetic peptides from LM, had no effect on adhesion of PMA-stimulated cells on LM, implying that U937 cell adherence to LM is mediated through hitherto distinct receptors. In the presence of rIFN-gamma, differentiating U937 cells did not adhere to LM and lost the capacity to bind to FN. Loss of adhesion to FN was correlated with the concomitant decrease in the expression of alpha 4 and alpha 5 integrin subunits. In contrast, TGF-beta 1 mimicked most of the effects of PMA by enhancing the attachment of maturating U937 cells on FN through alpha 5 receptors and by promoting adherence to LM. TGF-beta 1 stimulation also promoted U937 cell spreading on both FN- and LM-coated surfaces. The data suggest that inflammatory cytokines such as IFN-gamma and TGF-beta 1 may be critically important in the homing of monocytic cells at sites of inflammation by modulating cell-surface expression of ECM receptors.

Characterization of specific proteases associated with the surface of human skin fibroblasts, and their modulation in pathology

Human skin fibroblasts were probed for cell surface protease activity. One activity removing dipeptides from the NH2-terminal end of Gly-Pro-pNA was specifically inhibited by di-isopropyl-fluorophosphate (DFP), phenylmethanesulphony fluoride (PMSF), and diprotin A, and thus was identified as dipeptidyl peptidase IV (DPP IV). A group of bestatin-sensitive N-exoaminopeptidase activities was also characterized when Ala-, Leu-, and Arg-pNA were used as chromogenic substrates. Using human monoclonal antibodies anti-CD 13 and anti-CD 26 that recognized, respectively, an N-Ala-aminopeptidase and DPP IV, it was found that human dermal fibroblasts expressed the CD 13 and CD 26 antigen on their surface. In addition, both peptidases were specifically immunoprecipitated by monoclonal antibodies anti-CD 13 and anti-CD 26 from plasma membranes. Cell surface proteolytic activities were also investigated in human fibroblasts derived from dermatological and rheumatic diseases (i.e., psoriasis, rheumatoid arthritis, and lichen planus). It was found that these fibroblasts also expressed both types of proteinases initially identified on normal skin fibroblasts and that the levels of Ala-aminopeptidase activities were similar in all cases. In contrast, the levels of Arg-, Leu-exoaminopeptidase, and DPP IV activities were significantly higher (up to 6.6-fold) in the three pathological fibroblast populations than in their normal counterparts. These proteolytic enzymes, therefore, can potentially serve as markers in dermatological diseases. Taken together, our results suggest that skin fibroblast-derived proteinases associated with both serine and N-aminopeptidase activities may play an important role by participating in the extracellular events associated with fibroblast behaviour.

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

Surface peptidase activities on the human monocytic lineage cell line U937 were characterized. Two diisopropyl phosphofluoridate (DFP)-inhibitable serine peptidases were identified by differences in their hydrolytic activities on chromogenic peptides: one removed tripeptides from the free NH2-terminal end of the synthetic peptide Ala-Ala-Phe-p-nitroanilide (pNA) and was not inhibited by inhibitors of metallo-, cysteic-, and aspartic-proteinases, or by those of elastase-, trypsin- and chymotrypsin-like enzymes, suggesting the presence of a hitherto unidentified serine tripeptidyl endopeptidase; the other peptidase catalyzed the release of Gly-Pro from Gly-Pro-pNA and was inhibited by DFP, phenylmethyl sulfonyl fluoride and diprotin A, thus resembling dipeptidyl peptidase IV (DPP IV) with respect to its substrate specificity and inhibitor profile. A group of N-exo-aminopeptidase activities specifically inhibited by bestatin, was also detected when Ala-, Leu-, Arg- and Lys-pNA were used a substrates. The activities were surface associated and not secreted as determined by extracellular location of product and enzymatic recovery in highly purified U937 cell membranes. Peripheral monocytes and macrophages were found to virtually exhibit identical levels of these two classes of peptidase activities when compared to those detected on U937 cells. The relative contributions of these hydrolytic enzymes to the cleavage of bioactive and radioiodinated cytokines including tumor necrosis factor-alpha (TNF-alpha), interleukin-1 alpha and interferon-gamma was next examined. The results indicated that N-aminopeptidases do not appear to participate in the catabolism of any tested cytokine. In contrast, the most interesting finding was that both serine peptidases participate in TNF-alpha degradation. Analysis of the final proteolytic digestion products demonstrated the disappearance of the native 17-kDa molecule TNF-alpha, and the concomitant release of biologically inactive fragments of less than or equal to 2 kDa. Together, these observations indicate new roles for both the DPP IV-like enzyme and the tripeptidyl endopeptidase located at the surface of human monocytic cells, including the regulation of the extracellular TNF-alpha concentration. Thus, the identification of functional ectopeptidases provides insight into their potential role in both normal and malignant monocytic function.

21.1.1, a novel activation marker of T and B cells

A new rat mAb designated mAb 21.1.1 was raised against a T cell hybridoma of mouse origin, T2D4. This antibody, an IgG2b, immunoprecipitates from the membrane extracts of iodinated T2D4 cells a 56-kDa glycoprotein of apparent pI 4.6 which gives a 34-kDa polypeptide after treatment with endoglycosidase F. MAb 21.1.1 reacts with an antigen expressed on murine mitogen-activated thymocytes and T cells, and on B cells stimulated by anti-IgM antibodies. Cells isolated from the spleen, lymph nodes and bone marrow are negative, as are purified resting B cells or T cells. This antigen is strongly expressed on most day-16 fetal thymocytes whereas adult thymocytes are almost negative. mAb 21.1.1 may be useful for the study of activation and differentiation of T and B cells.

Murine thymocytes possess specific cell surface-associated exoaminopeptidase activities: preferential expression by immature CD4-CD8- subpopulation

Murine thymocytes are shown to possess at least three well-defined exo-N-aminopeptidase activities on their surface. One of them cleaves the prolyl bond in the synthetic dipeptide nitroanilide Gly-Pro-pNA (Km 0.95 mM and Vmax 8 nmol/h at pH 7.4 and 37 degrees C) and is specifically inhibited by phenylmethane sulfonyl fluoride, diprotin A, Gly-Pro-Ala and Gly-Pro-Gly-Gly. These data further support identification of this enzyme with a serine exopeptidase dipeptidyl peptidase IV (DPP IV), previously reported to be specific for collagen. The two other forms of N-exopeptidase activities are detected when Ala-pNA and Leu-pNA are used as substrates. Leu-aminopeptidase activity (Km 1.4 mM, Vmax 15 nmol/h) and Ala-aminopeptidase activity (Km 4.0 mM, Vmax 20 nmol/h) are inhibited by inhibitors for thiol- and trypsin-like proteinases, i.e. tosyl lysyl chloromethyl ketone, leupeptin and N-ethylmaleimide. Addition inhibition of Leu-aminopeptidase activity by peptstatin, a known inhibitor of carboxyl proteases, suggests that aminopeptidase activity detected with Leu-pNA is different in part from Ala-aminopeptidase activity. Among the various lymphoid cell populations tested, the three aminopeptidase activities are increased by three- to fourfold in the immature CD4-CD8- thymocyte subset as well as in the thymoma BW5147. In contrast, cortisone-resistant thymocytes, lymph node and spleen cells exhibit levels of activities almost similar to that of unfractionated thymocytes. During ontogeny, the levels of these activities are increased four- to sevenfold on fetal thymocytes (from days 14 to 16). Finally, when thymocytes or spleen cells are cultured with a mitogenic concentration of concanavalin A, their proliferative responses are correlated with an enhancement of the aminopeptidase activities (1.3- to 5-fold). From these results, a correlation between the presence of these peptidases on the cell surface of immature and mature lymphoid cells and biological responsiveness is suggested.

A role for the thymic epithelium in the selection of pre-T cells from murine bone marrow

A rat thymic epithelial cell line IT45-R1 has been previously described as secreting soluble molecules that in vitro chemoattract rat hemopoietic precursor cells. The development of such an in vitro migration assay was based on the ability of cells to migrate across polycarbonate filters in Boyden chambers. In the present paper, by using the same strategy, we studied murine bone marrow cells capable of migrating in vitro toward IT45-R1 conditioned medium. The responding cells were shown to represent a minor bone marrow subpopulation characterized by a low capacity to incorporate tritiated thymidine in vitro (less than 10% of control). Moreover, this cell subset was considerably impoverished with respect to granulocyte-macrophage CFU (less than 7% of control) and pluripotent hemopoietic stem cells (less than 12% of control). Potential generation of T cells of donor-type in the lymphoid organs of irradiated recipients was measured by using C57BL/Ka Thy-1.1 and Thy-1.2 congenic mice. Thy-1.1 irradiated mice were injected intrathymically or intravenously with the selectively migrated cell subset of Thy-1.2 donor-type bone marrow cells. The use of an i.v. transfer route allowed us to show that these cells possess thymus-homing and colonization abilities. In a time-course study after intrathymic cell transfer, these migrated cells were able to generate Thy-1.2+ donor-type thymocytes represented by all cortical and medullary cell subsets in a single wave of repopulation from day 20 to day 30 after transfer, with a peak around days 23 to 25. The degree of repopulation closely resembled that seen with unfractionated bone marrow cells in terms of absolute numbers of donor cells per thymus (82% of control, 22 x 10(6) Thy-1.2+ cells) as well as in percent donor cells per thymus (105% of control). Thy-1.2+ cells were also detected in the lymph nodes and the spleens of reconstituted recipient mice. Taken together, these results support the idea that the supernatant of the established thymic epithelium IT45-R1 induces the migration of a murine bone marrow subset that contains hemopoietic stem cells already committed to the lymphoid lineage (i.e., pre-T cells).

A role for the thymic epithelium in the selection of pre-T cells from murine bone marrow

A rat thymic epithelial cell line IT45-R1 has been previously described as secreting soluble molecules that in vitro chemoattract rat hemopoietic precursor cells. The development of such an in vitro migration assay was based on the ability of cells to migrate across polycarbonate filters in Boyden chambers. In the present paper, by using the same strategy, we studied murine bone marrow cells capable of migrating in vitro toward IT45-R1 conditioned medium. The responding cells were shown to represent a minor bone marrow subpopulation characterized by a low capacity to incorporate tritiated thymidine in vitro (less than 10% of control). Moreover, this cell subset was considerably impoverished with respect to granulocyte-macrophage CFU (less than 7% of control) and pluripotent hemopoietic stem cells (less than 12% of control). Potential generation of T cells of donor-type in the lymphoid organs of irradiated recipients was measured by using C57BL/Ka Thy-1.1 and Thy-1.2 congenic mice. Thy-1.1 irradiated mice were injected intrathymically or intravenously with the selectively migrated cell subset of Thy-1.2 donor-type bone marrow cells. The use of an i.v. transfer route allowed us to show that these cells possess thymus-homing and colonization abilities. In a time-course study after intrathymic cell transfer, these migrated cells were able to generate Thy-1.2+ donor-type thymocytes represented by all cortical and medullary cell subsets in a single wave of repopulation from day 20 to day 30 after transfer, with a peak around days 23 to 25. The degree of repopulation closely resembled that seen with unfractionated bone marrow cells in terms of absolute numbers of donor cells per thymus (82% of control, 22 x 10(6) Thy-1.2+ cells) as well as in percent donor cells per thymus (105% of control). Thy-1.2+ cells were also detected in the lymph nodes and the spleens of reconstituted recipient mice. Taken together, these results support the idea that the supernatant of the established thymic epithelium IT45-R1 induces the migration of a murine bone marrow subset that contains hemopoietic stem cells already committed to the lymphoid lineage (i.e., pre-T cells).

Characterization of rat T cell precursors sorted by chemotactic migration toward thymotaxin

An established rat thymic cell line secretes a peptide in the 11 kd range called thymotaxin that attracts a small subset of juvenile rat bone marrow cells via a chemotactic mechanism. The selected cell subset (0.1% of the total bone marrow) is composed of low-density lymphoid cells that do not replicate, and display an immature Thy-1+T-B- phenotype. Thymotaxin-responding cells do not grow in semi-solid cultures under hemopoietic growth factors stimulation, and survive only in coculture with thymic stroma under steroid-free conditions. This stroma mimics the thymic microenvironment and allows a fraction of responding bone marrow cells to acquire T cell differentiation markers and to synthesize transcripts of the TCR alpha and beta chains. Chemotactic migration toward thymic epithelial cell peptides can be used in vitro to sort pre-T cells from the rat bone marrow. The sorted T cell precursors are resting stem cells possibly committed to lymphoid lineage.

Aspects of haemopoietic cell dynamics: ontogeny and targeted migration

In the developing avian and mammalian embryo, haemopoietic cells appear first in transient foci whose function is restricted to discrete periods of embryogenesis. These foci are essentially represented by the yolk sac, intraembryonic dispersed foci and the liver. Haemopoietic cells then repopulate the developing spleen, thymus and bone marrow, organs which persist and develop after birth. In the present review, we describe a number of possible mechanisms controlling specific adhesion, oriented migration and invasiveness of haemopoietic cells. One concerns the high specificity of the interactions of homing receptors on the surface of haemopoietic cells with determinants on vascular endothelium and/or thymic epithelium. A second is the importance of the presence of some macromolecules in the extracellular matrix, such as fibronectin, collagen, laminin and elastin. These components can interact with the haemopoietic cells (and/or induce chemotaxis) via the existence of specific receptors on the surface of the haemopoietic cells. Another mechanism is the activation of the haemopoietic cells through the interactions of cell-chemotactic factor, cell-extracellular matrix and/or cell-thymic epithelium. This activation can lead to: 1) the expression of new specific cell-surface receptors for the target foci; 2) the secretion of specific protease and glycosidase systems active upon the extracellular matrix; and 3) the differentiation of these cells in the thymus.

A collagen-binding glycoprotein on the surface of mouse fibroblasts is identified as dipeptidyl peptidase IV

A dipeptidyl aminopeptidase (DPP) was detected in plasma membranes from normal (3T3) and transformed (3T12) mouse fibroblasts. This enzyme was active in cleaving the prolyl bond in the synthetic dipeptide nitroanilide Gly-Pro-NH-Np, which is a specific substrate for DPP IV (Km 0.63 mM and Vmax 6.1 nmol/min per mg at pH 6.0 and 37 degrees C). However, it did not degrade Pro-NH-Np or other dipeptide nitroanilides such as Gly-Arg-NH-Np or Val-Ala-NH-Np. The enzyme was totally inhibited by di-isopropyl phosphorofluoridate (Pri2-P-F) and by phenylmethanesulphonyl fluoride, indicating a serine catalytic site for the proteinase. DPP IV is a glycoprotein that specifically recognized immobilized gelatin and type I collagen. Upon molecular exclusion chromatography, the proteinase exhibited an apparent Mr of 100,000. SDS/polyacrylamide-gel electrophoresis under non-reducing and reducing conditions revealed that the [3H]Pri2-P-protein was exclusively represented by a polypeptide of Mr 55,000. This suggested that DPP IV consists of two non-covalently linked 55,000-Mr subunits. Fibroblast adhesion to native or denatured collagen was significantly inhibited by the two dipeptide inhibitors of DPP IV, Gly-Pro-Ala and Ala-Pro-Gly, but not by the peptides Gly-Pro and Gly-Gly-Gly, which are not inhibitors of the proteinase. Moreover, preliminary fractionation of DPP IV by molecular exclusion chromatography and affinity chromatography indicated that this material was active in disrupting cell adhesion to collagens. Taken together, the above data suggest that a fibroblast membrane-associated collagen-binding glycoprotein, DPP IV, may play a role in cell attachment to collagen.

Initial adhesion of murine fibroblasts to collagen and fibronectin occurs by two mechanisms

The adhesion of Balb/c 3T12 cells to fibronectin (FN) and to denatured (DC) or native (NC) collagen is differentially sensitive to divalent cations and to sodium azide. Short-time adhesion (10 min) to FN requires either Mg2+ or Mn2+, whereas only Mn2+ stimulates attachment to DC and NC. Azide treatment only slightly affects adhesion of cells to FN, but strongly inhibits cell attachment to DC and NC. Attachment to any of these substrata is unaffected by monensin and by treatment of the cells with an intracellular fraction, making unlikely the possibility that molecules released by secretion or cell lysis participate in the adhesive process. Soluble collagen inhibits the adhesion of cells to DC and NC, but does not affect adhesion to FN. Finally, rabbit antiserum against collagen binding proteins inhibits cell attachment to NC and DC; the cells, however, attach normally to FN in presence of this antiserum. Taken together, our results support the view that 3T12 cells attach directly to native or denatured collagens and that FN is not required for this process.

A collagen:glucosyltransferase at the surface of malignant fibroblasts

3T12 fibroblasts possess glucosyltransferases that catalyze the transfer of glucose from UDP-Glucose to galactosylhydroxylysyl residues on collagenous acceptors. The presence of the enzyme activity at the cell surface is indicated by the following findings: a) suspensions of intact cells, as well as intact cell monolayers, glucosylate gelatinized collagen b) glucose transfer is not due to UDP-Glucose hydrolysis and subsequent intracellular utilization of the free glucose c) experiments using cell suspensions with known proportions of broken cells indicate that the glucosyltransferase activity is attributable to intact cells and not to contamination by intracellular enzymes from broken cells. The Km value for UDP-Glucose is about 20 microM. The enzyme has a pronounced requirement for manganese, and shows highest activity between 2 and 10 mM. The optimal Mn2+ concentration for the intracellular gelatin:glucosyltransferase activity is more restricted (5 to 10 mM). Glucosyltransferase activity is strongly inhibited by diamide and N-ethylmaleimide (5 mM), suggesting that intact sulfhydryl residues present in the enzyme are essential.

Characterization of a sialyl alpha 2-3 transferase and a sialyl alpha 2-6 transferase from human platelets occurring in the sialylation of the N-glycosylproteins

Two sialyltransferases (EC 2.4.99.-) are extracted with Triton X-100 from human platelets and characterized with asialo 3H-labelled alpha 1-acid glycoprotein, an N-glycosylprotein. Methylation analysis of their specificities indicates that the enzymes transfer selectively sialic acid in a 3 or 6 position to oligosaccharides possessing Gal(beta 1-4)GlcNAc structure. The sialyl alpha 2-3 transferase was separated from the sialyl alpha 2-6 transferase by Ultrogel AcA34 column chromatography. Through affinity chromatography on CDPethanolamine-Sepharose, the two sialyltransferases are partly purified (5- and 20-fold enrichment of their specific activity, respectively, for sialyl alpha 2-3 transferase and alpha 2-6 transferase) and appear to be structurally heterogeneous.

Discrimination between activity of (alpha 2-3)-sialyltransferase and (alpha 2-6)-sialyltransferase in human platelets using p-nitrophenyl-beta-D-galactoside as acceptor

Exogenous asialo-glycoproteins and endogenous acceptors are both sialylated by incubating cytidine 5'-monophosphate N-[14C]acetylneuraminic acid (CMP [14C]NeuAc) with a lysate of human platelets but their respective incorporation levels vary with the divalent cation concentration. P-Nitrophenyl-beta-D-galactoside has also been demonstrated to be an acceptor of sialyl residues, and two different sialyl derivatives are synthesized according to the concentration of divalent cations. P-Nitrophenyl-beta-D-[6-3H]galactoside has been prepared by reduction with tritiated borohydride of the compound previously oxidized by galactose oxidase. Using this labelled p-nitrophenyl-beta-D-galactoside as acceptor and unlabelled CMP-NeuAc as donor, the two sialyl derivatives have been identified by methylation analysis as alpha-sialosyl-(2-3)-p-nitrophenyl-beta-D-galactoside and alpha-sialosyl-(2-6)-p-nitrophenyl-beta-D-galactoside. In addition to their different responses to divalent cation requirements, the sialyltransferase activities responsible for the synthesis of the two sialylgalactoside isomers have been clearly distinguished by their temperature and pH optimal values. They also exhibit different susceptibilities to dithioerythritol and different stabilities. These results demonstrate the presence in human platelets of two sialyltransferases: a CMP-NeuAc: galactoside (alpha 2-3)-sialyltransferase and a CMP-NeuAc: galactoside (alpha 2-6)-sialyltransferase.

Glycoprotein-sialyltransferase activity of normal human, thrombasthenic and Bernard-Soulier platelets

Some properties of the sialyltransferase activity of homogenates prepared from normal human platelets were investigated using asialo-fetuin as substrate. The enzyme activity was optimal at pH 6.5 and was stimulated by divalent cations in the order Mg2+ greater than Mn2+ greater than Ca2+. Buffers of high ionic strength strongly reduced the activity. ATP and ADP were not inhibitors at 0.1 mM concentration, but AMP, CTP and CMP reduced the activity by 15-30%. A native endogenous acceptor for the enzyme activity was located in the platelet homogenates. The range of fetuin-sialyltransferase activity found in platelets isolated from 6 normal donors was 79 +/- 39 pmol/h/mg protein (mean +/- SD). The platelets of patients with Glanzmann's thrombasthenia and the Bernard-Soulier syndrome, which are characterized by different membrane glycoprotein deficiencies, were shown to have fetuin-sialyltransferase activities within the normal range indicating that the membrane glycoprotein defects in the platelets of these patients are not associated with the absence of sialyltransferase activity.

ABH and Lewis glycosyltransferases in human red cells, lymphocytes and platelets

The alpha-O-N-acetylgalactosaminyl-, alpha-3-D-galactosyl- and alpha-2-L-fucosyltransferases, the direct products of the respective A, B and H blood group genes have been identified in red cells, lymphocytes and platelets homogenates from secretor and non-secretor individuals of appropriate ABO group. The H enzyme was not detectable in red cell membranes from Bombay individuals. Since the uptake of A antigen from the plasma has been shown at least for red cells [10] and lymphocytes [25], the present results suggest that the ABH determinants of the blood cells may arise both from intrinsic and extrinsic origin, but the relative contribution of each mechanism is not known. In contrast, the Lewis enzyme was absent or inactive in all the investigated blood cell samples, which can be considered as an additional proof that the Lewis antigens of these cells are entirely derived from the plasma.

Interaction of adenosine and adenylnucleotides with the human platelet membrane. Further characterization of the ADP binding sites

The binding of adenosine and adenylnucleotides to the human platelet membrane has been measured and the subsequent effect on the binding of 14C-ADP has been determined. The following conclusions have been drawn: (1) Two reactions with different velocities (t 1/2 = 15--30 sec and t 1/2 = 4--6 min) seem to be involved in the binding of ADP to the platelet membrane. (2) AMP binds to the platelet membrane and partially inhibits binding of ADP in a competitive manner. These two findings suggest that ADP binding sites on the platelet membrane may be of more than one type. (3) At concentrations up to 10(-5) M, ATP does not itself bind to the platelet membrane but is rapidly transformed into ADP which, in turn, binds to the membrane and inhibits the binding of 14C-ADP. (4) Adenosine does not significantly interfere with the binding of 14C-ADP and has not been shown to bind to the platelet membrane.

Rapid binding of ADP to a small population of platelet receptor sites

By studying binding of ADP to isolated human plasma membranes, we have found that ADP binds with different affinities and/or different kinetics to several types of receptor sites whose nature and localization have been assessed by subjecting the membranes to various treatments such as proteolytic digestion or alkaline extraction. From kinetic results, two populations of receptor sites were distinguished, with t 1/2 = IE-30 secor (approximately 20 % of the sites) and with t 1/2 = 4-6 minutes (80 % of the sites). The binding of AMP was studied to determine whether, as expected from its inhibition of ADP-induced platelet shape change and aggregation, it could react with ADP receptor sit We found that AMP bound rapidly to the platelet membrane (t 1/2 =15-30 seconds) ; up to approximately 100 picomoles of AMP could bind to One milligram of membrane protein, which represented 20-30% of the total ADP binding capacity, with an affinity constat (Ka =0.6 × 106M-1) higher than that of ADP (Ka=0.4 × 106M-1). AMP partially and conspectitively inhibited the binding of ADP. It was shown mainly to inhibit those molecules of ADP which bind to the platelet membrane during the first 90 seconds of incubation and which represent approximately 20 - 30 % of the total ADP binding.

From this study, it is concluded that a population of receptor sites showirg high react vity towards ADP and AMP is present on the platelet membrane.

Heterogeneity of antibodies to adenosine 5'-monophosphate

Antibodies to adenosine 5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. AMP-specific antibodies were isolated by affinity chromatography. The antiserum was first applied on oligoadenylic acids-agarose column and then the unbound proteins on a morpholine derivative of AMP-agarose column. The antibodies purified on these two columns interact differently with AMP derivatives as shown by immunodiffusion. These results are confirmed by the values of the binding constants of the complexes Fab fragments- AMP and AMP derivatives. The study of Fab fragments -- C(8)-substituted AMP derivatives complexes suggest a syn conformation for the bound nucleotide. Thermodynamic parameters for the Fab fragments-AMP complexes have been determined (deltaHdegrees = --13 kcal/mol and deltaSdegrees = --15 cal - degree-1 - mol-1).