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M Pierres

Publications and source records attributed to M Pierres.

At least 19 recordsLinked to original sources
PubMed2000

Enhanced insulin secretion and improved glucose tolerance in mice lacking CD26.

A subset of prolyl oligopeptidases, including dipeptidyl-peptidase IV (DPP IV or CD26, EC ), specifically cleave off N-terminal dipeptides from substrates having proline or alanine in amino acid position 2. This enzyme activity has been implicated in the regulation of the biological activity of multiple hormones and chemokines, including the insulinotropic peptides glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Targeted inactivation of the CD26 gene yielded healthy mice that have normal blood glucose levels in the fasted state, but reduced glycemic excursion after a glucose challenge. Levels of glucose-stimulated circulating insulin and the intact insulinotropic form of GLP-1 are increased in CD26(-/-) mice. A pharmacological inhibitor of DPP IV enzymatic activity improved glucose tolerance in wild-type, but not in CD26(-/-), mice. This inhibitor also improved glucose tolerance in GLP-1 receptor(-/-) mice, indicating that CD26 contributes to blood glucose regulation by controlling the activity of GLP-1 as well as additional substrates. These data reveal a critical role for CD26 in physiological glucose homeostasis, and establish it as a potential target for therapy in type II diabetes.

Animals↗
PubMed1998

Engagement of T cell receptor triggers its recruitment to low-density detergent-insoluble membrane domains.

T-cell receptors (TCRs) upon binding to peptide-MHC ligands transduce signals in T lymphocytes. Tyrosine phosphorylations in the cytoplasmic domains of the CD3 (gammadeltaepsilon) and zeta subunits of the TCR complex by Src family kinases initiate the signaling cascades via docking and activation of ZAP-70 kinase and other signaling components. We examined the role of the low-density detergent-insoluble membranes (DIMs) in TCR signaling. Using mouse thymocytes as a model, we characterized the structural organization of DIMs in detail. We then demonstrated that TCR engagement triggered an immediate increase in the amount of TCR/CD3 present in DIMs, which directly involves the engaged receptor complexes. TCR/CD3 recruitment is accompanied by the accumulation of a series of prominent tyrosine-phosphorylated substrates and by an increase of the Lck activity in DIMs. Upon TCR stimulation, the DIM-associated receptor complexes are highly enriched in the hyperphosphorylated p23 zeta chains, contain most of the TCR/CD3-associated, phosphorylation-activated ZAP-70 kinases and seem to integrate into higher order, multiple tyrosine-phosphorylated substrate-containing protein complexes. The TCR/CD3 recruitment was found to depend on the activity of Src family kinases. We thus provide the first demonstration of recuitment of TCR/CD3 to DIMs upon receptor stimulation and propose it as a mechanism whereby TCR engagement is coupled to downstream signaling cascades.

Animals↗
PubMed1997

Thymocytes in Thy-1-/- mice show augmented TCR signaling and impaired differentiation.

Thy-1, a single variable-like immunoglobulin superfamily domain anchored in the plasma membrane by a glycosyl phosphaditylinositol tail [1], is a major surface glycoprotein in adult mammalian neurons and rodent thymocytes [2]; the function of Thy-1 has remained enigmatic since its discovery [3]. Studies in vitro have implicated Thy-1 in homotypic and heterotypic cell-cell interactions [2,4]. Ligation of Thy-1 initiates transmembrane signaling pathways that lead to diverse physiological outcomes in different cells [2,5-7]. In rodents, Thy-1 is highly expressed on the surface of CD4+CD8+ double-positive immature thymocytes and downregulated in mature T cells. Here, we report that thymocytes from Thy-1-/- mice [8] had altered cell-cell contacts, and hyperresponsiveness to T-cell receptor (TCR) triggering as demonstrated by the heightened activation of p56lck, phosphorylation of TCR subunits, Ca2+ fluxes and cell proliferation. Thy-1-/- thymocytes exhibited impaired maturation from the double positive to single positive stage of thymocyte development, possibly due to inappropriate negative selection, and were prone to T lymphomas in aged mice. These observations indicate that Thy-1 negatively regulates TCR-mediated signaling and controls activation thresholds during thymocyte differentiation.

Animals↗
PubMed1997

Thy-3, a developmentally regulated T-cell glycoprotein associated to Thy-1 in detergent-resistant membrane microdomains.

The function of the Thy-1 molecule, a major T-cell glycoprotein, is still obscure. Its functional properties might be due to the anchoring via a glycosylphosphatidylinositol group which favors gathering of molecules in functional membrane subregions called microdomains. Using novel monoclonal antibodies, we describe a 53-kDa Thy-1-associated glycoprotein called Thy-3. Thy-3 expression is restricted to T lymphocytes, becomes detectable on double-positive thymocytes, and depends on that of Thy-1. Anti-Thy-3 antibodies immunoprecipitate Thy-1 and Thy-3 or Thy-3 alone in detergents which preserve or disrupt microdomains, respectively. These antibodies induce thymocyte aggregation and interfere with adhesion of thymocytes to a thymic epithelial cell line as previously shown with anti-Thy-1 antibodies. Thus, Thy-3 is a T lineage-specific glycoprotein associated to Thy-1 in membrane microdomains and might contribute to the function of Thy-1 in T-cell differentiation.

Animals↗
PubMed1996

Synthetic peptides coupled to the lipotripeptide P3CSS induce in vivo B and Thelper cell responses to HIV-1 reverse transcriptase.

To evaluate the ability of the lipotripeptide P3CSS to increase peptide-specific immune responses in vivo, we immunized mice from different inbred strains (BALB/c, C3H/HeJ, C57BL/6) with the 22-mer lipopeptide conjugates P3CSS-[RT-(522-543)] and P3CSS-[RT-(528-549)] of HIV-1 reverse transcriptase (RT) which included an immunodominant Th epitope [i.e. RT-(528-543)] characterized previously. Analysis of T and B cell responses to these lipopeptide conjugates indicated that specific Th responses could be readily induced in vivo. The peptide segments could also efficiently prime mice for secondary recognition of native RT. The use of shorter peptides permitted a delineation of the minimal T cell recognition site of this RT C-terminal region [i.e. RT-(528-540)]. Close to this T cell epitope we identified a B cell determinant containing the motif EQVD [RT-(546-549)] which was recognized in three different strains of mice (H-2b, H-2d and H-2k). A comparison with X-ray analysis of the C-terminal region of HIV-1 reverse transcriptase indicated exposed positions of these Th and B cell epitopes. Both the presence of T and B cell sites and its limited polymorphism make the region RT-(528-549) a promising candidate for vaccine design. The use of the P3CSS adjuvant/carrier principle as a nontoxic adjuvant may be of major importance in the development of vaccines applicable to humans.

Adjuvants, Immunologic↗
PubMed1995

Deficient antigen presentation by thymic epithelial cells reveals differential induction of T cell clone effector functions by CD28-mediated costimulation.

Thymic epithelial cells participate in tolerance induction by deleting or inducing anergy of autoreactive lymphocytes. To explore this process in vitro, the antigen-presenting function of thymic epithelial cell lines was evaluated using a panel of T hybridoma and cloned cells displaying the same antigenic specificity. These mouse thymic epithelial cell lines could process different exogenous antigens and stimulate T hybridoma cells but only induced a partial activation of helper cloned T cells. This state of incomplete activation was characterized by the inability to produce IL-2 and IFN-gamma upon antigenic stimulation, whereas T cell IL-2R alpha expression and cytolytic potential were optimally induced. Thymic epithelial cells failed to express CD28 ligands detected by a CTLA-4/Ig probe even after induction by IFN-gamma. Optimal cloned T cell activation was only observed in the presence of LPS blasts or exogenous IL-2. Costimulation with anti-CD28 mAb was found to restore IFN-gamma but not IL-2 production. Thus, T cell activation by thymic epithelial cell lines provides a useful model to further dissect the requirements for costimulatory molecules, which, in addition to CD28, are required for optimal T cell activation.

Animals↗
PubMed1994

Structure of the mouse dipeptidyl peptidase IV (CD26) gene.

Dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5) is an ectopeptidase whose expression is modulated during thymocyte differentiation and T cell activation. We describe here the organization of the mouse DPP IV gene. This gene, which encompasses more than 90 kb, is composed of 26 exons separated by introns, the lengths of which vary from 100 bp to more than 20 kb. Reverse PCR performed on RNA from different tissues indicated that DPP IV transcripts do not contain alternatively spliced CDS sequences and, therefore, are supposed to yield a single polypeptide. However, two types of specific mRNA have been detected that differ in their 3'UTR sequences. They derive from alternative polyadenylation of the DPP IV primary transcript, since the different 3'UTR sequences are contiguous in the mouse DPP IV gene. Sequence analysis of the gene 5'-flanking region revealed several structural features found in the TATAA-box-less promoters, including a G+C-rich segment, a high frequency of dinucleotide CpG, and an imperfect symmetrical dyad. The DPP IV gene was assigned by in situ hybridization to the mouse [2C2-2D] region, which is syntenic with human chromosome 2. These data indicate that the human Dpp4 locus is located within this synteny region (i.e., 2q14-q37). The genomic organization of the mouse DPP IV gene is compared to that of classical serine proteases and serine hydrolases. As structural and mechanistic conservation in the absence of sequence similarity is the most remarkable feature among alpha/beta hydrolases [Ollis, D. L., et al. (1992) Protein Eng. 5, 197-211], we report the possible evolutionary link between the DPP IV related family and alpha/beta hydrolases.

Alternative Splicing↗
PubMed1994

Thy-1 triggers mouse thymocyte apoptosis through a bcl-2-resistant mechanism.

Programmed cell death plays an important role during thymocyte development, since a vast majority (97%) of mouse cortical thymocytes die in thymus, whereas only 3% of these cells are rescued from cell death and positively selected. Although it seems well established that thymocyte fate depends upon appropriate surface-expressed T cell receptor, little is known about the molecular mechanism(s) responsible for the massive thymocyte elimination that occurs in the thymus. We report here that Thy-1 is capable of triggering mouse thymocyte death in vitro through a bcl-2-resistant mechanism. We have previously shown that Thy-1 is involved in mouse thymocyte adhesion to thymic stroma through interaction with an epithelial cell ligand. To examine the Thy-1 signaling function in thymocytes, we have mimicked its interaction with stromal cells by culturing mouse thymocytes onto tissue culture plates coated with monoclonal antibodies (mAb) directed at distinct Thy-1 epitope regions. mAb recognizing determinants in a defined Thy-1 structural domain, but not others, were found to induce marked thymocyte apoptosis as evidenced by morphological and biochemical data. Use of a quantitative DNA dot blot assay indicated that Thy-1-mediated thymocyte apoptosis was not blocked by RNA or protein synthesis inhibitors, EGTA, or by cyclosporin A, and differed, therefore, from "activation-driven cell death". Moreover, Thy-1(+)-transfected, but not wild-type AKR1 (Thy-1-d) thymoma cells underwent apoptosis after ligation with apoptosis-inducing, Thy-1-specific mAb. In contrast to thymocytes, the latter event was inhibitable by RNA and protein synthesis inhibitors, an indication that thymocytes, but not thymoma cells, contain the molecular components necessary for Thy-1-driven apoptosis. We further showed that Thy-1-triggered thymocyte death is a developmentally regulated process operative in fetal thymocytes from day 17 of gestation, but not in peripheral T cells. Indeed, the target of apoptosis by anti-Thy-1 was found to reside mainly within the CD4+8+3- and CD4+8+3lo double positive immature thymocyte subsets. Finally, it is of major interest that Thy-1-mediated apoptosis, which was found to be readily detectable in thymocytes from bcl-2-transgenic mice, represents a thus far unique experimental system for studying bcl-2-resistant thymocyte death mechanism(s).

Animals↗
PubMed1994

Human immunodeficiency virus-1 reverse transcriptase immunodominant CD4+ T cell epitopes: a peptide-based multiparametric assessment in the mouse.

We previously identified an immunodominant CD4+ T cell determinant in the carboxy-terminal region of HIV-1 reverse transcriptase (RT528-543). The present study aimed at enumerating all the potential sites of HIV-1 RT recognized by Th cells in the BALB/c (H-2d) mouse model. To achieve this we used a panel of 62 overlapping 15-mer synthetic peptides covering the whole RT sequence to assay the following parameters: (i) immunogenicity in naive BALB/c mice injected either with peptides pools or individual peptides; (ii) antigenicity, as detected by their ability to restimulate in vitro T cells from BALB/c mice primed with native RT; (iii) MHC class II (Ad)-binding capacity as measured by the inhibition of the antigen-specific, Ad-restricted presentation of unfolded apamin (4-Acm) by fixed antigen-presenting cells to Ad/4-Acm-specific, interleukin-2-producing T hybridoma cells; and (iv) the presence of typical or degenerate consensus Ad-binding motifs. The results in this study permitted identification of three novel immunodominant RT mouse CD4+ T cell sites (RT276-290, RT375-389 and RT411-425) located in regions of limited polymorphism among RT from several HIV isolates. Some of these RT segments were found to be in the vicinity of B cell or H-2Kk- or HLA-A2-restricted cytotoxic T lymphocyte epitopes. Finally, the approach used in this study was found to be very efficient for enumerating most T cell recognition sites in a complex protein, a result that would have not been achieved by a single parameter-based analysis.

Amino Acid Sequence↗
PubMed1994

Thy-1 functions as a recognition/signaling molecule during mouse T lymphocyte development.

Thy-1 is a prototype of mammalian glycosyl phosphatidylinositol (GPI)-anchored molecules and belongs to the Ig superfamily. This cell surface glycoprotein is expressed on mouse T lymphocytes, neurons and hematopoietic stem cells. Despite detailed structural studies, little is known about the physiological role(s) of Thy-1. We discuss here our results on the role of Thy-1 in immature T lymphocytes during intrathymic maturation. It was observed that Thy-1-mediated adhesion of mouse thymocytes to thymic stromal cells occurs through interaction with an unknown ligand. The interaction occurs by a Ca(2+)-independent mechanism and does not require TCR/CD3 surface expression. To evaluate the signal transduction upon Thy-1 ligation in immature thymocytes, we cultured mouse thymocytes with monoclonal antibodies specific for Thy-1, immobilized onto the tissue culture plates. Monoclonal antibodies directed at determinants located in a defined epitope domain, but not others, triggered marked physiological cell death (apoptosis) of immature thymocytes, as evidenced by morphological and biochemical data. This apoptosis is independent of the cell surface expression of TCR/CD3. It is a developmentally regulated process since the period in which thymocytes are sensitive to Thy-1-dependent apoptosis corresponds to the developmental "window" during which massive death of immature thymocytes takes place within the thymus. Therefore, we propose that Thy-1 could function as a cell survival/death regulator in mouse T lymphocyte development.

Animals↗
PubMed1993

Identification of serine 624, aspartic acid 702, and histidine 734 as the catalytic triad residues of mouse dipeptidyl-peptidase IV (CD26). A member of a novel family of nonclassical serine hydrolases.

Dipeptidyl-peptidase IV (DPP IV, CD26, EC 3.4.14.5), a multifunctional ectoenzyme, is involved not only in the proteolytic cleavage of X-Pro from the NH2 terminus of a variety of biologically active peptides, but also in activation signal transduction and cell matrix adherence processes. We recently characterized mouse DPP IV cDNA and identified the serine protease Gly-X-Ser-X-Gly consensus motif in its extracellular domain. Mouse DPP IV does not exhibit sequence similarity with any of the classical members of this enzyme family (e.g. chymotrypsin and subtilisin) but shares a conserved structural domain of approximately 200 amino acids with several nonclassical serine hydrolases. In this study, analysis of the similarity of secondary structures and amino acid sequences between these enzymes led us to identify several conserved residues likely to be involved in the catalytic site of these DPP IV-related enzymes. These amino acids (Ser624, Asp702, and His734) were found to be arranged in a novel sequential order as compared with that of archetypal serine proteases (e.g. nucleophile (Ser)-acid-His versus His-acid-nucleophile (Ser), respectively). To directly explore the involvement of these residues in the catalytic function of these enzymes, we performed in vitro site-directed mutagenesis on mouse DPP IV cDNA. Our results indicate that although conservative or non-conservative permutations at these positions do not significantly alter the surface expression and biochemical properties of the mutant molecules, they completely impair their DPP IV enzymatic function. In contrast, mutagenesis of two other aspartic residues (Asp599 and Asp657), also conserved between these DPP IV-related enzymes, did not affect the enzymatic properties of the mouse enzyme. These data provide evidence that DPP IV and its related enzymes belong to a novel family that displays a catalytic triad distinct from that of the classical serine proteases.

Amino Acid Sequence↗
PubMed1992

Sulfated glycans directly interact with mouse Thy-1 and negatively regulate Thy-1-mediated adhesion of thymocytes to thymic epithelial cells.

Thy-1 is a major brain cell surface glycoprotein of adult mammal species also expressed in rodent thymus. Despite extensive studies, the function(s) of this molecule has remained so far ill defined. We have recently shown that Thy-1 was involved in the adhesion of mouse thymocytes to thymic epithelium through a specific interaction with a heterophilic ligand(s) expressed on the epithelial cell surface. In the present study, we aimed at evaluating the interaction of sulfated glycans with mouse Thy-1, as well as its consequence on Thy-1-mediated thymic lympho-epithelial cell interaction. It was shown that 125I-labeled Thy-1 directly bound to immobilized heparin. Sulfated glycans such as pentosan sulfate, dextran sulfate, and fucoidan were found to strongly inhibit the binding of Thy-1 to heparin. In contrast, chondroitin sulfate, keratan sulfate, and heparan sulfate were not inhibitory. Sulfated glycans (e.g., pentosan sulfate, assayed at a concentration of 50 micrograms/ml) completely blocked the Thy-1-dependent adhesion of T cells to a mouse thymic epithelial cell monolayer. To explore the mechanism of this inhibition, we compared the ability of T cell to adhere to mouse thymic epithelial cell monolayer or to sulfated glycans. Our results suggest that sulfated glycans bind to a Thy-1 site distinct from that with which this molecule interacts with its heterophilic ligand. Moreover, sulfate glycans could modulate the binding of rat mAb directed at spatially distinct Thy-1 epitopes. The present results identified a potential mechanism regulating Thy-1-mediated lympho-epithelial cell adhesion.

Animals↗
PubMed1992

cDNA cloning for mouse thymocyte-activating molecule. A multifunctional ecto-dipeptidyl peptidase IV (CD26) included in a subgroup of serine proteases.

Thymocyte-activating molecule (THAM) was initially characterized as a developmentally regulated, dimeric cell-surface molecule capable of activating mouse thymocytes and T lymphocytes upon monoclonal antibody (mAb)-mediated cross-linking. We recently obtained structural evidence indicating that this molecule is the mouse homologue of the human T cell-activating ectoenzyme CD26 (dipeptidyl peptidase IV, DPP IV). We describe here the cloning and the characterization of THAM cDNA. Two clones (3.3 and 2.8 kilobases) were isolated. THAM-3.3 cDNA contains an open reading frame of 2,280 nucleotides that encodes a protein of 760 amino acids having a calculated size of 87,500 Da. Complete N-glycosylation at each of the nine potential sites would result in a mature 110,000-Da molecule. Protein sequence comparisons revealed a significant homology (in particular in the COOH-terminal domain) between THAM and the rat or human DPP IV or the yeast dipeptidyl aminopeptidase B molecules (92, 85, and 30% sequence identity, respectively). Structural comparison of serine proteases (i.e. acyl-amino acid hydrolase or prolyl endopeptidase) with the most conserved domain of THAM identified a stretch of 200 amino acids containing a putative catalytic triad arranged in a novel topological order (Ser-624, Asp-702, and His-734) thereby defining a subfamily of nonclassical serine proteases. Expression of THAM during thymus ontogeny was found to be mainly regulated at the transcriptional level as determined by RNase protection assay. To investigate directly some of the functions which have been ascribed to DPP IV, we transfected an ovalbumin/Aq-reactive, THAM- T hybridoma cell line with THAM-3.3 cDNA. The resultant transfectants acquired (i) DPP IV enzymatic activity that precisely paralleled the density of surface-expressed THAM; (ii) an Mr = 115,000 (reduced) and 110,000/128,000 (nonreduced) molecule that could be immunoprecipitated by the THAM-specific mAb H194-112; and (iii) the capacity of being triggered by this mAb to release interleukin-2. These data indicate that a single cDNA species can encode a multifunctional molecule (e.g. activation signal-transducing structure and ectopeptidase), the heterodimeric state of which very likely results from a differential post-translational modification of the same protein core.

Amino Acid Sequence↗
PubMed1992

Isolation and characterization of a novel glycosyl-phosphatidylinositol-anchored glycoconjugate expressed by developing neurons.

In search of new markers for studying thymic and nervous system ontogeny, we raised rat monoclonal antibodies against glycosyl-phosphatidylinositol-anchored molecules among which larger groupings have been shown to be ectoenzymes and adhesion molecules. Two of these monoclonal antibodies (H193-4 and H194-563, IgG) were found to recognize glycosyl-phosphatidylinositol-anchored glycoconjugates of 28-33 kDa (P31) and 50-70 kDa in developing mouse brain and thymus respectively, when these tissues were analysed by immunoblot experiments. P31 antigen was found to be transiently expressed by neurons in neural primary cultures [Rougon, G., Alterman, L., Dennis, K., Guo, X. J. & Kinnon, K. (1991) Eur. J. Immunol. 21, 1397-1402]. We show in this report that, in developing mouse brain, a maximal expression occurred between embryonic day 17 and post-natal day 5, a period that corresponds to the formation of neuronal networks. P31 antigen was immunopurified and found to possess the following properties: (a) it was soluble in alkaline solvents; (b) it bound to DEAE-cellulose and was eluted by a salt gradient of 0-1 M NaCl; (c) it was sensitive to endoglycosidase F digestion; (d) it was insensitive to heparinase, hyaluronidase, chondroitinase ABC, endo-beta-galactosidase and sialidase treatment; (e) it was labile to mild acid hydrolysis without loss of immunoreactivity; (f) it contained phosphate; (g) it lost its immunoreactivity after treatment with phosphatidylinositol phospholipase C and treatment. These characteristics combine to suggest that P31 is an anionic glycoconjugate sharing similarities with Leishmania donovani lipophosphoglycan and with the heat-stable antigen recognized by J11d antibody on murine hematopoïetic cells. This last hypothesis was further confirmed by the observation that oligonucleotide probes derived from the heat-stable antigen-encoding cDNA detect, in developing brain, a 1.8-kb mRNA species similar in size to that reported for the heat-stable antigen mRNA and following the same developmental expression as P31 antigen.

Animals↗
PubMed1991

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

We previously described a developmentally regulated, Mr 115,000 (reduced) and 110,000/128,000 (nonreduced) mouse T cell-activating molecule (THAM) also expressed on a variety of epithelial cell surfaces, and associated with neutral exoaminopeptidase activity. In the present study, we show that THAM is the mouse counterpart of the human T cell-activating ectoenzyme CD26 (dipeptidyl peptidase IV, DPP IV) and that highly purified THAM lacks neutral exoaminopeptidase activity. This conclusion is based on the following: 1) the N-terminal segments of the THAM Mr 110,000 and 128,000 components shared the same amino acid sequence with the rat DPP IV. These N-termini comprised a short intracytoplasmic tail of six residues followed by a downstream hydrophobic transmembrane segment. 2) THAM-specific mAb H194-112-Affi-Gel immunoadsorbent was capable of removing DPP IV enzymatic activity from mouse thymoma cell detergent extracts. 3) H194-112 reactivity pattern on developing thymocytes was found to parallel that previously reported for membrane-bound DPP IV enzymatic activity. The extent of THAM N-glycosylation, as measured by N-glycanase treatment of H194-112 immunoprecipitates, was found to be similar to that of human and rat DPP IV (i.e., approximately 20 kDa). Cross-linking experiments indicated that THAM was expressed at the cell surface as a dimer of approximately 220 kDa. Its two subunits were found to be structurally related but not identical as shown by their different Mr under nonreducing conditions and by their slightly distinct peptide profiles after proteolytic cleavage. We conclude from these data that DPP IV, in addition to its extracellular matrix receptor and ectoenzymatic functions, is a T cell-activating structure in both human and mouse species.

Amino Acid Sequence↗
PubMed1991

Thy-1 supports adhesion of mouse thymocytes to thymic epithelial cells through a Ca2(+)-independent mechanism.

The aim of this study was to explore whether Thy-1, like other members of the Ig-like superfamily (e.g., CD2 and neural cell adhesion molecule), participates in cell-cell adhesion. This was investigated by measuring the binding of Thy-1+ probe cells (thymocytes or AKR1 T lymphoma cells) to Thy-1- cloned mouse thymic epithelial (MTE) cells using a quantitative cell adhesion assay. The results were as follows: (a) the thymo-epithelial cell interaction was found to be inhibitable (by 25-40%) by soluble Thy-1 molecules purified from phosphatidylinositol-specific phospholipase C-treated mouse thymocytes as well as by Fab' fragments of a Thy-1-specific mAb; (b) the binding of the Thy-1- AKR1 (Thy-1-d) mutant to MTE cells was found to be reduced (by 50%) as compared with that of the wild type T lymphoma; (c) the Thy-1-mediated adhesion pathway did not require Ca2+ and promoted the initial thymo-epithelial binding measured at 4 degrees C. These data provide the first direct evidence of an adhesive function of Thy-1 and suggest that this molecule, in addition to its T cell triggering properties, might play a role during the early T cell maturation by promoting thymocyte adhesion to thymic stroma.

Animals↗
PubMed1991

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

The predicted amino acid sequence of the cDNA encoding the murine B-lymphocyte differentiation antigen BP-1/6C3 suggested that it is a member of the zinc-dependent metalloprotease family, possibly an aminopeptidase related to aminopeptidase N [microsomal aminopeptidase; alpha-aminoacyl-peptide hydrolase (microsomal), EC 3.4.11.2]. In the present studies, we examined the enzymatic activity of this antigen. From brush border preparations of the small intestine, a rich source of many endopeptidases and exopeptidases, the BP-1 antibody selectively removed aminopeptidase A [APA; L-alpha-aspartyl(L-alpha-glutamyl)-peptide hydrolase, EC 3.4.11.7] activity. The APA activity of a panel of cell lines correlated in linear fashion with cell-surface levels of the BP-1/6C3 antigen. APA activity was demonstrated for the BP-1/6C3 antigen immunopurified from the pre-B-cell membrane. This activity was enhanced by alkaline earth metals such as Ca2+ and was abrogated by amastatin and angiotensin, which are known competitive inhibitors of APA. The data indicate that the murine BP-1/6C3 antigen is active APA, an enzyme that catalyzes specifically the removal of unsubstituted, N-terminal glutamic acid and aspartic acid residues from peptides.

Aminopeptidases↗