Mouse CD94 participates in Qa-1-mediated self recognition by NK cells and delivers inhibitory signals independent of Ly-49

Inhibitory receptors expressed on NK cells recognize MHC class I molecules and transduce negative signals to prevent the lysis of healthy autologous cells. The lectin-like CD94/NKG2 heterodimer has been studied extensively as a human inhibitory receptor. In contrast, in mice, another lectin-like receptor, Ly-49, was the only known inhibitory receptor until the recent discovery of CD94/NKG2 homologues in mice. Here we describe the expression and function of mouse CD94 analyzed by a newly established mAb. CD94 was detected on essentially all NK and NK T cells as well as small fractions of T cells in all mouse strains tested. Two distinct populations were identified among NK and NK T cells, CD94(bright) and CD94(dull) cells, independent of Ly-49 expression. The anti-CD94 mAb completely abrogated the inhibition of target killing mediated by NK recognition of Qa-1/Qdm peptide on target cells. Importantly, CD94(bright) but not CD94(dull) cells were found to be functional in the Qa-1/Qdm-mediated inhibition. In the presence of the mAb, activated NK cells showed substantial cytotoxicity against autologous target cells as well as enhanced cytotoxicity against allogeneic and "missing self" target cells. These results suggest that mouse CD94 participates in the protection of self cells from NK cytotoxicity through the Qa-1 recognition, independent of inhibitory receptors for classical MHC class I such as Ly-49.

CD44 binds a chondroitin sulfate proteoglycan, aggrecan

Here we report that CD44 binds a chondroitin sulfate (CS) proteoglycan, aggrecan, a major component of cartilage. Soluble CD44-IgG and CD44(+) cells bound to aggrecan from rat chondrosarcoma and bovine cartilage, immobilized on microtiter plates. In both cases, binding was blocked by a neutralizing anti-CD44 mAb or by the pretreatment of aggrecan with chondroitinase, but not hyaluronidase or keratanase, indicating that CD44 binds aggrecan in a manner dependent on CS side chains of aggrecan and that hyaluronic acid is not involved in the binding. Structural analysis showed that glycosaminoglycans of aggrecan from rat chondrosarcoma and bovine articular cartilage consist of mainly CS A and a mixture of CS A and C respectively. When immobilized on microtiter plates, both CS A and C bound CD44-IgG, and the reaction was specifically inhibited by an anti-CD44 mAb. In addition, aggrecan augmented apoptosis in cells expressing CD44-Fas chimeric molecules in synergy with a non-blocking anti-CD44 mAb IRAWB14.4, suggesting that CD44-aggrecan interaction can induce oligomerization of the chimeric molecules. These results suggest that aggrecan interacts with CD44 to mediate cell adhesion and to trigger oligomerization of CD44 molecules, which may lead to intracellular signaling.

Myopathy phenotype of transgenic mice expressing active site-mutated inactive p94 skeletal muscle-specific calpain, the gene product responsible for limb girdle muscular dystrophy type 2A

A defect of the gene for p94 (calpain 3), a skeletal muscle-specific calpain, is responsible for limb girdle muscular dystrophy type 2A (LGMD2A), or 'calpainopathy', which is an autosomal recessive and progressive neuromuscular disorder. To study the relationships between the physiological functions of p94 and the etiology of LGMD2A, we created transgenic mice that express an inactive mutant of p94, in which the active site Cys129 is replaced by Ser (p94:C129S). Three lines of transgenic mice expressing p94:C129S mRNA at various levels showed significantly decreased grip strength. Sections of soleus and extensor digitorum longus (EDL) muscles of the aged transgenic mice showed increased numbers of lobulated and split fibers, respectively, which are often observed in limb girdle muscular dystrophy muscles. Centrally placed nuclei were also frequently found in the EDL muscle of the transgenic mice, whereas wild-type mice of the same age had almost none. There was more p94 protein produced in aged transgenic mice muscles and it showed significantly less autolytic degradation activity than that of wild-type mice. Although no necrotic-regenerative fibers were observed, the age and p94:C129S expression dependence of the phenotypes strongly suggest that accumulation of p94:C129S protein causes these myopathy phenotypes. The p94:C129S transgenic mice could provide us with crucial information on the molecular mech-anism of LGMD2A.

Deficiency of a STE20/PAK family kinase LOK leads to the acceleration of LFA-1 clustering and cell adhesion of activated lymphocytes

Lymphocyte-oriented kinase (LOK) is a member of the STE20/p21-activated kinase (PAK) family and expressed predominantly in lymphoid organs. Generation of LOK-deficient mice revealed that the leukocyte-function-associated antigen (LFA-1)/intercellular adhesion molecules (ICAM)-mediated aggregation of mitogen-stimulated T cells was greatly enhanced in the absence of LOK. Though levels of total LFA-1 and ICAMs as well as the active form of LFA-1 on T cell blasts were comparable in the presence and absence of LOK, clustering of active LFA-1 detected by binding of soluble ICAM-1 was accelerated in the absence of LOK. These results suggest that LOK is potentially involved in the regulation of LFA-1-mediated lymphocyte adhesion.

The effect of flow on the neutrophil-mediated Ca2+ responses in human vascular endothelial cells stimulated by endotoxin

Leukocyte-vascular endothelial cell (EC) interactions which promote inflammatory and immune reactions involve bidirectional signaling between two cell types. We investigated the effects of flow on neutrophil-mediated changes in endothelial intracellular Ca2+ levels ([Ca2+]i). Cultured human umbilical vein ECs stimulated by endotoxin were labeled with Fura-2 and exposed to fluid flow with neutrophils. The individual changes in [Ca2+]i were monitored. The application of flow with neutrophils to stimulated ECs led to an increase in [Ca2+]i although either flow without neutrophils or neutrophils without flow rarely induced a rise in [Ca2+]i. Furthermore, flow application with neutrophils to unstimulated ECs also rarely promoted a rise in [Ca2+]i. These findings suggest that the flow might thus induce or enhance the inflammatory process by the induction of Ca2+ signaling in endotoxin-stimulated endothelium facing neutrophils in the blood flow.

Requirements for signal delivery through CD44: analysis using CD44-Fas chimeric proteins

CD44 is a transmembrane glycoprotein involved in various cell adhesion events, including lymphocyte migration, early hemopoiesis, and tumor metastasis. To examine the requirements of CD44 for signal delivery through the extracellular domain, we constructed a chimeric CD44 protein fused to the intracellular domain of Fas on its C-terminus. In cells expressing the CD44-Fas fusion protein, apoptosis could be induced by treatment with certain anti-CD44 mAbs alone, especially those recognizing the epitope group d, which has been previously shown to play a role in ligand binding, indicating that ligation of a specific region of the CD44 extracellular domain results in signal delivery. Of note was that appropriate ligation of the epitope h also resulted in the generation of apoptotic signal, although this region was not thought to be involved in ligand binding. In contrast, the so-called blocking anti-CD44 mAbs (epitope group f) that can abrogate the binding of hyaluronate (HA) failed to induce apoptosis even after further cross-linking with the secondary Ab, indicating that a mere mAb-induced oligomerization of the chimeric proteins is insufficient for signal generation. However, these blocking mAbs were instead capable of inhibiting apoptosis induced by nonblocking mAb (epitope group h). Furthermore, a chimeric protein bearing a mutation in the HA binding domain and hence lacking the ability to recognize HA was incapable of mediating the mAb-induced apoptosis, suggesting that the functional integrity of the HA binding domain is crucial to the signal generation in CD44.

Establishment of antigen-specific IgE transgenic mice to study pathological and immunobiological roles of IgE in vivo

We have established transgenic mice that carry the genes coding for heavy and light chains of TNP-specific IgE. They produced high titers of TNP-specific IgE (20-40 microg/ml in serum) and their mast cells were heavily loaded with IgE. The level of FcepsilonRI expression on their mast cells was 6-8 times higher than that in non-transgenic littermates. The expression of low-affinity IgE receptor FcepsilonRII (CD23) on splenic B cells was also 6-8 times higher in the transgenic mice. Consistent with this, substantial amounts of IgE were detected on B cells in the transgenic mice. When challenged with i.v. administration of the corresponding antigen, the transgenic mice exhibited systemic anaphylactic symptoms such as a drastic drop of body temperature and extravasation of administered dye. Biphasic (immediate and delayed) ear swelling response was also elicited in a TNP-specific manner by epicutaneous antigen challenge without any prior sensitization. Thus, IgE produced in the transgenic mice was found to be biologically active to induce both local and systemic allergic reactions in vivo upon the challenge of the corresponding antigen. Taken together, the antigen-specific IgE transgenic mice established for the first time in this study appear to provide an attractive model system to study the pathological roles of IgE in acute and chronic phases of allergic inflammation as well as their immunobiological roles in vivo. They may also be useful to develop novel therapeutic strategies for atopic disorders.

[Regulatory mechanisms of NK cell functions]

Natural Killer (NK) cells discriminate self from non-self in a manner distinct from T cells. NK cells exhibit cytotoxicity against "missing-self" by killing any cells in principle except normal self-cells. Cells expressing low levels of self MHC class I molecules such as tumor cells and foreign cells are killed, whereas normal self cells are neglected by NK cells. Although identities of activation receptors triggering NK activity are still unclear, recent studies have revealed molecules inhibiting cytotoxicity against normal self cells. In this review, we summarize current understanding of molecular basis for missing-self hypothesis and control mechanisms of NK cell activation.

Flow cytometric diagnosis of the cell lineage and developmental stage of acute lymphoblastic leukemia by novel monoclonal antibodies specific to human pre-B-cell receptor

Three novel monoclonal antibodies (MoAbs) have been established that recognize distinct epitopes of a human pre-B-cell receptor (pre-BCR) composed of a mu heavy (muH) chain and a lambda5/VpreB surrogate light (SL) chain. HSL11 reacts with lambda5 whereas HSL96 reacts with VpreB. Intriguingly, HSL2 does not bind to each component of the pre-BCR but does bind to the completely assembled pre-BCR complex. Flow cytometric analyses with cytoplasmic staining of a panel of human cell lines showed that HSL11 and HSL96 specifically stained cell lines derived from the pro-B and pre-B-cell stages of B-cell development. In contrast, HSL2 stained exclusively cell lines derived from the pre-B-cell stage. These results prompted us to explore the possibility of clinical application of these MoAbs for the determination of the cell lineage and developmental stage of acute lymphoblastic leukemia (ALL). Whereas none of mature B-lineage ALLs (B-ALLs), T-lineage ALLs (T-ALLs), and acute myeloid leukemias analyzed were stained in the cytoplasm with these three MoAbs, the vast majority of non-B- and non-T-ALLs (53 out of 56 cases) were found positive for either lambda5, Vpre-B, or both in their cytoplasm. Among these 53 cytoplasmic SL chain-positive ALLs, 19 cases were also positive for cytoplasmic muH chain, indicative of pre-B-cell origin. Interestingly, 6 out of these 19 pre-B-ALL cases were found negative for cytoplasmic staining with HSL2. From these results, we propose a novel classification of B-ALL in which five subtypes are defined on the basis of the differential expression of SL chain, muH chain, pre-BCR, and light chain along the B-cell development.

FK506 (tacrolimus) inhibits extravasation of lymphoid cells by abrogating VLA-4/VCAM-1 mediated transendothelial migration

Extravasation is a critical process for the physiological lymphocyte traffic as well as the hematogenous spread of malignant hemopoietic cells. Here we report that abrogation of calcineurin activity leads to in vitro transendothelial migration and in vivo infiltration of human lymphoma Nalm-6 cells, which are associated with the abrogation of the VLA-4/VCAM-1 mediated pathway. Rapamycin, which can antagonize FK506 but not CsA to inhibit calcineurin, abrogates FK-506 mediated but not CsA mediated inhibition of in vitro transendothelial migration. FK506 may exert its potent immunosuppressive action partly by inhibiting VLA-4/VCAM-1 mediated transendothelial migration or insinuation of lymphoid cells to tissues.

Intracellular Signal-transducing elements involved in transendothelial migration of lymphoma cells

To investigate the molecular mechanisms underlying transendothelial migration of tumor cells, an essential process for their hematogenous dissemination, we developed an in vitro model system that allows the separate monitoring of cell adhesion and transmigration processes. This system uses a human pre-B lymphoma cell line, Nalm-6, and a cultured mouse endothelial cell line, KOP2.16. Nalm-6 cells rapidly adhered to KOP2.16 and subsequently transmigrated underneath them. Using this model, we examined the effects on transendothelial migration, of various reagents which specifically interfere with the function of intracellular signal transduction molecules. Treatment of Nalm-6 cells with wortmannin (WMN), herbimycin A, pertussis toxin, or C3 exoenzyme of Clostridium botulinum, which specifically inhibit P13 kinase and/or myosin light chain kinase, herbimycin-sensitive tyrosine kinases, heterotrimeric G proteins, and the small G proteins, and the small G proteins rho/rac, respectively, reduced transmigration in a dose-dependent manner, Pretreatment of KOP2.16 endothelial cells with WMN also reduced transmigration in a dose-dependent manner. Binding of Nalm-6 binding to KOp2.16 was not affected, even when Nalm-6 or KOP2.16 cells were pretreated with these inhibitors, indicating that the reduction of transmigration was not due to a reduction of Nalm-6 to KOP2.16. These results also indicate that the signal transduction pathway(s) involved in transmigration can be dissociated from that of adhesion. Our results support the notion that endothelial cells are not a passive barrier in lymphoma extravasation, but that they assist lymphoma cell extravasation.

Widespread expression of chondroitin sulfate-type serglycins with CD44 binding ability in hematopoietic cells

Serglycin is a family of small proteoglycans with Ser-Gly dipeptide repeats and is modified with various types of glycosaminoglycan side chains. We previously demonstrated that chondroitin sulfate-modified serglycin is a novel ligand for CD44 involved in the adherence and activation of lymphoid cells. In this study, we investigated the production and distribution of CD44 binding serglycins in various hematopoietic cells and characterized their carbohydrate side chains. Immunoprecipitation analysis using CD44-IgG and polyclonal antibody against the serglycin core peptide demonstrated that various serglycin species capable of binding CD44 are produced by a variety of hematopoietic cells including lymphoid cells, myeloid cells, and a few tumor cell lines. Glycosaminoglycans on these serglycins, which are essential for CD44 binding, are composed of chondroitin 4-sulfate or a mixture of chondroitin 4-sulfate and chondroitin 6-sulfate, but no heparin or heparan sulfate side chain was detected. The serglycins are also secreted by normal splenocytes, lymph node lymphocytes, and bone marrow cells, whereas they are secreted in very small amounts by normal thymocytes. Secretion of serglycins is greatly enhanced by mitogenic stimulation with concanavalin A or lipopolysaccharide. Our results showed that serglycin, unlike hyaluronate, is produced and secreted in a functional (CD44 binding) form by many members of the hematopoietic system including various lymphocyte subsets. Our data suggest that serglycin may serve as a major ligand for CD44 in various events in the lymphohematopoietic system.

Exposure of phosphatidylethanolamine on the surface of apoptotic cells

In the early stages of apoptosis, phosphatidylserine (PS) is translocated from the inner side of the plasma membrane to the outer layer, which allows phagocytes to recognize and engulf the apoptotic cells. In this study we have analyzed the cell surface exposure of phosphatidylethanolamine (PE) in apoptotic CTLL-2 cells, a cytotoxic T cell line, using a tetracyclic polypeptide of 19 amino acids (Ro09-0198) which specifically recognizes the structure of PE and forms a tight equimolar complex with the phospholipid. Fluorescence microscopic analysis showed that the peptide, conjugated with fluorescence-labeled streptavidin (FL-SA-Ro), bound effectively to the cell surface of cells undergoing apoptosis in response to withdrawal of interleukin-2 from the culture media, but not to nonapoptotic cells. The binding of FL-SA-Ro to apoptotic cells was not uniform and the intense staining was observed on surface blebs of apoptotic cells. The FL-SA-Ro binding was inhibited specifically by liposomes containing PE, suggesting that PE is mainly exposed on the surface blebs of apoptotic cells. The specific binding of FL-SA-Ro to the apoptotic cells was also confirmed using a flourescence-activated cell sorter and the time-dependent cell surface exposure of PE correlated well with the exposure of PS, as detected by the binding of annexin V. This study provides the first direct evidence that PE as well as PS is exposed on the cell surface during the early stages of apoptosis, resulting in the total loss of asymmetric distribution of aminophospholipids in the plasma membrane bilayer.

The expression patterns of standard and variant CD44 molecules in normal uterine cervix and cervical cancer

CD44 is a cell-surface glycoprotein postulated to play a role in tumor-cell metastasis. We have examined the expression of the standard CD44 (CD44s), and alternative spliced variants of CD44 containing variant exons v6, v9, and v1O (CD44v6, CD44v9, and CD44v10 respectively) in 9 samples of normal cervix, 6 samples of cervical intraepithelial neoplasia (CIN), and 11 samples with invasive cervical carcinomas. RT/PCR demonstrated the presence of CD44s in all samples of normal cervix and those with invasive carcinomas. CD44v6 was also found in all normal cervical samples and in 9 tissue samples of invasive carcinomas. The results also suggested that some tumor specimens had several higher molecular transcripts containing exon v6 compared to specimens of normal cervix. Immunohistochemistry detected the presence of CD44s and the absence of CD44v10 in both epithelial and stromal cells in all specimens. In contrast, CD44v6 and CD44v9 were stained positive in epithelial cells but were absent in stromal cells. The intensity of CD44v6 and CD44v9 staining was strongest in normal cervical epithelium followed by CIN, invasive squamous cell carcinoma, and adenocarcinoma. In the malignant samples, heterogeneity in staining intensity among different clusters of tumor cells was observed. Furthermore, poorly differentiated and undifferentiated carcinomas from patients having poor prognosis did not stain at all. This study suggests that variant CD44 molecules may serve an important function in the cell contact of cervical epithelial cells, and that cervical epithelium acquires heterogeneity in the expression of CD44 adhesion molecules during carcinogenesis, which may be related to tumor metastasis.

A novel ligand for CD44 is serglycin, a hematopoietic cell lineage-specific proteoglycan. Possible involvement in lymphoid cell adherence and activation

The lymphocyte adhesion molecule CD44 recognizes a non-hyaluronate proteoglycan, gp600, secreted by mouse T cell line CTLL2. We now demonstrate that gp600 is identical to serglycin, a member of the small proteoglycan family stored in intracellular secretory granules of lymphoid, myeloid, and some tumor cells. Purified gp600 has the ability to bind specifically to CD44, and the binding is dependent on activation of CD44. The CD44-binding elements on gp600 or serglycin are glycosaminoglycans consisting of chondroitin 4-sulfate. Serglycin is readily exocytosed, and its interaction with active form CD44 augments the CD3-dependent degranulation of CD44 positive CTL clones. We conclude that the serglycin secreted from secretory granules of hematopoietic cells is a novel ligand for CD44, and could regulate lymphoid cell adherence and activation.

Down-regulation of vascular adhesion molecule-1 by fluid shear stress in cultured mouse endothelial cells

This study was undertaken to determine whether blood flow modulates the adhesive property of vascular endothelial cells to lymphocytes and, if it does, what adhesion molecules are involved. Cultured mouse endothelial cells were exposed to medium flow in a parallel plate chamber, and binding assay using fluorescence-labeled lymphocytes was carried out. The adhesion rate of endothelial cells to lymphocytes, which was high in the static control state, decreased when exposed to shear stress (1.5 dynes/cm2) for 6 h. The treatment of static endothelial cells with a monoclonal antibody of vascular cell adhesion molecule-1 (VCAM-1) depressed the adhesion rate to the same extent as that caused by flow, while monoclonal antibodies of CD44 and intercellular adhesion molecule-1 had no effect on it. Flow cytometric analysis revealed that the application of flow decreased markedly the amount of VCAM-1 expressed on the cell surface. A reverse transcriptase-polymerase chain reaction of mRNA showed that flow depressed VCAM-1 mRNA levels. These results suggest that blood flow can modulate the adhesive property of endothelial cells to lymphocytes via affecting the surface expression of adhesion molecules, e.g., down-regulation of VCAM-1.

A sulfated proteoglycan as a novel ligand for CD44

We have identified a novel ligand for CD44, a cell surface glycoprotein implicated in tumor metastasis and lymphocyte homing. When the mouse T cell line CTLL-2 was transfected with cDNA encoding a hemopoietic form of mouse CD44, CTLL-2 cells exhibited a new self-adhesive phenotype, forming large aggregates. The aggregation was blocked by neutralizing anti CD44 monoclonal antibody but unaffected by hyaluronidase, indicating the involvement of CD44 and its non-hyaluronate ligand in the cell aggregation. The ability to induce CD44-dependent aggregation was found in culture supernatants of CTLL-2 and its CD44 transfectants. The use of CD44-immunoglobulin chimeric protein revealed that CTLL-2 and its transfectants synthesized a large-molecular weight protein (gp600) which bound specifically to CD44. The gp600 was readily labeled with radioactive sulfate, and treatment of gp600 with chondroitinase ABC or ACII generated a lower molecular weight species (18-22 kDa), suggesting that gp600 consists of a small core protein with chondroitin sulfate glycosaminoglycan side chains. However, binding of CD44 to glycosaminoglycans such as chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate was undetectable, suggesting either that a novel chondroitin-type glycosaminoglycan is recognized by CD44 or that a particular configuration of the glycosaminoglycan is required for recognition by CD44.

A crucial effect of ligand clustering on the inhibition of binding by L-selectin in intercellular adhesion

Glucan sulfates were found to be potent ligands for L-selectin by a quantitative liquid phase analysis system (Yoshida, T. et al., Eur. J. Biochem., in press). The affinity of glucan sulfates to L-selectin-IgG chimera was dependent on the size of the glucan sulfates as well as on the inter-glucose linkages. In the current report, these glucan sulfates are shown to inhibit the interaction of an endothelial cell line with lymphocytes. The effect of ligand size appears to be more remarkable in the cell-cell binding than in the liquid phase analysis. The affinity of amylose sulfate continues to increase, as their size increases even beyond 12 kDa, at which its affinity reached a plateaux in the liquid phase analysis.

Shear stress inhibits adhesion of cultured mouse endothelial cells to lymphocytes by downregulating VCAM-1 expression

Monolayers of endothelial cells (EC) cultured from mouse lymph nodes were exposed to controlled levels of shear stress (0-7.1 dyn/cm2) in a parallel plate flow chamber, and binding between the flow-loaded EC and mouse lymph node-derived lymphocytes was assayed. A large number of lymphocytes adhered to the stationary control EC, but in EC exposed to a shear stress of 1.5 dyn/cm2 for 6 h, the adhesion decreased to 68.8 +/- 12.8% (SD; n = 19) of control (n = 29, P < 0.001). The decrease in adhesion induced by flow loading was time and shear stress dependent and reversible. Treatment of stationary EC with a monoclonal antibody (MAb) to vascular cell adhesion molecule-1 (VCAM-1) reduced the adhesion to 70.6 +/- 11.5% (n = 19) of control (P < 0.001), whereas MAb to CD44 and to intercellular adhesion molecule-1 had no effect on it. Flow cytometric analysis revealed that the amount of VCAM-1 expressed on the cell surface was decreased to 48.5 +/- 15.8% (n = 6) of control by flow loading (P < 0.001). Flow loading experiments using two perfusates with different viscosities demonstrated that the decrease in VCAM-1 expression due to flow was shear stress rather than shear rate dependent. The detection of mRNA by reverse transcriptase-polymerase chain reaction showed that VCAM-1 mRNA levels were markedly depressed in EC exposed to flow loading.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel ligand for CD44 is sulfated proteoglycan

We report herein identification of a novel ligand for CD44, a cell surface glycoprotein implicated in tumor metastasis, lymphocyte differentiation and homing. A mouse T cell line CTLL-2 transfected with cDNA encoding a hemopoietic form of mouse CD44 exhibited a new self-adhesive phenotype, forming large aggregates. The aggregation was blocked by anti-CD44 mAb but little affected by hyaluronidase, indicating the involvement of CD44 and its non-hyaluronate ligand in the cell aggregation. The ability to induce CD44-dependent aggregation was observed in culture supernatants of CTLL-2 and its CD44 transfectants. Immunoprecipitation analysis using a CD44-Ig chimeric molecule indicated that CTLL-2 and its transfectants synthesized a macromolecule (gp600) which bound specifically to CD44. gp600 was readily labeled with radioactive sulfate and treatment of gp600 with chondroitinase ABC or AC II generated a lower molecular weight species (18-22 kDa), suggesting that gp600 consists of a small core protein heavily modified with chondroitin sulfate glycosaminoglycan side chains. However, when binding of CD44 was tested in vitro to chondroitinase-sensitive purified glycosaminoglycans, such as chondroitin-4-sulfate, chondroitin-6-sulfate and dermatan sulfate, no binding was demonstrable, suggesting either that a novel type of chondroitinase-sensitive glycosaminoglycan is recognized by CD44 or that association of the glycosaminoglycan with a core protein is required for recognition by CD44.

The effect of flow on the expression of vascular adhesion molecule-1 by cultured mouse endothelial cells

Adherence of leukocytes to vascular endothelial cells (ECs) is known to be sensitive both to blood flow and adhesive proteins on EC surface. To elucidate the effect of blood flow on the surface expression of adhesive proteins, cultured ECs derived from mouse lymph nodes were exposed to different levels of wall shear stress in a flow-loading chamber, and changes in the expression of vascular adhesion molecule-1 (VCAM-1) and CD44 were evaluated by immunostaining with monoclonal antibodies and flow cytometry. Both proteins were expressed on non-activated cultured ECs. When exposed to flow with shear stress of 1.5 dynes/cm2 for 24 hr, VCAM-1 nearly disappeared on fluorescence micrographs, while CD44 showed no change. Flow cytometric analysis showed that the mean channel fluorescence of VCAM-1 was decreased about 75% by application of flow for 24 hr (p < 0.001), but that of CD44 remained unchanged. VCAM-1 expression began to decrease around 1 hr after the initiation of flow and became markedly reduced with time, reaching a minimum after 24 hr. When the cells subjected to flow for 24 hr were returned to stationary state, the reduced VCAM-1 expression was almost completely restored in 72 hr, indicating that the change was reversible. The magnitude of the reduction of VCAM-1 expression was also dependent on the intensity of the wall shear stress applied, ranging from 0 to 7.2 dynes/cm2. These results, demonstrating an explicit down-regulating effect of flow on VCAM-1 expression of cultured ECs, suggested preferential adhesion of leukocytes to ECs at low shear regions at the vascular wall.

Muscle-specific calpain, p94, is degraded by autolysis immediately after translation, resulting in disappearance from muscle

We previously identified a third type of the calpain large subunit named p94 as a cDNA whose mRNA is expressed exclusively in skeletal muscle at levels approximately 10-fold more abundant than those of the conventional calpain subunit. Rat skeletal muscle fractions were screened by two anti-peptide antibodies raised against two specific sequences in p94, but the p94 protein could not be found. To examine this apparent discrepancy between the amounts of mRNA and protein, wild-type p94 was expressed in COS cells. Although p94 mRNA was expressed normally in COS cells, only very small amounts of the protein and its presumed degradation products were detected by the antibodies described above. A series of COOH-terminal deletion mutants was constructed and expressed in COS cells and L8 cells, a rat myoblast cell line. When IS2, one of the specific regions of p94, was completely eliminated, the truncated p94 proteins were expressed normally, and the amount of the expressed proteins was at least 100-fold higher than with wild-type p94. Moreover, when site-directed mutagenesis was introduced to change the presumed active-site cysteine of p94 to serine or alanine, the mutated p94 proteins were highly expressed like the IS2-deleted mutants. These results indicate the following. 1) The mRNA for p94 is normally transcribed in COS, L8, and muscle cells; 2) the p94 protein becomes active in the cytosol immediately after translation; 3) the p94 protein virtually disappears from cells by autocatalytic degradation; and 4) the p94-specific IS2 region plays an important role in this degradation. In vitro translation experiments support this idea. Furthermore, p94 shows nuclear localization when expressed in COS cells. The physiological function of p94 in muscle is discussed on the basis of the analysis of these transfectants.

Activation of CD44 induces ICAM-1/LFA-1-independent, Ca2+, Mg(2+)-independent adhesion pathway in lymphocyte-endothelial cell interaction

We have established an endothelial cell line KOP2.16 from pooled mouse lymph nodes. Resting lymphocytes avidly bound to KOP2.16 and migrated underneath the cytoplasm. The binding was partly mediated by VLA-4 and VCAM-1, but apparently independent of CD44 since anti-CD44 antibody examined failed to inhibit the binding. However, pretreatment of lymphocytes with anti-CD44 resulted in the rapid appearance of Ca(2+)-, Mg(2+)-independent, LFA-1/ICAM-1-, CD2/LFA-3, VLA-4/VCAM-1-independent lymphocyte binding, indicating that a novel adhesion pathway was induced by the anti-CD44 treatment. Interestingly, the elicited adhesion was observed only when anti-CD44 that block hyaluronate recognition of CD44 were used for lymphocyte pretreatment. Neither hyaluronate itself nor non-blocking anti-CD44 up-regulated the adhesion. Fab fragment of the blocking anti-CD44 did not induce the up-regulation unless cross-linked with a second antibody, indicating that cross-linking of surface CD44 is necessary for induction of a novel adhesion pathway. We propose that the agonistic anti-CD44 antibodies induce a novel adhesion pathway by mimicking ligand binding to CD44 on the lymphocyte surface and that non-hyaluronate ligand(s) is involved in regulation of adhesive function of CD44. Potential involvement of such a regulatory mechanism in lymphocyte homing is discussed.

[Tumor metastasis and adhesion molecules]

Effective prevention of tumor metastasis would be a great contribution to the therapy of malignant tumors. Recent progress in the research of adhesion molecules has revealed that cell adhesion is an essential process in tumor metastasis. In this study, we discuss the possible involvement of adhesion molecules in various steps of tumor metastasis.

Reconstitution of the intermediate-affinity interleukin-2 receptor by cell fusion

Although IL-2 receptor beta chain (IL-2R beta) expressed in various lymphoid cell lines binds IL-2 with an intermediate affinity, IL-2R beta expressed in fibroblasts is unable to bind IL-2, suggesting that IL-2R beta is on its own not sufficient for generating the intermediate-affinity receptor and that lymphoid-specific regulatory control may be operated to allow IL-2R beta to bind IL-2. In the present study, we observed that human IL-2R beta expressed in a mouse myeloma X63-Ag8.653 (X63) by cDNA transfection did not bind IL-2, while the same IL-2R beta expressed in an IL-6-dependent mouse B cell hybridoma F12-28, which was obtained by cell fusion between X63 and lipopolysaccharide (LPS)-induced lymphoblasts, bound IL-2 with the intermediate affinity. Interestingly, when the human IL-2R beta cDNA-transfected X63 clone, which by itself manifests no IL-2 binding, was fused with LPS-induced lymphoblasts, the resultant hybridomas manifested intermediate-affinity IL-2 binding. The IL-2 binding was specifically inhibited by addition of antihuman IL-2R beta mAb (Mik-beta 1) but not by mAb against mouse IL-2R subunits, indicating that human IL-2R beta was responsible for the IL-2 binding, i.e. non-functional human IL-2R beta in X63 was converted to competent IL-2R beta by complementation with a mouse spleen cell-derived factor(s) through the cell fusion. Cross-linking experiments with [125I]IL-2 revealed the presence of a 61 kDa protein other than IL-2R beta in cells expressing the intermediate-affinity IL-2R.(ABSTRACT TRUNCATED AT 250 WORDS)