CD63, a member of tetraspan transmembrane protein family, induces cellular spreading by reaction with monoclonal antibody on substrata

Exosomal CD63 in critically ill patients with sepsis

CD63 is one of the tetraspanin protein family members that is ubiquitously expressed on exosomes and is involved in the signal transduction of various types of immune cells. It may thus contribute to immunometabolic mechanisms of cellular and organ dysfunction in sepsis. Nonetheless, the association of exosomal CD63 with the severity and mortality of sepsis is not well known. Therefore, in the present study, the overall levels of exosomal CD63 were evaluated to ascertain whether they were associated with organ failure and mortality in patients with sepsis. Exosomal CD63 was measured from prospectively enrolled critically-ill patients with sepsis (n = 217) and healthy control (n = 20). To detect and quantify exosomes in plasma, a commercially available enzyme-linked immunosorbent assay kit was used according to the manufacturer's protocol. The total number of exosomal CD63 was determined by quantifying the immunoreactive CD63. The association between plasma levels of exosomal CD63 and sequential organ failure assessment (SOFA) score was assessed by a linear regression method. The best cut-off level of exosomal CD63 for 28-day mortality prediction was determined by Youden's index. Among 217 patients with sepsis, 143 (66%) patients were diagnosed with septic shock. Trends of increased exosomal CD63 levels were observed in control, sepsis, and septic-shock groups (6.6 µg/mL vs. 42 µg/mL vs. 90 µg/mL, p < 0.001). A positive correlation between exosomal CD63 and SOFA scores was observed in patients with sepsis (r value = 0.35). When patients were divided into two groups according to the best cut-off level, the group with higher exosomal CD63 levels (more than 126 µg/mL) was significantly associated with 28-day and in-hospital mortality. Moreover, the Kaplan-Meier survival method showed a significant difference in 90-day survival between patients with high- and low-exosomal CD63 levels (log-rank p = 0.005). Elevated levels of exosomal CD63 were associated with the severity of organ failure and predictive of mortality in critically ill patients with sepsis.

Tetraspanin-8 promotes hepatocellular carcinoma metastasis by increasing ADAM12m expression

Recent evidence indicates that tetraspanin-8 (TSPAN8) promotes tumor progression and metastasis. In this study, we explored the effects of TSPAN8 and the molecular mechanisms underlying hepatocellular carcinoma (HCC) metastasis using various HCC cell lines, tissues from 149 HCC patients, and animal models of HCC progression. We showed that elevated expression of TSPAN8 promoted HCC invasion in vitro and metastasis in vivo, but did not influence HCC cell proliferation in vitro. Increased TSPAN8 expression in human HCC was predictive of poor survival, and multivariate analyses indicated TSPAN8 expression to be an independent predictor for both postoperative overall survival and relapse-free survival. Importantly, TSPAN8 enhanced HCC invasion and metastasis by increasing ADAM12m expression. We therefore conclude that TSPAN8 and ADAM12m may be useful therapeutic targets for the prevention of HCC progression and metastasis.

Molecular cloning, sequence characterization and expression analysis of a CD63 homologue from the coleopteran beetle, Tenebrio molitor

CD63, a member of the tetraspanin membrane protein family, plays a pivotal role in cell growth, motility, signal transduction, host-pathogen interactions and cancer. In this work, the cDNA encoding CD63 homologue (TmCD63) was cloned from larvae of a coleopteran beetle, Tenebrio molitor. The cDNA is comprised of an open reading frame of 705 bp, encoding putative protein of 235 amino acid residues. In silico analysis shows that the protein has four putative transmembrane domains and one large extracellular loop. The characteristic “Cys-Cys-Gly” motif and “Cys188” residues are highly conserved in the large extracellular loop. Phylogenetic analysis of TmCD63 revealed that they belong to the insect cluster with 50%–56% identity. Analysis of spatial expression patterns demonstrated that TmCD63 mRNA is mainly expressed in gut and Malphigian tubules of larvae and the testis of the adult. Developmental expression patterns of CD63 mRNA showed that TmCD63 transcripts are detected in late larval, pupal and adult stages. Interestingly, TmCD63 transcripts are upregulated to the maximum level of 4.5 fold, in response to DAP-type peptidoglycan during the first 6 h, although other immune elicitors also caused significant increase to the transcript level at later time-points. These results suggest that CD63 might contribute to T. molitor immune response against various microbial pathogens.

Tetraspanin CD63 promotes vascular endothelial growth factor receptor 2-β1 integrin complex formation, thereby regulating activation and downstream signaling in endothelial cells in vitro and in vivo

CD63 is a member of the transmembrane-4 glycoprotein superfamily (tetraspanins) implicated in the regulation of membrane protein trafficking, leukocyte recruitment, and adhesion processes. We have investigated the involvement of CD63 in endothelial cell (EC) signaling downstream of β1 integrin and VEGF. We report that silencing of CD63 in primary ECs arrested capillary sprouting and tube formation in vitro because of impaired adhesion and migration of ECs. Mechanistically, CD63 associated with both β1 integrin and the main VEGF receptor on ECs, VEGFR2. Our data suggest that CD63 serves to bridge between β1 integrin and VEGFR2 because CD63 silencing disrupted VEGFR2-β1 integrin complex formation identified using proximity ligation assays. Signaling downstream of β1 integrin and VEGFR2 was attenuated in CD63-silenced cells, although their cell surface expression levels remained unaffected. CD63 was furthermore required for efficient internalization of VEGFR2 in response to VEGF. Importantly, systemic delivery of VEGF failed to potently induce VEGFR2 phosphorylation and downstream signaling in CD63-deficient mouse lungs. Taken together, our findings demonstrate a previously unrecognized role for CD63 in coordinated integrin and receptor tyrosine kinase signaling in vitro and in vivo.

Tetraspanin CO-029 inhibits colorectal cancer cell movement by deregulating cell-matrix and cell-cell adhesions

Alterations in tetraspanin CO-029 expression are associated with the progression and metastasis of cancers in the digestive system. However, how CO-029 promotes cancer metastasis is still poorly understood. To determine the mechanism, we silenced CO-029 expression in HT29 colon cancer cells and found that the CO-029 knockdown significantly reduced cell migratory ability. The diminished cell migration was accompanied by the upregulation of both integrin-dependent cell-matrix adhesion on laminin and calcium-dependent cell-cell adhesion. The cell surface levels of laminin-binding integrin α3β1 and fibronectin-integrin α5β1 were increased while the level of CD44 was decreased upon CO-029 silencing. These changes contribute to the altered cell-matrix adhesion. The deregulated cell-cell adhesion results, at least partially, from increased activity of cadherins and reduced level of MelCAM. In conclusion, CO-029 functions as a regulator of both cell-matrix and cell-cell adhesion. During colon cancer progression, CO-029 promotes cancer cell movement by deregulating cell adhesions.

Promoter hypermethylation of tetraspanin members contributes to their silencing in myeloma cell lines

Multiple myeloma (MM) cell interactions with their microenvironment modulate acquired drug resistance and disease progression. Indeed, reported aberrant gene methylation underscores the possible role of epigenetic events in MM's molecular profile. Membranal tetraspanins are often inversely correlated with cancer prognosis and metastasis, however mutations were unidentified hitherto. Their promoter characteristics and frequent down-regulation conform to transcriptional silencing by chromatin remodeling. We delineated the baseline expression of select tetraspanins in MM cell lines (RPMI 8226, U266, ARP1, ARK, CAG and EBV transformed ARH77) and fresh bone marrow samples (n = 9) for the first time and determined reduced expression of CD9, CD81 and absence of CD82. Thus, we aimed to assess their promoter methylation status. Indeed, we established CD9, CD81 and CD82 promoter methylation in MM cell lines employing methyl-specific-PCR of bisulfite modified G-DNA and PCR of G-DNA digested with methylation-sensitive restriction enzyme (Hin6I). Re-transcription of assayed genes in the cell lines following de-methylation [5-aza-2'-deoxycytidine (5-aza-dC)] confirmed the mechanistic significance of methylation to their regulation. Combined de-methylation and de-acetylation [Trichostatin A (TsA)] induced synergistic elevation of CD82 mRNA. We conclude that chromatin remodeling contributes to tetraspanin silencing in MM.

CD63 as an activation-linked T cell costimulatory element

Dendritic cells (DC) are unique in their capacity to either stimulate or regulate T cells, and receptor/ligand pairs on DC and T cells are critically involved in this process. In this study we present such a molecule, which was discovered by us when analyzing the functional effects of an anti-DC mAb. This mAb, 11C9, reacted strongly with DC, but only minimally with lymphocytes. In MLR it constantly reduced DC-induced T cell activation. Therefore, we assumed that mAb 11C9 primarily exerts its functions by binding to a DC-structure. This does not seem to be the case, however. Preincubation of DC with mAb 11C9 before adding T cells had no inhibitory effect on T cell responses. Retroviral expression cloning identified the 11C9 Ag as CD63. This lysosomal-associated membrane protein (LAMP-3), is only minimally expressed on resting T cells but can, as we show, quickly shift to the surface upon stimulation. Cross-linkage of that structure together with TCR-triggering induces strong T cell activation. CD63 on T cells thus represents an alternative target for mAb 11C9 with its binding to activated T cells rather than DC being responsible for the observed functional effects. This efficient CD63-mediated costimulation of T cells is characterized by pronounced induction of proliferation, strong IL-2 production and compared with CD28 enhanced T cell responsiveness to restimulation. Particularly in this latter quality CD63 clearly surpasses several other CD28-independent costimulatory pathways previously described. CD63 thus represents an activation-induced reinforcing element, whose triggering promotes sustained and efficient T cell activation and expansion.

LAMP-1 and LAMP-2, but not LAMP-3, are reliable markers for activation-induced secretion of human mast cells

BACKGROUND

Mast cells are resident tissue cells that induce anaphylactic reactions by rapidly releasing mediators after antigen-mediated cross-linking of immunoglobulin E receptors. In the similarly active peripheral blood basophilic leukocyte, lysosome-associated membrane protein 3 (LAMP-3; CD63) has been described as an activation marker, but LAMPs have not been investigated in normal tissue mast cells.

METHODS

Intra- and extracellular expressions of LAMP-1 (CD107a), LAMP-2 (CD107b), and LAMP-3 (CD63) were analysed by flow cytometry, immunocytochemistry, and functional assays in unstimulated and stimulated leukemic human mast cell line 1 (HMC-1) and skin mast cells.

RESULTS

On flow cytometry, all mast cells expressed LAMP-3 at their cell membranes, whereas LAMP-1 and LAMP-2 were barely detectable (HMC-1 cells) or expressed at low levels (<10% of skin mast cells). After fixation and permeabilisation, high intracellular levels of all three LAMPs were noted in both cell types. After stimulation, a rapid translocation of intracellular LAMPs to the cell membrane, with an associated release of histamine, leukotriene C(4) and prostaglandin D(2), was ascertained in skin mast cells only.

CONCLUSION

These results show that LAMP-1 and LAMP-2 are activation markers for normal mast cells. The lack of LAMP translocation after activation of leukemic mast cells may be related to maturation or malignancy-associated defects of these cells.

Expression of tetraspanins in peripheral blood leukocytes: a comparison between normal and infectious conditions

The role of tetraspanins is undefined, despite their detection in diverse cell types and functions. This study addresses the characterization of tetraspanin expression levels in normal peripheral blood leukocytes (PBL) and in patients with bacterial infection. Membranal and cytoplasmic expression of CD9, CD53, CD63, CD81, CD82 and CD151 in polymorphonuclears (PMN), monocytes, B and T lymphocytes was assessed using flow cytometry. Results suggested that for normal PBL, PMN are distinguished by dominant cytoplasmic CD63; monocytes and B cells prevailingly express CD53; CD82 is primarily expressed on T-cell membranes. However, a major trend of downregulation was demonstrated for the examined tetraspanins, except CD63, in all patients' PBL subtypes. Therefore, tetraspanin modulation in infections may be attributed to elevated leukocyte motility in immune reactions and this is compatible with the previous publications of tetraspanins as metastasis suppressors. This work represents the first comprehensive baseline of tetraspanin expression in normal PBL and in infectious disorders.

Novel approaches to gene expression analysis of active polyarticular juvenile rheumatoid arthritis

Juvenile rheumatoid arthritis (JRA) has a complex, poorly characterized pathophysiology. Modeling of transcriptosome behavior in pathologic specimens using microarrays allows molecular dissection of complex autoimmune diseases. However, conventional analyses rely on identifying statistically significant differences in gene expression distributions between patients and controls. Since the principal aspects of disease pathophysiology vary significantly among patients, these analyses are biased. Genes with highly variable expression, those most likely to regulate and affect pathologic processes, are excluded from selection, as their distribution among healthy and affected individuals may overlap significantly. Here we describe a novel method for analyzing microarray data that assesses statistically significant changes in gene behavior at the population level. This method was applied to expression profiles of peripheral blood leukocytes from a group of children with polyarticular JRA and healthy control subjects. Results from this method are compared with those from a conventional analysis of differential gene expression and shown to identify discrete subsets of functionally related genes relevant to disease pathophysiology. These results reveal the complex action of the innate and adaptive immune responses in patients and specifically underscore the role of IFN-γ in disease pathophysiology. Discriminant function analysis of data from a cohort of patients treated with conventional therapy identified additional subsets of functionally related genes; the results may predict treatment outcomes. While data from only 9 patients and 12 healthy controls was used, this preliminary investigation of the inflammatory genomics of JRA illustrates the significant potential of utilizing complementary sets of bioinformatics tools to maximize the clinical relevance of microarray data from patients with autoimmune disease, even in small cohorts.

Overexpression of tetraspanin CO-029 in hepatocellular carcinoma

BACKGROUND/AIMS

The molecules involved in the progression of hepatocellular carcinoma (HCC) are not fully understood. The aim of this study was to elucidate the crucial genes involved in cancer progression and metastasis.

METHODS

Selectively expressed genes were screened using differential display analysis, and then further analyzed by real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry.

RESULTS

Tetraspanin CO-029 was found to be frequently and significantly overexpressed in HCC. Real-time quantitative RT-PCR showed that the CO-029 mRNA level was 1.7 times higher (P=0.030) in cancerous tissues than in non-cancerous tissues. mRNA expression of the other tetraspanins, CD9 and CD82, was downregulated in HCC, especially in tumors with intrahepatic spreading (portal vein invasion and/or intrahepatic metastasis). In contrast, mRNA expression of CO-029 tended to be increased in cancerous tissue showing intrahepatic spreading compared with tumors without such spreading. Immunohistochemical analysis revealed that CO-029 was overexpressed in poorly differentiated HCCs compared with well to moderately differentiated tumors (P<0.001), and in HCCs showing intrahepatic spreading compared with those without spreading (P=0.019).

CONCLUSIONS

Our findings suggest that CO-029 has some roles in the promotion of metastasis of HCC.

Allergen-induced basophil activation: CD63 cell expression detected by flow cytometry in patients allergic to Dermatophagoides pteronyssinus and Lolium perenne

BACKGROUND

In this study, we determined by flow cytometry the percentage of basophils activated after in vitro stimulation by allergens and expressing the CD63 marker. The diagnostic reliability of the technique was assessed as well as its correlation with other in vitro diagnostic parameters.

METHODS

Fifty-three patients suffering from asthma and/or allergic rhinitis following sensitization to Dermatophagoides pteronyssinus and 51 patients sensitized to Lolium perenne were investigated. Twenty-four atopic patients not sensitive to these allergens and 38 healthy subjects were also selected as controls. The basophil activation test determines the percentage of basophils which express CD63 as an activation marker, by means of flow cytometry, after in vitro stimulation with allergen, using double labelling with monoclonal antibody anti-CD63-PE and anti-IgE-FITC.

RESULTS

No differences in basal values (non-activated control) were found between sensitized patients, atopic controls and healthy controls. On the other hand, sensitized patients showed a significantly higher percentage of activated basophils after stimulation by allergens in vitro than both control groups (P < 0.001). We found a significant correlation between skin tests and basophil activation tests (r = 0.72, P < 0.001). We also found a positive and significant correlation between basophil activation tests and histamine release tests (r = 0.80, P < 0.001), allergen-specific sulphidoleukotriene production (r = 0.7, P < 0.001) and the occurrence of serum allergen-specific IgE (r = 0.71, P < 0.001).

CONCLUSION

The basophil activation test is a highly reliable technique in the diagnosis of allergy to inhalant allergens. The sensitivity of the basophil activation test was 93.3%, and its specificity 98.4%, when using a cut-off point of 15% activated basophils as positive result.

Chronic urticaria serum induces histamine release, leukotriene production, and basophil CD63 surface expression--inhibitory effects ofanti-inflammatory drugs

BACKGROUND

A role of potential histamine-releasing autoantibodies against the high-affinity IgE receptor on the surface of basophils and mast cells is discussed in the pathogenesis of chronic urticaria. This so-called autoimmune urticaria may be diagnosed by a positive intracutaneous autologous serum skin test, which is found in about 30% of patients with chronic urticaria.

OBJECTIVE

Our purpose was, first, to compare the effect of complement-inactivated sera of 20 patients with chronic urticaria and positive autologous serum skin tests, 20 patients with chronic urticaria and negative skin tests, and 20 control subjects without chronic urticaria (10 atopic and 10 nonatopic subjects) and, second, to analyze the effect of anti-inflammatory drugs on the serum activity.

METHODS

The following assay systems were used: release of histamine in whole blood samples, surface expression of the activation marker CD63 on basophils, and sulfidoleukotriene de novo production in leukocyte suspensions. Whole blood, basophils, and leukocyte suspensions were obtained from a nonatopic and an atopic donor.

RESULTS

Sera of patients with autologous serum skin test positive chronic urticaria resulted not only in significantly increased histamine release compared with skin test-negative chronic urticaria sera but also in a significant higher induction of basophil CD63 surface expression and sulfidoleukotriene de novo production. However, serum activity was neither characteristic for chronic urticaria nor for chronic urticaria with a positive autologous serum skin test. Preincubation with dapsone, chloroquine, and lidocaine dose dependently resulted in a significant reduction of all histamine release, CD63 expression, and sulfidoleukotriene production. In addition, mizolastine was able to inhibit serum-induced sulfidoleukotriene production.

CONCLUSION

Further studies investigating the in vivo effect of these drugs will have to clarify their role in the management of the subset of patients with chronic urticaria demonstrating serum-induced inflammatory effects.

Changes of platelet surface antigens in patients suffering from abdominal septic shock

Sepsis and related syndromes account for a high morbidity and mortality caused by the development of multiorgan failure. Pathogenesis of sepsis is complex, involving humoral as well as cellular factors. Since the role of platelets is still undefined in this concern, we investigated CD63, CD62P, CD36, and CD31 expression on platelets of patients in septic shock (n = 18) using a flow cytometric assay in whole blood. Samples were drawn within 24 hours of onset. We found thrombocytopenia accompanied by a significantly higher expression of CD63, CD62P, and CD31 and a significant downregulation of CD36 in comparison to healthy volunteers (n = 18). Changes in CD63 and CD62P expression indicates platelet activation. Because CD62P, CD36, and CD31 mediate interaction of platelets with leukocytes, subendothelial matrix and probably endothelial cells as well as platelet adhesion/aggregation, our findings suggest an involvement of platelets in leukocyte/endothelial cell interaction in septic shock. We suspect that thrombocytopenia is not due to bone marrow depression, but rather is due to consumption of highly activated platelets in the microcirculation. We feel that our observations may offer a rationale for potentially beneficial effects of antiplatelet therapy in sepsis; however, further studies have to evaluate its beneficial impact as well as its potential risk for bleeding complications.

Monoclonal antibody to rat CD63 detects different molecular forms in rat tissue

From mice immunized with rat endothelial cell membranes, we isolated several hybridomas secreting monoclonal antibodies (MAbs) to a 45-kDa glycoprotein expressed on the surface of cultured cells. One of these antibodies, 523-14A, was purified and used for immunoaffinity chromatography, Western blotting, and immunohistochemistry. The glycoprotein containing the antigen for MAb 523-14A, gp45, was isolated from rat lung endothelial cell membranes using wheat germ agglutinin and antibody affinity chromatography sequentially. Mass spectrometry of tryptic peptides from gel purified bands identified gp45 as rat CD63, a member of the transmembrane-4 superfamily. Western blot analyses of tissues from F344 rats showed that kidney, spleen, uterus, and ovaries expressed CD63 at high levels. Thymus, salivary gland, testicles, intestines, pancreas, and adrenals expressed lower amounts. Tissue cell types expressing CD63 were also examined and the results showed that, in addition to the expected expression on lymphoid cells, CD63 was expressed on many epithelial and muscle cells as well. The mobility of CD63 on SDS-PAGE varied widely, indicative of molecular masses ranging from 45 kDa in some tissues to nearly 60 kDa in others.