Joëlle Wiels

Targeted Disruption of Gb3/CD77 Synthase Gene Resulted in the Complete Deletion of Globo-series Glycosphingolipids and Loss of Sensitivity to Verotoxins

To examine whether globotriaosylceramide (Gb3/CD77) is a receptor for verotoxins (VTs) in vivo, sensitivity of Gb3/CD77 synthase null mutant mice to VT-2 and VT-1 was analyzed. Although wild-type mice died after administration of 0.02 μg of VT-2 or 1.0 μg of VT-1, the mutant mice showed no reaction to doses as much as 100 times that administered to wild types. Expression analysis of Gb3/CD77 in mouse tissues with antibody revealed that low, but definite, levels of Gb3/CD77 were expressed in the microvascular endothelial cells of the brain cortex and pia mater and in renal tubular capillaries. Corresponding to the Gb3/CD77 expression, tissue damage with edema, congestion, and cytopathic changes was observed, indicating that Gb3/CD77 (and its derivatives) exclusively function as a receptor for VTs in vivo. The lethal kinetics were similar regardless of lipopolysaccharide elimination in VT preparation, suggesting that basal Gb3/CD77 levels are sufficient for lethal effects of VTs.

Overexpression of MDM2, due to enhanced translation, results in inactivation of wild-type p53 in Burkitt's lymphoma cells

Numerous studies have indicated that inactivation of p53 is one of the essential requirements for the unrestrained growth of tumoral cells. When the status of the p53 gene was examined in various types of lymphoid malignancies, mutations in p53 have been predominantly detected in Burkitts lymphoma (BL) cells, therefore suggesting that alteration of p53 could specifically contribute to the malignant phenotype of these tumoral cells. In addition to mutations, functional inactivation of p53 can also occur through interaction of the wild-type gene product with various viral or cellular proteins. The cellular MDM2 protein, for example, is able to inhibit p53 tumor suppressor function by concealing its transactivation domain. Mdm2 gene amplification has been described in several types of sarcomas, resulting in overexpression of the MDM2 protein. In this study, we have examined the status of MDM2 and p53 in 20 BL cell lines. Four were found to contain wild-type p53 and to overexpress MDM2 protein. Within these BL cells, both molecules are physically associated since they can be co-precipitated and p53 is inactivated as cells neither arrest in G1 nor enter apoptosis following γ-radiation. We also report that the high level of the MDM2 protein in BL cells is neither associated with an amplification of the mdm2 gene nor with an elevated level of RNA or an increased protein stability, but is rather due to an enhanced translation ability of the mdm2 RNA. These results indicate that in certain BL cells, overexpression of MDM2 protein regulated at the posttranscriptional level, induces an escape from p53-controlled cell growth.

Structural Basis of the Preferential Binding for Globo-Series Glycosphingolipids Displayed by Pseudomonas aeruginosa Lectin I

The opportunistic pathogen Pseudomonas aeruginosa contains several carbohydrate-binding proteins, among which is the P. aeruginosa lectin I (PA-IL), which displays affinity for alpha-galactosylated glycans. Glycan arrays were screened and demonstrated stronger binding of PA-IL toward alphaGal1-4betaGal-terminating structures and weaker binding to alphaGal1-3betaGal ones in order to determine which human glycoconjugates could play a role in the carbohydrate-mediated adhesion of the bacteria. This was confirmed in vivo by testing the binding of the lectin to Burkitt lymphoma cells that present large amounts of globotriaosylceramide antigen Gb3/CD77/P(k). Trisaccharide moieties of Gb3 (alphaGal1-4betaGal1-4Glc) and isoglobotriaosylceramide (alphaGal1-3betaGal1-4Glc) were tested by titration microcalorimetry, and both displayed similar affinity to PA-IL in solution. The crystal structure of PA-IL complexed to alphaGal1-3betaGal1-4Glc trisaccharide has been solved at 1.9-A resolution and revealed how the second galactose residue makes specific contacts with the protein surface. Molecular modeling studies were performed in order to compare the binding mode of PA-IL toward alphaGal1-3Gal with that toward alphaGal1-4Gal. Docking studies demonstrated that alphaGal1-4Gal creates another network of contacts for achieving a very similar affinity, and 10-ns molecular dynamics in explicit water allowed for analyzing the flexibility of each disaccharide ligand in the protein binding site. The higher affinity observed for binding to Gb3 epitope, both in vivo and on glycan array, is likely related to the presentation effect of the oligosaccharide on a surface, since only the Gb3 glycosphingolipid geometry is fully compatible with parallel insertion of neighboring trisaccharide heads in two binding sites of the same tetramer of PA-IL.

NATURAL KILLER CELL ACTIVITY IN HUMAN BONE MARROW RECIPIENTS EARLY REAPPEARANCE OF PERIPHERAL NATURAL KILLER ACTIVITY IN GRAFT-VERSUS-HOST DISEASE

Natural killer (NK) cell activity toward K562 target cells and antibody-dependent cell-mediated cytotoxicity (ADCC) toward L1210 cells sensitized with anti-L1210 antisera were sequentially tested in peripheral blood lymphocytes (PBLs) from 24 human bone marrow (BM) recipients. Although consistently decreased before the transplant, NK cell activity was restored in all of the patients tested that argues for a bone marrow origin of NK progenitors in humans. In patients without graft-versus-host disease (GVHD), peripheral NK cell activity remained low during the 1st month after the transplant, then rapidly increased and reached normal values usually between days 30 and 50. By contrast, peripheral ADCC appeared earlier restored (since day 13), suggesting that NK and ADCC are two distinct effector mechanisms. When restored, peripheral NK cell activity remained within normal range, except in seven cases with a drastic fall in NK cell values contemporary with a severe viral infection, mainly with cytomegalovirus (CMV). NK cells are thus suggested to play an important role in the control of viral infections in these deeply immunodepressed patients. In patients with acute GVHD, strikingly high NK values were observed early after the transplant, and during the 1st month a strong correlation did exist between high NK values and acute GVHD occurrence. These results suggest that cells involved in GVHD mechanism are able to exert NK cell activity at some stages of their maturation. The assessment of NK cell activity could be an attractive routine procedure for monitoring the prophylaxis of GVHD in human BM recipients.

Induction of HLA expression in Daudi cells after cell fusion

The Daudi cell line, established from a Burkitt lymphoma, has recently been found to be HLA- andΒ2-microglobulin-negative, although it expresses B lymphocyte alloantigens. This report is concerned with the reexpression of HLA-A10, B38, and B17 on the Daudi cell, after cell fusion with another human cell line (Raji) or with mouse fibroblasts. In the latter fusion, the same HLA specificities are re-expressed, but not humanΒ2-microglobulin while mouseΒ2-microglobulin andH-2 could be detected. No such reexpression was observed when Daudi was fused with the F9 mouse teratocarcinoma, which lacks mouseΒ2-m andH-2. No HLA activity (alloantigenic and xenogenic activity) was detected in the membrane or cytoplasm of Daudi, using salt extraction and sonication. Therefore we postulate thatΒ2-microglobulin could be necessary for the expression and possible synthesis of the HLA antigen.

High Resolution Genome-Wide Analysis of Chromosomal Alterations in Burkitt's Lymphoma

Additional chromosomal abnormalities are currently detected in Burkitts lymphoma. They play major roles in the progression of BL and in prognosis. The genes involved remain elusive. A whole-genome oligonucleotide array CGH analysis correlated with karyotype and FISH was performed in a set of 27 Burkitts lymphoma-derived cell lines and primary tumors. More than half of the 145 CNAs<2 Mb were mapped to Mendelian CNVs, including GSTT1, glutathione s-transferase and BIRC6, an anti-apoptotic protein, possibly predisposing to some cancers. Somatic cell line-specific CNVs localized to the IG locus were consistently observed with the 244 K aCGH platform. Among 136 CNAs >2 Mb, gains were found in 1q (12/27), 13q (7/27), 7q (6/27), 8q(4/27), 2p (3/27), 11q (2/27) and 15q (2/27). Losses were found in 3p (5/27), 4p (4/27), 4q (4/27), 9p (4/27), 13q (4/27), 6p (3/27), 17p (3/27), 6q (2/27),11pterp13 (2/27) and 14q12q21.3 (2/27). Twenty one minimal critical regions (MCR), (range 0.04–71.36 Mb), were delineated in tumors and cell lines. Three MCRs were localized to 1q. The proximal one was mapped to 1q21.1q25.2 with a 6.3 Mb amplicon (1q21.1q21.3) harboring BCA2 and PIAS3. In the other 2 MCRs, 1q32.1 and 1q44, MDM4 and AKT3 appeared as possible drivers of these gains respectively. The 13q31.3q32.1 <89.58–96.81> MCR contained an amplicon and ABCC4 might be the driver of this amplicon. The 40 Kb 2p16.1 <60.96–61> MCR was the smallest gained MCR and specifically encompassed the REL oncogene which is already implicated in B cell lymphomas. The most frequently deleted MCR was 3p14.1 <60.43–60.53> that removed the fifth exon of FHIT. Further investigations which combined gene expression and functional studies are essential to understand the lymphomagenesis mechanism and for the development of more effective, targeted therapeutic strategies.

The Blood Group P1 Synthase Gene Is Identical to the Gb3/CD77 Synthase Gene A CLUE TO THE SOLUTION OF THE P1/P2/p PUZZLE

Blood group P1/P2 is a glycolipid antigen system for which the genetic mechanism has not yet been clarified. We analyzed the potential of the cloned Gb3/CD77 synthase to synthesize P1 antigen, because Gb3/CD77 and P1 share a common structure, Galα1,4Galβ1,4Glc (NAc)–. L cell transfectants with Gb3/CD77 synthase cDNA expressed marginal levels of P1 on the cell surface but contained high levels of P1 in the cytoplasm. P2-type erythrocytes, which were serotyped as P2, also contained definite P1 antigen inside cells, although the amounts were lower than those of P1 cells. Only p erythrocytes lacked P1 antigen corresponding with function-losing mutations in the Gb3/CD77 synthase gene. Synthesis of P1 antigen from paragloboside in vitro was demonstrated using membrane fraction of the transfectants and a fusion enzyme with protein A. These results strongly suggested that P1 synthase is identical to Gb3/CD77 synthase and appear to propose a clue for the solution of the long-pending P1/P2/p puzzle. The P1/P2 difference might result from the difference in P1 quantity based on either different enzyme activity or the presence/absence of other enzyme modulators. Because P2 erythrocytes showed lower levels of Gb3/CD77 synthase mRNA than P1, 5′-upstream promoter regions were analyzed, resulting in the identification of two P2-specific homozygous mutations. Differences in the transcriptional regulation in erythrocytes might be a major factor determining P1/P2.

Evidence of LMP1–TRAF3 interactions in glycosphingolipid-rich complexes of lymphoblastoid and nasopharyngeal carcinoma cells

Latent membrane protein 1 (LMP1) is an Epstein‐Barr virus (EBV) protein expressed in EBV‐transformed B lymphocytes and in approximately 50% of nasopharyngeal carcinomas (NPCs). LMP1 signaling involves several cellular signaling intermediates, especially TNF receptor–associated factors (TRAFs). We have shown previously that LMP1 is highly concentrated in a cell fraction called glycosphingolipid‐rich membrane complexes (GSL complexes). We report here that parallel accumulation of LMP1 and TRAF3, but not TRAF1 or TRADD, was observed in GSL complexes from lymphoblastoid and LMP1‐positive NPC cells. In contrast, TRAF3 was not concentrated in GSL complexes from LMP1‐negative cells. Binding of LMP1 and TRAF3 in GSL complexes was demonstrated in lymphoblastoid and NPC cells, by co‐immunoprecipitation with both anti‐LMP1 and anti‐TRAF3 antibodies. Int. J. Cancer 81:645–649, 1999.

Expression of the Gb3/CD77 synthase gene in megakaryoblastic leukemia cells: implication in the sensitivity to verotoxins

Expression levels of Gb3/CD77 synthase together with Gb3/CD77 antigen were analyzed using human hematopoietic tumor cell lines and normal cells. Among about 40 kinds of cells, Burkitt lymphoma cells showed the highest gene expression concomitant with the expression levels of Gb3/CD77. Unexpectedly, megakaryoblastic leukemia lines also expressed fairly high levels of mRNA of Gb3/CD77 synthase and its product. A megakaryoblastic leukemia line, MEG-01 was sensitive to verotoxins from Escherichia coli O157 and apoptosis was induced via the caspase pathway. We also demonstrated that the cell surface Gb3/CD77 expression was reduced on differentiated MEG-01 although the mRNA level of the α1,4Gal-T gene increased. In this case, the localization of Gb3/CD77 was changed from the cell surface to the cytoplasm as stained with a granular pattern, co-localizing with platelet GPIIb-IIIa, indicating that some of them were platelet precursors. Small particles outside of cells also showed similar staining patterns. These results agreed with the previous report that platelets produced in mature megakaryoblasts abundantly contained Gb3/CD77 antigen. Here, we propose the possibility that verotoxins bind immature megakaryoblasts and induce their apoptosis, leading to the arrest of platelet generation in the bone marrow. This may be one of the causes of thrombocytopenia in patients with hemolytic uremic syndrome.

Truncated Form of the Epstein-Barr Virus Protein EBNA-LP Protects against Caspase-Dependent Apoptosis by Inhibiting Protein Phosphatase 2A

ABSTRACT The Epstein-Barr virus (EBV)-encoded leader protein, EBNA-LP, strongly activates the EBNA2-mediated transcriptional activation of cellular and viral genes and is therefore important for EBV-induced B-cell transformation. However, a truncated form of EBNA-LP is produced in cells infected with variant EBV strains lacking EBNA2 due to a genetic deletion. The function of this truncated form is unknown. We show here that some Burkitts lymphoma cells harboring defective EBV strains are specifically resistant to the caspase-dependent apoptosis induced by verotoxin 1 (VT-1) or staurosporine. These cells produced low-molecular-weight Y1Y2-truncated isoforms of EBNA-LP, which were partly localized in the cytoplasm. The transfection of sensitive cells with constructs encoding truncated EBNA-LP isoforms, but not full-length EBNA-LP, induced resistance to caspase-mediated apoptosis. Furthermore, VT-1 induced protein phosphatase 2A (PP2A) activation in sensitive cells but not in resistant cells, in which the truncated EBNA-LP interacted with this protein. Thus, the resistance to apoptosis observed in cells harboring defective EBV strains most probably results from the inactivation of PP2A via interactions with low-molecular-weight Y1Y2-truncated EBNA-LP isoforms.