Regulation of memory B-cell survival by the BH3-only protein Puma.

Apoptosis is crucial for immune system homeostasis, including selection and survival of long-lived antibody-forming cells and memory cells. The interactions between proapoptotic and pro-survival proteins of the Bcl-2 family are critical for this process. In this report, we show that expression of the proapoptotic BH3-only Bcl-2 family member Puma was selectively up-regulated on in vitro activation with antigens or mitogens of both human and mouse B cells.

Caspase-3 triggers a TPCK-sensitive protease pathway leading to degradation of the BH3-only protein puma.

The protein Puma (p53-upregulated modulator of apoptosis) belongs to the BH3-only group of the Bcl-2 family and is a major regulator of apoptosis. Although the transcriptional regulation of Puma is clearly established, little is known about the regulation of its expression at the protein levels. We show here that various signals--including the cytokine TGFβ, the death effector TRAIL or chemical drugs such as anisomycin--downregulate Puma protein levels via a novel pathway based on the sequential activation of caspase-3 and a protease inhibited by the serpase inhibitor N-tosyl-L-phenylalanine chloromethyl ketone.

BimL upregulation induced by BCR cross-linking in BL41 Burkitt's lymphoma results from a splicing mechanism of the BimEL mRNA.

B lymphocyte receptor-mediated apoptosis is associated with increased expression of the BimL isoform of Bim. The mechanisms involved in the regulation of BimL protein expression are still unknown. We report that BimL expression following BCR activation is not associated with a specific increase of BimL mRNA but rather to the intron retention structure of the BimEL mRNA.

TGFbeta-mediated apoptosis of Burkitt's lymphoma BL41 cells is associated with the relocation of mitochondrial BimEL.

In this study, we showed that the transforming growth factor beta (TGFbeta)-mediated apoptosis of Burkitt's lymphoma BL41 cells is dependent on the BH3-only protein Bim. In contrast to what has been observed with other cell types, TGFbeta activation did not promote Bim upregulation in BL41 cells, but instead resulted in Bim release from the mitochondria. Indeed, Bim levels were high in healthy BL41 cells, in which they dimerized with the Bcl-2-like protein Mcl-1 at the mitochondrial surface.

p38 MAPK and MSK1 mediate caspase-8 activation in manganese-induced mitochondria-dependent cell death.

Heavy metals are important regulators of cell apoptosis. Manganese (Mn(2+)) is a potent inducer of apoptosis in different cell types, but the precise mechanisms that mediate such effects are not well defined. We previously reported that Mn(2+) was a potent apoptotic agent in human B cells, including lymphoma B cell lines.

EBV infection of human B lymphocytes leads to down-regulation of Bim expression: relationship to resistance to apoptosis.

EBV infects a large proportion of the human population worldwide and is one of the major viruses with human B lymphocyte tropism. It can immortalize human B lymphocytes and controls their resistance to apoptosis. EBV infection is associated with several lymphomas, including Burkitt's lymphoma.

B cell receptor-mediated apoptosis of human lymphocytes is associated with a new regulatory pathway of Bim isoform expression.

Studies in Bim-deficient mice have shown that the proapoptotic molecule Bim plays a key role in the control of B cell homeostasis and activation. However, the role of Bim in human B lymphocyte apoptosis is unknown. We show in this study that, depending on the degree of cross-linking, B cell receptors can mediate both Bim-dependent and apparent Bim-independent apoptotic pathways.

p38-mediated regulation of an Fas-associated death domain protein-independent pathway leading to caspase-8 activation during TGFbeta-induced apoptosis in human Burkitt lymphoma B cells BL41.

On binding to its receptor, transforming growth factor beta (TGFbeta) induces apoptosis in a variety of cells, including human B lymphocytes. We have previously reported that TGFbeta-mediated apoptosis is caspase-dependent and associated with activation of caspase-3. We show here that caspase-8 inhibitors strongly decrease TGFbeta-mediated apoptosis in BL41 Burkitt's lymphoma cells.

B cell receptor cross-linking triggers a caspase-8-dependent apoptotic pathway that is independent of the death effector domain of Fas-associated death domain protein.

We have previously reported that B cell receptors, depending on the degree to which they are cross-linked, can promote apoptosis in various human B cell types. In this study, we show that B cell receptors can trigger two apoptotic pathways according to cross-linking and that these pathways control mitochondrial activation in human Burkitt's lymphoma cells. Whereas soluble anti-mu Ab triggers caspase-independent mitochondrial activation, cross-linked anti-mu Ab induces an apoptotic response associated with a caspase-dependent loss of mitochondrial transmembrane potential.

Zinc-mediated regulation of caspases activity: dose-dependent inhibition or activation of caspase-3 in the human Burkitt lymphoma B cells (Ramos).

Divalent cations, including Zinc and Manganese ions, are important modulators of cell activation. We investigated the ability of these two divalent cations to modulate apoptosis in human Burkitt lymphoma B cells line (Ramos). We found that Zinc (from 10 to 50 microM) inhibited Manganese-induced caspase-3 activation and apoptosis of Ramos cells.

The expression of p18INK4 and p27kip1 cyclin-dependent kinase inhibitors is regulated differently during human B cell differentiation.

Cell cycle progression is under the control of cyclin-dependent kinases (cdks), the activity of which is dependent on the expression of specific cdk inhibitors. In this paper we report that the two cdk inhibitors, p27(Kip1) and p18(INK4c), are differently expressed and control different steps of human B lymphocyte activation. Resting B cells contain large amounts of p27(Kip1) and no p18(INK4c).

Cdk2 associates with MAP kinase in vivo and its nuclear translocation is dependent on MAP kinase activation in IL-2-dependent Kit 225 T lymphocytes.

Cell proliferation is controlled by cdk2 which in association with cyclin E and A regulates G1/S transition and S phase progression. cdk2 activation is dependent on its localization in the nucleus where regulatory mediators are found. We report that activation of cdk2 is associated with the formation of cdk2/MAP Kinase complexes.

Manganese induces apoptosis of human B cells: caspase-dependent cell death blocked by bcl-2.

Manganese ions block apoptosis of phagocytes induced by various agents. The prevention of apoptosis was attributed to the activation of manganous superoxide dismutase (Mn-SOD) and to the antioxidant function of free Mn2+ cations. However, the effect of Mn2+ on B cell apoptosis is not documented.

Role of caspases and possible involvement of retinoblastoma protein during TGFbeta-mediated apoptosis of human B lymphocytes.

In this study, we investigated the involvement of caspases in TGFbeta-induced apoptosis in human B cells. Our results show that TGFbeta-mediated nuclear fragmentation, observed in the Epstein-Barr virus-negative Burkitt's Lymphoma cell line BL41, was abolished in the presence of the tripeptide caspase inhibitor zVAD-fmk or the specific caspase-3 inhibitor DEVD-fmk. Other apoptotic manifestations such as cell shrinkage, surface phosphatidylserine expression and chromatin condensation were strongly inhibited by zVAD-fmk but only partially by DEVD-fmk.

BCMAp: an integral membrane protein in the Golgi apparatus of human mature B lymphocytes.

BCMA is a human gene expressed preferentially in mature B lymphocytes as a 1.2 kb mRNA, which encodes a 184 amino acid peptide (BCMAp). The study of BCMA mRNA expression, using human malignant B cell lines characteristic of different stages of B lymphocyte differentiation, demonstrated that the BCMA mRNA is absent in the pro-B lymphocyte stage.

Expression of VCAM-1 (CD106) by a subset of TCR gamma delta-bearing lymphocyte clones. Involvement of a metalloprotease in the specific hydrolytic release of the soluble isoform.

The cytokine-inducible vascular cell adhesion molecule 1/CD106 is widely distributed in endothelial, epithelial, macrophage, and dentritic cells. We previously have reported a mAb termed sTA that recognizes the CD106 molecule on various TCR gamma delta T cell clones that do not proliferate in response to an anti-CD3 stimulation. In the present report, further biochemical analysis reveals two intracellular precursors (82 and 98 kDa) of the membrane-bound 110-kDa form of CD106.

A monoclonal antibody to the Hodgkin's disease-associated antigen CD30 induces activation and long-term growth of human autoreactive gamma delta T cell clone.

In order to identify cell surface structures involved in the activation and growth of human-cloned T lymphocytes, we developed monoclonal antibodies against an autoreactive TcR gamma delta-bearing clone termed DS6. Antibodies were screened for their agonistic properties with the immunizing T cell clone. In the present report, we describe a CD30 mAb, termed BY88, that was capable of inducing, in a short-term assay, a strong proliferation of the T cell clone DS6 when added in combination with IL2 or phorbol myristate acetate.

Significant enlargement of a specific subset of CD3+CD8+ peripheral blood leukocytes mediating cytotoxic T-lymphocyte activity during human immunodeficiency virus infection.

We have obtained a monoclonal antibody termed BY55 that defines an 80-kDa cell-surface structure on a subset of circulating peripheral blood mononucleocytes. This structure, which was not detected on most cell lines or activated lymphocytes, was expressed exclusively on 15-25% of CD2+ circulating lymphocytes, including a major subset within the CD3- and the T-cell receptor gamma delta + lymphocytes and a small percentage of the CD3+CD8+ cells. Moreover, we have shown that the BY55 molecule delineated the competent killer circulating lymphocytes.

A novel 80-kD cell surface structure identifies human circulating lymphocytes with natural killer activity.

Human lymphocytes with natural killer (NK) activity, including most activated gamma/delta+ T lymphocytes, recognize and lyse tumor target cells without requiring recognition of major histocompatibility complex antigen. However, unlike gamma/delta+ T lymphocytes, NK cells do not express CD3/T cell receptor (TCR) molecules, and the receptors involved in cell-mediated cytotoxicity are unknown. To further delineate circulating NK cells, we developed monoclonal antibodies (mAbs) against the human NK leukemia YT2C2.

Identification of a novel functional 85-kD glycoprotein restricted to long-term dividing human lymphocytic lines.

Lymphocyte activation induces or increases the expression of several surface structures, some of which are directly involved in cell growth such as receptors for IL2 or transferrin. To identify new structures characteristic of activated lymphocytes, we developed a series of mAbs against functionally defined human T-cell clones or the NK-mediating cell line YT2C2. In this study, we report the isolation of an mAb termed AY19 recognizing, at the cell surface, an 85-kD glycoprotein whose expression is restricted to T-lymphocyte clones, leukemic T-cell lines, and T-ALL peripheral blood cells.

Inhibition of superoxide production in B lymphocytes by rac antisense oligonucleotides.

Rac1 and Rac2 gene products are small GTP-binding proteins showing 92% homology to each other. According to recent studies performed in cell-free systems, Rac1 and Rac2 proteins may be involved in the activation of NADPH-oxidase, the superoxide-generating enzymatic complex active in phagocytes. Epstein-Barr virus (EBV) transformed B lymphocytes, which express rac1 and rac2 genes, also efficiently release superoxide anions when triggered by various cell surface stimuli.

Mechanism of maturation and nature of carbohydrate chains of boar sperm acrosin.

The acrosin zymogen proacrosin exists in two molecular forms which are believed to be single-chain polypeptides. During autoactivation in a cell-free system, the 55 and 53 kDa zymogens are sequentially converted into the 49, 36, 31 and 25 kDa forms. A similar mechanism of maturation was revealed, when the calcium ionophore A23187 was added to suspensions of boar spermatozoa.

Differential inhibition of interleukin 2- and interleukin 4-mediated human B cell proliferation by ionomycin: a possible regulatory role for apoptosis.

Surface immunoglobulin (Ig) cross-linking by anti-IgM (mu) antibodies leads to B cell activation resulting in numerous early biochemical events including an increase in intracellular [Ca2+]. Furthermore, anti-mu-activated B cells become able to proliferate in response to interleukin (IL)2 and IL4. These studies examined the effect of the calcium ionophore ionomycin, an enhancer of cytoplasmic [Ca2+] levels, on IL2 and IL4-mediated proliferation of anti-mu-stimulated normal human B cells.

Proliferation of resting lymphocytes is induced by triggering T cells through an epitope common to the three CD18/CD11 leukocyte adhesion molecules.

LFA-1, Mac-1, and p150,95 are a family of functionally important leucocyte integrins that share a common beta-subunit and participate in cellular adhesion. Monoclonal antibody to LFA-1 were described to block T-cell-mediated killing by inhibiting adhesion to target cells and to decrease T cell responses by preventing cell-cell contact. Recently it was demonstrated that LFA-1 molecule was involved in signal transduction.