Expression of protein tyrosine kinases in the Ig complex of anti-mu-sensitive and anti-mu-resistant B-cell lymphomas: role of the p55blk kinase in signaling growth arrest and apoptosis

Toxicity evaluations of superparamagnetic iron oxide nanoparticles: cell "vision" versus physicochemical properties of nanoparticles

In the last few decades, nanoparticles (NPs) have been recognized as promising candidates for starting a new revolution in science and technology due to their unusual properties, attracting the attention of physicists, chemists, biologists, and engineers. The aim of this study is to evaluate the toxicities (at both cellular and molecular levels) of three forms of superparamagnetic iron oxide nanoparticles (SPIONs) of various surface chemistries (COOH, plain, and NH(2)) through the comparison with gene expression patterns of three cell types (i.e., human heart, brain, and kidney). For this purpose, both an MTT assay and a DNA microarray analysis were applied in three human cell lines--HCM (heart), BE-2-C (brain), and 293T (kidney)--under the exposure to SPIONs-COOH, SPIONs-NH(2), and bare SPIONs. The specific gene alteration and hierarchical clustering revealed that SPIONs-COOH altered genes associated with cell proliferative responses due to their reactive oxygen species (ROS) properties. It was also found that the cell type can have quite a significant role in the definition of suitable pathways for detoxification of NPs, which has deep implications for the safe and high yield design of NPs for biomedical applications and will require serious consideration in the future.

Disruption of membrane cholesterol stimulates MyD88-dependent NF-kappaB activation in immature B cells

Agents that extract or sequester membrane cholesterol stimulate IkappaB degradation and lead to NF-kappaB activation in a subset of B cells. Although the extraction of cholesterol by methyl-beta-cyclodextrin is the most potent stimulus of NF-kappaB, other agents that sequester cholesterol have similar effects. B cells and B cell lines with an immature phenotype are significantly more sensitive to the effects of cholesterol perturbation than their mature B cell counterparts. NF-kappaB activation does not involve signaling from the B cell receptor complex. Instead, the disruption of membrane cholesterol activates NF-kappaB through a MyD88-dependent pathway involving the pattern recognition receptor, Toll-like receptor 4. We suggest that lipid raft microdomains may serve not only to orchestrate receptor signaling, but to sequester signaling components one from one another, which serves to prevent receptor-mediated signaling from occurring. A role for this process during B cell development is suggested.

Activation-induced cell death in B lymphocytes

Upon encountering the antigen (Ag), the immune system can either develop a specific immune response or enter a specific state of unresponsiveness, tolerance. The response of B cells to their specific Ag can be activation and proliferation, leading to the immune response, or anergy and activation-induced cell death (AICD), leading to tolerance. AICD in B lymphocytes is a highly regulated event initiated by crosslinking of the B cell receptor (BCR). BCR engagement initiates several signaling events such as activation of PLCgamma, Ras, and PI3K, which generally speaking, lead to survival. However, in the absence of survival signals (CD40 or IL-4R engagement), BCR crosslinking can also promote apoptotic signal transduction pathways such as activation of effector caspases, expression of pro-apoptotic genes, and inhibition of pro-survival genes. The complex interplay between survival and death signals determines the B cell fate and, consequently, the immune response.

Selective phosphotyrosine phosphatase inhibition and increased ceramide formation is associated with B-cell death by apoptosis

Bis(maltolato)oxovanadium(IV) (BMOV), a protein phosphotyrosine phosphatase inhibitor, selectively induced apoptosis (as quantitated by TUNEL staining) in a B-cell line (Ramos) but not in a T-cell line (Jurkat). The pattern of BMOV-induced protein tyrosine phosphorylation was different in B-cells versus T-cells. Further, BMOV induced a 2-fold increase in ceramide levels in B-cells but not in T-cells and this resembled the ceramide increase following activation of the B-cell antigen receptor. A 2-fold increase in the ratio of ceramide to sphingomyelin in B-cells treated with BMOV suggested that sphingomyelinase activation was the result of the sustained tyrosine phosphorylation of specific proteins and activated the cell death pathway.

AML1 (CBFalpha2) cooperates with B cell-specific activating protein (BSAP/PAX5) in activation of the B cell-specific BLK gene promoter

AML1 plays a critical role during hematopoiesis and chromosomal translocations involving AML1 are commonly associated with different forms of leukemia, including pre-B acute lymphoblastic leukemia. To understand the function of AML1 during B cell differentiation, we analyzed regulatory regions of B cell-specific genes for potential AML1-binding sites and have identified a putative AML1-binding site in the promoter of the B cell-specific tyrosine kinase gene, blk. Gel mobility shift assays and transient transfection assays demonstrate that AML1 binds specifically to this site in the blk promoter and this binding site is important for blk promoter activity. Furthermore, in vitro binding analysis revealed that the AML1 runt DNA-binding domain physically interacts with the paired DNA-binding domain of BSAP, a B cell-specific transcription factor. BSAP has been shown previously to be important for B cell-specific regulation of the blk gene. Physical interaction of AML1 with BSAP correlates with functional cooperativity in transfection studies where AML1 and BSAP synergistically activate blk promoter transcription by more than 50-fold. These results demonstrate physical and functional interactions between AML1 and BSAP and suggest that AML1 is an important factor for regulating a critical B cell-specific gene, blk.

Constitutive Nuclear Translocation of NF-κB in B Cells in the Absence of IκB Degradation

Members of the NF-κB/Rel family of transcription factors are involved in many aspects of B lymphocyte development and function. NF-κB is constitutively active in these cells, in contrast with most other cell types. In the inactive form, NF-κB/Rel proteins are sequestered in the cytoplasm by members of the IκB family of NF-κB inhibitors. When activated, NF-κB is translocated to the nucleus, a process that involves the phosphorylation and proteasomal degradation of IκB proteins. Thus, NF-κB activation is accompanied by the rapid turnover of IκB proteins. We show that while this “classical” mode of NF-κB activation is a uniform feature of IgM+ B cell lines, all IgG+ B cells analyzed contain nuclear NF-κB yet have stable IκBα, IκBβ, and IκBε. Furthermore, Iκβε levels are at least 10 times lower in IgG+ B cells than in IgM+ B cells, an additional indication that the regulation of constitutive NF-κB activity in these two types of B cells is fundamentally different. These data imply the existence of a novel mechanism of NF-κB activation in IgG+ B cells that operates independently of IκB degradation. They further suggest that different isoforms of the B cell receptor may have distinct roles in regulating NF-κB activity.

Cellular functions regulated by Src family kinases

Src family protein tyrosine kinases are activated following engagement of many different classes of cellular receptors and participate in signaling pathways that control a diverse spectrum of receptor-induced biological activities. While several of these kinases have evolved to play distinct roles in specific receptor pathways, there is considerable redundancy in the functions of these kinases, both with respect to the receptor pathways that activate these kinases and the downstream effectors that mediate their biological activities. This chapter reviews the evidence implicating Src family kinases in specific receptor pathways and describes the mechanisms leading to their activation, the targets that interact with these kinases, and the biological events that they regulate.

Negative signaling in B cells by surface immunoglobulins

Cross-linking of surface immunoglobulins generates negative signals that cause B-cell death unless appropriate rescue signals are provided. Surface IgM is the main transducer of the negative signaling, but surface IgD and IgG may also transduce negative signaling when cross-linked intensively. In the surface IgM+, IgD+ human malignant B lymphoma cell lines B104 and DND-39, cross-linking of surface IgM by anti-IgM antibodies induced cell death. Anti-IgM antibody-induced B104 cell death was inhibited by stimulation with alpha- and beta-interferons but not stimulation with anti-CD40 antibody or IL-4, whereas anti-IgM antibody-induced DND-39 cell death was inhibited by stimulation with anti-CD40 antibody but not stimulation with alpha- and beta-interferons. Anti-IgM antibody-stimulated B104 cells had morphologic features compatible with necrosis, whereas anti-IgM antibody-stimulated DND-39 cells showed morphologic features of apoptosis. CD11a/CD54-dependent cell adhesion induced by stimulation with anti-CD40 antibody was involved in anti-CD40 antibody-mediated inhibition of anti-IgM antibody-induced DND-39 cells. In normal human mature B cells, cross-linking of surface IgM induced different signaling consequences, including DNA synthesis or cell division (positive signaling) or cell cycle arrest or death (negative signaling). In this system, too, CD40-transduced signal inhibited anti-IgM antibody-induced negative signaling, and CD11a/CD54-dependent cell adhesion played a role in the rescue process. It is suggested that quantitatively different intensities of surface IgM cross-linking induce qualitatively different signaling consequences; relatively weak cross-linking may induce DNA synthesis; moderate cross-linking may induce DNA synthesis with cell cycle arrest at the G2/M interphase; and intense cross-linking may induce apoptotic cell death. The reasons for this difference are not yet known. Further elucidation of the molecular mechanisms responsible for surface IgM-mediated negative signaling and its rescue signaling may contribute toward development of therapy for allergic disorders by artificial modulation of specific immunoglobulin production.

Role of protein kinase activity in apoptosis

The transmission of signals from the plasma membrane to the nucleus involves a number of different pathways all of which have in common protein modification. The modification is primarily in the form of phosphorylation which leads to the activation of a series of protein kinases. It is now evident that these pathways are common to stimuli that lead to mitogenic and apoptotic responses. Even the same stimuli under different physiological conditions can cause either cell proliferation or apoptosis. Activation of specific protein kinases can in some circumstances protect against cell death, while in others it protects the cell against apoptosis. Some of the pathways involved lead to activation of transcription factors and the subsequent induction of genes involved in the process of cell death or proliferation. In other cases, such as for the tumour suppressor gene product p53, activation may be initiated both at the level of gene expression or through pre-existing proteins. Yet in others, while the initial steps in the pathway are ill-defined, it is clear that downstream activation of a series of cystein proteases is instrumental in pushing the cell towards apoptosis. In this report we review the involvement of protein kinases at several different levels in the control of cell behaviour.

Expression of exogenous p59fyn modulates signaling in an immature B cell line, WEHI-231

The WEHI-231 B lymphoma line is representative of immature B cells, which undergo growth arrest/apoptosis following cross-linking of surface immunoglobulin M (sIgM). In B cells, sIgM engagement has been shown to induce immediate (within seconds) activation of src family protein tyrosine kinases (PTKs) such as p53lyn/56lyn, p55blk, p56lck and p59fyn which are associated with B cell antigen receptor (BCR) complex. However, p59fyn expression is very low in both normal immature B cells and apoptosis-prone B cell lines, including WEHI-231. Such a finding prompted us to investigate the effects of ectopic expression of p59fyn in growth regulation of WEHI-231 cells. We have obtained WEHI-231 transfectants expressing the exogenous p59fyn by retroviral mediated gene transfer method. The transfectants demonstrated increased [Ca2+]i level in both the non-stimulated condition and sIgM cross-linking. The expression of ectopic p59fyn also increased the sensitivity of the transfectants to growth arrest signal by sIgM cross-linking. The results suggest that p59fyn can modulate signal transduction and growth regulation when expressed in the immature B cell line.

Selective regulation of Lyn tyrosine kinase by CD45 in immature B cells

It has been well established that protein-tyrosine phosphatase CD45 is critically involved in the regulation of initial tyrosine phosphorylation and effector functions of T and B cells. However, the signaling pathway governed by CD45 is not completely understood. In B cells, it has not been unequivocally resolved as to which protein-tyrosine kinases (PTKs) associated with B cell antigen receptor are regulated by CD45 in intact cells. As a first step toward the elucidation of CD45-initiated signaling events, we have tried to identify physiological substrates for CD45 by analyzing PTK activity in CD45-deficient clones recently generated from the immature B cell line WEHI-231. The results clearly demonstrated that among PTKs examined (Lyn, Lck, and Syk), only Lyn kinase is dysregulated in the absence of CD45 such that without B cell antigen receptor ligation, Lyn is hyperphosphorylated and activated in CD45-negative clones. Thus, Lyn seems to be a selective in vivo substrate for CD45 in immature B cells.

Modulation of drug-induced apoptosis in a human B-lymphoma cell line (HT58)

The cytotoxic effect of etoposide (ETO), a topoisomerase II inhibitor, and staurosporine (STA), a non-selective protein kinase inhibitor, were studied on a human lymphoma cell line of B-cell origin (HT58). Apoptosis, induced dose dependently by both drugs, was accompanied with nucleosomal DNA fragmentation detected by flow cytometry. On the other hand, induction of cell death failed using phorbol ester (PMA), anti-IgM antibody (a-IgM) or dexamethasone (DEX), although, all of these agents arrested the cells in G1. Furthermore, PMA pretreatment retarded ETO-induced apoptosis, but enhanced STA cytotoxicity. DEX increased the sensitivity of cells to STA, but did not to ETO. Activity of STA or DEX was only slightly modified by a-IgM pretreatment. The results support the possibility that different apoptotic pathways exist in HT58 cells. The differences in pathways could be manifested either in the signaling routes, or in the molecular effectors of apoptosis.

Lineage-specific induction of B cell apoptosis and altered signal transduction by the phosphotyrosine phosphatase inhibitor bis(maltolato)oxovanadium(IV)

Protein tyrosine phosphorylation is known to play key roles in lymphocyte signal transduction, and phosphotyrosine phosphatases (PTP) can act as both positive and negative regulators of these lymphocyte signals. We sought to examine the role of PTP further in these processes by characterizing the effects of bis(maltolato)-oxovanadium(IV) (BMLOV), previously known to be a nontoxic insulin mimetic agent in vivo. BMLOV was found to be a potent phosphotyrosine phosphatase inhibitor. BMLOV induced cellular tyrosine phosphorylation in B cells in a pattern similar to that observed following antigen receptor stimulation, whereas little tyrosine phosphorylation was induced in T cells. In B cells, BMLOV treatment resulted in tyrosine phosphorylation of Syk and phospholipase C gamma 2, while sIgM-induced signals were inhibited. By contrast, T cell receptor signals were moderately increased by BMLOV, and the cells displayed greater induction of IL-2 receptor without toxicity. The compound selectively induced apoptosis in B cell lymphoma and myeloid leukemia cell lines, but not in T cell leukemia or colon carcinoma cells. Interleukin-4 plus anti-CD40 antibody treatment of normal human peripheral B cells rescued the cells from BMLOV-induced death. These results suggest that phosphotyrosine phosphatase inhibitors can activate B cell signal pathways in a lineage-specific manner, resulting in desensitization of receptor-mediated signaling and induction of apoptosis.

Tumor dormancy and cell signaling. II. Antibody as an agonist in inducing dormancy of a B cell lymphoma in SCID mice

Tumor dormancy can be induced in a murine B cell lymphoma (BCL1) by immunizing BALB/c mice with the tumor immunoglobulin (Ig) before tumor cell challenge. In this report, we have investigated the immunological and cellular mechanisms underlying the induction of dormancy. BCL1 tumor cells were injected into SCID mice passively immunized with antibody against different epitopes on IgM or IgD with or without idiotype (Id)-immune T lymphocytes. Results indicate that antibody to IgM is sufficient to induce a state of dormancy. Antibodies against other cell surface molecules including IgD and CD44 (Pgp1) had no effect on tumor growth. Id-immune T cells by themselves also had no effect on tumor growth in SCID mice. However, simultaneous transfer of anti-Id and Id-immune T cells enhanced both the induction and duration of the dormant state. In vitro studies indicated that antibody to IgM induced apoptosis within several hours and cell cycle arrest by 24 h. Hyper cross-linking increased apoptosis. The Fc gamma RII receptor played little or no role in the negative signaling. Antibodies that did not negatively signal in vitro did not induce dormancy in vivo. The results suggest that anti-IgM plays a decisive role in inducing tumor dormancy to BCL1 by acting as an agonist of IgM-mediated signal transduction pathways.

Signaling properties of anti-immunoglobulin--resistant variants of WEHI-231 B lymphoma cells

Stimulation of the B cell antigen receptor (BCR) of the murine immature WEHI-231 B lymphoma with anti-immunoglobulin antibodies leads to irreversible growth arrest and apoptosis. As in normal B cells, membrane immunoglobulin (mIg) ligation in WEHI-231 cells triggers a series of signaling cascades from the BCR to intracellular compartments. In order to address the role of early signals in mediating the growth arrest of WEHI-231 cells, we have generated two variants resistant to the anti-Ig-mediated inhibitory effect. Some of the properties of these variants have been recently described in terms of bcl-2 and c-myc gene regulation. We report here that these variants can be further distinguished from the wild type on the basis of significant alterations in the early biochemical events which follow mIg ligation. Both Ca2+ signals and patterns of protein tyrosine phosphorylation were affected in these variants, suggesting that alterations in the early signal transduction machinery may have profound effects on the fate of B cells. In addition, we found that expression of the p75HS1 substrate of p53/56lyn was strikingly reduced in both variants as compared to the wild type. These findings support the view that p75HS1 may play a critical role in BCR-dependent signaling cascades.

Activation-induced apoptosis in lymphocytes

Activation-induced apoptosis has been proposed as a mechanism for purging the immune repertoire of anti-self specificities, not only in development but also during the generation of somatic mutation in germinal centers. The pathways involved in driving immature and mature T and B cells to programmed cell death are reviewed with respect to two hypotheses, the pre-emptive death model, in which certain signals are obligatory for programmed cell death, and the two signal: death/survival model. Depending on the system, some data support the former pathway, in which certain signals are obligatory for programmed cell death, whereas other data are consistent with the two signal hypothesis. Moreover, recent data suggests that the c-myc protein plays a pivotal role in controlling this process. Finally conflicting roles of protein kinases, bcl-2 and p53 are reviewed and contrasted for involvement in activation-induced cell death in T and B lymphocytes.

Lyn tyrosine kinase signals cell cycle arrest but not apoptosis in B-lineage lymphoma cells

Signal transduction initiated by binding of antibodies to cell surface molecules can have an important impact on the growth of tumor cells. The malignant behavior of the murine lymphoma BCL1 can be suppressed and the neoplastic cells can be induced to enter a dormant state by in vivo ligation of membrane immunoglobulin. Anti-CD19 antibodies can prolong the survival of SCID mice challenged with the human Burkitt lymphoma cell line, Daudi. Here, we show that cross-linking of membrane immunoglobulin on both murine BCL1 and human Daudi cells initiates a cascade of signals leading to the induction of both apoptosis and cell cycle arrest in vitro. Using antisense oligonucleotides, we demonstrate that the immunoglobulin-associated Lyn tyrosine kinase is required for anti-immunoglobulin-mediated cell cycle arrest but is not required for the signal leading to apoptosis. These results define a branch point in the cytosolic signaling pathways mediating cell cycle arrest and apoptosis. In Daudi cells, Lyn is also critical for cell cycle arrest induced by anti-CD19 signaling. Thus, the Lyn tyrosine kinase may be an important mediator of cell cycle arrest in neoplastic B lymphocytes and, perhaps, other cell types.

Induction of phosphatidylinositol turnover and EGR-1 mRNA expression by crosslinking of surface IgM and IgD in the human B cell line B104

We have previously shown that a human B lymphoma cell line, B104, expressed surface IgM (sIgM) and surface IgD (sIgD), and that crosslinking of sIgM and sIgD by anti-IgM antibody (Ab) and anti-IgD Ab, respectively, induced Ca2+ influx to almost the same degree, whereas only sIgM-crosslinking caused B104 cell death. Here, we investigated the accumulation of cyclic AMP (cAMP), the hydrolysis of inositol phosphates, protein kinase C (PKC) activity and the induction of Egr-1 and c-fos mRNA expression by sIgM- and sIgD-crosslinking to examine differences in the signals mediated through sIgM and sIgD in B104 cells. Both sIgM- and sIgD-crosslinking with antibodies induced elevation of cAMP levels, phosphatidylinositol turnover, PKC activation and expression of Egr-1 and c-fos mRNA, although sIgM-crosslinking was more effective than sIgD-crosslinking, presumably due to the higher expression of sIgM than of sIgD. Egr-1 mRNA expression induced by sIgM- and sIgD-crosslinking was inhibited by H7, erbstatin and genistein, but not by HA1004. Erbstatin and genistein inhibited the sIg-crosslinking-induced Egr-1 mRNA expression in a dose-dependent manner parallel to that observed in the inhibition of sIg-crosslinking-induced protein tyrosine phosphorylation. Phorbol myristate acetate induced Egr-1 mRNA expression but forskolin and dibutyryl cyclic AMP did not. These findings suggest that the Egr-1 mRNA activating signals through sIgM and sIgD are protein tyrosine kinase- and PKC-dependent, but protein kinase A-independent. Cyclosporin A (CsA) and FK506 rescued B104 cells from death induced by anti-IgM Ab, but did not affect the expression of Egr-1 and c-fos mRNA, showing that CsA and FK506 affect signal transducers differently from or downstream to these molecules. The difference in signals transduced through sIgM and sIgD in B104 cells is discussed.

Antisense oligodeoxynucleotides to the blk tyrosine kinase prevent anti-mu-chain-mediated growth inhibition and apoptosis in a B-cell lymphoma

Crosslinking of membrane immunoglobulin (mIg) receptors by anti-Ig causes growth inhibition and subsequent cell death due to apoptosis in a murine B-cell lymphoma model. The earliest signal transduction via mIg has recently been shown to be dependent on the activation of one or more protein tyrosine kinases (PTKs). In this study, we utilized the CH31 lymphoma, which is extremely sensitive to growth inhibition by anti-Ig, to examine the role of PTKs in cell cycle arrest. This cell line expresses multiple PTKs, whose activities are stimulated by crosslinking mIg. To determine whether PTK activity is essential for the inhibition of cell growth, we exposed CH31 cells to antisense oligodeoxynucleotides for the blk PTK prior to the growth inhibition assay. We found that exposure of CH31 cells to blk antisense effectively prevented anti-mu-chain-mediated growth inhibition and subsequent apoptosis. Corresponding blk sense or antisense oligonucleotides for other PTKs had no protective effect against anti-mu. Moreover, antisense blk oligonucleotides had no effect on transforming growth factor beta-mediated growth arrest and apoptosis. Further experiments showed significantly reduced endogenous p55blk in blk antisense-treated cells. In addition, anti-mu stimulation of antisense-treated cells failed to induce any detectable increase in kinase activity of p55blk, a result suggesting the uncoupling of blk proteins from normal signal pathways that are essential for growth inhibition. These results implicate a role of blk kinase in anti-mu-mediated pathway to cell cycle arrest.