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

Hygiene Hypothesis as the Etiology of Kawasaki Disease: Dysregulation of Early B Cell Development

Kawasaki disease (KD) is an acute systemic vasculitis that occurs predominantly in children under 5 years of age. Despite much study, the etiology of KD remains unknown. However, epidemiological and immunological data support the hygiene hypothesis as a possible etiology. It is thought that more sterile or clean modern living environments due to increased use of sanitizing agents, antibiotics, and formula feeding result in a lack of immunological challenges, leading to defective or dysregulated B cell development, accompanied by low IgG and high IgE levels. A lack of B cell immunity may increase sensitivity to unknown environmental triggers that are nonpathogenic in healthy individuals. Genetic studies of KD show that all of the KD susceptibility genes identified by genome-wide association studies are involved in B cell development and function, particularly in early B cell development (from the pro-B to pre-B cell stage). The fact that intravenous immunoglobulin is an effective therapy for KD supports this hypothesis. In this review, I discuss clinical, epidemiological, immunological, and genetic studies showing that the etiopathogenesis of KD in infants and toddlers can be explained by the hygiene hypothesis, and particularly by defects or dysregulation during early B cell development.

The autoimmunity-associated BLK haplotype exhibits cis-regulatory effects on mRNA and protein expression that are prominently observed in B cells early in development

The gene B lymphocyte kinase (BLK) is associated with rheumatoid arthritis, systemic lupus erythematosus and several other autoimmune disorders. The disease risk haplotype is known to be associated with reduced expression of BLK mRNA transcript in human B cell lines; however, little is known about cis-regulation of BLK message or protein levels in native cell types. Here, we show that in primary human B lymphocytes, cis-regulatory effects of disease-associated single nucleotide polymorphisms in BLK are restricted to naïve and transitional B cells. Cis-regulatory effects are not observed in adult B cells in later stages of differentiation. Allelic expression bias was also identified in primary human T cells from adult peripheral and umbilical cord blood (UCB), thymus and tonsil, although mRNA levels were reduced compared with B cells. Allelic regulation of Blk expression at the protein level was confirmed in UCB B cell subsets by intracellular staining and flow cytometry. Blk protein expression in CD4(+) and CD8(+) T cells was documented by western blot analysis; however, differences in protein expression levels by BLK genotype were not observed in any T cell subset. Blk allele expression differences at the protein level are thus restricted to early B cells, indicating that the involvement of Blk in the risk for autoimmune disease likely acts during the very early stages of B cell development.

Association of the C8orf13-BLK region with systemic sclerosis in North-American and European populations

OBJECTIVE

Genetic studies in the systemic sclerosis (SSc), an autoimmune disease that clinically manifests with dermal and internal organ fibrosis and small vessel vasculopathy, have identified multiple susceptibility genes including HLA-class II, PTPN22, IRF5, and STAT4 which have also been associated with other autoimmune diseases, such as systemic lupus erythematosus (SLE). These data suggest that there are common autoimmune disease susceptibility genes. The current report sought to determine if polymorphisms in the C8orf13-BLK region (chromosome 8p23.1-B lymphoid tyrosine kinase), which is associated with SLE, are associated also with SSc.

METHODS

Two variants in the C8orf13-BLK region (rs13277113 & rs2736340) were tested for association with 1050 SSc cases and 694 controls of North Americans of European descent and replicated in a second series 589 SSc cases and 722 controls from Spain.

RESULTS

The "T" allele at rs2736340 variant was associated with SSc in both the U.S. and Spanish case-control series (P = 6.8 x 10(-5), OR 1.27, 95% CI 1.1-1.4). The "A" allele at rs13277113 variant was associated with SSc in the U.S. series only (P = 3.6 x 10(-4), OR 1.32, 95% CI 1.1-1.6) and was significant in the combined analyses of the two series (P = 2.0 x 10(-3); OR 1.20, 95% CI 1.1-1.3). Both variants demonstrated an association with the anti-centromere antibody (P = 2.2 x 10(-6) and P = 5.5 x 10(-4), respectively) and limited SSc (P = 3.3 x 10(-5) and P = 2.9 x 10(-3), respectively) in the combined analysis. Peripheral blood gene expression profiles suggest that B-cell receptor and NFkappaB signaling are dysregulated based on the risk haplotype of these variants.

CONCLUSION

We identify and replicate the association of the C8orf13-BLK region as a novel susceptibility factor for SSc, placing it in the category of common autoimmune disease susceptibility genes.

Clinical stage EGFR inhibitors irreversibly alkylate Bmx kinase

Irreversible HER/erbB inhibitors selectively inhibit HER-family kinases by targeting a unique cysteine residue located within the ATP-binding pocket. Sequence alignment reveals that this rare cysteine is also present in ten other protein kinases including all five Tec-family members. We demonstrate that the Tec-family kinase Bmx is potently inhibited by irreversible modification at Cys496 by clinical stage EGFR inhibitors such as CI-1033. This cross-reactivity may have significant clinical implications.

Multiple cell death pathways as regulators of tumour initiation and progression

Acquired defects in signalling pathways leading to programmed cell death (PCD) are among the major hallmarks of cancer. Although focus has been on caspase-dependent apoptotic death pathways, evidence is now accumulating that nonapoptotic PCD also can form an important barrier against tumour initiation and progression. Akin to the earlier landmark discoveries that lead to the identification of the major cancer-related proteins like p53, c-Myc and Bcl-2 as controllers of spontaneous and therapy-induced apoptosis, numerous proteins with properties of tumour suppressors and oncoproteins have recently been identified as key regulators of alternative death programmes. The emerging data on the molecular mechanisms regulating nonapoptotic PCD may have potent therapeutic consequences.

The ALG-2/AIP-complex, a modulator at the interface between cell proliferation and cell death? A hypothesis

During the development of an organism cell proliferation, differentiation and cell death are tightly balanced, and are controlled by a number of different regulators. Alterations in this balance are often observed in a variety of human diseases. The role of Ca(2+) as one of the key regulators of the cell is discussed with respect to two recently discovered proteins, ALG-2 and AIP, of which the former is a Ca(2+)-binding protein, and the latter is substrate to various kinases. The two proteins interact with each other in a Ca(2+)-dependent manner, and the role of the complex ALG-2/AIP as a possible modulator at the interface between cell proliferation and cell death is discussed.

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.

The B-cell-specific Src-family kinase Blk is dispensable for B-cell development and activation

The B-cell lymphocyte kinase (Blk) is a src-family protein tyrosine kinase specifically expressed in B-lineage cells of mice. The early onset of Blk expression during B-cell development in the bone marrow and the high expression levels of Blk in mature B cells suggest a possible important role of Blk in B-cell physiology. To study the in vivo function of Blk, mice homozygous for the targeted disruption of the blk gene were generated. In homozygous mutant mice, neither blk mRNA nor Blk protein is expressed. Despite the absence of Blk, the development, in vitro activation, and humoral immune responses of B cells to T-cell-dependent and -independent antigens are unaltered. These data are consistent with functional redundancy of Blk in B-cell development and immune responses.

Role of the outward delayed rectifier K+ current in ceramide-induced caspase activation and apoptosis in cultured cortical neurons

We studied the novel hypothesis that an up-modulation of channels for outward delayed rectifier K+ current (I(K)) plays a key role in ceramide-induced neuronal apoptosis. Exposure for 6-10 h to the membrane-permeable C2-ceramide (25 microM) or to sphingomyelinase (0.2 unit/ml), but not to the inactive ceramide analogue C2-dihydroceramide (25 microM), enhanced the whole-cell I(K) current without affecting the transient A-type K+ current and increased caspase activity, followed by neuronal apoptosis 24 h after exposure onset. Tetraethylammonium (TEA) or 4-chloro-N,N-diethyl-N-heptylbenzenebutanaminium tosylate (clofilium), at concentrations inhibiting I(K), attenuated the C2-ceramide-induced caspase-3-like activation as well as neuronal apoptosis. Raising extracellular K+ to 25 mM similarly blocked the C2-ceramide-induced cell death; the neuroprotection by 25 mM K+ or TEA was not eliminated by blocking voltage-gated Ca2+ channels. An inhibitor of tyrosine kinases, herbimycin A (10 nM) or lavendustin A (0.1-1 microM), suppressed I(K) enhancement and/or apoptosis induced by C2-ceramide. It is suggested that ceramide-induced I(K) current enhancement is mediated by tyrosine phosphorylation and plays a critical role in neuronal apoptosis.

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.

CD22 Cross-Linking Generates B-Cell Antigen Receptor-Independent Signals That Activate the JNK/SAPK Signaling Cascade

CD22 is a B-cell–specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-xL, Mcl-1, and Bax) showed a downregulation of Bcl-xL and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

CD22 Cross-Linking Generates B-Cell Antigen Receptor-Independent Signals That Activate the JNK/SAPK Signaling Cascade

CD22 is a B-cell–specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-xL, Mcl-1, and Bax) showed a downregulation of Bcl-xL and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

Microfilament assembly is involved in B-cell apoptosis

Crosslinking of the B-cell antigen receptor (BCR) initiates a chain of reactions which culminate in a number of biologic responses, including entry into the cell cycle or cell death. The signals and processes which lead to cell death are slowly being unraveled. Based on the dramatic changes in cell shape which occur during progression of the apoptotic response, activation of cytoskeletal assembly may be critical as this appears to be essential to the mitogenic response. In this study, we demonstrate that crosslinking of the human BCR with anti-IgM antibodies results in the rapid assembly of actin. Our data also suggest that this conversion of G- to F-actin may be a prerequisite for the apoptosis response, as prevention of this conversion by botulinum C2 toxin or cytochalasin D results in rescue of the cells from apoptosis. Prevention of tyrosine kinase activation, disruption of microfilament assembly, and rescue of B lymphocytes from apoptosis imply that tyrosine phosphorylation is needed for both microfilament assembly and apoptosis. In each instance where microfilament assembly is inhibited, anti-IgM-induced activation of the protease CPP32 (caspase) is also inhibited. Taken together, these results suggest that the microfilament system is actively involved in delivering signals for apoptosis.

Protein phosphorylation associated with epipodophyllotoxin-induced apoptosis of lymphoid cells: role of a serine/threonine protein kinase

We have previously shown that apoptosis induced in thymocytes by dexamethasone or teniposide (VM-26) could be inhibited by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) and sangivamycin, both relatively specific inhibitors for protein kinase C, but not by N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA1004), a more specific inhibitor for cAMP-dependent protein kinases. Apoptosis in this model system was not blocked by EGTA and no increase in cytosolic Ca2+ was observed during apoptosis induced by either dexamethasone or VM-26, suggesting that this kinase was Ca2+-independent. In the present study, we demonstrate that addition of 10 microM sangivamycin to thymocyte cultures up to 2 h after addition of either inducer resulted in virtually complete inhibition of apoptosis. Addition of 10 microM sangivamycin at 3 or 4 h after addition of inducer resulted in partial inhibition of apoptosis. Computerized image analysis of two-dimensional PAGE analyses of whole-cell lysates demonstrated that treatment of mouse thymocytes with VM-26 resulted in a limited number of de novo phosphorylation events within 1 h of treatment. The most prominent phosphorylation events associated with VM-26-induced apoptosis were that two intracellular protein species (Protein 1: m.w. = 22.9 kDa, pI, 5.11; and Protein 2: m.w. = 22.9 kDa, pI, 4.98). Similar phosphorylation events were seen in cells treated with dexamethasone. Finally, Western blot analysis suggests that de novo protein phosphorylation induced by VM-26 is on serine/threonine residues. These results provide further evidence that the mechanism of VM-26-induced apoptosis of murine thymocytes involves the action of one or more serine/threonine kinases.

Apoptosis may be either suppressed or enhanced with strategic combinations of antineoplastic drugs or anti-IgM

A variety of drugs have been used to treat B-lymphocyte neoplasms, including both cell cycle-specific (CCS) and non-cell-cycle-specific drugs. Although the therapy for such cancers is complex and can include both types of drugs, the efficacy of these drugs in inducing cell death remains unclear. In this paper we have concentrated on specific CCS drugs and have examined their ability to induce programmed cell death (apoptosis) in Burkitt's lymphoma cell lines derived from patients. The CCS drugs chosen were hydroxyurea and aphidicolin (active in late G1, early S phase), the topoisomerase poisons camptothecin and etoposide (S, early G2 phase) and vincristine and Taxol (late G2, M phase). These choices allow comparison of two drugs with differing modes of action for each of the various phases of the cell cycle. Our results indicate that the variation in apoptosis between drugs that act at the same phase of the cell cycle is negligible. Both S/G2 and G2/M blockers are very potent at inducing apoptosis whereas G1/S blockers are ineffective in the induction of apoptosis. In addition, marked kinetic variations in the rate of apoptosis induction were observed, etoposide and camptothecin being more rapid in their action than the other agents. The order of effectiveness in inducing apoptosis on a kinetic basis was S/G2 agents >> G2/M agents >> G1/S agents. In this study we have also found that growth inhibition was induced by all the CCS agents chosen and by anti-IgM in various Burkitt's lymphoma lines. Furthermore c-myc was down-regulated under similar conditions. Since apoptosis was only selectively induced by some of the CCS agents, it implies c-myc expression is associated with growth regulation and c-myc down-regulation is an insufficient condition for the induction of apoptosis. In addition, cotreatments using the CCS and other agents revealed the following: Cotreatment using two CCS drugs which act at the same stage in the cell cycle showed either no change or only additivity to the effects seen with either agent alone. However, cotreatment with CCS drugs showed that an inhibitory effect is found between G1/S and G2/M drugs or S/G2 and G2/M drugs. No effect was found between G1/S and S/G2 drugs. Anti-IgM, which by itself was capable of inducing apoptosis, was observed to augment apoptosis induced by very low concentrations of G2/M-acting drugs but it has little effect on G1/S or the S/G2 drugs. The inhibitory effect of anti-CD40 or TNF-alpha on anti-IgM-induced apoptosis did not carry over to an effect on apoptosis induction by the CCS agents. Thus specific combinations of agents may lead to either enhancement, inhibition, or no interactive effect on apoptosis.

The transcription factor NF-kappaB/p50 interacts with the blk gene during B cell activation

The B cell-specific transcription factor Pax-5 has been shown previously to interact with the promoter of the blk gene in vitro. blk encodes a tyrosine kinase associated with the B cell receptor, which is expressed during the early but not the final stages of B cell development. To investigate whether Pax-5 regulates expression of the blk gene in vivo during B cell development and/or activation, Pax-5a was overexpressed in B cell lines. Increases in blk promoter activity using a chloramphenicol acetyltransferase reporter gene system suggested a role for Pax-5a as a transcriptional activator. Subsequent site-specific mutagenesis studies showed that mutations of the Pax-5 binding site on blk significantly alter promoter activity, although results suggested that other factors could bind to this region as well. Using mobility shift assays, we detected an inducible transcription factor that interacts strongly with a sequence overlapping the Pax-5 site on the blk promoter and identified this as a homodimer of NF-kappaB/p50, a member of the NF-kappaB/Rel family of transcription factors. This factor was present at high levels in lipopolysaccharide-activated normal B cells and in plasma cell lines but either at low levels or undetectable levels in resting normal B cells or pre-B or mature B cell lines. In contrast, lipopolysaccharide induction of a pre-B cell line (703/Z) induced a complex that contained both NF-kappaB/p50 and p65. These studies suggest that different NF-kappaB complexes are able to interact with a sequence overlapping the Pax-5 site on the blk promoter and that the relative levels of "bound" factor influence levels of blk expression. Since p50 homodimers and p50/p65 heterodimers of the NF-kappaB complex should have opposing effects on blk transcription, this could provide a mechanism to differentially regulate blk expression during B cell development and activation.

The role of calcium in the regulation of apoptosis

Apoptosis (programmed cell death) has gained widespread attention due to its roles in a variety of physiological and pathological processes, yet precisely how apoptosis is regulated by external and internal cues remains unclear. Work from our laboratories and others has implicated alterations in intracellular Ca2+ in apoptosis, and more recent work has defined particular biochemical processes that are targeted by Ca2+ in apoptotic cells. This review will summarize the role of Ca2+ in apoptosis within the context of what is known about the core components of the effector machinery for apoptosis.

Oxygen-dependent fragmentation of cellular DNA by nitric oxide

Although active oxygen species and related metabolites, such as nitric oxide (NO), have been postulated to play important roles in the apoptosis of various cells, a precise mechanism leading to cell death remains to be elucidated. Recently we found that the lifetime of NO depends greatly on the concentration of environmental oxygen and that NO reversibly inhibits mitochondrial respiration and ATP synthesis; the inhibitory effect is stronger at physiologically low oxygen tension than under atmospheric conditions (Arch. Biochem. Biophys. 323, 27-32, 1995). The present work describes the effects of the NO-generating agent, 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18) and oxygen tension on the respiration, ATP synthesis and apoptosis of HL-60 cells. When respiration was inhibited by NOC 18, cellular ATP levels decreased significantly and DNA fragmentation was elicited. Both events were enhanced by decreasing oxygen tension and suppressed by adding NO-trapping agents, such as 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) and oxyhemoglobin. The fragmentation of cellular DNA was inhibited in a dose dependent manner by herbimycin A, a tyrosine kinase inhibitor. Fragmentation of the DNA of HL-60 cells was also induced either by peroxynitrite, superoxide or hydroxyl radical by some mechanism which was diminished by lowering the oxygen tension. These results indicated that the decrease in cellular ATP and activation of tyrosine kinase might play important roles in NO-induced apoptosis particularly under physiologically low oxygen tensions.

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.

Delayed neuronal death in ischemic hippocampus involves stimulation of protein tyrosine phosphorylation

Glutamate triggers neuronal degeneration after ischemia-reperfusion in the brain. However, the details of intracellular signal transduction that propagates cell death remain unknown. The present work investigated whether protein tyrosine phosphorylation mediates neuronal death in the ischemic brain. Transient forebrain ischemia for 5-10 min in Mongolian gerbils or intoxication with the glutamate analogue kainic acid (12 mg/kg) in Sprague-Dawley rats caused neuronal death selectively in the hippocampus 2-4 days or 1 day later, respectively. Under these conditions, 160-, 115-, 105-, 92-, and 85-kDa proteins showed a significant increase in tyrosyl residue phosphorylation selectively in the hippocampus 3-12 h after ischemia or 4-8 h after kainic acid-induced seizures. Tyrosine kinases, including pp60c-src, were activated without a change of tyrosine phosphatases. Administration of radicicol, a selective inhibitor of tyrosine kinases, attenuated stimulation of tyrosine phosphorylation and hippocampal degeneration after ischemia or kainic acid injection. The results suggest that protein tyrosine phosphorylation might propagate delayed neuronal death in the mature hippocampus through glutamate overload after ischemia-reperfusion.

Recent status of the antisense oligonucleotide approaches in oncology

Antisense oligonucleotides designed to complement a region of a particular messenger RNA may inhibit gene expression potentially through sequence-specific hybridization. Their inhibiting effect has been shown in a variety of in vitro and in vivo models in oncology, whereas much rarer clinical trials have been carried out. Rigorous demonstration of in vitro and in vivo specific effects upon their targets is mandatory before their use as drugs in cancer therapy.

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.

In vivo radiosensitizing effects of recombinant interleukin 6 on radiation resistant BCL-1 B-lineage leukemia cells in a murine syngeneic bone marrow transplant model system

The ability of total body irradiation (TBI) to eradicate clonogenic leukemia cells from B-lineage acute lymphoblastic leukemia patients prior to bone marrow transplantation (BMT) is greatly hampered by their inherent or acquired radiation resistance. The radiorefractory nature of these cells is believed to contribute to the high relapse rate subsequent to TBI and BMT in patients with B-lineage acute lymphoblastic leukemia (ALL). A method by which clonogenic leukemia cells could be radiosensitized in vivo could be clinically beneficial. In the present study, we used a highly radiation resistant subclone of the murine B-lineage leukemia cell line BCL-1 in a syngeneic BMT model to investigate if any of the B-cell stimulatory cytokines interleukin 2, interleukin 4, interleukin 5, or interleukin 6 could have radiosensitizing effects. All untreated BALB/c mice (N = 33) inoculated with 1 x 10(6) BCL-1 cells died of disseminated leukemia within 24 days with a median survival of 13.3 days. TBI (700 cGy = LD100/30 for BALB/c mice) followed by syngeneic BMT (N = 70) extended the median survival to 23.6 days (P < 0.001 by log-rank test). A single intraperitoneal bolus injection of 100 ng, 500 ng, or 2500 ng recombinant murine interleukin 6(rmIL-6) 2-4 hours before TBI extended the median survival to 32.5 days, 31.0 days, and 30.5 days, respectively (P < 0.01 by log-rank test for all dose groups). The improved survival was not due to any direct anti-leukemic activity of rmIL-6 and all control BALB/c mice (N = 15) that received the same doses of rmIL-6 but did not undergo TBI and BMT died of BCL-1 leukemia within 28 days with a median survival of 13.6 days. In contrast to rmIL-6, recombinant murine interleukin 5 (rmIL-5) had minimal radiosensitizing effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Apoptosis overview emphasizing the role of oxidative stress, DNA damage and signal-transduction pathways

Apoptosis (programmed cell death) is a central protective response to excess oxidative damage (especially DNA damage), and is also essential to embryogenesis, morphogenesis and normal immune function. An understanding of the cellular events leading to apoptosis is important for the design of new chemotherapeutic agents directed against the types of leukemias and lymphomas that are resistant to currently used chemotherapeutic protocols. We present here a review of the characteristic features of apoptosis, the cell types and situations in which it occurs, the types of oxidative stress that induce apoptosis, the signal-transduction pathways that either induce or prevent apoptosis, the biologic significance of apoptosis, the role of apoptosis in cancer, and an evaluation of the methodologies used to identify apoptotic cells. Two accompanying articles, demonstrating classic apoptosis and non-classic apoptosis in the same Epstein-Barr virus-transformed lymphoid cell line, are used to illustrate the value of employing multiple criteria to determine the type of cell death occurring in a given experimental system. Aspects of apoptosis and programmed cell death that are not covered in this review include histochemistry, details of cell deletion processes in the sculpting of tissues and organs in embryogenesis and morphogenesis, and the specific pathways leading to apoptosis in specific cell types. The readers should refer to the excellent books and reviews on the morphology, biochemistry and molecular biology of apoptosis already published on these topics. Emphasis is placed, in this review, on a proposed common pathway of apoptosis that may be relevant to all cell types.

Antigen receptor-triggered apoptosis in immature B cell lines is associated with the binding of a 44-kDa phosphoprotein to the PTP1C tyrosine phosphatase

While cross-linking of the membrane IgM (mIgM) molecules expressed on WEHI 231 lymphoma cells induces these cells to undergo apoptosis, we have previously observed that ligation of the mIgD expressed on IgD-transfected WEHI 231 (W delta) cells is not associated with induction of cell death. Thus mIgM+IgD+ W delta cells provide a valuable reagent for delineating the molecular events which modulate the physiologic outcome of B cell antigen receptor (BCR) engagement. In view of recent data implicating the cytosolic phosphotyrosine phosphatase PTP1C in the regulation of BCR signaling capacity, we used W delta cells to investigate the potential role for PTP1C in modulating the cell response to BCR activation. The results of this analysis revealed PTP1C to undergo rapid tyrosine phosphorylation following mIgM or mIgD cross-linking and to associate with a number of other phosphoproteins in stimulated W delta cells. Among these latter phosphoproteins, one prominent species of about 44 kDa (pp44) which co-precipitated with PTP1C in mIgM-ligated cells was not detected in PTP1C immunoprecipitates from mIgD-ligated cells. The association of PTP1C with this 44-kDa phosphoprotein following mIgM cross-linking was also observed in two additional B cell lines representing an immature state of differentiation, but was not detected after BCR engagement in two representative mature B cell lines or in splenic B cells. Initial data concerning the identity of pp44 indicate that this molecule does not represent the Shc, MAPK or Ig-beta proteins and may, therefore, constitute a previously unidentified signaling effector. While the structural and biochemical properties of pp44 require further definition, the findings suggest that BCR-triggered interactions of PTP1C with pp44 occur only in the context of an immature state of cellular differentiation and the induction of apoptosis. These data therefore suggest that PTP1C interactions with pp44 may be relevant to the transduction of BCR signals which evoke cell death.

Restoration of surface IgM-mediated apoptosis in an anti-IgM-resistant variant of WEHI-231 lymphoma cells by HS1, a protein-tyrosine kinase substrate

The HS1 protein is one of the major substrates of non-receptor-type protein-tyrosine kinases and is phosphorylated immediately after crosslinking of the surface IgM on B cells. The mouse B-lymphoma cell line WEHI-231 is known to undergo apoptosis upon crosslinking of surface IgM by anti-IgM antibodies. Variants of WEHI-231 that were resistant to anti-IgM-induced apoptosis expressed dramatically reduced levels of HS1 protein. Expression of the human HS1 protein from an expression vector introduced into one of the variant cell lines restored the sensitivity of the cells to apoptosis induced by surface IgM crosslinking. These results suggest that HS1 protein plays a crucial role in the B-cell antigen receptor-mediated signal transduction pathway that leads to apoptosis.

The SH2 domains of Src family kinases associate with Syk

Src family kinases (Lyn, Fyn, Lck, and Blk) and Syk, a tandem SH2 domain containing tyrosine kinase, have been demonstrated to be associated with the antigen receptor in B cells. Both of these categories of tyrosine kinases are presumed to be critical players in the process of antigen-mediated signal transduction. Cross-linking of membrane immunoglobulin on the surface of B cells leads to the activation of Lyn, Fyn, and Blk, which presumably associate with the cytoplasmic tails of the membrane immunoglobulin-associated Ig alpha/beta heterodimer. Receptor ligation also leads to the tyrosine phosphorylation and catalytic activation of Syk, but the mechanism of association of this kinase with the antigen receptor remains to be established. A number of phosphoproteins that can associate with the SH2 domains of Blk, Lyn, and Fyn have been described in activated B cells. We demonstrate here that Syk is one of the proteins in the lysates of activated B cells which bind to the SH2 domains of Src family kinases. Syk binds directly to the SH2 domain of Blk and complexes in vivo with Lyn and Blk in activated B cells.

Signal transduction by the antigen receptors of B and T lymphocytes

B and T lymphocytes of the immune system recognize and destroy invading microorganisms but are tolerant to the cells and tissues of one's own body. The basis for this self/non-self-discrimination is the clonal nature of the B and T cell antigen receptors. Each lymphocyte has antigen receptors with a single unique antigen specificity. Multiple mechanisms ensure that self-reactive lymphocytes are eliminated or silenced whereas lymphocytes directed against foreign antigens are activated only when the appropriate antigen is present. The key element in these processes is the ability of the antigen receptors to transmit signals to the interior of the lymphocyte when they bind the antigen for which they are specific. Whether these signals lead to activation, tolerance, or cell death is dependent on the maturation state of the lymphocytes as well as on signals from other receptors. We review the role of antigen receptor signaling in the development and activation of B and T lymphocytes and also describe the biochemical signaling mechanisms employed by these receptors. In addition, we discuss how signal transduction pathways activated by the antigen receptors may alter gene expression, regulate the cell cycle, and induce or prevent programmed cell death.

Protein-tyrosine phosphorylation regulates apoptosis in human eosinophils and neutrophils

Early signaling events that control the process of programmed cell death are largely unknown. Tyrosine phosphorylation plays a major role in transmembrane signal transduction through most cell surface receptors. Granulocyte/macrophage colony-stimulating factor (GM-CSF), a cytokine released by activated T cells, has been shown to increase tyrosine phosphorylation in several cells and to inhibit granulocyte cell death in vitro. In this study, we demonstrate that the effect of GM-CSF on granulocyte cell death can be blocked by the tyrosine kinase inhibitor genistein, suggesting that increases in tyrosine phosphorylation are essential to inhibit cell death. To analyze the role of tyrosine phosphorylation for the regulation of granulocyte cell death more precisely, we increased levels of tyrosine phosphorylation using the protein-tyrosine phosphatase inhibitor phenylarsine oxide (PAO). Similar to GM-CSF, treatment of the cells with PAO was followed by high increases in tyrosine phosphorylation and inhibition of programmed cell death in human eosinophils and neutrophils. Strikingly, at low concentrations of the inhibitor and low induction of tyrosine phosphorylation, acceleration of apoptosis was observed. Genistein and herbimycin A reversed the effects of PAO on tyrosine phosphorylation and granulocyte apoptosis. These results suggest that programmed eosinophil and neutrophil death is regulated by early events of signal transduction pathways such as tyrosine phosphorylation.

Temporal differences in the activation of three classes of non-transmembrane protein tyrosine kinases following B-cell antigen receptor surface engagement

We evaluated in WEHI 231 B cells the time-dependent responses of Lyn, Blk, Btk, Syk, and three members of the Jak family of protein tyrosine kinases following antibody-mediated surface engagement of the B-cell antigen receptor. Our results show that the enzyme activities of Lyn and Blk were stimulated within seconds of antigen receptor engagement and correlated with the initial tyrosine phosphorylation of the Ig alpha and Ig beta subunits of the B-cell antigen receptor. Btk enzyme activity was also transiently stimulated and was maximal at approximately 5 min after B-cell receptor surface binding. Syk activity gradually increased to a maximum at 10-30 min following receptor ligation and was found to parallel the association of Syk with the tyrosine phosphorylated Ig alpha and Ig beta subunits of the receptor. While the specific activities of the Jak1, Jak2, and Tyk2 protein tyrosine kinases were unaltered following B-cell receptor ligation, the abundance of Jak1 and Jak2 were increased 3- to 4-fold within 10 min of receptor engagement. These results demonstrate that multiple families of non-transmembrane protein tyrosine kinases are temporally regulated during the process of B-cell antigen receptor-initiated intracellular signal transduction.

Tyrosine phosphorylation of Blk and Fyn Src homology 2 domain-binding proteins occurs in response to antigen-receptor ligation in B cells and constitutively in pre-B cells

Proteins that bind to discrete domains of the Blk, Fyn, Lyn, and Btk protein tyrosine kinases were examined in pre-B cells that had not been subjected to any external stimulation, as well as in nonstimulated and antigen-receptor-ligated B cells. Proteins that bind to the Src homology 2 domains of Blk and Fyn were identified in B cells that had been activated with anti-IgM but were not identified in unstimulated B cells. A number of Blk and Fyn Src homology 2 domain-binding phosphoproteins were also observed in pre-B cells that had not been stimulated in vitro. The phosphoproteins seen in activated B cells potentially represent substrates that play a role in the pathway of antigen-receptor-mediated signaling. Distinct signaling pathways involving distinguishable kinase substrates may be relevant in pre-B-cell-receptor-mediated cell survival during ontogeny. These results indirectly support models that predict constitutive ligand-independent signaling by the pre-antigen receptor during lymphoid ontogeny.

Purification and identification of tyrosine-phosphorylated proteins from B lymphocytes stimulated through the antigen receptor

The activation of protein tyrosine kinase (PTKs) and subsequent tyrosine phosphorylation of cellular proteins is a critical initial signal in the response of eukaryotic cells to mitogens, differentiative signals, and other stimuli. A number of PTK substrates have been identified and many of these are components of signal transduction pathways that regulate cell function. However, the majority of proteins that are tyrosine-phosphorylated in response to receptor signaling remain unidentified. As some of these unidentified PTK substrates may also be signal-transducing proteins, their identification and functional characterization is an important objective towards understanding receptor signaling. We describe the development of a comprehensive and general process for the isolation and structural characterization of tyrosine-phosphorylated proteins. The method involves enrichment by anti-phosphotyrosine affinity chromatography, electrophoretic concentration and separation, and proteolytic fragmentation of individual purified phosphoproteins. Resulting peptide fragments are separated by microbore reverse-phase high performance liquid chromatography (RP-HPLC) and a portion of the eluted peptides are subjected to electrospray-mass spectrometry (ES/MS) for accurate determination of peptide masses. Proteolytic fragmentation of a protein produces a characteristic set of peptide masses that can be used to rapidly identify the protein by searching databases containing the peptide mass "fingerprints" for all known proteins. The identity of the protein established by this method can be confirmed by sequence analysis of selected peptides. We have applied this procedure to the analysis of PTK substrates from B lymphocytes that have been stimulated through the B cell antigen receptor (BCR). Signaling by this receptor is involved in the generation of antibodies against foreign molecules (antigens). The BCR activates multiple PTKs which phosphorylate at least 30 different proteins. We have identified several of these tyrosine-phosphorylated proteins, including Syk, a PTK that is known to be tyrosine-phosphorylated in activated B cells. Thus, the procedure described here can be used to identify regulatory proteins of low abundance. The process consists of a logical succession of compatible steps that avoids pitfalls inherent to prior attempts to characterize low abundance phosphoproteins and should find wide use for the identification of tyrosine-phosphorylated proteins in other cell types.