Membrane-associated CD19-LYN complex is an endogenous p53-independent and Bc1-2-independent regulator of apoptosis in human B-lineage lymphoma cells

FINDER: A Fluidly Confined CRISPR-Based DNA Reporter on Living Cell Membranes for Rapid and Sensitive Cancer Cell Identification

The accurate, rapid, and sensitive identification of cancer cells in complex physiological environments is significant in biological studies, personalized medicine, and biomedical engineering. Inspired by the naturally confined enzymes on fluid cell membranes, a fluidly confined CRISPR-based DNA reporter (FINDER) was developed on living cell membranes, which was successfully applied for rapid and sensitive cancer cell identification in clinical blood samples. Benefiting from the spatial confinement effect for improved local concentration, and membrane fluidity for higher collision efficiency, the activity of CRISPR-Cas12a was, for the first time, found to be significantly enhanced on living cell membranes. This new phenomenon was then combined with multiple aptamer-based DNA logic gate for cell recognition, thus a FINDER system capable of accurate, rapid and sensitive cancer cell identification was constructed. The FINDER rapidly identified target cells in only 20 min, and achieved over 80 % recognition efficiency with only 0.1 % of target cells presented in clinical blood samples, indicating its potential application in biological studies, personalized medicine, and biomedical engineering.

Gene expression profiling analysis of castration-resistant prostate cancer

Background

Prostate cancer is a global health issue. Usually, men with metastatic disease will progress to castration-resistant prostate cancer (CRPC). We aimed to identify the differentially expressed genes (DEGs) in tumor samples from non-castrated and castrated men from LNCaP Orthotopic xenograft models of prostate cancer and to study the mechanisms of CRPC.

Material/Methods

In this work, GSE46218 containing 4 samples from non-castrated men and 4 samples from castrated men was downloaded from Gene Expression Omnibus. We identified DEGs using limma Geoquery in R, the Robust Multi-array Average (RMA) method in Bioconductor, and Bias methods, followed by constructing an integrated regulatory network involving DEGs, miRNAs, and TFs using Cytoscape. Then, we analyzed network motifs of the integrated gene regulatory network using FANMOD. We selected regulatory modules corresponding to network motifs from the integrated regulatory network by Perl script. We preformed gene ontology (GO) and pathway enrichment analysis of DEGs in the regulatory modules using DAVID.

Results

We identified total 443 DEGs. We built an integrated regulatory network, found three motifs (motif 1, motif 2 and motif 3), and got two function modules (module 1 corresponded to motif 1, and module 2 corresponded to motif 2). Several GO terms (such as regulation of cell proliferation, positive regulation of macromolecule metabolic process, phosphorylation, and phosphorus metabolic process) and two pathways (pathway in cancer and Melanoma) were enriched. Furthermore, some significant DEGs (such as CAV1, LYN, FGFR3 and FGFR3) were related to CPRC development.

Conclusions

These genes might play important roles in the development and progression of CRPC.

Src kinase signaling in leukaemia

Role of Src kinases in acute lymphoblastic leukaemia has been recently demonstrated in leukaemia mouse model. Retained activation of Src kinases by the BCR-ABL oncoprotein in leukaemic cells following inhibition of BCR-ABL kinase activity by imatinib indicates that Src activation by BCR-ABL is independent of BCR-ABL kinase activity and provides an explanation for reduced effectiveness of the BCR-ABL kinase activity inhibitors in Philadelphia chromosome-positive acute lymphoblastic leukaemia. Simultaneous inhibition of kinase activity of both BCR-ABL and Src kinases results in long-term survival of mice with acute lymphoblastic leukaemia. Leukaemic stem cells exist in acute lymphoblastic leukaemia, and complete eradication of this group of cells would provide a curative therapy for this disease.

Src kinases as targets for B cell acute lymphoblastic leukaemia therapy

The participation of Src kinases in the induction of BCR-ABL-induced B cell acute lymphoblastic leukaemia (B-ALL), but not chronic myeloid leukaemia (CML), demonstrates cell type-specific signalling in Philadelphia chromosome-positive (Ph+) leukaemias. Different therapeutic strategies are therefore needed for B-ALL and CML. Activation of Src kinases is independent of BCR-ABL kinase activity for activation. Thus, Src kinases provide a mechanism for resistance to the BCR-ABL kinase inhibitors and potential targets for B-ALL therapy. Simultaneous targeting of both BCR-ABL and Src kinases may benefit human B-ALL patients. Leukaemic stem cells may exist in Ph+ B-ALL, and eradication of this group of cells would provide a curative method for this disease.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

The SH2 domain containing tyrosine phosphatase-1 down-regulates activation of Lyn and Lyn-induced tyrosine phosphorylation of the CD19 receptor in B cells

SHP-1 is a cytosolic tyrosine phosphatase implicated in down-regulation of B cell antigen receptor signaling. SHP-1 effects on the antigen receptor reflect its capacity to dephosphorylate this receptor as well as several inhibitory comodulators. In view of our observation that antigen receptor-induced CD19 tyrosine phosphorylation is constitutively increased in B cells from SHP-l-deficient motheaten mice, we investigated the possibility that CD19, a positive modulator of antigen receptor signaling, represents another substrate for SHP-1. However, analysis of CD19 coimmunoprecipitable tyrosine phosphatase activity in CD19 immunoprecipitates from SHP-1-deficient and wild-type B cells revealed that SHP-1 accounts for only a minor portion of CD19-associated tyrosine phosphatase activity. As CD19 tyrosine phosphorylation is modulated by the Lyn protein-tyrosine kinase, Lyn activity was evaluated in wild-type and motheaten B cells. The results revealed both Lyn as well as CD19-associated Lyn kinase activity to be constitutively and inducibly increased in SHP-1-deficient compared with wild-type B cells. The data also demonstrated SHP-1 to be associated with Lyn in stimulated but not in resting B cells and indicated this interaction to be mediated via Lyn binding to the SHP-1 N-terminal SH2 domain. These findings, together with cyanogen bromide cleavage data revealing that SHP-1 dephosphorylates the Lyn autophosphorylation site, identify Lyn deactivation/dephosphorylation as a likely mechanism whereby SHP-1 exerts its influence on CD19 tyrosine phosphorylation and, by extension, its inhibitory effect on B cell antigen receptor signaling.

EGF-genistein inhibits neointimal hyperplasia after vascular injury in an experimental restenosis model

A murine model of vascular injury-induced neointimal hyperplasia was developed by using a photoactive dye, rose bengal. Photoactivation of rose bengal induced vascular injury to the femoral arteries of C57B1/6 mice and resulted in an occlusive neointimal hyperplasia after 4 weeks. The cellular elements of the hyperplastic neointima were found to be alpha-actin-positive vascular smooth muscle cells expressing epidermal growth factor (EGF) receptor at high levels. EGF-Gen, an EGF-R-specific inhibitor with potent anticancer activity, suppressed the formation of hyperplastic neointima. Morphometric analysis of serial tissue sections at 4 weeks after vascular injury showed that in 75% of the EGF-Gen-treated mice, the maximal stenosis index was only 0.44 +/- 0.13, whereas in 75% of phosphate-buffered saline (PBS)-treated mice, the maximal stenosis index was 1.20 +/- 0.25. The mean neointima/media ratios for areas of maximum neointimal hyperplasia were 0.59 +/- 0.16 (n = 24) for the EGF-Gen-treated group, 0.99 +/- 16 (n = 45) for the PBS group (EGF-Gen vs. PBS, p = 0.0017), and 1.03 +/- 18 (n = 8) for group treated with unconjugated genistein (EGF-Gen vs. Gen, p = 0.0088). EGF-Gen treatment of mice with vascular injury to the left femoral artery was not associated with any clinical signs of toxicity or histopathologic lesions in any of the organs, including the uninjured right femoral artery. EGF-Gen also inhibited VSMC migration in vitro, without affecting VSMC proliferation and viability, suggesting that EGF-Gen is blocking neointima formation by inhibiting cellular migration to vascular injury sites. In conclusion, EGF-Gen may be useful as a nontoxic prophylactic agent for prevention of restenosis in clinical settings.

Clinical pharmacokinetics of the CD19 receptor-directed tyrosine kinase inhibitor B43-Genistein in patients with B-lineage lymphoid malignancies

The authors examined the pharmacokinetics of the CD19 receptor-directed tyrosine kinase inhibitor B43-Genistein in 17 patients (4 children, 13 adults) with B-lineage lymphoid malignancies, including 12 patients with acute lymphoblastic leukemia (ALL) and 5 patients with non-Hodgkin's lymphoma (NHL). The immunoconjugate was administered intravenously as a 1-hour continuous infusion at a dose level of either 0.1 mg/kg (N = 12) or 0.18 mg/kg (N = 5), and the plasma concentration-time data were modeled by using the WinNonlin program to estimate the pharmacokinetic parameters. Pharmacokinetic analyses revealed a plasma half-life of 19 +/- 4 hours, mean residence time of 22 +/- 4 hours, and a systemic clearance of 18 +/- 2 mL/h/kg. The average (mean +/- SEM) values for the maximum plasma concentration Cmax, volume of distribution at steady state (Vss), and area under curve (AUC) were 1092 +/- 225 ng/ml, 291 +/- 37 mL/kg, and 9987 +/- 2021 micrograms x h/L, respectively. The AUC values were higher at the 0.18 mg/kg dose level than at the 0.1 mg/kg dose level (16,848 +/- 5118 micrograms x h/L vs. 7128 +/- 1156 micrograms x h/L, p = 0.009). Patients with ALL had a significantly larger volume of distribution at steady state (332 +/- 47 mL/kg vs. 191 +/- 12 mL/kg, p = 0.04), faster clearance (21 +/- 3 mL/h/kg vs. 11 +/- 2 mL/h/kg, p = 0.03), and lower dose-corrected AUC than patients with NHL (6010 +/- 836 micrograms x h/L vs. 12,044 +/- 2707 micrograms x h/L, p = 0.006). There was a trend toward faster clearance rates (23 +/- 4 mL/h/kg vs. 16 +/- 3 mL/h/kg, p = 0.1), shorter elimination half-lives (5.7 +/- 3.6 hours vs. 13 +/- 8.8 hours, p = 0.1), and shorter mean residence times (11 +/- 3 hours vs. 25 +/- 5 hours, p = 0.08) for non-Caucasian patients as compared to Caucasian patients. When compared to adult patients, pediatric patients showed a significantly larger volume of distribution at steady state (418 +/- 82 mL/kg vs. 252 +/- 34 mL/kg, p = 0.02) and a longer elimination half-lives (18.4 +/- 13.6 hours vs. 8.7 +/- 6.7 hours, p = 0.04). The pharmacokinetics of B43-Genistein was not affected by the gender of the patients or by bone marrow transplantation in past medical history. Overall, B43-Genistein showed favorable pharmacokinetics in this heavily pretreated leukemia/lymphoma patient population, which is reminiscent of its recently reported favorable pharmacokinetics in cynomolgus monkeys. To our knowledge, this is the first clinical pharmacokinetics study of a tyrosine kinase inhibitor containing immunoconjugate.

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.

Metabolic oxidative stress activates signal transduction and gene expression during glucose deprivation in human tumor cells

The mechanism of glucose deprivation-induced activation of Lyn kinase (Lyn), c-Jun N-terminal kinase 1 (JNK1) and increased expression of basic fibroblast growth factor (bFGF) and c-Myc was investigated in MCF-7/ADR adriamycin-resistant human breast carcinoma cells. Glucose deprivation significantly increased steady state levels of oxidized glutathione content (GSSG) and intracellular prooxidants (presumably hydroperoxides) as well as caused the activation of Lyn, JNK1, and the accumulation of bFGF and c-Myc mRNA. The suppression of GSSG accumulation and prooxidant production by treatment with the thiol antioxidant, N-acetylcysteine, also suppressed all the increases in kinase activation and gene expression observed during glucose deprivation. In addition, glucose deprivation was shown to induce oxidative stress in IMR90 SV40 transformed human fibroblasts, indicating that this phenomena is not limited to the MCF-7/ADR cell line. These and previous observations from our laboratory show that glucose deprivation-induced oxidative stress in MCF-7/ADR cells activates signal transduction involving Lyn, JNK1, and mitogen activated protein kinases (ERK1/ERK2) which results in increased bFGF and c-Myc mRNA accumulation. These results provide support for the hypothesis that alterations in intracellular oxidation/reduction reactions link changes in glycolytic metabolism to signal transduction and gene expression in these human tumor cells.

CD77-dependent retrograde transport of CD19 to the nuclear membrane: functional relationship between CD77 and CD19 during germinal center B-cell apoptosis

A region of the N-terminal extracellular domain of the B-cell restricted cell differentiation antigen, CD19, has high amino acid sequence similarity to the receptor binding subunit B of verotoxin 1 (VT), an Escherichia coli elaborated cytotoxin, which specifically binds to the cell surface glycolipid, globotriaosylceramide, also known as the germinal center (GC) B-cell differentiation antigen, CD77. We have previously provided evidence of the association of CD19 and CD77 on the cell surface and in CD19-mediated homotypic adhesion of the Daudi Burkitt Lymphoma cell line, one normal counterpart of which is a subset of GC B cells. Evidence for the role of CD77 in CD19-induced apoptosis is now presented. Initial cell surface distribution, antibody-induced redistribution, internalization, and intracellular routing of CD19 were studied by confocal microscopy, IF, and postembedding IEM in CD77+ve and CD77-ve cells to investigate the possible role of CD77 in CD19 internalization and signaling. Daudi Burkitt's lymphoma cells were used as CD77+ve cells and as CD77-ve cells, Daudi mutant VT500 cells, and Daudi cells treated with PPMP, an inhibitor of CD77 synthesis, were used. Antibody ligated CD19 surface redistribution, internalization, and subcellular distribution of internalized CD19 was found to be different in CD77+ve and CD77-ve cells. A delay in internalization of antibody-CD19 complex was observed in CD77-ve cells. Internalized CD19 was targeted to the nuclear envelope in CD77+ve cells in a manner similar to that reported for VT, but not in CD77-ve cells. Internalization of CD77 by ligation with verotoxin prevented the internalization of ligated CD19. Induction of apoptosis following crosslinking of cell surface CD19 was greater in CD77+ve cells than in CD77-ve cells. The nuclear targeting of internalized CD19 and induction of apoptosis following CD19 crosslinking only in CD77+ve cells indicates a role for CD77-dependent CD19 retrograde transport from the B cell surface via the ER to the nuclear envelope in CD19-mediated signal transduction for apoptosis.

Role of tyrosine kinases in induction of the c-jun proto-oncogene in irradiated B-lineage lymphoid cells

Exposure of B-lineage lymphoid cells to ionizing radiation induces an elevation of c-jun proto-oncogene mRNA levels. This signal is abrogated by protein-tyrosine kinase (PTK) inhibitors, indicating that activation of an as yet unidentified PTK is mandatory for radiation-induced c-jun expression. Here, we provide experimental evidence that the cytoplasmic tyrosine kinases BTK, SYK, and LYN are not required for this signal. Lymphoma B-cells rendered deficient for LYN, SYK, or both by targeted gene disruption showed increased c-jun expression levels after radiation exposure, but the magnitude of the stimulation was lower than in wild-type cells. Thus, these PTKs may participate in the generation of an optimal signal. Notably, an inhibitor of JAK-3 (Janus family kinase-3) abrogated radiation-induced c-jun activation, prompting the hypothesis that a chicken homologue of JAK-3 may play a key role in initiation of the radiation-induced c-jun signal in B-lineage lymphoid cells.

Antiviral protection and germinal center formation, but impaired B cell memory in the absence of CD19

Coligation of CD19, a molecule expressed during all stages of B cell development except plasmacytes, lowers the threshold for B cell activation with anti-IgM by a factor of 100. The cytoplasmic tail of CD19 contains nine tyrosine residues as possible phosphorylation sites and is postulated to function as the signal transducing element for complement receptor (CR)2. Generation and analysis of CD19 gene-targeted mice revealed that T cell-dependent (TD) antibody responses to proteinaceous antigens were impaired, whereas those to T cell-independent (TI) type 2 antigens were normal or even augmented. These results are compatible with earlier complement depletion studies and the postulated function of CD19. To analyze the role of CD19 in antiviral antibody responses, we immunized CD19(-/-) mice with viral antigens of TI-1, TI-2, and TD type. The effect of CD19 on TI responses was more dependent on antigen dose and replicative capacity than on antigen type. CR blocking experiments confirmed the role of CD19 as B cell signal transducer for complement. In contrast to immunization with protein antigens, infection of CD19(-/-) mice with replicating virus led to generation of specific germinal centers, which persisted for >100 d, whereas maintenance of memory antibody titers as well as circulating memory B cells was fully dependent on CD19. Thus, our study confirms a costimulatory role of CD19 on B cells under limiting antigen conditions and indicates an important role for B cell memory.

Production of recombinant DTctGMCSF fusion toxin in a baculovirus expression vector system for biotherapy of GMCSF-receptor positive hematologic malignancies

The fusion toxin DTctGMCSF has been constructed by genetically replacing the native receptor-binding domain of diphtheria toxin (DT) with human granulocyte-macrophage colony stimulating factor (GMCSF). This recombinant fusion toxin preserves the catalytic (c) and membrane translocation (t) domains of DT and includes a sterically neutral peptide linker separating the toxin and growth factor domains. Previous work using DTctGMCSF produced in Escherichia coli has shown that this chimeric toxin is selectively cytotoxic to GMCSF receptor (R)-positive acute myeloid leukemia (AML) cells both in vitro and in vivo. Its clinical development has been hampered due to very low expression levels, requirements for solubilization with guanidine hydrochloride and subsequent refolding, and concerns about bacterial endotoxin contamination. These difficulties prompted us to investigate the utility of a baculovirus/insect cell expression system for the production of DTctGMCSF. Here, we report that a soluble form of DTctGMCSF can be produced in the baculovirus expression vector system (BEVS) and purified to homogeneity by column chromatography. The BEVS-derived DTctGMCSF fusion toxin caused apoptotic death in GMCSF-R-positive human AML cells at nanomolar concentrations. In contrast to the 100 microg/L yields of purified DTctGMCSF obtained from E. coli, the BEVS allows us to routinely generate 8-10 mg/L of purified DTctGMCSF. This increased capacity provided by the BEVS for the production of DTctGMCSF makes it now possible to obtain sufficient quantities to carry out preclinical and clinical trials. To our knowledge, this is the first report of the successful utilization of the BEVS for producing a therapeutic fusion toxin.

In vivo toxicity and pharmacokinetic features of B43(Anti-CD19)-Genistein immunoconjugate

B43(anti-CD19)-Genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase inhibitory isoflavone to the membrane-associated anti-apoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-Genistein as well as unconjugated genistein were evaluated in mice. B43-Genistein and genistein were administered either as single bolus injections or daily injections for 10 consecutive days via the intraperitoneal route to mice. Genistein was not toxic to mice at the highest dose of 40 mg/kg and no test article-related histopathological lesions were found in any of the 64 genistein-treated mice. B43-Genistein had a significantly longer elimination half-life and slower plasma and tissue clearance than unconjugated genistein. B43-Genistein was not toxic to mice at the highest single dose of 40 mg/kg or highest cumulative dose of 100 mg/kg and no test article-related histopathological lesions were found in any of the 108 mice treated with B43-genistein. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate.

A deficiency in Syk enhances ceramide-induced apoptosis in DT40 lymphoma B cells

Syk deficiency significantly enhanced ceramide-induced apoptosis. Ectopic expression of wild-type or kinase-inactive Syk rendered Syk-negative cells resistant to ceramide-induced apoptosis. Furthermore, ceramide could not activate Syk, indicating that Syk protected DT40 cells from ceramide-induced apoptosis, via a mechanism independent of its activity. In addition, a deficiency in Lyn also resulted in the cells becoming susceptible to ceramide-induced apoptosis. However, no difference of Ara-C-induced apoptosis between wild-type and mutant cells was observed. c-Jun N-terminal kinases appeared not to be important in mediating the enhanced apoptosis, as they were still activated in mutant cells following ceramide treatment.

Large scale manufacturing of B43(anti-CD19)-genistein for clinical trials in leukemia and lymphoma

We have conjugated the murine monoclonal anti-CD19 antibody B43 to the tyrosine kinase inhibitor genistein to construct an effective immunoconjugate against CD19 antigen positive hematologic malignancies. The scaled-up production and purification of B43 antibody, genistein, and B43-Genistein immunoconjugate permitted the manufacturing of a highly purified clinical-grade B43-Genistein preparation. In clonogenic assays, B43-Genistein elicited selective and potent cytotoxicity against CD19 antigen positive human leukemia cells. To our knowledge, this work represents the first effort of producing a clinical-grade genistein immunoconjugate for treatment of B-lineage leukemia and lymphoma.

Rad51-deficient vertebrate cells accumulate chromosomal breaks prior to cell death

Yeast rad51 mutants are viable, but extremely sensitive to gamma-rays due to defective repair of double-strand breaks. In contrast, disruption of the murine RAD51 homologue is lethal, indicating an essential role of Rad51 in vertebrate cells. We generated clones of the chicken B lymphocyte line DT40 carrying a human RAD51 transgene under the control of a repressible promoter and subsequently disrupted the endogenous RAD51 loci. Upon inhibition of the RAD51 transgene, Rad51- cells accumulated in the G2/M phase of the cell cycle before dying. Chromosome analysis revealed that most metaphase-arrested Rad51- cells carried isochromatid-type breaks. In conclusion, Rad51 fulfils an essential role in the repair of spontaneously occurring chromosome breaks in proliferating cells of higher eukaryotes.

Distinctive functions of Syk and Lyn in mediating osmotic stress- and ultraviolet C irradiation-induced apoptosis in chicken B cells

By taking advantage of the established chicken B cell line, DT40 cells, which do not express tyrosine kinase Syk or Lyn, functional roles of Syk and Lyn in apoptotic response elicited by cellular stress were investigated. DT40 cells underwent apoptosis after hyperosmotic stress. In Syk-deficient DT40 cells, this apoptotic process was significantly enhanced. Ectopic expression of wild type, but not kinase-inactive, porcine Syk in Syk-deficient cells rescued cells from osmotic stress-induced apoptosis, demonstrating that the presence of functionally active Syk is necessary to protect cells from osmotic stress-induced apoptosis. In comparison, there was no effect on osmotic stress-induced apoptosis in Lyn-deficient DT40 cells. Interestingly, while Syk was not involved in ultraviolet C (UVC)-induced apoptosis, a deficiency of Lyn rendered cells resistant to UVC irradiation. These observations defined Syk and Lyn as important mediators of apoptosis in DT40 cells in response to osmotic stress and UVC irradiation, respectively. Furthermore, osmotic stress, but not UVC irradiation, could activate c-Jun N-terminal kinase (JNK) in DT40 cells. A deficiency in either Syk or Lyn did not affect the osmotic stress-induced activation of JNK. We, therefore, concluded that Syk and Lyn regulate the apoptotic responses to osmotic stress and UVC irradiation independently of the JNK pathway in DT40 cells.

Cellular Expression of Antiapoptotic BCL-2 Oncoprotein in Newly Diagnosed Childhood Acute Lymphoblastic Leukemia: A Children's Cancer Group Study

We found a marked variation in BCL-2 oncoprotein expression levels of primary leukemic cells from 338 children with newly diagnosed acute lymphoblastic leukemia (ALL). None of the high-risk features predictive of poor treatment outcome in childhood ALL, such as older age, high white blood cell (WBC) count, organomegaly, T-lineage immunophenotype, ability of leukemic cells to cause overt leukemia in severe combined immunodeficient (SCID) mice, presence of MLL-AF4, and BCR-ABL fusion transcripts were associated with high levels of BCL-2 expression. Overall, high BCL-2 levels were not associated with slow early response, failure to achieve complete remission, or poor event-free survival. High BCL-2 levels in primary leukemic cells predicted slow early response only in T-lineage ALL patients, which comprised approximately 15% of the total patient population. Even for this small subset of patients, the level of BCL-2 expression did not have a significant impact on the short-term event-free survival.

Cellular Expression of Antiapoptotic BCL-2 Oncoprotein in Newly Diagnosed Childhood Acute Lymphoblastic Leukemia: A Children's Cancer Group Study

We found a marked variation in BCL-2 oncoprotein expression levels of primary leukemic cells from 338 children with newly diagnosed acute lymphoblastic leukemia (ALL). None of the high-risk features predictive of poor treatment outcome in childhood ALL, such as older age, high white blood cell (WBC) count, organomegaly, T-lineage immunophenotype, ability of leukemic cells to cause overt leukemia in severe combined immunodeficient (SCID) mice, presence of MLL-AF4, and BCR-ABL fusion transcripts were associated with high levels of BCL-2 expression. Overall, high BCL-2 levels were not associated with slow early response, failure to achieve complete remission, or poor event-free survival. High BCL-2 levels in primary leukemic cells predicted slow early response only in T-lineage ALL patients, which comprised approximately 15% of the total patient population. Even for this small subset of patients, the level of BCL-2 expression did not have a significant impact on the short-term event-free survival.

Hypoglycemia-induced c-Jun phosphorylation is mediated by c-Jun N-terminal kinase 1 and Lyn kinase in drug-resistant human breast carcinoma MCF-7/ADR cells

We studied the signal transduction mechanism that is involved in c-Jun phosphorylation evident after glucose deprivation in MCF-7/ADR cells. Glucose deprivation caused an immediate increase in tyrosine phosphorylation in MCF-7/ADR cells and specifically activated Lyn kinase, a src family tyrosine kinase. In addition, hypoglycemic treatment strongly activated c-Jun N-terminal kinase 1 (JNK1), leading to the phosphorylation and activation of c-Jun. Experiments with Lyn antisense oligonucleotides demonstrated that Lyn kinase activation was responsible for the activation of JNK1 but not extracellular signal-regulated kinase. We also observed glucose deprivation-induced Ras activation in MCF-7/ADR cells. These results indicate a possible Ras-dependent signaling pathway involving Lyn kinase and JNK1, which leads to the glucose deprivation-induced responses in MCF-7/ADR cells.

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.

Activation of B lymphocytes: integrating signals from CD19, CD22 and Fc gamma RIIb1

Three accessory membrane proteins, CD19, CD22 and Fc gamma RIIb1, alter signaling through membrane immunoglobulin of B cells by binding cytosolic proteins containing SH2 domains. Recent biochemical and genetic studies have shown that these receptors enable B cells to amplify responses to certain T-cell-dependent antigens (CD19), to restrict their response to T-cell zones of secondary lymphoid organs (CD22), and to dampen their response to antigens for which IgG is already available (Fc gamma RIIb1).