Phorbol 12-myristate 13-acetate inhibits granulocyte-macrophage colony stimulating factor-induced protein tyrosine phosphorylation in a human factor-dependent hematopoietic cell line

Low concentrations of ethanol do not affect radioligand binding to the delta-subunit-containing GABAA receptors in the rat brain

In the present study, we investigated the co-localization pattern of the delta subunit with other subunits of GABA(A) receptors in the rat brain using immunoprecipitation and Western blotting techniques. Furthermore, we investigated whether low concentrations of ethanol affect the delta-subunit-containing GABA(A) receptor assemblies in the rat brain using radioligand binding to the rat brain membrane homogenates as well as to the immunoprecipitated receptor assemblies. Our results revealed that delta subunit is not co-localized with gamma(2) subunit but it is associated with the alpha(1), alpha(4) or alpha(6), beta(2) and/or beta(3) subunit(s) of GABA(A) receptors in the rat brain. Ethanol (1-50 mM) neither affected [(3)H]muscimol (3 nM) binding nor diazepam-insensitive [(3)H]Ro 15-4513 (2 nM) binding in the rat cerebellum and cerebral cortex membranes. However, a higher concentration of ethanol (500 mM) inhibited the binding of these radioligands to the GABA(A) receptors partially in the rat cerebellum and cerebral cortex. Similarly, ethanol (up to 50 mM) did not affect [(3)H]muscimol (15 nM) binding to the immunoprecipitated delta-subunit-containing GABA(A) receptor assemblies in the rat cerebellum and hippocampus but it inhibited the binding partially at a higher concentration (500 mM). These results suggest that the native delta-subunit-containing GABA(A) receptors do not play a major role in the pharmacology of clinically relevant low concentrations of ethanol.

Effect of chronic administration of ethanol on the regulation of tyrosine kinase phosphorylation of the GABAA receptor subunits in the rat brain

One of the many pharmacological targets of ethanol is the GABA inhibitory system, and chronic ethanol (CE) is known to alter the polypeptide levels of the GABA(A )receptor subunits in rat brain regions. In the present study, we investigated the regulation of the tyrosine kinase phosphorylation of the GABA(A) receptor alpha(1)-, beta(2)- and gamma(2)-subunits in the rat cerebellum, cerebral cortex and hippocampus following chronic administration of ethanol to the rats. We observed either down-regulation or no change in the tyrosine kinase phosphorylation of the alpha(1) subunit, whereas there was an up-regulation or no change in the case of beta(2)- and gamma(2)-subunits of the GABA(A) receptors depending on the brain region following chronic administration of ethanol to the rats. These changes reverted back to the control level following 48 h of ethanol-withdrawal. These results suggest that tyrosine kinase phosphorylation of GABA(A )receptors may play a significant role in ethanol dependence.

Reproducible isolation of distinct, overlapping segments of the phosphoproteome

The ability to routinely analyze and quantitatively measure changes in protein phosphorylation on a proteome-wide scale is essential for biological and clinical research. We assessed the ability of three common phosphopeptide isolation methods (phosphoramidate chemistry (PAC), immobilized metal affinity chromatography (IMAC) and titanium dioxide) to reproducibly, specifically and comprehensively isolate phosphopeptides from complex mixtures. Phosphopeptides were isolated from aliquots of a tryptic digest of the cytosolic fraction of Drosophila melanogaster Kc167 cells and analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry. Each method reproducibly isolated phosphopeptides. The methods, however, differed in their specificity of isolation and, notably, in the set of phosphopeptides isolated. The results suggest that the three methods detect different, partially overlapping segments of the phosphoproteome and that, at present, no single method is sufficient for a comprehensive phosphoproteome analysis.

An integrated chemical, mass spectrometric and computational strategy for (quantitative) phosphoproteomics: application to Drosophila melanogaster Kc167 cells

Current methods for phosphoproteome analysis have several limitations. First, most methods for phosphopeptide enrichment lack the specificity to truly purify phosphopeptides. Second, fragmentation spectra of phosphopeptides, in particular those of phosphoserine and phosphothreonine containing peptides, are often dominated by the loss of the phosphate group(s) and therefore lack the information required to identify the peptide sequence and the site of phosphorylation, and third, sequence database search engines and statistical models for data validation are not optimized for the specific fragmentation properties of phosphorylated peptides. Consequently, phosphoproteomic data are characterized by large and unknown rates of false positive and false negative phosphorylation sites. Here we present an integrated chemical, mass spectrometric and computational strategy to improve the efficiency, specificity and confidence in the identification of phosphopeptides and their site(s) of phosphorylation. Phosphopeptides were isolated with high specificity through a simple derivatization procedure based on phosphoramidate chemistry. Identification of phosphopeptides, their site(s) of phosphorylation and the corresponding phosphoproteins was achieved by the optimization of the mass spectrometric data acquisition procedure, the computational tools for database searching and the data post processing. The strategy was applied to the mapping of phosphorylation sites of a purified transcription factor, dFOXO and for the global analysis of protein phosphorylation of Drosophila melanogaster Kc167 cells.

Phosphorylation-independent ubiquitylation and endocytosis of Fc gammaRIIA

Endocytosis of the Fc receptor Fc gammaRIIA depends on a functional ubiquitin conjugation system, and the receptor becomes ubiquitylated upon ligand binding. Phosphorylation of tyrosines in Fc gammaRIIA by Src family kinases is thought to be the initiating event in its signaling. However, although the Src family kinase inhibitor PP1 inhibited both ligand-induced phosphorylation of Fc gammaRIIA and phagocytosis in ts20 cells expressing Fc gammaRIIA, it did not inhibit receptor ubiquitylation or endocytosis of soluble ligands. Conversely, genistein and the proteasomal inhibitor MG132 did not inhibit receptor phosphorylation but strongly inhibited both receptor ubiquitylation and endocytosis. A region of the receptor lying within the immunoreceptor tyrosine-based activation motif was found to be necessary for both ubiquitylation and endocytosis. Ubiquitylation occurs at the plasma membrane before internalization. Endocytosis of Fc gammaRIIA is dependent on clathrin but independent of the adaptor protein AP-2. These findings point to a novel mechanism for ubiquitylation and endocytosis of this immunoreceptor.

Tyrosine kinase phosphorylation of GABAA receptor subunits following chronic ethanol exposure of cultured cortical neurons of mice

Previous studies from our laboratory revealed that acute ethanol exposure inhibits phosphorylation of mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinases (ERK) in mice. In the present study, we have further investigated effect of chronic administration of ethanol on tyrosine kinase phosphorylation of GABA(A) receptor subunits in the mouse cultured cortical neurons. We observed that there was an up-regulation in tyrosine kinase phosphorylation of the GABA(A) receptor beta(2) and gamma(2) subunits following chronic ethanol exposure, whereas there was no effect on alpha(1) subunit of the GABA(A) receptor in the cultured cortical neurons of mice as determined by Western blotting. These results suggest a potential role for tyrosine kinase phosphorylation of some of the GABA(A) receptor subunits in chronic ethanol-induced tolerance and dependence.

Bisperoxovanadium compounds are potent PTEN inhibitors

The tumour suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) shares homology with protein tyrosine phosphatases (PTPases). Similarly, bisperoxovanadium (bpV) molecules that are well-established PTPase inhibitors were shown to inhibit PTEN, but at up to 100-fold lower concentrations. The preference and potency of the bpVs towards PTEN was validated in vivo as demonstrated by: (i) an increase of Ser473 phosphorylation of protein kinase B (PKB) at similar low nanomolar doses, (ii) the lack of any effect on the PKB phosphorylation in the PTEN negative cell line UM-UC-3, (iii) the ability to rescue Ly294002-induced phosphoinositide 3-kinase inhibition and (iv) a lack of tyrosine phosphorylation at low nanomolar doses.

Viability and protein phosphorylation patterns of boar spermatozoa agglutinated by treatment with a cell-permeable cyclic adenosine 3',5'-monophosphate analog

Boar spermatozoa become agglutinated with one another at the head when their intracellular cyclic adenosine 3',5'-monophosphate (cAMP)-signaling cascades are activated in the head. The aim of the present study is to examine viability and protein phosphorylation patterns of cAMP-dependently agglutinated boar spermatozoa. Ejaculated spermatozoa were washed and then incubated in a modified Krebs-Ringer HEPES medium containing polyvinyl alcohol (mKRH-PVA) plus 0.1 mM Sp-5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole-3',5'-monophosphorothioate (cBiMPS, a cell-permeable cAMP analog) at 38.5 degrees C up to 180 minutes. Aliquots of the sperm suspensions were recovered after various incubation periods and then used to examine the state of agglutination, the viability by SYBR14-PI staining and motility assay, and the state of protein phosphorylation by Western blotting and indirect immunofluorescence. In the control samples incubated without cBiMPS for 180 minutes, less than 30% of the total spermatozoa were agglutinated with one another at the heads, and more than 70% of the agglutinated spermatozoa were propidium iodide (PI)-positive (dead). However, the incubation with cBiMPS rapidly increased the percentages of head-to-head agglutinated spermatozoa to approximately 60% within 30 minutes, but did not significantly change them thereafter. In the samples incubated with cBiMPS for 180 minutes, moreover, the percentages of PI-positive cells of the agglutinated spermatozoa (approximately 30%) were significantly lower than those obtained in the control samples (more than 70%). This result was supported by the observation that the percentages of motile cells of the agglutinated spermatozoa were much higher in the samples incubated with cBiMPS for 180 minutes than in the control samples incubated without cBiMPS. As revealed by Western blotting and indirect immunofluorescence, cBiMPS-induced serine/threonine phosphorylation of the proteins (eg, >220 kd, 220 kd, 180 kd, 84 kd, and 54 kd) appeared mainly in the connecting and principal pieces of both agglutinated and free spermatozoa within 30 minutes, and additional phosphorylation occurred in the middle piece later than 30 minutes. Moreover, tyrosine phosphorylation of the proteins (eg, >220 kd, 190 kd, 93 kd, 59 kd, 54 kd, and 32 kd) was induced intensely in the connecting and principal pieces and moderately in the middle piece of almost one half of the agglutinated spermatozoa after incubation with cBiMPS for more than 30 minutes, but rarely in those of the free spermatozoa. These findings are consistent with the following suggestions: activation of the cAMP-signaling cascades leads to rapid (within 30 minutes) head-to-head agglutination in live spermatozoa; rapid (within 30 minutes) protein serine/threonine phosphorylation in the connecting and principal pieces of both cAMP-dependently agglutinated and free spermatozoa and subsequent (later than 30 minutes) phosphorylation in the middle piece of them; and slow (later than 30 minutes) protein tyrosine phosphorylation in the connecting, middle, and principal pieces of the cAMP-dependently agglutinated spermatozoa. Based on these suggestions, we conclude that many of cAMP-dependently agglutinated spermatozoa are live cells in which cAMP-signaling cascades leading to protein serine/threonine and tyrosine phosphorylation are activated in the whole flagellum.

Phosphorylated tyrosine-containing proteins in primary lung cancer correlates with proliferation and prognosis

To determine the usefulness of tyrosine phosphorylation in evaluating biological characteristics, we attempted to evaluate the relationship between the amount of phosphorylated tyrosine-containing proteins and clinicopathological factors, cell proliferation and outcome in non-small cell lung cancer. To evaluate phosphorylated tyrosine-containing proteins we used 96 surgically resected materials of non-small cell lung cancer and normal peripheral lung, while immunohistochemical evaluation was performed. Cell proliferating ability was evaluated using the labelling index of proliferating cell nuclear antigen-positive nuclear staining cells. There were statistically significant differences between the expression levels of phosphorylated tyrosine-containing proteins of normal and cancerous tissues (P<0.0001). Evaluations based on clinicopathological factors apart from histopathological differentiation, showed no statistically significant differences of phosphorylated tyrosine-containing proteins expression. However, phosphorylated tyrosine-containing proteins correlated with cell proliferation activity evaluated (P((Low, High))<0.0001; P((Low, Int)) <0.0001; P((Int, High))<0.0001). Furthermore, non-small cell lung cancer cases with high expression and intermediate expression of phosphorylated tyrosine-containing proteins had a significantly shorter disease-free postoperative survival than those with low expression of phosphorylated tyrosine-containing proteins using log-rank analysis (P((Low, Int)) <0.0028; P((Low, High))=0.0002). Furthermore, phosphorylated tyrosine-containing proteins expression level statistically contributed to disease-free survival in Cox's proportional hazard model. Therefore, phosphorylated tyrosine-containing proteins in non-small cell lung cancer tissues seem to reflect its biological malignancy, and this evaluation may be valuable for constructing the most appropriate therapeutic strategy.

Phosphatidylinositol 3-kinase regulates PMA-induced differentiation and superoxide production in HL-60 cells

Treatment of the human promyelocytic leukemia cell line HL-60 with phorbol myristate acetate (PMA) is associated with induction of monocytic or myelocytic differentiation. Since phosphatidylinositol 3-kinase (PI3-kinase) is a critical player in cell proliferation, survival, and differentiation, we studied the role of PI3-kinase during induction of the differentiated monocytic phenotype and superoxide production. In treatment of HL-60 cells with PMA, the PI3-kinase inhibitors LY294002 and wortmannin inhibited cell adhesion and spreading and phagocytic activity. LY294002 and wortmannin also inhibited the proliferation of HL-60 cells. During PMA-induced monocytic differentiation, LY294002 induced apoptosis in a dose dependent manner. The phosphorylation of p85alpha derived from PMA-stimulated HL-60 cells was shown in the time dependent manner. However, p70 S6 kinase inhibitor, rapamycin, did not inhibit PMA-induced monocytic differentiation. During PMA-induced monocytic differentiation, LY294002 inhibited c-jun protein expression and decrease of c-myc protein level. In contrast, LY294002 induced production of superoxide in the HL-60 cells stimulated with forskolin. Moreover, staurosporine and H7, PKC inhibitors, enhanced superoxide production in dibutyryl cAMP-induced HL-60 cells. These results suggest that PI3-kinase may regulate PMA-induced differentiation signal and provide a crucial link between PKC and cAMP in HL-60 cells.

Phosphatidylinositol 3-kinase regulates proliferation of RAW 264.7 macrophages

Phosphatidylinositol 3-kinase (P13-kinase) is an enzyme that acts as a direct biochemical link between a novel phosphatidylinositol pathway and a number of proteins containing intrinsic or associated kinase activities. Here we demonstrate that wortmannin, P13-kinase inhibitor, decreases the proliferation of RAW 264.7 macrophages and that another structurally unrelated inhibitor of P13-kinase, LY294002. also inhibits the proliferation. These results indicate a possible involvement of P13-kinase in RAW 264.7 macrophages growth regulation. Wortmannin stimulation of RAW 264.7 macrophages is followed by sustained expression of the mRNA of c-fos and a transient expression of the mRNA of c-jun. We also show that the wortmannin and LY294002 induce a cell cycle arrest in asynchronously growing cells leading to an inhibition of cell proliferation after 12 h of treatment. In addition, wortmannin or LY294002 inhibited the phorbol 12-myristate 13-acetate-induced macrophages proliferation potently. These results suggest that P13-kinase plays an important role in growth regulation of RAW 264.7 macrophages and that protein kinase C is a down stream effector of P13-kinase.

Interaction of fusarium mycotoxins, fusaproliferin and fumonisin B1, with DNA studied by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) in negative ion mode was used to monitor the possible noncovalent adduct formations between DNA analogue oligonucleotides and two Fusarium mycotoxins, fumonisin B1 and fusaproliferin. Using mild experimental ESI conditions specific noncovalent interactions were detected between both single- and double-stranded model oligonucleotides and fusaproliferin with 1:1 stoichiometry. Similar association complexes were observed for the deacetyl derivative of fusaproliferin. There were no peaks due to adduct formation present in the mass spectra of fumonisin B1, incubated with oligonucleotides in a wide concentration range, suggesting no specific interaction for this molecule. In a competitive complexation reaction, another mycotoxin, the beauvericin, forms more stable association complex with DNA than fusaproliferin. These findings can be of use in the understanding of molecular mechanisms of action during apoptosis and can be correlated with the teratogenic effect of fusaproliferin.

A role for phosphorylation of glycogen synthase kinase-3alpha in bovine sperm motility regulation

The long-term goal of our work is to understand biochemical mechanisms underlying sperm motility and fertility. In a recent study we showed that tyrosine phosphorylation of a 55-kDa protein varied in direct proportion to motility. Tyrosine phosphorylation of the protein was low in immotile compared to motile epididymal sperm. Inhibition or stimulation of motility by high calcium levels or cAMP, respectively, results in a corresponding decrease or increase in tyrosine phosphorylation of the 55-kDa protein. Here we report purification and identification of this motility-associated protein. Soluble extracts from bovine caudal epididymal sperm were subjected to DEAE-cellulose, Affi-Gel blue, and cellulose phosphate chromatography. Tyrosine phosphate immunoreactive fractions contained glycogen synthase kinase-3 (GSK-3) activity, suggesting a possible correspondence between these proteins. This suggestion was verified by Western blot analyses following one-dimensional and two-dimensional gel electrophoresis of the purified protein using monoclonal and affinity-purified polyclonal antibodies against the catalytic amino-terminus and carboxy-terminus regions of GSK-3. Further confirmation of the identity of these proteins came from Western blot analysis using antibodies specific to the tyrosine phosphorylated GSK-3. Using this antibody, we also showed that GSK-3 tyrosine phosphorylation was high in motile compared to immotile sperm. Immunocytochemistry revealed that GSK-3 is present in the flagellum and the anterior portion of the sperm head. These data suggest that GSK-3, regulated by phosphorylation, could be a key element underlying motility initiation in the epididymis and regulation of mature sperm function.

Granulocyte-macrophage colony-stimulating factor-activated signaling pathways in human neutrophils. Involvement of Jak2 in the stimulation of phosphatidylinositol 3-kinase

Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates many of the biological activities of human neutrophils. The signaling pathways via which these effects are mediated are not fully understood. We have shown previously that GM-CSF treatment of human neutrophils activates the Janus kinase/signal transducers and activators of transcription (Jak/STAT) pathway and, more specifically, Jak2, STAT3, and STAT5B in neutrophils. GM-CSF also stimulates the activity of the phosphatidylinositol 3-kinase (PI3-kinase) in a tyrosine kinase-dependent manner. Here we report that pretreating the cells with a Jak2 inhibitor (AG-490) abolishes tyrosine phosphorylation of the p85 subunit of PI3-kinase induced by GM-CSF. Furthermore, p85 was found to associate with Jak2, but not with Lyn, in stimulated cells in situ and with its autophosphorylated form in vitro; however, Jak2 did not bind to either of the two Src homology 2 (SH2) domains of the p85 subunit of PI3-kinase. Although STAT5B bound to the carboxyl-terminal SH2 domain of p85, it was absent from the complex containing PI3-kinase and Jak2. These results suggest that stimulation of the activity of PI3-kinase induced by GM-CSF is mediated by Jak2 and that the association between Jak2 and p85 depends on an adaptor protein yet to be identified.

mcl-1 is an immediate-early gene activated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway and is one component of the GM-CSF viability response

mcl-1, a bcl-2 family member, was originally identified as an early gene induced during differentiation of ML-1 myeloid leukemia cells. In the present study, we demonstrate that Mcl-1 is tightly regulated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway. Upon deprivation of survival factor from TF-1 myeloid progenitor cells, Mcl-1 levels quickly dropped prior to visible detection of apoptosis of these cells. Upon restimulation of these deprived cells with GM-CSF, the mcl-1 mRNA was immediately induced and its protein product was accordingly resynthesized. Analysis with Ba/F3 cells expressing various truncation mutants of the GM-CSF receptor revealed that the membrane distal region between amino acids 573 and 755 of the receptor beta chain was required for mcl-1 induction. Transient-transfection assays with luciferase reporter genes driven by various regions of the mcl-1 promoter demonstrated that the upstream sequence between -197 and -69 is responsible for cytokine activation of the mcl-1 gene. Overexpression of mcl-1 delayed but did not completely prevent apoptosis of cells triggered by cytokine withdrawal. Its down regulation by antisense constructs overcame, at least partially, the survival activity of GM-CSF and induced the apoptosis of TF-1 cells. Taken together, these results suggest that mcl-1 is an immediate-early gene activated by the cytokine receptor signaling pathway and is one component of the GM-CSF viability response.

Proliferative reaction of myelogenous leukemia cells with cytokines G-CSF, GM-CSF, M-CSF, SCF and TPO

In recent years, many cytokines have been defined and some of them used clinically. In hematological malignancies, cytokines, including granulocyte colony-stimulating factor (G-CSF), have been widely used for leukopenia after chemotherapy. However, in acute myelogenous leukemia (AML), some leukemic cells may be induced to proliferate by these cytokines and they must be used with care. In this study, we have investigated cell reactivity and proliferation with G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CMF), macrophage colony-stimulating factor (M-CSF), stem cell factor (SCF) and thrombopoietin (TPO) in cases of AML. We have also investigated the reactivity of some myeloid leukemia cell lines to TPO. G-CSF, GM-CSF, M-CSF, SCF and TPO caused proliferation of leukemic cells in 25%, 58.3%, 8.3%, 21.1% and 0% of cases, respectively. Because of this result, the use of G-CSF in AML should be regarded as potentially hazardous. TPO did not cause proliferation of leukemic cells in any case of AML, or in cell lines except MO7E, which is a megakaryocytic cell line. This result suggests that TPO might cause proliferation of some megakaryocytic leukemia cells. We cannot conclude that TPO does not cause proliferation of other AML cells, as the number of cases was small and it has been reported elsewhere that leukemia cells may proliferate when exposed to TPO in 50% of AML cases. Reactivity of AM L cells to TPO is an important factor when deciding the indications of TPO in AML and myelodysplastic syndrome.

Granulocyte-Macrophage Colony-Stimulating Factor–Activated Signaling Pathways in Human Neutrophils. I. Tyrosine Phosphorylation-Dependent Stimulation of Phosphatidylinositol 3-Kinase and Inhibition by Phorbol Esters

Phosphatidylinositol 3-kinase (PI3-kinase) is a cytosolic enzyme that plays key roles in mediating signaling through many receptors. The heterodimeric form of PI3-kinase is made up of a regulatory subunit, p85, and a catalytic subunit, p110. Although granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to activate PI3-kinase, the mechanisms by which this activation is mediated and regulated are incompletely understood. Here we show that treatment of human neutrophils with GM-CSF induced both time- and concentration-dependent increases in the level of tyrosine phosphorylation of p85. The ability of GM-CSF to activate PI3-kinase was abolished by pretreating the cells with erbstatin, a tyrosine kinase inhibitor. The simultaneous treatment of the cells with GM-CSF and phorbol esters such as phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBu) significantly inhibited both the tyrosine phosphorylation of p85 and the activation of PI3-kinase. The inhibitory effects of phorbol esters were not induced by their inactive analogues and they were selective to the stimulation of tyrosine phosphorylation of p85 since phorbol esters did not alter the enhancement of the pattern of tyrosine phosphorylation of other cellular proteins, including that of Jak2 induced by GM-CSF. However, PMA significantly inhibited the in situ tyrosine phosphorylation and the activation of lyn observed in response to GM-CSF. The results suggest that the activation of PI3-kinase by GM-CSF is mediated by the tyrosine phosphorylation of p85 and that this activation is downregulated by PKC possibly via the inhibition of lyn.

Immunoprecipitation of a phospholipase D activity with antiphosphotyrosine antibodies

When granulocyte-macrophage colony-stimulating factor (GM-CSF)-treated human neutrophils were challenged with the chemotactic factor fMet-Leu-Phe, it was possible to detect a time-dependent increase in the hydrolytic (as measured by the production of phosphatidic acid, PA) and the transphosphatidylation (as measured by the production of phosphatidylethanol, PEt) activities of phospholipase D in intact cells prelabeled with a radioactive fatty acid. Both activities were inhibited by preincubation of cells with genistein. Appropriate conditions were developed to test the PLD transphosphatidylation activity against exogenous phosphatidylcholine (PCho) in an in vitro system. As in intact cells, increased PLD activity could be detected in cell lysates obtained from fMet-Leu-Phe-treated cells compared with controls. When lysates were immunoprecipitated with antiphosphotyrosine antibodies, a PLD activity was found only in immune complexes that were prepared from fMet-Leu-Phe-treated cells. Conversely, no activity was found in lysates immunoprecipitated with an irrelevant antibody (GTPase-activating protein, GAP) that nevertheless was able to recognize a tyrosylphosphorylated form of GAP, as demonstrated by western blotting. These data suggest that a PCho-PLD, or a tightly bound protein, is tyrosine phosphorylated during cell activation.

Inhibition of the T-cell receptor-mediated signal transduction by microinjection of anti-Lck monoclonal antibody into T-cells

Engagement of T-cell receptor (TcR)/CD3 complexes on T-cells rapidly provokes tyrosine phosphorylation of cellular proteins, which is thought to be an essential step to the following events of T-cell activation. p56lck, a member of src-related, non-receptor type protein tyrosine kinases, is expressed predominantly in lymphocytes. Accumulating data suggest that p56lck is one of the kinases responsible for TcR-mediated protein tyrosine phosphorylation. To investigate the role of p56lck in TcR-signaling in detail, we injected anti-Lck monoclonal antibody (mAb), MOL171 or MOL294, both specifically suppress Lck kinase activity in vitro, into Jurkat T-cells by the erythrocyte-ghost procedure in order to block the activity of p56lck. In Jurkat cells injected with anti-Lck mAb, intracellular Ca2+ mobilization induced by TcR-stimulation was markedly reduced in comparison with control mouse IgG-injected samples. This block of Ca2+ influx seems to be specific for TcR-signaling because anti-Lck mAb-injection did not cause significant suppression of phytohaemagglutinin-induced Ca2+ increase. Furthermore, injection of anti-Lck mAb inhibited TcR-mediated protein tyrosine phosphorylation of 100 kDa protein and phospholipase C gamma 1. These results confirm that p56lck is an indispensable element of TcR-signaling and p100 and phospholipase C gamma 1 are strongly presumed to be candidates for substrates for p56lck.

Protein kinase C inhibitors, H7 and calphostin C, inhibit induction of DNA synthesis by cytosolic extracts of exponentially growing neuroblastoma cells in isolated nuclei

Cytoplasmic extracts from proliferating Neuro-2a cells contain a protein factor, ADR (activator of DNA replication) that induces DNA synthesis in isolated quiescent nuclei. Cytoplasmic extracts derived from quiescent-made Neuro-2a cells contain none or very little ADR activity, but this activity can be generated after a brief exposure of cytosolic extracts to a membrane-enriched fraction derived from exponentially growing Neuro-2a cells. ADR activity appears at the beginning of the S phase of the cell cycle. Moreover it appears to be a protease, because aprotinin inhibits ADR activity. ADR activity can be also inhibited by the protein kinase C inhibitors, 1-(5-isoquinoline-sulfonyl)-2- methylpiperazine (H7) and calphostin C.

Isolation and characterization of Bsk, a growth factor receptor-like tyrosine kinase associated with the limbic system

Neuronal degeneration has been shown to be involved in various neurological disorders. Growth/trophic factors and their receptors are known to be important for the regeneration and survival of neurons. We report here the molecular cloning of a receptor-like protein tyrosine kinase, bsk, (for brain specific kinase). Bsk is highly related to the eph/elk receptor-like kinase family members. Northern blot analysis shows that it is expressed specifically in the brain, with no expression detected in adult heart, spleen, lung, liver, skeletal muscle, and kidney. In situ hybridization analysis of adult mouse brain sections indicates that bsk is expressed at high levels in the hippocampus, tenia tecta, indusium griseum, and the piriform cortex, major components of the limbic system that are important for learning and memory. In addition, elevated levels of expression are found in other areas of the limbic system such as the amygdala, medial septum, and nucleus of the diagonal band, and in the olfactory bulb, which has close connections to the limbic system. The highest level of expression is found in the CA3 region of the hippocampus and the pyramidal cell layer of the piriform cortex. In 16.5 day mouse embryos, bsk is expressed predominantly in the primordial cortex of the telencephalon. An antibody against a C-terminal peptide of bsk recognized a 105 kD protein in the 16.5 day embryonic head extract. Our analysis shows that bsk is a growth factor receptor-like protein tyrosine kinase and that its greatest expression in the adult brain is associated with components of the limbic system.

Expression, function and activation of the proto-oncogene c-kit product in human leukemia cells

The c-kit proto-oncogene encodes a receptor tyrosine kinase that is considered to play important roles in hematopoiesis. The proto-oncogene c-kit product is expressed on various types of human cell lines derived from leukemic cells of erythroid, megakaryocytic and mast-cell lineages. Also, the c-kit product is detectable in blast cells in most cases of acute myeloblastic leukemia (AML) and in some cases of chronic myelogenous leukemia (CML) in blastic crisis (BC). By contrast, little or no expression of c-kit is observed in human leukemia cell lines of lymphoid lineage and in blast cells in acute lymphoblastic leukemia (ALL). Tyrosine phosphorylation and activation of the c-kit product with the ligand for c-kit (stem cell factor: SCF) results in proliferation of some human leukemia cell lines, such as M07E, and blast cells in a substantial fraction of AML cases. In addition, SCF appears to have an activity in inducing differentiation of certain types of leukemic cells. In some cases, further, the c-kit product is found to be activated in leukemic cells even before the stimulation with SCF. These results suggest that c-kit may be involved in excessive proliferation and aberrant differentiation of human leukemia cells.

GM-CSF triggers a rapid, glucose dependent extracellular acidification by TF-1 cells: evidence for sodium/proton antiporter and PKC mediated activation of acid production

The extracellular acidification rate of the human bone marrow cell line, TF-1, increases rapidly in response to a bolus of recombinant granulocyte-macrophage colony stimulating factor (GM-CSF). Extracellular acidification rates were measured using a silicon microphysiometer. This instrument contains micro-flow chambers equipped with potentiometric sensors to monitor pH. The cells are immobilized in a fibrin clot sandwiched between two porous polycarbonate membranes. The membranes are part of a disposable plastic "cell capsule" that fits into the microphysiometer flow chamber. The GM-CSF activated acidification burst is dose dependent and can be neutralized by pretreating the cytokine with anti-GM-CSF antibody. The acidification burst can be resolved kinetically into at least two components. A rapid component of the burst is due to activation of the sodium/proton antiporter as evidenced by its elimination in sodium-free medium and in the presence of amiloride. A slower component of the GM-CSF response is a consequence of increased glycolytic metabolism as demonstrated by its dependence on D-glucose as a medium nutrient. Okadaic acid (a phospho-serine/threonine phosphatase inhibitor), phorbol 12-myristate 13-acetate (PMA, a protein kinase C (PKC) activator), and ionomycin (a calcium ionophore) all produce metabolic bursts in TF-1 cells similar to the GM-CSF response. Pretreatment of TF-1 cells with PMA for 18 h resulted in loss of the GM-CSF acidification response. Although this treatment is reported to destroy protein kinase activity, we demonstrate here that it also down-regulates expression of high-affinity GM-CSF receptors on the surface of TF-1 cells. In addition, GM-CSF driven TF-1 cell proliferation was decreased after the 18 h PMA treatment. Short-term treatment with PMA (1-2 h) again resulted in loss of the GM-CSF acidification response, but without a decrease in expression of high-affinity GM-CSF receptors. Evidence for involvement of PKC in GM-CSF signal transduction was obtained using calphostin C, a specific inhibitor of PKC, which inhibited the GM-CSF metabolic burst at a subtoxic concentration. Genistein and herbimycin A, tyrosine kinase inhibitors, both inhibited the GM-CSF response of TF-1 cells, but only at levels high enough to also inhibit stimulation by PMA. These results indicate that GM-CSF activated extracellular acidification of TF-1 cells is caused by increases in sodium/proton antiporter activity and glycolysis, through protein kinase signalling pathways which can be both activated and down-regulated by PMA.

Granulocyte-macrophage colony-stimulating factor and steel factor induce phosphorylation of both unique and overlapping signal transduction intermediates in a human factor-dependent hematopoietic cell line

Steel factor (SF), the ligand for the proto-oncogene c-kit, acts synergistically with GM-CSF or IL-3 to support the growth of normal human hematopoietic progenitor cells. We examined the effects of SF on GM-CSF or IL-3 induced proliferation of a human factor-dependent cell line, MO7. SF supported MO7 cell proliferation as well as IL-3 or GM-CSF alone, and its addition dramatically enhanced (three- to sixfold) maximal GM-CSF or IL-3 stimulated proliferation. SF did not increase the number or affinity of cell surface GM-CSF receptors. We examined several early events of signal transduction in an effort to elucidate the biochemical mechanisms of synergy of these factors. Since each of these three cytokines is believed to function in part through activation of a tyrosine kinase, we examined their effects on cellular phosphotyrosine containing proteins. Each cytokine induced rapid, transient, and concentration dependent tyrosine phosphorylation of a number of substrates. For GM-CSF and IL-3, these phosphoproteins were indistinguishable (150, 125, 106, 93, 80, 79, 73, 44, 42, and 36 kDa), while SF induced major or minor tyrosine phosphorylation of 205, 140-150, 116, 106, 94, 90, 80, 79, 73, 44, 42, 39, 36, 32 kDa phosphoproteins. Two other signal transduction intermediates known to be phosphorylated and activated by GM-CSF and IL-3, the 70-75 kDa Raf-1 kinase, and p42 mitogen-activated protein kinase-2 (MAPK), were also phosphorylated by SF. Combinations of GM-CSF or IL-3 with SF did not further increase the phosphorylation of Raf-1 or p42 MAPK when compared to any of the factors alone. In contrast SF, but not GM-CSF or IL-3, induced tyrosine phosphorylation of phospholipase C-gamma (PLC-gamma). These results indicate that SF and GM-CSF/IL-3 have partially overlapping effects on early signal transducing events, as well as striking differences, such as tyrosine phosphorylation of PLC-gamma. This cell line should provide a useful model system to investigate the complicated process of hematopoietic growth factor synergy.

Granulocyte-macrophage colony-stimulating factor primes phospholipase D activity in human neutrophils in vitro: role of calcium, G-proteins and tyrosine kinases

The addition of granulocyte-macrophage colony-stimulating factor (GM-CSF) to human peripheral blood neutrophils primes phospholipase D (PLD) to subsequent stimulation by N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate (PMA). The present investigation was directed at the elucidation of the pathway(s) involved in the regulation of the activity of PLD in untreated as well as in GM-CSF-primed neutrophils. Pretreatment with pertussis toxin (PT) totally inhibited fMLP-induced activation of PLD in control or GM-CSF-treated cells. PT did not affect the activation of PLD by PMA but inhibited the priming effect of GM-CSF. Activation of PLD by fMLP was dose-dependently inhibited by erbstatin, an inhibitor of tyrosine kinases. Furthermore, pre-incubation with GM-CSF accelerated the tyrosine phosphorylation response to fMLP (as analysed by protein immunoblot with antiphosphotyrosine antibodies). In PMA-stimulated neutrophils, erbstatin antagonized the priming effect of GM-CSF on PLD without affecting the direct effects of the phorbol ester. Buffering cytoplasmic calcium with the chelator BAPTA inhibited fMLP-induced activation of PLD as monitored by the formation of phosphatidylethanol. The stimulation of PLD by PMA was partially attenuated in BAPTA-loaded cells while the priming effect of GM-CSF was abolished. Thus, priming of human neutrophil PLD by GM-CSF may be mediated by G-proteins, by increases in the levels of cytosolic free calcium, and by stimulation of protein kinase C and/or tyrosine kinase(s).