Expression of the mammalian c-fes protein in hematopoietic cells and identification of a distinct fes-related protein

Targeting Tyrosine Kinases in Acute Myeloid Leukemia: Why, Who and How?

Acute myeloid leukemia (AML) is a myeloid malignancy carrying a heterogeneous molecular panel of mutations participating in the blockade of differentiation and the increased proliferation of myeloid hematopoietic stem and progenitor cells. The historical "3 + 7" treatment (cytarabine and daunorubicin) is currently challenged by new therapeutic strategies, including drugs depending on the molecular landscape of AML. This panel of mutations makes it possible to combine some of these new treatments with conventional chemotherapy. For example, the FLT3 receptor is overexpressed or mutated in 80% or 30% of AML, respectively. Such anomalies have led to the development of targeted therapies using tyrosine kinase inhibitors (TKIs). In this review, we document the history of TKI targeting, FLT3 and several other tyrosine kinases involved in dysregulated signaling pathways.

Dual Roles of Fer Kinase Are Required for Proper Hematopoiesis and Vascular Endothelium Organization during Zebrafish Development

Fer kinase, a protein involved in the regulation of cell-cell adhesion and proliferation, has been shown to be required during invertebrate development and has been implicated in leukemia, gastric cancer, and liver cancer. However, in vivo roles for Fer during vertebrate development have remained elusive. In this study, we bridge the gap between the invertebrate and vertebrate realms by showing that Fer kinase is required during zebrafish embryogenesis for normal hematopoiesis and vascular organization with distinct kinase dependent and independent functions. In situ hybridization, quantitative PCR and fluorescence activated cell sorting (FACS) analyses revealed an increase in both erythrocyte numbers and gene expression patterns as well as a decrease in the organization of vasculature endothelial cells. Furthermore, rescue experiments have shown that the regulation of hematopoietic proliferation is dependent on Fer kinase activity, while vascular organizing events only require Fer in a kinase-independent manner. Our data suggest a model in which separate kinase dependent and independent functions of Fer act in conjunction with Notch activity in a divergent manner for hematopoietic determination and vascular tissue organization.

Pathological significance and predictive value for biochemical recurrence of c-Fes expression in prostate cancer

BACKGROUND

c-Fes is a proto-oncogene encoded non-receptor protein-tyrosine kinase (PTK). However, genetic studies have indicated that it has anti-tumorigenic effects in certain cancers. The pathological and clinical significance of c-Fes in prostate cancer are unknown.

METHODS

Expression of c-Fes was evaluated in normal glands, prostatic intraepithelial neoplasia (PIN), cancer cells in tissues of knock-in mouse adenocarcinoma prostate (KIMAP) model, and prostate cancer patients free of metastasis. Expression of c-Fes was analyzed by immunohistochemistry, and quantified by using the immunoreactivity score (IRS) (staining intensity × percentage of positive cells). Relationships between c-Fes expression and pT stage, Gleason's score (GS), and biochemical recurrence in patients who underwent radical surgery were also investigated.

RESULTS

In KIMAP, the percentage in normal glands, PIN and cancer cells positive for c-Fes expression were 0 (0/7), 25.0 (2/8), and 100% (7/7), respectively. In human tissues, c-Fes expression was also significantly higher in cancer cells than in normal cells and PIN, and it correlated with pT stage (P < 0.001) and GS (P = 0.047). Multivariate analysis showed that c-Fes expression was an independent predictor of poor outcome poor prognosis (hazard ratio = 3.21, 95% confidence interval = 1.11-9.37, P = 0.032).

CONCLUSION

The results suggested that c-Fes expression is a useful predictor of biochemical recurrence after radical surgery. The results also suggested that c-Fes is a potentially useful therapeutic target in prostate cancer and a predictor of biochemical recurrence after radical prostatectomy.

The Fps/Fes kinase regulates leucocyte recruitment and extravasation during inflammation

Fps/Fes and Fer comprise a distinct subfamily of cytoplasmic protein-tyrosine kinases, and have both been implicated in the regulation of innate immunity. Previous studies showed that Fps/Fes-knockout mice were hypersensitive to systemic lipopolysaccharide (LPS) challenge, and Fer-deficient mice displayed enhanced recruitment of leucocytes in response to localized LPS challenge. We show here for the first time, a role for Fps in the regulation of leucocyte recruitment to areas of inflammation. Using the cremaster muscle intravital microscopy model, we observed increased leucocyte adherence to venules, and increased rates and degrees of transendothelial migration in Fps/Fes-knockout mice relative to wild-type animals subsequent to localized LPS challenge. There was also a decreased vessel wall shear rate in the post-capillary venules of LPS-challenged Fps/Fes-knockout mice, and an increase in neutrophil migration into the peritoneal cavity subsequent to thioglycollate challenge. Using flow cytometry to quantify the expression of surface molecules, we observed prolonged expression of the selectin ligand PSGL-1 on peripheral blood neutrophils from Fps/Fes-knockout mice stimulated ex vivo with LPS. These observations provide important insights into the observed in vivo behaviour of leucocytes in LPS-challenged Fps/Fes-knockout mice and provide evidence that the Fps/Fes kinase plays an important role in the innate immune response.

The Fps/Fes kinase regulates the inflammatory response to endotoxin through down-regulation of TLR4, NF-kappaB activation, and TNF-alpha secretion in macrophages

Fps/Fes and Fer are members of a distinct subfamily of cytoplasmic protein tyrosine kinases that have recently been implicated in the regulation of innate immunity. Previous studies showed that mice lacking Fps/Fes are hypersensitive to systemic LPS challenge, and Fer-deficient mice displayed enhanced recruitment of leukocytes in response to local LPS challenge. This study identifies physiological, cellular, and molecular defects that contribute to the hyperinflammatory phenotype in Fps/Fes null mice. Plasma TNF-alpha levels were elevated in LPS challenged Fps/Fes null mice as compared with wild-type mice and cultured Fps/Fes null peritoneal macrophages treated with LPS showed increased TNF-alpha production. Cultured Fps/Fes null macrophages also displayed prolonged LPS-induced degradation of IkappaB-alpha, increased phosphorylation of the p65 subunit of NF-kappaB, and defective TLR4 internalization, compared with wild-type macrophages. Together, these observations provide a likely mechanistic basis for elevated proinflammatory cytokine secretion by Fps/Fes null macrophages and the increased sensitivity of Fps/Fes null mice to endotoxin. We posit that Fps/Fes modulates the innate immune response of macrophages to LPS, in part, by regulating internalization and down-regulation of the TLR4 receptor complex.

Spatial and temporal changes in the subcellular localization of the nuclear protein-tyrosine kinase, c-Fes

Tyrosine phosphorylation has emerged as a mechanism to control cellular events in the nucleus. The c-Fes protein-tyrosine kinase is an important regulator of cell growth and differentiation in several cell types, and is found in the nucleus of hematopoietic cells. In this study, we showed nuclear localization of c-Fes in both hematopoietic (K562, TF-1, HEL, U937, and HL-60) and nonhematopoietic cell lines (293T, CaOv3, TfxH, MG-63, HeLa, DU-145) by immunofluorescence and confocal microscopy. c-Fes showed striking changes in subcellular localization at specific stages of mitosis. In interphase cells, the intranuclear distribution of c-Fes was diffuse with occasional bright foci. Some c-Fes was present in the cytosol after breakdown of the nuclear membrane, in prometaphase. At prometaphase and metaphase c-Fes was also associated with the chromosomes, in a punctate pattern that partially overlapped with the centromere. Further comparison with proteins that are known components of the kinetochore suggested that some c-Fes protein was located at the centromeric alpha-satellite DNA, between the kinetochores. At anaphase and telophase, c-Fes was entirely cytoplasmic and no protein was found associated with the chromosomes. The timing of c-Fes' appearance at the centromere coincides with the period of kinetochore assembly. These data suggest that c-Fes is recruited to the kinetochore during mitosis.

Expression of c-Fes Protein Isoforms Correlates with Differentiation in Myeloid Leukemias

The cellular fes gene encodes a 93-kilodalton protein-tyrosine kinase (p93) that is expressed in both normal and neoplastic myeloid cells. Increased c-Fes expression is associated with differentiation in normal myeloid cells and cell lines. Our hypothesis was that primary leukemia cells would show a similar pattern of increased expression in more differentiated cells. Therefore, we compared c-Fes expression in cells with an undifferentiated, blast phenotype (acute myelogenous leukemia--AML) to cells with a differentiated phenotype (chronic myelogenous leukemia--CML). Instead of differences in p93 expression levels, we found complex patterns of c-Fes immunoreactive proteins that corresponded with differentiation in normal and leukemic myeloid cells. The "blast" pattern consisted of c-Fes immunoreactive proteins p93, p74, and p70; the "differentiated" pattern showed two additional c-Fes immunoreactive proteins, p67 and p62. Using mRNA from mouse and human cell lines, we found deletion of one or more exons in the c-fes mRNA. Those deletions predicted truncation of conserved domains (CDC15/FCH and SH2) involved in protein-protein interactions. No deletions were found, however, within the kinase domain. We infer that alternative splicing generates a family of c-Fes proteins. This may be a mechanism to direct the c-Fes kinase domain to different subcellular locations and/or substrates at specific stages of myeloid cell differentiation.

Activated Fps/Fes tyrosine kinase regulates erythroid differentiation and survival

OBJECTIVE

A substantial body of evidence implicates the cytoplasmic protein tyrosine kinase Fps/Fes in regulation of myeloid differentiation and survival. In this study we wished to determine if Fps/Fes also plays a role in the regulation of erythropoiesis.

METHODS

Mice tissue-specifically expressing a "gain-of-function" mutant fps/fes transgene (fps(MF)) encoding an activated variant of Fps/Fes (MFps), were used to explore the in vivo biological role of Fps/Fes. Erythropoiesis in these mice was assessed by hematological analysis, lineage marker analysis, bone-marrow colony assays, and biochemical approaches.

RESULTS

fps(MF) mice displayed reductions in peripheral red cell counts. However, there was an accumulation of immature erythroid precursors, which displayed increased survival. Fps/Fes and the related Fer kinase were both detected in early erythroid progenitors/blasts and in mature red cells. Fps/Fes was also activated in response to erythropoietin (EPO) and stem cell factor (SCF), two critical factors in erythroid development. In addition, increased Stat5A/B activation and reduced Erk1/2 phosphorylation was observed in fps(MF) primary erythroid cells in response to EPO or SCF, respectively.

CONCLUSIONS

These data support a role for Fps/Fes in regulating the survival and differentiation of erythroid cells through modulation of Stat5A/B and Erk kinase pathways induced by EPO and SCF. The increased numbers and survival of erythroid progenitors from fps(MF) mice, and their differential responsiveness to SCF and EPO, implicates Fps/Fes in the commitment of multilineage progenitors to the erythroid lineage. The anemic phenotype in fps(MF) mice suggests that downregulation of Fps/Fes activity might be required for terminal erythroid differentiation.

Fps/Fes and Fer protein-tyrosinekinases play redundant roles in regulating hematopoiesis

OBJECTIVE

The highly related protein-tyrosine kinases Fps (also called Fes) and Fer are sole members of a subfamily of kinases. In this study, knock-in mice harboring kinase-inactivating mutations in both fps and fer alleles were used to assess functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

METHODS

Mice harboring kinase-inactivating mutations in fps and fer alleles were generated previously. Compound homozygous mice were bred that lack both Fps and Fer kinase activities and progeny were analyzed for potential defects in viability and fertility. Potential differences in hematopoiesis were analyzed by lineage analysis of bone marrow cells, peripheral blood counts, and hematopoietic progenitor cell colony-forming assays.

RESULTS

Mice devoid of both Fps and Fer kinase activities were viable and displayed reduced fertility. Circulating levels of neutrophils, erythrocytes, and platelets were elevated in compound mutant mice compared to wild-type controls, suggesting that hematopoiesis is deregulated in the absence of Fps and Fer kinases. Compound mutant mice also showed reduced overall bone marrow cellularity, and lineage analysis revealed elevated CD11b(hi)Ly-6G(lo) myeloid cells, which may reflect increased granulocyte progenitors. Although no differences in the overall number of granulocyte/monocyte colony-forming progenitors were observed, qualitative differences in myeloid colonies from compound mutant mice suggested a role for Fps and Fer kinases in regulating cell-cell adhesion or a skewing in cellularity of colonies.

CONCLUSIONS

Mice lacking both Fps and Fer kinase activities develop normally, show reduced fertility, and display defects in hematopoiesis, thus providing evidence for functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

Fes tyrosine kinase promotes survival and terminal granulocyte differentiation of factor-dependent myeloid progenitors (32D) and activates lineage-specific transcription factors

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is involved in myeloid cell development and function. We have recently shown that expression of an activated allele of Fes (Fes(act)) in monocyte precursors resulted in their differentiation into functional macrophages through the activation of lineage-specific transcription factors. We now report that this kinase also plays a role in the survival and terminal differentiation of granulocyte progenitors. The expression of Fes(act) in factor-dependent 32D cells prevented their apoptotic death after interleukin-3 removal, but Fes(act)-expressing cells remained factor-dependent for proliferation. Removal of interleukin-3 from the Fes(act)-expressing cells was followed by granulocytic differentiation in the absence of granulocyte colony-stimulating factor within 4-8 days. The differentiated cells had distinctive granulocyte morphology and there was up-regulation of CD11b, Gr-1, and late differentiation markers such as lactoferrin, suggesting that this kinase induced terminal granulocytic differentiation. Concomitantly, Fes(act) down-regulated the macrophage marker F4/80, suggesting that the biological activity of Fes was coordinated in a lineage-specific manner. Further analysis showed that Fes(act) caused activation of CCAAT/enhancer-binding protein-alpha and STAT3, two transcription factors that are involved in granulocyte differentiation. Our results provide evidence that Fes may be a key component of the granulocyte differentiation machinery, and suggest a potential mechanism by which this kinase may regulate granulocyte-specific gene expression.

Direct binding of plectin to Fer kinase and negative regulation of its catalytic activity

Plectin is a cyoskeletal linker protein that protects tissues against mechanical stress. We report here that the N-terminal domain of the nonreceptor tyrosine kinase Fer interacts with N-terminal sequences of plectin. Recombinant protein encoded by exon 12-24 of rat plectin bound directly to amino acid 1-329 of murine Fer. Using an antiserum prepared to a recombinant N-terminal fragment of Fer kinase, plectin was coimmunoprecipitated with Fer from cell lysates of cultured mouse fibroblasts. Plectin was shown to partially colocalize with Fer in these cells. Upon transfection of full length Fer cDNA into plectin-negative mouse fibroblasts, hyperphosphorylation of Fer was observed; hyperphosphorylation was strongly reduced when N-terminal Fer deletion mutants were transfected. Immunocomplex kinase assays showed that the activity of Fer kinase transfected into plectin-negative fibroblasts was increased compared to that transfected into wild type cells. We conclude that Fer interacts with plectin and that this interaction may serve to negatively regulate Fer's activity.

Truncation of c-fes via gene targeting results in embryonic lethality and hyperproliferation of hematopoietic cells

The c-fes protooncogene encodes a nonreceptor tyrosine kinase (Fes) implicated in cytokine receptor signal transduction, granulocyte survival, and myeloid differentiation. To study the role of c-fes during myelopoiesis, we generated embryonic stem (ES) cells with a targeted disruption of the c-fes locus. Targeted mutagenesis deletes the C-terminal SH2 and tyrosine kinase domains of c-fes (referred to as c-fes(Delta c/Delta c)). We demonstrate that the c-fes(Delta c/Delta c) allele results in a truncated Fes protein that retains the N-terminal oligomerization domain, but lacks both the SH2 and the tyrosine kinase domain. In vitro differentiation of c-fes(Delta c/Delta c) ES cells results in hyperproliferation of an early myeloid cell. Generation of c-fes(Delta c/Delta c) mutant chimeric mice causes lethality by E13.5 with embryos exhibiting pleiotropic defects, the most striking being cardiovascular abnormalities. These results establish that c-fes is an important regulator of myeloid cell proliferation and embryonic development.

Absence of Fer protein-tyrosine kinase exacerbates leukocyte recruitment in response to endotoxin

The group IV cytoplasmic protein-tyrosine kinase Fer has been linked to cellular signaling responses to many different stimuli, including growth factors and cytokines. However, the biological relevance of Fer activation in vivo has not been demonstrated to date. Recently, we generated a transgenic mouse line in which Fer protein is expressed but lacks catalytic activity. Homozygous mutant mice were viable and fertile, and showed no overt defects. In this study, we used intravital microscopy to examine the role of Fer kinase in leukocyte recruitment (rolling adhesion and emigration) in response to LPS challenge in skeletal muscle microcirculation. In addition, we measured vascular permeability changes (FITC-albumin leakage, venular-to-interstitial space) in response to Ag to examine general endothelial cell function. Local administration of LPS induced decreased leukocyte rolling velocity and increased leukocyte adhesion and emigration in wild-type mice. LPS-induced changes in leukocyte rolling velocity and rolling flux were not significantly different in Fer mutants. However, LPS-induced leukocyte adhesion (23 +/- 3 vs 11 +/- 3 cells/100 microm) and emigration (100 +/- 5 vs 28 +/- 7 cells/field) were significantly elevated in Fer-mutant mice relative to wild-type mice, respectively, suggesting an essential role for the Fer kinase in regulating inflammation-induced leukocyte emigration. Vascular permeability increases in response to Ag were similar between the two groups, indicating that the ability of endothelial cells to retract is intact in the absence of Fer kinase. These data provide the first evidence for a biological role for Fer in regulation of leukocyte recruitment during the innate immune response.

Tyrosine kinase oncogenes in normal hematopoiesis and hematological disease

Tyrosine kinase oncogenes are formed as a result of mutations that induce constitutive kinase activity. Many of these tyrosine kinase oncogenes that are derived from genes, such as c-Abl, c-Fes, Flt3, c-Fms, c-Kit and PDGFRbeta, that are normally involved in the regulation of hematopoiesis or hematopoietic cell function. Despite differences in structure, normal function, and subcellular location, many of the tyrosine kinase oncogenes signal through the same pathways, and typically enhance proliferation and prolong viability. They represent excellent potential drug targets, and it is likely that additional mutations will be identified in other kinases, their immediate downstream targets, or in proteins regulating their function.

Closing in on the biological functions of Fps/Fes and Fer

Fps/Fes and Fer are the only known members of a distinct subfamily of the non-receptor protein-tyrosine kinase family. Recent studies indicate that these kinases have roles in regulating cytoskeletal rearrangements and inside out signalling that accompany receptor ligand, cell matrix and cell cell interactions. Genetic analysis using transgenic mouse models also implicates these kinases in the regulation of inflammation and innate immunity.

Fes mediates the IL-4 activation of insulin receptor substrate-2 and cellular proliferation

Although Jak kinases are essential for initiating cytokine signaling, the role of other nonreceptor tyrosine kinases in this process remains unclear. We have examined the role of Fes in IL-4 signaling. Examination of Jak1-deficient cell lines demonstrates that Jak1 is required for the activation of Fes by IL-4. Experiments studying signaling molecules activated by IL-4 receptor suggest that IL-4 signaling can be subdivided into Fes-dependent and Fes-independent pathways. Overexpression of kinase-inactive Fes blocks the IL-4 activation of insulin receptor substrate-2, but not STAT6. Fes appears to be a downstream kinase from Jak1/Jak3 in this process. Further examination of downstream signaling demonstrates that kinase-inactive Fes inhibits the recruitment of phosphoinositide 3-kinase to the activated IL-4 receptor complex and decreases the activation of p70(S6k) kinase in response to IL-4. This inhibition correlates with a decrease in IL-4-induced proliferation. In contrast, mutant Fes does not inhibit the activation of Akt by IL-4. These data demonstrate that signaling pathways activated by IL-4 require different tyrosine kinases. This differential requirement predicts that specific kinase inhibitors may permit the disruption of specific IL-4-induced functions.

The protein-tyrosine kinase fer associates with signaling complexes containing insulin receptor substrate-1 and phosphatidylinositol 3-kinase

In a screen for 3T3-F442A adipocyte proteins that bind SH2 domains, we isolated a cDNA encoding Fer, a nonreceptor protein-tyrosine kinase of the Fes/Fps family that contains a functional SH2 domain. A truncated splicing variant, iFer, was also cloned. iFer is devoid of both the tyrosine kinase domain and a functional SH2 domain but displays a unique 42-residue C terminus and retains the ability to form oligomers with Fer. Expression of both Fer and iFer proteins are strikingly increased upon differentiation of 3T3-L1 fibroblasts to adipocytes. Platelet-derived growth factor treatment of the cultured adipocytes caused rapid tyrosine phosphorylation of Fer and its recruitment to complexes containing platelet-derived growth factor receptor and the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase. Insulin treatment of 3T3-L1 adipocytes stimulated association of Fer with complexes containing tyrosine phosphorylated IRS-1 and PI 3-kinase but did not stimulate tyrosine phosphorylation of Fer. PI 3-kinase activity in anti-Fer immunoprecipitates was also acutely activated by insulin treatment of cultured adipocytes. These data demonstrate the presence of Fer tyrosine kinase in insulin signaling complexes, suggesting a role of Fer in insulin action.

A minimal c-fes cassette directs myeloid-specific expression in transgenic mice

The c-fes proto-oncogene encodes a 92-kd protein tyrosine kinase whose expression is restricted largely to myeloid and endothelial cells in adult mammals. A 13.2-kilobase (kb) humanc-fes genomic fragment was previously shown to containcis-acting element(s) sufficient for a locus control function in bone marrow macrophages. Locus control regions (LCRs) confer transgene expression in mice that is integration site independent, copy number dependent, and similar to endogenous murine messenger RNA levels. To identify sequences required for this LCR,c-fes transgenes were analyzed in mice. Myeloid-cell–specific, deoxyribonuclease-I–hypersensitive sites localized to the 3′ boundary of exon 1 and intron 3 are required to confer high-level transgene expression comparable to endogenous c-fes, independent of integration site. We define a minimal LCR element as DNA sequences (nucleotides +28 to +2523 relative to the transcription start site) located within intron 1 to intron 3 of the human locus. When this 2.5-kb DNA fragment was linked to a c-fes complementary DNA regulated by its own 446–base-pair promoter, integration-site–independent, copy-number–dependent transcription was observed in myeloid cells in transgenic mice. Furthermore, this 2.5-kb cassette directed expression of a heterologous gene (enhanced green fluorescent protein) exclusively in myeloid cells. The c-fes regulatory unit represents a novel reagent for targeting gene expression to macrophages and neutrophils in transgenic mice.

A minimal c-fes cassette directs myeloid-specific expression in transgenic mice

The c-fes proto-oncogene encodes a 92-kd protein tyrosine kinase whose expression is restricted largely to myeloid and endothelial cells in adult mammals. A 13.2-kilobase (kb) humanc-fes genomic fragment was previously shown to containcis-acting element(s) sufficient for a locus control function in bone marrow macrophages. Locus control regions (LCRs) confer transgene expression in mice that is integration site independent, copy number dependent, and similar to endogenous murine messenger RNA levels. To identify sequences required for this LCR,c-fes transgenes were analyzed in mice. Myeloid-cell–specific, deoxyribonuclease-I–hypersensitive sites localized to the 3′ boundary of exon 1 and intron 3 are required to confer high-level transgene expression comparable to endogenous c-fes, independent of integration site. We define a minimal LCR element as DNA sequences (nucleotides +28 to +2523 relative to the transcription start site) located within intron 1 to intron 3 of the human locus. When this 2.5-kb DNA fragment was linked to a c-fes complementary DNA regulated by its own 446–base-pair promoter, integration-site–independent, copy-number–dependent transcription was observed in myeloid cells in transgenic mice. Furthermore, this 2.5-kb cassette directed expression of a heterologous gene (enhanced green fluorescent protein) exclusively in myeloid cells. The c-fes regulatory unit represents a novel reagent for targeting gene expression to macrophages and neutrophils in transgenic mice.

Abnormal Stat activation, hematopoietic homeostasis, and innate immunity in c-fes-/- mice

The c-fes protooncogene encodes a nonreceptor tyrosine kinase (Fes) implicated in cytokine receptor signal transduction, neutrophil survival, and myeloid differentiation. To determine the role of Fes in embryonic development and hematopoiesis, we engineered a null mutation of the murine c-fes locus. c-fes-/- mice are viable but not born in the expected Mendelian ratios. Live born c-fes-/- mice exhibit lymphoid/myeloid homeostasis defects, compromised innate immunity, and increased Stat activation in response to GM-CSF and IL-6 signaling. Therefore, increased cytokine responsiveness in the absence of Fes leads to abnormal myeloid proliferation and functional defects in the macrophage lineage.

Kinase inhibitors in cancer therapy: a look ahead

The most essential kinases involved in cell membrane receptor activation, signal transduction and cell cycle control or programmed cell death and their interconnections are reviewed. In tumours, the genes of many of those kinases are mutated or amplified or the proteins are overexpressed. The use of key kinases offers the possibility to screen in vitro for synthetic small molecule kinase inhibitors. In view of the many interconnections of cellular kinases, their role in preventing or inducing programmed cell death and the possibility that a considerable number of signal transducing proteins are still unknown, cellular test systems are recommended in which the respective key kinase or one of its main partner molecules are overexpressed.

Disruption of coiled-coil domains in Fer protein-tyrosine kinase abolishes trimerization but not kinase activation

The protein-tyrosine kinase Fer and the highly homologous proto-oncoprotein Fps/Fes are implicated in signaling from a variety of growth factor and cytokine receptors. Here we examine the molecular basis of Fer kinase activation with an emphasis on the role of oligomerization. We show that Fer forms trimers in vivo and that disruption of either the first or second coiled-coil domain abolishes oligomerization, suggesting a cooperative interaction between these two domains. Although Fps/Fes also forms homotypic oligomers, probably via homologous coiled-coil domains, no heterotypic interactions were observed between Fer and Fps/Fes. Incorporation of catalytically inactive Fer peptides into the oligomeric complex caused only mild reduction of wild type Fer kinase activity, suggesting that kinase-inactive Fer would not behave as a potent dominant negative. Although oligomerization of Fer can potentiate autophosphorylation in trans at three major phosphorylation sites, these residues can likely also be phosphorylated in cis. In contrast, the testis-specific FerT isomer does not oligomerize and is able to autophosphorylate in cis at two of the same three residues autophosphorylated in Fer. These results suggest that although oligomerization potentiates autophosphorylation in trans, this is apparently not necessary for Fer activation.

Growth factor-dependent phosphorylation of the actin-binding protein cortactin is mediated by the cytoplasmic tyrosine kinase FER

Previous characterization of the nonreceptor tyrosine kinase FER identified a tight physical association with the catenin pp120 and led to the suggestion that FER may be involved in cell-cell signaling. To further understand the function of FER, we have continued our analyses of the interaction of FER with pp120 and other proteins. The majority of FER is localized to the cytoplasmic fraction where it forms a complex with the actin-binding protein cortactin. The Src homology 2 sequence of FER is required for directly binding cortactin, and phosphorylation of the FER-cortactin complex is up-regulated in cells treated with peptide growth factors. Using a dominant-negative mutant of FER, we provided evidence that FER kinase activity is required for the growth factor-dependent phosphorylation of cortactin. These data suggest that cortactin is likely to be a direct substrate of FER. Our observations provide additional support for a role of FER in mediating signaling from the cell surface, via growth factor receptors, to the cytoskeleton. The nature of the FER-cortactin interaction, and their putative enzyme-substrate relationship, support the previous proposal that one of the functions of the Src homology 2 sequences of nonreceptor tyrosine kinases is to provide a binding site for their preferred substrates.

c-Fes tyrosine kinase binds to and activates STAT3 after granulocyte-macrophage colony-stimulating factor stimulation

Granulocyte-macrophage colony stimulating factor (GM-CSF) induces proliferation and maturation of myeloid progenitor cells and also activates neutrophils. In order to investigate the pleiotropic effects of GM-CSF stimulation, we examined the signaling pathways of protein tyrosine kinases (PTKs) and signal transducers and activators of transcription (STATs) in GM-CSF-dependent proliferation of leukemia cells. Using TF-1, a GM-CSF-dependent human erythroleukemia cell line, we found that GM-CSF enhanced DNA-binding and tyrosine phosphorylation of STAT3. GM-CSF receptor (GM-CSFR) and c-Fes tyrosine kinase were also activated upon GM-CSF stimulation. Furthermore, c-Fes formed a complex with STAT3. Experiments using a c-Fes mutant that lacked tyrosine kinase activity revealed that the activation of STAT3 is kinase-dependent, but that the c-Fes-STAT3 interaction is not affected by c-Fes tyrosine kinase activity. The results suggest that STAT3 is activated by c-Fes tyrosine kinase through direct interaction during hematopoietic cell proliferation induced by GM-CSF.

Fibroblast transformation by Fps/Fes tyrosine kinases requires Ras, Rac, and Cdc42 and induces extracellular signal-regulated and c-Jun N-terminal kinase activation

The small GTP-binding proteins Ras, Rac, and Cdc42 link protein-tyrosine kinases with mitogen-activated protein kinase (MAPK) signaling cascades. Ras controls the activation of extracellular signal-regulated kinases (ERKs), while Rac and Cdc42 regulate the c-Jun N-terminal kinases (JNKs). In this study, we investigated whether small G protein/MAPK cascades contribute to signal transduction by transforming variants of c-Fes, a nonreceptor tyrosine kinase implicated in cytokine signaling and myeloid differentiation. First, we investigated the effects of dominant-negative small G proteins on Rat-2 fibroblast transformation by a retroviral homolog of c-Fes (v-Fps) and by c-Fes activated via N-terminal addition of the v-Src myristylation signal (Myr-Fes). We observed that dominant-negative Ras, Rac, and Cdc42 inhibited v-Fps- and Myr-Fes-induced growth of Rat-2 cells in soft agar, indicating that activation of these small GTP-binding proteins is required for fibroblast transformation by Fps/Fes tyrosine kinases. To determine whether MAPK pathways are activated downstream of these small G proteins, we measured ERK and JNK activity in the v-Fps- and Myr-Fes-transformed Rat-2 cells. Both ERK and JNK activities were elevated in the transformed cells, suggesting that these pathways are involved in cellular transformation. Dominant-negative mutants of Ras (but not Rac or Cdc42) specifically inhibited ERK activation by v-Fps and Myr-Fes, demonstrating that ERK activation occurs exclusively downstream of Ras. All three dominant-negative small G proteins inhibited JNK activation by v-Fps and Myr-Fes, indicating that JNK activation by these tyrosine kinases requires both Ras and Rho family GTPases. These data demonstrate that multiple small G protein/MAPK cascades are involved in downstream signal transduction by Fps/Fes tyrosine kinases.

Activation of STAT3 by the c-Fes protein-tyrosine kinase

STATs (signal transducers and activators of transcription) are transcription factors that contain SH2 domains and are activated by tyrosine phosphorylation, often in response to cytokine stimulation. Recent evidence indicates that the transforming tyrosine kinases encoded by the v-Src, v-Abl, and v-Fps oncogenes can induce STAT activation, suggesting that their normal cellular homologs may contribute to STAT activation under physiological conditions. In this report, we provide direct evidence that c-Fes, the normal human homolog of v-Fps, potently activates STAT3. Transient transfection of human 293T cells with STAT3 and Fes resulted in strong stimulation of STAT3 DNA binding activity. In contrast, only modest activation of STAT5 by Fes was observed in this system, indicative of possible selectivity. To determine whether Fes-induced STAT3 activation is dependent upon endogenous mammalian kinases, co-expression studies were also performed in Sf-9 insect cells. Fes also induced a dramatic increase in STAT3 DNA binding activity in this system, whereas no activation of STAT5 was observed. As a positive control, both STAT3 and STAT5 were shown to be activated by the Bcr-Abl tyrosine kinase in Sf-9 cells. Fes induced strong tyrosine phosphorylation of STAT3 in both expression systems, consistent with the gel-shift results. Fes and STAT3 have been independently linked to myeloid differentiation. Results presented here suggest that these proteins may cooperate to promote differentiation signaling in response to hematopoietic cytokines.

Expression of two myeloid cell-specific genes requires the novel transcription factor, c-fes expression factor

The protein product of the c-fes proto-oncogene has been implicated in the normal development of myeloid cells (macrophages and granulocytes). We have previously shown that 151 base pairs of c-fes 5'-flanking sequences are sufficient for myeloid cell-specific expression and include functional binding sites for Sp1, PU.1, and a novel nuclear factor (Heydemann, A., Juang, G., Hennessy, K., Parmacek, M. S., and Simon, M. C. (1996) Mol. Cell. Biol. 16, 1676-1686). This novel hematopoietic transcription factor, termed FEF (c-fes expression factor), binds to a cis-acting element that is located at nucleotides -9 to -4 of the c-fes promoter between two Ets binding sites (at -19 to -15 and -4 to +1) which bind PU.1. We now show that a FEF binding site exists in the myeloid cell-specific regulatory region of a second gene, the -2.7-kilobase pair enhancer of chicken lysozyme. The lysozyme FEF site is immediately 5' to a PU. 1 site, analogous to their arrangement in the c-fes promoter, and allows the formation of a preliminary FEF consensus site, 5'-GAAT(C/G)A-3'. This consensus site does not match any sites for known transcription factors. Importantly, although PU.1 binds immediately 3' of the FEF site in both the c-fes promoter and the chicken lysozyme enhancer (CLE), we show that they bind independently. The FEF sites are required for high levels of transcription by both the CLE and the c-fes promoter in transient transfection experiments. Importantly, elimination of the CLE FEF site abolishes all transcriptional activity of this enhancer element. Mutation of the adjacent PU.1 site in either the c-fes promoter or the CLE, reduces activity by approximately 50%. Therefore, transcription of both lysozyme and fes in myeloid cells requires FEF and PU.1. UV cross-linking experiments show that the FEF binding activity consists of a single 70-kDa protein in both human and murine cell lines. FEF binding activity is not affected by antibodies that specifically recognize a number of cloned transcription factors. Collectively, these data indicate that we have identified a novel transcription factor that is functionally important for the expression of at least two myeloid cell-specific genes.

Oligomerization of the Fes tyrosine kinase. Evidence for a coiled-coil domain in the unique N-terminal region

The c-fes proto-oncogene encodes a non-receptor tyrosine kinase (Fes) that has been implicated in cytokine receptor signal transduction and myeloid differentiation. Previous work from our laboratory has shown that Fes autophosphorylates via an intermolecular mechanism more commonly associated with growth factor receptor tyrosine kinases. Analysis of the Fes amino acid sequence with the COILS algorithm indicates that the N-terminal region of the protein has a very high probability of forming coiled-coil structures often associated with oligomeric proteins. These findings suggest that oligomerization may be a prerequisite for trans-autophosphorylation and activation of Fes. To establish whether the active form of Fes is oligomeric, we performed gel-filtration experiments with recombinant Fes and found that it eluted as a single symmetrical peak of approximately 500 kDa. No evidence of the monomeric, 93-kDa form of the protein was observed. Deletion of the unique N-terminal domain (amino acids 1-450, including the coiled-coil homology region) completely abolished the formation of oligomers. Furthermore, co-precipitation assays demonstrated that an immobilized glutathione S-transferase fusion protein containing the Fes N-terminal region bound to full-length Fes but not to a mutant lacking the N-terminal region. Similarly, a recombinant Fes N-terminal domain protein was readily cross-linked in vitro, whereas the SH2 and kinase domains were refractory to cross-linking. Incubation of wild-type Fes with a kinase-inactive Fes mutant or with the isolated N-terminal region suppressed Fes autophosphorylation in vitro, suggesting that oligomerization may be essential for autophosphorylation of full-length Fes. The presence of an oligomerization function in the Fes family of tyrosine kinases suggests a novel mechanism for non-receptor protein-tyrosine kinase regulation.

The Fes protein-tyrosine kinase phosphorylates a subset of macrophage proteins that are involved in cell adhesion and cell-cell signaling

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is expressed at high levels in macrophages. We have previously shown that overexpression of c-fps/fes in a CSF-1-dependent macrophage cell line (BAC1.2F5) partially released these cells from their factor dependence and that this correlated with the tyrosine phosphorylation of a subset of proteins in a tissue-specific manner. We have now identified one of the macrophage substrates of Fes as the crk-associated substrate (Cas) and a second substrate as a 130-kDa protein that has been previously described as a T cell activation-dependent substrate and is unrelated to Cas. Both of these proteins, which have optimal consensus sequences for phosphorylation by Fes, were tightly associated with this kinase through its SH2 domain, suggesting that they were direct substrates of Fes. Remarkably, when the Fes SH2 domain was used as an affinity reagent to identify potential substrates of endogenous Fes in control BAC1.2F5 cells, the phosphotyrosyl proteins that were recognized were the same as those that were specifically phosphorylated when Fes was overexpressed in the same cells. We conclude that the substrates we identified may be structurally related or identical to the physiological targets of this kinase in macrophages. The known functions of Cas and p130 suggest that Fes kinase may play a role in signaling triggered by cell adhesion and cell-cell interactions during immune responses of macrophages.

Antisense Inhibition of c-fes Proto-oncogene Blocks PMA-Induced Macrophage Differentiation in HL60 and in FDC-P1/MAC-11 Cells

To gain some insight into the role of c-fes in macrophage differentiation, we have analyzed the ability of HL60 leukemic promyelocytic cells and FDC-P1/MAC-11 murine myeloid precursor cells to differentiate in response to phorbol esters after inhibition of c-fes function. Fes inactivation has been obtained by using oligodeoxynucleotides (ODN) complementary to the 5′ region of c-fes mRNA and to 5′ splice junctions of c-fes primary transcript. After 5 days (d) in culture, in several separate experiments performed with different ODN preparations, a complete inhibition of c-fes expression was observed in HL60 and in FDC-P1/MAC-11 cells. No perturbation of cell growth was evident in our experimental conditions in both cell lines after c-fes inhibition. Furthermore, in HL60 cells lacking c-fes product, an almost complete downregulation of the α4β1 fibronectin receptor occurred. However, in both cell lines, the induction of macrophage differentiation by phorbol esters resulted in an almost complete maturation arrest as evaluated by morphological, cytochemical, immunological criteria, and by the cytofluorimetric cell cycle analysis. A loss of the adhesion capacity of both myeloid cell lines, when compared to terminally differentated macrophages, was also observed. These results suggest that HL60 and FDC-P1/MAC-11 cells, when treated with phorbol 12-myristate 13-acetate, require c-fes protein expression to activate the genetic program underlying macrophage differentiation.

Antisense Inhibition of c-fes Proto-oncogene Blocks PMA-Induced Macrophage Differentiation in HL60 and in FDC-P1/MAC-11 Cells

To gain some insight into the role of c-fes in macrophage differentiation, we have analyzed the ability of HL60 leukemic promyelocytic cells and FDC-P1/MAC-11 murine myeloid precursor cells to differentiate in response to phorbol esters after inhibition of c-fes function. Fes inactivation has been obtained by using oligodeoxynucleotides (ODN) complementary to the 5′ region of c-fes mRNA and to 5′ splice junctions of c-fes primary transcript. After 5 days (d) in culture, in several separate experiments performed with different ODN preparations, a complete inhibition of c-fes expression was observed in HL60 and in FDC-P1/MAC-11 cells. No perturbation of cell growth was evident in our experimental conditions in both cell lines after c-fes inhibition. Furthermore, in HL60 cells lacking c-fes product, an almost complete downregulation of the α4β1 fibronectin receptor occurred. However, in both cell lines, the induction of macrophage differentiation by phorbol esters resulted in an almost complete maturation arrest as evaluated by morphological, cytochemical, immunological criteria, and by the cytofluorimetric cell cycle analysis. A loss of the adhesion capacity of both myeloid cell lines, when compared to terminally differentated macrophages, was also observed. These results suggest that HL60 and FDC-P1/MAC-11 cells, when treated with phorbol 12-myristate 13-acetate, require c-fes protein expression to activate the genetic program underlying macrophage differentiation.

Co-expression with BCR induces activation of the FES tyrosine kinase and phosphorylation of specific N-terminal BCR tyrosine residues

The human BCR gene encodes a protein with serine/threonine kinase activity and regulatory domains for the small G-proteins RAC and CDC42. Previous work in our laboratory has established that BCR is a substrate for c-FES, a non-receptor tyrosine kinase linked to myeloid growth and differentiation. Tyrosine phosphorylation led to the association of BCR with the RAS guanine nucleotide exchange complex GRB2-SOS in vivo via the GRB2 SH2 domain, linking BCR to RAS signaling (Maru, Y., Peters, K. L., Afar, D. E. H., Shibuya, M., Witte, O. N., and Smithgall, T. E. (1995) Mol. Cell. Biol. 15, 835-842). In the present study, we demonstrate that BCR Tyr-246 and at least one of the closely spaced tyrosine residues, Tyr-279, Tyr-283, and Tyr-289 (3Y cluster), are phosphorylated by FES both in vitro and in 32Pi-labeled cells. Mutagenesis of BCR Tyr-177 to Phe completely abolished FES-induced BCR binding to the GRB2 SH2 domain, identifying Tyr-177 as an additional phosphorylation site for FES. Co-expression of BCR and FES in human 293T cells stimulated the tyrosine autophosphorylation of FES. By contrast, tyrosine phosphorylation of BCR by FES suppressed BCR serine/threonine kinase activity toward the 14-3-3 protein and BCR substrate, BAP-1. These data show that tyrosine phosphorylation by FES affects the interaction of BCR with multiple signaling partners and suggest a general role for BCR in non-receptor protein-tyrosine kinase regulation and signal transduction.

Autophosphorylation of the Fes tyrosine kinase. Evidence for an intermolecular mechanism involving two kinase domain tyrosine residues

The human c-fes proto-oncogene encodes a cytoplasmic tyrosine kinase (Fes) that is associated with multiple hematopoietic cytokine receptors. Fes tyrosine autophosphorylation sites may regulate kinase activity and recruit downstream signaling proteins with SH2 domains. To localize the Fes autophosphorylation sites, full-length Fes and deletion mutants lacking either the unique N-terminal or SH2 domain were autophosphorylated in vitro and analyzed by CNBr cleavage. Identical phosphopeptides of 10 and 4 kDa were produced with all three proteins, localizing the tyrosine autophosphorylation sites to the C-terminal kinase domain. Substitution of kinase domain tyrosine residues 713 or 811 with phenylalanine resulted in a loss of the 10- and 4-kDa phosphopeptides, respectively, identifying these tyrosines as in vitro autophosphorylation sites. CNBr cleavage analysis of Fes isolated from 32PO4-labeled 293T cells showed that Tyr-713 and Tyr-811 are also autophosphorylated in vivo. Mutagenesis of Tyr-713 reduced both autophosphorylation of Tyr-811 and transphosphorylation of Bcr, a recently identified Fes substrate, supporting a major regulatory role for Tyr-713. Wild-type Fes transphosphorylated a kinase-inactive Fes mutant on Tyr-713 and Tyr-811, suggesting that Fes autophosphorylation occurs via an intermolecular mechanism analogous to receptor tyrosine kinases.

Transcriptional regulation of c-Fes in myeloid leukemia cells

The c-Fes proto-oncogene encodes a myeloid-specific protein-tyrosine kinase that is expressed preferentially in differentiated myeloid cells, but not in early myeloblast progenitor cells. To examine the basis for the phenotypic expression of c-Fes, the transcription initiation sites of the human c-Fes gene were mapped in myeloid leukemia cells and regulatory elements in the genomic c-Fes sequence were characterized. Two major transcription initiation sites were found in the myeloid leukemia cell line THP-1 which delineated exon 1 to be 72-83 bp. When the activity of the CAT reporter gene under the control of the c-Fes promoter region, untranslated exon 1 and intron 1 was measured in TF-1, K562 and MCF-7 cells, only TF-1 cells exhibited chloramphenicol acetyltransferase activity. In contrast, all cell lines supported reporter gene activity when intron 1 was deleted. Deletion analyses revealed a negative regulatory region in intron 1, which was localized by Southwestern analysis and DNA footprinting to a 14 bp region. This negative regulatory region suppressed reporter CAT activity in K562 and TF-1 cells when inserted downstream to the SV40 early promoter. These results suggest that the tissue-specific expression of c-Fes may result, in part, from the negative regulation of transcription in myeloid and nonmyeloid cells.

Role of c-Fes in normal and neoplastic hematopoiesis

The study of oncogenes has provided numerous insights, not only into the mechanisms by which growth regulation becomes uncontrolled in cancer cells, but also into signal transduction processes which regulate the orderly proliferation and maturation of cells. c-fes/fps is a cellular oncogene which has been transduced frequently by mammalian and avian retroviruses. There are several features about Fes which suggest it may play a unique role in myeloid cell growth and differentiation. While it contains a tyrosine kinase and SH2 domain, there is no SH3 domain or carboxy terminal regulatory phosphotyrosine such as found in the Src family of kinases. Fes has a unique N-terminal domain of over 400 amino acids of unknown function. It has been implicated in signaling by a variety of hematopoietic growth factors, and is predominantly a nuclear protein.

Activation of Fes tyrosine kinase by gp130, an interleukin-6 family cytokine signal transducer, and their association

gp130 is a signal-transducing subunit of receptors for the interleukin-6 (IL-6)-related cytokine subfamily including IL-6, leukemia inhibitory factor, oncostatin M, IL-11, and ciliary neurotrophic factor, indicating that gp130-mediated signals are involved in the immune response, hematopoiesis, inflammation, and endocrine and nervous system activity. We previously showed that gp130 stimulation rapidly activates Jak, Btk, and Tec tyrosine kinases, all of which constitutively associate with gp130. To further elucidate intracellular signal transduction through gp130, we examined the possible involvement of another nonreceptor tyrosine kinase, p92c-fes (Fes). We showed that gp130 stimulation rapidly induced tyrosine phosphorylation of Fes and actually activated its kinase activity in hematopoietic lineage cells. Furthermore, Fes associated with gp130 independently of ligand stimulation like Jak, Btk, and Tec tyrosine kinases. These results indicate that multiple nonreceptor tyrosine kinases are involved in the gp130-mediated signal transduction pathway. Because both gp130 and Fes are expressed not only in hematopoietic lineage cells but also in heart and nerve cells, Fes may play a role in signal transduction through gp130 in these tissues.

Phosphorylation of a Fes-related protein in response to granulocyte-macrophage colony stimulating factor

Previous work has suggested that a 97-kDa protein (p97) is involved in the signal transduction pathway of granulocyte-macrophage colony stimulating factor (GM-CSF) as well as interleukin 3, erythropoietin, and interleukin 2. We have examined the relationship of p97 to the protein tyrosine kinase Fes in the GM-CSF signal transduction pathway in erythroid and myeloid cell lines. GM-CSF stimulation of three different cell lines induced tyrosine phosphorylation of p97 as well as a number of other phosphotyrosylproteins. Although each cell line expressed the proto-oncogene product Fes, antisera specific for Fes did not recognize p97 in immunoblotting experiments. Furthermore, immunodepletion of Fes did not reduce the amount of p97 in GM-CSF-treated cells. Two-dimensional gel electrophoresis demonstrated that p97 and Fes have similar charge to mass ratios, and limited proteolytic mapping of p97 and Fes suggested that these proteins may be related but are not identical. Our studies demonstrate that p97 is not Fes but is probably a Fes-related protein.

Conversion of human fibroblasts to tissue macrophages by the Snyder-Theilen feline sarcoma virus (ST:FeSV(FeLV)): productive infection by Leishmania major

The decisive role of macrophages in T-cell differentiation is best exemplified by cutaneous leishmaniasis. During infection, Leishmania attach to macrophages, the only site of replication for the parasite. We have recently demonstrated the conversion of human fibroblasts to tissue macrophages (TM) by transduction with the Snyder-Theilen feline sarcoma virus (ST:FeSV-(FeLV)). Since Leishmania have tropism only for macrophages, we have used the parasite to ascertain the functional phenotype of the ST:FeSV-induced TM. Here, we have demonstrated the productive infection of the ST:FeSV-induced TM by L. major. These results point to the utility of ST:FeSV-induced TM in studies that concern the role of human macrophages in T-cell differentiation during the course of infection by Leishmania.

A retrovirus encoding the v-fps protein-tyrosine kinase induces factor-independent growth and tumorigenicity in FDC-P1 cells

There is increasing evidence that protein-tyrosine kinases play pivotal roles in the response to growth-factor signals. The cytoplasmic tyrosine kinase c-fps/fes, due to its restricted expression in hematopoietic tissue, is likely to participate in hematopoietic growth-factor signalling. We have introduced a retrovirus containing an activated fps gene (encoding P130gag-fps) into the growth factor-dependent myeloid cell line FDC-P1. Clonal cell lines were derived by selection for a marker gene coding for G418 resistance in the absence or presence of the hematopoietic growth factor IL-3. G418 resistant clones expressed P130gag-fps and its associated protein-tyrosine kinase activity and displayed either a factor-independent or IL-3 hypersensitive phenotype and were tumorigenic in syngeneic recipients. Thus, introduction of the activated v-fps gene was able to circumvent the requirement for exogenous growth factors by FDC-P1 cells. Bioassay of conditioned medium from the various clones did not detect hematopoietic growth factor activity and PCR analysis for IL-3 transcripts were negative, suggesting that growth-factor independence was achieved by a mechanism other than autocrine production of a growth factor. We suggest that P130gag-fps is acting to directly stimulate a hematopoietic growth-factor signalling pathway, perhaps one that normally involves the endogenous c-fps/fes protein-tyrosine kinase of FDC-P1 cells.

Regulation of hematopoietic cell function by protein tyrosine kinase-encoding oncogenes, a review

Tyrosine phosphorylation of proteins by protein tyrosine kinases (PTKs) is an important mechanism in the regulation of various cellular processes such as proliferation, differentiation, and transformation. Accumulating data implicate PTKs as essential intermediates in the transduction of extracellular signals to the interior of the cell. This review summarizes the mechanism of action of PTKs from the major subclasses and the involvement of PTK-encoding oncogenes in the regulation of hematopoietic cell function.

Construction of a cDNA for the human c-fes protooncogene protein-tyrosine kinase and its expression in a baculovirus system

Previous studies have established that the 93-kDa protein-tyrosine kinase (PTK) encoded by the human c-fes protooncogene plays an active role in the induction of terminal myeloid differentiation. However, this enzyme is expressed at very low levels in myeloid cells, making isolation of sufficient quantities for detailed biochemical analysis difficult. To overcome this problem, we used the polymerase chain reaction to construct a full-length c-fes cDNA from overlapping 5' and 3' partial cDNA sequences. The c-fes cDNA was expressed at high levels in a baculovirus system, and the catalytically active recombinant c-fes gene product p93c-fes was partially purified by DEAE-Sepharose and tyrosine-agarose chromatography. Recombinant p93c-fes was indistinguishable from the native protein in terms of its apparent molecular weight following SDS-PAGE, catalytic activity, Km for poly(Glu,Tyr)4:1, antigenicity, and phosphopeptide pattern generated with Staphylococcus aureus protease.

Macrophages in tissues and in vitro

Macrophages have specialized functions in different tissue microenvironments such as lymphohaemopoietic organs and the nervous system. Recently, progress has been made in defining cellular and molecular properties of isolated and tissue macrophages in the developing and adult animal.

Development and characterization of a panel of monoclonal antibodies against the catalytic domain of the human fes proto-oncogene product

In developing monoclonal antibodies (Moabs) against the human fes proto-oncogene product, recombinant DNA technology was used to target reactivity of the Moabs towards the catalytic domain of it. Therefore, sequences of human fes exons 15-19 encoding amino acid residues 612 to 822 which harbor the catalytic domain except the presumed ATP-binding region, were fused in phase to the bacterial trp E gene which encodes anthranilate synthase. After partial purification of it, the bacterially produced hybrid product of this trp E-delta fes fusion gene was used as immunogen. A series of twelve mouse Moabs was obtained which recognized the human p92fes protein and the viral oncogene product p85gag-fes encoded by the Snyder-Theilen strain of feline sarcoma virus. Reactivity appeared to be directed towards the catalytic domain of the human fes proto-oncogene product. This was demonstrated by in vitro transcription and translation experiments using human fes coding sequences from exons 16-19. Upon testing their functional activity in divers immunological techniques, the whole panel of Moabs appeared to be useful in immunoprecipitation, Western blot and immunohistochemical analysis. Immunocytochemical analysis indicated that p85gag-fes is predominantly a cytoplasmic protein.