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

Phospholipase D2 (PLD2) shortens the time required for myeloid leukemic cell differentiation: mechanism of action

Cell differentiation is compromised in acute leukemias. We report that mammalian target of rapamycin (mTOR) and S6 kinase (S6K) are highly expressed in the undifferentiated promyelomonocytic leukemic HL-60 cell line, whereas PLD2 expression is minimal. The expression ratio of PLD2 to mTOR (or to S6K) is gradually inverted upon in vitro induction of differentiation toward the neutrophilic phenotype. We present three ways that profoundly affect the kinetics of differentiation as follows: (i) simultaneous overexpression of mTOR (or S6K), (ii) silencing of mTOR via dsRNA-mediated interference or inhibition with rapamycin, and (iii) PLD2 overexpression. The last two methods shortened the time required for differentiation. By determining how PLD2 participates in cell differentiation, we found that PLD2 interacts with and activates the oncogene Fes/Fps, a protein-tyrosine kinase known to be involved in myeloid cell development. Fes activity is elevated with PLD2 overexpression, phosphatidic acid or phosphatidylinositol bisphosphate. Co-immunoprecipitation indicates a close PLD2-Fes physical interaction that is negated by a Fes-R483K mutant that incapacitates its Src homology 2 domain. All these suggest for the first time the following mechanism: mTOR/S6K down-regulation→PLD2 overexpression→PLD2/Fes association→phosphatidic acid-led activation of Fes kinase→granulocytic differentiation. Differentiation shortening could have a clinical impact on reducing the time of return to normalcy of the white cell counts after chemotherapy in patients with acute promyelocytic leukemia.

Protein tyrosine kinase signaling during oocyte maturation and fertilization

The oocyte is a highly specialized cell capable of accumulating and storing energy supplies as well as maternal transcripts and pre-positioned signal transduction components needed for zygotic development, undergoing meiosis under control of paracrine signals from the follicle, fusing with a single sperm during fertilization, and zygotic development. The oocyte accomplishes this diverse series of events by establishing an array of signal transduction pathway components that include a select collection of protein tyrosine kinases (PTKs) that are expressed at levels significantly higher than most other cell types. This array of PTKs includes cytosolic kinases such as SRC-family PTKs (FYN and YES), and FAK kinases, as well as FER. These kinases typically exhibit distinct patterns of localization and in some cases are translocated from one subcellular compartment to another during meiosis. Significant differences exist in the extent to which PTK-mediated pathways are used by oocytes from species that fertilize externally versus internally. The PTK activation profiles as well as calcium signaling pattern seems to correlate with the extent to which a rapid block to polyspermy is required by the biology of each species. Suppression of each of the SRC-family PTKs as well as FER kinase results in failure of meiotic maturation or zygote development, indicating that these PTKs are important for oocyte quality and developmental potential. Future studies will hopefully reveal the extent to which these factors impact clinical assisted reproductive techniques in domestic animals and humans.

Fer tyrosine kinase is required for germinal vesicle breakdown and meiosis-I in mouse oocytes

The control of microtubule and actin-mediated events that direct the physical arrangement and separation of chromosomes during meiosis is critical since failure to maintain chromosome organization can lead to germ cell aneuploidy. Our previous studies demonstrated a role for FYN tyrosine kinase in chromosome and spindle organization and in cortical polarity of the mature mammalian oocyte. In addition to Fyn, mammalian oocytes express the protein tyrosine kinase Fer at high levels relative to other tissues. The objective of the present study was to determine the function of this kinase in the oocyte. Feline encephalitis virus (FES)-related kinase (FER) protein was uniformly distributed in the ooplasm of small oocytes, but became concentrated in the germinal vesicle (GV) during oocyte growth. After germinal vesicle breakdown (GVBD), FER associated with the metaphase-I (MI) and metaphase-II (MII) spindles. Suppression of Fer expression by siRNA knockdown in GV stage oocytes did not prevent activation of cyclin dependent kinase 1 activity or chromosome condensation during in vitro maturation, but did arrest oocytes prior to GVBD or during MI. The resultant phenotype displayed condensed chromosomes trapped in the GV, or condensed chromosomes poorly arranged in a metaphase plate but with an underdeveloped spindle microtubule structure or chromosomes compacted into a tight sphere. The results demonstrate that FER kinase plays a critical role in oocyte meiotic spindle microtubule dynamics and may have an additional function in GVBD.

The tyrosine kinase FES is an essential effector of KITD816V proliferation signal

KIT is a tyrosine kinase receptor that is aberrantly activated in several neoplasms. In human pathologies, the most frequent mutation of KIT occurs at codon 816. The resulting KIT mutant protein is activated in the absence of ligand and is resistant to the clinically available inhibitors of KIT. In this report, we provide evidence for an essential function of the cytoplasmic tyrosine kinase FES downstream of KITD816V. FES is phosphorylated on tyrosine residues in cells that carry KITD816V mutation, and this phosphorylation is KIT dependent. Reduction of FES expression using RNA interference results in decreased cell proliferation in human or murine cells harboring KITD816V or the homologous mouse mutation KITD814Y. The reduced cell growth can be rescued using another cytokine (granulocyte-macrophage colony-stimulating factor [GM-CSF]) and is not observed when the closely related fer gene is targeted. Finally, signaling downstream of KITD816V is altered in cells lacking FES expression. This study shows a major function of FES downstream of activated KIT receptor and thereby points to FES as a novel target in KIT-related pathologies.

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.

A catalogue of gene expression in the developing kidney

BACKGROUND

Although many genes with important function in kidney morphogenesis have been described, it is clear that many more remain to be discovered. Microarrays allow a more global analysis of the genetic basis of kidney organogenesis.

METHODS

In this study, Affymetrix U74Av2 microarrays, with over 12,000 genes represented, were used in conjunction with robust target microamplification techniques to define the gene expression profiles of the developing mouse kidney.

RESULTS

Microdissected murine ureteric bud and metanephric mesenchyme as well as total kidneys at embryonic day E11.5, E12.5, E13.5, E16.5, and adult were examined. This work identified, for example, 3847 genes expressed in the E12.5 kidney. Stringent comparison of the E12.5 versus adult recognized 428 genes with significantly elevated expression in the embryonic kidney. These genes fell into several functional categories, including transcription factor, growth factor, signal transduction, cell cycle, and others. In contrast, surprisingly few differences were found in the gene expression profiles of the ureteric bud and metanephric mesenchyme, with many of the differences clearly associated with the more epithelial character of the bud. In situ hybridizations were used to confirm and extend microarray-predicted expression patterns in the developing kidney. For three genes, Cdrap, Tgfbi, and Col15a1, we observed strikingly similar expression in the developing kidneys and lungs, which both undergo branching morphogenesis.

CONCLUSION

The results provide a gene discovery function, identifying large numbers of genes not previously associated with kidney development. This study extends developing kidney microarray analysis to the powerful genetic system of the mouse and establishes a baseline for future examination of the many available mutants. This work creates a catalogue of the gene expression states of the developing mouse kidney and its microdissected subcomponents.

Vascular defects in gain-of-function fps/fes transgenic mice correlate with PDGF- and VEGF-induced activation of mutant Fps/Fes kinase in endothelial cells

BACKGROUND

Fps/Fes is a cytoplasmic tyrosine kinase that is abundantly expressed in the myeloid, endothelial, epithelial, neuronal and platelet lineages. Genetic manipulation in mice has uncovered potential roles for this kinase in hematopoiesis, innate immunity, inflammation and angiogenesis.

OBJECTIVE

We have utilized a genetic approach to explore the role of Fps/Fes in angiogenesis.

METHODS

A hypervascular line of mice generated by expression of a 'gain-of-function' human fps/fes transgene (fps(MF)) encoding a myristoylated variant of Fps (MFps) was used in these studies. The hypervascular phenotype of this line was extensively characterized by intravital microscopy and biochemical approaches.

RESULTS

fps(MF) mice exhibited 1.6-1.7-fold increases in vascularity which was attributable to increases in the number of secondary vessels. Vessels were larger, exhibited varicosities and disorganized patterning, and were found to have defects in histamine-induced permeability. Biochemical characterization of endothelial cell (EC) lines derived from fps(MF) mice revealed that MFps was hypersensitive to activation by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF).

CONCLUSIONS

MFps mediates enhanced sensitization to VEGF and PDGF signaling in ECs. We propose that this hypersensitization contributes to excessive angiogenic signaling and that this underlies the observed hypervascular phenotype of fps(MF) mice. These phenotypes recapitulate important aspects of the vascular defects observed in both VEGF and angiopoietin-1 transgenic mice. The fps/fes proto-oncogene product therefore represents a novel player in the regulation of angiogenesis, and the fps(MF) line of mice constitutes a unique new murine model for the study of this process.

Role for Fes/Fps tyrosine kinase in microtubule nucleation through is Fes/CIP4 homology domain

We have previously demonstrated that Fes/Fps (Fes) tyrosine kinase is involved in Semaphorin3A-mediated signaling. Here we report a role for Fes tyrosine kinase in microtubule dynamics. A fibrous formation of Fes was observed in a kinase-dependent manner, which associated with microtubules and functionally correlated with microtubule bundling. Microtubule regeneration assays revealed that Fes aggregates colocalized with gamma-tubulin at microtubule nucleation sites in a Fes/CIP4 homology (FCH) domain-dependent manner and that expression of FCH domain-deleted Fes mutants blocked normal centrosome formation. In support of these observations, mouse embryonic fibroblasts derived from Fes-deficient mice displayed an aberrant structure of nucleation and centrosome with unbundling and disoriented filaments of microtubules. Our findings suggest that Fes plays a critical role in microtubule dynamics including microtubule nucleation and bundling through its FCH domain.

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.

Requirement of the coiled-coil domains of p92(c-Fes) for nuclear localization in myeloid cells upon induction of differentiation

The nonreceptor tyrosine kinase Fes is implicated in myeloid cells differentiation. It has been observed that its localization can be cytoplasmic, perinuclear, or nuclear. To further characterize this point, we studied Fes subcellular localization in myeloid cell lines (HL60 and K562) and in COS1 cells. Fes was observed in both the nucleus and the cytoplasm of HL60, K562 cells overexpressing Fes and only in the cytoplasm of COS1 cells, suggesting that nuclear localization is cell context dependent. Moreover, in myeloid cells, the treatment with differentiation-inducing agents such as retinoic acid, phorbol esters and vitamin D, is followed by an increase of the oligomeric form of Fes in the nucleus. In fact, oligomerization seems to be necessary for translocation to occur, since Fes mutants missing the coiled-coil domains are not able to form oligomers and fail to localize in the nucleus. The active form of Fes is tyrosine phosphorylated; however, phosphorylation is not required for Fes to localize in the nucleus, since tyrosine kinase inhibitors do not block the translocation process.