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Reassessment of the v-fms sequence: threonine phosphorylation of the COOH-terminal domain.

The v-fms oncogene product of the McDonough strain of feline sarcoma virus is a member of the receptor tyrosine kinase family. Its cellular counterpart, the c-fms product, is the receptor for colony-stimulating factor 1 (CSF-1) of macrophages. We have reanalyzed the v-fms gene by direct sequencing of a biologically active clone. An additional A nucleotide was detected in position 2810 of the published v-fms sequence. The frameshift changed the COOH-terminal sequence of the v-fms protein from -R-937-G-P-P-L-COOH to -Q-937-R-T-P-P-V-A-R-COOH. Antibodies against a synthetic peptide representing this new sequence precipitated the v-fms proteins from transformed NRK cells as well as from feline sarcoma virus (McDonough)-infected feline fibroblasts. We show by tryptic peptide mapping that threonine 939 present in the new sequence is phosphorylated by a yet unknown serine/threonine kinase in vivo. In chicken fibroblasts expressing the v-fms gene, this phosphorylation clearly depended on the addition of exogenous CSF-1. Furthermore, addition of CSF-1 appeared to activate the serine/threonine kinase, as judged by phosphorylation of the synthetic peptide QRTPPVAR.

Amino Acid Sequence↗

Effect of all-trans-retinoic acid on c-fms proto-oncogene [colony-stimulating factor 1 (CSF-1) receptor] expression and CSF-1-induced invasion and anchorage-independent growth of human breast carcinoma cells.

Abnormal expression of c-fms proto-oncogene, which encodes for the macrophage colony-stimulating factor-1 (CSF-1) receptor, has been observed in a variety of carcinomas of epithelial origin, including those of the breast. Here, we have investigated the effect of retinoic acid (RA), an important regulator of normal differentiation of mammary epithelial tissues, on the expression of the c-fms gene and CSF-1/CSF-1 receptor-induced invasion and anchorage-independent growth in breast carcinoma cells. We have demonstrated that all-trans-RA (atRA) significantly increases levels of c-fms transcripts in the estrogen receptor-negative but RA receptor alpha-positive breast carcinoma cell lines BT20 and SKBR3. The atRA-induced increase in fms transcript levels was completely abolished by RO41-5253, a synthetic RA receptor alpha antagonist. Our results indicate that atRA could enhance fms expression by up-regulating the activity of the first promoter of the fms gene. DNase I protection, mobility shift, and mutational analysis revealed that a potential activator protein 1 (AP-1) site in the first fms promoter sequence could mediate the observed atRA effect on fms transcription. Our results also showed that atRA, by itself and in the presence of CSF-1, can increase the ability of breast carcinoma cells to invade in vitro. Furthermore, we demonstrated that atRA is able to abolish the CSF-1-induced increase in anchorage-independent growth of breast carcinoma cells without affecting the anchorage-dependent growth. In summary, our findings suggest that retinoids may play conflicting roles throughout breast cancer progression, depending on the stage of cancer development. Although retinoids might suppress growth at the early stages of tumor formation, they might promote malignant transformation at later stages by stimulating the invasive capacity of certain cell variants in the breast tumor population.

Antineoplastic Agents↗

Organization and nucleotide sequence of the human KIT (mast/stem cell growth factor receptor) proto-oncogene.

We have cloned and sequenced the human KIT proto-oncogene, which contains 21 exons and spans more than 34 kb of DNA on chromosome segment 4q12. We also establish physical linkage between the KIT gene and the related PDGFRA gene. The organization of the KIT gene is virtually identical to that of the homologous FMS gene, located on chromosome 5. Together, these data suggest that the KIT and PDGFRA genes on chromosome 4 and the FMS and PDGFRB genes on chromosome 5 arose by duplication of a common ancestral gene, followed by duplication of a chromosome.

Amino Acid Sequence↗

Mouse NIH 3T3 cells expressing human colony-stimulating factor 1 (CSF-1) receptors overgrow in serum-free medium containing human CSF-1 as their only growth factor.

Mouse NIH 3T3 cells expressing the human c-fms protooncogene encoding the receptor for colony-stimulating factor 1 (CSF-1) are able to proliferate in serum-free medium containing platelet-derived growth factor (PDGF), insulin, transferrin, and albumin as the only exogenous proteins. When PDGF and insulin were replaced by purified human recombinant CSF-1, the cells became spindle shaped and refractile, were no longer contact inhibited, and proliferated to high densities. Thus, transduction of the human c-fms gene into mouse fibroblasts can not only reprogram their growth factor requirements but can also induce ligand-dependent features of cell transformation. NIH 3T3 cells stably transformed by the feline v-fms oncogene or by a mutated, oncogenic human c-fms gene were able to proliferate in the absence of exogenous growth factors. A monoclonal antibody that prevents signal transduction by the human CSF-1 receptor inhibited the growth of cells transformed by the activated c-fms oncogene, confirming that CSF-1 receptor function was required to abrogate growth factor requirements and to maintain the transformed state.

Animals↗

Analysis of functional domains of the v-fms-encoded protein of Susan McDonough strain feline sarcoma virus by linker insertion mutagenesis.

The Susan McDonough strain of feline sarcoma virus contains an oncogene, v-fms, which is capable of transforming fibroblasts in vitro. The mature protein product of the v-fms gene (gp140fms) is found on the surface of transformed cells; this glycoprotein has external, transmembrane, and cytoplasmic domains. To assess the functional role of these domains in transformation, we constructed a series of nine linker insertion mutations throughout the v-fms gene by using a dodecameric BamHI linker. The biological effects of these mutations on the function and intracellular localization of v-fms-encoded proteins were determined by transfecting the mutated DNA into Rat-2 cells. Most of the mutations within the external domain of the v-fms-encoded protein eliminated focus formation on Rat-2 cells; three of these mutations interfered with the glycosylation of the v-fms protein and interfered with formation of the mature gp140fms. One mutation in the external domain led to cell surface expression of v-fms protein even in the absence of complete glycosylational processing. Cell surface expression of mutated v-fms protein is probably necessary, but is not sufficient, for cell transformation since mutant v-fms protein was found on the surface of several nontransformed cell lines. Mutations that were introduced within the external domain had little effect on in vitro kinase activity, whereas mutations within the cytoplasmic domain all had strong inhibitory effects on this activity.

Cell Compartmentation↗

Absence of point mutations in a functionally important part of the extracellular domain of the c-kit proto-oncogene in a series of patients with acute myeloid leukemia (AML).

The proto-oncogenes c-fms and c-kit belong to a family of growth factor receptors possessing protein kinase activity. It has been shown that transfection of a c-fms gene carrying a point mutation at codon 301, leads to a ligand-independent transformation of mouse NIH3T3 cells. In human acute myeloid leukemia (AML), point mutations at codon 301 of the c-fms gene have been observed implying an important role in the transformation process. The possibility of a point mutation of the c-kit proto-oncogene was investigated. We sequenced a segment of the c-kit proto-oncogene coding for a part of the extracellular domain. This segment was 40.7% homologous to the c-fms region encompassing codon 301. c-DNA was prepared from peripheral blood or bone marrow cells from 25 patients with AML, from four patients with myelodysplastic syndrome (MDS) and from three human myeloid cell lines. The region of interest was amplified with two rounds of polymerase chain reactions (PCR) with nested primers and directly sequenced. No point mutations were found in the investigated samples. Thus, point mutations in this segment of the c-kit gene do not seem to play an important role in the transformation process of human acute leukemia.

Acute Disease↗

High level expression of fms proto-oncogene mRNA is observed in clinically aggressive human endometrial adenocarcinomas.

Six micron paraffin sections of paraformaldehyde-fixed endometrial currettings of 21 benign and neoplastic endometrial specimens were assayed for tumor cell-specific oncogene expression by in situ hybridization with probes for six oncogenes, beta-actin, and the E. coli plasmid pBR322. In the benign hyperplasias and invasive adenocarcinomas, multiple oncogenes, including erbB, fms, c-myc, and Ki-ras were expressed at significant levels. For the adenocarcinomas, statistical analysis demonstrated that high levels of expression of fms-complementary mRNA correlated strongly with clinicopathologic features (high FIGO histologic grade, high FIGO clinical stage, deep myometrial penetration) predictive of aggressive clinical behavior and poor outcome. The authors discuss the role which M-CSF receptor (the fms gene product) and locally-produced M-CSF may play in the development of the observed aggressively-malignant phenotypes. They also propose that pre-hysterectomy assay of fms gene expression in endometrial currettings in FIGO Stage I patients might be clinically useful to help identify preoperatively those patients with deep myometrial penetration or other locoregional spread.

Adenocarcinoma↗

Introduction of a human colony stimulating factor-1 gene into a mouse macrophage cell line induces CSF-1 independence but not tumorigenicity.

The SV40-immortalized mouse macrophage cell line, BAC1.2F5, is strictly dependent on CSF-1 for its survival and proliferation in culture. Introduction of a retroviral vector containing a 1.6 kilobase (kb) pair human CSF-1 cDNA into these cells abrogated their growth factor dependence but did not render the cells tumorigenic in nude mice. The infected macrophages contained multiple copies of the vector provirus, expressed both membrane-bound and secreted forms of CSF-1, and exhibited constitutive down modulation of the murine CSF-1 receptor. Because insertion of the v-fms gene has previously been shown to abrogate factor dependence and induce tumorigenicity in BAC1.2F5 macrophages, the failure of these cells to express a fully transformed phenotype after persistent stimulation by endogenous CSF-1 suggests that the v-fms and c-fms gene products provide different signals for cell proliferation.

Animals↗

Identification of the ligand-binding regions in the macrophage colony-stimulating factor receptor extracellular domain.

The c-fms gene encodes the receptor for the macrophage colony-stimulating factor (M-CSF), and its extracellular domain consists of five immunoglobulin-like subdomains. To identify which of the five immunoglobulin-like regions are involved in ligand binding, we polymerase chain reaction-cloned five segments of the extracellular domain of the murine c-fms gene, each starting with the normal initiation codon and containing successive additions of the immunoglobulin-like subdomains. These protein segments are designated A, B, C, D, and E and contain, from the N-terminal end, either one, two, three, four, or all five immunoglobulin-like subdomains, respectively. Each segment was expressed as a secreted soluble protein from a baculovirus expression vector in Sf9 insect cells. In addition, segments A, B, C, and E were produced as soluble alkaline phosphatase fusion proteins, as was a segment containing only the fourth and fifth immunoglobulin domains. These segments of the Fms extracellular domain were used to assess M-CSF binding by competition radioimmunoassays, plate binding immunoassays, and immunoprecipitation analyses. The results indicated that the first two N-terminal immunoglobulin-like domains did not interact with M-CSF but, in combination with the third immunoglobulin-like domain, provided high-affinity M-CSF binding. The fourth and fifth immunoglobulin-like domains near the cell membrane did not exhibit M-CSF binding and may inhibit interaction of M-CSF with the first three immunoglobulin domains. These results suggest that the three N-terminal immunoglobulin-like domains constitute the high-affinity M-CSF binding region and that the fourth and fifth immunoglobulin-like domains may perform functions other than ligand binding.

Animals↗

Differential transcription factor occupancy but evolutionarily conserved chromatin features at the human and mouse M-CSF (CSF-1) receptor loci.

The c-FMS gene encodes the macrophage colony-stimulating factor receptor (M-CSFR or CSF1-R), which is a tyrosine kinase growth factor receptor essential for macrophage development. We have previously characterized the chromatin features of the mouse gene; however, very little is known about chromatin structure and function of the human c-FMS locus. Here we present a side-by-side comparison of the chromatin structure, histone modification, transcription factor occupancy and cofactor recruitment of the human and the mouse c-FMS loci. We show that, similar to the mouse gene, the human c-FMS gene possesses a promoter and an intronic enhancer element (c-fms intronic regulatory element or FIRE). Both elements are evolutionarily conserved and specifically active in macrophages. However, we demonstrate by in vivo footprinting that both murine and human c-FMS cis-regulatory elements are recognised by an overlapping, but non-identical, set of transcription factors. Despite these differences, chromatin immunoprecipitation experiments show highly similar patterns of histone H3 modification and a similar distribution of chromatin modifying and remodelling activities at individual cis-regulatory elements and across the c-FMS locus. Our experiments support the hypothesis that the same regulatory principles operate at both genes via conserved cores of transcription factor binding sites.

3T3 Cells↗

Gene mutations in myelodysplasia.

The myelodysplastic syndrome is a paradigm of human preleukaemia. Normal haemopoiesis is progressively displaced by an abnormal clone derived from a mutated stem cell. The initial mutation is unknown but its occurrence may be related to the overall load of random mutations which are a consequence of both intrinsic DNA defects and external mutagens. Evolution of the pathological population is marked by an increasing load of genetic lesions at the molecular and cytogenetic levels. Ras mutations can be detected in the blood of about 50% of MDS patients. Fms mutations are less common but these lesions can be found both in patients and in haematologically normal subjects who have previously received cytotoxic therapy suggesting that they can occur early in the preleukaemic process. Clonal haemopoiesis in the absence of either ras or fms mutations can occur in these subjects. The data suggest the inability of mutant ras or fms genes alone to produce observable preleukaemic changes but that subjects with these mutations may be predisposed to future MDS. Ras mutations are a common accompaniment of a wide variety of malignancies and experimental transfection of the mutant gene can induce a malignant phenotype in cultured cells. There are many possible mechanisms for this transformation which may be relevant in a clinical context. Experimentally observed effects include a direct influence on the cell cycle, the induction of drug resistance and the stimulation of autocrine growth factor production. It may eventually be possible to define which gene mutations are important in conferring a malignant state, which determine phenotype and which are of incidental significance.

Genes, fms↗

Increased expression of growth factor genes for macrophages and fibroblasts in bronchoalveolar lavage cells of a patient with pulmonary histiocytosis X.

Pulmonary histiocytosis X is the local manifestation of a systemic disorder of unknown cause characterised by infiltration of Langerhans cell like histiocytes and parenchymal fibrosis. In a male smoker with histologically proved histiocytosis X and functional impairment bronchoalveolar lavage showed an increase in CD-1/OKT-6 antigen positive histiocytes to 8%. Northern blot analysis of RNA from bronchoalveolar lavage cells showed an exaggerated expression of the M-CSF gene and of the c-fms gene encoding for the corresponding receptor. An increased level of c-sis RNA, which encodes the B chain of platelet derived growth factor, was also found. Diffuse reticulonodular infiltrates on the chest radiograph resolved with glucocorticoid treatment and CD-1/OKT-6 antigen positive histiocytes fell to 3%. Macrophage colony stimulating factor, c-fms and c-sis gene expression were reduced almost to normal after treatment. The results suggest that macrophage colony stimulating factor and platelet derived growth factor may have a role in the initiation or maintenance of pathological reactions in pulmonary histiocytosis X.

Adult↗

Isolation of v-fms and its human cellular homolog.

The integrated form of McDonough FeSV proviral DNA, including cellular flanking sequences, was molecularly cloned from nonproductively transformed Fisher rat cells. Acquired cellular-derived (v-fms) sequences within the cloned proviral DNA were mapped from between 2.6 and 5.5 kb from the 5'LTR. Upon transfection, the cloned proviral DNA was biologically active; it caused induction of the transformed phenotype and the resulting transformed cells expressed the major McDonough FeSV translational product, P170gag-fms at high level. Using a series of molecular probes representing subgenomic regions of the viral v-fms gene, a cosmid library of human lung carcinoma DNA was screened for v-fms homologous sequences. Three cosmid clones containing overlapping v-fms homologous cellular DNA inserts, representing a contiguous region of cellular DNA sequence of approximately 64 kb in length, were isolated. Within this region of human genomic DNA, v-fms homologous sequences are dispersed over a total region of around 32 kb. These represent the entire human cellular homolog of v-fms, are colinear with the viral v-fms transforming gene, and contain a minimum of four intervening sequences. At least 12 regions of highly repetitive DNA sequences have been mapped in close proximity to c-fms coding sequences.

Animals↗

The kinase activity of the v-fms encoded protein has a low pH optimum.

The protein encoded by v-fms, the oncogene of the Susan McDonough strain of feline sarcoma virus, is a member of the protein tyrosine kinase family. The kinase activity of the v-fms encoded protein has been reported to be low compared to other members of this enzyme family. We found that the optimal pH in vitro for the autophosphorylation of the immunoprecipitated v-fms encoded protein kinase activity was about pH 5.0; the activity at this pH was 15-fold higher than at the pH (7.4) used in standard kinase assays. The low pH optimum of the kinase activity of the v-fms encoded protein was observed when this protein was immunoprecipitated with each of four independent polyclonal antisera. v-fms proteins from transfected rat, mink or hamster cells all showed the same pH optimum for the kinase activity, as did the protein encoded by the feline c-fms gene. Autophosphorylation of v-fms in vitro at pH 5.0 occurred exclusively on tyrosine residues. Enolase was a substrate for the v-fms encoded protein kinase, and the pH profile for phosphorylation of this substrate in vitro paralleled that seen for the autophosphorylation of v-fms encoded proteins. The discovery of the low pH optimum of the kinase activity exhibited by v-fms proteins may be useful for further characterization of this activity in vitro, as well as for phenotypic classification of other members of the protein tyrosine kinase family.

Hydrogen-Ion Concentration↗

[Analysis of c-onc genes in choriocarcinoma cells].

Regulatory or structural alterations of c-onc genes including amplification, rearrangement and point mutation was implicated in the causation of various malignant tumors. However, such changes of molecular levels have not been reported so far in choriocarcinoma cells. In the present study, thus, 5 choriocarcinoma cell lines were analyzed by hybridization using 16 oncogene probes. By Southern blot hybridization of DNA extracted from these cells, 8 fold amplification of c-myc gene and rearrangement of c-fms gene were shown in ENAMI cells, although the role of these alterations remained unknown. Northern blot hybridization performed simultaneously demonstrated multiple expression of c-onc genes. 4 choriocarcinoma cell lines (HCCM, CHl, CCl, ENAMI) expressed at least 11 c-onc genes (H-ras, K-ras, N-ras, c-myc, N-myc, fos, fms, src, yes, erb B and raf); though the degree of expression of H-ras, C-myc, erb B and fms in these cells was either similar or enhanced as compared with normal fibroblast, the expression of two c-onc genes (N-myc and fos) was extremely enhanced. However, expression of K-ras and myb was either low or not detected. The multiple expression of c-onc genes seems to reflect partly on growth advantages of trophoblast. Transfection assay using NIH3T3 cells failed to form any transformed foci. Since choriocarcinoma cells which derived from the transformation of trophoblast of complete mole possess the genetic characteristics identical to the one of cells of complete mole, chromosomal instability was assumed to play a major role for multiple oncogene expression in choriocarcinoma cells.

Cell Line↗

Comparison of the expression and function of the transcription factor PU.1 (Spi-1 proto-oncogene) between murine macrophages and B lymphocytes.

The expression of mRNA encoding the DNA-binding protein PU.1 (Spi-1) is restricted to B lymphocytes and macrophages. The role of PU.1 in tissue-specific transcriptional regulation in the two cell types was examined by co-transfection of a PU.1 expression plasmid with vectors containing B cell (IgH enhancer) or macrophage-specific (c-fms) transcription control elements. Cotransfection of the PU.1 expression plasmid in MOPC31C B cells trans-repressed the IgH enhancer but trans-activated the c-fms promoter. The latter was insufficient to overcome a block to transcription elongation that determines macrophage-specific c-fms gene expression. In the macrophage line RAW264, PU.1 had no effect on the c-fms promoter, but trans-repressed the activity of a c-fms reporter plasmid containing the transcription attenuator. The effects of PU.1 in both cell types were distinct from those of c-ets-2, a related factor, which trans-activated the c-fms promoter in both B cells and macrophages but also repressed the IgH enhancer. PU.1 was shown to be one of several nuclear proteins that bound a critical cis-acting element of the IgH enhancer, microB, but analysis of nuclear extracts of a wide range of B cell and macrophage lines demonstrated a strong correlation between macrophage phenotype and nuclear PU.1 expression. The data suggest that differences in nuclear PU.1 expression and function between macrophages and B cells may play a role in lineage divergence.

Animals↗

Transformation by the v-fms oncogene product: an analog of the CSF-1 receptor.

The product of the c-fms proto-oncogene is related to, and possibly identical with, the receptor for the macrophage colony-stimulating factor, M-CSF (CSF-1). Unlike the product of the v-erbB oncogene, which is a truncated version of the EGF receptor, the glycoprotein encoded by the v-fms oncogene retains an intact extracellular ligand-binding domain so that cells transformed by v-fms express CSF-1 receptors at their surface. Although fibroblasts susceptible to transformation by v-fms generally produce CSF-1, v-fms-mediated transformation does not depend on an exogenous source of the growth factor, and neutralizing antibodies to CSF-1 do not affect the transformed phenotype. An alteration of the v-fms gene product at its extreme carboxyl-terminus represents the major structural difference between it and the c-fms-coded glycoprotein and may affect the tyrosine kinase activity of the v-fms-coded receptor. Consistent with this interpretation, tyrosine phosphorylation of the v-fms products in membranes was observed in the absence of CSF-1 and was not enhanced by addition of the murine growth factor. Cells transformed by v-fms have a constitutively elevated specific activity of a guanine nucleotide-dependent, phosphatidylinositol-4,5-diphosphate-specific phospholipase C. We speculate that the tyrosine kinase activity of the v-fms/c-fms gene products may be coupled to this phospholipase C, possibly through a G regulatory protein, thereby increasing phosphatidylinositol turnover and generating the intracellular second messengers diacylglycerol and inositol triphosphate.

Animals↗

Expression of M-CSF and its receptor (C-FMS) during factor-independent cell line evolution from hematopoietic progenitor cells cocultivated with gamma irradiated marrow stromal cell lines.

Gamma irradiation of plateau-phase clonal bone marrow stromal cell lines produces factor-independent growth of cocultivated clonal interleukin-3/granulocyte-macrophage colony-stimulating factor-dependent hematopoietic progenitor cell lines. The process is associated with three biologic changes including: (i) adherence of hematopoietic cells to stromal cells forming 'cobblestone islands'; (ii) an intermediate stage [during which the cells show proliferation in suspension in the presence in leukemogenic stromal factor (LSF), a factor similar to macrophage colony-stimulating factor (M-CSF) released by irradiated stromal cells, and transient hematopoietic cell surface expression of MAC-1, and c-fms (M-CSF receptor)]; and (iii) a third stage of factor-independence. A monoclonal antibody to M-CSF receptor inhibited proliferation of intermediate stage but not all factor-independent cell subclones. In the present studies, a subclonal factor-independent malignant subline of FDC-P1JL26 derived by cocultivation with gamma-irradiated stromal cells as well as the parent clone and intermediate stage cells were shown to express significant levels of M-CSF polyA+ mRNA and M-CSF of at least two sizes (23 and 15 kDa) as detected by 35S-methionine labelling and immunoprecipitation with polyclonal anti-M-CSF antiserum. There was no significant difference in intracellular M-CSF protein size between cells at each of the three stages of biologic change. This M-CSF was not detected on the cell surface by fluorescence-activated cell sorting (FACS). In contrast, c-fms expression at the cell surface was detected by FACS analysis and c-fms polyA+ mRNA was only detected during the intermediate stage of induction of factor-independence. FDC-P1JL26 parent cells, the subclone stimulated by LSF, and the factor-independent subclone, showed little or no detectable autophosphorylation of the c-fms receptor at tyrosine. There was no detectable rearrangement of the M-CSF or c-fms genes by Southern analysis between clonal lines during the three stages. While we cannot rule out an autocrine mechanism or mutated c-fms receptor mechanism, the data also suggest that evolution of hemopoietic cell factor-independence during cocultivation with irradiated stromal cells may involve a mechanism distal to the c-fms receptor/M-CSF interaction.

Animals↗