Human gene (c-fes) related to the onc sequences of Snyder-Theilen feline sarcoma virus

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.

Studies of the proliferation and differentiation of immature myeloid cells in vitro: 4: Preculture proto-oncogene expression and the behaviour of myeloid leukemia cells in vitro

Studies were conducted to determine the relationship between the pretherapy characteristics of leukemia cells and their behaviour during culture in vitro. Leukemia cells which proliferated well in vitro also proliferated well in vivo. Cells which manifested myeloid or monocytic differentiation in vivo tended to manifest differentiation along these lines in vitro. Cells which manifested high levels of expression of c-fms, c-fes, or triose phosphate isomerase prior to culture were likely to differentiate in vitro, with high levels of c-fes expression being related to myeloid maturation. These observations suggest that differentiation at the molecular level prior to culture is a requisite for leukemia cell differentiation in vitro. The same may be true for differentiation in vivo under the influence of exogenously administered agents such as cytotoxic chemotherapy or recombinant growth factors.

Studies of proto-oncogene expression in the chronic and blastic phases of chronic myelogenous leukemia

Chronic and blastic phase chronic myelogenous leukaemia cells have been studied by northern and Southern blot analysis. DNA from matched chronic and blastic phase cells obtained from the same patient demonstrated that the rearrangement site within the breakpoint cluster region did not change at the time of blastic crisis. A search for a mutation in a controlling region of the first exon of c-myc also failed to demonstrate any new abnormality at the time of blastic crisis. While some differences in the transcript levels for several genes (c-myc, p53, histone H3, MRS) were detected, these differences could be ascribed to differences in the proportions of immature cells during the chronic and blastic phases. The data suggested that the c-myc transcripts in blastic phase cells and in immature chronic phase cells differ in that the latter contain some c-myc transcripts that are not polyadenylated. Differences in c-myc transcript half-life could contribute to the differences in the behaviour of chronic phase and blastic phase immature cells.

Avian sarcoma viruses

Twelve independent isolates of avian sarcoma viruses (ASVs) can be divided into four groups according to the transforming genes harbored in the viral genomes. The first group is represented by viruses containing the transforming sequence, src, inserted in the viral genome as an independent gene; the other three groups of viruses contain transforming genes fps, yes or ros fused to various length of the truncated structural gene gag. These transforming sequences have been obtained by avian retroviruses from chicken cellular DNA by recombination. The src-containing viruses code for an independent polypeptide, p60src; and the representative fps, yes and ros-containing ASVs code for P140/130gag-fps, P90gag-yes and P68gag-ros fusion polypeptides respectively. All of these transforming proteins are associated with the tyrosine-specific protein kinase activity capable of autophosphorylation and phosphorylating certain foreign substrates. p60src and P68gag-ros are integral cellular membrane proteins and P140/130gag-fps and P90gag-yes are only loosely associated with the plasma membrane. Cells transformed by ASVs contain many newly phosphorylated proteins and in most cases have an elevated level of total phosphotyrosine. However, no definitive correlation between phosphorylation of a particular substrate and transformation has been established except that a marked increase of the tyrosine phosphorylation of a 34,000 to 37,000 dalton protein is observed in most ASV transformed cells. The kinase activity of ASV transforming proteins appears to be essential, but not sufficient for transformation. The N-terminal domain of p60src required for myristylation and membrane binding is also crucial for transformation. By contrast, the gag portion of the FSV P130gag-fps is dispensable for in vitro transformation and removal of it has only an attenuating effect on in vivo tumorigenicity. The products of cellular src, fps and yes proto-oncogenes have been identified and shown to also have tyrosine-specific protein kinase activity. The transforming potential of c-src and c-fps has been studied and shown that certain structural changes are necessary to convert them into transforming genes. Among the cellular proto-oncogenes related to the four ASV transforming genes, c-ros most likely codes for a growth factor receptor-like molecule. It is possible that the oncogene products of ASVs act through certain membrane receptor(s) or enzyme(s), such as protein kinase C, in the process of cell transformation.

Differing patterns of proto-oncogene expression in immature and mature myeloid cells

Comparisons of the level of proto-oncogene expression in neoplastic cells and in normal cells are being made to determine the role of these genes in neoplastic development. Recent papers have reported that leukemic cells differ from normal cells in having higher c-myc RNA levels. One problem in interpreting these data is that leukemic and normal cell populations differ in the proportion of immature cells present in each. The studies described here, using chronic phase chronic myelogenous leukemia (CML) cells, compared the level of proto-oncogene expression in immature and mature myeloid cells. Substantial differences in the level and pattern of expression were found with the immature cells containing higher c-myc RNA levels and the mature cells containing higher histone H3 RNA levels. c-fos RNA levels parallel the distribution of monocytes. While the c-myc RNA level in the CML cell population as a whole is similar to that in normal marrow cell populations and less than that in the bone marrow cells of patients with acute myelogenous leukemia (AML), c-myc RNA levels in subpopulations of immature chronic phase CML myeloid cells approximate that found in AML cells. Additionally, the studies described here suggest that the presence of high c-myc and c-fos RNA levels in light density immature cells may be a unique characteristic of acute myeloid leukemic cells.

Expression of cellular oncogenes in teratoma-derived cell lines

The expression of ten proto-oncogenes was studied in cell lines derived from transplantable mouse teratomas. The cell lines represent different forms of early embryonic cell specialization. The analysis included two embryonal carcinoma (EC) lines (PCC3 and F9), and four differentiated cell lines derived from teratocarcinoma, namely trophoblastoma (3-TDM), parietal endoderm (PYS-2), visceral endoderm (PSA5-E) and skeletal myoblasts (Cl10). The expression of c-oncogenes was studied by analysing poly(A)+RNA for complementary sequences by dot blot and Northern blot hybridization. The results were related to the rate of cell multiplication and the state of differentiation by examining [3H]thymidine incorporation, growth curves and tissue-specific differentiation markers. Expression of c-myc and c-Ki-ras was found in all cell lines. In dot blot assays, poly(A)+RNA from all cell lines also hybridized with v-abl and v-sis probes. A marked decrease in c-myc expression was found in teratoma-derived myoblasts differentiating into myotubes. A similar reduction was found when 'nullipotent' F9 cells were induced by retinoic acid (RA) to form primitive endoderm. However, reduction of the growth rates of the parietal and visceral endodermal cell lines were not accompanied by decreased expression of c-myc or c-Ki-ras. Hybridization signals obtained with a v-sis probe was low in all teratoma-derived cell lines tested, except for the myogenic cell line Cl10. Both in exponentially growing and differentiated cultures of this line, two size classes of transcripts hybridized strongly to the v-sis probe. However, these transcripts, 7 and 3 kb, most likely represent endogenous retroviral transcripts and not c-sis transcripts. Expression of c-myb, c-mos, c-fes, c-src and c-erb A and c-erb B could not be detected in any of the cell lines studied.

Expression of human c-fes onc-gene occurs at detectable levels in myeloid but not in lymphoid cell populations

Total cellular RNA from a variety of myeloid and lymphoid cell populations, normal and leukaemic, was analysed for the expression of a human cellular onc-gene, c-fes, by northern blot hybridization assays. The probe used was a molecularly cloned human DNA sequence homologous to the 5' terminal sequence of v-fes. All the myeloid cellular populations expressed the c-fes gene. In some cell populations at an advanced stage of differentiation (circulating leucocytes from Chronic myeloid leukaemia (CML), HL60 cells induced to differentiate by retinoic acid) the level of expression was even higher than in early stages of the myeloid lineage (blast cells from AML, uninduced HL60 cells). No transcript of the c-fes gene was detected in the different lymphoid populations studied. The occurrence of an RNA complementary to the c-fes sequence appears sufficiently characteristic of a myeloid population to distinguish it from a lymphoid population, normal and leukaemic.

Molecular cloning of the feline c-fes proto-oncogene and construction of a chimeric transforming gene

The feline c-fes proto-oncogene, different parts of which were captured in feline leukemia virus (FeLV) to generate the transforming genes (v-fes) of the Gardner-Arnstein (GA) strain of feline sarcoma virus (FeSV) and the Snyder-Theilen strain (ST) of FeSV, was cloned and its genetic organization determined. Southern blot analysis revealed that the c-fes genetic sequences were distributed discontinuously and colinearly with the v-fes transforming gene over a DNA region of around 12.0 kb. Using cloned c-fes sequences, complementation of GA-FeSV transforming activity was studied. Upon replacement of the 3' half of v-fesGA with homologous feline c-fes sequences and transfection of the chimeric gene, morphological transformation was observed. Immunoprecipitation analysis of these transformed cells revealed expression of high Mr fusion proteins. Phosphorylation of these proteins was observed in an in vitro protein kinase assay, and tyrosine residues appeared to be involved as acceptor amino acid.

Variation in myc gene amplification and expression in sublines of HL60 cells

Three sublines of the human promyelocytic leukaemia cell line HL60 have been isolated. Histochemical, karyotypic and immunological analyses have confirmed the identity of the three sublines as HL60. However, the extent to which c-myc homologous DNA sequences are amplified in the genomes of these cells varies from 4- to 30-fold. Moreover, the relative abundance of c-myc-related RNA sequences in uninduced cells of each subline is directly proportional to the gene copy number. It is concluded that, while high levels of the c-myc gene and its transcripts may have had a role in the establishment of HL60 cells, these are not required for maintenance of the HL60 phenotype. However we cannot rule out the possibility that a low level of amplification and enhancement of transcription has a role in maintenance of this phenotype.

Chromosomal sublocalization of human c-myb and c-fes cellular onc genes

The transforming genes of acutely transforming retroviruses are derived from conserved cellular genes (c-onc genes) which are believed to be important in normal cell growth and differentiation. Recent studies indicate that altered expression of c-onc genes, for example, by insertion of viral genomes, gene amplification or chromosomal translocation, can lead to development of malignant diseases in man and animals. c-myb and c-fes are homologues of the transforming genes of avian myeloblastosis virus and feline sarcoma virus (Gardner and Snyder-Theilen strains), respectively. c-myb is transcribed preferentially in immature haematopoietic cells and probably codes for a protein important in differentiation of these cells. The viral fes gene, like several other viral onc genes, encodes a tyrosine-specific protein kinase. However, c-fes transcripts have not been detected in the types of human cells examined so far. c-myb and c-fes have been assigned to human chromosomes 6 and 15, respectively. Specific aberrations involving these chromosomes have been observed at high frequency in several human neoplasms. We have now sublocalized c-myb to 6q22-24 and c-fes to 15q25-26 by in situ hybridization of the human c-onc probes to human mitotic chromosome preparations. These chromosomal segments are indeed involved in nonrandom translocations in several human tumours. The results encourage further investigation into the role of onc genes in the pathogenesis of specific neoplasms.

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.

Cellular onc genes: their role as progenitors of viral onc genes and their expression in human cells

Viral transforming (v-onc) genes are derived from cellular (c-onc) genes that are highly conserved among vertebrates. Comparative studies of v-onc and c-onc genes have shed some light on the mechanism leading to formation of the transforming viruses. A specific example of the sis gene is presented here for illustration. Studies on the expression of six c-onc genes in human cells revealed at least three categories of onc genes: (a) those that are universally expressed and probably are important in basic cellular functions, (b) those that are not detectably expressed in the cells examined and may have very transient expression in development, and (c) those that are only expressed in specific cell types and may be important in tissue differentiation. Our studies do not show conclusively a role of these onc genes in human neoplasias.