Cytotoxic activity of a diptheria toxin/FGF6 mitotoxin on human tumour cell lines

The FGFs constitute a family of, at least, 12 polypeptides (FGF1 to FGF12) implicated in a number of physiological and pathological processes throughout embryogenesis and adult life. They bind to at least three types of cell surface molecules, including four high affinity transmembrane tyrosine kinase receptors (FGFR1 to FGFR4). In addition to important roles during development, FGF involvement in pathological conditions, including tumour formation, has been suspected, and overexpression of FGFR in tumour specimens is well documented. Diphtheria Toxin/FGF6 (DT/FGF6) mitotoxin has been shown to selectively and effectively target FGFR1-expressing cells. We show here that DT/FGF6 targets myoblasts engineered to express either one of the four FGFR, as well as FGFR-expressing tumour cells.

Regional assignment of 64 human gene transcripts on chromosome 8

A panel of somatic cell hybrids specific for human chromosome 8 was used to localize 64 expressed sequence-tagged site (ESTS) markers to six individual regions by PCR amplification. Nine ESTS correspond to 8 known human genes and 6 others show similarities with vertebrate genes, whereas the remaining 49 ESTS markers correspond to novel genes with no database similarities. These gene transcript markers will contribute to the developing physical and expression maps of chromosome 8, and to the search for candidate genes for various human diseases.

Of worms and men: an evolutionary perspective on the fibroblast growth factor (FGF) and FGF receptor families

FGFs (fibroblast growth factors) play major roles in a number of developmental processes. Recent studies of several human disorders, and concurrent analysis of gene knock-out and properties of the corresponding recombinant proteins have shown that FGFs and their receptors are prominently involved in the development of the skeletal system in mammals. We have compared the sequences of the nine known mammalian FGFs, FGFs from other vertebrates, and three additional sequences that we extracted from existing databases: two human FGF sequences that we tentatively designated FGF10 and FGF11, and an FGF sequence from Caenorhabditis elegans. Similarly, we have compared the sequences of the four FGF receptor paralogs found in chordates with four non-chordate FGF receptors, including one recently identified in C. elegans. The comparison of FGF and FGF receptor sequences in vertebrates and nonvertebrates shows that the FGF and FGF receptor families have evolved through phases of gene duplications, one of which may have coincided with the emergence of vertebrates, in relation with their new system of body scaffold.

Emergency aortocoronary bypass grafting after failed percutaneous transluminal angioplasty versus elective bypass grafting

From January 1980 through July 1994 fiftyseven patients underwent emergency coronary bypass grafting (CABG) after unsuccessful percutaneous transluminal angioplasty (PTCA), (Group I). This group was compared with a cohort of 57 patients, who underwent elective coronary bypass grafting (Group II). The 2 groups were compared in the rate of perioperative myocardial infarction, amount of blood loss, rethoracotomy because of bleeding, use of blood units and products, and length of stay in the intensive care unit. The data of both groups were retrospectively analyzed. Significant differences were observed: Perioprative myocardial infarction in group I was 18 patients (31%) versus 2 patients (3%) in group II (p<0.0008). Amount of blood loss was higher (p<0.038), and the use of packed red blood cells was higher too (p<0.000) in group I. The length of stay in the intensive care unit was longer (p<0.000) in group I. Six rethoracotomies (10%) occured in group I versus 0 in group II. There were no hospital mortalities in either groups. We conclude there is a significant increase in morbidity in patients with emergency CABG after failed PTCA than patients who underwent elective CABG.

Biochemical and genetic characterization of multiple splice variants of the Flt3 ligand

We have performed a comprehensive analysis of cell lines and tissues to compare and contrast the expression patterns of Flt3 ligand (FL), c-Kit ligand (KL), and macrophage colony-stimulating factor as well as their receptors, Flt3, c-Kit, and c-Fms. The message for FL is unusually ubiquitous, whereas that of its receptor is quite restricted, apparently limiting the function of the ligand to fetal development and early hematopoiesis. We have also sequenced a mouse FL genomic clone, revealing how the three splice variant FL mRNAs that we have isolated arise. The chromosomal location of the FL gene has been mapped, by in situ hybridization, to chromosome 7 in mouse and chromosome 19 in human. Natural FL protein has been purified from a stromal cell line and shown to be a 65 kD nondisulfide-linked homodimeric glycoprotein comprised of 30 kD subunits, each containing 12 kD of N- and O-linked sugars. Pulse-chase experiments show that one of the splice variants (T110) is responsible for producing the bulk of soluble FL, but only after it has first been expressed at the cell surface as a membrane-bound form. The other splice-variant forms produce molecules that are either obligatorily soluble (T169) or membrane-bound but released only very slowly (T118). Finally, even though most cell lines express some amount of FL mRNA, we found that very little FL protein is actually made, with T cells and stromal cells being the major producers. The data suggests that FL plays its roles over very short distances, perhaps requiring cell-cell contact.

Phosphatidylinositol-3' kinase is not required for mitogenesis or internalization of the Flt3/Flk2 receptor tyrosine kinase

Flt3/Flk2 is a receptor tyrosine kinase that is expressed on early hematopoietic progenitor cells. Flt3/Flk2 belongs to a family of receptors, including Kit and colony-stimulating factor-1R, which support growth and differentiation within the hematopoietic system. The Flt3/Flk2 ligand, in combination with other growth factors, stimulates the proliferation of hematopoietic progenitors of both lymphoid and myeloid lineages in vitro. We report that phosphatidylinositol 3'-kinase (PI3K) binds to a unique site in the carboxy tail of murine Flt3/Flk2. In distinction to Kit and colony-stimulating factor-1R, mutant receptors unable to couple to PI3K and expressed in rodent fibroblasts or in the interleukin 3-dependent cell line Ba/F3 provide a mitogenic signal comparable to wild-type receptors. Flt3/Flk2 receptors that do not bind to PI3K also normally down-regulate, a function ascribed to PI3K in the context of other receptor systems. These data point to the existence of other unidentified pathways that, alone or in combination with PI3K, transduce these cellular responses following the activation of Flt3/Flk2.

Truncation at conserved terminal regions of BRCA1 protein is associated with highly proliferating hereditary breast cancers

The existence of two subgroups of BRCA1-associated breast cancer (BC) families has been recently posited: the first with highly proliferating tumors, and the second composed of cases with a low proliferation rate. Our aim was to test whether the proliferation rate of BRCA1-associated breast cancers was affected by the site of the germ line mutation in the BRCA1 gene. We analyzed the distribution of the mitotic index, a histoprognostic grade component shown to segregate in families, matching for germ line mutation location in a series of 28 breast cancers from 20 kindreds. We observed a prevalence of highly proliferating tumors when the mutation occurs in the two terminal conserved domains of the BRCA1 protein, ie., in the amino and carboxyl termini (P = 0.0024). Our data provide evidence for a genotype-phenotype correlation and along with their strong conservation during evolution argue for the importance of these two regions in the control of mammary cell growth.

Cumulative regional allelotyping of human breast carcinomas

We have analyzed losses of heterozygosity (LOH) at markers from chromosomes 1, 2, 4 and 5 in a panel of 53 consecutive breast carcinomas. Together with a parallel analysis of LOH at chromosome 3, this allowed the identification of twenty-one regions of LOH. In contrast, in a comparative analysis of chromosome X, no region of loss could be defined. Cumulative regional allelotyping of 38 tumors with 71 markers from the five autosomes (37% of the genome) enabled the study of the respective distribution of regions of frequent loss, to identify associations of regions of LOH, and to distinguish tumors frequently affected by LOH such as lobular carcinomas.

Structure and developmental expression of mouse Garp, a gene encoding a new leucine-rich repeat-containing protein

Proteins with leucine-rich repeats (LRR) constitute a large family of molecules playing a role in protein-protein interactions and signal transduction. They are involved in various cellular processes in different species. We characterized the organization and pattern of expression of the mouse Garp gene. It is composed of two coding exons, expressed as a major 4.3 kb mRNA, and encodes a putative LRR transmembrane protein with an extracellular region almost entirely made of 20 repeats, and a short intracytoplasmic region. The mouse GARP deduced amino-acid sequence is highly similar to that of the human protein. The Garp gene is expressed in various areas in the mid-gestation developing embryo, including skin, lens fibre cells, nasal cavity, smooth and skeletal muscles, lung, and megakaryocytes of the fetal liver. In the adult it is expressed in the megakaryocytes of the spleen and in endothelial cells of the placenta. The data suggests that GARP might be involved in platelet-endothelium interactions.

Expression of FGF1 and FGFR1 in human melanoma tissues

Fibroblast growth factor 2 (FGF2) has been implicated in the pathogenesis of malignant melanoma (MM), but the role of other FGFs and their receptors (FGFRs) is not elucidated. To determine whether FGF1 and FGFR1 may be involved in MM growth in vivo, we have studied the expression of the FGF1 and FGFR1 genes in 77 fresh MM biopsy samples, using RT-PCR analysis. Samples of benign nevi, normal skin and carcinoma cell lines were included as controls. Using RT-PCR analysis, expression of FGF1 and FGFR1 was observed in 69/77 and 68/77 cases, respectively. Immunohistochemical detection of the FGFR1 protein was positive in reactive stromal cells and at a much lower level in neoplastic cells. In situ hybridization experiments demonstrated FGFR1 mRNA mainly located in the stromal component. Southern blot analysis of genomic DNA prepared from MM tumors did not show any structural alteration of the FGFR1 gene. There was no correlation between FGF1/FGFR1 expression and the usual clinicopathological parameters of MM. We conclude that FGF1 and FGFR1 are frequently co-expressed in MM, a situation that may contribute to aberrant autocrine and paracrine pathways. Due to the absence of correlation with clinico-pathological parameters, this expression cannot be used as a marker of prognosis in the management of MM patients.

Interaction with the phosphotyrosine binding domain/phosphotyrosine interacting domain of SHC is required for the transforming activity of the FLT4/VEGFR3 receptor tyrosine kinase

The FLT4 gene encodes two isoforms of a tyrosine kinase receptor, which belongs to the family of receptors for vascular endothelial growth factor. As the result of an alternative processing of primary mRNA transcripts, the long isoform differs from the short isoform by an additional stretch of 65 amino acid residues located at the C terminus and containing three tyrosine residues, Tyr1333, Tyr1337, and Tyr1363. Only the long isoform is endowed with a transforming capacity in fibroblasts. We show that this activity is related to the capacity of the tyrosine 1337-containing sequence to interact with the phosphotyrosine binding domain of the SHC protein. This demonstrates that a functional property of this newly described domain includes relay of mitogenic signals. In addition, it shows that the same receptor can mediate different functions through the optional binding of the phosphotyrosine binding domain and that the alternative use of this domain is sufficient to direct the signal toward different pathways.

Expression of the FLT4/VEGFR3 receptor tyrosine kinase encoding gene in hepatic tumors

The FLT4/VEGFR3 tyrosine kinase receptor belongs to a class of receptors for growth factors of the vascular endothelial growth factor family and is important for the biology of lymphatic endothelium. It may play an important role in tumor growth. We have looked for the expression of the FLT4 gene in tumors of various origins. FLT4 expression was not found except in some particular type of tumors: mouse hepatic tumors but not cell lines were shown to expressed Flt4 at a high frequency while Flt4 mRNA was absent or weakly expressed in normal liver, suggesting that Flt4 de novo expression in liver nonparenchymal cells participates in tumor development of this tissue.

FGF6 modulates the expression of fibroblast growth factor receptors and myogenic genes in muscle cells

Fgf6 is the only known member of the FGF family whose expression is restricted to the muscle cell lineage during development, suggesting it may have a role in myogenesis. Muscle satellite cells but not C2 myoblast cells were found to express Fgf6. We have used purified recombinant FGF6 protein to explore the effect of this factor on C2 cells in culture. FGF6 stimulated the proliferation of C2 myoblasts and, in combination with heparin, induced their morphological transformation. FGF6, added at 5 ng/ml and in the presence of heparin, increased the expression of a subset of muscle cell differentiation markers. In contrast, at 25 ng/ml, it down-regulated the expression of myogenic markers and myogenic transcription factors examined and delayed differentiation into myotubes of C2 cells. It also up-regulated the expression of FgfR1 and had an opposite effect on FgfR4. These results suggest that intramuscular FGF6 concentrations could influence the proliferation and differentiation processes taking place during development.

Predominant expression of the long isoform of Bcl-x (Bcl-xL) in human lymphomas

Bcl-x is a member of the bcl-2 family of proteins which are characterized by their ability to modulate apoptosis. Alternative splicing results in two distinct bcl-x mRNAs encoding a long isoform, bcl-xL, which acts as a bcl-2 agonist; and a short isoform, bcl-xS, which inhibits bcl-2 effects. The aim of the study was to determine whether bcl-x is expressed in lymphoma tissues and to characterize the respective production of bcl-xs and bcl-xL. We investigated the expression of bcl-x mRNA in a series of 50 non-Hodgkin's lymphomas (NHL) and Hodgkin's disease (HD) cases using a RT-PCR method in order to amplify both transcripts simultaneously, and to estimate their relative abundance. The rearrangements of the bcl-2 gene were analysed by RT-PCR expression of the hybrid bcl-2-lgH mRNA. In addition, 20 PCR-positive NHL cases and three HD cases were analysed by immunohistochemistry using bcl-x polyclonal antisera. RT-PCR showed bcl-x expression in 43/45 NHLs and 5/5 HD cases. The bcl-xL transcript was predominant in all positive cases and was associated with variable amounts of bcl-xS. There was no significant correlation between the profile of bcl-xL/bcl-xS expression and the histological and immunological subtyping. Bcl-x immunodetection was positive in the neoplastic cell component in all analysed cases, but the degree of staining was highly variable between cases. Expression of the hybrid bcl-2-IgH gene was detected by RT-PCR in five cases of follicular NHL and in one case of HD, but this group of tumours did not display a particular profile of bcl-xL/bcl-xS expression. We conclude that bcl-x is commonly expressed by malignant cells in various types of malignant lymphomas, with a predominance of the bcl-xL transcript. Since the corresponding bcl-xL isoform can block the cell death machinery and potentialize bcl-2 effects, it may be involved in some pathways of lymphomagenesis.

Integrated map of the chromosome 8p12-p21 region, a region involved in human cancers and Werner syndrome

Detailed physical maps of the human genome are important resources for the identification and isolation of disease genes and for studying the structure and function of the genome. To improve the definition of the 8p12-p21 chromosomal region, an integrated physical and genetic map was constructed extending from the genes. NEFL to FGFR1. The map comprises a series of contigs (the larger of these being around 9 Mb) of yeast artificial chromosomes (YACs) spanning the proximal region of deletion involved in a broad range of human cancers, including breast carcinomas, and in the Werner syndrome. In addition, losses of heterozygosity at 8p markers and linkage analysis of breast cancer families were also detailed. Finally, several genes potentially involved in 8p-associated diseases, namely GTF2E2, PPP2CB, and HGL, were precisely mapped within the YAC contigs. The reported map and contigs of YACs should facilitate the search for putative genes involved in sporadic and familial breast cancer as well as in the Werner syndrome.

Effects of FLT3 ligand on human leukemia cells. I. Proliferative response of myeloid leukemia cells

The growth of cells in vitro and in vivo is regulated by several environmental signals among which growth factors (cytokines) figure prominently. FLT3 is a novel cytokine receptor with intrinsic ligand-stimulated (FLT3 ligand, FL) tyrosine kinase activity. Here, using a specific anti-FLT3 monoclonal antibody (McAb) and flow cytometry we determined the expression pattern of the receptor protein in 55 human leukemia-lymphoma cell lines and in 20 primary samples from patients with acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML). FLT3 receptor surface expression was found predominantly in pre-B cell, myeloid and monocytic cell lines and in pre-B-ALL and AML cells, FL was overexpressed in baby hamster kidney cells producing a recombinant protein that was functional in receptor binding and signaling. Incubation with FL induced 3H-thymidine uptake-measured proliferation in some myeloid cell lines and in 2/9 AML cases. The strongest proliferative response was seen in the two growth factor-dependent myeloid leukemia cell lines MUTZ-2 and OCI-AML-5. Long-term substitution of the commonly used cytokines with FL sustained the continuous proliferation of these two cell lines suggesting that also upon permanent activation FLT2 can function as a mitogenic signaling molecule. Despite the high density of FLT3 receptor expression on cultured and fresh pre-B-ALL cells, no proliferation could be stimulated in any of these specimens. Incubation with the anti-FLT3 McAb had agonistic proliferative effects in MUTZ-2 and OCI-AML-5; and anti-FL reagent blocked FL-stimulated proliferation. To summarize, we demonstrated that FL is effective in inducing proliferation of leukemic myeloid cells and that protein expression does not necessarily indicate an FL-responsive cell. While the present data clearly demonstrate that FL might play a proliferative role in leukemogenesis, further studies are needed to clarify whether the signals provided by FL:FLT3 interaction are confined to a proliferation-inducing function or whether maturational progression could also be elicited in certain cells.

Human FLT3/FLK2 receptor tyrosine kinase is expressed at the surface of normal and malignant hematopoietic cells

FLT3/FLK2 is a receptor tyrosine kinase (RTK) which is thought to play an important role in early stages of hematopoiesis. Monoclonal antibodies (mAbs) against the extracellular domain of human FLT3 were generated to study the cell surface expression of this class III RTK on normal bone marrow cells and on leukemic blasts from patients with acute leukemias. Functional analysis of five mAbs (SF1 series) revealed that all of them can mimic to variable extents the activity of the FLT3 ligand (FL) upon receptor activation and modulation, while only one mAb weakly inhibited ligand binding. Using flow cytometry, we detected surface expression of FLT3 on cell lines of the myeloid (4/8) and B lymphoid (7/10) lineages. On normal human bone marrow cells, the expression of FLT3 is restricted, in agreement with a presumed function of this receptor at the level of the stem cells and early committed progenitors. Expression of FLT3 was found on a fraction of CD34-positive and CD34-negative cells. Three-color analysis further revealed that most of the CD34 FLT3+ cells coexpress CD117 (KIT) at a high level. Finally, FLT3 is expressed on leukemic blasts of 18/22 acute myeloid leukemias (AML) and 3/5 acute lymphoid leukemias (ALL) of the B lineage, providing a possible application in diagnosis and therapy of these diseases.

Germ line mutation at BRCA1 affects the histoprognostic grade in hereditary breast cancer

Histoprognostic grade is a determinant parameter to select the initial therapeutic strategy in breast cancer. Our aim was to analyze the grade repartition in BRCA1-associated breast cancer (BC) and to explore the possible connections between grade and the BRCA1 gene function. We first compared 27 BRCA1-associated BCs from 14 families with 4,461 cases from an administrative district registry and 242 cases from a hospital-based registry, matching for grade and constitutive elements, and then considered their repartition in families. We observed a prevalence of grade 3 (P < 0.0001) in BRCA1-associated BC. This was attributed mainly to nuclear polymorphism (P < 0.0001), mitotic activity (P < 0.0001), and tubular differentiation (P = 0.0004), implying that BRCA1-associated BCs are highly proliferating tumors. Moreover, it is suggested that grade segregates as a genetic trait within families (P = 0.0015), and this was attributed to the mitotic index segregation only (P = 0.0005). Therefore grade, through its components, could be interpreted as the morphological translation of the BRCA1 germ line mutation. Thus, a genotype-phenotype correlation may exist between the type of mutation and the aggressiveness of the disease. These findings are bound to have an important impact in the care management of hereditary breast cancer at the individual and at the familial level and in the comprehensive approach of breast cancer development.

Molecular analysis of the NPM-ALK rearrangement in Hodgkin's disease

The fusion gene NPM-ALK occurs in a subset of anaplastic large cell lymphomas (ALCLs), as a result of a chromosomal translocation, t(2;5) (p23;q35). It has been suggested that Hodgkin's disease (HD) and ALCL share a common histogenesis because of pathological and phenotypical similarities. In order to check this hypothesis, reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to detect the hybrid NPM-ALK gene in 30 tumour samples, including 22 lymph node biopsies from HD and eight ALCL specimens. The threshold level of sensitivity was shown to reach at least 1/10(4) by dilution experiments using cell lines as positive and negative controls. The expected 177 bp product indicative of the NPM-ALK rearrangement was identified in Karpas 299 and SUDHL-1 cell lines and in two out of eight ALCLs. The 22 HD cases were negative, even after two successive tests. Thus, since the ALCL-specific genetic alteration was absent in our series of HD cases, the present study does not support the hypothesis that HD and ALCL are histogenetically related entities.

A 3.1-Mb YAC contig within the Werner syndrome region, on the short arm of human chromosome 8

The locus for Werner syndrome (WRN) has been localized to human chromosome 8p21 --> p12, close to the anonymous marker D8S339. A 3.1-Mb contig of yeast artificial chromosomes (YACs) was assembled around D8S339. Results from analyses of somatic cell hybrids, FISH, and physical mapping suggest the following loci order: tel-NEFL-D8S131-D8S339-[D8S540/GSR]-D8S124 -D8S259-D8S87-FGFR1-cen. Close physical linkage between D8S540 and GSR was established within a DNA fragment of 200 kb. These two loci are not more than 400 kb from D8S339. In addition, D8S339, D8S540, D8S124, and GSR are within 1.1 Mb. These data establish a primary physical map of the Werner syndrome region and identify useful YAC clones for the isolation of new markers and of the corresponding gene.

Expression and signal transduction of the FLT3 tyrosine kinase receptor

FLT3 is a receptor tyrosine kinase of 130-55 kDa expressed on normal bone marrow stem and early progenitor cells and on leukemic blasts from patients with acute leukemias. The FLT3 ligand, FL, is a new cytokine which acts on hematopoietic progenitors in synergy with other cytokines. FLT3 transduces FL-mediated signal through interaction with a number of cytoplasmic substrates.

[Abnormal signal transduction and cancer]

Molecules involved in communication and signal transduction play a key role in the control of cell growth and differentiation. Growth factors are multifunctional regulatory peptides acting through membrane receptors, a number of which has tyrosine kinase activity. Downstream, cytoplasmic substrates transduce the signal to the nucleus. This cascade can be altered by structural mutations or by deregulation and thus participate to tumorigenesis.

Mutation at tyrosine residue 1337 abrogates ligand-dependent transforming capacity of the FLT4 receptor

In humans, the FLT4 gene encodes two isoforms of a tyrosine kinase receptor, which differ in their carboxy terminal regions. As compared to the short form, the long form has an additional stretch of 65 amino acids containing three tyrosine residues (Y1333, Y1337 and Y1363). Once expressed in fibroblast cells, only the long form is able to elicit both anchorage-independent growth in a soft agar assay and tumors in nude mice, and thus appears endowed with a potential ligand-dependent transforming capacity. Replacement of tyrosine 1337 by phenylalanine abrogates the transforming capacity of the long form. This residue was identified as a potential autophosphorylation site, and a docking site for a substrate important in the signal transduction specific of the long FLT4 isoform. We demonstrate that the GRB2 and SHC cytoplasmic substrates are involved in FLT4 signal transduction. SHC interaction could be crucial to FLT4-mediated transforming activity associated with the long isoform. Finally, trancripts for the two forms are detected in tissues positive for FLT4 gene expression.

A diphtheria toxin/fibroblast growth factor 6 mitotoxin selectively kills fibroblast growth factor receptor-expressing cell lines

The fibroblast growth factors (FGFs) constitute a family of nine polypeptides implicated in a number of physiological and pathological processes. They bind to at least three types of cell surface molecules, including low and high affinity receptor families. The role of FGFs and their receptors in human tumorigenesis has been suspected but not formally proven. FGF6 is an oncogene encoding a precursor protein of 208 amino acids that has been shown to bind to FGF receptors. Its normal function has not been identified, but its restricted pattern of expression suggests a role in muscle development or function. We have constructed, produced, and purified a diphtheria toxin/FGF6 mitotoxin that selectively kills FGF receptor-expressing cells. Interestingly, at least two cell lines that normally respond to FGF6 have been found resistant to DT/FGF6, suggesting that FGF6 acts on these cells through a transduction pathway that does not involve FGF receptor.

Patterns of loss of heterozygosity at loci from chromosome arm 13q suggests a possible involvement of BRCA2 in sporadic breast tumors

Loss of heterozygosity (LOH) at loci from chromosome 13 is frequently observed in breast cancer. Chromosome 13 contains at least two cancer genes, the well-characterized RB1 gene located at 13q14 and the breast cancer-susceptibility gene, BRCA2, recently localized to 13q12. To investigate the possible involvement of BRCA2 in sporadic breast tumors, we looked at LOH at eight microsatellite (CA)n markers distributed along chromosome 13 in a panel of 59 primary breast carcinomas. We show that some LOH does not include the RB1 locus and is associated with the BRCA2 gene region.

Expression of FLT3 receptor and FLT3-ligand in human leukemia-lymphoma cell lines

The FLT3 gene encodes a receptor tyrosine kinase that is closely related to two well-known receptors, KIT and FMS, that regulate with their respective ligands, stem cell factor (SCF) and macrophage colony-stimulating factor (M-CSF), proliferation and differentiation of hematopoietic cells. The ligand for FLT3, FL, is active in both soluble and membrane-bound forms. We examined expression of FL and FLT3 mRNA in a panel of some 110 continuous human leukemia-lymphoma cell lines from all major hematopoietic cell lineages by Northern blot analysis. FLT3 mRNA is expressed primarily in pre-B cell lines, myeloid and monocytic cell lines whereas FL mRNA was detected in most cell lines from all cell lineages. Analysis of FLT3 receptor protein expression examined with a specific anti-FLT3 monoclonal antibody and flow cytometry in 17 cell lines confirmed the results obtained at the mRNA level. Forty of 110 cell lines displayed both receptor and ligand mRNA suggesting a possible autocrine or intracrine stimulation. In normal hematopoietic cells expression of FLT3 was reported to be associated with CD34 positivity, a cell surface marker of immature and precursor cells. No correlation between FLT3 and CD34 expression was found in the cell lines analyzed. These studies served to illustrate further the importance of the FL-FLT3 ligand-receptor system in the regulation of hematopoietic cells.

Expression of Flt3 tyrosine kinase receptor gene in mouse hematopoietic and nervous tissues

The Flt3 gene encodes a tyrosine kinase receptor highly related to the Kit and Fms gene products. We have studied the expression of Flt3 by using in situ hybridization of mouse tissue sections. The results show that Flt3 RNAs are present in certain regions of lymphohematopoietic organs, placenta and nervous system. Flt3 is expressed in the medullary area of fetal and newborn thymus, in the paracortical regions of lymph nodes and in the red pulp of spleen. In placenta, labyrinthine trophoblasts express Flt3. Finally, Flt3 RNAs are found in several regions of the brain and in cerebellar Purkinje cells. Western-blot analysis showed that the FLT3 protein is present in the tissues positive for Flt3 RNA expression. Our observations allow for a comparison with the distribution of the Kit gene and analysis of a possible redundancy between KIT and FLT3 receptors.

Expression of FGF and FGF receptor genes in human breast cancer

The family of FGF growth factors is involved in several biological processes and might play an important role in tumorigenesis. We have studied the respective expression of 8 of the 9 characterized FGF genes, and of the 4 known FGF receptor genes, in a panel of 10 tumor-cell lines and 103 breast-tumor samples, using RT-PCR and Northern-blot analyses. FGF1 and FGF2 were expressed in almost all samples, while expression of FGF5, FGF6, FGF7, and FGF9 was more restricted. FGFR1, FGFR2 and FGFR4 were expressed at high levels in respectively 22%, 4% and 32% of tumors. FGFR3 expression was not detected. The transcript encoding an FGFR1 isoform with 2 immunoglobulin-like domains was the most prevalent.

Characterization of the region of the short arm of chromosome 8 amplified in breast carcinoma

Chromosomal region 8p11.2-p12 is consistently amplified in human breast cancer. We have constructed a 2.8 Mb YAC contig of this region, centered on the human Fibroblast Growth Factor Receptor 1 (FGFR1) locus and encompassing the Adrenergic beta 3 Receptor (ADRB3) locus. A smaller centromeric YAC contig spanning 1.4 Mb was also assembled, and included the Ankyrin 1 (ANK1) and Tissue-type Plasminogen Activator (PLAT) genes. Results from mapping of the contigs showed physical linkage of the ADRB3 and FGFR1 genes, which were colocalized within the same YAC clone and separated by about 900 kb, FGFR1 being in centromeric position. It also showed physical linkage of ANK1 and PLAT genes, which appear to be separated by a maximum of 700 kb. In parallel, several loci were mapped according to their amplification status in a large panel of breast tumor samples. The overall amplification pattern suggested a continuous amplicon with a core around FGFR1. Data from both the detailed physical map and the amplification status allowed to establish the following gene order, from telomere to centromere: ADRB3-D8S105-FGFR1-ANK1-PLAT-POLB. The precise localization and YAC cloning of the core of the amplicon will allow to isolate a putative oncogene involved in mammary carcinogenesis.

Biochemical characterization of two isoforms of FLT4, a VEGF receptor-related tyrosine kinase

The FLT4 gene encodes a tyrosine kinase receptor related to the two identified receptors for vascular endothelial growth factor (VEGF), FLT1 and FLK1/KDR. Two isoforms of FLT4, differing by their C-terminal ends, have been identified. The long form has 65 additional amino acid residues. We have shown that FLT4 is a highly glycosylated, relatively stable, cell surface associated kinase of approximately 180 kDa. In order to study the signal transduction molecules associated with the FLT4 pathway, and in the absence of a known ligand, we constructed two chimeric molecules (FF4S and FF4L) made of the extracellular region of the CSF1 receptor (Fms gene product) and of the transmembrane and intracellular regions of either form of FLT4. These two chimeric forms were expressed in Rat 2 transfectants. We assayed the ligand-induced capacity of the FF4 short and long forms to sustain growth of Rat 2 cells in semisolid medium. In a soft agar assay, only the long form was able to induce the growth of Rat 2 cells upon ligand treatment. The two forms of FLT4 therefore have different functional capacities. We looked for association and/or phosphorylation of phospholipase C gamma (PLC gamma) and phosphatidylinositol-3'-phosphate (PI3K), after stimulation of the FF4 molecules by CSF1. Finally, we have studied the expression of the Flt4 gene in mouse embryos and in the adult by in situ hybridization. Flt4 transcripts were found at day 12.5 post-coïtum and thereafter, including the adult mouse, predominantly in the pericardium, pleural membranes and in the lung.

Identification and characterization of a functional murine FLT3 isoform produced by exon skipping

The FLT3 gene encodes an hematopoietic receptor related to the receptors for colony-stimulating factor 1, FMS, and for Steel factor, KIT. The extracellular part of these molecules is exclusively composed of five immunoglobulin (Ig)-like domains, designated 1 to 5, from the amino terminus to the carboxyl terminus of the extracellular region. We have isolated a unique murine FLT3 cDNA that codes for a variant isoform of FLT3, devoid of the fifth Ig-like domain, by comparison with the prototypic form. The corresponding mRNA is the result of a splicing event that leads to the elimination of two coding exons. mRNA coding for this variant was detected in almost all the tissues expressing the mRNA coding for the prototypic molecule, although at a lower level. Ligand-induced tyrosine phosphorylation of the two isoforms was equivalent in COS-1 transfected cells, indicating that the fifth Ig-like domain is not strictly necessary for either ligand-binding or kinase activation.

Oesophageal cancer and amplification of the human cyclin D gene CCND1/PRAD1

The human CCND1/PRAD1 gene, located in the 11q13 chromosomal region, encodes a cyclin D protein with potential oncogenic capacity and is involved in several human malignancies. The amplification and expression status of CCND1 was investigated in a series of oesophageal tumours. CCND1 is amplified in 54% and overexpressed in 63% of the tumours of the squamous cell type.

Allelic loss at markers of chromosomal band 7q31 is not a frequent event in human breast-cancer

Loss of heterozygosity (LOH) at loci from the long arm of chromosome 7 was shown to occur in breast carcinomas. However, the frequency with which this alteration is observed varies from 0 to 40%. We report LOH at three microsatellite markers located at 7q3 in 16 of 66 (24%) breast tumor samples.