Showing papers by "Kari Alitalo published in 1993"

Two alternative mRNAs coding for the angiogenic factor, placenta growth factor (PlGF), are transcribed from a single gene of chromosome 14.

Abstract: We have previously reported on the identification of a cDNA (placenta growth factor, PlGF) coding for a novel angiogenic factor expressed in placental tissue that is similar to vascular permeability factor/vascular endothelial growth factor (VPF/VEGF). Biochemical and functional characterization of PlGF derived from transfected COS-1 cells revealed that it is a glycosylated dimeric secreted protein able to stimulate endothelial cell growth in vitro. Here, we report the isolation and characterization of the PlGF gene located on chromosome 14. At least two different mRNAs are produced from this single-copy gene in different cell lines and tissues. Sequence comparison of the polypeptides encoded by the two different isolated cDNAs indicates that they are identical except for the insertion of a highly basic 21 amino acid stretch at the carboxyl end of the protein. RNA expression analysis of several tissues, tumors and cell lines indicates differential distribution of the two PlGF mRNAs. Finally, preliminary results indicate that the PIGF gene has been conserved in evolution, since the human PlGF cDNA hybridizes to sequences present in the genomic DNA of Drosophila, Xenopus, chicken and mouse.

The related FLT4, FLT1, and KDR receptor tyrosine kinases show distinct expression patterns in human fetal endothelial cells.

Abstract: The growth factor receptors expressed on endothelial cells are of special interest because of their potential to program endothelial cell growth and differentiation during development and neovascularization in various pathological states, such as wound healing and angiogenesis associated with tumorigenesis. Vascular endothelial growth factor ([VEGF] also known as vascular permeability factor) is a potent mitogen and permeability factor, which has been suggested to play a role in embryonic and tumor angiogenesis. The newly cloned FLT4 receptor tyrosine kinase gene encodes a protein related to the VEGF receptors FLT1 and KDR/FLK-1. We have here studied the expression of FLT4 and the other two members of this receptor family in human fetal tissues by Northern and in situ hybridization. These results were also compared with the sites of expression of VEGF and the related placenta growth factor (PlGF). Our results reveal FLT4 mRNA expression in vascular endothelial cells in developing vessels of several organs. A comparison of FLT4, FLT1 and KDR/FLK-1 receptor mRNA signals shows overlapping, but distinct expression patterns in the tissues studied. Certain endothelia lack one or two of the three receptor mRNAs. These data suggest that the receptor tyrosine kinases encoded by the FLT gene family may have distinct functions in the regulation of the growth/differentiation of blood vessels.

Two human FLT4 receptor tyrosine kinase isoforms with distinct carboxy terminal tails are produced by alternative processing of primary transcripts.

Abstract: FLT4 is a recently cloned gene encoding a transmembrane tyrosine kinase related to the FLT1 and KDR/FLK1 vascular endothelial growth factor receptors. We have previously shown that FLT4 is expressed as transcripts of 4.5 and 5.8 kb in several human fetal and adult tissues. Here we show that these transcripts encode two polypeptides, FLT4s (short) and FLT41 (long), which are proteolytically processed in transfected cells and leukemia cells and which have different carboxy terminal tails. The 3' coding region of the 5.8 kb mRNA was found to be 65 codons longer than that of the the 4.5 kb mRNA. Analysis of the genomic structure of the region encoding the two carboxy termini revealed that the two transcripts are generated by alternative polyadenylation and subsequent alternative splicing during RNA processing. Our findings thus show regulation of FLT4 structure in the carboxy terminal tail considered important for receptor function. The significance of the two forms may relate to the role of additional potential autophosphorylation sites in the FLT4 long form.

Structural and functional specificity of FGF receptors

Abstract: Fibroblast growth factors (FGFs) represent a group of polypeptide mitogens eliciting a wide variety of responses depending on the target cell type. The knowledge of the cell surface receptors mediating the effects of FGFs has recently expanded remarkably. Perhaps not surprisingly, the complexity of the FGF family and FGF induced responses is reflected in the diversity and redundancy of the FGF receptors. The molecular cloning of the signal transducing receptors for fibroblast growth factors has revealed a tyrosine kinase gene family with at least four members. Differential splicing and polyadenylation creates further diversity in the FGF receptor system. These numerous receptor forms have both distinct and redundant properties. We are only now beginning to understand how the different receptors are activated by the various FGFs and how they are expressed by various cells and tissues. FGF binding to the tyrosine kinase receptors needs the assistance of heparan sulphate side chains of proteoglycans present at the cell surface and in the extracellular matrix. As several other growth factors share the heparin binding property of FGFs, the dual receptor system for FGFs might be an example of a more widely used principle.

Tie, a novel endothelial cell receptor tyrosine kinase

Abstract: The cloning, sequencing and expression of a novel receptor tyrosine kinase, termed tie, is described. The tie precursor comprises 1138 amino acid residues, about 1117 residues of which comprise the mature tie. The tie extracellular domain contains distinct stretches of amino acid sequence having features of the imunoglobulin, epidermal growth factor and fibronectin type III repeat protein families. Alternative splicing creates variants of tie which lack one of the epidermal growth factor homology domains. A specific tyrosine phosphorylated 117 kD glycoprotein is detected by specific tie-antisera from cultured cells expressing the tie gene. The tie mRNA is expressed in cultured endothelial cells as well as in a few tumor cell lines. In situ hybridization of human fetal and mouse embryonic tissues shows specific expression in endothelial cells of blood vessels. The tie DNAs and polypeptides of the invention may be useful in the diagnosis and treatment of certain diseases involving endothelial cells and their tie receptor such as neoplastic diseases involving tumor angiogenesis, wound healing, thromboembolic diseases, atherosclerosis and inflammatory diseases.

The human ryk cDNA sequence predicts a protein containing two putative transmembrane segments and a tyrosine kinase catalytic domain.

Abstract: The human ryk tyrosine kinase cDNA was originally identified as a PCR-amplified cDNA fragment (JTK5) from K562 leukemia cells and found to represent a ubiquitously expressed gene (Partanen et al, 1990) The open reading frame of human ryk, reported here, encodes a novel type of putative tyrosine kinase of 607 amino acid residues, having two potential transmembrane domains and homology to receptor tyrosine kinases, such as met (HGF/SF-R) and IGF-1R, in its catalytic domain The gene maps to human chromosome 3q11-25 Expression of the 34 kb ryk mRNA was found in all human adult tissues examined

Enhanced bFGF gene expression in response to transforming growth factor-beta stimulation of AKR-2B cells.

Abstract: Treatment of quiescent cultures of mouse embryo-derived AKR-2B cells with transforming growth factor beta resulted in an induction of basic fibroblast growth factor (bFGF) mRNA and bFGF protein in the stimulated cells. In contrast to bFGF, acidic fibroblast growth factor (aFGF) was not induced by TGF beta. The mitogenic effect of transforming growth factor beta on AKR-2B cells may be mediated by the induction of bFCF in these cells.

FLT4 receptor tyrosine kinase gene mapping to chromosome band 5q35 in relation to the t(2;5), t(5;6), and t(3;5) translocations.

Abstract: FLT4 is a recently cloned receptor tyrosine kinase cDNA, which is characterized by seven immunoglobulin-like loops in its extracellular domain. We have previously mapped the FLT4 gene to chromosome segment 5q33-qter using somatic cell hybrids. Here we have refined the localization to band 5q35 by fluorescence in situ hybridization and show that the gene is translocated to chromosomes 2 and 6 in the t(2;5)(p23;q35) and t(5;6)(q35;p21) translocations, respectively, of Ki-1-positive lymphomas, as well as to chromosome 3 in the t(3;5)(q25.1;q34) translocation, which is occasionally found in myelodysplastic syndromes and acute myeloid leukemia. No evidence was obtained for a rearrangement or deregulation of the translocated FLT4 gene. We further show that abundant FLT4 mRNA expression occurs only in erythroid and megakaryoblastoid cell lines among nine leukemia cell lines studied. © 1993 Wiley-Liss, Inc.

A sub-set of immediate early mRNAs induced by tumor necrosis factor-α during cellular cytotoxic and non-cytotoxic responses

Abstract: TNF-alpha is a multifunctional cytokine which is cytotoxic for some cell lines. In order to characterize the early genomic response to TNF-alpha, we have analyzed the induction of a sub-set of serum-inducible immediate early genes in WEHI-S and L929 fibrosarcoma cell lines, which are sensitive to TNF-alpha, and in the 3T3-LI pre-adipocytic cell line, which is resistant to TNF-alpha cytotoxicity. Among 77 immediate early mRNAs screened by dot blot and/or Northern blot analyses, the expression of 23 mRNAs was found to be induced by TNF-alpha. Ten of these mRNAs encode proteins known to function as pro-inflammatory cytokines or transcription factors, while 13 others have as yet uncharacterized activities. The magnitude of c-fos induction by TNF-alpha inversely correlated with cell-type-specific cytotoxicity. Rapid and transient mRNA responses were observed in the TNF-alpha-resistant cells, whereas a slower and more persistent response was characteristic for TNF-alpha-sensitive cells. The prolonged induction of immediate early mRNAs may contribute to TNF-alpha-induced cellular cytotoxic responses.