PubMed Health⌕ Search

Biomedical subjects

R Alitalo

Publications and source records attributed to R Alitalo.

13 recordsLinked to original sources
PubMed1992

FLT4 receptor tyrosine kinase contains seven immunoglobulin-like loops and is expressed in multiple human tissues and cell lines.

The fms-like tyrosine kinase 4 (FLT4) complementary DNA was cloned from a human HEL erythroleukemia cell library by polymerase chain reaction-amplification. We previously reported a partial sequence of FLT4 and showed that the FLT4 gene maps to chromosomal region 5q33-qter (O. Aprelikova, K. Pajusola, J. Partanen, E. Armstrong, R. Alitalo, S. Bailey, J. McMahon, J. Wasmuth, K. Huebner, and K. Alitalo, Cancer Res., 52: 746-748, 1992). Here we present the full-length sequence of the predicted FLT4 protein. The extracellular domain of FLT4 consists of 7 immunoglobulin-like loops, including 12 potential glycosylation sites. On the basis of structural similarities FLT4 and the previously known FLT1 and kinase insert domain-containing receptor tyrosine kinase/fetal liver kinase 1 (KDR/FLK1) receptors constitute a subfamily of class III tyrosine kinases. FLT4 was expressed as 5.8- and 4.5-kilobase mRNAs which were found to differ in their 3' sequences and to be differentially expressed in the HEL and DAMI leukemia cells. Interestingly, a Wilms' tumor cell line, a retinoblastoma cell line, and a nondifferentiated teratocarcinoma cell line expressed FLT4, whereas differentiated teratocarcinoma cells were negative. Most fetal tissues also expressed the FLT4 mRNA, with spleen, brain intermediate zone, and lung showing the highest levels. In in situ hybridization the FLT4 autoradiographic grains decorated bronchial epithelial cells of fetal lung. No evidence was obtained for the expression of FLT4 in the endothelial cells of blood vessels.

Amino Acid Sequence↗
PubMed1992

Expression of fibroblast growth factor receptors in human leukemia cells.

We have previously cloned from K562 leukemia cells two novel fibroblast growth factor receptors (FGFR-3 and FGFR-4; J. Partanen et al., EMBO J., 10: 1347-1354, 1991). Here we have analyzed the mRNA expression of four different FGFRs, including the two novel genes in human leukemia cell lines. We show FGFR-1, FGFR-3, and FGFR-4 mRNAs in several leukemia cell lines at levels similar to those in solid tumor cell lines. Ligand cross-linking experiments indicate that K562 cells have receptors binding acidic FGF but not basic FGF. Expression of FGFRs in leukemia cells may reflect their presence on normal hematopoietic precursor cells or induction during leukemogenesis or cell culture.

Blotting, Northern↗
PubMed1992

FLT4, a novel class III receptor tyrosine kinase in chromosome 5q33-qter.

The receptors for at least two hematopoietic growth factors, namely the stem cell factor and colony-stimulating factor 1, belong to class III receptor tyrosine kinases. Here we describe cloning of a partial complementary DNA for FLT4, an additional member of this gene family from human leukemia cells. The FLT4 tyrosine kinase domain is 79% homologous with the previously cloned FLT1 (M. Shibuya et al., Oncogene, 5: 519-524, 1990) tyrosine kinase and maps to the chromosomal region 5q33-qter. We have found FLT4 expression in human placenta, lung, heart, and kidney, whereas the pancreas and brain appeared to contain very little if any FLT4 RNA. The results suggest that FLT4 functions in multiple adult tissues.

Adult↗
PubMed1991

Expression of L-myc and N-myc proto-oncogenes in human leukemias and leukemia cell lines.

The myc proto-oncogenes encode nuclear phosphoproteins, which are believed to participate in the control of cell proliferation and differentiation. Deregulated expression of c-myc has been implicated in several human hematopoietic malignancies. We have studied the expression and mRNA processing of human L-myc, N-myc, and c-myc genes in a panel of human leukemias, leukemia cell lines, and normal hematopoietic cells. L-myc mRNA was expressed in three acute myeloid leukemias (AML) studied and in several myeloid leukemia cell lines. Only low expression levels were observed in adult bone marrow and in fetal spleen and thymus. The K562 and Dami leukemia cell lines showed a unique pattern of L-myc mRNA processing, with approximately 40% of L-myc mRNA lacking exon III and intron I. N-myc was expressed in five of six AML cases studied, in one of nine acute lymphocytic leukemia (ALL) cases, and in several leukemia cell lines, while c-myc mRNA was detected in all leukemias and leukemia cell lines studied. Coexpression of all three myc genes was observed in Dami and MOLT-4 cell lines and in two AMLs, and either L-myc or N-myc was coexpressed with c-myc in several other cases. These results show that in addition to c-myc, the L-myc and N-myc genes are expressed in some human leukemias and leukemia cell lines, and suggest a lack of mutually exclusive cross-regulation of the myc genes in human leukemia cells.

Blotting, Northern↗
PubMed1990

Increased erythroid potentiating activity/tissue inhibitor of metalloproteinases and jun/fos transcription factor complex characterize tumor promoter-induced megakaryoblastic differentiation of K562 leukemia cells.

Molecular cloning has revealed that erythroid potentiating activity (EPA) and tissue inhibitor of metalloproteinases (TIMP) represent two distinct activities of a single protein. We have studied the expression of the EPA/TIMP gene at the mRNA and protein levels during 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced megakaryoblastic differentiation of K562 human chronic myeloid leukemia cells. Northern hybridization analysis showed that the EPA/TIMP mRNA was increased within 3 hours of TPA-induction and reached maximal levels (about 50-fold induction) during the first day of treatment. The expression of mRNAs for two major metalloproteinases, collagenase-I and stromelysin, were activated in parallel in the differentiation-induced K562 cells. The increase of EPA/TIMP mRNA correlated with increased EPA/TIMP protein biosynthesis and secretion: the TPA-induced cells secreted substantially enhanced amounts of metabolically labeled proteins, of which EPA/TIMP represented up to 50% after the first day of treatment (over 100-fold induction). The induction of EPA/TIMP mRNA was associated with its increased transcription. EPA/TIMP induction required continuous protein synthesis, being completely inhibited by addition of the protein synthesis inhibitor cycloheximide simultaneously with TPA, but only partially inhibited in a time-dependent manner if cycloheximide was added after TPA. Unlike in other cells tested, the jun and c-fos transcription factor mRNAs showed a prolonged biphasic induction response in K562 cells during TPA treatment. This response was associated with enhanced activity of a transfected recombinant reporter plasmid containing binding sites for the jun/fos transcription factor complex (AP-1) similar to the TPA-responsive element (TRE) sequence we found in the EPA/TIMP gene promoter. We suggest that the induction of EPA/TIMP and several other genes specific for the differentiating K562 cells may be a consequence of the sustained activation of immediate early genes encoding transcription factors, such as jun and c-fos.

Cell Line↗
PubMed1990

Induced differentiation of K562 leukemia cells: a model for studies of gene expression in early megakaryoblasts.

The K562 leukemia cell line has been extensively used in studies of erythroid differentiation but it has been less well appreciated that treatment of K562 cells with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) leads to loss of their erythroid properties and to acquisition of several megakaryoblastoid characteristics. These include synthesis and surface expression of glycoprotein IIIa, an increase in platelet peroxidase positivity, enhancement of thromboxane A2 receptors, and increased cell volume and DNA ploidy. TPA-treated K562 cells also synthesize and secrete platelet derived growth factor (PDGF), transforming growth factor beta 1 (TGF beta 1), urokinase-plasminogen activator (u-PA) and its specific inhibitor, type 1 plasminogen activator inhibitor (PAI-1). Induction of all these proteins, which have also been found in platelet granules (u-PA on platelet surface receptors) occurs at the level of mRNA accumulation. Therefore, in addition to facilitating studies and cloning of genes specific for erythroid differentiation, the K562 cells offer a tool to approach early steps of megakaryoblast commitment and differentiation. Observations made with the K562 cell line and several other leukemia cell lines co-expressing erythroid and megakaryocyte markers suggest that the erythroid and megakaryocyte lineages diverge from a common bipotent precursor cell.

Cell Differentiation↗
PubMed1990

Divergent in vitro effects of recombinant interferons on human osteosarcoma cells.

We investigated the in vitro effects of human recombinant interferon alpha (rIFN alpha) and interferon gamma (rIFN gamma) on the proliferation and MCH class II antigen expression of two human osteosarcoma cell lines SAOS-2 and U2-OS. Addition of low concentrations of either rIFN alpha (10 U/mL) or rIFN gamma (100 U/mL) to the cultures almost completely inhibited the 3H-thymidine incorporation in SAOS-2 cells while even high amounts (10,000 U/mL) of rIFN alpha or rIFN gamma did not affect the growth rate of U2-OS cells. This difference was not caused by lack of IFN receptors in U2-OS cells since both cell lines responded to rIFN gamma treatment with rapid accumulation of HLA class II mRNA and de novo surface expression of HLA-DR, -DP and -DQ antigens. The induced HLA class II antigens were functionally intact. Osteosarcoma cells treated with rIFN gamma stimulated a mixed lymphocyte culture (MLC) response in allogeneic T-lymphocytes while untreated osteosarcoma cells were unable to provoke T-lymphocyte proliferation. These findings indicate that IFNs display divergent effects on two phenotypically closely related tumor cell lines. This should be appreciated also when therapeutic effects of IFNs are evaluated.

Antibodies, Monoclonal↗
PubMed1990

Putative tyrosine kinases expressed in K-562 human leukemia cells.

Tyrosine phosphorylation is important in the transmission of growth and differentiation signals; known tyrosine kinases include several oncoproteins and growth factor receptors. Interestingly, some differentiated cell types, such as erythrocytes and platelets contain high amounts of phosphotyrosine. We analyzed tyrosine kinases expressed in the K-562 chronic myelogenous leukemia cell line, which has a bipotential erythroid and megakaryoblastoid differentiation capacity. Analysis of 359 polymerase chain reaction-amplified cDNA clones led to the identification of 14 different tyrosine kinase-related sequences (JTK1-14). Two of the clones (JTK2 and JTK4) represent unusual members of the fibroblast growth factor receptor gene family, and the clones JTK5, JTK11, and JTK14 may also belong to the family of receptor tyrosine kinases but lack a close relationship to any known tyrosine kinase. Each of these different genes has its own characteristic expression pattern in K-562 cells and several other human tumor cell lines. In addition, the JTK11 and JTK14 mRNAs are induced during the megakaryoblastoid differentiation of K-562 cells. These tyrosine kinases may have a role in the differentiation of megakaryoblasts or in the physiology of platelets.

Amino Acid Sequence↗
PubMed1989

Down-regulation of proteolytic activity in 12-O-tetradecanoyl-phorbol-13-acetate-induced K562 leukemia cell cultures: depletion of active urokinase by excess type 1 plasminogen activator inhibitor.

The human chronic myeloid leukemia cell line K562 acquires several megakaryoblastoid features when cultured in the presence of the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). We observed strongly increased secretion of several proteins into the culture media of K562 cells within a few hours of TPA treatment. Two of the major secreted polypeptides were identified by immunoprecipitation from media of metabolically labeled cultures as the tissue inhibitor of metalloproteinases (TIMP) and the type 1 plasminogen activator inhibitor (PAI-1). Maximal amounts of PAI-1 mRNA and secretion of PAI-1 polypeptides were observed after 24 hr of TPA treatment and PAI-1 persisted at elevated levels for several days. The induction of PAI-1 mRNA was dependent on de novo protein synthesis. Uninduced and induced cells secreted urokinase plasminogen activator in its single-chain proenzyme form (pro-u-PA), which was cleaved extracellularly to the active two-chain form as shown by pulse-chase labeling experiments. Upon TPA induction, the secretion of u-PA polypeptides increased severalfold, and there was a transient accumulation of pro-u-PA in the culture medium. However, this did not lead to increased u-PA activity in the cultures, since active u-PA was removed by complex formation with the large excess of coinduced PAI-1. Induction of u-PA mRNA was biphasic: The first peak of about tenfold increase in steady-state u-PA mRNA at 3 hr was followed by a steep decline to the baseline level at 12 hr, and a second, slower accumulation of u-PA mRNA occurred over the next few days. The biphasic accumulation of u-PA mRNA was also reflected in u-PA protein synthesis. We conclude that concerted changes in favor of a nonproteolytic extracellular environment occur in TPA-induced K562 cultures undergoing megakaryoblastoid differentiation. These changes include excessive secretion of TIMP and inhibition of the induced u-PA by the simultaneous accumulation of PAI-1.

Cell Line↗