Biomedical subjects

A Ostman

Publications and source records attributed to A Ostman.

At least 19 recordsLinked to original sources

PubMed2006

DEP-1 protein tyrosine phosphatase inhibits proliferation and migration of colon carcinoma cells and is upregulated by protective nutrients.

The transmembrane protein-tyrosine phosphatase (PTP) DEP-1 (density-enhanced phosphatase) is a candidate tumor suppressor in the colon epithelium. We have explored the function of DEP-1 in colon epithelial cells by inducible re-expression in a DEP-1-deficient human colon cancer cell line. Density-enhanced phosphatase-1 re-expression led to profound inhibition of cell proliferation and cell migration, and was associated with cytoskeletal rearrangements. These effects were dependent on the PTP activity of DEP-1 as they were not observed with cells expressing the catalytically inactive DEP-1 C1239S variant. shRNA-mediated suppression of DEP-1 in a colon epithelial cell line with high endogenous DEP-1 levels enhanced proliferation, further supporting the antiproliferative function of DEP-1. Nutrients, which are considered to be chemoprotective with respect to colon cancer development, including butyrate, green tea and apple polyphenols, had the capacity to elevate transcription of endogenous DEP-1 mRNA and expression of DEP-1 protein. Upregulation of DEP-1 expression, and in turn inhibition of cell growth and migration may present a previously unrecognized mechanism of chemoprevention by nutrients.

Adenocarcinoma↗

PubMed2006

Characterization of an imatinib-sensitive subset of high-grade human glioma cultures.

High-grade gliomas, including glioblastomas, are malignant brain tumors for which improved treatment is urgently needed. Genetic studies have demonstrated the existence of biologically distinct subsets. Preliminary studies have indicated that platelet-derived growth factor (PDGF) receptor signaling contributes to the growth of some of these tumors. In this study, human high-grade glioma primary cultures were analysed for sensitivity to treatment with the PDGF receptor inhibitor imatinib/Glivec/Gleevec/STI571. Six out of 15 cultures displayed more than 40% growth inhibition after imatinib treatment, whereas seven cultures showed less than 20% growth inhibition. In the sensitive cultures, apoptosis contributed to growth inhibition. Platelet-derived growth factor receptor status correlated with imatinib sensitivity. Supervised analyses of gene expression profiles and real-time PCR analyses identified expression of the chemokine CXCL12/SDF-1 (stromal cell-derived factor 1) as a predictor of imatinib sensitivity. Exogenous addition of CXCL12 to imatinib-insensitive cultures conferred some imatinib sensitivity. Finally, coregulation of CXCL12 and PDGF alpha-receptor was observed in glioblastoma biopsies. We have thus defined the characteristics of a novel imatinib-sensitive subset of glioma cultures, and provided evidence for a functional relationship between imatinib sensitivity and chemokine signaling. These findings will assist in the design and evaluation of clinical trials exploring therapeutic effects of imatinib on malignant brain tumors.

Antineoplastic Agents↗

PubMed2004

Smad2 suppresses the growth of Mv1Lu cells subcutaneously inoculated in mice.

Smad2 and Smad3 are intracellular signal transduction proteins of importance in transforming growth factor-beta (TGFbeta)-mediated inhibition of epithelial cell proliferation. Inactivating mutations in the Smad2 and Smad3 genes have been found in various human malignancies. Here, we show that expression of Smad2 leads to the inhibition of growth of Mv1Lu cells inoculated with Matrigel subcutaneously (s.c.) in severe combined immunodeficient (SCID) mice. In histological appearance, the Matrigel plugs with Smad2-transfected cells showed strongly reduced cell density, proliferation and angiogenesis compared with the small tumour nodules of similar size formed by the vector- or Smad3-transfected cells. The histological appearance of vector- and Smad3-transfected cells inoculated in mice was identical. Overexpression of Smad2 and Smad3 in Mv1Lu cells led to the inhibition of cell growth in three-dimensional cultures when compared with vector-transfected cells. Overexpression of Smad2 and Smad3 also decreased the hyperphosphorylation of pRb in Smad-transfected cells. Thus, increased expression of Smad2 leads to inhibition of Mv1Lu cell proliferation and a reduction in the growth of the Smad2-expressing cells inoculated in mice.

Animals↗

PubMed2001

An extracellular ligand increases the specific activity of the receptor-like protein tyrosine phosphatase DEP-1.

Cellular growth, differentiation and migration is regulated by protein tyrosine phosphorylation. Receptor-like protein tyrosine phosphatases are thus likely to be key regulators of vital cellular processes. The regulation of these enzymes is in general poorly understood. Ligands have been identified only for a small subset of the receptor-like protein tyrosine phosphatases and in no case has upregulation of the specific activity by extracellular ligands been demonstrated. Prompted by earlier findings of ligands for receptor-like protein tyrosine phosphatases in extracellular matrix we investigated if Matrigel, a preparation of extracellular matrix proteins, contained modulators of the specific activity of the receptor-like protein tyrosine phosphatase DEP-1. Matrigel stimulation of cells increased the specific activity of immunoprecipitated DEP-1. Also, incubation of immunoprecipitated DEP-1 with Matrigel led to an increase in DEP-1 activity, which was blocked by soluble DEP-1 extracellular domain. Finally, immunoprecipitated DeltaECD-DEP-1, a mutant form of DEP-1 lacking most of the extracellular domain, failed to respond to Matrigel stimulation. These experiments identify Matrigel as a source of DEP-1 agonist(s) and provide the first evidence for upregulation of the specific activity of receptor-like protein tyrosine phosphatases by extracellular ligands.

Animals↗

PubMed2001

Growth inhibition of dermatofibrosarcoma protuberans tumors by the platelet-derived growth factor receptor antagonist STI571 through induction of apoptosis.

Dermatofibrosarcoma protuberans (DFSP) and giant cell fibroblastoma (GCF) are recurrent, infiltrative skin tumors that presently are treated with surgery. DFSP and GCF tumors are genetically characterized by chromosomal rearrangements fusing the collagen type Ialpha1 (COLIA1) gene to the platelet-derived growth factor B-chain (PDGFB) gene. It has been shown that the resulting COL1A1/PDGF-B fusion protein is processed to mature PDGF-BB. Autocrine PDGF receptor stimulation has therefore been predicted to contribute to DFSP and GCF tumor development and growth. Here we demonstrate presence of activated PDGF receptors in primary cultures derived from six different DFSP and GCF tumors. Three of the primary cultures were further characterized; their in vitro growth displayed an increased sensitivity to treatment with the PDGF receptor tyrosine kinase inhibitor STI571, as compared with normal fibroblasts. Transplantable tumors, displaying a DFSP-like histology, were established from one of the DFSP primary cultures. Treatment of tumor-bearing severe combined immunodeficient mice with STI571 reduced tumor growth. The growth-inhibitory effects in vitro and in vivo occurred predominantly through induction of tumor cell apoptosis. Our study demonstrates growth-inhibitory effects of PDGF receptor antagonists on human DFSP- and GCF-derived tumor cells and demonstrates that autocrine PDGF receptor stimulation provides antiapoptotic signals contributing to the growth of these cells. These findings suggest targeting of PDGF receptors as a novel treatment strategy for DFSP and GCF.

Adult↗

PubMed2001

Ligand stimulation reduces platelet-derived growth factor beta-receptor susceptibility to tyrosine dephosphorylation.

Ligand binding to the platelet-derived growth factor (PDGF) beta-receptor leads to increased receptor tyrosine phosphorylation as a consequence of dimerization-induced activation of the intrinsic receptor tyrosine kinase activity. In this study we asked whether ligand-stimulated PDGF beta-receptor tyrosine phosphorylation, to some extent, also involved reduced susceptibility to tyrosine dephosphorylation. To investigate this possibility we compared the sensitivity of ligand-stimulated and non-stimulated forms of tyrosine-phosphorylated PDGF beta-receptors to dephosphorylation using various preparations containing protein-tyrosine phosphatase activity. Ligand-stimulated or unstimulated tyrosine-phosphorylated receptors were obtained after incubation of cells with pervanadate only or pervanadate, together with PDGF-BB, respectively. Dephosphorylation of receptors immobilized on wheat germ agglutinin-Sepharose, as well as of receptors in intact cell membranes, was investigated under conditions when rephosphorylation did not occur. As compared with unstimulated receptors the ligand-stimulated PDGF beta-receptors showed about 10-fold reduced sensitivity to dephosphorylation by cell membranes, a recombinant form of the catalytic domain of density-enhanced phosphatase-1, or recombinant protein-tyrosine phosphatase 1B. We conclude that ligand-stimulated forms of the PDGF beta-receptor display a reduced susceptibility to dephosphorylation. Our findings suggest a novel mechanism whereby ligand stimulation of PDGF beta-receptor, and possibly other tyrosine kinase receptors, leads to a net increase in receptor tyrosine phosphorylation.

Agglutinins↗

PubMed2001

Inhibition of platelet-derived growth factor receptors reduces interstitial hypertension and increases transcapillary transport in tumors.

Most solid malignancies display interstitial hypertension and a poor uptake of anticancer drugs. Platelet-derived growth factor (PDGF) and the cognate tyrosine kinase receptors are expressed in many tumors. Signaling through PDGFbeta receptors was shown recently to increase interstitial fluid pressure (IFP) in dermis after anaphylaxis-induced lowering of IFP. In this study, we show that treatment with the selective PDGF receptor kinase inhibitor, STI571, formerly known as CGP57148B, decreased the interstitial hypertension and increased capillary-to-interstitium transport of 51Cr-EDTA in s.c. growing rat PROb colonic carcinomas. Furthermore, treatment with an antagonistic PDGF-B oligonucleotide aptamer decreased interstitial hypertension in these tumors. PDGFbeta receptors were expressed in blood vessels and stromal cells but not in the tumor cells of PROb colonic carcinomas. Our study indicates a previously unrecognized role of PDGF receptors in tumor biology, although similar effects of PDGF on IFP have been demonstrated previously in the dermis. The data suggest interference with PDGF receptors, or their ligands, as a novel strategy to increase drug uptake and therapeutic effectiveness of cancer chemotherapy.

Animals↗

PubMed2001

Involvement of platelet-derived growth factor in disease: development of specific antagonists.

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Animals↗

PubMed2001

Regulation of receptor tyrosine kinase signaling by protein tyrosine phosphatases.

Signaling through receptor tyrosine kinases (RTKs) is a major mechanism for intercellular communication during development and in the adult organism, as well as in disease-associated processes. The phosphorylation status and signaling activity of RTKs is determined not only by the kinase activity of the RTK but also by the activities of protein tyrosine phosphatases (PTPs). This review discusses recently identified PTPs that negatively regulate various RTKs and the role of PTP inhibition in ligand-induced RTK activation. The contributions of PTPs to ligand-independent RTK activation and to RTK inactivation by other classes of receptors are also surveyed. Continued investigation into the involvement of PTPs in RTK regulation is likely to unravel previously unrecognized layers of RTK control and to suggest novel strategies for interference with disease-associated RTK signaling.

Cell Communication↗

PubMed2001

PDGF-D is a specific, protease-activated ligand for the PDGF beta-receptor.

The term 'platelet-derived growth factor' (PDGF) refers to a family of disulphide-bonded dimeric isoforms that are important for growth, survival and function in several types of connective tissue cell. So far, three different PDGF chains have been identified - the classical PDGF-A and PDGF-B and the recently identified PDGF-C. PDGF isoforms (PDGF-AA, AB, BB and CC) exert their cellular effects by differential binding to two receptor tyrosine kinases. The PDGF alpha-receptor (PDGFR-alpha) binds to all three PDGF chains, whereas the beta-receptor (PDGFR-beta) binds only to PDGF-B. Gene-targeting studies using mice have shown that the genes for PDGF-A and PDGF-B, as well as the two PDGFR genes, are essential for normal development. Furthermore, overexpression of PDGFs is linked to different pathological conditions, including malignancies, atherosclerosis and fibroproliferative diseases. Here we have identify and characterize a fourth member of the PDGF family, PDGF-D. PDGF-D has a two-domain structure similar to PDGF-C and is secreted as a disulphide-linked homodimer, PDGF-DD. Upon limited proteolysis, PDGF-DD is activated and becomes a specific agonistic ligand for PDGFR-beta. PDGF-DD is the first known PDGFR-beta-specific ligand, and its unique receptor specificity indicates that it may be important for development and pathophysiology in several organs.

Amino Acid Sequence↗

PubMed2000

Antiangiogenic effects of latent antithrombin through perturbed cell-matrix interactions and apoptosis of endothelial cells.

Antithrombin is a plasma protein of the serpin superfamily that may occur as several conformational variants. The native form of antithrombin is a major regulator of blood clotting. In the present study, we have identified the mechanism underlying the antiangiogenic action of a heat-denatured form, denoted latent antithrombin. Fibroblast growth factor (FGF)-induced angiogenesis in the chick embryo and angiogenesis in mouse fibrosarcoma tumors were inhibited by treatment with latent antithrombin at 1 mg/kg/day. Thermolysin-cleaved and native antithrombin were less efficient in these respects. Treatment with latent antithrombin induced apoptosis of cultured endothelial cells and inhibited cell migration toward FGF-2. Under these conditions, FGF-2-stimulated FGF receptor kinase activity was unaffected. However, actin reorganization, activation of focal adhesion kinase, and focal adhesion formation were disturbed by latent antithrombin treatment of FGF-2-stimulated endothelial cells. These data indicate that latent antithrombin induces apoptosis of endothelial cells by disrupting cell-matrix interactions through uncoupling of focal adhesion kinase.

Allantois↗

PubMed2000

Site-selective dephosphorylation of the platelet-derived growth factor beta-receptor by the receptor-like protein-tyrosine phosphatase DEP-1.

Ligand stimulation of PDGF beta-receptors leads to autophosphorylation of the regulatory tyrosine 857 and of tyrosine residues that in their phosphorylated form serve as docking sites for Src homology 2 domain-containing proteins. Regulation of the PDGF beta-receptor by protein-tyrosine phosphatases is poorly understood. We have investigated PDGF beta-receptor dephosphorylation by receptor-like protein-tyrosine phosphatase DEP-1 using a cell line with inducible DEP-1 expression and by characterizing in vitro dephosphorylation of the PDGF beta-receptor and of receptor-derived phosphopeptides by DEP-1. After DEP-1 induction PDGF beta-receptor.DEP-1 complexes and reduced receptor tyrosine phosphorylation were observed. Phosphopeptide analysis of the PDGF beta-receptors from DEP-1-expressing cells and of the receptors dephosphorylated in vitro by DEP-1 demonstrated that dephosphorylation of autophosphorylation sites of the receptor differed and revealed that the regulatory Tyr(P)(857) was not a preferred site for DEP-1 dephosphorylation. When dephosphorylation of synthetic receptor-derived peptides was analyzed, the selectivity was reproduced, indicating that amino acid sequence surrounding the phosphorylation sites is the major determinant of selectivity. This notion is supported by the observation that the poorly dephosphorylated Tyr(P)(562) and Tyr(P)(857), in contrast to other analyzed phosphorylation sites, are surrounded by basic amino acid residues at positions -4 and +3 relative to the tyrosine residue. Our study demonstrates that DEP-1 dephosphorylation of the PDGF beta-receptor is site-selective and may lead to modulation, rather than general attenuation, of signaling.

Amino Acid Sequence↗

PubMed2000

Predimerization of recombinant platelet-derived growth factor receptor extracellular domains increases antagonistic potency.

Platelet-derived growth factor (PDGF) is a dimeric growth factor acting through tyrosine kinase alpha- and beta-receptors. In both receptors, the extracellular parts are composed of five Ig-like domains. Functional mapping of the extracellular part of the receptors have shown that ligand-binding occurs to Ig-like domains 2 and 3 and that Ig-like domain 4 is involved in receptor-receptor interactions. Recombinant GST-fusion proteins of PDGF alpha-receptor Ig-like domains 1-4 and beta-receptor Ig-like domains 1-3 (alphaRD1-4-GST and betaRD1-3-GST) were generated and compared with their cleaved counterparts (alphaRD1-4 and betaRD1-3) with regard to their ability to block PDGF binding to cell surface receptors. In the case of both the alpha- and the beta-receptors, 100-1000-fold lower concentrations of the GST-fusion proteins were required, as compared to the cleaved forms, for inhibition of PDGF binding to cell surface receptors. alphaRD1-4-GST and betaRD1-3-GST, in contrast to alphaRD1-4 and betaRD1-3, were shown to occur as ligand independent dimers. Covalently cross-linked alphaRD1-4 dimers displayed a 50-fold increased potency as compared to alphaRD1-4. We thus conclude that the dimeric nature of alphaRD1-4-GST and betaRD1-3-GST is responsible for the high antagonistic potency of the fusion proteins.

Animals↗

PubMed2000

Dependence of autocrine growth factor stimulation in platelet-derived growth factor-B-induced mouse brain tumor cells.

In human gliomas, platelet-derived growth factor (PDGF) ligand and receptor mRNA are often co-expressed, which suggests the presence of an autocrine loop. To further investigate the significance of PDGF stimulation in brain tumors, we used a previously developed mouse tumor model, in which malignant brain tumors of neuroepithelial origin were induced by injecting a murine retrovirus containing the human PDGF B-chain gene into the brains of neonatal mice. In the present investigation, we have characterized a cell line established from such an experimentally induced tumor in an INK4a-/- mouse. Cultured tumor cells expressed nestin and NG2 chondroitin sulfate proteoglycan and are thus most likely derived from an oligodendrocyte precursor cell. Tumor cells produced PDGF-B protein and displayed constitutively activated PDGF alpha receptors. Autocrine receptor activation could be blocked with the specific PDGF receptor tyrosine kinase inhibitor CGP 57148B, which led to almost complete inhibition of cell proliferation, which was much less affected by a PDGF B-chain aptamer that inhibits binding of PDGF-B to PDGF receptors and is unlikely to be able to pass through the plasma membrane. Our results imply an important role for PDGF autocrine stimulation in both initiation and progression of a subtype of gliomas.

Animals↗

PubMed2000

PDGF-C is a new protease-activated ligand for the PDGF alpha-receptor.

Platelet-derived growth factors (PDGFs) are important in many types of mesenchymal cell. Here we identify a new PDGF, PDGF-C, which binds to and activates the PDGF alpha-receptor. PDGF-C is activated by proteolysis and induces proliferation of fibroblasts when overexpressed in transgenic mice. In situ hybridization analysis in the murine embryonic kidney shows preferential expression of PDGF-C messenger RNA in the metanephric mesenchyme during epithelial conversion. Analysis of kidneys lacking the PDGF alpha-receptor shows selective loss of mesenchymal cells adjacent to sites of expression of PDGF-C mRNA; this is not found in kidneys from animals lacking PDGF-A or both PDGF-A and PDGF-B, indicating that PDGF-C may have a unique function.

Animals↗

PubMed2000

Intimal hyperplasia recurs after removal of PDGF-AB and -BB inhibition in the rat carotid artery injury model.

Several antagonists specific for platelet-derived growth factor (PDGF) or its receptors have recently been developed and shown to inhibit intimal hyperplasia formation in various animal models, but data investigating the durability of this intervention is limited. The present study was designed to investigate the potency of PDGF B-chain aptamer, a novel type of PDGF-AB and -BB antagonist, in the rat carotid model and to characterize intermediate-term effects on lesion formation. One hundred thirty-four animals were randomized to aptamer treatment or placebo. Daily treatment with the antagonist resulted in a 50% reduction in lesion size at 2 weeks (P<0.001). The beneficial effect involved increased apoptosis and possibly an interference with smooth muscle cell migration. Discontinuing administration 1 week earlier did not give any significant benefit compared with phosphate-buffered saline-treated controls. When the antagonist was administered for 2 weeks and the vessels analyzed 6 weeks later, the beneficial effect was lost and the treated lesions had a higher intima-media and area-cell ratio compared with the treated lesions in the 2-week-endpoint study. Our findings confirm a role of PDGF B-chain in intimal hyperplasia, but the successful use of PDGF antagonists may require either prolonged treatment or combination therapy with other agents.

Angioplasty, Balloon↗

PubMed1999

Characterization of the chronic myelomonocytic leukemia associated TEL-PDGF beta R fusion protein.

The t(5;12) translocation, associated with chronic myelomonocytic leukemia, generates a novel gene encoding a protein, TEL-PDGF beta R, composed of the 154 amino-terminal amino acids of the transcription factor TEL and the transmembrane and intracellular part of the PDGF beta-receptor (PDGF beta R). TEL also occurs as a tumor-associated fusion partner for the tyrosine kinases c-ABL, JAK2 and TRK-C. Previous studies have demonstrated growth promoting activity of TEL-PDGF beta R and also indicated that the TEL moiety activates the tyrosine kinase of the PDGF beta R through the formation of TEL-PDGF beta R oligomers. We demonstrate that tyrosine phosphorylation of the fusion protein can be attenuated through overexpression of the TEL part of TEL-PDGF beta R, suggesting a strategy for antagonizing the signaling of TEL-PDGF beta R, and other TEL-fusion proteins containing tyrosine kinase domains. Comparison of BaF/3 cell lines expressing TEL-PDGF beta R and ligand-stimulated PDGF beta R revealed that only TEL-PDGF beta R expression conferred IL-3-independent growth, suggesting differences in signaling capacity of the two proteins. Finally, tyrosine residues 17 and 27 in TEL-PDGF beta R was identified as autophosphorylation sites in TEL-PDGF beta R.

Animals↗

PubMed1999

The dermatofibrosarcoma protuberans-associated collagen type Ialpha1/platelet-derived growth factor (PDGF) B-chain fusion gene generates a transforming protein that is processed to functional PDGF-BB.

Dermatofibrosarcoma protuberans (DFSP) displays chromosomal rearrangements involving chromosome 17 and 22, which fuse the collagen type Ialpha1 (COLIA1) gene to the platelet-derived growth factor (PDGF) B-chain (PDGFB) gene. To characterize the functional and structural properties of the COLIA1/PDGFB fusion protein, we generated a stable NIH3T3 cell line that contained a tumor-derived chimeric gene resulting from a COIA1 intron 7-PDGFB intron 1 fusion. Expression of the fusion protein led to morphological transformation and increased growth rate of these cells. The PDGF receptor kinase inhibitor CGP57148B reversed the transformed phenotype and reduced the growth rate of COLIA1/PDGFB-expressing cells but had no effects on control cells. The presence of dimeric COLIA1/PDGFB precursors was demonstrated through PDGFB immunoprecipitations of metabolically labeled cells and also by PDGFB immunoprecipitations followed by immunoblotting with COLIA1 antibodies. Pulse-chase studies demonstrated that the COLIA1/PDGFB precursor was processed to an end product that was indistinguishable from wild-type PDGF-BB. Finally, COLIA1/PDGFB-expressing cells generated tumors after s.c. injection into nude mice, and tumor growth was reduced by treatment with CGP57148B. We conclude that the COLIA1/PDGFB fusion associated with DFSP contributes to tumor development through ectopic production of PDGF-BB and the formation of an autocrine loop. Our findings, thus, suggest that PDGF receptors could be a target for pharmacological treatment of DFSP and giant cell fibroblastoma, e.g., through the use of PDGF receptor kinase inhibitors such as CGP57148B.

3T3 Cells↗