Papers by Bengt Westermark
Development, 1989
It has been shown previously that cultures of rat optic nerve contain three types of macroglial c... more It has been shown previously that cultures of rat optic nerve contain three types of macroglial cells - oligodendrocytes and two types of astrocytes. Type-1 astrocytes develop from their own precursor cells beginning before birth, while oligodendrocytes and type-2 astrocytes develop postnatally from a common bipotential precursor called the O-2A progenitor cell. Proliferating O-2A progenitor cells give rise to postmitotic oligodendrocytes beginning around birth, and to type-2 astrocytes beginning in the second postnatal week. Studies in vitro have suggested that platelet-derived growth factor (PDGF), secreted by type-1 astrocytes, plays an important part in timing oligodendrocyte development: PDGF seems to keep O-2A progenitor cells proliferating until an intrinsic clock in the progenitor cells initiates the process leading to oligodendrocyte differentiation. The clock apparently determines when a progenitor cell becomes unresponsive to PDGF, at which point the cell stops dividing a...
Induction of platelet-derived growth factor alpha- and beta-receptor mRNA and protein by platelet-derived growth factor BB
Journal of Biological Chemistry, 1991
Journal of Cell Science, 1990
Platelet-derived growth factor CPDGF) is a connective tissue cell mitogen that originally was pur... more Platelet-derived growth factor CPDGF) is a connective tissue cell mitogen that originally was purified from human platelets, but recently has been found to be produced by many different cell types (reviewed by Ross et al. 1986; Heldin and Westermark, 1989). The in vivo function of PDGF remains speculative, but the fact that PDGF is released by platelets and by cells involved in the inflammatory reaction and that it stimulates proliferation, chemotaxis and matrix production, suggest a role in tissue repair processes. It is also possible that PDGF is involved in regulation of cell growth and differentiation during embryonal development, since it has been found to be expressed in mouse (Rappolee et al. 1988) and Xenopus (Mercóla et al. 1988) embryos and in human placenta (Goustin et al. 1985). Such a function has been demonstrated in the developing rat optic nerve where PDGF secreted by type-1 astrocytes control the differentiation of O-2A progenitor cells into oligodendrocytes and typ...
Characterization of the retention motif in the C-terminal part of the long splice form of platelet-derived growth factor A-chain
Journal of Biological Chemistry, 1994
The EMBO Journal, 1986
Previous studies have indicated that the oncogene v-sis of simian sarcoma virus (SSV) encodes a g... more Previous studies have indicated that the oncogene v-sis of simian sarcoma virus (SSV) encodes a growth factor that is structurally and functionally similar to platelet-derived growth factor (PDGF). In the present investigation we have analysed the phenotypic characteristics of human foreskin fibroblasts transformed by SSV. It was found that the PDGF receptors were extensively down-regulated. This finding is consistent with a high, local, extracellular concentration of a PDGF-like factor, synthesized by the transformed cell. The receptors were up-regulated by suranin, a drug that is known to dissociate PDGF and the v-sis product from the PDGF receptors. A cell-associated v-sis product of mol. wt 24 000 was identified by immunoprecipitation with PDGF antibodies; release of this component was induced by a high concentration of exogenous PDGF, indicating that a fraction of the product is associated with the PDGF receptors. SSV was not found to be an immortalizing virus; when serially passaged, SSV-transformed cells had essentially the same lifespan as their non-transformed counterparts. Moreover, SSV did not induce growth in soft agar beyond the level afforded by exogenously added PDGF. Thus, the present study favors the notion that SSV transformation is mediated by a growth factor that mimics PDGF but has no further cellular effects.
The EMBO Journal, 1987
Platelet-drived growth factor (PDGF) is one of the most important polypeptide growth factors in h... more Platelet-drived growth factor (PDGF) is one of the most important polypeptide growth factors in human serum. It is composed of two polypeptide chains linked by disulfide bonds. The B-chain is encoded by the c-sis proto-oncogene, which is expressed in several malignant and non-malignant cells including K562 cells differentiating towards megakaryoblasts. Expression of the A-chain has been reported to occur in human solid tumor cell lines independently of c-sis expression. We report here the non-coordinate expression of the Aand B-chains in human leukemia cell lines. The PDGF-A and B-chain (c-sis) RNA expression as well as secretion of PDGF polypeptides are induced in the K562 cell line upon induction of megakaryoblastic differentiation with 12-0tetradecanoyl phorbol-13-acetate (TPA) whereas erythroid differentiation induced with sodium butyrate is accompanied by c-sis expression only. Simultaneously with megakaryoblastic differentiation the RNA level for another platelet protein, the transforming growth factor-beta was also increased, but in a complex manner. The promyelocytic leukemia cell line HL-60 does not express PDGF-A RNA, whereas the promonocytic cell line U937 does. Preferential induction of the A-chain RNA is obtained in both cell lines after treatment with TPA which causes monocytic differentiation. PDGF-A expression in HL-60 cells is also observed after treatment with the tumor necrosis factor-alpha but granulocytic differentiation of HL-60 cells induced with dimethyl sulfoxide or the granulocyte colony-stimulating factor is not associated with PDGF gene expression.
The c-sis gene encodes a precursor of the B chain of platelet-derived growth factor
The EMBO Journal, 1984
Physiological Reviews, 1999
Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain ... more Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the α-receptor and the β-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involve...
Reversion of autocrine transformation by a dominant negative platelet-derived growth factor mutant
Molecular and Cellular Biology, 1993
A non-receptor-binding mutant of the platelet-derived growth factor (PDGF) A chain, PDGF-0, was g... more A non-receptor-binding mutant of the platelet-derived growth factor (PDGF) A chain, PDGF-0, was generated by exchanging 7 amino acids in the sequence. The mutant chains formed dimers that were similar to wild-type PDGF-AA with regard to stability and rate of processing to the mature 30-kDa secreted forms. Moreover, the mutant chains formed disulfide-bonded heterodimers with the PDGF B chain in NIH 3T3 cells heterodimer underwent the same processing and secretion as PDGF-AB. Transfection of c-sis-expressing 3T3 cells with PDGF-0 significantly inhibited the transformed phenotype of these cells, as determined by the following criteria. (i) Compared with PDGF-0-negative clones, PDGF-0-producing clones showed a reverted morphology. (ii) Clones producing PDGF-0 grew more slowly than PDGF-0-negative clones, with a fivefold difference in cell number after 14 days in culture. (iii) The expression of PDGF-0 completely inhibited the ability of the c-sis-expressing 3T3 cells to form colonies in...
Platelet-derived growth factor in autocrine transformation
Cancer research, 1991
Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1992
Previous studies have shown that platelet-derived growth factor (PDGF) and PDGF receptors are exp... more Previous studies have shown that platelet-derived growth factor (PDGF) and PDGF receptors are expressed in the mammalian central nervous system and that primary cultured neuroblasts from rat hindbrain have functional PDGF beta-receptors. Here, it is shown that cultured human neuroblastoma cells express PDGF alpha- and beta-receptors, but not PDGF-A and PDGF-B chain mRNA. In contrast to alpha-receptor expression, beta-receptor expression appears to be associated with a mature neuronal phenotype. Under serum-free growth conditions, PDGF-AA and -BB induce a trophic and weak mitogenic response in SH-SY5Y neuroblastoma cells, showing that the PDGF receptors in these cells are functional. In combination with 12-O-tetradecanoylphorbol-13-acetate, all three PDGF isoforms induce sympathetic neuronal differentiation of the SH-SY5Y cells, as shown by morphology and by increased expression of the genes coding for growth-associated protein 43 and neuropeptide tyrosine, respectively. This indicat...
Induction of brain tumors in mice using a recombinant platelet-derived growth factor B-chain retrovirus
Cancer research, 1998
In existing mouse models for malignant brain tumors, genes with no proven pathogenical relevance ... more In existing mouse models for malignant brain tumors, genes with no proven pathogenical relevance for humans have been used. Coexpression of platelet-derived growth factor (PDGF) and PDGF receptors suggests an autocrine mechanism of growth factor stimulation in the development of brain tumors in man. A murine retrovirus coding for the PDGF B-chain was, therefore, used to induce brain tumors in mice. Of 35 mice who received injections, 15 developed brain tumors of oligo- or monoclonal origin. They coexpressed PDGF B-chain and alpha-receptor mRNA, as expected, from an autocrine mechanism of transformation. Most tumors displayed characteristics of glioblastoma multiforme or of a primitive neuroectodermal tumor, and the consistent expression of nestin suggested that they were all derived from an immature neuroglial progenitor. The results show that an autocrine mechanism of transformation may be an initial or early event in neuro-oncogenesis. The present model provides an ideal system fo...
The Journal of cell biology, 1991
The complementary DNAs for wildtype and tyrosine kinase-inactivated (K634A) forms of the PDGF bet... more The complementary DNAs for wildtype and tyrosine kinase-inactivated (K634A) forms of the PDGF beta-receptor were expressed in porcine aortic endothelial cells. We examined the internalization and degradation of ligands and receptors after exposure of receptor expressing cells to PDGF-BB, which binds to the beta-receptor with high affinity, and PDGF-AB, which binds with lower affinity. Cells expressing wildtype beta-receptors were able to internalize and degrade the receptor, as well as the ligand, after exposure to PDGF-BB or -AB. Cells expressing the kinase-inactivated mutant receptor also internalized and degraded both receptor and ligand, but with lower efficiency compared with the wildtype receptor cells. The degradation of either form of receptor was inhibited by treatment of the cells with the lysosomotropic drug chloroquine. Exposure of wildtype and K634A receptor expressing cells to PDGF-AB resulted in a twofold slower rate of internalization of this ligand as compared with ...
The Journal of cell biology, 1992
Platelet-derived growth factor is a potent mitogen for cells of mesenchymal origin. It is made up... more Platelet-derived growth factor is a potent mitogen for cells of mesenchymal origin. It is made up of two polypeptide chains (A and B) combined in three disulfide-linked dimeric forms (AA, AB, and BB). Here, the biosynthesis and proteolytic processing of the two homodimeric forms of PDGF (AA and BB) were studied in CHO cells stably transfected with A-chain (short splice version) or B-chain cDNA. PDGF-AA was processed to a 30-kD molecule which was secreted from the cells. In contrast, PDGF-BB formed two structurally distinct end products; a minor secreted 30-kD form and a major cell-associated 24-kD form. Immunocytochemical studies at light- and electron-microscopical levels revealed presence of PDGF in the Golgi complex, in lysosomes, and to a smaller extent in the ER. From analysis of cells treated with brefeldin A, an inhibitor of ER to Golgi transport, it was concluded that dimerization occurs in the ER, whereas the proteolytic processing of PDGF-AA and PDGF-BB precursors normally...
B-type receptor for platelet-derived growth factor mediates a chemotactic response by means of ligand-induced activation of the receptor protein-tyrosine kinase
Proceedings of the National Academy of Sciences, 1990
Porcine aorta endothelial cells are devoid of receptors for platelet-derived growth factor (PDGF)... more Porcine aorta endothelial cells are devoid of receptors for platelet-derived growth factor (PDGF). We have transfected such cells with cDNA for the PDGF B-type receptor, both the wild-type receptor and a mutant form of the receptor (K634A), in which the putative nucleotide-binding lysine of the protein-tyrosine domain has been changed to alanine. Immunoprecipitation studies of metabolically labeled cells showed that both types of receptors were synthesized and processed to the mature form of Mr 190,000. In cells expressing the wild-type receptor, PDGF-BB, the natural ligand for the B-type receptor, induced membrane ruffling and reorganization of actin. Such a response has previously been seen in cells expressing the natural PDGF B-type receptor in response to PDGF-BB. No such effect was induced in nontransfected cells or in cells expressing the K634A mutant receptor. PDGF was also shown to be chemotactic for cells expressing the wild-type receptor, whereas no chemotactic response wa...
Surface binding and internalization of platelet-derived growth factor in human fibroblasts
Proceedings of the National Academy of Sciences, 1983
Surface binding and uptake of platelet-derived growth factor (PDGF) in human fibroblasts cultivat... more Surface binding and uptake of platelet-derived growth factor (PDGF) in human fibroblasts cultivated in vitro were studied by quantitative electron microscopic autoradiography using 125I-labeled PDGF and by indirect immunofluorescence using PDGF antibodies. After 120 min at 12 degrees C PDGF was found preferentially in coated regions of the plasma membrane. Warming the cells to 37 degrees C initiated rapid ingestion of the factor via small vesicles, usually lacking a membrane coat. After 10 min PDGF started to appear in lysosomes, and it showed maximal concentration within these organelles after 30 min. There were also signs of passage of PDGF through the Golgi complex, but only after 60 min. Treatment of the cells with chloroquine, a weak base that inhibits intralysosomal degradation, prevented disappearance of tracer from the lysosomes. The observations indicate that PDGF was internalized via coated regions of the plasma membrane and carried to lysosomes for degradation. Subsequent...
Proceedings of the National Academy of Sciences, 1988
Receptors for platelet-derived growth factor (PDGF) have previously only been found on cells of m... more Receptors for platelet-derived growth factor (PDGF) have previously only been found on cells of mesenchymal and glial origin. This study shows PDGF receptors on an anaplastic thyroid carcinoma cell line, C 643, that was found to express thyroglobulin mRNA, confirming its origin from thyroid epithelium. Northern blot analysis of poly(A)+ RNA hybridized with a human PDGF B-type receptor cDNA probe revealed a 5.4-kilobase transcript in the C 643 cells. The existence of receptor protein on the cell surface was shown by immunofluorescence microscopy with a PDGF receptor monoclonal antibody. Binding experiments with 125I-labeled dimeric forms of PDGF indicated that the cells contain B-, but not A-, type PDGF receptors. The addition of PDGF to C 643 membranes in the presence of [32P]ATP induced phosphorylation of the receptor. A polyclonal PDGF B-type receptor peptide antiserum was used to immunoprecipitate a receptor protein from metabolically labeled C 643 cells; the receptor was found t...
Efficient reversion of simian sarcoma virus-transformation and inhibition of growth factor-induced mitogenesis by suramin
Proceedings of the National Academy of Sciences, 1986
Simian sarcoma virus, an acutely transforming primate retrovirus with capacity to induce gliomas ... more Simian sarcoma virus, an acutely transforming primate retrovirus with capacity to induce gliomas and sarcomas in experimental animals, has acquired its transforming properties by transducing the cellular gene sequences that encode one of the constituent chains of platelet-derived growth factor. Suramin, a drug used in the treatment of trypanosomiasis and onchocerciasis, has previously been reported to inhibit the interaction of platelet-derived growth factor with its cell surface receptor. We show here that suramin efficiently reverts the simian sarcoma virus-induced transformed phenotype in human and rat fibroblasts and propose that this is due to neutralization of an externalized v-sis product. Moreover, we show that suramin inhibits the action of a broad spectrum of growth factors.
Specific receptors for platelet-derived growth factor on cells derived from connective tissue and glia
Proceedings of the National Academy of Sciences, 1981
A cellular receptor for platelet-derived growth factor (PDGF) was demonstrated by incubation of 1... more A cellular receptor for platelet-derived growth factor (PDGF) was demonstrated by incubation of 125I-labeled PDGF with human foreskin fibroblast cultures followed by liberation of cell-bound radioactivity with Triton X-100. The cellular binding of labeled PDGF in the presence of increasing amounts of unlabeled PDGF showed saturation; Scatchard analysis of binding data indicated a single class of receptors having kd = 1 X 10(-9) M. The number of PDGF binding sites was approximately 3 X 10(5)/cell. Labeled PDGF binding reached an apparent equilibrium after 3 hr at 4 degrees C. At 37 degrees C, it passed a maximum after 30 min and then decreased with time due to degradation of the tracer. A large excess of unlabeled PDGF reduced labeled PDGF binding by more than 90% whereas similar doses of epidermal growth factor, fibroblast growth factor, or insulin had no effect. It was concluded that PDGF did not share receptors with these factors. PDGF receptors were found on skin fibroblasts, nor...
Platelet-derived growth factor (PDGF) in oncogenesis: development of a vascular connective tissue stroma in xenotransplanted human melanoma producing PDGF-BB
Proceedings of the National Academy of Sciences, 1993
Human WM9 melanoma cells, previously shown to be devoid of PDGF expression, were stably transfect... more Human WM9 melanoma cells, previously shown to be devoid of PDGF expression, were stably transfected with a PDGF-B cDNA under the transcriptional control of a cytomegalovirus promoter. Northern blot analysis revealed high expression of an mRNA of the expected size in the PDGF-B-transfected cells. Synthesis and secretion of PDGF-BB was confirmed by immunoprecipitation. Furthermore, conditioned medium from PDGF-B-transfected cells contained a mitogenic activity for fibroblasts. For analysis of tumor growth in vivo, cells of each type were injected subcutaneously into BALB/c nu/nu mice. Tumors from mice injected with WM9 cells transfected with the vector only contained large necrotic areas; only scant blood vessels with narrow lumina were observed. No connective tissue was present. In the tumors from PDGF-B-transfected WM9 cells, nests of tumor were divided by connective tissue septa. An abundance of blood vessels was observed in the connective tissue septa and within the tumor cell nes...
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Papers by Bengt Westermark