Chromosomal mapping of the simian sarcoma virus onc gene analogue in human cells

Dental Pulp Stem Cells: Advances to Applications

Dental pulp stem cells (DPSCs) have a high capacity for differentiation and the ability to regenerate a dentin/pulp-like complex. Numerous studies have provided evidence of DPSCs’ differentiation capacity, such as in neurogenesis, adipogenesis, osteogenesis, chondrogenesis, angiogenesis, and dentinogenesis. The molecular mechanisms and functions of DPSCs’ differentiation process are affected by growth factors and scaffolds. For example, growth factors such as basic fibroblast growth factor (bFGF), transforming growth factor-β (TGF-β), nerve growth factor (NGF), platelet-derived growth factor (PDGF), and bone morphogenic proteins (BMPs) influence DPSC fate, including in differentiation, cell proliferation, and wound healing. In addition, several types of scaffolds, such as collagen, hydrogel, decellularized bioscaffold, and nanofibrous spongy microspheres, have been used to characterize DPSC cellular attachment, migration, proliferation, differentiation, and functions. An appropriate combination of growth factors and scaffolds can enhance the differentiation capacity of DPSCs, in terms of optimizing not only dental-related expression but also dental pulp morphology. For a cell-based clinical approach, focus has been placed on the tissue engineering triad [cells/bioactive molecules (growth factors)/scaffolds] to characterize DPSCs. It is clear that a deep understanding of the mechanisms of stem cells, including their aging, self-renewal, microenvironmental homeostasis, and differentiation correlated with cell activity, the energy for which is provided from mitochondria, should provide new approaches for DPSC research and therapeutics. Mitochondrial functions and dynamics are related to the direction of stem cell differentiation, including glycolysis, oxidative phosphorylation, mitochondrial metabolism, mitochondrial transcription factor A (TFAM), mitochondrial elongation, and mitochondrial fusion and fission proteins. This review summarizes the effects of major growth factors and scaffolds for regenerating dentin/pulp-like complexes, as well as elucidating mitochondrial properties of DPSCs for the development of advanced applications research.

Weak association of the platelet-derived growth factor beta (PDGFB) and PDGF receptor beta (PDGFRB) genes with schizophrenia and schizoaffective disorder

Schizophrenia is a severe neuropsychiatric disorder with diverse characterization of symptoms. Extensive research has been performed to elucidate the etiology of schizophrenia. One of the most convincing hypotheses comes from the dopaminergic system although none of the core genes has been consistently positive in association studies.

OBJECTIVE

In this investigation, we explored the possibility that the genes for platelet-derived growth factor beta (PDGFB) and its receptor (PDGFRB) might play an important role in the development of schizophrenia based on previous reports pointing to their ability to interact with the dopamine D(2)/D(4) and NMDA receptors as well as their role in neurite outgrowth.

METHODS

We investigated the association of variants around these genes with schizophrenia and schizoaffective disorder in 104 small nuclear families using the Sib-Transmission Disequilibrium Test (TDT-STDT). Furthermore, quantitative trait analysis using family-based association test was applied to determine possible association of age at onset (AAO).

RESULTS

Allele G in PDGFRB(rs758588) was associated with AAO (P=0.019). An over-transmission of allele T in PDGFB(rs130650) polymorphism (P=0.043) and an over-transmission of allele A in PDGFRB(rs6865659) polymorphism (P=0.046) were observed. Furthermore, the combined TDT-STDT yielded consistent results.

CONCLUSION

Overall, PDGFB and PDGFRB genes might play a role in the etiology of schizophrenia.

The PDGF family: four gene products form five dimeric isoforms

Platelet-derived growth factors (PDGFs) were discovered more than two decades ago. Today the PDGF family of growth factors consists of five different disulphide-linked dimers built up of four different polypeptide chains encoded by four different genes. These isoforms, PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, act via two receptor tyrosine kinases, PDGF receptors alpha and beta. The classic PDGFs, PDGF-A and PDGF-B, undergo intracellular activation during transport in the exocytic pathway for subsequent secretion, while the novel PDGFs, PDGF-C and PDGF-D, are secreted as latent factors that require activation by extracellular proteases. The classical PDGF polypeptide chains, PDGF-A and PDGF-B, are well studied and they regulate several physiological and pathophysiological processes, mainly using cells of mesenchymal or neuroectodermal origin as their targets. The discovery of two additional ligands for the two PDGF receptors suggests that PDGF-mediated cellular signaling is more complex than previously thought.

Characterisation and application of antibodies specific for the long platelet-derived growth factor A and B chains

The platelet-derived growth factor (PDGF) family comprises important mitogens for mesenchymal cells. The active dimeric form of PDGF consists of four structurally related A, B, C, and D chains. All PDGF-variants bind to PDGF-receptors. The A and B chains occur with and without basic C-terminal amino acid extensions as long (A(L) and B(L)) and short (A(S) and B(S)) isoforms. PDGF-A and -B form homo- or heterodimers. The biological relevance of short and long isoforms is unknown, although it may relate to different affinities for glycosaminoglycans of the cell glycocalix and intercellular matrix. Commercially available anti-PDGF-A and anti-PDGF-B antibodies cannot discriminate between the short and the long isoforms. Thus, to investigate the function of the long and short isoforms, we raised antibodies specific for the long A and B chain isoforms. The antibodies were affinity-purified and their properties analysed by surface plasmon resonance. Inhibition studies with different PDGF homodimers and dot-blot studies proved their high specificity for the respective isoforms. Both antibodies recognised the target PDGF homodimers complexed to the glycocalix of human arterial smooth muscle cells and human monocyte-derived macrophages. By using these specific antibodies, we were able to confirm at the protein level the synthesis of PDGF-A and -B during differentiation of human monocyte-derived macrophages and to demonstrate the presence of the PDGF-A(L) and PDGF-B(L) isoforms in human arterial tissue.

Transcription of the platelet-derived growth factor A-chain gene

The molecular mechanisms which control the transcription of growth factor genes underlie such diverse biological processes as embryonic development, cellular differentiation and wound healing. Moreover, disruption of these controls is implicated in the development and progression of a wide variety of human diseases, including cancer, atherosclerosis and fibrotic disease. This review highlights progress made in the study of the gene encoding platelet-derived growth factor A-chain (PDGF-A) from the perspective of its normal patterns of expression, as well as possible mechanisms leading to dysregulation and disease. A particular focus has been placed on the identification and characterization of specific DNA elements, DNA-binding proteins and other aspects of transcriptional regulation involved in activation and repression of the human PDGF-A promoter.

Novel PDGF family members: PDGF-C and PDGF-D

Platelet-derived growth factors (PDGFs) were discovered almost two decades ago. The classical PDGF polypeptide chains, PDGF-A and PDGF-B, are well studied and they regulate a number of physiological and pathophysiological processes in many types of mesenchymal cells via two receptor tyrosine kinases, PDGF receptors alpha and beta. Recently, two additional PDGF polypeptide chains were discovered, namely PDGF-C and PDGF-D. The discovery of two additional ligands for the two PDGF receptors suggests that PDGF-mediated signaling is more complex than previously anticipated.

Analysis of genetic alterations in salivary gland tumors by comparative genomic hybridization

In order to define and map chromosomal copy number alterations in salivary gland tumors (SGTs), a comparative genomic hybridization (CGH) technique was applied to two pleomorphic adenomas (PAs), one adenoid cystic carcinoma (ACC), and one basal cell adenocarcinoma (BCAC). The PAs exhibited regional copy number losses at 5q12.4-q14.1, 9q12-q21.13, and 16q11.2, as well as a gain at 20p12.1; among these, the losses at the 9q12-q21.11 and 16q11.2 regions were common to both PAs. The ACC showed overrepresentations of the entire regions of chromosomes 16 and 20, a regional gain at 22q12.3-q13.1, and no losses. In the BCAC, regional gains at 9p21.1-pter, 18q21.1-q22.3, and 22q11.23-q13.31 as well as losses at 2q24.2 and 4q25-q27 were seen; the gain at 22q12.3-q13.1 was common in both the ACC and the BCAC. These CGH data indicate that different genetic alterations are present in the different types of SGTs, and that the alterations involve several chromosomes. The discovery of common alterations in the same and/or different types of tumors might be important in the understanding of the development and progression of the SGTs.

Growth factors in glioma angiogenesis: FGFs, PDGF, EGF, and TGFs

It has become well accepted that solid tumors must create a vascular system for nutrient delivery and waste removal in order to grow appreciably. This process, angiogenesis, is critical to the progression of gliomas, with vascular changes accompanying the advancement of these tumors. The cascade of events in this process of blood vessel formation involves a complex interplay between tumor cells, endothelial cells, and their surrounding basement membranes in which enzymatic degradation of surrounding ground substance and subsequent endothelial cell migration, proliferation, and tube formation occurs. It is likely that a host of growth factors is responsible for mediating these key events. To date, a role for Vascular Endothelial Growth Factor (VEGF) in glioma angiogenesis has been convincingly demonstrated. This review explores the contribution of other growth factors--Fibroblast Growth Factors (FGFs), Platelet-Derived Growth Factor (PDGF), Epidermal Growth Factor (EGF), and Transforming Growth Factors (TGFs)--to glioma angiogenesis. These growth factors may influence glioma angiogenesis by directly stimulating endothelial cell proliferation, by mediating the expression of key proteases on endothelial cells necessary for angiogenesis, or by regulating the expression of VEGF and of each other.

Induction of platelet-derived growth factor B-chain expression by transforming growth factor-beta involves transactivation by Smads

Transforming growth factor-beta (TGF-beta) regulates a diverse array of biological processes, such as proliferation, differentiation, extracellular matrix production, and apoptosis. In cultured vascular endothelial cells, TGF-beta induces the expression of platelet-derived growth factor (PDGF) B-chain, a mitogen and chemoattractant, at the level of transcription. The molecular mechanism(s) underlying this process are not presently understood. In this study, we performed serial 5' deletion and transient transfection analysis to define a region in the PDGF-B promoter mediating inducible responsiveness to TGF-beta. This region contains an atypical nucleotide recognition element for the Smad family of transcriptional regulators. Electrophoretic mobility shift analysis revealed that nuclear proteins bound to this site in a transient and specific manner. Supershift studies demonstrated the physical association of Smad4 with the promoter. Overexpression of Smad4 activated the PDGF-B promoter and superinduced PDGF-B promoter-dependent expression in cells exposed to TGF-beta. Moreover, simultaneous cotransfection of Smad3 and Smad4 activated the PDGF-B promoter. This effect was attenuated when Smad4 was substituted with its dominant negative counterpart. Mutation of the (-81)CAGA(-78) motif in the PDGF-B promoter abrogated Smad-inducible promoter-dependent expression. Overexpression of Smad2 and Smad3 transactivated the PDGF-B promoter in a synergistic manner. These findings demonstrate the existence of a novel, functional binding element in the proximal region of the PDGF-B promoter mediating responsiveness to TGF-beta.

Novel negative regulatory element in the platelet-derived growth factor B chain promoter that mediates ERK-dependent transcriptional repression

Platelet-derived growth factor (PDGF), which consists of an A and/or B chain, stimulates migration and proliferation in vascular smooth muscle cells as well as a large number of other cell types. Investigations over recent years have defined roles for several positive regulatory transcription factors in the PDGF-B promoter. However, little is known about the transcriptional mechanisms that negatively regulate this gene. Here, we used transient transfection and 5' deletion analysis to define a specific region in the PDGF-B promoter-mediating repression in vascular smooth muscle cells. Gel retardation assays revealed this region is bound by nuclear protein(s) in a specific manner. Supershift assays excluded the direct association of Sp1, Sp3, and Egr-1. Mutation of the negative regulatory element no longer supported nucleoprotein complex formation and, when introduced into the PDGF-B promoter, rescued the promoter from repression. Promoter activity was also restored by transfection of oligonucleotide decoys bearing the repressor binding site. The MEK1/2 inhibitor, PD98059, and a dominant negative construct generating inactive ERK1 increased reporter expression driven by the PDGF-B promoter. In contrast, the MEK inhibitor had no effect on the activity of the mutant PDGF-B promoter. These effects were cell type-specific, since neither suppression of the PDGF-B promoter nor nucleoprotein complex formation was observed in vascular endothelial cells. These findings define a distinct negative regulatory element in the PDGF-B promoter that interacts with nuclear protein(s) and inhibits PDGF-B promoter-dependent gene expression in an ERK-dependent manner.

Mechanism of action and in vivo role of platelet-derived growth factor

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 alpha-receptor and the beta-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 involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Processing of PDGF gene products determines interactions with glycosaminoglycans

The platelet derived growth factor (PDGF), a mitogen for mesenchymal cells, may be bound to and inhibited by heparin and other glycosaminoglycans. PDGF is a homo- or heterodimer of A- and B-chains. They occur as short (A109 and B110) and long (A125 and B160) isoforms. The latter contain basic carboxyl-terminal extensions. Dimeric A125 binds to heparin through its basic extension in a two-step reaction. The mechanism involves a conformational change and is consistent with a Monod-Wyman-Changeux allosteric model. Previous indirect experiments suggested that three critical amino acids (basic R111, K116 and polar T125) might be involved. Here, direct binding experiments using dimeric full-length mutants in surface plasmon resonanse analysis showed that all three critical amino acids in an R(X)4K(X)8T-motif contributed in a concerted manner to the high affinity binding. Mutations of these amino acids to alanine resulted in large thermodynamic changes, loss of the allosteric mechanism and order(s) of magnitude lower binding affinity. The binding mechanism and affinity of long dimeric rB were similar to the mutants. Short dimeric rA109 and rB110 showed 100 times lower binding affinity than rA125. Consequently, interactions with glycosaminoglycans in tissues varies between PDGF isoforms and may influence their local accumulation and activity.

Human FIGF: cloning, gene structure, and mapping to chromosome Xp22.1 between the PIGA and the GRPR genes

We report the identification, structural characterization, and mapping of the human FIGF gene. FIGF is the human homologue of mouse figf (c-fos-induced growth factor), a new member of the platelet-derived growth factor/vascular endothelial growth factor (PDGF/VEGF) family. It codes for a secreted factor with mitogenic and morphogenic activity on fibroblast cells. The predicted amino acid sequence of FIGF is 84% identical to that of the mouse protein, and it is highly conserved (up to 40%) in the dimerization domain with respect to the VEGF members of the family. The 2.5-kb mRNA of FIGF was detected in adult lung and heart tissues. The gene spans about 50 kb and is organized into seven exons and six introns. The FIGF promoter contains an optimal AP-1-binding site and lacks a canonical TATA box. Fluorescence in situ hybridization mapped FIGF to chromosomal region Xp22.1. The subsequent identification of YAC positive clones from this region allowed us to refine the map and localize FIGF centromeric to the phosphatidylinositol glycan complementation class A (PIGA) gene and telomeric to the gastrin-releasing peptide receptor (GRPR) gene. FIGF and PIGA genes lie next to each other in a head-to-tail orientation, with the FIGF polyadenylation signal about 12 kb from the PIGA transcriptional start site.

Effect of phenotype on the transcription of the genes for platelet-derived growth factor (PDGF) isoforms in human smooth muscle cells, monocyte-derived macrophages, and endothelial cells in vitro

Proliferation of arterial smooth muscle cells (ASMCs) contributes considerably to enlargement of the arterial wall during atherosclerosis. The platelet-derived growth factor (PDGF) is a well-known mitogen and chemoattractant for ASMCs. Quantitative reverse transcription-polymerase chain reaction showed that cells appearing in atherosclerotic lesions, such as ASMCs, endothelial cells, and monocytes/macrophages, expressed mRNAs for both PDGF A and B chains in vitro, with the highest expression in endothelial cells. On proliferation, ASMCs and endothelial cells upregulated PDGF A mRNA. Differentiation of macrophages increased the amount of both mRNAs. Thus, the regulation of PDGF A- and B-chain expression depends on cell types and phenotypic states of the cells, which have also been found in vivo in human atherosclerotic lesions. PDGF A can be produced as short and long isoforms. The latter binds with high affinity to glycosaminoglycans. Irrespective of phenotype, only the minor part of total PDGF A mRNA consisted of the long variant in ASMCs, while endothelial cells produced 40% of total PDGF A as the long form. The differentiation of macrophages increased the production of the long PDGF A mRNA from 10% to 40%. Thus, increasing numbers of stimulated cells in the atherosclerotic lesion may increase the transcription of PDGF isoforms, and particularly of the long PDGF A isoform. Together with increasing amounts of ASMC-derived proteoglycans in developing lesions, this may contribute to accumulation of PDGF in the arterial wall matrix, resulting in prolonged stimulation of ASMCs.

Repression of platelet-derived growth factor A-chain gene transcription by an upstream silencer element. Participation by sequence-specific single-stranded DNA-binding proteins

Platelet-derived growth factor A-chain is a potent mitogen expressed in a restricted number of normal and transformed cells. Transient transfection and deletion analysis in BSC-1 (African green monkey, renal epithelial) cells revealed that the -1680 to -1374 region of the A-chain gene repressed homologous and heterologous promoter activities by 60-80%. An S1 nuclease-hypersensitive region (5'SHS) was identified within this region (-1418 to -1388) that exhibited transcriptional silencer activity in BSC-1 and a variety of human tumor cell lines (U87, HepG2, and HeLa). Electrophoretic mobility shift assays conducted with 5'SHS oligodeoxynucleotide probes revealed several binding protein complexes that displayed unique preferences for binding to sense, antisense, and double-stranded forms of the element. Southwestern blot analysis revealed that the antisense strand of 5'SHS binds to nuclear proteins of molecular mass 97, 87, 44, and 17 kDa, whereas the double-stranded form of 5'SHS is recognized by a 70-kDa factor. Mutations within 5'SHS element indicated the necessity of a central 5'-GGGGAGGGGG-3' motif for protein binding and silencer function, while nucleotides flanking both sides of the motif were also critical for repression. These results support a model in which silencer function of 5'SHS is mediated by antisense strand binding proteins, possibly by stabilizing single-stranded DNA conformations required for interaction with enhancer sequences in the proximal promoter region of the A-chain gene.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.

A novel human c-sis mRNA species is transcribed from a promoter in c-sis intron 1 and contains the code for an alternative PDGF B-like protein

The human platelet-derived growth factor (PDGF) B chain precursor is usually translated from a 3.5 kb c-sis/PDGF B gene transcript. The first exon of the c-sis/gene contains the code for the signal peptide of the PDGF B chain precursor, preceded by a 1 kb long untranslated sequence with potent translation inhibitory activity. In this paper we show that a novel 2.6 kb c-sis mRNA present in the human choriocarcinoma cell line JEG-3 initiates at an alternative exon 1, which we refer to as exon 1a. The 90 bp long exon 1a is located in the center of the first intron of the gene. It coincides with a very pronounced DNase-I-hypersensitive site and is preceded by a functional promoter. Of the three ATG codons present in exon 1a, the third one perfectly matches the criteria of a consensus start codon. It initiates an open reading frame that is continuous with the code for the PDGF B chain precursor but lacks the code for a signal peptide. We conclude that this novel 2.6 kb c-sis mRNA species lacks the strong translation inhibitory potential of the regular exon 1 and contains the code for a PDGF B-like protein that may be targeted to the cell nucleus.

In vivo footprinting and functional analysis of the human c-sis/PDGF B gene promoter provides evidence for two binding sites for transcriptional activators

By in vivo DMS footprint and reporter gene analyses we identified two transcription factor binding sites in the human c-sis/PDGF B gene promoter. The low basal activity of the PDGF B promoter in HeLa and undifferentiated K562 cells, which express low PDGF B mRNA levels, and in PC3 cells, which express a high PDGF B mRNA level, results from binding of a weak transcriptional activator between positions -64 and -61 relative to the transcription start site. Cytotrophoblast-like JEG-3 cells, which do not express the 3.5 kb PDGF B mRNA, contain a transcriptional activator directed at the -64/-61 sequence, but DNA methylation may render the endogenous promoter inaccessible to this activator. A CCACCCAC element at position -61/-54 was identified as the in vivo binding site for a strong transcriptional activator in phorbol ester-treated megakaryocytic K562 cells, which express a high PDGF B mRNA level. Primary human fibroblasts, which do not transcribe the PDGF B gene, contain a transcriptional activator that recognizes an element between positions -60 and -45 but does not bind to the endogenous unmethylated promoter. Our results show that the complex expression pattern of the human PDGF B gene involves the cell type-specific expression of weak and strong transcriptional activators and regulation of promoter accessibility to these factors.

Karyotype analyses of 20 human glioma cell lines

Human malignant gliomas are frequently associated with loss of gonosomes and chromosomes 13, 17, and 22. Their progression from anaplastic glioma to glioblastoma is marked by additional loss of chromosome 10. In addition, structural and numerical aberrations of chromosome 7 are frequently found. We report on the karyotypes of a series of 20 human gliomas of which 11 were analysed as established cell lines; 9 cases were investigated in early culture, 5 of which later also became established lines. In addition to the frequently reported overrepresentation of chromosome 7, four cell lines with polysomy for chromosome 22 were seen. A high incidence of structural chromosomal aberrations was present in early cultures as well as in cell lines after various in vitro passages. We found that the general characteristics of karyotypic aberrations found in early cultures or direct preparations of dispersed tumour material were reflected in the pattern of aberrations present in cell lines at much later time points. Thus it appears as if no systematic changes can be attributed to long-term cultures. Suspicious losses of chromosomes 14, 18, and 19 or gain of chromosome 22 indicate that individual cases may have originated due to other mechanisms than the ones already hypothesized, i.e., different suppressor genes or amplification of genes other than the EGF-R-gene. None of the established cell lines had a genomic rearrangement of c-erbB 1, c-erbB 2 or of the p 53 gene.

BCNU-resistant human glioma cells with over-representation of chromosomes 7 and 22 demonstrate increased copy number and expression of platelet-derived growth factor genes

We used standard karyotypic analyses of first-division cells to identify a subpopulation of cells in primary malignant gliomas with over-representation of chromosomes 7 and 22. These cells are a minor subpopulation in the primary tumor but become the dominant population after treatment in vitro of the cells with the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). The selection for a cell with this specific karyotypic abnormality suggests that these chromosomes contain genes important to the growth of BCNU-resistant cells. Southern blot hybridization analyses demonstrate an increased copy number of the genes encoding platelet-derived growth factor (PDGF) A-chain and B-chain, which have been mapped to chromosomes 7 and 22, respectively. Reverse transcription followed by polymerase chain reaction (RT-PCR) analysis demonstrates increased expression of these genes. In addition, these cells secrete a mitogenic factor that stimulates 3H-thymidine uptake in NIH 3T3 cells. This factor is sensitive to anti-PDGF antibodies and beta-mercaptoethanol, but not to anti-EGF antibodies. These data suggest that autocrine and/or paracrine mechanisms occur in human malignant gliomas, and that over-expression of PDGF may play a role in the growth of BCNU-resistant cells in these tumors.

DNase-I-hypersensitive sites located far upstream of the human c-sis/PDGF-B gene comap with transcriptional enhancers and a silencer and are preceded by (part of) a new transcription unit

The human c-sis gene encodes the B chain of platelet-derived growth factor (PDGF), a potent mitogen for cultured cells of mesenchymal origin. PDGF is stored in the alpha-granules of blood platelets, which are derived from bone marrow megakaryocytes and lack transcriptional machinery. Human myeloid leukemia cell line K562 can be used as a model for megakaryocytes. Phorbol-ester-mediated megakaryocytic differentiation of K562 cells is accompanied by more than 200-fold increase in the c-sis mRNA level. We have now localized transcriptional enhancers at -8.6 kb and -9.9 kb relative to the human c-sis gene transcription start site. The enhancer at -8.6 kb increases activity of the c-sis promoter by 40-60-fold specifically in K562 cells and comaps with a DNase-I-hypersensitivity (DH) site. The enhancer at -9.9 kb increases c-sis promoter activity by 5-10-fold in K562 cells and DH at that site accompanies phorbol-ester-induced megakaryocytic differentiation. In phorbol-ester-treated K562 cells the two enhancers may be negatively influenced by a silencer that comaps with DH at -10.7/-11.0 kb. Reporter gene analysis predicted that combined activity of the upstream enhancers and the c-sis promoter may result in 100-1000-fold higher promoter activity in phorbol-ester-treated K562 cells compared with untreated cells, which can fully explain the more than 200-fold increase in c-sis mRNA level. DH at -8.6 kb and -9.9 kb was also detected in human fibroblasts and in the carcinoma cell lines HeLa and PC3, which express, respectively, undetectable, low and high levels of c-sis mRNA. Although the individual DH sites displayed 4-10-fold enhancer activity in all these cells, they lost most of their biological activity when combined in a larger fragment. In addition we localized (part of) a new transcription unit at approximately 13 kb upstream of the c-sis transcription start site. The corresponding 0.45-kb sis upstream region (sur) transcript is constitutively expressed in all cell lines examined. The expression of the sur transcript is independent of the expression of c-sis mRNA and of the pattern of DH sites far upstream of the c-sis gene. Thus, at present, there is no indication that the upstream DH sites are involved in regulation of expression of the sur gene.

Phenytoin increases gene expression for platelet-derived growth factor B chain in macrophages and monocytes

The mechanism by which phenytoin (PHT) induces gingival overgrowth remains unclear. We hypothesized that PHT increases macrophage production of platelet-derived growth factor (PDGF), an important cytokine in connective tissue growth and repair, and that excessive production PDGF in gingiva could lead to redundant growth. To test the hypothesis, rat peritoneal macrophages and human blood monocytes were cultured in the presence of PHT (5 to 20 micrograms/ml medium) or an equal volume of its solvent for 3 days and tested for expression of PDGF-B mRNA by in situ hybridization. Approximately 300 cells/culture well were examined (3 wells/drug level) for positive indication of PDGF-B mRNA. Data were compared by chi square test. All levels of PHT in both cell types induced a 2- to 8-fold increase in PDGF-B mRNA positive cells, significant in all cases at P < 0.001. Northern blot analysis of RNA from similarly cultured rat macrophages confirmed these findings. Cells treated with 10 micrograms PHT/ml medium or solvent revealed 2.2 +/- 0.3 and 1.0 +/- 0.2 (mean +/- SEM) arbitrary units PDGF mRNA respectively (t tests, P < 0.05). Additionally, rat macrophages were cultured in presence of 5 micrograms PHT/medium or its solvent and medium was analyzed for PDGF secretion by radioimmunoassay. Mean values (+/- SEM) were 1.28 +/- 0.49 and 0.78 +/- 0.07 ng/mg protein respectively (t test, P < 0.05). These data showed that PHT augmented the expression of c-sis, the gene for PDGF-B, and offered a possible explanation for PHT-induced gingival overgrowth.

Localization and functional analysis of DNase-I-hypersensitive sites in the human c-sis/PDGF-B gene transcription unit and its flanking regions

We studied the regulation of the expression of the human c-sis/PDGF-B gene in the following panel of cell lines: K562 cells, in which expression is inducible by phorbol esters; cytotrophoblast-derived cell lines JEG-3 and JAR; carcinoma-derived cell lines PC3, T24 and HeLa, which show extensive differences in c-sis mRNA content; dermal fibroblasts, which do not express the gene. We demonstrate that the wide variety of levels of c-sis mRNA in these cells is mainly determined at the transcription level. Extensive gene rearrangements or amplifications, or significant differences in the stability of the c-sis transcript could not be found. In fibroblasts and placenta cell lines, inaccessibility of the c-sis promoter, rather than the absence of transcription factors that activate it, inhibits expression of the endogenous gene. Examination of the chromatin structure of the transcription unit and immediate flanking regions revealed several cell-type-specific DNase-I-hypersensitivity (DH) sites. Functional analysis of genomic fragments harbouring one or more DH sites showed the presence of negative regulatory elements within intron 1, and of an activating element downstream of the gene. A DH site, located immediately downstream of the promoter in dermal fibroblasts, may regulate accessibility of the promoter by means of specific nucleosome phasing.

Tumorigenic conversion of human mesothelial cells as a consequence of platelet-derived growth factor-A chain overexpression

Overexpression of platelet-derived growth factor (PDGF)-A as well as PDGF-B chain mRNA has previously been reported in human mesothelioma cell lines. In this report, it has been established that the A but not the B chain protein is expressed at detectable levels in cell lysates and conditioned medium from these cell lines. In order to investigate the effect of overexpression of PDGF-A chain in a human mesothelial cell model system, a retroviral vector containing a human PDGF-A chain cDNA insert under the control of the Moloney murine leukemia virus (MoMLV) promoter was inserted into the SV-40 T-antigen immortalized human mesothelial cell line MeT-5A. Selected cells showed overexpression of PDGF-A chain relative to MeT-5A and induced tumors in athymic nude mice. PDGF-A chain overexpression was also found in the tumor specimens excised from the mice. PDGF-A mRNA and protein were expressed at a higher level in the tumor explant cell lines, suggesting a correlation of tumorigenicity with A chain production.

Characterization of the mouse PDGF A-chain gene. Evolutionary conservation of gene structure, nucleotide sequence and alternative splicing

The mouse platelet-derived growth factor (PDGF) A-chain gene has been structurally characterized and compared with its human counterpart. The organization of the two genes is similar. Both consist of 7 exons spaced by 6 introns of corresponding sizes. As in the human gene, exon 6 encodes a sequence which is alternatively spliced. When present, it codes for an alternative C-terminus of the A-chain. In intron 5, conserved stretches of nucleotides, potentially involved in the regulation of the alternative splicing, are identified. The untranslated sequences show a high degree of nucleotide sequence identity and several conserved consensus binding sites for transcription factors are identified within the 5' untranslated as well as in the 5' flanking region.

Platelet-derived growth factor (PDGF) A-chain mRNA heterogeneity generated by the use of alternative promoters and alternative polyadenylation sites

Expression of the platelet-derived growth factor (PDGF) A-chain gene is known to give rise to multiple transcripts of different sizes. Northern blot analysis, using a set of DNA probes corresponding to various parts of the human PDGF A-chain gene, indicated heterogeneity in both the 5' and 3' end of the transcripts. The 3' heterogeneity was shown to be the result of differential use of three polyadenylation signals. S1-nuclease protection- and chloramphenicol acetyltransferase (CAT)-assays, revealed the 5' heterogeneity to be the consequence of two alternative promoters. Whereas the upstream promoter contained typical TATA- and CAAT-boxes, the downstream promoter lacked a TATA-box but seemed to be composed of several GC-boxes.

Effects of fractionated x-irradiation on the Ly-6--Ril-1--Pol-5 region

Our laboratory has focused on defining, localizing, and understanding the mode of action of genes involved in fractionated x-irradiation (FXI) leukemia in susceptible and restraint mouse strains. We have described the genetic and molecular evidence suggesting the existence of multiple independent loci involved in FXI-induced leukemogenesis. These studies indicated that one of these, Ril-1, a locus on the distal portion of chromosome 15, is the major locus influencing susceptibility to the disease. Our data unequivocally place Ril-1 in the gene complex Ly-6--Ril-1--Sis--H-30--Pol-5. Ril-1 appears to be closest to Ly-6 and Sis. We report that in FXI-induced leukemias there are hypomethylation changes in the Ly-6 region as compared to normal thymocytes. In contrast, Sis was found to be hypermethylated and not expressed. In addition, we have noted DNA rearrangements in the Ly-6--Pol-5 region in the majority of tumors examined using the Ly-6 and spleen focus-forming virus (SFFLV) molecular probes. Increased expression of Ly-6 and other surface markers encoded in this region has been noted in FXI-induced thymomas.

Platelet-derived growth factor and its receptor in blood cell differentiation and neoplasia

Platelet-derived growth factor (PDGF) is a family of dimeric protein molecules synthesized by differentiated, non-dividing and proliferating blood cells. Experimental findings indicate that PDGF is involved in development and/or maintenance of physiological functions of certain normal blood cells. Also, PDGF synthesis correlates with certain blood cell proliferative diseases caused either spontaneously or associated with viral infection. There is increasing evidence that the diverse effects of PDGF in both normal and abnormal physiological functions of blood cells may be regulated at the level of its receptor. New experimental findings are discussed relating to PDGF receptors in normal leukemic, and virally-infected human cells of myeloid and lymphocytic lineages. At specific developmental stages this regulation may take the form of PDGF and its receptor being expressed or co-expressed; the unmodified or modified form of receptor that specifically interacts with PDGF; the cellular site at which the PDGF-receptor interacts with its ligand; and co-expression of the PDGF-receptor with other receptors associated with specific cell lineage or functions. Elucidation of events involved in synthesis, processing, and interactions of PDGF isoforms and their respective receptors will enable us to develop pharmacological means that may either interfere with, or enhance these desired blood cell functions. This review focuses on PDGF and its receptor in human blood cell differentiation and neoplasia.

Coexpression of platelet-derived growth factor (PDGF) and PDGF-receptor genes by primary human astrocytomas may contribute to their development and maintenance

The present studies investigated the expression of the two PDGF genes (c-sis/PDGF-2 and PDGF-1) and the PDGF-receptor b gene (PDGF-R) in 34 primary human astrocytomas. Northern blot analysis demonstrated the coexpression of the c-sis/PDGF-2 protooncogene and the PDGF-R gene in all astrocytomas examined. The majority of the tumors also expressed the PDGF-1 gene. There was no correlation between the expression of the two PDGF genes. Nonmalignant human brain tissue expressed the PDGF-R and PDGF-1 genes but not the c-sis/PDGF-2 protooncogene. In situ hybridization of astrocytoma tissue localized the expression of the c-sis and PDGF-R mRNA's in tumor cells. Capillary endothelial cells also expressed c-sis mRNA. In contrast, nonmalignant human brain tissue expressed only PDGF-R mRNA but not c-sis/PDGF-2 mRNA. The coexpression of a potent mitogenic growth factor protooncogene (c-sis) and its receptor gene in astrocytoma tumor cells suggests the presence of an autocrine mechanism that may contribute to the development and maintenance of astrocytomas. The expression of c-sis mRNA in tumor cells but not in nonmalignant brain cells may serve as an additional diagnostic criterion for the detection of astrocytomas in small tissue specimen using in situ hybridization for the detection of c-sis mRNA and/or immunostaining for the recognition of its protein product.

Enhancement of c-sis proto-oncogene transcription in bronchoalveolar mononuclear cells from patients with pulmonary sarcoidosis

The expression of c-sis proto-oncogene in bronchoalveolar mononuclear cells was studied in seven patients with pulmonary sarcoidosis. By means of nuclear run on transcription assay, the transcriptional level of c-sis proto-oncogene in bronchoalveolar mononuclear cells was investigated. Expression of c-sis proto-oncogene in bronchoalveolar mononuclear cells was enhanced. Enhancement of c-sis transcription may be involved in the process of activation of bronchoalveolar mononuclear cells in patients with pulmonary sarcoidosis.

Platelet-derived growth factor and its role in health and disease

Platelet-derived growth factor (PDGF) was first discovered in platelets because they are the principal source of mitogenic activity in whole blood serum for mesenchymal cells in culture. PDGF is ubiquitous in that it can be formed by a large number of normal cells as well as many varieties of transformed cells. However, its expression and biological activity appear to be controlled at a number of different levels. The molecule consists of two peptide chains (termed 'A' and 'B') and is found as one of at least three possible isoforms, (AB, AA or BB). Each of these isoforms binds to a high-affinity cell-surface receptor that is composed of two different subunits, each of which has specificity for one or the other of the peptide chains of PDGF. The two receptor subunits are present in differing amounts on different cell types, and therefore the capacity of the different isoforms of PDGF to induce mitogenesis depends on the specific PDGF isoform and the relative numbers of receptor subunits present on the responding cell. In addition to inducing cell replication, PDGF elicits a number of intracellular signals related to mitogenesis, is chemotactic, is a vasoconstrictor, activates leukocytes, and modulates extracellular matrix turnover. This growth factor is probably involved in a number of biologically important events including wound repair, embryogenesis and development, and inflammation, leading to fibrosis, atherosclerosis and neoplasia.

Cytokines of the lung

Communication between cells determines the steady-state composition of the lung in health and becomes a critical determinant of outcome in pathologic processes resulting in anatomic remodeling. This review presents the evolving concepts of the biology of cytokines (also known as peptide growth factors or biological response modifiers) in maintaining normal tissue growth and homeostasis. How these extracellular signaling proteins are involved in such pathologic disorders as spontaneous pulmonary fibrosis, sarcoidosis, pneumoconiosis, and the evolution and recovery from acute lung injury is also discussed. During the past decade the cytokines have come to the fore as important multifunctional mediators of cell behavior and cell-cell communication. A wide range of cellular responses are influenced or triggered when cytokines interact with cells. These include mitosis, chemotaxis, angiogenesis, cytoskeleton arrangement, immunomodulation, and extracellular matrix production. Cytokines influence cell behavior by binding to specific high affinity surface receptors on target cells. These receptors are linked in turn at the cell membrane to a complex array of intracellular signaling pathways. Individual cytokines may inhibit as well as promote cellular functions such as mitosis and thereby play a critical role in homeostasis of normal tissue elements. Hence, cytokines are intimately involved in normal tissue homeostasis as well as in processes eventuating in growth and remodeling. All cells produce and secrete cytokines at some time during their life. Each cytokine is capable of modulating more than one cellular function. Although produced by a variety of cell types, the triggers that induce a specific cytokine to be produced differ between cells. Many of the cytokines share regions of homologous nucleic acid sequences, suggesting that they are members of larger gene families. Given that tissues and cells are exposed to complex cytokine mixtures rather than to individual cytokines, recent attention has turned to understanding how cytokines interact. The combined effects of cytokine mixtures have proved to be both complex and unpredictable based on knowledge of the separate actions of the individual cytokines involved. In studies of the role of cytokines in lung disease, early research attention has focused on those cytokines released by alveolar macrophages (the so-called macrophage-derived growth factors). However, structural cells as well as immune effector cells of the lung are capable of cytokine production and release. The cytokines receiving the most attention to date in relation to pulmonary diseases include platelet-derived growth factor (PDGF), interleukin-1 (IL-1), transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha), insulinlike growth factor I (IGF-I), and, most recently, interleukin-6 (IL-6).(ABSTRACT TRUNCATED AT 400 WORDS)

Increased H-2Dd expression following infection by a molecularly cloned ecotropic MuLV

The biological consequences of radiation leukemia virus (RadLV) infection include the stimulation of H-2Dd antigen expression in resistant mouse strains and thymoma induction in susceptible strains. In an effort to understand the genetic basis of these phenomena, the integrated ecotropic RadLV genome has been examined in a number of primary RadLV-induced tumors, as well as thymomas adapted to in vitro passage; considerable heterogeneity was observed. Examination of these polymorphic viral sequences should help define the viral gene(s) involved in the biological effects of RadLV infection; toward this end, integrated RadLV genomes were molecularly cloned and examined. The genomes and their flanking sequence were characterized by restriction enzyme analysis. Three unique viral genomes were obtained which represent four integration sites. The three RadLV genomes are shown to carry polymorphisms of the original tumor. Following DNA transfection, one of the three genomes replicated in and reinfected both mouse thymocytes and fibroblasts, but not mink fibroblasts in vitro. Virus encoded by the other two DNA genomes could not be recovered following transfection into any of the three cell types. One of these two apparently defective retroviruses encodes a truncated p15E molecule, while the other has elongated long terminal repeats (LTRs). The non-defective ecotropic isolate was collected from in vitro tissue culture supernatants, concentrated, and used to infect mice. Thymocytes of infected, resistant mice were shown to express elevated levels of H-2Dd antigen as early as 12 days post infection, a hallmark of RadLV infection.

Coexpression of platelet-derived growth factor (PDGF) A-chain and PDGF receptor genes in human gastric carcinomas

In this study we examined the expression of platelet-derived growth factor (PDGF) A-chain and PDGF receptor genes in seven human gastric carcinoma cell lines and 15 gastric carcinoma tissues. Expression of mRNA for PDGF A-chain was found in all gastric cell lines and all gastric carcinoma tissues. Two of the seven gastric carcinoma cell lines expressed PDGF receptor mRNA. Out of the 15 gastric carcinoma tissues, eight showed enhanced expression of PDGF receptor mRNA and all of them demonstrated prominent fibrous stroma. Moreover, the incidence of enhanced expression of PDGF receptor mRNA was higher in scirrhous carcinoma than in well differentiated adenocarcinoma. These results strongly suggest that PDGF produced by tumor cells acts as a paracrine growth factor for production of fibrous stroma in gastric carcinomas.

Regulation of expression of the c-sis proto-oncogene

Regulation of expression of platelet derived growth factor polypeptide B encoded by the c-sis proto-oncogene is important in a number of physiological and pathological conditions. Sequences in the 1028 nucleotide long 5' untranslated region of the c-sis mRNA were found to inhibit protein synthesis. The inhibition is relieved by deletion of nucleotides 154-378 or 398-475. Sequences within 375 nucleotides upstream of the RNA initiation site are important for transcriptional activity. Sequences in two portions of this region, between -375 and -235 nucleotides and between -235 and -99 nucleotides relative to the RNA CAP site are important for full activity. A transcriptional enhancer activity is demonstrated by its ability to increase the activity of the human T lymphotropic virus type (HTLV) I promoter at a distance and in an orientation-independent manner. Furthermore, sequences upstream of the c-sis RNA CAP site respond to the HTLV I transactivator protein to increase RNA synthesis from either the c-sis or HTLV I promoter.

An update on the cellular and molecular biology of brain tumors

Patients with tumors of the central nervous system (CNS) remain difficult to treat despite recent advances in surgical, chemotherapeutic and radiotherapeutic techniques. A better understanding of the molecular and cellular biology of neoplasia is providing neuroscientists with a framework on which to devise novel therapies for these patients. It thus becomes imperative that neurologists and neurosurgeons be aware of these advances in basic science that may eventually have a positive impact on patient management. This paper reviews our present knowledge of the process of CNS oncogenesis and the roles that chemicals, viruses, oncogenes, growth inhibitor genes, and growth factors play in the process.

The molecular biology of CML: a review

The t(9;22) generating the Ph1 chromosome in CML creates a new fusion gene (bcr/abl), which combines bcr sequence from chromosome 22 with abl sequence from chromosome 9. This gene generates a new fusion protein which has a much greater protein tyrosine kinase activity than the normal abl protein, and it is this ptk activity which has been shown to be essential for the transforming activity of the v-abl gene and for other related oncogenes which contain the homologous ptk region. The fusion gene is present in almost all patients with CML, including a sizable fraction of the patients with Ph1(-) CML. The Ph1 chromosome and CML have provided one of the most exciting stories of oncogene activation in human malignancy, and much more information, at both the level of basic and of clinical science, will result from the investigations currently underway in a number of laboratories.

The potential role of platelet-derived growth factor as an autocrine or paracrine factor for human bone cells

Platelet-derived growth factor, PDGF, is a potent mitogen for cells of mesenchymal origin such as fibroblasts, smooth muscle cells and glial cells. PDGF is thought to have the potential to act as both a paracrine and an autocrine factor. Studies described here extend these observations to human bone-derived cells. Exogenous PDGF induces biologic activity in two human osteogenic sarcoma cell lines and in one of these, the two PDGF genes, PDGF-1 and PDGF-2/c-sis are expressed. In addition, PDGF stimulates proliferation of normal osteoblastic cells derived from adult human cancellous bone. The expression of the PDGF-1 gene but not the PDGF-2/c-sis gene is demonstrated in normal human adult bone-derived cells by Northern blot analysis and synthesis of PDGF is shown by immunoprecipitation with PDGF antisera. These studies indicate that PDGF has the potential to act as a paracrine or autocrine regulator of bone cells.

Selective expression of mRNA encoding platelet-derived growth factor B chain following transfection of foreign genes into cell lines derived from baby hamster kidney

The genes for platelet-derived growth factor (PDGF) A and PDGF B chains are expressed in a variety of biological situations. Active PDGF consists of two distinct but homologous polypeptide chains, PDGF A and PDGF B, which are found as heterodimers or homodimers. We report a novel situation in which there is selective expression of mRNA encoding PDGF B in cell lines derived from baby hamster kidney (BHK) following transfection with various gene/cDNA constructs and following growth selection with methotrexate. The process of transfection itself, and not expression of the proteins encoded by the transfected genes/cDNAs (hormones, enzymes, and structural proteins), induces expression of PDGF B. No PDGF B mRNA is detectable in control cell lines. Low levels of mRNA encoding PDGF A are constitutively present and are not changed by transfection and or growth selection. PDGF-like activity is present in the medium whenever PDGF B mRNA is detected. The composition of the secreted PDGF dimer cannot be established from our data, but quantitative analysis of mRNA suggests that the PDGF is a B-B dimer. However, the data show that transcription of the PDGF A and PDGF B genes in BHK cells is regulated independently, similar to that reported for some human tumor cells. Furthermore, the selective expression of PDGF B in response to the introduction of foreign genes and to growth selection may be an important aspect of the reaction of these cells to nonoptimal growth conditions, allowing survival and growth of the cells that express PDGF B.

Characterization of a high-molecular-weight protein immunoprecipitated by platelet-derived growth factor antisera

We previously demonstrated that a high-molecular-weight glycoprotein could be immunoprecipitated from metabolically labeled U-2 OS cells with platelet-derived growth factor (PDGF) antiserum and that it appears to be derived from a different precursor than is the 30 kD PDGF-like mitogen produced by these cells. These findings were unexpected, since the molecular weight of this glycoprotein is too large to be encoded by the PDGF structural genes. From experiments with metabolically labeled U-2 OS human osteosarcoma, fibroblasts, and NRK cells, we report here that a 185 kD protein immunoprecipitated with PDGF antiserum has the following characteristics. 1) It is a PDGF binding protein that is unrelated to alpha 2-macroglobulin. 2) It is phosphorylated in response to PDGF stimulation. 3) It is immunoprecipitated by phosphotyrosine antibodies. 4) It is not a substrate of epidermal growth factor-induced tyrosine kinase activity. These studies indicate that high-molecular-weight proteins immunoprecipitated by antiserum to PDGF represent a complex between PDGF and a binding protein capable of being phosphorylated by a PDGF-induced tyrosine kinase. These characteristics are identical to those of the PDGF receptor.

Expression of platelet-derived growth factor (PDGF)-related transcripts and synthesis of biologically active PDGF-like proteins by human malignant epithelial cell lines

Human malignant epithelial cell lines were analyzed for expression of platelet-derived growth factor (PDGF) genes. Of the 12 cell lines tested, 9, derived from breast, lung, gastric, and ovarian carcinomas, were found to express both PDGF-1 and PDGF-2 genes. The levels of both PDGF-1 and PDGF-2 transcripts were superinduced when these cells were treated with cycloheximide, an inhibitor of protein synthesis. These cells also released an activity that in studies with BALB-c/3T3 cells, inhibited binding of 125I-labeled PDGF and stimulated incorporation of [3H]thymidine. This stimulating activity was inhibited after reduction of the conditioned media by mercaptoethanol or after preincubation with antibodies to PDGF. Moreover, this activity was not affected by heat treatment. Immunoprecipitation studies revealed that breast, lung, and gastric carcinoma cells produced PDGF-like proteins that migrated as 30- and 32-kD species under nonreducing conditions and as 15- and 16-kD species under reducing conditions. In contrast, malignant cells of ovarian origin produced 14-16-kD PDGF-like proteins that were unchanged in mobility after reduction. As PDGF receptors were not detected on these malignant epithelial cells, the production of PDGF-like proteins may affect other cells in the microenvironment by paracrine mechanisms and may contribute to excessive cell proliferation, inflammatory reactions, and connective tissue remodeling seen in certain carcinomas.

Expression of recombinant platelet-derived growth factor A- and B-chain homodimers in rat-1 cells and human fibroblasts reveals differences in protein processing and autocrine effects

The autocrine effects of platelet-derived growth factor (PDGF) A- and B-chain homodimers (PDGF-AA and PDGF-BB) on rat-1 cells and human fibroblasts have been investigated by using human PDGF A- and B-chain cDNA clones expressed in a retroviral vector. Infection with replication-defective virus carrying the B-chain cDNA resulted in a phenotypical transformation resembling that induced by simian sarcoma virus. The resulting cells were focus forming in monolayer cultures, grew to high saturation densities, and formed large colonies in soft agar. The PDGF A-chain transfectants showed no transformed morphology and lacked focus-forming activity but grew to high saturation density in monolayer culture and formed small colonies in soft agar. A similar but weaker effect was obtained with an A-chain cDNA variant containing a 69-base-pair insertion in the 3' end of the protein-coding domain. A- and B-chain transfectants released PDGF receptor-competing activity into the medium, but only the medium conditioned by the B-chain transfectants possessed potent mitogenic activity on human fibroblasts. Both types of transfectants had downregulated levels of PDGF receptors; however, the B-chain transfectants were downregulated to significantly lower levels. Metabolic labeling and immunoprecipitations with PDGF antiserum showed that the PDGF B-chain protein was processed to a 24-kilodalton cell-associated and a 30-kilodalton secreted dimeric protein. The A-chain protein was rapidly secreted as a 31-kilodalton dimeric protein. The present study shows a marked difference in the autocrine effects of PDGF-AA and -BB expressed under the control of a retroviral promoter and suggests that different biological properties may be assigned to these two PDGF isoforms.