Binding of different dimeric forms of PDGF to human fibroblasts: evidence for two separate receptor types

The binding of the three dimeric forms of platelet-derived growth factor (PDGF), PDGF-AA, PDGF-AB and PDGF-BB, to human fibroblasts was studied. Cross-competition experiments revealed the existence of two different PDGF receptor classes: the type A PDGF receptor bound all three dimeric forms of PDGF, whereas the type B PDGF receptor bound PDGF-BB with high affinity and PDGF-AB with lower affinity, but not PDGF-AA. The sizes of the two receptors were estimated with affinity labeling techniques; the A type receptor appeared as a major component of 125 kd and a minor of 160 kd, and the B type receptor as two components of 160 and 175 kd. A previously established PDGF receptor monoclonal antibody, PDGFR-B2, was shown to react with the B type receptor only. The different abilities of the three dimeric forms of PDGF to stimulate incorporation of [3H]TdR into human fibroblasts indicated that the major mitogenic effect of PDGF is mediated via the B type receptor.

A glioma-derived PDGF A chain homodimer has different functional activities from a PDGF AB heterodimer purified from human platelets

Glioma-derived growth factor I (GDGF-I) is structurally similar to a platelet-derived growth factor (PDGF) A chain homodimer, whereas PDGF purified from human platelets is a heterodimer of one A and one B chain. Binding experiments revealed that GDGF-I and PDGF bound to a common receptor on human fibroblasts, but also suggested the presence of a second receptor type recognizing only PDGF. In contrast to PDGF, GDGF-I had only a limited mitogenic activity, a low ability to stimulate receptor autophosphorylation and actin reorganization, and no chemotactic activity. GDGF-I did, however, cause transmodulation of EGF receptors, suggesting that it, like PDGF, activates protein kinase C in fibroblasts. These data indicate that different PDGF-like growth factors have different functional activities, which are possibly mediated via different receptors.

Endothelial cell hyperplasia in human glioblastoma: coexpression of mRNA for platelet-derived growth factor (PDGF) B chain and PDGF receptor suggests autocrine growth stimulation

The genes for platelet-derived growth factor (PDGF) A chain, B chain/c-sis, and the PDGF receptor are expressed in human malignant glioma cell lines. In the present investigation we have studied the expression of these genes in biopsy specimens from human glioblastomas. Hyperplasia of the vascular endothelium is a prominent characteristic of human glioblastoma multiforme and simian sarcoma virus-induced gliomas in primates. RNA transfer blot analysis of biopsies from glioblastoma multiforme showed transcripts for PDGF A and B chains and the PDGF receptor. Tissue sections from this tumor examined by in situ hybridization techniques revealed that the proliferating vascular endothelial cells contained large quantities of mRNA for PDGF B chain/c-sis and its receptor and, to a lesser extent, for PDGF A chain. In contrast, the tumor cells expressed more mRNA for PDGF A chain than for PDGF B chain and PDGF receptor. The latter two were also expressed at higher levels in glioma cells than in glial cells of nontumorous human brain tissue. Thus, an autocrine stimulation by the PDGF B chain/c-sis product via its receptor, evoked by interaction with surrounding glioma cells, could be the mechanism behind the pathological proliferation of endothelial cells characteristically found in this type of malignancy.

Neurotrophic activity of platelet-derived growth factor (PDGF): Rat neuronal cells possess functional PDGF beta-type receptors and respond to PDGF

The different isoforms of PDGF bind with different affinities to two different receptor types. Previously, these receptors have been demonstrated mainly on mesenchymal and glial cells. We show here that PDGF beta-type receptors are present also on rat brain neurons in vivo as well as in vitro. Immunohistochemical analysis of a sequentially sectioned brain of a newborn rat revealed the presence of PDGF beta receptors in neurons throughout the central nervous system. These beta-receptor-bearing cells were shown to contain neurofilaments by double immunofluorescence staining. Furthermore, the PDGF-BB isoform bound to cells in a neuron-enriched culture from newborn rat brains and induced c-Fos protein in these cells. Continuous PDGF-BB treatment of primary rat brain cell cultures resulted in outgrowth of neurites and prolonged survival. These results indicate a neurotrophic effect of PDGF-BB.

The effect of platelet-derived growth factor on morphology and motility of human glial cells

Platelet-derived growth factor (PDGF) is a mitogen for several cell types in culture. It is documented in this work that one of the earliest effects of PDGF on serum-starved glial cells is an induction of intensive motile activity. Within the first minute after the addition of PDGF thin membrane lamellae grow out around almost all of the cell circumference. Later, circular arrangements of small ruffles appear on the dorsal surface of the cells. These rings of ruffles vary in size and some encircle almost the whole cell. The organization of the peripheral weave of microfilaments in the PDGF-induced advancing lamellae was closely similar to that of normally growing cells. In the regions of the circular arrangements of ruffles there was an extensive reorganization of the surface actin with unusual arrangements of microfilament bundles and polygonal networks. There was also a general intensification of the translocation of membrane ruffles and spikes from the cell periphery towards the centre of the cell, increased micropinocytotic activity and shuttling of intracellular particles.

Platelet-derived growth factor in human glioma

Platelet-derived growth factor (PDGF) is a 30 kDa protein consisting of disulfide-bonded dimers of A- and B-chains. PDGF receptors are of two types, alpha- and beta-receptors, which are members of the protein-tyrosine kinase family of receptors. The receptors are activated by ligand-induced dimerization, whereby the receptors become phosphorylated on tyrosine residues. These form attachment sites for signalling molecules, which inter alia activate the Ras.Raf pathway. PDGF has important functions in development and is required for a proper timing of oligodendrocyte differentiation. The v-sis oncogene of simian sarcoma virus (SSV) is a retroviral homolog of the B-chain gene, and induces transformation by an autocrine activation of PDGF receptors at the cell surface. SSV induces malignant glioma in experimental animals, suggesting a role for autocrine PDGF in glioma development. PDGF and PDGF receptors are frequently coexpressed in human glioma cell lines. Specific and nonspecific PDGF antagonists block the growth of some glioma cell lines in vitro and in vivo, suggesting that autocrine PDGF is involved in transformation and tumorigenesis. In situ studies of human gliomas show overexpression of alpha-receptors in glioma cells of high-grade tumors. In a few cases, overexpression is caused by receptor amplification. Since high-grade glioma cells also express the PDGF A-chain, an autocrine activation of the alpha-receptor may drive the proliferation of glioma cells in vivo.

A glioma-derived analog to platelet-derived growth factor: demonstration of receptor competing activity and immunological crossreactivity

A human clonal glioma cell line, U-343 MGa Cl 2, cultured under serum-free conditions, was found to release a factor that competed with 125I-labeled platelet-derived growth factor (125I-PDGF) for binding to human foreskin fibroblasts. The concentration of competing activity in conditioned medium was equal to 20-30 ng of PDGF per ml. The PDGF receptor competing activity had an elution position on Sephadex G-200 close to that of tracer PDGF. The same fractions in the chromatogram also contained growth-promoting activity and material active in a PDGF radioimmunoassay. Incubation of partially purified, 125I-labeled glioma factor with fibroblasts, or rabbit anti-PDGF serum, led to the selective binding of a component with an estimated Mr of 31,000, as shown by NaDodSO4/gel electrophoresis under nonreducing conditions. After reduction this component migrated as a Mr 18,000 protein. Thus, the behavior in NaDodSO4/gel electrophoresis was similar to that of PDGF. Furthermore, incubation of partially purified glioma factor with immobilized PDGF antibodies markedly decreased the amount of PDGF receptor competing activity remaining in the supernatant. These results suggest that the factor produced by glioma cells has structural, immunological, and functional resemblance to PDGF. We previously reported that a human osteosarcoma cell line produces a PDGF-like molecule with growth-promoting activity. Taken together with the recent finding that PDGF is homologous to the transforming gene product of simian sarcoma virus, our present data give additional support for the idea that an autocrine activation of the PDGF receptor may be operational in the growth of human tumors of mesenchymal or glial origin.

Rat brain capillary endothelial cells express functional PDGF B-type receptors

Immunohistochemical staining revealed the presence of platelet-derived growth factor (PDGF) B-type receptors on capillaries of normal rat brain. Furthermore, capillary endothelial cells isolated from rat brain and grown in tissue culture bound [125I]PDGF-BB but not [125I]PDGF-AA, suggesting that they expressed B-type, but not A-type, PDGF receptors. PDGF-BB and PDGF-AB, but not PDGF-AA, also stimulated incorporation of [3H]thymidine into these cells. Thus, rat brain capillary endothelial cells have functional B-type receptors, and thereby differ from endothelial cells derived from large blood vessels, that do not express PDGF receptors. Our data suggest a possible role for PDGF-BB as an angiogenic factor.

Ultraviolet light induces expression of p53 and p21 in human skin: effect of sunscreen and constitutive p21 expression in skin appendages

It has been suggested that p53 plays an important role in skin carcinogenesis. The p21 molecule acts as a downstream effector of wild-type p53 by enacting cell cycle arrest. We studied p53 and p21 expression in sun-exposed skin. Healthy volunteers were exposed to ultraviolet irradiation (UVA + UVB) in normal, previously non-sun-exposed skin, and skin biopsies were taken. Immunohistochemically detectable p53 and p21 were quantified, and the pattern of distribution was recorded. p53 was induced in epidermal cells 4 h after irradiation and returned to nearly normal levels after 120 h. Suprabasal cells showed a peak at 4 h, whereas basal cells peaked later, at 48 h. In epidermis, the expression of p21 was induced with a pattern that mirrored that of p53. In addition, p21 was induced in mesenchymal cells of the upper dermis, where there was no p53, suggesting an alternative pathway for p21 induction. Topical sunscreen and pigmentation (skin type 5) nearly eliminated UV-induced expression of p53 and p21. In contrast to the complete absence of p53 in skin never exposed to UV radiation, p21 reactivity was found in sharply demarcated areas of anagen hair follicles and sebaceous glands, as well as in scattered epidermal cells. The prevalence and distribution suggest a physiologic role of p21 in stopping the cell cycle in terminally differentiating skin epithelium. Archival skin material from the vicinity of skin lesions with variable sun exposure were also stained for p53. There was an increased "disperse" reactive staining pattern in skin samples excised in the summer as compared with less sunny seasons. Intensely stained p53 foci were detected as "compact bands" in morphologically normal epidermis, predominantly in sun-exposed areas of the skin, suggesting the existence of clonal proliferation of p53 mutated keratinocytes. These data show that p53 and p21 play a role in the human skin response to UV exposure and that p21 is implicated in the homeostasis of differentiating skin appendages.

Induction of senescence in human malignant glioma cells by p16INK4A

p16INK4A is a G1-specific cell cycle inhibitor which maps to human chromosome 9p21, a region frequently mutated or deleted in cancer cell lines and primary tumors. In glioblastomas the frequency of homozygous deletions is 40-70% making it one of the most common mutations in this tumor type. We have analysed the significance of the loss of this gene in gliomas by introducing the cDNA for p16INK4A into the human glioma cell line U-1242 MG which has a deleted CDKN2 locus. We used the tetracycline repressible vector system and obtained two stably transfected clones that expressed p16INK4A upon induction. p16INK4A expression caused a G1 arrest and enlargement of the cells similar to that of senescent cells. When staining for Senescence-Associated beta-galactosidase activity, described to be specific for senescent cells, we could show that the enlarged cells specifically gave a positive staining reaction. This senescence phenotype was dependent on the continuous expression of p16INK4A since it was reversed upon reintroduction of tetracycline suppression. Thus, the induced expression of p16INK4A in these glioma cells reverted their immortal phenotype and caused an immediate cellular senescence.

Enhanced expression of transforming growth factor-beta and its type-I and type-II receptors in human glioblastoma

Immunohistochemical studies of transforming growth factor-beta (TGF-beta) and its receptors have been carried out on 16 glioma tissues and compared with 5 cases of gliosis. Significantly higher expressions of TGF-beta I, as well as type-I and type-II TGF-beta receptors (T beta R-I and T beta R-II, respectively), were observed in advanced-malignant-glioma tissues when compared with non-tumorous gliosis. Immunoreactivities of TGF-beta and T beta R-I were localized in the cytoplasm of spindle-shaped tumor cells surrounding proliferating vessels or around areas of necrosis. The advancing edge of the tumor clusters frequently stained positive. Similar expression patterns were found for TGF-beta 2 and TGF-beta 3, whereas only weak or no expression was found for endoglin. In low-grade astrocytomas and in gliosis cases, the expression was moderate for T beta R-I and weak for TGF-beta and T beta R-II. In 3 examined human malignant glioma cell lines, clear immunostainings were detected for TGF-beta and its receptors. Ligand-induced heteromeric complexes of the receptors were formed in these cell lines, but the amount of the receptors was less than that of mink lung epithelial cells, which are sensitive target cells for TGF-beta. TGF-beta I showed no growth-inhibitory activity on any of these glioma cell lines. These results suggest that malignant gliomas produce TGF-beta and receptors, but are refractory to TGF-beta, implying dysregulation in the signalling pathway in the tumor cells. It is possible that the released TGF-beta acts on neighboring cells and affects stromal growth, angiogenesis, metastasis or immune surveillance in human glioma.

Activated platelet-derived growth factor autocrine pathway drives the transformed phenotype of a human glioblastoma cell line

Human glioblastoma cells (A172) were found to concomitantly express PDGF-BB and PDGF beta-receptors. The receptors were constitutively autophosphorylated in the absence of exogenous ligand, suggesting the presence of an autocrine PDGF pathway. Neutralizing PDGF antibodies as well as suramin inhibited the autonomous PDGF receptor tyrosine kinase activity and resulted in up-regulation of receptor protein. The interruption of the autocrine loop by the PDGF antibodies reversed the transformed phenotype of the glioblastoma cell, as determined by (1) diminished DNA synthesis, (2) inhibition of tumor colony growth, and (3) reversion of the transformed morphology of the tumor cells. The PDGF antibodies showed no effect on the DNA synthesis of another glioblastoma cells line (U-343MGa 31L) or on Ki-ras-transformed fibroblasts. The present study demonstrates an endogenously activated PDGF pathway in a spontaneous human glioblastoma cell line. Furthermore, we provide evidence that the autocrine PDGF pathway drives the transformed phenotype of the tumor cells, a process that can be blocked by extracellular antagonists.

Molecular pathology in basal cell cancer with p53 as a genetic marker

Human basal cell cancer (BCC) has unique growth characteristics with virtual inability to metastasize. We investigated clonality and genetic progression using p53 mutations as marker. Sampling was done through microdissection of frozen immunohistochemically stained 16 microm slices of tumors. From 11 BCC tumors 78 samples were analysed. Direct DNA sequencing of exons 5-8 was performed, haplotypes were determined after cloning of p53 exons and loss of heterozygosity (LOH) ascertained by microsatellite analysis. All tumors had p53 mutations and in a majority both p53 alleles were affected, commonly through missense mutations. Microdissection of small parts (50-100 cells) of individual tumors showed BCC to be composed of a dominant cell clone and prone to genetic progression with appearance of subclones with a second and even third p53 mutation. Samples from normal immunohistochemically negative epidermis always showed wild type sequence, except for a case of previously unknown germline p53 mutation. Our analysis also included p53 immunoreactive patches i.e. morphologically normal epidermis with a compact pattern of p53 immunoreactivity. Mutations within those were never the same as in the adjacent BCC. This detailed study of only one gene thus uncovered a remarkable heterogeneity within a tumor category famous for its benign clinical behavior.

Epithelial-stromal interactions in basal cell cancer: the PDGF system

A proposed progenitor cell for basal cell carcinoma is a stem cell located in the bulge of the hair follicle. Previous investigations have shown that basal cell carcinoma has a specific stroma requirement for its growth. Likewise the development of a normal hair follicle requires the inductive force of a specialized structure with condensed mesenchyme that eventually forms the dermal hair papilla. Investigations in mouse embryos also strongly indicate that induction/growth of skin structures is dependent on platelet-derived growth factor (PDGF) alpha-receptor expression in the mesenchyme. We therefore investigated the expression of PDGF A and B chain and PDGF alpha and beta receptors in basal cell carcinoma and in normal skin by immunohistochemistry and in situ hybridization. alpha and beta receptors were found in the specific stroma components of basal cell carcinoma, dermal hair papilla, and sweat glands, but not in the epithelial structures. The A and B chains, on the other hand, were mainly found in basal cell carcinoma cells, in hair matrix, and in sweat gland epithelium. This "appositional" expression of PDGF/PDGF receptor closely resembles that found in epithelial/mesenchymal structures during normal development. The findings also suggest that PDGF receptor expression is one of the characteristics of the specific stroma that is necessary for basal cell carcinoma growth.

A human glioma cell line secretes three structurally and functionally different dimeric forms of platelet-derived growth factor

A human malignant glioma cell line, U-343 MGa Cl2:6, has previously been shown to secrete platelet-derived-growth-factor(PDGF)-like activity [Nistér, M., Heldin, C.-H., Wasteson, A. and Westermark, B. (1984) Proc. Natl Acad. Sci. USA 81, 926-930]. We report here that this activity consists of three different molecules separable by reversed-phase chromatography and immobilized-metal-ion affinity chromatography. HPLC reversed-phase chromatography resolved two peaks of activity, which were denoted glioma-derived growth factor-I (GDGF-I) and GDGF-II. GDGF-I was purified to greater than 90% purity; in SDS gel electrophoresis, it appeared as a 31-kDa component which by reduction was converted to 17 kDa. Immunoprecipitation of radiolabeled, reduced and alkylated GDGF-I with antisera made against peptides from the A and B chains of PDGF, gave a specific signal only with antiserum against the A chain. Furthermore, when reduced and alkylated GDGF-I was analyzed by reversed-phase HPLC, it eluted at the position of PDGF A chains. We conclude that GDGF-I is a homodimer of a polypeptide similar to the A chain of PGDF. GDGF-II was found to have higher mitogenic activity than GDGF-I. Analysis by immunoprecipitation with PDGF-chain-specific antisera revealed that GDGF-II contained a polypeptide similar to the B chain of PDGF. Immobilized-metal-ion affinity chromatography revealed that 95% of the mitogenic activity of GDGF-II consisted of a heterodimer of one A and one B chain, whereas 5% consisted of a B-chain homodimer. Thus, U-343 MGa Cl 2:6 cells secrete all three possible dimeric forms of PDGF.

Two distinct p53 immunohistochemical patterns in human squamous-cell skin cancer, precursors and normal epidermis

Specimens of squamous-cell neoplasms (81 invasive cancers, 36 in situ cancers, 70 dysplasias, 5 keratoacanthomas, 19 papillomas) and normal skin were immunostained with p53 antibody. Nuclear accumulation of p53 was visualized as following 2 distinct patterns: dispersed or compact. The former is interpreted as a reversible reaction to sunlight, whereas the latter, after microdissection and sequencing of DNA, has been shown to reflect clonal multiplication of keratinocytes with mutated p53. The dispersed pattern was diffusely distributed and usually only involved a small proportion of epidermal cells. The compact pattern was characterized as a contiguous area of homogeneously stained cells sharply demarcated from its surroundings. It involved patches of normal epidermis or large areas of dysplastic or malignant squamous epithelium. Immature cells were always stained, whereas immunoreactivity was variably present in differentiating keratinocytes. Dispersed patterns occurred in 94.7% of strongly UV-exposed skin (mainly face) and to a lesser extent in less exposed parts of the body. It showed no correlation to the age of the individual. About two-thirds of biopsies from individuals over age 50 displayed compact patterns in sun-exposed, otherwise normal, epidermis. About 65% of pre-malignant and malignant squamous-cell neoplasms had a compact pattern. The presence of p53 immunoreactivity as a compact pattern supports the idea that mutations of the p53 gene are early events in the sequence from dysplasia to invasive squamous-cell cancer of the skin. Also, even in the absence of cellular atypia, patches of epidermal cells can accumulate p53 in a way that is indistinguishable from that of cancer and pre-cancer.

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.

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.

Expression of transforming-growth-factor (TGF)-beta receptors and Smad proteins in glioblastoma cell lines with distinct responses to TGF-beta1

A panel of 6 human glioma cell lines was examined for TGF-beta1 responsiveness. U-178 MG and U-251 MG AgCl1 were significantly inhibited by TGF-beta1, while U-343 MGa 31L and U-343 MGa 35L were potently stimulated to proliferate. TGF-beta1 induced endogenous PAI-1 protein synthesis, Smad binding element/(CAGA)12-luciferase-reporter activity, as well as mRNA expression of Smad6 and Smad7 in all gliomas. Interestingly, TGF-beta1 differentially stimulated or inhibited the expression of TbetaR-I and TbetaR-II mRNA in the gliomas. Affinity cross-linking studies using 125I-TGF-beta1 revealed that the gliomas expressed TGF-beta-type-I(TbetaR-I) and -type-II(TbetaR-II) receptors, although binding to TbetaR-II in U-343 MGa 31L and U-251 MG AgCl1 was low to undetectable. Smad2 protein was abundantly present in U-178 MG, U-343 MG, and U-343 MGa 35L, while Smad3 was readily detectable in U-178 MG, U-343 MG, U-343 MGa 35L and U-251 MG AgCl1. In all gliomas, TGF-beta1 induced phosphorylation of Smad2. The level to which TGF-beta1 could activate the pathway leading to induction of the (CAGA)12-luciferase reporter seemed to correlate to the expression levels of TGF-beta receptors, Smad3 and Smad4 proteins. However, despite the plethora of data regarding TGF-beta1 signalling in the different glioma cell lines, the mechanism underlying the differential growth effects mediated by TGF-beta1 is still unclear. The results suggest that a complex balance between several components in the TGF-beta signalling pathway controls glioma responsiveness to TGF-beta1, and extend reports indicating that distinct signal transduction pathways are involved in growth inhibition and other cellular responses.

Expression of PDGF beta-receptors in human meningioma cells

Meningioma is a generally benign tumor derived from arachnoid tissue. We have investigated the presence of functionally active PDGF-receptors on human meningioma cells in culture. Tumor samples were obtained from 3 surgically removed benign meningiomas and normal arachnoid tissue from an autopsy case. Binding studies were performed by using 125I-labelled recombinant PDGF-AA and PDGF-BB. Only 125I-PDGF-BB showed specific binding to all tumor-cell cultures after incubation of cells for 2 hr at 4 degrees C. Effects of PDGF-AA and PDGF-BB on DNA synthesis were measured as 3H-thymidine incorporation during 48 hr of labelling cells maintained in Eagle's minimum essential medium 0.5% fetal calf serum. PDGF-BB but not PDGF-AA stimulated DNA synthesis in all 3 tumor-cell cultures. Total cellular RNA was analyzed by Northern blotting and hybridization with a 32P-labelled human PDGF beta-receptor probe, and PDGF beta-receptor mRNA was found in both tumor and arachnoid cell cultures. Furthermore, PDGF beta-receptor mRNA was shown to be present in 2 meningioma biopsies and immunohistochemical staining revealed that PDGF beta-receptors are present in meningioma and arachnoid tissues in vivo. It appears that a possible way of maintaining human meningioma cell growth in vivo is through activation of PDGF beta-receptors.

A human YAC transgene rescues craniofacial and neural tube development in PDGFRalpha knockout mice and uncovers a role for PDGFRalpha in prenatal lung growth

The platelet-derived growth factor alpha-receptor (PDGFRalpha) plays a vital role in the development of vertebrate embryos, since mice lacking PDGFRalpha die in mid-gestation. PDGFRalpha is expressed in several types of migratory progenitor cells in the embryo including cranial neural crest cells, lung smooth muscle progenitors and oligodendrocyte progenitors. To study PDGFRalpha gene regulation and function during development, we generated transgenic mice by pronuclear injection of a 380 kb yeast artificial chromosome (YAC) containing the human PDGFRalpha gene. The YAC transgene was expressed in neural crest cells, rescued the profound craniofacial abnormalities and spina bifida observed in PDGFRalpha knockout mice and prolonged survival until birth. The ultimate cause of death was respiratory failure due to a defect in lung growth, stemming from failure of the transgene to be expressed correctly in lung smooth muscle progenitors. However, the YAC transgene was expressed faithfully in oligodendrocyte progenitors, which was not previously observed with plasmid-based transgenes containing only upstream PDGFRalpha control sequences. Our data illustrate the complexity of PDGFRalpha genetic control, provide clues to the location of critical regulatory elements and reveal a requirement for PDGF signalling in prenatal lung growth, which is distinct from the known requirement in postnatal alveogenesis. In addition, we found that the YAC transgene did not prolong survival of Patch mutant mice, indicating that genetic defects outside the PDGFRalpha locus contribute to the early embryonic lethality of Patch mice.

Detection of TP53 gene mutation in human meningiomas: a study using immunohistochemistry, polymerase chain reaction/single-strand conformation polymorphism and DNA sequencing techniques on paraffin-embedded samples

Mutations in the TP53 tumor suppressor gene have been studied in different types of brain tumors. Little is known about this genetic event in human meningioma, a mostly benign tumor. To investigate the frequency of TP53 gene mutations in human tumors derived from meningeal tissues, paraffin-embedded tissues from 30 cases (including 2 malignant and 4 atypical meningiomas, as well as 2 hemangioblastomas and 3 hemangiopericytomas) were screened by immunohistochemistry. Polymerase chain reaction/single strand conformational polymorphism (PCR/SSCP) and direct DNA sequencing were thereafter performed in selected cases. Nuclear p53 staining was not seen in any of the 19 benign meningiomas tested, while atypical meningiomas, hemangioblastomas, and hemangiopericytomas displayed nuclear staining in a subpopulation of tumor cells in 4 out of 5, 2 out of 2, and 3 out of 3 cases, respectively. One malignant meningioma showed an intense nuclear staining and a band shift in SSCP. In this case, we identified a mutation in the TP53 gene at codon 161 changing GCC to ACC and resulting in an alteration of alanine to threonine in this position. Our results indicate that TP53 gene mutation may be considered as a marker for malignant transformation in meningioma. p53 immunoreactivity, even in the absence of detectable gene mutation, is also associated with atypia and does not appear in regular benign meningiomas.

Effects of inducible glial fibrillary acidic protein on glioma cell motility and proliferation

We have studied the effect of induced glial fibrillary acidic protein (GFAP) on motility, cell morphology, and proliferation of two originally GFAP-negative human glioma cell lines. Glioma cell lines U-1242 MG and U-251 MG sp subclone 3A were transfected with a vector system that allows for an inducible GFAP expression. This experimental system creates an "on/off" situation in which GFAP expression is suppressed by tetracycline. Inducible expression of GFAP in the absence of tetracycline was confirmed by immunofluorescence staining and Northern and Western blotting. The study showed that forced GFAP expression resulted in an inhibition of cell motility measured as the phagokinetic track area of individual cells seeded sparsely on a surface covered with gold particles. It also resulted in a change in cell morphology, with extended cell processes, and it was associated with a low fraction of cells in S-phase. We conclude that the down-regulation of GFAP expression that is often seen in gliomas in vivo may be an important parameter of tumor progression related mainly to the motile and thereby invasive properties of malignant glioma cells.