Growth factors as transforming proteins

PDGFRA mRNA is overexpressed in oral cancer patients as compared to normal subjects with a significant trend of overexpression among tobacco users

BACKGROUND

Platelet-derived growth factors alpha (PDGFA) is a tyrosine kinase receptor activator which is known to be amplified in the malignancies, and their expression levels are correlated to tumor progression and reduced overall survival. The expression of PDGFRA is different among the tumors and normal tissues; furthermore, their expression level is site specific. Under a physiological condition, PDGFRA and its ligand are expressed in distinct cell populations and activated in a paracrine manner. Nevertheless, heterodimer characteristic of PDGFRA allows it to be trans-activated by non-specific ligands or via autocrine manner. The future of cancer therapy can be based on PDGFRA receptor blockade and therefore warrants further investigation to determine the differing expression of PDGFRA between controls and patients with oral squamous cell carcinoma (OSCC).

METHODS

We performed a case-control study of 111 patients with newly diagnosed tongue squamous cell carcinoma and 111 control subjects without a cancer diagnosis, matched for age and gender, to evaluate the association between PDGFRA expression levels in oral mucosa. We then performed smoking stratification in each cohort. Independent t test analysis was applied for case-control comparisons.

RESULTS

Mean value of PDGFRA mRNA level (-ΔCt) for normal cohort is -30.242, whereas mean value of PDGFRA mRNA level for patients with OSCC is -11.516. PDGFRA mRNA level (-ΔCt) was significantly higher in oral cancer cohort, P<.001. Smokers have a significantly higher PDGFRA mRNA expression in comparison with non-smokers (P=.002) among the non-cancer group. Likewise, this trend is observed in cancer cohort too, P=.044.

CONCLUSION

PDGFRA expression is significantly higher in oral cancer cohort with or without the establishment of tobacco risk factor.

Multifarious functions of PDGFs and PDGFRs in tumor growth and metastasis

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are frequently expressed in various tumors and their expression levels correlate with tumor growth, invasiveness, drug resistance, and poor clinical outcomes. Emerging experimental evidence demonstrates that PDGFs exhibit multiple functions in modulation of tumor growth, metastasis, and the tumor microenvironment by targeting malignant cells, vascular cells, and stromal cells. Understanding PDGF-PDGFR-mediated molecular signaling may provide new mechanistic rationales for optimizing current cancer therapies and the development of future novel therapeutic modalities.

Colony stimulating factor-1 (CSF-1) in pregnancy

Uterine growth factors appear to play a role in the regulation of pregnancy. One of these, colony stimulating factor-1 (CSF-1), synthesized by the uterine epithelium under the control of female sex steroids, has been shown to have important functions both before implantation and during the formation of the placenta. In the female reproductive tract the CSF-1 receptor, the product of the c-fms proto-oncogene, is expressed in decidual cells, trophoblasts and macrophages, indicating that these cells are the primary targets for CSF-1. This article reviews the biology of CSF-1 during gestation as well as the possible involvement of CSF-1 and its receptor in the aetiology of gynaecological tumours.

Tyrosine phosphorylation of p145met mediated by EGFR and Src is required for serum-independent survival of human bladder carcinoma cells

Here we address the molecular mechanism of serum-independent survival and growth of human bladder carcinoma cell line 5637. Serum starvation promoted tyrosine phosphorylation of a 145-kDa protein and activation of the tyrosine kinase Src and the receptor for epidermal growth factor (EGFR) over a slow time course (>8 hours). The phosphorylated 145-kDa protein was identified as the beta-subunit of c-Met/hepatocyte growth factor (HGF) receptor, p145(met), in which tyrosine residues 1003, 1234, and 1235 were phosphorylated. Inhibitors of Src (PP2, SU6656) or EGFR (AG99), but not p145(met) (K252a), effectively blocked tyrosine phosphorylation of p145(met) and promoted cell death accompanied by activation of caspase-like proteases. Conditioned medium from the serum-starved 5637 cells or purified EGF readily promoted the activation of Src and EGFR, and tyrosine phosphorylation of p145(met) in normally grown 5637 cells, suggesting that autocrine signaling of EGFR ligands is responsible for signal transduction events in serum-starved cells. Consistent with this idea, a monoclonal antibody against EGFR that would interfere with the ligand binding to EGFR blocked tyrosine phosphorylation events and promoted the caspase activation and cell death in serum-free conditions. Such apoptotic cell death was also induced by pretreatment of cells with a high concentration of HGF that downregulated endogenous p145(met). Nevertheless, Cu2+ ions, competitive inhibitors for HGF-binding to p145(met), did not show any effect on cellular functions in serum-free conditions. These results suggest that the serum-independent growth of 5637 cells involves the transmembrane signaling cascade via EGFR ligand(s) (but not HGF), EGFR, Src and p145(met).

Transiently truncated and differentially regulated expression of midkine during mouse embryogenesis

Midkine (MK) is a retinoic acid response cytokine, mostly expressed in embryonic tissues. Aberrant expression of MK was found in numerous cancers. In human, a truncated MK was expressed specifically in tumor/cancer tissues. Here we report the discovery of a novel truncated form of MK transiently expressed during normal mouse embryonic development. In addition, MK is concentrated at the interface between developing epithelium and mesenchyme as well as highly proliferating cells. Its expression, which is closely coordinated with angiogenesis and vasculogenesis, is spatiotemporally regulated with peaks in extensive organogenesis period and undifferentiated cells tailing off in maturing cells, implying its role in nascent blood vessel (endothelial) signaling of tissue differentiation and stem cell renewal/differentiation. Cloning and sequencing analysis revealed that the embryonic truncated MK, in which the conserved domain is in-frame deleted, presumably producing a novel secreted small peptide, is different from the truncated form in human cancer tissues, whose deletion results in a frame-shift mutation. Our data suggest that MK may play a role in epithelium-mesenchyme interactions, blood vessel signaling, and the decision of proliferation vs differentiation. Detection of the transiently expressed truncated MK reveals its novel function in development and sheds light on its role in carcinogenesis.

Analysis of epidermal growth factor receptor and activated epidermal growth factor receptor expression in pituitary adenomas and carcinomas

Epidermal growth factor receptor plays an important role in the pathogenesis of many malignancies. Various growth factors, including epidermal growth factor receptor, have been shown to influence pituitary tumor growth and differentiation. To analyze the role of epidermal growth factor receptor in pituitary tumor development, we examined normal pituitaries (n=8), pituitary adenomas (n=158), and pituitary carcinomas (n=7) for expression of epidermal growth factor receptor protein and messenger RNA using tissue microarrays and RT-PCR. We also examined (a) the expression of phospho-epidermal growth factor receptor, the activated form of epidermal growth factor receptor, in pituitary tumors and normal pituitaries by immunohistochemistry and (b) the effects on epidermal growth factor receptor expression of treating pituitary cells (HP75 cell line) with epidermal growth factor. Epidermal growth factor receptor and the phosphorylated variant expression were present in normal pituitary cells. Epidermal growth factor receptor messenger RNA was also detected in normal pituitaries, pituitary adenomas, and carcinomas by in situ hybridization and RT-PCR. Most pituitary adenomas showed expression of epidermal growth factor receptor and the phosphorylated variant. Nonfunctional adenomas showed higher levels of expression of epidermal growth factor receptor (76 vs 34%) and of phospho-epidermal growth factor receptor (26 vs 8%) as compared to functional adenomas. Five of seven pituitary carcinomas showed strong expression of both epidermal growth factor receptor and phospho-epidermal growth factor receptor. When a human pituitary cell line (HP75) was cultured in the presence of epidermal growth factor receptor, there was an increase in the levels of both epidermal growth factor receptor and phospho-epidermal growth factor receptor after 5 h of treatment, thus confirming that epidermal growth factor receptor signaling was active in pituitary tumors. These results indicate that activated epidermal growth factor receptor is expressed in pituitary adenomas and carcinomas. Higher levels in pituitary carcinomas suggest a role in pituitary tumor progression.

Medical biotechnology in India

The potential of biotechnology has just began to emerge in the 20th century. After the full knowledge of human genomes is available, biotechnology is going to play a major role in shaping the concept of future drug discovery, drug delivery, diagnostic methodology, clinical trials, and to a great extent the major lifestyle of the human society. This article is a comprehensive review of the major impact of biotechnology in diagnostics, antibiotics, r-proteins, vaccines, and antibodies production. It also highlights the future aspects of gene therapy in the management of healthcare. A comprehensive list of biotech products in healthcare management has been given. Also, the growth of biotechnology throughout the world at large and in the Indian industries in particular has been highlighted. Constraints, concerns and difficulties in biotechnology in India have been addressed mainly related to human resources, training institutions in India, funding in biotechnology, patent-related issues and regulatory hurdles. Like in information technology, India has great potential in bioinformatics as well. Some of the recent information on bioinformatics centers in India has been summarized. Indian biotechnology industries have the potential to use the modern discoveries in life sciences to reach an enviable position in the world of biotechnology.

Effects of glycosaminoglycans on proliferation of epithelial and fibroblast human malignant mesothelioma cells: a structure-function relationship

Proteoglycans interact with other effective macromolecules regulating a variety of cellular events via their glycosaminoglycan (GAG) chains. The effects of all known glycosaminoglycans (GAGs) produced by normal cells and tissues on the proliferation of two human malignant mesothelioma cell lines, one with fibroblast-like morphology and the other with epithelial differentiation - both able to produce hyaluronan (HA), galactosaminoglycans (GalAGs) and heparan sulphate (HS) containing proteoglycans - have been studied. Cell proliferation was assessed by measuring [3H]thymidine incorporation and cell number. GalAGs, i.e. chondroitin sulphates (CSs) and dermatan sulphate (DS), strongly stimulate the proliferation of fibroblast-like cells in a dose-dependent manner (170-250% at 100 microg/ml), independently of their sulphation pattern. In epithelial cells, however, only DS stimulates cell proliferation. The effects of CSs on proliferation of epithelial cells are not depended on their sulphation pattern. Thus, CSs either with -[GlcA-GalNAc-(-6-O-SO(3)-)]- or -[GlcA-GalNAc-(-4-O-SO(3)-]- as the commonest unit, had no significant effect. L-Iduronic acid (IdoA)-rich heparin and fast-moving HS (fm-HS), a HS fraction with a heparin-like structure, had significant antiproliferative effects on mesothelioma cells of both types (30-70% at 1.0 microg/ml and 85-90% at 100 microg/ml, respectively). GlcA-rich HS, however, had no significant effects. HA inhibits only the proliferation of fibroblast-like cells by 25% at 50 and 100 microg/ml. Keratan sulphate suppresses cell proliferation (10-30%) in both cell lines. In the view of these findings, a structure-function relationship of GAGs on cell proliferation of the two human malignant mesothelioma cell lines is discussed. Other factors, such as chain conformation and geometry, as well as interactions of growth factors with GAGs, possibly involved in the regulation of cell proliferation, are also discussed.

Prognostic assessment of PTK activity in T1-T2, N0-N1, M0 breast cancer: a multicentric retrospective study

Protein tyrosine kinases (PTKs) play a major role in the transduction of intracellular mitogenic signal. PTKs are also involved in the process of cellular transformation. A number of studies have reported increased PTK activities in cytosolic fractions from human breast carcinoma. However, the possible pronostic value of these activities is difficult to establish from these studies, mostly conducted on limited numbers of patients. In order to clear up the issue, we have investigated a large series of patients with a long follow-up, using a retrospective multicentric study (894 breast cancers T1-T2, N0-N1, M0; median follow-up: 67 months). PTKs were measured using a radioenzymatic assay as described in our previously report. We confirmed the already observed correlation between PTK activities and Scarff-Bloom grading (p < 10(-5)), negative estrogen receptor (ER), and progesterone receptor (PR) status. By contrast, we found in this study a correlation between PTK values and clinical nodal status (p = 0.00027) not showed in our precedent analysis. In Cox multivariate analysis, PTK activity does not emerge as a significant pronostic parameter. On the other hand, tumor PTK activity assay may prove of great interest in clinical research using newly developed tyrosine kinase inhibitors in order to assess their biological impact and eventually to predict the responsiveness to these new therapeutic agents.

Identification of a tyrosine kinase-phosphorylated protein in arachidonic acid- and prostaglandin A(2)-treated cells in vitro

The effects of 20 microg/ml exogenous arachidonic acid (AA) and prostaglandin A(2) (PGA(2)) were evaluated on total tyrosine kinase (TK) activity and tyrosine phosphorylation status in HeLa and MCF-7 cells. AA and PGA(2) increased TK activity in both HeLa and MCF-7 cells. Western blotting employing an anti-phosphotyrosine antibody showed only one protein of approximately 55 kDa (approximately 55 kDa) to be phosphorylated in the MCF-7 cells, while a variety of proteins were phosphorylated in the HeLa cells, including the approximately 55 kDa protein. Amino acid analyses as well as Matrix Assisted Laser Desorption Ionization were conducted on this protein from different cell lines and it was shown to be similar. Comparison to p53 did not show similarities. The identity of this protein needs to be further characterized to help elucidate the signal transduction pathways of AA and PGA(2).

Overexpression of CXC chemokines by an adrenocortical carcinoma: a novel clinical syndrome

A patient with adrenocortical carcinoma presented with fever, leukocytosis, and increased acute phase reactants. The tumor was infiltrated with neutrophils. Immunohistochemical staining of the tumor showed positive signal for epithelial neutrophil-activating protein-78, an angiogenic and chemotactic CXC chemokine. Conditioned medium from tumor-derived cells (RL-251) showed high concentration of IL-8, epithelial neutrophil-activating protein-78, Gro alpha, and Gro gamma, angiogenic CXC chemokines with a potential role in tumorigenesis. An adrenal cancer/severe combined immunodeficiency mouse chimera was developed. Mice grew tumors rapidly, and circulating levels of IL-8 and epithelial neutrophil-activating protein-78 were detected. In contrast, animals transplanted with NCI-H295 cells, a nonchemokine-secreting cell line, grew tumors more slowly and did not have detectable chemokine levels. Similar to the patient, mice with RL-251 tumors developed marked leukocytosis and neutrophilia, and their tumors were infiltrated with neutrophils. Mice were passively immunized with epithelial neutrophil-activating protein-78 antisera. A marked decrease in tumor growth was observed. Potential for chemokine production by other adrenocortical tumors was investigated by RT-PCR in archival material. Six of seven adrenal carcinomas and one of three adenomas had cDNA for IL-8; six of seven carcinomas and the three adenomas had cDNA for epithelial neutrophil-activating protein-78. We concluded that the clinical presentation of this case resulted from increased tumor production of chemotactic chemokines. Through their angiogenic and chemotactic properties these chemokines may play an important role in adrenal tumorigenesis.

Human glioma cells transformed by IGF-I triple helix technology show immune and apoptotic characteristics determining cell selection for gene therapy of glioblastoma

AIMS

Insulin-like growth factor type I (IGF-I) antisense cellular gene therapy of tumours is based on the following data: rat glioma or hepatoma cells transfected with the vector encoding IGF-I antisense cDNA lose their tumorigenicity and induce a tumour specific immune response involving CD8(+) T cells. Recently, using the IGF-I triple helix approach in studies of tumorigenicity, major histocompatibility complex class I (MHC-I) antigens were demonstrated in rat glioma transfected cells. This study used comparative IGF-I antisense and triple helix technologies in human primary glioma cells to determine the triple helix strategy that would be most appropriate for the treatment of glioblastoma.

METHODS

The cells were transfected using the IGF-I triple helix expression vector, pMT-AG, derived from the pMT-EP vector. pMT-AG contains a cassette comprising a 23 bp DNA fragment transcribing a third RNA strand, which forms a triple helix structure within a target region of the human IGF-I gene. Using pMT-EP, vectors encoding MHC-I or B7 antisense cDNA were also constructed.

RESULTS

IGF-I triple helix transfected glioma cells are characterised by immune and apoptotic phenomena that appear to be related. The expression of MHC-I and B7 in transfected cells (analysed by flow cytometry) was accompanied by programmed cell death (detected by dUTP fluorescein terminal transferase labelling of nicked DNA and electron microscopic techniques). Cotransfection of these cells with MHC-I and B7 antisense vectors suppressed the expression of MHC-I and B7, and was associated with a pronounced decrease in apoptosis.

CONCLUSION

When designing an IGF-I triple helix strategy for the treatment of human glioblastoma, the transfected tumour cells should have the following characteristics: the absence of IGF-I, the presence of both MHC-I and B7 molecules, and signs of apoptosis.

Identification of membrane calcium channels essential for cytoplasmic and nuclear calcium elevations induced by vascular endothelial growth factor in human endothelial cells

Vascular endothelial growth factor (VEGF) is mitogenic for endothelial cells and has been shown to induce angiogenesis and endothelial cell migration through stimulation of endothelial tyrosine-kinase receptors. Here, using confocal microscopy and the patch-clamp technique on endothelial cells, membrane permeability to calcium as well as cytoplasmic and nuclear free calcium levels have been investigated in the first stages of tyrosine-kinase receptor activation by VEGF. VEGF (0.5nM) as well as inositol trisphosphate (IP3) induced an activation of membrane calcium-permeable channels exhibiting a similar low conductance in the range of 10 pS. The VEGF-triggered activation of these calcium channels, mediated by IP3 and involving the intracellular calcium stores, results in an increase in both cytoplasmic and nuclear calcium levels in endothelial cells, potentially modulating gene expression. Finally, the effect of Ni2+, a calcium channel blocker, on endothelial cell proliferation has been studied. The results show that inhibition of extracellular calcium influx significantly inhibits VEGF-induced cell proliferation. In the process of cell stimulation by VEGF, and possibly by other growth factors, activation of calcium channels could then be a key step in calcium-regulated gene expression and cell activation. These results suggest that the use of calcium channel blockers could be a novel way of prevention or reversion of VEGF-induced tumoral angiogenesis.

The effects of exogenous growth factors on matrix metalloproteinase secretion by human brain tumour cells

Matrix metalloproteinases (MMPs) are a growing family of zinc-dependent endopeptidases that are capable of degrading various components of the extracellular matrix. These enzymes have been implicated in a variety of physiological and pathological conditions including embryogenesis and tumour invasion. The synthesis of many MMPs is thought to be regulated by growth factors, cytokines and hormones. In this study, we investigated the effects of five exogenous growth factors known to be expressed by gliomas [epidermal growth factor (EGF), basic growth factor (bFGF), transforming growth factor beta (TGF-beta1,2) and vascular endothelial growth factor (VEGF)].on MMP-2 and MMP-9 expression in an ependymoma, two grade III astrocytomas, a grade III oligoastrocytoma and a benign meningioma. Zymogram analysis revealed that the effects of the growth factors depended upon the cell lines used in the study. Growth factors generally up-regulated MMP-2 and MMP-9 expression in the gliomas but were least effective in the meningioma; the effect being most prominent with TGF-beta1 and TGF-beta2 in all the cell lines. It is hypothesized that paracrine growth factor interplay may be crucial in the regulation of MMP expression by glioma invasion of the normal brain.

Overexpression of midkine in lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine in rats and its increase with progression

The expression of midkine (MK) in lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats was examined. The animals were administered 2000 p.p.m. of BHP in their drinking water for 12 weeks, then maintained without further treatment until being killed 20-28 weeks after the beginning of the experiment. MK mRNA expression of adenocarcinomas and squamous cell carcinomas assessed by means of the reverse transcriptase-polymerase chain reaction and northern blot analysis was significantly higher than in rat embryonic tissues (positive controls) and contrasted strongly with the lack in normal lungs. MK protein was detected immunohistochemically in 58.3% of alveolar hyperplasias, 92.3% of adenomas and 100% of adenocarcinomas and squamous cell carcinomas. The extent of staining significantly increased along with malignant progression in adenomatous (pre-)neoplastic lesions and tended to become more pronounced with malignant progression in squamous lesions. The results suggest that MK may play some essential roles in the development and progression of lung tumors induced by BHP in rats.

Decrease in protein tyrosine phosphorylation is associated with F-actin reorganization by retinoic acid in human endometrial adenocarcinoma (RL95-2) cells

Transformed cells often express elevated levels of tyrosine-phosphorylated proteins. Inhibition of protein tyrosine kinases causes reversion of malignant cells to the normal phenotype. In the present study, we evaluated the possibility that the reversion of human endometrial adenocarcinoma RL95-2 cells to a stationary phenotype induced by retinoic acid was associated with inhibition of tyrosine phosphorylation of cellular proteins. We found that retinoic acid decreased the levels of tyrosine-phosphorylated proteins, as assessed by immunostaining and immunoprecipitations using specific anti-phosphotyrosine antibodies. In addition, the inhibitors of tyrosine kinases herbimycin A and tyrphostin mimicked retinoic acid, inducing F-actin reorganization and increasing the size of RL95-2 cells, as determined by measurement of cell perimeters. Because focal adhesions that connect actin filaments with the plasma membrane are major sites of tyrosine phosphorylation, we further investigated whether selected focal adhesion proteins were affected by retinoic acid. We found that retinoic acid altered the localization of focal adhesion kinase. All-trans retinoic acid was effective in reducing the levels of focal adhesion kinase and paxillin protein. Thirteen-cis retinoic acid increased the levels of vinculin protein in the cytosolic fraction of cells. These changes are consistent with actin reorganization and reversion toward a stationary phenotype induced by retinoic acid in endometrial adenocarcinoma RL95-2 cells. Our results indicate that the differentiating effects of retinoids on endometrial cells are associated with decreases in tyrosine phosphorylation and changes in the levels and distribution of focal adhesion proteins. These findings suggest that signaling pathways that involve tyrosine kinases are potential targets for drug design against endometrial cancer.

Excessive activation of tyrosine kinases leads to inhibition of proliferation in a thyroid carcinoma cell line

Autocrine stimulation of growth is a hallmark of many tumor cell lines. In this work we investigated the synthesis and secretion of growth factors and the expression of their corresponding receptors in HTC-TSHr thyroid carcinoma cells. These cells synthesize epidermal growth factor (EGF) receptors and platelet-derived growth factor beta (PDGF beta) receptors and in addition transforming growth factor alpha (TGF alpha), PDGF-A and PDGF-B chains, respectively. Addition of EGF or PDGF-BB to the culture medium resulted in growth inhibition of HTC-TSHr cells. In contrast, treatment of the cells with low concentrations of neutralizing anti-TGF alpha antibodies or tyrosine kinase inhibitors led to stimulation of cell proliferation. Low concentrations of neutralizing anti-PDGF-B antibodies did not affect growth of the cells. As expected, cell proliferation was inhibited when high concentrations of either neutralizing anti-TGF alpha antibodies or anti-PDGF-B antibodies were applied. PDGF-AA did not influence growth of HTC-TSHr cells. We conclude that growth of HTC-TSHr thyroid carcinoma cells is influenced by two autocrine loops between TGF alpha and EGF receptors and between PDGF-B and PDGF beta receptors. However, our data suggest that excessive activation of tyrosine kinase receptors in these cells results in a relative inhibition rather than stimulation of growth.

Growth factors in gliomas: antisense and dominant negative mutant strategies

Antisense and dominant negative mutant strategies were developed as 'magic bullets' to suppress the function of a particular gene while preserving the remaining cellular activities. While experience with these techniques has dispelled some of the 'magic', these strategies remain useful for understanding the function of particular gene products. Antisense strategies involve the administration of either a synthetic oligodeoxynucleotide or a plasmid construct which produces a sequence that is complementary to the DNA or mRNA of the gene of interest. Antisense binding should inhibit transcription or translation of the gene, and thus decrease synthesis of the protein for which the gene encodes. Conversely, dominant negative mutations inhibit activity of a gene product by encoding for a second protein which suppresses the function of the gene of interest. For example, a single mutant subunit in a multimeric protein might allow normal assembly of the protein while inhibiting its activity. The use of these techniques for investigating the role of various growth factor pathways in glial neoplasia and their potential therapeutic applications are reviewed below.

Midkine expression in human breast cancers: expression of truncated form

The expression of midkine (MK), a growth/differentiation factor, was assessed in 34 surgically resected specimens of primary breast cancer or mastopathy. Using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, all of the non-cancerous and cancerous tissues were found to express MK except for one breast cancer specimen. Northern blot analysis revealed that MK mRNA was also expressed in the normal breast tissues examined. Immunohistochemical analysis of the MK protein was performed on a limited number of the specimens, showing that some cancerous tissues were immunoreactive with anti-MK antibodies. Furthermore, using RT-PCR analysis, expression of not only the wild-type but also a truncated form of MK, which was recently found in various human tumor cell lines, was detected in 6 of 26 cancerous tissues but not in non-cancerous tissues.

Interleukin 2 exerts autocrine stimulation on murine T-cell leukaemia growth

As it has been suggested that an autocrine mechanism may control tumour cell growth, in this work cells from a spontaneous murine T lymphocyte leukaemia (LB) expressing the interleukin-2 receptor (IL-2R) (CD25) were evaluated in vitro for IL-2-mediated autocrine growth. Cells grew readily in culture and proliferation was enhanced by the addition of recombinant IL-2 but inhibited by monoclonal antibodies against either IL-2 or IL-2 receptor, in the absence of exogenous IL-2. Cyclosporin A also inhibited LB cell growth. However, when exogenous IL-2 was added together with cyclosporin A, cell proliferation proved similar to controls. Using reverse transcription polymerase chain reaction (PCR), mRNA for IL-2 was found to be present in tumour cells. Our findings support the hypothesis that LB tumour cell proliferation is mediated by an autocrine pathway involving endogenous IL-2 generation, despite the fact that these cells are not dependent on exogenous IL-2 to grow in culture.

Expression of truncated midkine in human colorectal cancers

Midkine (MK) is a growth differentiation factor originally found as the product of a retinoic acid-responsive gene. The expression of MK was examined in 35 surgically resected specimens of primary colorectal cancer using the reverse transcription-polymerase chain reaction (RT-PCR). All of the cancerous tissues expressed MK. In 5/25 cancerous tissues a truncated form of MK, which was recently found in various human tumor cell lines, was detected in addition to the full-size MK. In contrast, the truncated from of MK could not be detected in non-cancerous tissues, whereas the wild-type form was detected in 8/10 non-cancerous tissues. These results suggest that the expression of the truncated form of MK may be associated with tumorigenesis.

Rational design for the development of epidermal growth factor receptor antagonists

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) bind with similar high affinity to the human EGF receptor. Using a domain-exchange strategy we have shown that the C-terminal linear region of these molecules is involved in high affinity receptor binding. By further single amino acid substitution in this linear C-terminal region, a putative interaction site of these ligands with their receptor has been identified. This identification of a receptor binding domain in EGF/TGF alpha provides an important initial step in the development of EGF receptor antagonists with significant clinical potential.

Increased midkine gene expression in human gastrointestinal cancers

Midkine (MK) is a product of a retinoic acid-responsive gene, and is a novel growth differentiation factor. We examined the expression of the MK gene in specimens of 47 surgically removed human carcinomas of the gastrointestinal organs, namely, gastric, colorectal, hepatocellular, pancreatic, esophageal, ampullary duodenal and bile duct carcinomas. In most cases, the MK mRNA level was higher in cancer specimens than in the corresponding non-cancerous tissues. Furthermore, MK mRNA was more highly expressed in the colon adenocarcinoma lesion than in the adenoma lesions, in the two familial polyposis cases. While MK mRNA was not detected in the normal liver, it became detectable in cirrhotic tissues in 2 of 4 cases, and its expression was increased in the cancerous tissues. Thus, the increase of MK mRNA level is a phenomenon seen in many human gastrointestinal carcinomas. The increased expression of the MK gene in gastric carcinoma was significantly more prominent in well and moderately differentiated adenocarcinomas than in poorly differentiated adenocarcinomas and signet ring cell carcinomas.

Expression of growth factors and growth factor receptors in normal and tumorous human thyroid tissues

A number of growth factors have been implicated as stimuli of thyroid cell proliferation; overexpression of these growth factors and/or their receptors may play a role in the growth of thyroid tumors. To determine if immunohistochemical detection of growth factors and/or their receptors correlates with morphological alterations in proliferative lesions of thyroid, we examined the localization of epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha) and their common receptor, EGF-receptor (EGF-R), insulin-like growth factor-1 (IGF-1), IGF-1-receptor (IGF-R) and IGF binding proteins (IGFBP)-1, -2, -3, and -4, nerve growth factor (NGF), and its receptor NGF-receptor (NGF-R), transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (bFGF), in normal thyroid tissue and various thyroid tumors. We applied the streptavidin-biotin technique to formalin-fixed, paraffin-embedded tissues. We studied 8-16 different cases of each of the following: normal human thyroid, multinodular hyperplasia, follicular adenoma, papillary carcinoma, follicular carcinoma, medullary carcinoma, and anaplastic carcinoma. EGF, TGF-alpha, and their receptor EGF-R were widely expressed in normal thyroid and in all the thyroid lesions examined. IGF-1 and IGFBP-1 were diffusely present in all different thyroid tissues as well. There was no difference in staining intensity or distribution that correlated with the pathological process. IGFBP-4 seemed to have a variable expression. IGFBP-2 and -3 were detected only in medullary carcinomas.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of the substance immunologically cross-reactive with insulin in insulin RIA is an artifact caused by insulin tracer degradation: involvement of the insulin-degrading enzyme

In previous literature, the existence of a new insulin-like substance found in tumor tissues, termed substance immunologically cross-reactive with insulin (SICRI), has been proposed. In these studies, insulin-specific radioimmunoassay (RIA) was the only detection method for SICRI. The mouse melanoma B16BL6 cell line was found to be a rich source of SICRI. In this paper, we show that SICRI is not expressed in B16BL6 cells. Previous RIA measurements were wrongly ascribed to SICRI. What was really measured was a positive artifact caused by insulin tracer degradation in RIA. Several lines of evidence indicate that protease responsible for insulin degradation in B16BL6 cells in insulin-degrading enzyme (IDE; EC 3.4.22.11). First, SICRI activity of B16BL6 cytosol measured by insulin RIA was inhibited by thiol protease inhibitor N-ethylmaleimide (NEM). Thiol active agents as well as metal chelators, both potent IDE blockers, inhibited also the insulin-degrading activity of the same sample. Second, cross-linking to 125I-labeled insulin of partially purified sample with highest insulin RIA activity specifically labeled only a single protein with molecular mass similar to IDE (110 kDa). Labeling was blocked by 'cold' insulin in excess. Third, kinetic studies of insulin degradation by RIA active chromatographic fractions revealed an apparent Kd of 90 nM which is very similar to the reported affinity of insulin for IDE (Kd = 100 nM). Additionally, in B16BL6 as well as in mouse myeloid leukemia cells, IDE gene is actively transcribed and this expression was found to be much stronger than in normal mouse tissues. In conclusion, our results strongly question the real existence of SICRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroblastomas in Denmark 1943-80. Epidemiological and clinical studies

Two-hundred-and-fifty patients were registered in a population-based study of neuroblastomas in Denmark in the period 1943-80. The major epidemiological findings were an increased incidence with an unchanged mortality rate during the study period. The increase in incidence related solely to children 0-4 years of age and was most pronounced in infants under 1 year of age. Several reasons for the observed epidemiological rates include (i) changes in the composition of the population, (ii) improved diagnostic procedures, (iii) a shift in the diagnostic criteria, and (iv) an increase in environmental carcinogens of importance in the induction of neuroblastoma. Associated with an increased risk were lower socio-economic levels and young or advanced parental age, suggesting the importance of environmental as well as genetic factors for the induction of neuroblastoma. The epidemiological findings of an increased incidence with an unchanged mortality rate, which suggests the inclusion of borderline lesions in recent years, are of major importance in interpreting the results of mass screening for the disease. The clinical findings in 253 patients treated in Denmark from 1943 to 1980 (including 5 patients resident outside Denmark and excluding 2 patients without available hospital records) were analysed. The major finding was a zero-time shift, that is, earlier diagnosis of the disease during the study period, with increasing survival rates from decade to decade mostly due to a better age and stage distribution, a zero-time shift which was also apparent in the changes of the symptomatology. Independent prognostic variables were age, stage, and treatment with chemotherapy for children over 1 year of age with stage II disease, and for infants with stages III-IV disease. Analysis of data from a subset of the 253 children suggested that high proliferative activity detected by flow cytometry may be an important prognostic variable. The study also suggests that the pattern of metastatic spread might have changed as a consequence of prolonged survival obtained by improved treatment modalities, stressing the importance of a high frequency of autopsy among cancer patients. Hypotheses generated by the study included (i) that most neuroblastomas might be congenital, (ii) that the age influence on prognosis might be explained in terms of growth rate, cell cycle transit time, and duration of the disease, and (iii) that some neuroblastomas might be borderline lesions.

Regulation of insulin-like growth factor 1 binding protein 3 levels by epidermal growth factor and retinoic acid in cervical epithelial cells

Insulin-like growth factors (IGFs) are important regulators of epithelial cell growth. The mitogenic activity of these factors is influenced by the levels of extracellular IGF binding proteins, including insulin-like growth factor binding protein 3 (IGFBP-3). In the present report we study the effects of epidermal growth factor (EGF) and all-trans-retinoic acid (RA) on IGFBP-3 RNA and protein levels in human papillomavirus-immortalized cervical epithelial cells. Treatment of ECE16-1 cells with 3-20 ng/ml EGF causes a marked reduction in IGFBP-3 levels. In contrast, 1 microM RA increases IGFBP-3 mRNA and protein levels in the presence or absence of 20 ng/ml EGF. The response is concentration dependent with a half-maximal increase observed at 1 nM RA. RA is able to reverse the EGF suppression when added simultaneously or 3 days after initiation of EGF treatment. Conversely, when cells are treated with RA, IGFBP-3 levels increase within 24 h and subsequent addition of EGF is without effect. Thus, the RA-dependent increase in IGFBP-3 levels is dominant over the EGF suppression. The increased IGFBP-3 levels are correlated with RA suppression of proliferation. Similar RA effects on IGFBP-3 mRNA levels were observed in other cervical epithelial cell lines (i.e., ECE16-D1, ECE16-D2, and CaSki). These results suggest that RA may act to inhibit cervical cell growth by increasing IGFBP-3 levels and reducing the extracellular concentration of free insulin-like growth factor I (IGFI) and/or alternatively, IGFBP-3 may inhibit cell growth by direct effects on the cell, independent of IGFI.

Gene therapy of murine teratocarcinoma: separate functions for insulin-like growth factors I and II in immunogenicity and differentiation

Teratocarcinoma is a germ-line carcinoma giving rise to an embryoid tumor with structures derived from the three embryonic layers: mesoderm, endoderm, and ectoderm. Teratocarcinoma is widely used as an in vitro model system to study regulation of cell determination and differentiation during mammalian embryogenesis. Murine embryonic carcinoma (EC) PCC3 cells express insulin-like growth factor I(IGF-I) and its receptor, while all derivative tumor structures express IGF-I and IGF-II and their receptors. Therefore the system lends itself to dissect the role of these two growth factors during EC differentiation. With an episomal antisense strategy, we define a role for IGF-I in tumorigenicity and evasion of immune surveillance. Antisense IGF-I EC transfectants are shown to elicit a curative anti-tumor immune response with tumor regression at distal sites. In contrast, IGF-II is shown to drive determination and differentiation in EC cells. Since IGF-I and IGF-II bind to type I receptor and antisense sequence used for IGF-II cannot form duplex with endogenous IGF-I transcripts, it follows that this receptor is not involved in determination and differentiation.

Carcinogenesis and initiation of cell cycling by charge-induced membrane clusters may be due to mitogen receptors and Na+/H+ antiports

The membrane cluster hypothesis of mitogenesis and carcinogenesis is extended by proposing that much of the Na+ ingress across a cell's plasma membrane at surface charge-induced (SCI) aggregates is due to mitogen-induced activation of Na+/H+ antiports. Intrinsic proteins (including mitogen receptors and antiports) are electrostatically attracted to and become part of the aggregate. In this location, close proximity facilitates antiport activation. Resulting Na+ ingress may cause sustained partial depolarization, cytoplasmic alkalinization, and initiation of cell cycling. Chronic phosphorylation-dephosphorylation at SCI aggregates too weak to induce cycling, may slowly form polyionic bonds between adjacent proteins at the inner lipid layer. These bonds convert the SCI aggregates to 'permanent' clusters that pass to a daughter cell with parental plasma membrane at mitosis, and are associated with malignancy. EGF and PDGF growth factors are used to develop the hypothesis, which is also applied to steroid and dioxin receptors and to oncogene products.

Expression of SV40 tumour antigens enables human endothelial cells to grow independently from foetal calf serum and exogenous growth factors

Human endothelial cells were transfected with a plasmid containing the coding sequence of the large T protein of simian virus 40. Transfected cells were selected for their ability to grow in defined medium (DM). Several cell lines were derived and characterized in their response to endothelial cell growth supplement (ECGS), epidermal growth factor (EGF) and insulin (INS). In addition to cell lines that were dependent on these additives, others growing without any exogenous growth factor could be selected. No evidence of autocrine growth stimulation was found. For growth studies, a simple assay was used based on the acid phosphatase activity as a parameter for the cell number. Cell lines in defined medium showed less chromosome aberrations than those grown in serum-containing medium. Because of their long in vitro life span of about 100 generation doublings and defined medium requirements these cells represent valuable test material for all kinds of investigations on the vascular endothelium.

Stimulation of PAI-1 expression in endothelial cells by cultured vascular smooth muscle cells

Regulation of endothelial cell (EC) plasminogen activator inhibitor type-1 (PAI-1), the primary physiological inhibitor of tissue-type plasminogen activator (TPA) and urokinase-type plasminogen activator (UPA), by various stimuli has been well characterized. We report the upregulation of secreted and intracellular PAI-1 in human umbilical ECs when cocultured with human smooth muscle cells (SMCs) on amniotic membranes or incubated with SMC conditioned medium (CM) under serum-free conditions as determined by enzyme-linked immunosorbent assay. Cocultured human umbilical vein ECs and SMCs, or human umbilical artery ECs and SMCs, displayed a 73% and 68% increase, respectively, in released PAI-1. SMC-derived stimulatory factor release showed tissue specificity, since only human aortic, umbilical vein, and umbilical artery SMCs upregulated PAI-1 synthesis, whereas SMCs from human mammary artery, pulmonary artery, and saphenous vein did not. Stimulation of EC PAI-1 by SMC CM was both time and concentration dependent, with as much as five- and fourfold increases in supernatants and lysates, respectively. PAI-1 synthesis and activity in ECs from other vascular beds were also upregulated by SMC CM. Northern blot analysis paralleled the protein results, showing as much as a 2.7-fold increase in specific EC PAI-1 mRNA expression after incubation with SMC CM for 8 hours. PAI-1 stimulatory activity in SMC CM was completely abolished by boiling or incubation with protamine sulfate and was reduced by transient acidification or heparin-Sepharose pretreatment by 33% or 48%, respectively. The stimulatory factor(s) appeared to have a molecular mass of 23 kD as determined by gel filtration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of gravity on the cellular response to epidermal growth factor

EGF and related polypeptides are involved in the regulation of cell growth and differentiation of continuously regenerating tissues, in tissue repair processes and in placental and fetal development. Their initial mode of action generally constitutes binding to specific plasma membrane localized receptors, transduction of the signal across the plasma membrane, subsequent activation of signalling pathways in the cell, and the induction of early nuclear gene expression. EGF-induced signal transmission from the plasma membrane to the nucleus has been studied in microgravity in order to gain insight in the molecular mechanisms that constitute the effects of gravity on cell growth. Exposure of human A431 cells to microgravity strongly suppresses EGF- and PMA-induced c-fos and c-jun expression. In contrast, forskolin- and A23187-induced c-fos expression and constitutive beta-2 microglobulin expression remain unaffected. This suggests that microgravity differentially modulates EGF-induced signal transduction pathways. Since both EGF and PMA are known to be activators of PKC, which is not the case for forskolin and A23187, PKC-mediated signal transduction may be a cellular target for microgravity. Inhibition of EGF-induced c-fos expression by microgravity occurs downstream of the initiation of EGF-induced signal transduction, i.e., EGF binding and EGFR redistribution. In addition to PKC signaling, actin microfilament organization appears to be sensitive to microgravity. Therefore, the inhibition of signal transduction by microgravity may be related to alterations in actin microfilament organization. The fact that early gene expression is affected by agents that alter the organization of the actin microfilament system supports this hypothesis. The decrease in c-fos and c-jun expression in microgravity may result in the decreased formation of the FOS and JUN proteins. Consequently, a short-term reduction in gene expression in microgravity may have a more dramatic effect over the long term, since both the JUN and FOS protein families are required for normal cell cycle progression. However, since more than 20 years of manned spaceflight have shown that humans can survive in microgravity for prolonged periods, it appears that cells in the human body can partly or completely overcome gravitational stress. Although some insight in the molecular basis on human cells has been obtained, future studies will be needed for a better understanding of the grounds for alterations in the cellular biochemistry due to altered gravity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Gene expression of insulin-like growth factor II in human intracranial meningioma

BACKGROUND

Insulin-like growth factor II (IGF-II) is synthesized in the normal brain of adult humans predominantly in the choroid plexus and meninges and is secreted in the cerebrospinal fluid. The authors measured IGF-II transcripts and peptides in biopsy specimens from human intracranial tumors including astrocytomas, glioblastomas, and meningiomas.

METHODS

The presence of IGF-II mRNA was analyzed in 12 human brain tumors by Northern analysis of total RNA extracted from tumor biopsies and by in situ hybridization of tissue sections. The amount of immunoreactive IGF-II was determined by radioimmunoassay of tumor extracts.

RESULTS

Northern analysis of RNA from four meningiomas showed IGF-II mRNA of 6.0, 4.8, and 2.2 kb, and in situ hybridization revealed that meningioma tumor cells contained IGF-II mRNA. In contrast, biopsy specimens from four astrocytomas, one oligoastrocytoma, and four glioblastomas showed no IGF-II mRNA. Radioimmunoassay of IGF-II in tumor extracts showed that all tumors contained IGF-II (40-160 ng/g tissue). Two meningiomas contained the highest amounts of IGF-II (144 and 160 ng/g tissue).

CONCLUSIONS

IGF-II mRNA is present in higher amounts in benign meningiomas than in malignant glioblastomas and astrocytomas, whereas the content of immunoreactive IGF-II is similar. On the basis of these findings, the authors believe that IGF-II may be involved in growth regulation of meningiomas.

The rat liver epithelial (RLE) cell nuclear protein database

The master two-dimensional computer database of rat liver epithelial (RLE) cellular proteins (Wirth et al., Electrophoresis 1991, 12, 931-954) has been expanded to include detailed information concerning 1100 nucleoplasmic (cytosolic) and 850 particulate associated [35S]methionine labeled as well as 215 nucleoplasmic and 269 particulate associated [32P]orthophosphate labeled RLE nuclear polypeptides, respectively. The RLE nuclear protein database developed using the Elsie 5 gel analysis system contains both qualitative and quantitative annotations including polypeptide identification number, protein name (if known), molecular weight and pI information, quantitation and polypeptide spot shape, subcellular location, as well as specific information regarding transformation (chemical and spontaneous) and growth-related characteristics. Microsequencing of polypeptides directly from two-dimensional (2-D) blotted membranes has recently been established in our laboratory and provides a highly efficient and rapid means of polypeptide identification in the absence of specific antibodies. At present the RLE protein database is still in the developmental stage and is continually being updated as additional information is obtained. Nonetheless, it is anticipated that knowledge obtained concerning the identification and characterization of specific transformation and/or growth regulatory proteins in the RLE in vitro cell system will not only have direct application to other rodent and human 2-D protein databases currently under development but will also complement them.

Lactogenic hormones and extracellular matrix regulate expression of IGF-1 linked to MMTV-LTR in mammary epithelial cells

The cell line MD-IGF-1, containing an ovine IGF-1 cDNA driven by the mouse mammary tumor virus-long terminal repeat (MMTV-LTR) promoter, was used to study expression of IGF-1 linked to the MMTV-LTR in bovine mammary epithelial cells in response to various hormonal and substratum stimuli. Acute sensitivity of the MMTV-LTR promoter to glucocorticoids and sex steroids was ascertained by transient transfection of parental MAC-T cells with an MMTV-CAT construct. Specifically, CAT activity was induced by glucocorticoids, but not by 17 beta-estradiol or progesterone. Induction of MD-IGF-1 cells with dexamethasone (DEX) alone triggered a 29.5-fold increase in secretion of recombinant IGF-1 (348.9 vs 11.8 pg/micrograms DNA), and stimulated a 1.7-fold increase in total DNA within 72 h. Growth of MD-IGF-1 cells was enhanced by exogenous IGF-1, insulin, and TGF-alpha. In contrast, TGF-beta inhibited cell proliferation, while epidermal growth factor, estrogen, progesterone, and testosterone had no effect. Extracellular matrix from the Engelbreth-Holm-Swarm (EHS) tumor, in the presence of DEX, prolactin (PRL), and insulin stimulated a 29.4-fold increase in secretion of IGF-1 (591.9 pg/microgram DNA), compared with cells in absence of hormones (20.1 pg/micrograms DNA). EHS and DEX plus PRL triggered a 63.2-fold increase in IGF-1 secretion (689.1 pg/micrograms DNA), compared with MD-IGF-1 cells cultured on plastic (10.9 pg/micrograms DNA), in the absence of hormones. These data indicate that the MMTV-LTR is regulated by both lactogenic hormones and extracellular matrix in MD-IGF-1 cells and that the MMTV-LTR may be a useful regulatory element for targeting expression of foreign proteins in bovine mammary epithelial cells.

Autocrine growth regulation in neuroectodermal tumors as detected with oligodeoxynucleotide antisense molecules

The cell lines of three neuroectodermal tumors, two glioblastomas (HTZ-146, HTZ-17) and one melanoma (HTZ-19) were established and screened for the expression of growth factors by northern blotting and immunochemical methods. All three tumors were positive for platelet-derived growth factor- (PDGF-) A-, -B-chain, and basic fibroblast growth factor (bFGF) messenger ribonucleic acids. Cultured cells as well as original tumor material were also positive for PDGF-AA-, PDGF-BB, and bFGF protein, as shown by immunochemistry. To investigate the possible pathophysiological role of PDGF and bFGF, antisense technology was employed with chemically modified nuclease-stable 14-mer phosphorothioate oligodeoxynucleotides. Proliferation of all three tumors was reduced to a different extent with antisense phosphorothioate oligodeoxynucleotides in vitro, targeted against PDGF-A-chain-, -B-chain-, and -bFGF-messenger ribonucleic acid. These data indicate autocrine stimulatory loops for PDGF and bFGF, which may be blocked, may have different relevance in neuroectodermal tumors in vitro, and may have conceivable future therapeutic implications.

The importance of blood cell-vessel wall interactions in tumour metastasis

Tumour cell dissemination is a complex process, depending on the ability of malignant cells to escape from the primary tumour and penetrate and flow through the bloodstream. Circulating tumour cells can adhere to the vessel wall, dissolve the basal lamina and extravasate, giving origin to metastases. Interactions between tumour cells, blood platelets and leukocytes favour tumour cell adhesion to the vessel wall, migration in extravascular spaces and growth in secondary sites. The biochemical and molecular mechanisms regulating tumour cell adhesion to the vessel wall and intercellular contacts have been studied extensively in recent years. Moreover, it has been shown that either tumour cells or blood cells release growth factors and inflammatory proteins, such as cytokines and chemokines, that may be involved in tumour cell migration and proliferation. Finally, tumour cells and cells of the surrounding tissue possess procoagulant and fibrinolytic properties that may be important in modulating the extracellular matrix around the tumour, to allow tumour cell invasion and progression. We have described the cell types (i.e. blood platelets, leukocytes, endothelial cells), the matrix components (i.e. fibronectin, thrombospondin and laminin) and the growth factors/cytokines (i.e. platelet-derived growth factor, transforming growth factor beta, tumour necrosis factor) involved in these processes. In particular, we have described cell-cell and cell-matrix interactions, cell migration and release of growth factors, cytokines, chemotactic peptides and proteolytic enzymes. This survey has also considered a few innovative approaches for the prevention and cure of cancer and metastasis that are based on these new concepts.

Mitogenic action of insulin-like growth factor-I on human osteosarcoma MG-63 cells and rat osteoblasts maintained in situ: the role of glucose-6-phosphate dehydrogenase

The mechanisms involved in the mitogenic actions of insulin-like growth factor-I (IGF-I) on skeletal cells are at present unclear. We have investigated the role of glucose-6-phosphate dehydrogenase (G6PD) in this mechanism and provide strong evidence that stimulation of G6PD activity is required for the growth promoting activities of IGF-I. IGF-I (10 ng/ml) significantly elevated G6PD activity in MG-63 human osteosarcoma cells within 30 min which preceded the IGF-I induced DNA synthesis in these cells. Inhibition of G6PD activity by epiandrosterone decreased DNA synthesis in IGF-I stimulated MG-63 cells but this was partly overcome by the addition of a combination of the four deoxyribonucleosides. IGF-I did not cause a general increase in cell metabolism as succinate dehydrogenase and iso-citrate dehydrogenase activity were not altered. Although IGF-I caused a significant increase in lactate dehydrogenase activity this was not inhibited by epiandrosterone. The culture of metatarsals of 4-week-old rats with IGF-I (10 ng/ml) also stimulated G6PD activity in osteoblasts lining the metaphyseal trabeculae.

Coexpression of neurotrophins and their receptors in neurons of the central nervous system

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are neuronal survival molecules which utilize the Trk family of tyrosine kinase receptors. Using double-label in situ hybridization, we demonstrate that mRNAs for BDNF and its high-affinity receptor TrkB are coexpressed in hippocampal and cortical neurons. Also, a large number of neurons in these areas coexpress NGF and BDNF mRNAs. Epileptic seizures lead to increased levels of both BDNF/TrkB and NGF/BDNF mRNAs in double-labeled cells. Our results show that individual neurons of the central nervous system can coexpress neurotrophins and their receptors and produce two neurotrophic factors. These factors could support neuronal survival after brain insults, not only via retrograde transport but also through autocrine mechanisms.

Production of autostimulatory growth factors by the human carcinoma line, RPMI 2650

The human carcinoma line RPMI 2650 produces autocrine factors; they are detected by the ability of RPMI 2650 conditioned medium (CM) to stimulate growth in soft agar of RPMI 2650 cells plated at low density. The autocrine activity in crude CM can be fractionated by ultrafiltration into a lower molecular weight (MW) fraction (R1-30), which concentrates molecules in the 1000-30,000 Da range; and a higher MW fraction (R30) with molecules greater than 30,000 Da in a more concentrated form. R1-30 is labile to acid, base, and heat treatment, whereas R30 is stable to (and sometimes activated by) these treatments. Boiling of R30, however, renders it labile to acid, base, and trypsin treatments. CM can be separated into a weakly heparin-binding fraction (with stability properties similar, but not identical, to R1-30), and a non-heparin binding fraction (with stability properties similar to R30). RPMI 2650 cells secrete transforming growth factor (TGF)alpha- and TGF beta-like molecules, but the R1-30 fraction can be distinguished from these TGFs, and from most other known growth factors, by its unusual combination of acid lability and weak affinity for heparin. Since the R30/non-heparin binding fraction is rendered labile by boiling or acid treatment, it may represent a bound or conformationally stable form of a growth factor.

Treatment and prevention of rat glioblastoma by immunogenic C6 cells expressing antisense insulin-like growth factor I RNA

Rat C6 glioma cells express insulin-like growth factor I (IGF-I) and form rapidly growing tumors in syngeneic animals. When transfected with an episome-based vector encoding antisense IGF-I complementary DNA, these cells lost tumorigenicity. Subcutaneous injection of IGF-I antisense-transfected C6 cells into rats prevented formation of both subcutaneous tumors and brain tumors induced by nontransfected C6 cells. The antisense-transfected cells also caused regression of established brain glioblastomas when injected at a point distal to the tumor. These antitumor effects result from a glioma-specific immune response involving CD8+ lymphocytes. Antisense blocking of IGF-I expression may reverse a phenotype that allows C6 glioma cells to evade the immune system.