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M Groot

Publications and source records attributed to M Groot.

6 recordsLinked to original sources
PubMed2003

[Autocrine stimulation of receptor-tyrosine kinases (RTK) in human tumor cell lines in vitro: therapeutic implications].

AIMS: The VEGF/VEGFR system is known to play an important role in the development of new blood vessels during tumor formation. There is evidence that VEGFRs are not only present on endothelial cells but also on tumor cells. Since VEGF is able to induce proliferation and migration via VEGFR-2 we have studied the expression of VEGFRs and related receptor tyrosine kinases (RTKs) in different tumor cell lines and the effect of growth factor stimulation. METHODS: RTK expression was investigated in 5 different human tumor cell lines on protein and mRNA levels. Tumor cell lines were exposed to growth factors such as VEGF and the phosphorylation of downstream molecules involved in proliferation, migration and apoptosis were assessed. Under comparable conditions proliferation and migration essays were performed. Endogenous production of VEGF and PDGF by the tumor cells was measured by ELISA of cell culture supernatants. RESULTS: Most tested cell lines expressed all known VEGFR's, PDGFR-beta on protein and mRNA levels to a varying extent. 3 out of 5 cell lines could be stimulated after addition of VEGF reflected by an increased phosphorylation of MAPK, AKT/PKB and to a lesser extent of p38. This was underlined by an increased cell number and reduced number of apoptotic cells. After stimulation with PDGF-BB a stronger induction of MAPK and AKT/PKB phosphorylation than for VEGF could be seen. In contrast, no effect on tumor cell migration was detectable in all examined cell lines. The investigation of cell culture supernatants revealed that most cell lines do not produce VEGF or PDGF. CONCLUSIONS: Tumor cell lines express RTKs and the receptor is stimulable after addition of growth factors such as VEGF. Thus, secretion of groth factors in the tumor microenvironment is not only able to stimulate proliferation and survival of endothelial cells but also tumor cells themselve. One cell line displayed high levels of endogenous VEGF which could explain the lack of an increased cell number after addition of VEGF. It remains obscure why another cell line could not be stimulated although receptors were present at the cellular surface. Further investigations should prove that RTK's could be influenced by therapeutic drugs in order to suppress cell proliferation and migration and induce apoptosis in tumor cell lines.

Cell Line, Tumor↗
PubMed2001

Endocrine disrupting compounds: effect of octylphenol on reproduction over three generations.

With the growing concern that environmental chemicals might impair human and animal fertility, it is important to investigate the possible influence of these substances on sexual differentiation and genital development of mammals. Many of these substances are suspected to interfere with endocrine processes, and exposure during critical periods of prenatal development might affect reproductive performance over several generations. Alkylphenols and their metabolites are lipophilic substances exerting apparent estrogenic action in in vitro and in vivo testing systems. With the widespread industrial use of alkylphenols, these are disseminated in the environment with sewage sludge, and domestic animals and humans are likely to be exposed via the food chain. Using the pig as an in vivo model, we studied the effect of intrauterine exposure to tertiary octylphenol (OP) on essential reproductive parameters over 3 generations. Sows were treated daily from D 23 to 85 of pregnancy with either 0, 10 or 1000 micrograms OP/kg body weight. Treatment with OP extended pregnancy length and induced basal cell proliferation in the cervical epithelium of the parental generation. In F1 offspring of sows treated with the low dosage of OP, onset of puberty was accelerated. Furthermore, when F1 gilts and F1 boars originating from sows treated with high dosages of OP were bred, the litter size was reduced. The results of the present study are compared with previous reports on estrogenicity of OP, and the usefulness of in vivo animal or embryo models for the evaluation of possible consequences of human exposure to endocrine disrupting compounds is discussed. Furthermore, possible consequences of exposure to endocrine disrupting compounds for the embryo transfer industry are addressed.

Animals↗
PubMed2000

Nerve growth factor- and epidermal growth factor-regulated gene transcription in PC12 pheochromocytoma and INS-1 insulinoma cells.

PC12 and INS-1 cells both express the nerve growth factor (NGF) receptors trkA and p75NTR and the epidermal growth factor receptor (EGF). In PC12 cells, NGF treatment initiates a signaling cascade that ultimately leads to a change of the genetic program of the cell. We have investigated the role of NGF in regulating gene transcription in PC12 and INS-1 cells, in order to define if there are NGF-regulated genes per se. Furthermore, to distinguish between growth factor stimulation via receptor tyrosine kinases in general and NGF-specific changes in gene transcription, we analyzed the effects of EGF on gene transcription. First, we tested the biological activities of fusion proteins consisting of the DNA-binding domain of the yeast transcription factor GAL4 and the phosphorylation-dependent activation domains of the transcription factors Elk1, CREB, ATF2 and c-jun in NGF- or EGF-treated PC12 cells. We found a striking increase in the transcriptional activity of the GAL4-Elk1 fusion protein that is a major substrate for the extracellular signal-regulated protein kinase (ERK). This effect was observed in NGF- as well as in EGF-treated PC12 cells. In INS-1 cells, however, the activity of the GAL4-Elk1 fusion protein was induced by NGF, but not by EGF. The effects of NGF and EGF on gene transcription were subsequently studied with plasmids containing reporter genes under control of the Egr-1, c-jun, HES-1 or Bc12 regulatory sequences. NGF stimulated Egr-1 promoter activities in PC12 and INS-1 cells, although the effect was much more pronounced in PC12 cells than in INS-1 cells. EGF also stimulated Egr-1 promoter activity in both PC12 and INS-1 cells. Stimulation of c-jun promoter activity by NGF was observed only in PC12 cells. Deletion mutagenesis demonstrated the importance of the 12-O-tetradecanoylphorbol-13-acetate response elements within the c-jun promoter for basal and NGF-mediated transcriptional induction. Likewise, NGF activated HES1 and Bcl2 P1 promoter activities in PC12 cells but not in INS-1 cells and EGF did not show any effects on these promoters. We conclude that in PC12 and INS-1 cells, NGF signaling leads to an activation of the ERK subtype of mitogen-activated protein kinases in the nucleus and a subsequent activation of Egr-1 gene transcription. The NGF-induced transcription of the c-jun, HES1 and Bc12 genes is, in contrast, cell type-specific, indicating that NGF can trigger different gene expression programs dependent on the signaling pathways present in a particular cell type. EGF is clearly able to activate gene transcription, suggesting that the differences in the biological activities of EGF and NGF cannot be explained by the inability of EGF to stimulate gene transcription.

Activating Transcription Factor 2↗
PubMed1997

Simultaneous determination of eight lipid peroxidation degradation products in urine of rats treated with carbon tetrachloride using gas chromatography with electron-capture detection.

One of the major processes that occur as a result of radical-induced oxidative stress is lipid peroxidation (LPO). Degradation of lipid peroxides results in various products, including a variety of carbonyl compounds. In the present study eight different lipid degradation products, i.e., formaldehyde, acetaldehyde, acetone, propanal, butanal, pentanal, hexanal and malondialdehyde were identified and measured simultaneously and quantitatively in rat urine after derivatization with O-(2,3,4,5,6-pentafluorbenzyl)hydroxylamine hydrochloride, extraction with heptane and using gas chromatography-electron-capture detection (GC-ECD). The identity of the respective oximes in urine was confirmed by gas chromatography-negative ion chemical ionization mass spectrometry (GC-NCI-MS). Simultaneously measured standard curves were linear for all oxime-products and the detection limits were between 39.0 +/- 5.3 (n=9) and 500 +/- 23 (n=9) fmol per microl injected sample. Recoveries of all products from urine or water were 73.0 +/- 5.2% and higher. In urine of CCl4-treated rats an increase in all eight lipid degradation products in urine was found 24 h following exposure. ACON showed the most distinct increase, followed by PROPA, BUTA and MDA. It is concluded that the rapid, selective and sensitive analytical method based on GC-ECD presented here is well suited for routine measurement of eight different lipid degradation products. These products appear to be useful as non-invasive biomarkers for in vivo oxidative stress induced in rats by CCl4.

Acetone↗
PubMed1997

Cellular responses to interferon-gamma.

Interferons are cytokines that play a complex and central role in the resistance of mammalian hosts to pathogens. Type I interferon (IFN-alpha and IFN-beta) is secreted by virus-infected cells. Immune, type II, or gamma-interferon (IFN-gamma) is secreted by thymus-derived (T) cells under certain conditions of activation and by natural killer (NK) cells. Although originally defined as an agent with direct antiviral activity, the properties of IFN-gamma include regulation of several aspects of the immune response, stimulation of bactericidal activity of phagocytes, stimulation of antigen presentation through class I and class II major histocompatibility complex (MHC) molecules, orchestration of leukocyte-endothelium interactions, effects on cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes whose functional significance remains obscure. The implementation of such a variety of effects by a single cytokine is achieved by complex patterns of cell-specific gene regulation: Several IFN-gamma-regulated genes are themselves components of transcription factors. The IFN-gamma response is itself regulated by interaction with responses to other cytokines including IFN-alpha/beta, TNF-alpha, and IL-4. Over 200 genes are now known to be regulated by IFN-gamma and they are listed in a World Wide Web document that accompanies this review. However, much of the cellular response to IFN-gamma can be described in terms of a set of integrated molecular programs underlying well-defined physiological systems, for example the induction of efficient antigen processing for MHC-mediated antigen presentation, which play clearly defined roles in pathogen resistance. A promising approach to the complexity of the IFN-gamma response is to extend the analysis of the less understood IFN-gamma-regulated genes in terms of molecular programs functional in pathogen resistance.

Animals↗