Biomedical subjects

W Kruijer

Publications and source records attributed to W Kruijer.

At least 37 records · Page 2Linked to original sources

PubMed1997

Insulin activates Stat3 independently of p21ras-ERK and PI-3K signal transduction.

The binding of insulin to its receptor initiates multiple signal transduction pathways regulating such diverse processes as proliferation, differentiation, glucose transport, and glycogen metabolism. The STAT-family of transcription factors has been demonstrated to play a critical role in gene induction by a variety of hemopoietic cytokines and hormones. Furthermore, constitutive activation of STATs is observed in transformed cells. Here we describe activation of a transcriptional complex binding to a consensus STAT-transcriptional element in response to insulin challenge. This complex is induced rapidly after tyrosine autophosphorylation of the insulin receptor, and is sustained for several hours. Supershift analysis of the insulin-induced complex reveals that it specifically contains the transcription factor Stat3. DAN binding of this complex is inhibited by pre-incubation with tyrosine, but not serine/threonine protein kinase inhibitors, whereas transcriptional activation is inhibited by both. Utilising a dominant negative mutant of p21ras we demonstrate that both insulin-induced Stat3 DNA-binding and also transactivation do not require p21ras. Furthermore, although previous studies have suggested a role for MAP kinases (ERKs) and PI-3K in STAT activation, utilising the specific MEK inhibitor PD098059 and the PI-3K inhibitor wortmannin, we demonstrate that activation of ERKs or PI-3K are not required for insulin induced Stat3 phosphorylation or transactivation.

3T3 Cells↗

PubMed1997

Anomalies of the CD8+ T cell pool in haemochromatosis: HLA-A3-linked expansions of CD8+CD28- T cells.

The present study consists of a phenotypic and functional characterization of peripheral blood T lymphocytes in a group of 21 patients with hereditary haemochromatosis (HH), an MHC class I-linked genetic disease resulting in iron overload, and a group of 30 healthy individuals, both HLA-phenotyped. The HH patients studied showed an increased percentage of CD8+ CD28- T cells with a corresponding reduction in the percentage of CD8+ CD28+ T cells in peripheral blood relative to healthy blood donors. No anomalies of CD28 expression were found in the CD4+ subset. The presence of the HLA-A3 antigen but not age accounted for these imbalances. Thus, an apparent failure of the CD8+ CD28+ T cell population 'to expand', coinciding with an 'expansion' of CD8+ CD28- T cells in peripheral blood of HLA-A3+ but not HLA-A3- HH patients was observed when compared with the respective HLA-A3-matched control group. A significantly higher percentage of HLA-DR+ but not CD45RO+ cells was also found within the peripheral CD8+ T cell subset in HH patients relative to controls. Phytohaemagglutinin (PHA) stimulation of peripheral blood mononuclear cells (PBMC) for 5 days showed: (i) that CD8+ CD28+ T cells both in controls and HH were able to expand in vitro; (ii) that CD8+ CD28- T cells decreased markedly after activation in controls but not in HH patients. Moreover, functional studies showed that CD8+ cytotoxic T lymphocytes (CTL) from HH patients exhibited a diminished cytotoxic activity (approx. two-fold) in standard 51Cr-release assays when compared with CD8+ CTL from healthy controls. The present results provide additional evidence for the existence of phenotypic and functional anomalies of the peripheral CD8+ T cell pool that may underlie the clinical heterogeneity of this iron overload disease. They are of particular relevance given the recent discovery of a novel mutated MHC class I-like gene in HH.

Adult↗

PubMed1996

Regulation of the zebrafish goosecoid promoter by mesoderm inducing factors and Xwnt1.

Goosecoid is a homeobox gene that is expressed as an immediate early response to mesoderm induction by activin. We have investigated the induction of the zebrafish goosecoid promoter by the mesoderm inducing factors activin and basic fibroblast growth factor (bFGF) in dissociated zebrafish blastula cells, as well as by different wnts in intact embryos. Activin induces promoter activity, while bFGF shows a cooperative effect with activin. We have identified two enhancer elements that are functional in the induction of the goosecoid promoter. A distal element confers activin responsiveness to a heterologous promoter in the absence of de novo protein synthesis, whereas a proximal element responds only to a combination of activin and bFGF. Deletion experiments show that both elements are important for full induction by activin. Nuclear proteins that bind to these elements are expressed in blastula embryos, and competition experiments show that an octamer site in the activin responsive distal element is specifically bound, suggesting a role for an octamer binding factor in the regulation of goosecoid expression by activin. Experiments in intact embryos reveal that the proximal element contains sequences that respond to Xwnt1, but not to Xwnt5c. Furthermore, we show that the distal element is active in a confined dorsal domain in embryos and responds to overexpression of activin in vivo, as well as to dorsalization by lithium. The distal element is to our knowledge the first enhancer element identified that mediates the induction of a mesodermal gene by activin.

Activins↗

PubMed1995

UV activation of receptor tyrosine kinase activity.

The exposure of mammalian cells to ultraviolet radiation (UV) may lead to DNA damage resulting in mutation and thus possibly cancer, while irradiation can further act as a potent tumor promoter. In addition UV induces p21ras-mediated signalling leading to activation of transcription factors such as AP-1 and NF-kappa B, as well as activation of the Src tyrosine kinase. This 'UV-response' has been well studied in mammalian cells and furthermore is conserved in yeast, however the most upstream components of this signal transduction pathway have remained elusive. Here we show that UV rapidly activates both the EGF receptor and insulin receptor, as shown by tyrosine phosphorylation of these receptors. We demonstrate that this activation is due to autophosphorylation as it only occurs in cells containing receptors with a functional kinase domain. We have further analysed the propagation of the UV-induced signal to downstream events such as, IRS-1 and Shc tyrosine phosphorylation, phosphatidylinositol 3-kinase activation, leukotriene synthesis, MAP kinase activation and gene induction all of which are activated by UV irradiation. Importantly, we demonstrate that in cells expressing a 'kinase-dead' receptor mutant the UV-response is inhibited, blocking leukotriene synthesis, MAP kinase activation and transcriptional induction. Furthermore, prior-stimulation of cells with UV appears to reduce further responsiveness to addition of growth factor suggesting a common signaling pathway. These data demonstrate a critical role for receptor-mediated events in regulating the response mammalian cells to UV exposure.

3T3 Cells↗

PubMed1995

EGF receptor deletions define a region specifically mediating STAT transcription factor activation.

Binding of EGF to its cognate receptor results in receptor-dimerisation, auto-phosphorylation and activation of intracellular signal transduction pathways. Autophosphorylated tyrosine residues in the receptor complex bind to SH2-domain containing signalling molecules and these are then often themselves phosphorylated by the receptor kinase. A critical role for these SH2-binding sites, however, is unclear. We have investigated the stimulation of (SH2-domain containing) STAT transcription factor activity, in comparison with MAP kinase activity, in cell lines expressing EGF receptor deletion mutations. Data indicate that two autophosphorylated tyrosine residues Y1068 and Y1086 are critical for STAT activation in contrast to MAP kinase activation. Significantly, these tyrosine residues conform to a consensus YXXQ binding site and suggest direct binding of STAT-proteins to the EGF receptor.

Amino Acid Sequence↗

PubMed1995

Transcriptional regulation of the junB promoter: analysis of STAT-mediated signal transduction.

The product of the junB gene is a member of the AP-1 family of transcription factors that activate transcription by binding to TPA-responsive elements (TREs) within the promoters of target genes. Components of AP-1 are immediate-early genes whose expression is upregulated by a plethora of extracellular stimuli and are important in mediating cellular proliferation and differentiation. Such stimuli include the pleiotropic cytokine interleukin-6 (IL-6) which plays a role in immune and inflammatory responses and ciliary neurotrophic factor (CNTF) which enhances survival and differentiation of neurons and glia. We have analysed expression from junB promoter-CAT reporter constructs in HepG2 cells and found that a region between -196 and -91 can mediate response to IL-6 and CNTF and was able to confer responsiveness to a heterologous promoter. We further show by gel retardation analysis that distinct nuclear factors induced by IL-6 specifically bind to this interleukin-6 response element (IRE). This region contains both a putative ETS- and a STAT-transcription factor binding site. We show by mutational analysis and supershift data that the IL-6 induced complex indeed contains the transcription factor APRF/Stat3 that is both necessary and sufficient for activation. Interestingly this site does not appear to bind Stat1 itself, as shown by supershift analysis and a lack of response to IFN-gamma both at the DNA-binding and transcriptional level. Furthermore, we demonstrate that the junB IRE-binding activity induced by IL-6 requires tyrosine kinase activity, whereas induced transactivation of IRE-constructs additionally occurs through an H7-sensitive pathway that is p21ras-independent, implicating serine/threonine kinases in the transactivation of IRE-binding factors.

Animals↗

PubMed1995

Interleukin-6-induced serine phosphorylation of transcription factor APRF: evidence for a role in interleukin-6 target gene induction.

The cytokine interleukin-6 (IL-6) rapidly activates a latent cytoplasmic transcription factor, acute-phase response factor (APRF), by tyrosine phosphorylation. Activation and DNA binding of APRF are inhibited by inhibitors of protein tyrosine kinases but not serine/threonine kinases. However, immediate-early gene induction by IL-6 and, as we show here, stimulation of the promoters of the genes for alpha 2-macroglobulin, Jun-B, and intercellular adhesion molecule-1 (ICAM-1) are blocked by the serine/threonine kinase inhibitor H7. We now show that IL-6 triggers a delayed phosphorylation of APRF at serine resudues which can be reversed in vitro by protein phosphatase 2A and is also inhibited by H7. Therefore, APRF serine phosphorylation is likely to represent a crucial event in IL-6 signal transduction leading to target gene induction.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1995

Regulation of Oct-4 gene expression during differentiation of EC cells.

The stem cell-specific factor Oct-4 is expressed in undifferentiated embryonal carcinoma and embryonic stem cells and is quickly down regulated upon RA-induced differentiation. Irrespective of the direction of differentiation, Oct-4 repression in P19 EC cells requires treatment with high doses of either all-trans or 9-cis RA. Unlike in P19 cells, no RA-induced down regulation of Oct-4 expression is observed in the P19-derived RA-resistant RAC65 cells. However, in these cells Oct-4 promoter repression can be rescued in a RA-dependent manner by cotransfection of RAR alpha 2 or RAR beta 2 but not RARr gamma 1, matching previously reported transactivation properties of these receptor types. In the vicinity of the transcription initiation site of the Oct-4 gene, three Hormone Response Element HRE half sites are present which are arranged as direct repeats with different spacing. In vitro translated RAR and RXR proteins bind to this HRE as heterodimers with low affinity, in such a way that all three HRE half sites contribute to complex formation. Although P19 EC cells contain weak binding activity interacting with the Oct-4 promoter HRE, strong binding activity is observed in nuclear extracts from RA-treated P19 cells. This binding activity was shown to correspond to COUP-TFs but not nuclear RA receptors. Moreover, the presence of these binding factors in nuclear extracts corresponds to silencing of Oct-4 expression. These results implicate RA and the action of its nuclear receptors in silencing Oct-4 expression upon differentiation of EC cells. The observed silencing is most likely not exerted by direct binding of RARs to the Oct-4 proximal promoter HRE. Our results support models in which different nuclear receptor complexes sequentially occupy different sites in the Oct-4 promoter HRE to silence Oct-4 expression during RA-induced differentiation.

Cell Differentiation↗

PubMed1995

Localization of transcripts of the related nuclear orphan receptors COUP-TF I and ARP-1 in the adult mouse brain.

The chicken ovalbumin upstream promoter transcription factor, COUP-TF I, and the protein ARP-1 (COUP-TF II) are two highly homologous orphan receptors of the nuclear hormone receptor family. In this study we investigated their expression patterns in the adult nervous system of the mouse. In situ hybridizations were performed on brain sections with 35S-labeled cRNA probes derived from the 3'-non-coding regions of the mARP-1 and mCOUP-TF I mRNAs. Both COUP-TF I and ARP-1 were shown to be expressed in the adult brain and they displayed restricted and distinct expression patterns. COUP-TF I transcripts were predominantly found in the rostral and caudal parts of the adult mouse brain, whereas ARP-1 transcripts prevaled in the middle part of the brain. High expression of COUP-TF I was detected in the olfactory nucleus, in neocortex layers I/II and V/VL, in the dentate gyrus and in areas CA1/CA3/CA4 of the hippocampus, and in the granular layer of the cerebellum. Only low amounts of COUP-TF I mRNA were detected in the ventral, the laterodorsal and in the interanteromedial thalamic nuclei. Small amounts of COUP-TF I transcripts were also found in the epithelial layer of the ventricle and in arachnoid membranes. High expression of ARP-I was detected in the reticular, the ventral lateral and the gelatinosus thalamic nuclei. Other hot spots of ARP-1 mRNA expression were the amygdaloid nucleus and the arachnoid membranes. Lower amounts of ARP-1 transcripts were found in the anterior and lateral hypothalamic areas, in the suprachiasmatic nucleus, and in the choroid plexus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Stimulation of receptor protein-tyrosine phosphatase alpha activity and phosphorylation by phorbol ester.

Receptor Protein-Tyrosine Phosphatase alpha (RPTP alpha) is a transmembrane protein with two cytoplasmic catalytic protein-tyrosine phosphatase (PTP) domains and a relatively short (123 amino acids) extracellular domain. Here we report that treatment of transfected cells that express RPTP alpha with the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate, a direct activator of protein kinase C, induced a rapid, transient increase in RPTP alpha activity due to a 2- to 3-fold increase in substrate affinity. A transient increase in RPTP alpha serine phosphorylation was concomitant with the enhanced activity. Tryptic phosphopeptide mapping of RPTP alpha demonstrated that phosphorylation of three tryptic peptides was enhanced in response to phorbol ester. In vitro dephosphorylation of RPTP alpha from phorbol ester-treated cells reduced RPTP alpha activity to prestimulation levels, indicating that enhanced serine phosphorylation directly accounted for the increase in activity. Our results demonstrate that serine phosphorylation may play a key role in the regulation of the activity of transmembrane PTPs.

Cell Line↗

PubMed1994

Stimulation of the human intercellular adhesion molecule-1 promoter by interleukin-6 and interferon-gamma involves binding of distinct factors to a palindromic response element.

Intercellular adhesion molecule-1 (ICAM-1) is a transmembrane glycoprotein that promotes adhesion in immunological and inflammatory reactions. ICAM-1 is expressed on cells of many lineages and is induced by interleukin-6 (IL-6) and interferon-gamma (IFN-gamma). Functional analysis of ICAM-1 promoter-luciferase constructs in HepG2 cells enabled us to identify a region between -110 and -37 mediating IL-6 and IFN-gamma responsiveness and containing a palindromic IL-6/IFN-gamma response element (pIRE). Site-directed mutagenesis of key nucleotides in the ICAM-1 pIRE abolished the effect of both IL-6 and IFN-gamma stimulation, while this pIRE element was sufficient to confer IL-6 and IFN-gamma responsiveness to a heterologous promoter. We further show by gel retardation analysis that distinct nuclear factors induced by both IL-6 or IFN-gamma specifically bind to this pIRE. Furthermore, treatment with IL-6 results in the formation of multiple complexes while IFN-gamma induces a single binding complex, both in HepG2 and monocytic U937 cells. Differentiation of U937 cells by exposure to 12-O-tetradecanoyl phorbol-13-acetate abolishes response to IL-6 but not IFN-gamma. Supershift data utilizing the ICAM-1 pIRE revealed that IFN-gamma and IL-6 both induce a factor antigenically related to IFN-gamma activation factor. We further provide data suggesting that IL-6 additionally activates an ICAM-1 pIRE binding factor related to the previously described acute-phase response factor in disparate cell types. We therefore conclude that the activation of these related nuclear factors by IL-6 and IFN-gamma is important in the regulation of ICAM-1 gene expression.

Base Sequence↗

PubMed1994

Isolation and developmental expression of retinoic-acid-induced genes.

The vitamin A derivative retinoic acid (RA) is involved in vertebrate anteroposterior axis formation and cellular differentiation and has been shown to modulate the expression of a number of genes implicated in the control of early embryonal development. Under defined culture conditions, all-trans-RA induces differentiation of P19 embryonal carcinoma cells into neural derivatives. In this report, we describe the isolation and partial characterization of 14 RA-regulated genes from P19 cells committed to differentiate along the neural pathway. In addition to the previously recognized genes encoding vimentin, heat stable antigen, neural cadherin, Hox-B2, F52/MacMARCKS, thymosin beta 4b, and the murine homolog of COUP-TF1, we identified 7 novel genes, 5 of which are predominantly expressed in developing neural tissues as shown by in situ hybridization. The results confirm the usefulness of the P19 system in the isolation and study of the regulation of developmentally expressed genes.

Amino Acid Sequence↗

PubMed1994

Effects of retinoic acid on the expression of retinoic acid receptors during zebrafish embryogenesis.

The cDNAs encoding the zebrafish homologs of retinoic acid receptor alpha(zRAR alpha) and gamma (zRAR gamma) were isolated and their expression studied in normal and retinoic acid (RA) treated embryos. Expression boundaries in the central nervous system are clearly different from those observed in the mouse, which can only partly be explained by morphogenetic differences. Treatment of embryos with RA induces ectopic zRAR gamma expression in anterior brain structures and both zRAR alpha and zRAR gamma expression in the eyes. Furthermore, striking differences occur in the zRAR gamma expression pattern in pharyngeal arch mesenchyme. Since the development of all of these structures has been shown to be affected by exogenous RA, our data suggest a role for zRAR alpha and zRAR gamma in the establishment of the RA phenotype in zebrafish.

Amino Acid Sequence↗

PubMed1994

Cloning and expression during development of three murine members of the COUP family of nuclear orphan receptors.

We have isolated the murine homologs of the members of the COUP-family of steroid hormone receptors, COUP-TF1, ARP-1 and EAR2. The proteins encoded by the murine genes appeared to be highly conserved when compared to their human counterparts. The expression of COUP-TF1 and ARP-1 was induced during differentiation of P19 embryonal carcinoma (EC) cells into derivatives of all three germ layers. Retinoic acid (RA) treatment rapidly induced expression of both genes, while other methods of differentiation were less effective. Undifferentiated P19 cells were found to express EAR2 mRNA and the expression level was only slightly elevated by RA-treatment. In addition, we analyzed the expression in P19 cells of three members of the retinoid X receptor (RXR) family, which have been shown to heterodimerize with members of the COUP-family. During RA mediated differentiation of P19 cells, RXR alpha expression was induced while RXR beta expression was not modulated and RXR gamma expression was down regulated. Gel shift analysis revealed that in P19 cells the members of the COUP-family comprise the major portion of proteins binding to a RA-responsive direct repeat of the consensus steroid hormone receptor binding half site (AGGTCA) spaced by one nucleotide (DR + 1). The members of the COUP-family appeared to down regulate RA-induced activation of RA-response element-containing reporter constructs in a promoter context-dependent manner. The expression patterns of COUP-TF1, ARP-1 and EAR2 during development were investigated by in situ hybridization. In agreement with the results obtained in vitro, the three genes appeared to be expressed in tissues derived from all three germ layers. However, COUP-TF1 and ARP-1 were found to be expressed predominantly in the developing central nervous system in mutually exclusive domains. Furthermore, strong ARP-1 expression was detected in lung and kidney. Our data strongly suggest an important role for the members of the COUP-family in the hormonal control of gene expression regulating embryogenesis.

Amino Acid Sequence↗

PubMed1994

Characterization of a negative retinoic acid response element in the murine Oct4 promoter.

Expression of Oct4 in embryonic stem cells is controlled by a distal upstream stem cell-specific enhancer that is deactivated during retinoic acid (RA)-induced differentiation by an indirect mechanism not involving binding of RA receptors (H. Okazawa, K. Okamoto, F. Ishino, T. Ishino-Kaneko, S. Takeda, Y. Toyoda, M. Muramatsu, and H. Hamada, EMBO J. 10:2997-3005, 1991). Here we report that in RA-treated P19 embryonal carcinoma cells the Oct4 promoter is also subject to negative regulation by RA. The minimal Oct4 promoter sequence mediating repression consists of a promoter-proximal sequence containing a GC-rich SP1 consensus-like sequence and several hormone response element half-sites that can be arranged into direct repeats with different spacing. The GC box binds a nuclear factor that is invariably present in undifferentiated and RA-treated differentiated P19 cells. By contrast, the hormone response element-containing sequence binds factors that are induced following RA treatment. Mutational analysis and competition experiments show that the functional entity binding the RA-induced factor is a direct repeat sequence with a spacing of one nucleotide, previously shown to be a binding site for COUP transcription factors (COUP-TFs). Cotransfected orphan receptors COUP-TF1, ARP-1, and EAR-2 were able to repress the activity of Oct4 promoter-driven reporters in P19 EC cells, albeit with different efficiencies. Furthermore, the negative transcriptional effect of COUP-TFs is dominant over the activating effect of the Oct4 embryonic stem cell-specific enhancer. These results show that negative regulation of Oct4 expression during RA-induced differentiation of embryonic stem cells is controlled by two different mechanisms, including deactivation of the embryonic stem cell-specific enhancer and promoter silencing by orphan nuclear hormone receptors.

Animals↗

PubMed1994

junB promoter regulation: Ras mediated transactivation by c-Ets-1 and c-Ets-2.

The Jun gene family encode components of the AP-1 transcription factor complex that regulate a variety of TRE-containing target promoters. Expression of family members is induced by a wide variety of extracellular stimuli and thought to be important in mediating cellular proliferation and differentiation. We have localized cis-acting DNA sequences in the murine junB promoter capable of mediating transcriptional activation by the proto-oncogene products c-Ets-1 and c-Ets-2. We show by promoter deletion analysis that multiple elements located between -848 and -574, and between -196 and -91 can mediate transactivation by ETS-family members in different cell types. In vitro DNA binding assays indicate that the elements identified can specifically interact with c-Ets-1 protein. Furthermore, we show that ETS-transactivation of a variety of reporter constructs is dramatically enhanced by introduction of oncogenic Ha-ras. The activation of Ras by extracellular stimuli invokes a phosphorylation cascade that includes the downstream mitogen-activated protein (MAP) kinase p44ERK-1. We further show that addition of activated p44ERK-1 MAP kinase can also enhance ETS-transactivation of junB promoter reporter constructs. Here we propose that ETS-family members play a role in the activation of junB transcription by a Ras-stimulated signal transducing pathway that includes MAP kinase(s).

Animals↗

PubMed1993

c-fos induction by stress can be mediated by the SRE.

The proto-oncogene c-fos is important in cell growth, differentiation and development. Several promoter elements have been identified as mediators for the induction of c-fos by serum, tumor promoting agents, epidermal growth factor and other stimuli. Stressors, including heat shock, arsenite and cadmium can induce c-fos transcription, but a heat shock element in the c-fos promoter has not been described. In this report we show that the induction of c-fos by heat shock, arsenite and cadmium can be mediated by the serum response element. Furthermore we show that casein kinase II, which has been proposed to be involved in serum induction via the serum response element, may also be involved in heat shock, arsenite and cadmium induction of c-fos.

Animals↗

PubMed1993

Receptor protein tyrosine phosphatase alpha activates pp60c-src and is involved in neuronal differentiation.

Here we report that protein tyrosine phosphatases (PTPases), like their enzymatic counterpart the protein tyrosine kinases, can play an important role in cell differentiation. Expression of the transmembrane PTPase receptor protein tyrosine phosphatase alpha (RPTP alpha) is transiently enhanced during neuronal differentiation of embryonal carcinoma (EC) and neuroblastoma cells. Retinoic acid induces wild type P19 cells to differentiate into endoderm- and mesoderm-like cells. By contrast, retinoic acid treatment leads to neuronal differentiation of P19 cells, ectopically expressing functional RPTP alpha, as illustrated by their ability to generate action potentials. Endogenous pp60c-src kinase activity is enhanced in the RPTP alpha-transfected cells, which may be due to direct dephosphorylation of the regulatory Tyr residue at position 527 in pp60c-src by RPTP alpha. Our results demonstrate that RPTP alpha is involved in neuronal differentiation and imply a role for pp60c-src in the differentiation process.

Animals↗