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At least 1,747 records · Page 97Linked to original sources
PubMed2004

FGF and PI3 kinase signaling pathways antagonistically modulate sex muscle differentiation in C. elegans.

Myogenesis in vertebrate myocytes is promoted by activation of the phosphatidyl-inositol 3'-kinase (PI3 kinase) pathway and inhibited by fibroblast growth factor (FGF) signaling. We show that hyperactivation of the Caenorhabditis elegans FGF receptor, EGL-15, similarly inhibits the differentiation of the hermaphrodite sex muscles. Activation of the PI3 kinase signaling pathway can partially suppress this differentiation defect, mimicking the antagonistic relationship between these two pathways known to influence vertebrate myogenesis. When ectopically expressed in body wall muscle precursor cells, hyperactivated EGL-15 can also interfere with the proper development of the body wall musculature. Hyperactivation of EGL-15 has also revealed additional effects on a number of fundamental processes within the postembryonic muscle lineage, such as cell division polarity. These studies provide important in vivo insights into the contribution of FGF signaling events to myogenesis.

Animals↗
PubMed2004

RhoA controls myoblast survival by inducing the phosphatidylinositol 3-kinase-Akt signaling pathway.

The small GTPase RhoA regulates the expression of the myogenic transcription factor, MyoD, and the transcription of muscle-specific genes. We report that RhoA also affects the survival of differentiating myoblasts. Two signaling pathways, extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3-K)-Akt, are involved in myoblast survival. Here, we show that inhibition of RhoA prevents the phosphorylation of Akt, but does not affect the phosphorylation of ERK. Constitutive expression of an active form of Akt prevents apoptosis in myoblasts treated with the Rho inhibitor C3-transferase. These results indicate that RhoA functions to prevent myoblast death by inducing the PI3-K-Akt pathway.

Animals↗
PubMed2005

Signaling pathways involved in human vascular smooth muscle cell proliferation and matrix metalloproteinase-2 expression induced by leptin: inhibitory effect of metformin.

Accumulating evidence suggests that high concentrations of leptin observed in obesity and diabetes may contribute to their adverse effects on cardiovascular health. Metformin monotherapy is associated with reduced macrovascular complications in overweight patients with type 2 diabetes. It is uncertain whether such improvement in the cardiovascular outcome is related to specific vasculoprotective effects of this drug. In the present study, we determined the effect of leptin on human aortic smooth muscle cell (HASMC) proliferation and matrix metalloproteinase (MMP)-2 expression, the signaling pathways mediating these effects, and the modulatory effect of metformin on these parameters. Incubation of HASMCs with leptin enhanced the proliferation and MMP-2 expression in these cells and increased the generation of intracellular reactive oxygen species (ROS). These effects were abolished by vitamin E. Inhibition of NAD(P)H oxidase and protein kinase C (PKC) suppressed the effect of leptin on ROS production. In HASMCs, leptin induced PKC, extracellular signal-regulated kinase (ERK)1/2, and nuclear factor-kappaB (NF-kappaB) activation and inhibition of these signaling pathways abrogated HASMC proliferation and MMP-2 expression induced by this hormone. Treatment of HASMCs with metformin decreased leptin-induced ROS production and activation of PKC, ERK1/2, and NF-kappaB. Metformin also inhibited the effect of leptin on HASMC proliferation and MMP-2 expression. Overall, these results demonstrate that leptin induced HASMC proliferation and MMP-2 expression through a PKC-dependent activation of NAD(P)H oxidase with subsequent activation of the ERK1/2/NF-kappaB pathways and that therapeutic metformin concentrations effectively inhibit these biological effects. These results suggest a new mechanism by which metformin may improve cardiovascular outcome in patients with diabetes.

Aorta↗
PubMed2006

Angiopoietin 2 induces glioma cell invasion by stimulating matrix metalloprotease 2 expression through the alphavbeta1 integrin and focal adhesion kinase signaling pathway.

Accumulating evidence reveals a significant correlation between angiopoietin 2 (Ang2) expression and tumor invasion and metastasis in various human cancers, but the major focus of recent studies has been on the angiogenic effects of Ang2. We recently reported that Ang2-stimulated glioma cell invasion results from the up-regulation and activation of matrix metalloprotease 2 (MMP-2) in tumor cells. In this study, we identify a novel mechanism by which Ang2 stimulates MMP-2 expression leading to glioma cell invasion. We show that Ang2 interacts with alpha(v)beta(1) integrin in Tie2-deficient human glioma cells, activating focal adhesion kinase (FAK), p130(Cas), extracellular signal-regulated protein kinase (ERK) 1/2, and c-jun NH(2)-terminal kinase (JNK) and substantially enhancing MMP-2 expression and secretion. The Ang2/alpha(v)beta(1) integrin signaling pathway was attenuated by functional inhibition of beta(1) and alpha(v) integrins, FAK, p130(Cas), ERK1/2, and JNK. Furthermore, expression of a negative regulator of FAK, FAK-related nonkinase, by U87MG/Ang2-expressing glioma xenografts suppressed Ang2-induced MMP-2 expression and glioma cell infiltration in the murine brain. These data establish a functional link between Ang2 interaction with alpha(v)beta(1) integrin and glioma cell invasion through the FAK/p130(Cas)/ERK1/2 and JNK-mediated signaling pathway.

Angiopoietin-2↗
PubMed1996

Substance P-induced mitogenesis in human astrocytoma cells correlates with activation of the mitogen-activated protein kinase signaling pathway.

The neuropeptide substance P (SP) regulates many biological processes through binding to and activating the SP receptor (NK-1 subtype). Activation of the SP receptor induces mitogenesis in several cell types. In this study, we characterized the mitogenic response induced by SP peptide in the U-373MG astrocytoma cell line and showed that activation of the SP receptor induces [3H]thymidine incorporation into DNA. We also found that SP potently induces c-myc mRNA and protein in the U-373MG cells. Tyrphostin A25, which blocks activity of tyrosine kinases, significantly inhibited SP-induced mitogenesis, suggesting that the mitogenic response induced by SP peptide involves phosphorylation by tyrosine kinases. Furthermore, stimulation of the SP receptor activates tyrosine phosphorylation and enzymatic activity of extracellular signal-regulated kinases (Erk1 and Erk2), also called the mitogen-activated protein kinases (MAPKs). This result suggests that MAPKs participate in the SP peptide-induced signaling pathway. The addition of CP 96,345 ([(2S,3S)-cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1 -azabicyclo[2.2.2]octan-3-amine]; an NK-1 receptor antagonist) or PD 098059 (MEK1 inhibitor) inhibited both DNA synthesis and activation of the MAPK pathway, substantiating that SP stimulates mitogenesis by activating the MAPK pathway through receptors of the NK-1 subtype. Our results demonstrate that SP peptide is a strong mitogen in the U-373MG astrocytoma cell line and establish a clear correlation between SP-induced mitogenesis and activation of MAPK signaling pathway.

Amino Acid Sequence↗
PubMed2000

Signal pathways mediating oxytocin stimulation of prostaglandin synthesis in select target cells.

A major action of oxytocin is to stimulate prostaglandin production in reproductive tissues. The two major enzyme systems involved are cytosolic phospholipase A2 (cPLA2), which catalyses the formation of arachidonic acid from membrane glycerophospholipids, and prostaglandin endoperoxide-H synthases-1 and -2, which allow conversion of arachidonic acid to prostaglandins. During gestation, the concentrations of all three enzymes rise in the rabbit amnion. Agonists, including oxytocin, increase cPLA2 activity, in part, by elevating intracellular Ca2+ concentration, which causes cPLA2 to be translocated from the cytosol to intracellular membrane binding sites. Cytosolic PLA2 is then activated by a mitogen-activated protein kinase (MAPK)-dependent step. Our studies have elucidated signal pathways involved in oxytocin-stimulated prostaglandin output in both rabbit amnion cells and Chinese hamster ovary cells stably transfected with the rat oxytocin receptor. The two cell types are alike with respect to oxytocin-stimulated intracellular Ca2+ transients, mediation via Gq, and the specific MAPK that catalyses the phosphorylation of cPLA2. However, they differ with respect to the mechanisms of upregulation of key enzymes involved in prostaglandin E2 synthesis. These findings illustrate the tiers of complementary mechanisms involved in oxytocin stimulation of prostaglandin E2, and the extent of the diversity in the cellular signalling pathways involved.

Animals↗
PubMed2005

Multiple signaling pathways are activated during insulin-like growth factor-I (IGF-I) stimulated breast cancer cell migration.

In order to display the full metastatic phenotype, the cancer cell must acquire the ability to migrate. In breast cancer, we have previously shown that insulin-like growth factor I (IGF-I) enhances cell motility in the highly metastatic MDA-231BO cell line by activating the type I IGF receptor (IGF1R). This motility response requires activation of IRS-2 and integrin ligation. In order to identify the key molecules downstream of IRS-2, we examined several signaling pathways known to be involved in cell motility. Focal adhesion kinase (FAK) was not activated by IGF-I, but IGF-I caused redistribution of FAK away from focal adhesion plaques. IGF-I treatment of MDA-231BO cells activated RhoA and inhibition of Rho-kinase (ROCK) inhibited the IGF-mediated motility response. The mitogen activated protein kinase (MAPK), p38, was also activated by IGF-I and inhibition of p38 by SB203580 blocked IGF-I induced cell motility. ROCK inhibition with Y-27632 also inhibited p38 phosphorylation suggesting that p38 lies downstream of ROCK. Both Erk1,2 and phosphatidyl-3 kinase (PI3K) were required for IGF-I stimulated cell motility, but only PI3K appeared to be directly downstream of IGF-I. Thus, IGF-I activation of its receptor coordinates multiple signaling pathways required for cell motility. Defining the key molecules downstream of the type I IGF receptor may provide a basis for optimizing therapies directed at this target.

Amides↗
PubMed2006

Activation of signaling pathways and stress-response genes in an experimental model of retinal detachment.

PURPOSE: Despite the high metabolic demands of the neural retina, its detachment from the retinal pigment epithelium does not lead to immediate death for most of the cells. This study was undertaken to test the hypothesis that intrinsic protective mechanisms are activated in the neural retina during early stages of retinal detachment. METHODS: Retinal detachments were created in Brown Norway rats by injection of 1% hyaluronic acid into the subretinal space. Gene expression profiles of retinas detached for 24 hours were generated with a gene microarray (rat U34 GeneChips; Affymetrix, Santa Clara, CA) and compared to the profiles from control attached retinas in a robust multiarray protocol and false-discovery-rate analysis. Changes in individual, differentially expressed genes were validated by quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Additional qRT-PCR and immunoblot analyses were performed for additional selected genes. RESULTS: Genome-wide expression profiling revealed 27 genes that are differentially expressed in retinas detached for 24 hours. In silico analysis and functional clustering suggested that most genes belonged to three signaling pathways: interleukin-6/STAT, transforming growth factor-beta/Smad, and aryl hydrocarbon receptor oxidative stress response. Additional analyses of selected genes from these pathways demonstrated a time-dependent increase in their expression in detached retinas. CONCLUSIONS: Retinal detachment results in the early activation of stress-response genes and specific signaling pathways. This adaptive response may enable the photoreceptor cells to survive the acute phase of a retinal detachment, and it is the breakdown of these protective mechanisms in chronic disease that leads to the ultimate death of the cell.

Animals↗
PubMed2001

Conservation of signaling pathways of xenobiotic-sensing orphan nuclear receptors, chicken xenobiotic receptor, constitutive androstane receptor, and pregnane X receptor, from birds to humans.

Chicken xenobiotic receptor, pregnane X receptor, and constitutive androstane receptor are orphan nuclear receptors that have recently been discovered to regulate drug- and steroid-mediated induction of hepatic cytochromes P450 (CYP). This induction is part of an adaptive response involving numerous genes to exposure to drugs and chemicals and has major clinical and toxicological implications. Here we report experiments in the chicken hepatoma cell line LMH that suggest evolutionary conservation of the signaling pathways triggered by pregnane X receptor, constitutive androstane receptor, and chicken xenobiotic receptor. Thus, the phenobarbital-inducible enhancer units of the mouse Cyp2b10, rat CYP2B2, and human CYP2B6 genes were activated in reporter gene assays by the same compounds that activate the chicken CYP2H1 phenobarbital-inducible enhancer units. Chicken xenobiotic receptor, pregnane X receptor, and constitutive androstane receptor all bound to the CYP2H1 phenobarbital-inducible enhancer units in gel-shift experiments. In CV-1 cell transactivation assays, mammalian pregnane X receptors activate the chicken phenobarbital-inducible enhancer units to the same extent as does chicken xenobiotic receptor, each receptor maintaining its species-specific ligand spectrum. To assess the reported role of protein phosphorylation in drug-mediated induction, we treated LMH cells with okadaic acid and observed increased mRNA of delta-aminolevulinate synthase and CYP2H1 whereas expression of CYP3A37 was decreased. The effects of okadaic acid and other modifiers of protein phosphorylation in LMH cells are comparable to those seen on CYP2Bs and CYP3As in mammalian primary hepatocyte cultures. These results indicate that closely related nuclear receptors, transcription factors, and signaling pathways are mediating the transcriptional activation of multiple genes by xenobiotics in chicken, rodents, and man.

Animals↗
PubMed2000

Combined immunodeficiencies due to defects in signal transduction: defects of the gammac-JAK3 signaling pathway as a model.

Combined immune deficiencies comprise a spectrum of genetic disorders characterized by developmental or functional defects of both T and B lymphocytes. Recent progress in cell biology and molecular genetics has unraveled the pathophysiology of most of these defects. In particular, the most common form of severe combined immune deficiency in humans, with lack of circulating T cells, a normal or increased number of B lymphocytes, and an X-linked pattern of inheritance (SCIDXI) has been shown to be due to defects of the IL2RG gene, encoding for the common gamma chain (gammac), shared by several cytokine receptors. Furthermore, defects of the JAK3 gene, encoding for an intracellular tyrosine kinase required for signal transduction through gammac-containing cytokine receptors, have been identified in patients with autosomal recessive T-B+ SCID. Characterization of the functional properties of cytokines that signal through the gammac-JAK3 signaling pathway has been favored by the detailed analysis of SCID patients. Specifically, the key role of IL-7 in promoting T cell development has been substantiated by the identification of rare patients with T-B+ SCID who have a defect in the alpha subunit of the IL-7 receptor (IL7Ralpha). The heterogeneity of genetic defects along the same signaling pathway that may lead to combined immune deficiency is paralleled by the heterogeneity of immunological phenotypes that may associate with defects in the same gene, thus creating a need for detailed immunological and molecular investigations in order to dissect the spectrum of combined immune deficiencies in humans.

Animals↗
PubMed2003

Cyclooxygenase-2 is up-regulated by interleukin-1 beta in human colorectal cancer cells via multiple signaling pathways.

Overexpression of cyclooxygenase-2 (COX-2) has been observed in human colorectal cancer. COX-2 expression in human tumors can be induced by growth factors, cytokines, oncogenes, and other factors. The mechanisms regulating COX-2 expression in human colon cancer have not been completely elucidated. We hypothesized that the proinflammatory cytokine interleukin-1 beta (IL-1 beta) mediates COX-2 expression in HT-29 human colon cancer cells. Treatment of HT-29 cells with IL-1 beta induced expression of COX-2 mRNA and protein in a time- and dose-dependent manner. Inhibitors of the extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase, P38 mitogen-activated protein kinase, and nuclear factor-kappa B (NF-kappa B) signaling pathways blocked the ability of IL-1 beta to induce COX-2 mRNA. In contrast, Wortmannin, a phosphoinositide 3-kinase inhibitor upstream of protein kinase B/Akt, led to a slight increase in COX-2 mRNA expression after IL-1 beta treatment. Electrophoretic mobility shift assay on nuclear extracts demonstrated that IL-1 beta induced NF-kappa B DNA binding activity in HT-29 cells, and the activated NF-kappa B complex was eliminated after treatment with an inhibitor of NF-kappa B. Supershift assay indicated that the two NF-kappa B subunits, p65 and p50, were involved in activation of NF-kappa B complex by IL-1 beta stimulation. The stability of COX-2 mRNA was not altered by IL-1 beta treatment. These data demonstrate that IL-1 beta induces COX-2 expression in HT-29 cells through multiple signaling pathways and NF-kappa B.

Colonic Neoplasms↗
PubMed2005

Involvement of adenylate cyclase and tyrosine kinase signaling pathways in response of crayfish stretch receptor neuron and satellite glia cell to photodynamic treatment.

Neuroglial interactions are most profound during development or damage of nerve tissue. We studied the responses of crayfish stretch receptor neurons (SRN) and satellite glial cells to photosensitization with sulfonated aluminum phthalocyanine Photosens. Although Photosens was localized mainly in the glial envelope, neurons were very sensitive to photodynamic treatment. Photosensitization gradually inhibited and then abolished neuron activity. Neuronal and glial nuclei shrank. Some neurons and glial cells lost the integrity of the plasma membrane and died through necrosis after the treatment. The nuclei of other glial cells but not neurons become fragmented, indicating apoptosis. The number of glial nuclei around neuron soma increased, probably indicating proliferation for enhanced neuron protection. Adenylate cyclase (AC) inhibition by MDL-12330A, or tyrosine kinase (TK) inhibition by genistein, shortened neuron lifetime, whereas AC activation by forskolin or protein tyrosine phosphatases (PTP) inhibition by sodium orthovanadate prolonged neuronal activity. Therefore, cAMP and phosphotyrosines produced by AC and TK, respectively, protected SRN against photoinactivation. AC inhibition reduced photodamage of the plasma membrane and subsequent necrosis in neuronal and glial cells. AC activation prevented apoptosis in photosensitized glial cells and stimulated glial proliferation. TK inhibition protected neurons but not glia against photoinduced membrane permeabilization and subsequent necrosis whereas PTP inhibition more strongly protected glial cells. Therefore, both signaling pathways involving cAMP and phosphotyrosines might contribute to the maintenance of neuronal activity and the integrity of the neuronal and glial plasma membranes. Adenylate cyclase but not phosphotyrosine signaling pathways modulated glial apoptosis and proliferation under photooxidative stress.

Adenylyl Cyclases↗
PubMed1996

Cisplatin and taxol activate different signal pathways regulating cellular injury-induced expression of GADD153.

Signal transduction pathways activated by injury play a central role in coordinating the cellular responses that determine whether a cell survives or dies. GADD153 expression increases markedly in response to some types of cellular injury and the product of this gene causes cell cycle arrest. Using induction of GADD153 as a model, we have investigated the activation of the cellular injury response after treatment with taxol and cisplatin (cDDP). Activation of the GADD153 promoter coupled to the luciferase gene and transfected into human ovarian carcinoma 2008 cells correlated well with the increase in endogenous GADD153 mRNA after treatment with taxol but not after treatment with cDDP. Following treatment with cDDP, the increase in endogenous GADD153 mRNA was 10-fold greater than the increase in GADD153 promoter activity. Likewise, at equitoxic levels of exposure (IC80), cDDP produced a 5-fold greater increase in endogenous GADD153 mRNA than taxol. The tyrosine kinase inhibitor tyrophostin B46 had no significant effect on the ability of taxol to activate the GADD153 promoter, but inhibited activation of the GADD153 promoter by cDDP in a concentration-dependent manner. Tyrphostin B46 synergistically enhanced the cytotoxicity of cisplatin; however, the same exposure had no significant effect on the cytotoxicity of taxol. We conclude that (1) taxol and cDDP activate GADD153 promoter activity through different mechanisms; (2) the signal transduction pathway mediating induction by cDDP involves a tyrosine kinase inhibitable by tyrphostin B46; and (3) that inhibition of this signal transduction pathway by tyrphostin synergistically enhances cDDP toxicity.

Antineoplastic Agents↗
PubMed1999

Dissection of the impact of various intracellular signaling pathways on stable cell aggregate formation of rat thymocytes after initial lectin-dependent cell association of using a plant lectin as model and target-selective inhibitors.

Bivalent lectins as bridging molecules between cells or cell surface lectins as docking points are involved in mediation of cell adhesion by specific recognition of suitable glycoconjugates on an opposing surface. The initial contact formation by a lectin can lead to intracellular post-binding events which effect stable cell association even in the presence of the haptenic sugar. To delineate the participation of intracellular signaling pathways in the cascade of reactions to establish firm association, reagents with proven inhibitory capacity on certain biochemical targets provide suitable tools. Using this approach with rat thymocytes and the galactoside-binding lectin from mistletoe (Viscum album L. agglutinin, VAA) as a model, a panel of 27 inhibitors with impact on e.g. several types of kinases, tyrosine phosphatases, NO synthases, G proteins, enzymes of arachidonate and cyclic nucleotide metabolism and calmodulin was systematically tested with respect to their capacity to impair the formation of lactose-resistant cell aggregates. In addition to the recently reported effectiveness of N-ethylmaleimide, nordihydroguaiaretic acid, and trifluoperazine the agents diacylglycerol kinase inhibitor II, emodin, D609, DPI, KT5720, KT5926, MK-886, bisindolylmaleimide I, and (+/-)methoxyverapamil were able to reduce aggregate stability in the presence of the haptenic sugar. Thus, various types of kinases including p561lck tyrosine kinase, lipoxygenases, phosphatidylcholine-specific phospholipase C as well as calmodulin and Ca(2+)-currents, but not modulators of the metabolism of cyclic nucleotides, NO synthases, MAP kinases, tyrosine phosphatases and phospholipase A (preferentially group II) and C can play a role in eliciting contact stability. More than one principal signaling pathway appears to be linked to the measurable parameter, since inhibitory substances show additive properties in co-incubation assays and differentially affect two lectin-elicited cellular activities, i.e. intracellular movement of Ca(2+)-ions and H2O2-generation, which can accompany cell adhesion and aggregation. Pronounced differences in the extent of modulation of H2O2-generation in human neutrophils by the same set of substances emphasizes that general conclusions on the post-binding effects for a certain lectin in different cell types are definitely precluded. In aggregate, the approach to employ inhibitors with target selectivity intimates an involvement of protein kinases A, C, Ca2+/calmodulin-dependent protein kinase II, p56lck tyrosine kinase, leukotrienes and/or hydroxyeicosatetraenoic acids, phosphatidylcholine-specific phospholipase C and Ca(2+)-fluxes in events following initial binding of a galactoside-specific plant lectin to rat thymocytes which establish firm cell contacts.

Animals↗
PubMed2000

Molecular mechanism of a cross-talk between oestrogen and growth factor signalling pathways.

Oestrogen (E2) plays significant roles in variety of biological events such as the development and maintenance of female reproductive organs, bone and lipid metabolisms. More recently, from study of knock-out mice deficient in oestrogen receptor (ER) alpha and ERbeta it turned out that normal spermatogenesis requires the E2 actions. Furthermore, this female steroid hormone is also well known to be deeply involved in many pathophysiological events such as osteoporosis and cancer development in female reproductive organs. It is particularly well known that most breast cancer is dependent on E2 in its development. Such E2 actions are thought to be mediated through two subtypes of ERs. Growth factors have been shown to synergize in this E2 signalling pathway, although the actual molecular mechanism largely remains unknown. Recently, we found that the MAP kinase activated by growth factors phosphorylates the Ser118 residue of the human ERalpha A/B domain and this phosphorylation potentiates the N-terminal transactivation function (AF-1) of human ERalpha, indicating the possible molecular mechanism of a novel cross-talk between E2 and growth factor signalling pathways. More recently, we have identified a coactivator associating with the hERalpha AF-1 in a MAPK-mediated phosphorylation-dependent manner. In this review, the molecular mechanism of this cross-talk is discussed in terms of the transactivation function of ERs, and their coactivators.

Animals↗
PubMed2001

Systematic analysis of the TGF-beta-Smad signaling pathway in gastrointestinal cancer cells.

The transforming growth factor-beta (TGF-beta)-Smad signaling pathway has an important role in carcinogenesis. To study the frequency and mechanism of functional impairment of this pathway in human gastrointestinal cancers, we used a reporter assay to examine the response of 38 cell lines (11 colorectal, 9 pancreatic, 10 gastric, and 8 hepatic cancers) to TGF-beta. We then analyzed TGF-beta type II receptor (T beta RII) gene, immunoblots of Smad4, and restoration of the pathway by rescuing T beta R or Smad. We observed impaired signaling in 91% of colorectal, 67% of pancreatic, and 40% of gastric cancer cell lines, but in none of the hepatic cancer cells. We suggest that this pathway does not function as a tumor suppressor in hepatic carcinogenesis. The impairment is due to inactivation of T beta RII and Smad4 in colorectal and pancreatic cancers. However, because the signal was not recovered by rescuing T beta R or Smad genes in TGF-beta-response-defective gastric cancer cell lines, we suggest that novel molecules or mechanisms are involved in the impaired pathway in some gastric cancers.

Blotting, Western↗
PubMed1999

Distinct calcium signaling pathways regulate calmodulin gene expression in tobacco.

Cold shock and wind stimuli initiate Ca(2+) transients in transgenic tobacco (Nicotiana plumbaginifolia) seedlings (named MAQ 2.4) containing cytoplasmic aequorin. To investigate whether these stimuli initiate Ca(2+) pathways that are spatially distinct, stress-induced nuclear and cytoplasmic Ca(2+) transients and the expression of a stress-induced calmodulin gene were compared. Tobacco seedlings were transformed with a construct that encodes a fusion protein between nucleoplasmin (a major oocyte nuclear protein) and aequorin. Immunocytochemical evidence indicated targeting of the fusion protein to the nucleus in these plants, which were named MAQ 7.11. Comparison between MAQ 7.11 and MAQ 2.4 seedlings confirmed that wind stimuli and cold shock invoke separate Ca(2+) signaling pathways. Partial cDNAs encoding two tobacco calmodulin genes, NpCaM-1 and NpCaM-2, were identified and shown to have distinct nucleotide sequences that encode identical polypeptides. Expression of NpCaM-1, but not NpCaM-2, responded to wind and cold shock stimulation. Comparison of the Ca(2+) dynamics with NpCaM-1 expression after stimulation suggested that wind-induced NpCaM-1 expression is regulated by a Ca(2+) signaling pathway operational predominantly in the nucleus. In contrast, expression of NpCaM-1 in response to cold shock is regulated by a pathway operational predominantly in the cytoplasm.

Aequorin↗
PubMed1998

Cell adhesion and the integrin-linked kinase regulate the LEF-1 and beta-catenin signaling pathways.

The integrin-linked kinase (ILK) is an ankyrin repeat containing serine-threonine protein kinase that can interact directly with the cytoplasmic domains of the beta1 and beta3 integrin subunits and whose kinase activity is modulated by cell-extracellular matrix interactions. Overexpression of constitutively active ILK results in loss of cell-cell adhesion, anchorage-independent growth, and tumorigenicity in nude mice. We now show that modest overexpression of ILK in intestinal epithelial cells as well as in mammary epithelial cells results in an invasive phenotype concomitant with a down-regulation of E-cadherin expression, translocation of beta-catenin to the nucleus, formation of a complex between beta-catenin and the high mobility group transcription factor, LEF-1, and transcriptional activation by this LEF-1/beta-catenin complex. We also find that LEF-1 protein expression is rapidly modulated by cell detachment from the extracellular matrix, and that LEF-1 protein levels are constitutively up-regulated at ILK overexpression. These effects are specific for ILK, because transformation by activated H-ras or v-src oncogenes do not result in the activation of LEF-1/beta-catenin. The results demonstrate that the oncogenic properties of ILK involve activation of the LEF-1/beta-catenin signaling pathway, and also suggest ILK-mediated cross-talk between cell-matrix interactions and cell-cell adhesion as well as components of the Wnt signaling pathway.

Animals↗