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At least 1,531 records · Page 85Linked to original sources
PubMed2003

Lymphoid enhancer factor 1 makes cells resistant to transforming growth factor beta-induced repression of c-myc.

The activation of lymphoid enhancer factor (LEF)/T-cell factor (TCF)-mediated transcription by sustained expression of beta-catenin and the loss of transforming growth factor beta (TGF-beta) signaling are essential steps in carcinogenesis, particularly for cancers of the colon, breast, and liver. The oncogene c-myc is a common target of both of these signaling pathways and a key regulator of cell cycle progression. Here we have identified a novel LEF/TCF-responsive element in the promoter of the human c-myc gene. beta-Catenin activated the transcriptional activity of the c-myc promoter by binding to this element in various cell lines. When TCF-4 was bound to this element, TGF-beta dissociated beta-catenin and repressed the transcriptional activity of the c-myc promoter. However, TGF-beta could not dissociate beta-catenin and could not repress c-myc transcription when LEF-1 was bound to the element instead of TCF-4. These findings suggest that enhanced expression of LEF-1, which occurs frequently in colon cancer, may make cells refractory to the down-regulation of c-myc and the subsequent growth arrest induced by TGF-beta.

3T3 Cells↗
PubMed1992

Human 55-kDa receptor for tumor necrosis factor coupled to signal transduction cascades.

The numerous biological activities of tumor necrosis factor (TNF) appear mediated by two types of receptors of 55 kDa (TR55) and 75 kDa (TR75) molecular mass. To test TR55 for its individual role in signaling across the membrane, a cDNA coding for the human TR55 was stably expressed in murine 70Z/3 pre-B cells, which lack binding sites for, and proved nonresponsive to human TNF. The transfected TR55 showed high affinity ligand binding and active internalization. It is demonstrated that the TNF signaling cascade, i.e. stimulation of protein kinase C, sphingomyelinase, and phospholipase A2, production of the second messengers diacylglycerol and ceramide, can occur completely through exclusive binding of TNF to TR55. The p55 TNF-binding site functions as an autonomous TNF receptor that mediates key signal transduction pathways, which may control the majority of TNF actions.

Animals↗
PubMed2002

[Endothelium and vascular protection: an update].

Endothelial cells (EC) are highly specialized cells cable of modulating their functional stage in response to different stimuli. The endothelium has various atheroprotective functions: it regulates coagulation, thrombosis and the fibrinolytic system; it modulates the activity of smooth muscle cells (vascular tone/proliferation) and controls the traffic of macromolecules and inflammatory cells to the vessel wall. Impairment of these functions (endothelial dysfunction) potentiates the development of atherosclerotic lesions. High levels of plasma lipids, particularly, low-density (LDL) and very-low-density lipoproteins (VLDL) are among the pathophysiologic stimuli that induce endothelial dysfunction. LDLs have been implicated in the induction of changes in permeability, cell adhesion and secretion of vasoactive molecules (nitric oxide [NO], prostacycline [PGI2]), while VLDLs seem to modulate the fibrinolytic system [tissue plasminogen activator (t-PA) and its inhibitor (PAI-I)]. Endothelial function is controlled by a small number of genes (transcription factors) that modulate EC response to inflammatory stimuli (nuclear factor kappa beta, NF-kappabeta) or flow conditions (genes-regulated by shear-stress-responsive elements, SSREs). In addition, the control of key cellular biosynthetic pathways, such as endothelial cholesterol biosynthesis, are regulated by sterol-regulatory-elements binding proteins (SREBPs) that could be involved in the maintenance of normal endothelial function.

Blood Vessels↗
PubMed2005

[Nuclear Receptor PPARs and magnesium].

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that are activated by fatty acids and their derivatives. PPARs consist of three isotypes named PPAR alpha (NR1C1), PPAR beta/delta (NR1C2) and PPAR gamma (NR1C3) in vertebrates. Each of them is encoded in a separate gene and binds fatty acids and eicosanoids. Although each isotype fulfills distinct functions, PPARs function not only as an important fatty acid sensor that regulate lipid, carbohydrate and amino acid metabolism but also play an important role in various signaling pathways (immunity, inflammation, apoptosis and cell differentiation). Dysfunction of PPAR-mediated signals leads to various diseases such as diabetes, obese, hyperlipidemia, inflammation and cancer. Importantly, magnesium appears to play a pivotal role in regulating the PPAR-mediated signaling pathways as a key cofactor in the protein phosphorylation. Therefore, restrict control of magnesium concentration in the body appears to be very important for protection for these diseases. In this review, I focus on emerging knowledge about relationship between PPAR-mediated signals and magnesium.

Animals↗
PubMed1992

Radiosensitization and cell kinetics: clinical implications for S-phase-specific radiosensitizers.

Rapid repopulation of tumor cells during conventional radiation therapy has been recently recognized as a factor that might significantly impair tumor response in several different tumor sites. One clinical strategy to overcome rapid tumor proliferation is to use S-phase-specific radiosensitizers such as hydroxyurea and the halopyrimidines 5-iododeoxyuridine (IUDR), 5-bromo-2'-deoxyuridine (BUDR), 5-fluoro-2'-deoxy-beta-uridine (FUDR), and 5-fluorouracil (5-FU). Indeed, several recent clinical trials have shown the positive antiproliferative effects of these radiosensitizers in various human tumors. In spite of this resurgence of clinical interest, the basic mechanism(s) of radiosensitization is not clearly understood. Although the halopyrimidines have similar biochemical pathways involving two key regulatory enzymes, thymidine kinase and thymidylate synthase, it appears that DNA-incorporation is important for radiosensitization by BUDR and IUDR but not for FUDR or 5-FU. Recent laboratory data suggest that biochemical modulation of the key regulatory enzymes can result in selective tumor radiosensitization with halopyrimidines. Hydroxyurea, like 5-FU, sensitizes cells when present prior to and following irradiation; this interaction may be related to cell synchronization as well as altered DNA damage repair. Exploiting differences in cell proliferation and cellular metabolism of these S-phase-specific radiosensitizers in tumors and normal tissues will be a major focus of clinical research in human tumor radiosensitization over the next few years.

Cell Cycle↗
PubMed2006

[cDNA microarray-based study of gene expression profile changes in human esophageal squamous cell carcinoma].

OBJECTIVE: To investigate the differentially expressed genes between human esophageal squamous cell carcinoma (ESCC) and normal esophageal mucosa and explore an effective method with high throughput for screening the molecular markers closely correlated with the development, invasion and metastasis of ESCC. METHODS: With cDNA microarray and laser capture microdissection, T7-based amplification were used to detect the mRNA from both the primary carcinoma and the corresponding esophageal epithelium in 15 ESCC cases, and the results were analyzed by bioinformatics methods. RESULTS: Among the 886 target genes, 110 (12.42%) genes were differentially expressed commonly at least twice in all the 15 samples, including 56 (6.32%) up-regulated by at least 2 folds and 54 (6.09%) down-regulated by at least 0.5 folds. CONCLUSION: Many ESCC-associated genes were screened by the high-throughput gene chip method, and functional study of these genes may help to identify the key genes or pathways involved in the pathogenesis and development of ESCC.

Carcinoma, Squamous Cell↗
PubMed2006

The role of the hypoxia-inducible factor in tumor metabolism growth and invasion.

Oxygen deprivation leading to hypoxia is a common feature of solid tumours. Under these conditions a signalling pathway involving a key oxygen-response regulator termed the hypoxia-inducible factor (HIF) is switched on. HIF is a transcription factor that, in hypoxia, drives the induction or repression of a myriad of genes controlling multiple cell functions such as angiogenesis, metabolism, invasion/metastasis and apoptosis/survival. Thus, the level of oxygen in a cell dictates the molecular response of cells through modulation of gene expression. Here we review the central role of HIF in cancer progression through the tumour response to hypoxia. Within this context the following aspects will be discussed: i) the mechanism by which oxygen deprivation inhibits two oxygen-sensor hydroxylases, thereby releasing the alpha subunit of HIF from programmed destruction by the ubiquitin-proteasome system and from a lock on its transcriptional activity; ii) the way in which the bi-transcriptional activity of HIF-alpha, which is regulated by the interplay between an oxygen-sensor attenuator and co-activators, determines the repertoire of gene expression; and iii) the role that HIF plays in tumour metabolism, in particular in glycolysis, and consequent acidification of the microenvironment, which influences both cell survival and cell death. Finally, the direct link of HIF to tumourigenesis and metastasis will be investigated and approaches for fighting tumour progression through a better understanding of HIF-mediated modulation of tumour metabolism and cell death will be considered.

Cell Death↗
PubMed2006

Formaldehyde uptake by Methylobacterium sp. MF1 and Acidomonas methanolica MB 58 with the different formaldehyde assimilation pathways.

Methylobacterium sp. MF1 (an obligate methylotrophic bacterium isolated newly by the authors) and Acidomonas methanolica MB58 (a facultative methylotrophic bacterium) uptake formaldehyde similarly. It was found that the former assimilated formaldehyde via the serine pathway whereas the latter did so via the ribulose-monophosphate pathway from the measurement of the key enzyme activities in each assimilation pathway. That is, hydroxy pyruvate reductase was detected in only the above-mentioned MF1 strain, but hexulose phosphate synthase (HPS) was not. The efficiencies of formaldehyde consumption by both strains under a continuous chemostat cultivation in the steady state were almost the same in spite of their different assimilation pathways. That is, the consumption efficiencies of the MF strain and the MB58 strain were ca. 1.2 g/L/d and ca. 1.8 g/L/d, respectively, under the experimental conditions. In the future, optimal continuous operating conditions will be investigated.

Formaldehyde↗
PubMedDate not supplied

Apoptosis in SLE--too little or too much?

Cells of the immune system are, most likely, programmed to die unless recruited into an immune response. An active cell death program may also be induced by a variety of soluble and surface signals, many of which have only recently been recognized. The importance of these pathways in maintaining tolerance is highlighted by the development of lupus-like diseases in three different mouse strains that have spontaneous mutations in the Fas/APO-1 receptor or its ligand. The known function of Fas/APO-1 in signalling apoptosis explains the persistence of self reactive cells in lpr mice although it is unclear, at present, whether Fas defects effect both central and peripheral tolerance. Whereas Fas/APO-1 receptor expression appears to be normal in humans with SLE, other defects in the Fas/APO-1 pathway or other key molecules in the cell death survival require further study.

Animals↗
PubMed1994

2nd International Symposium on Reverse Cholesterol Transport: report on a meeting.

The purpose of this symposium was to provide a forum for presenting recent findings and for exchange of ideas concerning reverse cholesterol transport. Because the mechanism involving HDL in the prevention and/or reversal of atherosclerosis is still unknown, this area is of intense interest. Although reverse cholesterol transport as an essential physiological mechanism has been validated, the clinical significance of this pathway remains unclear. Key elements of knowledge are lacking that would allow the linking of cholesterol efflux from cells and tissues with specific events in HDL metabolism, particularly those that are relevant to the prevention and/or reversal of atherosclerosis. Because of the intricate nature of the interaction between the components of reverse cholesterol transport, this second conference involving the leading investigators proved particularly valuable for presentation and extensive discussion of unpublished and occasionally controversial findings. Following this conference, an agreement was reached between the organizers and Dr. Norman E. Miller to combine this symposium with the previously held International Symposia on High Density Lipoproteins in Atherosclerosis (organized by Dr. Miller).

Animals↗
PubMed1997

Phosphorylation of the NC-1.1 receptor and regulation of natural cytotoxicity by protein kinase C and cyclic GMP-dependent protein kinase.

Natural cytotoxicity (NC) against cancer involves receptor-ligand interactions between lymphohemopoietic cells that mediate NC against tumor cells. The only candidate for a receptor on cells mediating NC is NC-1.1, identified using mAb 1C4. In this study we showed that mAb 1C4 blocked NC-1.1+ cell conjugation to WEHI-164 tumor cells, indicating that NC-1.1 is a surface protein required for cell-cell interaction. Affinity-purified NC-1.1 was a 45-kDa monomeric protein. It was a good in vitro substrate for cyclic GMP (cGMP)-dependent protein kinase (PKG) and protein kinase C (PKC) and a relatively poor substrate for cAMP-dependent protein kinase (PKA). Phosphopeptide mapping revealed one phosphopeptide phosphorylated by PKG and PKA, and two additional peptides phosphorylated by PKC. Phosphorylation by PKG or PKA abolished phosphorylation at the PKC sites, while coincubation of NC-1.1 with both PKG and PKC reduced phosphorylation of all sites. NC-1.1 was also a phosphoprotein after immunoprecipitation from intact spleen cells and its phosphorylation was increased after cell stimulation with PKC or PKG activators (phorbol esters or 8-bromo-cGMP). The possible consequences of intracellular signaling were tested in functional assays for NC. Phorbol ester activation of spleen cells increased NC, while 8-bromo-cGMP and 8-bromo-cAMP had little effect. However, coincubation with both phorbol ester and either 8-bromo-cGMP or 8-bromo-cAMP virtually abolished NC without affecting cell conjugation. These results suggest that NC-1.1 is a receptor for a ligand on certain tumor cells and reveal that key intracellular signaling pathways involving PKC, PKG, and PKA interact to effect a coordinated control of NC.

Animals↗
PubMed1998

Depolarization stimulates initial calcitonin gene-related peptide expression by embryonic sensory neurons in vitro.

The neuropeptide calcitonin gene-related peptide (CGRP) is expressed by one-third of adult rat lumbar dorsal root ganglion (DRG) neurons, many of which mediate pain sensation or cause vasodilation. The factors that regulate the developmental expression of CGRP are poorly understood. Embryonic DRG neurons initially lack CGRP. When these neurons were stimulated in culture by serum or persistent 50 mM KCl application, the same percentage of CGRP-immunoreactive (CGRP-IR) neurons developed in vitro as was seen in the adult DRG in vivo. The addition of the L-type calcium channel blockers, 5 microM nifedipine or 10 microM verapamil, dramatically decreased the proportion of CGRP-IR neurons that developed, although the N-type calcium channel blocker, 2.5 microM omega-conotoxin, was less effective. By contrast, the sodium channel blocker 1 microM tetrodotoxin had no effect on CGRP expression after depolarization. Fura-2 ratiometric imaging demonstrated that mean intracellular free calcium levels increased from 70 to 135 nM with chronic depolarization, and the addition of nifedipine inhibited that increase. Only a subpopulation of neurons had elevated calcium concentrations during chronic depolarization, and they were correlated with CGRP expression. Key signal transduction pathways were tested pharmacologically for their role in CGRP expression after depolarization; the addition of the CaM kinase inhibitor KN-62 reduced the proportion of CGRP-IR neurons to basal levels. By contrast, protein kinase A and protein kinase C were not implicated in the depolarization-induced CGRP increases. These data suggest that depolarization and the subsequent Ca2+-based signal transduction mechanisms play important roles in the de novo expression of CGRP by specific embryonic DRG neurons.

Animals↗
PubMed2005

Exploring gender and socioeconomic differences in treatment of coronary heart disease.

BACKGROUND: Earlier studies on gender and socioeconomic differences in the treatment of coronary heart disease have focused mainly on structural features of the health-care system on the one hand and on coronary patients' psychosocial characteristics on the other. The aim of this exploratory qualitative study was to trace key points in the pathways of treatment where patients' experience varies and which can contribute to gender and socioeconomic differences in treatment. METHODS: The data consist of 30 interviews among persons diagnosed with or suspected to have coronary heart disease in the Health 2000, a representative cross-sectional interview and health examination survey. Purposive sampling was used to ensure variation in gender, socioeconomic status and disease severity. The data were analysed using qualitative content analysis. RESULTS: Gender and socioeconomic differences were found in two key points in the pathways of treatment: doctor-patient interaction and the organization of primary care. The three features commonly distinguished in doctor-patient interaction, i.e. treatment decision-making, information exchange and interpersonal relationship, were all found to be relevant. A second key point was organization of primary care in terms of both access to examinations and care, and continuity of care. CONCLUSIONS: These results should sensitize us to gender and socioeconomic differences in coronary patients' problems in access to and continuity of care, as well as to potential problem areas in doctor-patient interaction.

Aged↗
PubMed2005

FTIR difference spectra of Wolinella succinogenes quinol:fumarate reductase support a key role of Glu C180 within the "E-pathway hypothesis" of coupled transmembrane electron and proton transfer.

Electrochemically induced static FTIR difference spectroscopy has been employed to investigate redox-driven protonation changes of individual amino acid residues in the quinol:fumarate reductase (QFR) from Wolinella succinogenes. The difference spectra presented were taken in the mid-infrared region from 1800 to 1000 cm(-1), and the signals obtained represent transitions between the reduced and oxidized states of the enzyme. Analysis of the difference spectra shows evidence for structural reorganizations of the polypeptide backbone upon the induced redox reaction. Furthermore, spectral contributions were found above 1710 cm(-1) where stretching vibrations of protonated carboxyl groups from aspartic or glutamic acid side chains absorb. With the help of site-directed mutagenesis and hydrogen/deuterium isotope exchange, it was possible to identify amino acid residue Glu C180, which is located in the membrane-spanning, diheme-containing subunit C of QFR, as being partially responsible for the derivative-shaped spectral feature with a peak/trough at 1741/1733 cm(-1) in the reduced-minus-oxidized difference spectrum. This signal pattern is interpreted as a superposition of a protonation/deprotonation and a change of the hydrogen-bonding environment of Glu C180. This residue is the principal constituent of the recently proposed "E-pathway hypothesis" of coupled transmembrane proton and electron transfer in QFR [Lancaster, C. R. D. (2002) Biochim. Biophys. Acta 1565, 215-231]. Thus, the study presented yields experimental evidence which supports a key role of Glu C180 within the framework of the E-pathway hypothesis.

Amino Acids↗
PubMed2006

Regulation of mouse hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase, a key enzyme in the tryptophan-nicotinamide adenine dinucleotide pathway, by hepatocyte nuclear factor 4alpha and peroxisome proliferator-activated receptor alpha.

Nicotinamide adenine dinucleotide (NAD) plays a critical role in the maintenance of cellular energy homeostasis. alpha-Amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) is the key enzyme regulating de novo synthesis of NAD from l-tryptophan (Trp), designated the Trp-NAD pathway. Acmsd gene expression was found to be under the control of both hepatocyte nuclear factor 4alpha (HNF4alpha) and peroxisome proliferator-activated receptor alpha (PPARalpha). Constitutive expression of ACMSD mRNA levels were governed by HNF4alpha and downregulated by activation of PPARalpha by the ligand Wy-14,643 ([4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid]), as revealed by studies with hepatic HNF4alpha-null mice and PPARalpha-null mice, respectively. Transient transfection and electrophoretic mobility shift analyses showed an HNF4alpha binding site in the Acmsd gene promoter that directed transactivation of reporter gene constructs by HNF4alpha. The Acmsd promoter was not responsive to PPARalpha in transactivation assays. Wy-14,643 treatment decreased HNF4alpha protein levels in wild-type, but not PPARalpha-null, mouse livers, with no changes in HNF4alpha mRNA. These results show that Wy-14,643, through PPARalpha, post-transcriptionally down-regulates HNF4alpha protein levels, leading to reduced expression of the HNF4alpha target gene Acmsd.

Animals↗
PubMed2006

ATM-mediated response to DNA double strand breaks in human neurons derived from stem cells.

Ataxia-telangiectasia (A-T) is a multi-system genomic instability syndrome that is caused by loss or inactivation of the ATM protein kinase. ATM is largely nuclear in proliferating cells, and activates an extensive network of pathways in response to double strand breaks (DSBs) in the DNA by phosphorylating key proteins in these pathways. The prominent symptom of A-T is neuronal degeneration, making the elucidation of ATM's functions in neurons essential to understanding the disease. It has been suggested that ATM is cytoplasmic in neurons and functions in processes that are not associated with the DNA damage response. Recently we showed that in human neuron-like cells obtained by in vitro differentiation of neuroblastomas, ATM was largely nuclear and mediated the DSB response as in proliferating cells. We have now extended these studies to two additional model systems: neurons derived from human embryonic stem cells, and cortical neurons derived from neural stem cells. The results substantiate the notion that ATM is nuclear in human neurons and mediates the DSB response, the same as it does in proliferating cells. We present here unique and powerful model systems to further study the ATM-mediated network in neurons.

Ataxia Telangiectasia↗
PubMed2000

Regulation of cholesterol biosynthetic pathway in patients with the Smith-Lemli-Opitz syndrome.

The Smith-Lemli-Opitz syndrome (SLOS) is a recessively inherited birth disorder caused by a defect in 7-dehydrocholesterol (3beta-hydroxysteroid) delta7-reductase, the final enzyme in cholesterol biosynthesis. To investigate in vivo regulation of the cholesterol biosynthetic pathway in SLOS, we measured hepatic microsomal sterol concentrations and activities of several key enzymes in the pathway, including HMG-CoA synthase, HMG-CoA reductase, squalene synthase and 7-dehydrocholesterol delta7-reductase in liver specimens from a patient with SLOS and 11 controls. Hepatic microsomal 7-dehydrocholesterol delta7-reductase activity in the patient was less than 1% of the control mean, and decreased cholesterol concentration and markedly increased 7- and 8-dehydrocholesterol concentrations were observed in the patient's microsomes. HMG-CoA synthase and squalene synthase activities in the patient were upregulated to 149% and 532%, respectively, while the activity of HMG-CoA reductase, the rate-limiting enzyme in the pathway, was reduced to 39% of the control mean. Downregulation of HMG-CoA reductase activity in SLOS was supported by measuring plasma levels of mevalonic acid, the immediate product of HMG-CoA reductase. The levels in SLOS patients (n = 9) were significantly low compared with age-matched controls (n = 8) (12+/-2 vs 28 + 6nmol/L, p < 0.05). These results suggest that in most SLOS patients in vivo HMG-CoA reductase is not stimulated in spite of blocked cholesterol biosynthetic pathway and reduced plasma and hepatic cholesterol concentrations.

Case-Control Studies↗