Search PubMed⌕ Search

Biomedical subjects

C Chen

Publications and source records attributed to C Chen.

At least 433 records · Page 24Linked to original sources
PubMed1999

The membrane association domain of RGS16 contains unique amphipathic features that are conserved in RGS4 and RGS5.

Regulators of G protein signaling (RGS proteins) modulate G protein-mediated signaling pathways by acting as GTPase-activating proteins for Gi, Gq, and G12 alpha-subunits of heterotrimeric G proteins. Although it is known that membrane association is critical for the biological activities of many RGS proteins, the mechanism underlying this requirement remains unclear. We reported recently that the NH2 terminus of RGS16 is required for its function in vivo. In this study, we show that RGS16 lacking the NH2 terminus is no longer localized to the plasma membrane as is the wild type protein, suggesting that membrane association is important for biological function. The region of amino acids 7-32 is sufficient to confer the membrane-targeting activity, of which amino acids 12-30 are predicted to adopt an amphipathic alpha-helix. Site-directed mutagenesis experiments showed that the hydrophobic residues of the nonpolar face of the helix and the strips of positively charged side chains positioned along the polar/nonpolar interface of the helix are crucial for membrane association. Subcellular fractionation by differential centrifugation followed by conditions that distinguish peripheral membrane proteins from integral ones indicate that RGS16 is a peripheral membrane protein. We show further that RGS16 membrane association does not require palmitoylation. Our results, together with other recent findings, have defined a unique membrane association domain with amphipathic features. We believe that these structural features and the mechanism of membrane association of RGS16 are likely to apply to the homologous domains in RGS4 and RGS5.

Amino Acid Sequence↗
PubMed1999

Study of diet, biomarkers and cancer risk in the United States, China and Costa Rica.

One striking paradox in epidemiologic research is the strong association between diet and cancer in ecologic studies compared with the weaker associations reported in many within-country case-control and cohort studies. However, most ecologic studies have relied on indirect measures of dietary intake, such as food disappearance data. The objectives of our study were to assess the feasibility of collecting dietary and biomarker data from individuals living in countries having markedly different dietary patterns and cultures and to examine the magnitude of the between-country variation in their measurement. Adults surveyed in Shanghai (China), Costa Rica and King County (Washington, USA) completed a 24-hr dietary recall, a cancer risk factor survey, and provided a blood sample. We analyzed a subset of the blood specimens for vitamins C, E, carotenoids and phospholipid fatty acids. We observed substantial differences in nutrient intakes and in mean plasma concentrations of dietary biomarkers across the study populations. For example, King County participants had the highest daily intake of vitamin C (mean 78.3 +/- 12.2 mg compared with 42.6 +/- 38.3 mg in Shanghai and 34.8 +/- 43.8 mg in Costa Rica). The mean plasma vitamin C level in King County was also the highest of the 3 study sites: 927.9 +/- 43.9 microg/dl in King County, 585.7 +/- 35.9 microg/dl in Shanghai and 461.1 +/- 33.1 microg/dl in Costa Rica. Plasma trans fatty acids (a biomarker of a diet high in hydrogenated fats) were highest in King County and lowest in Shanghai.

Adult↗
PubMed1999

The antioxidant EPC-K1 attenuates NO-induced mitochondrial dysfunction, lipid peroxidation and apoptosis in cerebellar granule cells.

In this study we investigated the effects of nitric oxide (NO) on cultured cerebellar granule cells. Exposure to NO donors, S-nitrosoglutathione (GSNO; 250 microM) or sodium nitroprusside (SNP; 500 microM), triggered apoptosis in immature cultures of cerebellar granule cells, which was characterized by chromatin condensation, nuclei fragmentation, and DNA laddering. Exposure of cerebellar granule cells to NO donors led to a decrease in the mitochondrial transmembrane potential and intracellular ATP content, which suggested that NO treatment caused mitochondrial dysfunction. NO treatment also induced oxidative stress in cerebellar granule cells as measured by thiobarbituric acid (TBA) assay. Pretreating cells with L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H -1-benzopyran-6-yl-hydrogen phosphate] potassium salt (EPC-K1), a novel antioxidant, attenuated NO-induced mitochondrial dysfunction and oxidative stress to some extent, and prevented the cells from apoptosis. The results of the present investigation suggest that a superoxide/peroxynitrite-mediated oxidative stress may be an important pathway leading to NO-associated neuronal damage. Pretreating cells with the antioxidant EPC-K1 attenuated NO-induced neurotoxicity by scavenging superoxide/peroxynitrite and/or its breakdown products.

Animals↗
PubMed1999

A new structure for the murine Xist gene and its relationship to chromosome choice/counting during X-chromosome inactivation.

In this report, we present structural data for the murine Xist gene. The data presented in this paper demonstrate that the murine Xist transcript is at least 17.4 kb, not 14.3 kb as previously reported. The new structure of the murine Xist gene described herein has seven exons, not six. Exon VII encodes an additional 3.1 kb of information at the 3' end. Exon VII contains seven possible sites for polyadenylation; four of these sites are located in the newly discovered 3' end. Consequently, it is possible that several distinct transcripts may be produced through differential polyadenylation of a primary transcript. Alternative use of polyadenylation signals could result in size changes for exon VII. Two major species of Xist are detectable by Northern analysis, consistent with differential polyadenylation. In this paper, we propose a model for the role of the Xist 3' end in the process of X-chromosome counting and choice during embryonic development.

3' Untranslated Regions↗
PubMed1999

Inhibition of ubiquitin-proteasome pathway activates a caspase-3-like protease and induces Bcl-2 cleavage in human M-07e leukaemic cells.

The ubiquitin-proteasome pathway is the principal mechanism for the degradation of short-lived proteins in eukaryotic cells. Here we examine the possibility that ubiquitin-proteasome is involved in regulating the levels of Bcl-2, which is abundantly expressed in M-07e cells, a granulocyte/macrophage colony-stimulating factor (GM-CSF)-dependent human leukaemic cell line. Apoptosis in M-07e cells, induced by GM-CSF withdrawal, was associated with a gradual cleavage of Bcl-2 into a 22 kDa fragment. Treatment of M-07e cells with benzyloxycarbonyl-Leu-Leu-l-leucinal (Z-LLL-CHO; MG-132), a reversible ubiquitin-proteasome inhibitor, markedly accelerated the cleavage of Bcl-2 and promoted cell death through the apoptotic pathway. The cleavage of Bcl-2 was inhibited by a caspase-3 (CPP32)-specific inhibitor [acetyl-Asp-Glu-Val-Asp-CHO (DEVD-CHO)] but not caspase 1 inhibitor (acetyl-Tyr-Val-Ala-Asp-CHO), suggesting that Bcl-2 is a proteolytic substrate of a caspase-3-like protease activated during apoptosis. The simultaneous addition of recombinant human GM-CSF (rhGM-CSF) to M-07e cultures delayed the activation of caspase 3 and Bcl-2 cleavage triggered by Z-LLL-CHO, suggesting that the activation of the GM-CSF signalling pathway can partly overcome the apoptotic effect induced by Z-LLL-CHO. Apoptosis induced by inhibition of the proteasome pathway was verified in studies with lactacystin, a highly specific and irreversible proteasome inhibitor. Lactacystin-induced apoptosis in M-07e cells was remarkably similar to that induced by Z-LLL-CHO, which included caspase 3 activation, cleavage of Bcl-2 into a 22 kDa fragment and, ultimately, cell death. These results showed that inhibition of the ubiquitin-proteasome pathways can lead to the activation of a DEVD-CHO-sensitive caspase and induces Bcl-2 cleavage, which might have a role in mediating apoptosis in M-07e cells.

Acetylcysteine↗
PubMed1999

Association of the androgen receptor gene (AR) with ADHD and conduct disorder.

The male predominance of externalizing behaviors suggests that the X-linked androgen gene might be involved. Since the shorter alleles of the CAG and GGC polymorphisms of the AR gene are associated with increased gene expression we sought to determine whether they were also associated with externalizing behaviors. We examined 302 subjects consisting of Tourette syndrome probands and controls. ANOVA showed a significant association between the AR haplotypes and ADHD (p < 0.0001), conduct disorder (CD; p < 0.017), and oppositional defiant disorder (ODD; p < 0.004) with the lowest scores in those with the longer alleles at both polymorphisms. These results suggest that genetic variation at the human AR gene plays a role in human externalizing disorders.

Adolescent↗
PubMed1999

Sea urchin TgBMP2/4 gene encoding a bone morphogenetic protein closely related to vertebrate BMP2 and BMP4 with maximal expression at the later stages of embryonic development.

We have cloned a gene fragment (named TgBMP2/4) that encodes a protein homologous to vertebrate bone morphogenetic protein (BMP) 2 and BMP4 in the sea urchin Tripneustes gratilla. This peptide sequence contains 204 amino acids with 7 conserved cysteine residues at the C-terminus of the coding region and a cluster of basic amino acids that may serve as a signal for proteolytic cleavage. Sequence comparison and phylogenetic analyses reveal that TgBMP2/4 is closely related to vertebrate BMP2 and BMP4 as well as to amphioxus BMP2/4, with similarity levels ranging from 90% to 94% at the mature C-terminal domain. Northern blot analyses show that a 6.3-kb TgBMP2/4 mRNA appears first at the mesenchyme blastula stage and increases to a maximal level at the gastrula and pluteus stages. This expression pattern is different from that of a BMP2/4-related gene previously found in sea urchin.

Amino Acid Sequence↗
PubMed1999

Subcellular distribution of selenium and Se-containing proteins in human liver.

Selenium is an essential trace element in many living organisms. In the present paper, the subcellular distribution of selenium and Se-containing proteins in human liver samples, which were obtained from normal subjects who had an accidental death, was investigated by differential centrifugation and column chromatography. Selenium was mainly enriched in nuclei, mitochondria and cytosol. Almost half of Se existed in the nuclei due to their large amount in liver and high Se concentration. 15-30% of Se was found in small compounds with Mr<2000 in the liver components separated by dialysis. The average abundance of Se in small molecular mass species of whole-liver was 23.6%, which suggested most of Se associated with biological macromolecules. Eight kinds of Se-containing proteins with molecular mass of 335+/-20, 249+/-15, 106+/-11, 84.6+/-5.8, 70. 5+/-5.4, 45.6+/-1.5, 14.8+/-2.6, 8.5+/-1.2 kDa were found in the subcellular fractions of human liver. Among them the 335, 84.6 and 8. 5 kDa proteins were individually present in one subcellular fraction, whereas the others coexisted in two, three or four subcellular fractions. The most abundant Se-containing proteins, 70.5 and 14.8 kDa, accounted for 33.6% and 48.5% in the whole-liver soluble Se-containing protein, respectively. The former was enriched in cytosol and the latter was mainly present in nuclei and mitochondria.

Adult↗
PubMed1999

Antioxidant properties of EPC-K1: a study on mechanisms.

Scavenging effects of L-ascorbic acid 2-[3,4-dihydro-2,5,7,8- tetramethyl-2-(4,8,12-trimethytridecyl)-2H-1-benzopyran- 6-yl-hydrogen phosphate] potassium salt (EPC-K1) on hydroxyl radicals, alkyl radicals and lipid radicals were studied with ESR spin trapping techniques. The inhibition effects of EPC-K1 on lipid peroxidation were assessed by TBA assay. The kinetics of EPC-K1 reacting with hydroxyl radicals and linoleic acid radicals were studied by pulse radiolysis. The active site of EPC-K1 and the structure-antioxidative activity relationships were discussed. The superoxide radicals scavenging capacity of the brain homogenate of EPC-K1-treated rats was measured. The results revealed that in comparison with Trolox and vitamin C, EPC-K1 showed better overall antioxidative capacity in vitro and in vivo. EPC-K1 was a moderate scavenger on hydroxyl radicals and alkyl radicals, a potent scavenger on lipid radicals, and an effective inhibitor on lipid peroxidation. EPC-K1 could react with hydroxyl radicals with a rate constant of 7.1 x 10(8) dm3 mol-1 s-1 and react with linoleic acid radicals with a rate constant of 2.8 x 10(6) dm3 mol-1 s-1. The active site of EPC-K1 was the enolic hydroxyl group. After administration of EPC-K1, the ability of rat brain to scavenge superoxide radicals was significantly increased. The potent scavenging effects of EPC-K1 on both hydrophilic and hydrophobic radicals were relevant with its molecular structure, which consisted of both hydrophilic and hydrophobic groups.

Animals↗
PubMed1999

Functional role of the spatial proximity of Asp114(2.50) in TMH 2 and Asn332(7.49) in TMH 7 of the mu opioid receptor.

We examined whether a proposed spatial proximity between Asp114(2.50) and Asn332(7.49) affected the functional properties of the mu opioid receptor. The D114(2.50)N mutant had reduced binding affinities for morphine, DAMGO and CTAP, but not for naloxone and [3H]diprenorphine; this mutation also abolished agonist-induced increase in [35S]GTPgammaS binding. The N332(7.49)D mutation eliminated detectable binding of either [3H]diprenorphine or [3H]DAMGO. The combined D114(2.50)N-N332(7.49)D mutation restored high affinity binding for [3H]diprenorphine, CTAP and naloxone, and restored partially the binding affinities, potencies and efficacies of morphine and DAMGO. Thus, reciprocal mutations of Asp114(2.50) and Asn332(7.49) compensate for the detrimental effects of the single mutations, indicating that the residues are adjacent in space and that their chemical functionalities are important for ligand binding and receptor activation.

Animals↗
PubMed1999

Prolactin-releasing peptide-immunoreactivity in A1 and A2 noradrenergic neurons of the rat medulla.

Distribution of prolactin-releasing peptide-like immunoreactivity (PrRP-LI) was investigated in the rat medulla with the use of a rabbit polyclonal antiserum against the human PrRP-31 peptide. PrRP-positive neurons were noted mainly in two areas of the caudal medulla: ventrolateral reticular formation and commissural nucleus of the nucleus of the solitary tract (NTS), corresponding to the A1 and A2 areas. PrRP-LI neurons were absent in the medulla rostral to the area postrema. Double-labeling the sections with PrRP antisera and tyrosine hydroxylase (TH) monoclonal antibodies revealed extensive colocalization of PrRP- and TH-like immunoreactivity (TH-LI) in neurons of the A1 and A2 areas. Our results show that PrRP-LI is expressed in a population of A1 and A2 noradrenergic neurons of the rat caudal medulla.

Animals↗
PubMed1999

Familial aggregation of blood pressure in a rural Chinese community.

This study investigated blood pressure in 1,183 Chinese nuclear families (mother, father, and first two children) via a cross-sectional 1994-1997 survey. The mother's, the father's, and the first sibling's blood pressures were each significantly and independently related to the second sibling's blood pressure after adjustment for sex, age, height, weight, education, smoking, and alcohol consumption. The association was consistent across the four age strata (6-10, 11-14, 15-19, and > or = 20 years). The rate of high systolic blood pressure in the second sibling was lowest (2.3%) when both parents and the first sibling were in the low blood pressure tertile (low-low group) and highest (26.0%) when these family members were in the high blood pressure tertile (high-high group). The rate was intermediate if only the parents (10.7%, high-low group) or the first sibling (8.4%, low-high group) was in the high blood pressure tertile. As compared with the low-low group, the odds ratios for the high-high, high-low, and low-high groups were 14.3 (95% confidence interval 4.3-48.2), 4.3 (95% confidence interval 1.2-15.6), and 3.9 (95% confidence interval 1.1-14.4), respectively. A similar pattern was found for diastolic blood pressure. The data indicate a strong familial aggregation of blood pressure in this population and show that such a familial influence on blood pressure can be detected from early childhood onward.

Adolescent↗
PubMed1999

The prosurvival Bcl-2 homolog Bfl-1/A1 is a direct transcriptional target of NF-kappaB that blocks TNFalpha-induced apoptosis.

Bcl-2-family proteins are key regulators of the apoptotic response. Here, we demonstrate that the pro-survival Bcl-2 homolog Bfl-1/A1 is a direct transcriptional target of NF-kappaB. We show that bfl-1 gene expression is dependent on NF-kappaB activity and that it can substitute for NF-kappaB to suppress TNFalpha-induced apoptosis. bfl-1 promoter analysis identified an NF-kappaB site responsible for its Rel/NF-kappaB-dependent induction. The expression of bfl-1 in immune tissues supports the protective role of NF-kappaB in the immune system. The activation of Bfl-1 may be the means by which NF-kappaB functions in oncogenesis and promotes cell resistance to anti-cancer therapy.

Apoptosis↗
PubMed1999

Innate immunity in insects: the role of multiple, endogenous serum lectins in the recognition of foreign invaders in the cockroach, Blaberus discoidalis.

Unlike vertebrates, insects do not have an Ab-based nonself recognition system, and must rely totally on innate immunity to defend themselves from microbial invaders. The most likely candidates for recognizing foreign material in insects are the lectins, which have already been shown to be important in mammalian innate immunity. The hemolymph of the cockroach, Blaberus discoidalis, contains multiple lectins, designated BDL1, BDL2, BDL3, and GSL (beta-1,3-glucan-specific lectin), two of which, namely BDL1 and GSL, have close similarities to acute phase reactants. These endogenous molecules, as well as Con A, wheat germ agglutinin, and Helix pomatia agglutinin, have been shown to induce an enhanced phagocytic response by B. discoidalis plasmatocytes. This effect is related to the carbohydrates presented on the surface of the microorganism and to the sugar specificities of the lectins. Thus, the mannose-specific lectins, BDL1 and Con A, both increase the phagocytosis of baker's yeast and Escherichia coli, whereas the N-acetyl-D-glucosamine/N-acetyl-D-galactosamine-specific lectins, BDL2, wheat germ agglutinin, and H. pomatia agglutinin, induce the phagocytosis of Bacillus cereus and E. coli. GSL, specific for beta-1,3-glucan, and the N-acetyl-D-galactosamine-specific BDL3, only enhance the phagocytosis of yeast and B. cereus, respectively. Phenylthiourea, an inhibitor of the prophenoloxidase system, caused either total, partial, or no inhibition of the lectin-induced increase in phagocytosis, indicating that this immune enhancement results, in some cases, from at least two closely linked mechanisms. These results show that the endogenous lectins in the cockroach hemolymph are capable of acting as nonself recognition molecules for a wide range of microorganisms, and thus obviate the necessity of Abs in these animals.

Animals↗
PubMed1999

Growth hormone and the expression of mRNAs for matrix proteins and oncogenes in bone.

To examine the effects of growth hormone (GH) on the expression of the mRNAs of bone matrix proteins, three experiments were carried out with 3-month-old female Sprague-Dawley rats. In the first experiment rats were given a single subcutaneous injection of recombinant human GH (8 mg rhGH/kg b. wt.), sacrificed 15 min, 1 h, 2 h, 4 h, 8 h, 16 h and 24 h later, and RNA isolated from cancellous bone from the distal femoral metaphysis. Growth hormone increased the level of type I collagen mRNA by 187, 417, and 509% over the control level at 15 min, 1 h and 2 h, respectively; the mRNA levels declined to 119 and 99% at 4 and 8 h, respectively, and then rose again to 351 and 423% over the control level at 16 and 24 h, respectively. Osteocalcin mRNA transcript increased by 89, 90, 325, 342, 361, and 407% over the control level at 15 min, 1 h, 2 h, 4 h, 8 h and 16 h, respectively, and fell to 66% at 24 h. The level of IGF-I mRNA increased by 45, 83, 120, 140, and 175% over the control level at 2, 4, 8, 16, and 24 h, respectively. In the second experiment, following the administration of rhGH (8 mg/kg b. wt.) bone osteocalcin mRNA increased by 127, 177, 361, and 413% over the control level at 30 min, 1 h, 2 h and 4 h, respectively; IGF-I mRNAs increased by 38, 33, 87, and 437 at 30 min, 1 h, 2 h and 4 h, respectively, but the levels did not become significant until 2 h; c-fos mRNA increased significantly at 30 min, and c-jun and c-myc mRNAs did not increase until 4 h. In the third experiment, animals were given a single injection of rhGH (8 mg/kg b. wt.) and the animals were bled at timed intervals and acid ethanol-extractable serum IGF-I determined. Serum IGF-I increased significantly only at 12 h following rhGH administration. Our data indicate that GH stimulates a rapid increase in the expression of mRNAs for the bone matrix proteins, type I collagen and osteocalcin, by a mechanism that appears to be independent of IGF-I, the early response oncogenes or an increase in osteoblast number.

Animals↗
PubMed1999

High affinity very late antigen-4 subsets expressed on T cells are mandatory for spontaneous adhesion strengthening but not for rolling on VCAM-1 in shear flow.

The very late Ag-4 (VLA-4) integrin supports both rolling and firm adhesion of leukocytes on VCAM-1 under shear flow. The molecular basis for the unique ability of a single adhesion molecule to mediate these versatile adhesive processes was investigated. VLA-4 occurs in multiple activation states, with different affinities to ligand. In this study we tested how these states regulate VLA-4 adhesiveness under shear flow in Jurkat T cells and PBL. VLA-4 on nonstimulated Jurkat cells supported rolling and spontaneous arrest on VCAM-1, whereas a Jurkat activation mutant with reduced VLA-4 affinity failed to spontaneously arrest after tethering to or during rolling on VCAM-1. The contribution of VLA-4 affinity for ligand to rolling and spontaneous arrests on immobilized VCAM-1 was dissected using soluble VLA-4 ligands, which selectively block high affinity states. VLA-4 saturation with ligand completely blocked spontaneous adhesion strengthening post-tethering to VCAM-1, but did not impair rolling on the endothelial ligand. High affinity VLA-4 was found to comprise a small subset of VLA-4 on resting Jurkat cells and PBL. This subset is essential for firm adhesion but not for tethering or rolling adhesions on VCAM-1. Interestingly, low and high affinity VLA-4 states were found to mediate similar initial tethering to ligand. High affinity VLA-4, constitutively expressed on circulating T cells, may control their early adhesion strengthening on VCAM-1-expressing endothelium before exposure to vascular chemokines and activation of additional integrins.

Cell Adhesion↗