Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 865 records · Page 48Linked to original sources

PubMed2000

Stimulus-specific signaling pathways in rabbit carotid body chemoreceptors.

The carotid body is an arterial chemosensory organ which responds to multiple natural and pharmacological stimuli, including hypoxia and nicotine. Numerous studies have investigated the initial molecular events which activate chemosensory type I cells in the carotid body, but less attention has been focused on later steps in the transduction cascade, which mediate neurotransmitter release from type I cells and excitation of chemoreceptor afferent fibers in the carotid sinus nerve. In the present study, we examined the effects of a highly specific inhibitor of calcium/calmodulin-dependent kinase II, KN-62, and a calmodulin inhibitor, trifluoperazine, on carotid sinus nerve activity and catecholamine release evoked from rabbit carotid bodies superfused in vitro. KN-62 did not alter sinus nerve activity and catecholamine release evoked by hypoxia, but this agent significantly reduced nerve activity and neurotransmitter release evoked by 100 microM nicotine. Trifluoperazine (10 microM), likewise inhibited activity evoked by nicotine, as well as hypoxia. Basal levels of nerve activity and catecholamine release (established in superfusate equilibrated with 100% O2) were unaffected by all drug treatments. Separate biochemical experiments showed that Ca2+/calmodulin-dependent incorporation of 32P into carotid body particulate proteins is significantly reduced following incubation of intact carotid bodies in nicotine, but not following exposure to hypoxia. Our observations suggest that excitation of the carotid body by diverse stimuli may involve the activation of distinct, stimulus-specific transduction pathways. Furthermore, these data correlate with our previous findings which showed that hypoxia, on the one hand, and nicotine on the other, evoke the preferential release of either dopamine or norepinephrine, respectively, from carotid bodies incubated in vitro.

Animals↗

PubMed2000

16S rDNA sequence analysis of Xylella fastidiosa strains.

The 16S rDNA encoding the small subunit ribosomal RNA were amplified by PCR, cloned, and sequenced from 16 strains of Xylella fastidiosa originating from nine different hosts. In pair-wise comparisons, X. fastidiosa strains showed a maximum variation of 1.0% or 14 nucleotide positions. When all 16 sequences were considered as a set, 54 variable positions were found. Analysis of the sequence data indicated that the X. fastdiosa strains formed three rDNA groups. Group one includes Pierce's disease and mulberry leaf scorch strains; Group two, periwinkle wilt, plum leaf scald, phony peach, oak leaf scorch, and elm leaf scorch strains; and Group three, citrus variegated chlorosis and coffee leaf scorch strains. All X. fastidiosa strains exhibited significantly higher levels of sequence heterogeneity (63 to 83 nucleotide positions) when compared to species from Xanthomonas and Stenotrophomonas. Our data demonstrate that 16S rDNA sequence data could provide valuable information for future classification of X. fastidiosa at the sub-species level.

DNA, Ribosomal↗

PubMed2000

Rapid and reproducible deactivation of rhodopsin requires multiple phosphorylation sites.

Efficient single-photon detection by retinal rod photoreceptors requires timely and reproducible deactivation of rhodopsin. Like other G protein-coupled receptors, rhodopsin contains multiple sites for phosphorylation at its COOH-terminal domain. Transgenic and electrophysiological methods were used to functionally dissect the role of the multiple phosphorylation sites during deactivation of rhodopsin in intact mouse rods. Mutant rhodopsins bearing zero, one (S338), or two (S334/S338) phosphorylation sites generated single-photon responses with greatly prolonged, exponentially distributed durations. Responses from rods expressing mutant rhodopsins bearing more than two phosphorylation sites declined along smooth, reproducible time courses; the rate of recovery increased with increasing numbers of phosphorylation sites. We conclude that multiple phosphorylation of rhodopsin is necessary for rapid and reproducible deactivation.

Animals↗

PubMed2000

Expression patterns of FHL/SLIM family members suggest important functional roles in skeletal muscle and cardiovascular system.

LIM domain containing proteins play critical roles in animal development and cellular differentiation. Here, we describe the cloning and expression patterns of three members of the four and a half LIM domain-only protein family, FHL1, 2, and 3, from mouse. A comparison of embryonic expression patterns of these three highly-related genes indicates that they are expressed in an overlapping pattern in the developing cardiovascular system, and skeletal muscle. In adult tissues, the three genes are expressed in a predominant and overlapping manner in cardiac and skeletal muscle. Of the three genes, FHL2 appears to have the most restricted expression pattern during development, in heart, blood vessels, and skeletal muscle. Expression in heart is highest in cardiac septa and in the region adjacent to the atrio-ventricular ring, suggesting a potential role in septation or conduction system development. In the heart, FHL1expression was observed strongly in developing outflow tract, and to a lesser extent in myocardium. FHL3 displays low and ubiquitous expression during mouse development. Cardiac ventricular expression of FHL1, but not FHL2 or FHL3, was upregulated in two mouse models of cardiac hypertrophic and dilated cardiomyopathy. Taken together, these data indicate the potential importance of this FHL family in the development and maintenance of the cardiovascular system and striated muscle, and suggest that FHL1 may play a role in the development of heart disease.

Amino Acid Sequence↗

PubMed2000

Synthesis of substituted indeno[1,2-b]quinoline-6-carboxamides, [1]benzothieno[3,2-b]quinoline-4-carboxamides and 10H-quindoline-4-carboxamides: evaluation of structure-activity relationships for cytotoxicity.

New substituted indeno[1,2-b]quinoline-6-carboxamides, [1]benzothieno[3,2-b]quinoline-4-carboxamides and 10H-quindoline-4-carboxamides were prepared from methyl 2-amino-3-formylbenzoate by a new Friedlander synthesis. Evaluation of these carboxamides for cytotoxicity in a panel of cell lines showed that small lipophilic substituents in the non-carboxamide ring, in a pseudo-peri position to the side chain, significantly increased cytotoxic potency while retaining a pattern of cytotoxicity consistent with a non-topo II mode of action. The methyl-substituted indeno[1,2-b]quinoline-6-carboxamide demonstrated substantial effectiveness (20-day growth delays) in a sub-cutaneous colon 38 in vivo tumor model. This is comparable to that reported for the dual topo I/II inhibitor DACA that is in clinical trial.

Animals↗

PubMed2000

Stereo-enriched phosphorothioate oligodeoxynucleotides: synthesis, biophysical and biological properties.

Stereo-enriched [Rp] and [Sp]-phosphorothioate oligodeoxynucleotides are synthesized using oxazaphospholidine derivatized monomers. Three different designs of phosphorothioate oligodeoxynucleotides (PS-oligos), (i) stereo-enriched all-[Rp] or all-[Sp] PS-linkages, (ii) stereo-random mixture of PS-linkages, and (iii) segments containing certain number of stereo-enriched [Rp] and [Sp] PS-linkages ([Sp-Rp-Sp] or [Rp-Sp-Rp]), have been studied. Thermal melting studies of these PS-oligos with RNA complementary strands showed that the binding affinities are in the order [Rp] > [Sp-Rp-Sp]-[Rp-Sp-Rp] > stereo-random > [Sp]. Circular dichroism (CD) studies suggest that the stereochemistry of the PS-oligo does not affect the global conformation of the duplex. The in vitro nuclease stability of these PS-oligos is in the order [Sp] > [Sp-Rp-Sp] > stereo-random > [Rp]. The RNase H activation is in the order [Rp] > stereo-random > [Rp-Sp-Rp] > [Sp] > [Sp-Rp-Sp]. Studies in a cancer cell line of PS-oligos targeted to MDM2 mRNA showed that all oligos had similar biological activity under the experimental conditions employed. Protein- and enzyme-binding studies showed insignificant stereo-dependent binding to proteins. The [Sp] and [Sp-Rp-Sp] chimeric and stereo-random PS-oligos that contained a CpG motif showed higher cell proliferation than [Rp] PS-oligo of the same sequence.

Animals↗

PubMed2000

Substance use in high school students in New South Wales, Australia, in relation to language spoken at home.

PURPOSE: To examine for the first time adolescent substance use by ethnicity, given the high proportion of migrants from non-English-speaking countries in New South Wales, (NSW), Australia. METHODS: Data from four surveys of NSW secondary school students in 1983, 1986, 1989, and 1992 were used for this analysis. The prevalence of substance use by whether English was spoken at home was stratified by sex and age using data from the most recent survey year. Adjusted odds ratios and 95% confidence intervals were produced by simultaneous logistic regression, adjusting for sex, age group, and the interaction term of sex and age for each of these substances, and for each survey year separately. Data from 1989 and 1992 were pooled together to examine rates of substance use by ethnic subgroups which reflect migration patterns. RESULTS: The prevalence of smoking and alcohol and illicit drug use was consistently lower among NSW adolescents speaking a language other than English at home, compared with those speaking English at home in all survey years. Only the prevalence of solvent sniffing was higher among younger adolescents speaking a language other than English at home. Students from Southeast Asia showed consistently lower rates of usage of all substances compared to all other groups. CONCLUSIONS: There may be different opportunities for the prevention of adolescent substance use among native English speakers to be gained from non-English-speaking cultures.

Adolescent↗

PubMed2000

Deletion of germline promoter PD beta 1 from the TCR beta locus causes hypermethylation that impairs D beta 1 recombination by multiple mechanisms.

The role of the germline transcriptional promoter, PD beta 1, in V(D)J recombination at the T cell receptor beta locus was investigated. Deletion of PD beta 1 caused reduced germline transcription and DNA hypermethylation in the Dbeta1-J beta 1 region and decreased D beta 1 rearrangement. Analyses of methylation levels surrounding recombination signal sequences (RSS) before, during, and after recombination revealed that under physiological conditions cleavage of hypomethylated alleles was preferred over hypermethylated alleles. Methylation of a specific CpG site within the heptamer of the 3' D beta 1 RSS was incompatible with cleavage by the V(D)J recombinase. These findings suggest that methylation can regulate V(D)J recombination both at a general level by influencing regional chromatin accessibility and specifically by blocking RSS recognition or cleavage by the V(D)J recombinase.

Animals↗

PubMed2000

A proposed mechanism for the induction of cytotoxic T lymphocyte production by heat shock fusion proteins.

A 65 kDa mycobacterial heat shock protein (hsp65), fused to a polypeptide that contains an octapeptide (SIYRYYGL) agonist for a particular T cell receptor (2C TCR), stimulated C57BL/6 mice as well as CD4-deficient mice to produce CD8+ cytolytic T lymphocytes (CTL) to the fusion partner's octapeptide. This and other hsp65 fusion proteins but not native hsp65 itself stimulated dendritic cells in vitro and in vivo to upregulate the levels of MHC (class I and II) and costimulatory (B7.2) molecules. The results suggest a mechanism for the general finding that hsp fusion proteins, having fusion partners of widely differing lengths and sequences, elicit CD8 CTL to peptides from the fusion partners without requiring exogenous adjuvants or the participation of CD4+ T cells.

Animals↗

PubMed2000

Erect bipedal stance exercise partially prevents orchidectomy-induced bone loss in the lumbar vertebrae of rats.

This study investigates the responses of the fourth and fifth lumbar vertebral bodies of 6-month-old male Sprague-Dawley (SD) rats to orchidectomy (orx) and to erect bipedal stance for feeding for 12 weeks in specially designed raised cages (RC) for which the heights were raised from 20 cm to 35.5 cm. A total of 30 rats were divided into groups of: baseline; sham + housed in normal height cage (NC); orx + NC; sham + RC; and orx + RC. Bone histomorphometry was performed on the triple-labeled undecalcified fourth sagittal (LVL-4) and fifth transverse (LVX-5) sections. We found that orchidectomy induced high-turnover trabecular and cortical bone loss in the lumbar vertebrae. Forcing the rats to rise to erect stance for feeding reduced trabecular and cortical bone loss caused by orx. Apparently, depressing the elevated bone resorption next to the marrow induced by orx, and stimulating bone formation at the ventral periosteal surfaces, caused these effects. Orchidectomy and raised cage had similar effects on the two vertebrae except that the percentage of trabecular bone loss was greater in the LVL-4 than in LVX-5, and that bipedal stance exercise increased the total tissue area and mineral apposition rates (0-80 day interval) of ventral periosteal and dorsal endocortical surfaces of LVX-5 to a greater extent than it did in LVL-4. Such findings suggest that forcing rats to rise to an erect bipedal stance for feeding helps prevent loss of trabecular and cortical bone "mass," and presumably bone strength, in orchidectomized rats. This method also provides an inexpensive, noninvasive, reliable model to increase in vivo vertebral loading in rats that is similar in humans.

Animals↗

PubMed2000

Alteration in p53 modulates glial proteins in human glial tumour cells.

In transformed human glial cells, abnormalities of the p53 gene and altered expression of glial-specific properties (GSPs) have been observed. We therefore investigated whether (i) expression of the altered p53 protein is involved in the reduced expression of GSPs; and (ii) expression of the wild-type p53 (wt-p53) gene leads to induction of GSPs. We first determined that the p53 gene is mutated in human glioblastoma U-373MG cells. In these cells, and in human T-98G glioblastoma cells reported to possess a mutated p53 (m-p53) gene, nuclear m-p53 expression was intense while GSP expression was low in the same cell as revealed by double labelling immunocytochemistry. Conversely, glial fibrillary acidic protein (GFAP) and glutamate synthase (GS) were expressed in cells devoid of nuclear m-p53 immnunoreactivity. Therefore, a mutually exclusive relationship exists between the cytoplasmic GSPs and nuclear m-p53. Upon treatment with retinoic acid (RA) and dibutyryl cyclic AMP (dbcAMP), overall GSP staining were increased concomitant with suppression of nuclear m-p53. Their mutually exclusive expression pattern was maintained suggesting a functional relationship. This is supported by the observation of a similar mutually exclusive expression pattern for p53 and GSPs in pathologic specimens of human glioblastoma tissues. We then explored the role of the wt-p53 gene in the induction of GSPs using a wt-p53 tetracycline-regulated conditional expression system in human LN-Z308 glioblastoma cells. These cells normally express no p53 and no appreciable levels of GS or GFAP. Induced expression of wt-p53 lead to induction of GSP. These observations are consistent with the hypotheses that (i) nuclear m-p53 expression and cytoplasmic expression of GFAP and GS are inversely correlated, and (ii) expression of the wt-p53 gene leads to the expression of GSPs.

Amino Acid Sequence↗

PubMed2000

Steroid binding by antibodies and artificial receptors: exploration of theoretical methods to determine the origins of binding affinities and specificities.

Binding mode calculations for complexes between an artificial paracyclophane receptor and digoxins, cholic acids as well as cortisone steroids show encapsulation of different ring combinations. Docking experiments were performed between the 26-10 antibody and digoxins. Coordination affinity arises from hydrophobic desolvation and van der Waals interactions rather than from hydrogen bonds. The specificity and affinity arises mainly from shape complementarity. Computed binding free energies and Kohonen neural network computations both point to physicochemical and structural similarities of natural antibodies and artificial receptors.

Antibodies↗

PubMed2000

Cloning, tissue expression pattern and genomic organization of latexin, a human homologue of rat carboxypeptidase A inhibitor.

Latexin, a carboxypeptidase A inhibitor, is expressed in a cell type-specific manner in both central and peripheral nervous systems in the rat. It is used as a molecular marker for the regional specification of the neocortex. In this study, a cDNA was isolated from a human fetal brain cDNA library. The cDNA (LXN) contains an open reading frame encoding 222 amino acids. The comparison between the deduced amino acid sequences of LXN and latexins of rat and mouse revealed high sequence identity (84.2 and 84.7%, respectively). Northern blot analysis showed that LXN was expressed as a transcript of 1.3 kb in 15 out of 16 tissues examined, except in peripheral blood leukocyte. The expression levels were high in heart, prostate, ovary, kidney, pancreas, and colon, moderate or low in other tissues including brain. It is noteworthy that the tissue distribution of human LXN differs greatly to that of its homologue in the model animal, rat latexin. In addition, the LXN gene contains at least 6 exons and spans 5.9 kb according to the genomic sequence of the clone RP11-79M21 and the gap sequence cloned in this paper. LXN was assigned to 3q25-q26.2 according to the position of the marker SHGC-35682 found adjacent to LXN gene.

Amino Acid Sequence↗

PubMed2000

Heritability of life span in mice and its implication for direct and indirect selection for longevity.

We found high narrow-sense heritability of life span based on the regression of offspring on average parental (midparent) life spans. In two mouse populations prepared using the 4-way-cross design, mean +/- SE heritabilities were 62 +/- 11% (P < 0.001) and 44 +/- 15% (P < 0.01). To reflect inherited rates of aging, rather than resistance to early disease, data from the first 25% to die were deleted, so that only about 40% of families were used for offspring-midparent regressions. Heritabilities still remained high, 38% and 55%, for the same two populations, respectively. Populations studied in two other experiments did not show nearly as high heritabilities; in one case probably due to environmental stress, and in the other probably because the strains used did not have sufficient additive variance in genes regulating longevity. Significant heritabilities occurred only when a wild derived inbred strain was included in the 4-way cross. The age when a female ceased to reproduce appeared to be related to the life spans of her offspring, but only weakly, not approaching significance for any individual experiment. The age when a female became infertile was related to her life span, but the relationship disappeared when short-lived mice were excluded from the analysis. Our findings indicate that, in sufficiently diverse mouse populations, selection for increased longevity should be possible and that the direct selection for parental life span will be a more efficient strategy than selection for female reproductive life span.

Animals↗

PubMed2000

Germline mutation screening of the STK11/LKB1 gene in familial breast cancer with LOH on 19p.

The recently cloned STK11/LKB1 on chromosome 19p has been shown to be a new tumor suppressor gene. Mutations in the LKB1/STK11 gene on chromosome 19p account for most cases of Peutz-Jeghers syndrome (PJS), in which intestinal hamartomas are associated with elevated risks of several cancer types, including breast cancer. A previous study revealed that familial breast cancer is associated with loss of heterozygosity (LOH) on 19p. To establish whether germline mutations of STK11/LKB1 account for familial breast cancer, 22 patients from 14 breast cancer families with LOH on 19p and one PJS family were selected for screening for germline mutations of LKB1/STK11. A combination of polymerase chain reaction (PCR)-heteroduplex, single-strand conformational polymorphism (SSCP) analyses, Southern blot analysis and direct sequencing were used for mutation detection. No mutations were identified. Germline mutations of LKB1/STK11 did not contribute to breast cancer in these families.

AMP-Activated Protein Kinase Kinases↗

PubMed2000

Enhanced replication of HIV-1 in vivo in pigtailed macaques (Macaca nemestrina).

Non-human primate models for acquired immunodeficiency syndrome (AIDS) are important for studies of prevention and intervention strategies. Ideally, such models would make use of human immunodeficiency virus type 1 (HIV-1) and animals that are readily available for research. HIV-1 was obtained from an infected macaque, and passaged sequentially in three groups of two Macaca nemestrina neonates each. Evidence for enhanced viral replication was first found in one of the group 2 animals, and in both group 3 animals. Observations that underlie this conclusion are sustained viral recovery from peripheral blood mononuclear cells (PBMCs), increased and accelerated production of antiviral antibodies, and the ability to detect plasma viral ribonucleic acid (RNA) months after infection. There was no evidence of CD4 depletion in any of the animals during the follow-up period. These data suggest that a useful non-human primate model for AIDS can be attained in pigtailed macaques (M. nemestrina).

Acquired Immunodeficiency Syndrome↗

PubMed2000

Efficient retrovirus-mediated transfer of the multidrug resistance 1 gene into autologous human long-term repopulating hematopoietic stem cells.

Pre-clinical studies indicate that efficient retrovirus-mediated gene transfer into hematopoietic stem cells and progenitor cells can be achieved by co-localizing retroviral particles and target cells on specific adhesion domains of fibronectin. In this pilot study, we used this technique to transfer the human multidrug resistance 1 gene into stem and progenitor cells of patients with germ cell tumors undergoing autologous transplantation. There was efficient gene transfer into stem and progenitor cells in the presence of recombinant fibronectin fragment CH-296. The infusion of these cells was associated with no harmful effects and led to prompt hematopoietic recovery. There was in vivo vector expression, but it may have been limited by the high rate of aberrant splicing of the multidrug resistance 1 gene in the vector. Gene marking has persisted more than a year at levels higher than previously reported in humans.

Adolescent↗

PubMed2000

Overexpression of DeltaFosB transcription factor(s) increases bone formation and inhibits adipogenesis.

Members of the AP-1 family of transcription factors participate in the regulation of bone cell proliferation and differentiation. We report here a potent AP-1-related regulator of osteoblast function: DeltaFosB, a naturally occurring truncated form of FosB that arises from alternative splicing of the fosB transcript and is expressed in osteoblasts. Overexpression of DeltaFosB in transgenic mice leads to increased bone formation throughout the skeleton and a continuous post-developmental increase in bone mass, leading to osteosclerosis. In contrast, DeltaFosB inhibits adipogenesis both in vivo and in vitro, and downregulates the expression of early markers of adipocyte differentiation. Because osteoblasts and adipocytes are thought to share a common precursor, it is concluded that DeltaFosB transcriptionally regulates osteoblastogenesis, possibly at the expense of adipogenesis.

Adipocytes↗