Search PubMed⌕ Search

Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 235 records · Page 13Linked to original sources
PubMed2001

Prism adaptation to rightward optical deviation improves postural imbalance in left-hemiparetic patients.

Left-hemiparetic patients show predominant postural imbalance as compared to right-hemiparetic patients. The right hemisphere is crucial for generating internal maps used for perceptual and premotor processing of spatial information. Predominant postural imbalance with right-brain damage could thus result from a distortion of an internal postural map. Well-known manifestations of distorted internal maps due to right-hemisphere lesions, such as hemineglect, may show improvement following prism adaptation shifting the visual field to the right. We therefore investigated the effect of prism adaptation on postural imbalance in left-hemiparetic patients. Three groups of five patients were either adapted to prisms deviating the visual field to the right or left or exposed to neutral prisms while performing reaching movements of the right arm. Postural imbalance was reduced only following prism adaptation to the right. Thus, brief adaptation (i.e., 3 min) to rightward-shifting prisms can dramatically improve postural imbalance. This result shows that the effect of exposure to prisms that horizontally shift the visual field to the right in a reaching task generalizes to the postural system, and it suggests an interaction between horizontal and vertical reference frames. This also supports the theory that predominant postural imbalance in patients with right-brain damage may be partly related to a distortion of an internal postural map.

Adult↗
PubMed2001

Changes of absorption spectra during heat-induced denaturation of Photosystem II core antenna complexes CP43 and CP47: revealing the binding states of chlorophyll molecules in these two complexes.

The Photosystem II (PSII) core antenna complexes, CP43 and CP47, were prepared from spinach (Spinacia oleracea L.). The absorption spectra in the red region at room temperature were recorded for the PSII core antenna samples after increased temperature treatment (up to 80 degrees C). Derivative and difference spectra revealed the existence of two groups of chlorophyll a (Chl a) molecules in both CP43 and CP47. The one with the absorption peak in the shorter wavelength region was designated as CP43-669 and CP47-669, while the other with the absorption peak in the longer wavelength region was designated as CP43-682 and CP47-680. The results of the thermal treatment experiment demonstrated that CP43-669 and CP47-669 may exist as monomers of Chl a and that their binding sites on the polypeptides are insensitive to thermal treatment, whereas CP43-682 and CP47-680 may exist as dimers or multimers of Chl a and their binding regions in the polypeptide chains are more sensitive to heat treatment. The excitation energy transfer mechanism between these two different groups of Chl a molecules is also analyzed.

Apoproteins↗
PubMed2001

The phosphatidylinositol 3-kinase pathway selectively controls sIL-1RA not interleukin-1beta production in the septic leukocytes.

Microbial components such as bacterial endotoxin lipopolysaccharide (LPS) can trigger highly lethal septic shock. The cardinal features of septic leukocytes include the repressed production of inflammatory cytokines, such as interleukin-1 beta (IL-1beta), and elevated production of anti-inflammatory cytokines, such as secretory interleukin-1 receptor antagonist (sIL-1RA). Pro- and anti-inflammatory cytokine gene transcriptions are equally repressed in septic leukocytes due to disruption of the LPS signaling pathway at the level of interleukin-1 receptor-associated kinase. The selective elevation of sIL-1RA protein in septic blood is caused by efficient translation of residual sIL-1RA message. In this study, we report that the LPS-inducible phosphatidylinositol 3-kinase (PI3-kinase)-dependent signaling pathway contributes to the elevated translation of sIL-1RA in septic/LPS-adapted leukocytes. We also observe that this pathway is gene specific and does not affect the production of proinflammatory IL-1beta protein.

Cell Line↗
PubMed2001

Tryptase 4, a new member of the chromosome 17 family of mouse serine proteases.

Genomic blot analysis raised the possibility that uncharacterized tryptase genes reside on chromosome 17 at the complex containing the three genes that encode mouse mast cell protease (mMCP) 6, mMCP-7, and transmembrane tryptase (mTMT). Probing of GenBank's expressed sequence tag data base with these three tryptase cDNAs resulted in the identification of an expressed sequence tag that encodes a portion of a novel mouse serine protease (now designated mouse tryptase 4 (mT4) because it is the fourth member of this family). 5'- and 3'-rapid amplification of cDNA ends approaches were carried out to deduce the nucleotide sequence of the full-length mT4 transcript. This information was then used to clone its approximately 5.0-kilobase pair gene. Chromosome mapping analysis of its gene, sequence analysis of its transcript, and comparative protein structure modeling of its translated product revealed that mT4 is a new member of the chromosome 17 family of mouse tryptases. mT4 is 40-44% identical to mMCP-6, mMCP-7, and mTMT, and this new serine protease has all of the structural features of a functional tryptase. Moreover, mT4 is enzymatically active when expressed in insect cells. Due to its 17-mer hydrophobic domain at its C terminus, mT4 is a membrane-anchored tryptase more analogous to mTMT than the other members of its family. As assessed by RNA blot, reverse transcriptase-polymerase chain reaction, and/or in situ hybridization analysis, mT4 is expressed in interleukin-5-dependent mouse eosinophils, as well as in ovaries and testes. The observation that recombinant mT4 is preferentially retained in the endoplasmic reticulum of transiently transfected COS-7 cells suggests a convertase-like role for this integral membrane serine protease.

Amino Acid Sequence↗
PubMed2001

Cellular responses to ionizing radiation damage.

PURPOSE: The purpose of this report is to provide current perspectives on studies of DNA damage and cell cycle response after ionizing radiation, and their applications in radiation oncology. METHODS AND MATERIALS: Presentations at the Seventh Annual Radiation Oncology Workshop, held at the International Festival Institute at Round Top, TX, were summarized. RESULTS: Eighteen speakers presented their current work covering a wide range of studies on cellular responses to ionizing radiation. These presentations and discussions form the framework of our report. CONCLUSION: In response to ionizing radiation, cells immediately activate a series of biochemical pathways that promote cell survival while maintaining genetic integrity. The main cellular defense system against ionizing radiation exposure is composed of two distinct types of biochemical pathways, that is, the DNA damage cell cycle checkpoint pathways and the DNA repair pathways. The DNA damage checkpoint pathways are activated directly by DNA damage, while the repair pathways are constitutively active and are likely modulated by checkpoint signals. Discussions here emphasize that the ATM protein is a central component of the ionizing radiation-responsive pyramid and is essential for activating divergent molecular responses that involve transcriptional regulation, cell cycle arrest, and modulation of DNA repair. The relationship between homologous recombinational repair and nonhomologous end joining of double-strand breaks is also discussed.

Animals↗
PubMed2001

Activated in prostate cancer: a PDZ domain-containing protein highly expressed in human primary prostate tumors.

Critical events in prostate tumorigenesis and metastasis likely include the abnormal activation and expression of specific genes. Using RNA expression profiling techniques, we have identified a transcript originating from the activated in prostate cancer (AIPC) gene, the expression of which is preferentially up-regulated in several cultured prostate tumor cell lines and human primary prostate tumors. Sequence analysis revealed that the AIPC protein encodes six PDZ domains, which are protein-protein binding domains likely involved in protein clustering and scaffolding. Immunohistochemical analysis of a tissue microarray comprising 158 tumor, 18 high-grade prostatic intraepithelial neoplasia, and 91 normal prostate specimens with an anti-AIPC antibody demonstrated abundant AIPC protein expression in 75% of tumors, 83% of prostatic intraepithelial neoplasia lesions, and 3% of normal tissues (P < 0.0001). These data suggest that the accumulation of AIPC protein may be closely associated with the initiation or early promotion of prostate tumorigenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Role of phosphoinositide 3-kinase in monocyte recruitment under flow conditions.

Chemokines such as the monocyte chemol attractant protein-1 (MCP-1) convert monocyte rolling to firm arrest under physiological flow conditions via integrin activation and simultaneously activate phosphoinositide 3-kinase (PI3K). Here we used adenoviral gene transfer and biochemical inhibitors to manipulate PI3K-dependent pathways in human monocytes. In in vitro lipid kinase assays from purified human monocytes, we showed that MCP-1 activates the "classical" PI3Kalpha pathway and not PI3Kgamma, a PI3K isoform thought to be activated only by the betagamma complex of heterotrimeric G proteins. The activity of PI3Kalpha in purified human monocytes was evident within 30 s. MCP-1-induced monocyte arrest was significantly inhibited both by wortmannin (n = 4; p < 0.01) and LY294002 (n = 4; p < 0.01) with restoration of the rolling phenotype (p < 0.05 for both inhibitors, compared with rolling of control monocytes after MCP-1 treatment). To test the hypothesis that activation of PI3K is sufficient to induce monocyte adhesion, we transduced the monocytic THP-1 cell line with a recombinant adenovirus (Ad) carrying a constitutively active mutant of PI3K (Ad.BD110). We examined the ability of these cells to adhere to human vascular endothelium (HUVEC) transduced with adenoviruses carrying E-selectin, intercellular adhesion molecule-1 (ICAM-1), and VCAM-1. Under flow conditions, ICAM-1- and VCAM-1-dependent firm adhesion of Ad.BD110-transduced THP-1 cells was enhanced compared with THP-1 cells infected with control Ad (n = 4; p < 0.01 for both). Adhesion augmented by constitutive PI3K activation was entirely abrogated by pretreatment with wortmannin (n = 3; p < 0.01). In contrast, a constitutively active Akt construct had no effect on THP-1 adhesion (n = 3; p = NS). We conclude that PI3K activation is necessary and sufficient to enhance monocytic adhesion under physiological flow conditions. BD110-expressing THP-1 cells should provide a useful tool for identifying the signaling pathways downstream of PI3K that are necessary for monocyte recruitment relevant to a variety of human vascular pathologies.

Cell Line↗
PubMed2001

Surfing for back pain patients: the nature and quality of back pain information on the Internet.

STUDY DESIGN: A prospective, systematic review of web sites related to back pain. OBJECTIVE: To assess the nature and quality of back pain-related information on the World Wide Web during a 2-year period. SUMMARY OF BACKGROUND DATA: The Internet has become a rich source of medical information. Limited knowledge is available, however, about the quality of online resources. Although previous systematic reviews on medical-related web sites found problems in varying degrees with the credibility of information, no such review was conducted to assess the back pain-related sites. METHODS: A search of web sites was conducted in November 1996 using five search engines (AltaVista, Infoseek, Lycos, Yahoo, and Magellan) and two key terms ("back pain" and "back problems"). A sample of sites was evaluated by two independent reviewers. Each site was described by the type and nature of the sponsor, target audience, and content. Overall quality was assessed in terms of evidence-based information available. RESULTS: Seventy-four web sites were reviewed in 1996, and nine of them (12.2%) were identified as high-quality sites. Advertising was the focus of 80.8% of the sites. Eleven sites (14.9%) were found to be discontinued 1 year later, and 20 (27.0%) were not accessible by the reviewers at the 2-year follow-up evaluation. Of the remaining 54 sites, 44.4% were produced by for-profit companies, and most sites targeted people with back pain (63.0%). Only seven out of the nine high-quality sites held their ratings at the 2-year follow-up evaluation. CONCLUSION: Most back pain-related web sites can be classified as advertising. The quality varied considerably, resulting in difficulties for patients to find useful information in this field. The increasing number of people seeking medical information on the Web creates a need for more high quality sites. Further, systematic review of web sites should be encouraged to monitor the accuracy of Internet publication.

Bias↗
PubMed2001

Investigating protein conformation-based inheritance and disease in yeast.

Our work supports the hypothesis that a protein can serve as an element of genetic inheritance. This protein-only mechanism of inheritance is propagated in much the same way as hypothesized for the transmission of the protein-only infectious agent in the spongiform encephalopathies; hence these protein factors have been called yeast prions. Our work has focused on [PSI(+)], a dominant cytoplasmically inherited factor that alters translational fidelity. This change in translation is produced by a self-perpetuating change in the conformation of the translation-termination factor, Sup35. Most recently, we have determined that new elements of genetic inheritance can be created by deliberate genetic engineering, opening prospects for new methods of manipulating heredity. We have also uncovered evidence that other previously unknown elements of protein-based inheritance are encoded in the yeast genome. Finally, we have begun to use yeast as a model system for studying human protein folding diseases, such as Huntington's disease. Proteins responsible for some of these diseases have properties uncannily similar to those that produce protein-based mechanisms of inheritance.

Fungal Proteins↗
PubMed2001

Whole-body and intravital optical imaging of angiogenesis in orthotopically implanted tumors.

The development of drugs for the control of tumor angiogenesis requires a simple, accurate, and economical assay for tumor-induced vascularization. We have adapted the orthotopic implantation model to angiogenesis measurement by using human tumors labeled with Aequorea victoria green fluorescent protein for grafting into nude mice. The nonluminous induced capillaries are clearly visible against the very bright tumor fluorescence examined either intravitally or by whole-body luminance in real time. The orthotopic implantation model of human cancer has been well characterized, and fluorescence shadowing replaces the laborious histological techniques for determining blood vessel density. Intravital images of orthotopically implanted human pancreatic tumors clearly show angiogenic capillaries at both primary and metastatic sites. A quantitative time course of angiogenesis was determined for an orthotopically growing human prostate tumor periodically imaged intravitally in a single nude mouse over a 19-day period. Whole-body optical imaging of tumor angiogenesis was demonstrated by injecting fluorescent Lewis lung carcinoma cells into the s.c. site of the footpad of nude mice. The footpad is relatively transparent, with comparatively few resident blood vessels, allowing quantitative imaging of tumor angiogenesis in the intact animal. Capillary density increased linearly over a 10-day period as determined by whole-body imaging. Similarly, the green fluorescent protein-expressing human breast tumor MDA-MB-435 was orthotopically transplanted to the mouse fat pad, where whole-body optical imaging showed that blood vessel density increased linearly over a 20-week period. These powerful and clinically relevant angiogenesis mouse models can be used for real-time in vivo evaluation of agents inhibiting or promoting tumor angiogenesis in physiological microenvironments.

Animals↗
PubMed2001

[Case control study of the relationship between type A character and type II diabetes mellitus].

OBJECTIVE: To explore the relationship between type A character and type II diabetes mellitus. METHODS: A frequency matched case control study based on hospital involving 185 newly diagnosed type II diabetics, 201 control cases without type II diabetes mellitus, and 197 healthy people was carried out in Xuzhou City, Jiangsu Province, using type A character questionnaire and unified questionnaire. Nonconditional univariate and multivariate logistic regression analyses were used with the software Statistical Package for the Social Sciences for Windows release 8.0. RESULTS: The score of TH (time hurry), CH (competition and hostility), and the sum of TH and CH of the type II diabetes mellitus cases were significantly higher than those of the control cases (P < 0.01). Compared with B-type character, type A character (OR = 2.59, 95% CI: 1.62 approximately 4.13) was more significantly associated with type II diabetes mellitus after adjustment of occupation, education, family history of diabetes mellitus, waist to hip ratio (WHR), smoking, drinking, dietary factors, leisure time physical activity and hypertension. CONCLUSION: Type A character may be one of the risk factors of type II diabetes mellitus.

Case-Control Studies↗
PubMed2001

Reaction mechanism for mammalian pyruvate dehydrogenase using natural lipoyl domain substrates.

The pyruvate dehydrogenase (E1) component of the pyruvate dehydrogenase complex (PDC) catalyzes a two-step reaction. Recombinant production of substrate amounts of the lipoyl domains of the dihydrolipoyl transacetylase (E2) component of the mammalian PDC allowed kinetic characterization of the rapid physiological reaction catalyzed by E1. Using either the N-terminal (L1) or the internal (L2) lipoyl domain of E2 as a substrate, analyses of steady state kinetic data support a ping pong mechanism. Using standard E1 preparations, Michaelis constants (Km) were 52 +/- 14 microM for L1 and 24.8 +/- 3.8 microM for pyruvate and k(cat) was 26.3 s(-1). With less common, higher activity preparations of E1, the Km values were > or =160 microM for L1 and > or =35 microM for pyruvate and k(cat) was > or =70 s(-1). Similar results were found with the L2 domain. The best synthetic lipoylated-peptide (L2 residues 163-177) was a much poorer substrate (Km > or =15 mM, k(cat) approximately equals 5 s(-1); k(cat)/Km decreased >1,500-fold) than L1 or L2, but a far better substrate in the E1 reaction than free lipoamide (k(cat)/Km increased >500-fold). Each lipoate source was an effective substrate in the dihydrolipoyl dehydrogenase (E3) reaction, but E3 had a lower Km for the L2 domain than for lipoamide or the lipoylated peptides. In contrast to measurements with slow E1 model reactions that use artificial acceptors, we confirmed that the natural E1 reaction, using lipoyl domain acceptors, was completely inhibited (>99%) by phosphorylation of E1 and the phosphorylation strongly inhibited the reverse of the second step catalyzed by E1. The mechanisms by which phosphorylation interferes with E1 activity is interpreted based on accrued results and the location of phosphorylation sites mapped onto the 3-D structure of related alpha-keto acid dehydrogenases.

Acetylation↗
PubMed2001

N-terminal intramolecularly conserved histidines of three domains in Gonyaulax luciferase are responsible for loss of activity in the alkaline region.

Gonyaulax luciferase is a single-chain ( approximately 137 kDa) polypeptide comprising 111 N-terminal amino acids followed by three contiguous homologous domains (377 amino acids each). Each domain has luciferase activity, accounting for the earlier observation that proteolytic fragments ( approximately 35 kDa) of luciferase are active. The activity of the full-length native enzyme is maximal at pH 6.3, dropping to near zero at pH 8; the activity of fragments also peaks at pH 6.3 but remains high at 8. While the activity loss at higher pH might be thought to be associated with the conformation of the full-length protein, we show here that this is a property of individual domains. The three intramolecularly homologous domains, separately cloned and expressed in Escherichia coli as fusion proteins, exhibit pH-activity curves similar to that of the full-length enzyme. For each domain the removal of approximately 50 N-terminal amino acids resulted in an increase in the ratio of luciferase activity at pH 8 relative to that at pH 6.3, such that their pH-activity profiles mimicked that of the proteolytic fragments reported earlier. Replacement of N-terminal histidines by alanine by site-directed mutagenesis identified four that are involved in the loss of activity at high pH. This system illustrates an unusual, possibly unique mechanism for pH regulation of enzyme activity, which has been postulated to be responsible for the control of the characteristic flashes of bioluminescence.

Amino Acid Sequence↗
PubMed2001

A TSG101/MDM2 regulatory loop modulates MDM2 degradation and MDM2/p53 feedback control.

The p53 tumor suppressor protein and the MDM2 oncoprotein form a feedback-control loop that up-regulates cellular MDM2 production, blocks p53 activity, and promotes p53 decay. tsg101 was discovered as a gene whose deficiency results in neoplastic transformation of NIH 3T3 cells and the ability to generate metastatic tumors in nude mice. Its protein product contains a domain, Ubc, characteristic of the catalytic domain of ubiquitin conjugase (E2) enzymes but lacking an active-site cysteine crucial for ubiquitin conjugase activity. Here we report that TSG101 participates with MDM2 in an autoregulatory loop that modulates the cellular levels of both proteins, and also of p53, by affecting protein decay. We show that the Ubc domain of TSG101 interferes with ubiquitination of MDM2, that TSG101 inhibits MDM2 decay and elevates its steady-state level, and that these events are associated with down-regulation of p53 protein. Conversely, pulse-chase and Western blot experiments in wild-type and mutant fibroblasts indicate that elevation of MDM2 by overexpression of wild-type p53, by amplification of the endogenous MDM2 gene, or by transfection of MDM2-expressing constructs promotes TSG101 loss, which we show occurs by 26S proteasome-dependent decay. Our results identify TSG101 as both a regulator of, and target of, MDM2/p53 circuitry.

3T3 Cells↗
PubMed2001

p53 accumulation, defective cell proliferation, and early embryonic lethality in mice lacking tsg101.

Functional inactivation of the tumor susceptibility gene tsg101 in NIH 3T3 fibroblasts results in cellular transformation and the ability to form metastatic tumors in nude mice. The N-terminal region of tsg101 protein is structurally similar to the catalytic domain of ubiquitin-conjugating enzymes, suggesting a potential role of tsg101 in ubiquitin-mediated protein degradation. The C-terminal domain of TSG101 can function as a repressor of transcription. To investigate the physiological function of tsg101, we generated a null mutation of the mouse gene by gene targeting. Homozygous tsg101-/- embryos fail to develop past day 6.5 of embryogenesis (E6.5), are reduced in size, and do not form mesoderm. Mutant embryos show a decrease in cellular proliferation in vivo and in vitro but no increase in apoptosis. Although levels of p53 transcripts were not affected in tsg101-/- embryos, p53 protein accumulated dramatically, implying altered posttranscriptional control of p53. In addition, transcription of the p53 effector, cyclin-dependent kinase inhibitor p21(WAF-1/CIP-1), was increased 5- to 10-fold, whereas activation of MDM2 transcription secondary to p53 elevation was not observed. Introduction of a p53 null mutation into tsg101-/- embryos rescued the gastrulation defect and prolonged survival until E8.5. These results demonstrate that tsg101 is essential for the proliferative burst before the onset of gastrulation and establish a functional connection between tsg101 and the p53 pathway in vivo.

Animals↗
PubMed2001

Different circular permutations produced different folding nuclei in proteins: a computational study.

There have been many studies about the effect of circular permutation on the transition state/folding nucleus of proteins, with sometimes conflicting conclusions from different proteins and permutations. To clarify this important issue, we have studied two circular permutations of a lattice protein model with side-chains. Both permuted sequences have essentially the same native state as the original (wild-type) sequence. Circular permutant 1 cuts at the folding nucleus of the wild-type sequence. As a result, the permutant has a drastically different nucleus and folds more slowly than wild-type. In contrast, circular permutant 2 involves an incision at a site unstructured in the wild-type transition state, and the wild-type nucleus is largely retained in the permutant. In addition, permutant 2 displays both two-state and multi-state folding, with a native-like intermediate state occasionally populated. Neither the wild-type nor permutant 1 has a similar intermediate, and both fold in an apparently two-state manner. Surprisingly, permutant 2 folds at a rate identical with that of the wild-type. The intermediate in permutant 2 is stabilised by native and non-native interactions, and cannot be classified simply as on or off-pathway. So we advise caution in attributing experimental data to on or off-pathway intermediates. Finally, our work illuminates the results on alpha-spectrin SH3, chymotrypsin inhibitor 2 and beta-lactoglobulin, and supports a key assumption in the experimental efforts to locate potential nucleation sites of real proteins via circular permutations.

Computer Simulation↗
PubMed2001

Muscle specificity encoded by specific serum response factor-binding sites.

Serum response factor (SRF) is a MADS box transcription factor that regulates muscle-specific and growth factor-inducible genes by binding the consensus sequence CC(A/T)6GG, known as a CArG box. Because SRF expression is not restricted solely to muscle, its expression alone cannot account for the muscle specificity of some of its target genes. To understand further the role of SRF in muscle-specific transcription, we created transgenic mice harboring lacZ transgenes linked to tandem copies of different CArG boxes with flanking sequences. CArG boxes from the SM22 and skeletal alpha-actin promoters directed highly restricted expression in developing smooth, cardiac, and skeletal muscle cells during early embryogenesis. In contrast, the CArG box and flanking sequences from the c-fos promoter directed expression throughout the embryo, with no preference for muscle cells. Systematic swapping of the core and flanking sequences of the SM22 and c-fos CArG boxes revealed that cell type specificity was dictated in large part by sequences immediately flanking the CArG box core. Sequences that directed widespread embryonic expression bound SRF more strongly than those that directed muscle-restricted expression. We conclude that sequence variations among CArG boxes influence cell type specificity of expression and account, at least in part, for the ability of SRF to distinguish between growth factor-inducible and muscle-specific genes in vivo.

Actins↗