Search PubMed⌕ Search

Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 1,513 records · Page 84Linked to original sources
PubMed1995

A serine protease inhibitor, protease nexin I, rescues motoneurons from naturally occurring and axotomy-induced cell death.

Protease nexin I (PNI) is a member of the family of serine protease inhibitors (serpins) that have been shown to promote neurite outgrowth in vitro from different neuronal cell types. These include neuroblastoma cells, hippocampal neurons, and sympathetic neurons. Free PNI protein is markedly decreased in various anatomical brain regions, including hippocampus, of patients with Alzheimer disease. Here, we report that PNI rescued spinal motoneurons during the period of naturally occurring (programmed) cell death in the chicken in a dose-dependent fashion. Furthermore, PNI prevented axotomy-induced spinal motoneuron death in the neonatal mouse. The survival effect of PNI on motoneurons during the period of programmed cell death was not associated with increased intramuscular nerve branching. PNI also significantly increased the nuclear size of motoneurons during the period of programmed cell death and prevented axotomy-induced atrophy of surviving motoneurons. These results are consistent with the possible role of PNI as a neurotrophic agent. They also support the idea that serine proteases or, more precisely, the balance of proteases and serpins may be involved in regulating the fate of neuronal cells during development.

Amyloid beta-Protein Precursor↗
PubMed1995

Developing motor neurons rescued from programmed and axotomy-induced cell death by GDNF.

During normal development of the vertebrate nervous system, large numbers of neurons in the central and peripheral nervous system undergo naturally occurring cell death. For example, about half of all spinal motor neurons die over a period of a few days in developing avian, rat and mouse embryos. Previous studies have shown that extracts from muscle and brain, secreted factors from glia, as well as several growth factors and neurotrophic agents, including muscle-derived factors, can promote the survival of developing motor neurons in vitro and in vivo. But because neurotrophins and other known trophic agents administered alone or in combination are insufficient to rescue all developing motor neurons from cell death, other neurotrophic molecules are probably essential for the survival and differentiation of motor neurons. Here we report that glial-cell-line-derived neurotrophic factor (GDNF), a potent neurotrophic factor that enhances survival of mammalian midbrain dopaminergic neurons, rescues developing avian motor neurons from natural programmed cell death in vivo and promotes the survival of enriched populations of cultured motor neurons. Furthermore, treatment with this agent in vivo also prevents the induced death and atrophy of both avian and mouse spinal motor neurons following peripheral axotomy.

Animals↗
PubMed1995

Identification of a brain- and reproductive-organs-specific gene responsive to DNA damage and retinoic acid.

We have identified and sequenced a new gene from human cells that is responsive to DNA damage and retinoic acid treatment, and it is highly expressed in brain and reproductive organs (BRE). This BRE gene encodes an mRNA of 1.7-1.9 kb, with an open reading frame of 1,149 bp, and gives rise to a deduced polypeptide of 383 amino acid residues. Treatment of fibroblast cell with UV and 4-nitroquinoline-1-oxide caused more than 90% and 50% decreases in BRE mRNA, respectively. Similar decreases in BRE expression were observed in RA-treatment of the brain glioma cell U-251 and the promyelocytic cell HL-60. Decrease in BRE mRNA was also observed in a squamous carcinoma cell, 1483, that showed X-ray resistance and has a more aggressive tumorigenic phenotype, but BRE expression was unchanged in cells after growth inhibition. These data indicate that BRE is a house-keeping gene and it may play a role in homeostatis or in certain pathways of differentiation in cells of neural, epithelial and germ line origins.

Amino Acid Sequence↗
PubMed1995

Cloning and characterization of the human megakaryocyte growth and development factor (MGDF) gene.

The megakaryocyte growth and development factor (MGDF) is a cytokine that regulates megakaryocyte development and is a ligand for the MPL receptor. In this study, we describe the genomic structure of the human MGDF gene. The MGDF gene was found to consist of seven exons and six introns spanning 8 kilobases. The protein is encoded by exons 3 through 7. The human MGDF gene has been mapped to chromosome 3q26.3. In addition to the previously described full-length cDNA, two cDNA variants were isolated from human fetal liver. Comparison of these two cDNA sequences with the genomic sequence indicates that they arise by differential splicing.

Amino Acid Sequence↗
PubMed1995

Chelation of intracellular Ca2+ inhibits murine keratinocyte differentiation in vitro.

The role of intracellular Ca2+ in the regulation of Ca(2+)-induced terminal differentiation of mouse keratinocytes was investigated using the intracellular Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA). A cell permeable acetoxymethyl (AM) ester derivative BAPTA (BAPTA/AM) was loaded into primary mouse keratinocytes in 0.05 mM Ca2+ medium, and then the cells were induced to differentiate by medium containing 0.12 or 0.5 mM Ca(2+) Intracellular BAPTA loaded by BAPTA/AM (15-30 microM) inhibited the expression of epidermal differentiation-specific proteins keratin 1 (K1), keratin 10 (K10), filaggrin and loricrin as detected by immunoblotting. The differentiation-associated redistribution of E-cadherin on the cell membrane was delayed but not inhibited as determined by immunofluorescence. BAPTA also inhibited the expression of K1, K10 and loricrin mRNA. Furthermore, BAPTA prevented the decrease in DNA synthesis induced by 0.12 and 0.5 mM Ca2+, indicating the drug was inhibiting differentiation but was not toxic to keratinocytes. To evaluate the influence of BAPTA on intracellular Ca2+, the concentration of intracellular free Ca2+ (Cai) in BAPTA-loaded keratinocytes was examined by digital image analysis using the Ca(2+)-sensitive fluorescent probe fura-2, and Ca2+ influx was measured by 45Ca2+ uptake studies. Increase in extracellular Ca2+ (Cao) in the culture medium of keratinocytes caused a sustained increase in both Cai and Ca2+ localized to ionomycin-sensitive intracellular stores in keratinocytes. BAPTA lowered basal Cai concentration and prevented the Cai increase. After 12 hours of BAPTA treatment, the basal level of Cai returned to the control value, but the Ca2+ localized in intracellular stores was substantially decreased. 45Ca2+ uptake was initially (within 30 min) increased in BAPTA-loaded cells. However, the total 45Ca2+ accumulation over 24 hours in BAPTA-loaded cells remained unchanged from control values. These results indicate that keratinocytes can maintain Cai and total cellular Ca2+ content in the presence of increased amount of intracellular Ca2+ buffer (e.g., BAPTA) by depleting intracellular Ca2+ stores over a long period. The inhibition by BAPTA of keratinocyte differentiation marker expression may result from depletion of the Ca(2+)-stores since this is the major change in intracellular Ca2+ detected at the time keratinocytes express the differentiation markers. In contrast, the redistribution of E-cadherin on the cell membrane may be more directly associated with Cai change.

Animals↗
PubMed1995

Homology modeling and molecular dynamics simulation of human prothrombin fragment 1.

The crystallographic structure of bovine prothrombin fragment 1 bound with calcium ions was used to construct the corresponding human prothrombin structure (hf1/Ca). The model structure was refined by molecular dynamics to estimate the average solution structure. Accommodation of long-range ionic forces was essential to reach a stable solution structure. The gamma-carboxyglutamic acid (Gla) domain and the kringle domain of hf1/Ca independently equilibrated. Likewise, the hydrogen bond network and the calcium ion coordinations were well preserved. A discussion of the phospholipid binding of the vitamin K-dependent coagulation proteins in the context of the structure and mutational data of the Gla domain is presented.

1-Carboxyglutamic Acid↗
PubMed1995

Dermo-1: a novel twist-related bHLH protein expressed in the developing dermis.

Transcription factors belonging to the basic helix-loop-helix (bHLH) family have been shown to control differentiation of a variety of cell types. Tissue-specific bHLH proteins dimerize preferentially with ubiquitous bHLH proteins to form heterodimers that bind the E-box consensus sequence (CANNTG) in the control regions of target genes. Using the yeast two-hybrid system to screen for tissue-specific bHLH proteins, which dimerize with the ubiquitous bHLH protein E12, we cloned a novel bHLH protein, named Dermo-1. Within its bHLH region, Dermo-1 shares extensive homology with members of the twist family of bHLH proteins, which are expressed in embryonic mesoderm. During mouse embryogenesis, Dermo-1 showed an expression pattern similar to, but distinct from, that of mouse twist. Dermo-1 was expressed at a low level in the sclerotome and dermatome of the somites, and in the limb buds at Day 10.5 post coitum (p.c.), and accumulated predominantly in the dermatome, prevertebrae, and the derivatives of the branchial arches by Day 13.5 p.c. As differentiation of prechondrial cells proceeded, Dermo-1 expression became restricted to the perichondrium. Expression of Dermo-1 increased continuously in the dermis through Day 17.5 p.c. and was also detected in the dermis of neonates, but became downregulated in adult tissues. The Dermo-1 protein bound the E-box consensus sequence in the presence of E12, but transcriptional activity was not detectable. Instead, Dermo-1 repressed transcriptional activity of myogenic bHLH proteins. The expression pattern of Dermo-1 suggests that it functions as a regulator of gene expression in a subset of mesenchymal cell lineages including developing dermis.

Amino Acid Sequence↗
PubMed1995

Effects of expressing human Hsp70 and its deletion derivatives on heat killing and on RNA and protein synthesis.

We have established rat cell lines stably and constitutively expressing intact human heat shock protein (hsp) 70 and its deletion mutant derivatives. Using these stable cell lines, the functions of the various domains of human hsp70 were studied. An elevated level of human hsp70 or fragments containing the C-terminal portion of the protein, but not fragments containing the amino-terminal portion of the protein, is found to protect cells against thermal killing. Only the expression of intact human hsp70, however, can reduce the degree of heat-induced inhibition of translation and most effectively accelerate the recovery from heat-induced inhibition of transcription and translation. The peptide-binding domain in the carboxyl portion of hsp70 is of primary importance in protecting cells from thermal stress, probably through its binding to unfolded or partially folded polypeptides; this interaction, in turn, retards detrimental thermal denaturation or aggregation of key cellular proteins and protects cells from thermal stress. ATP binding and hydrolysis, on the other hand, are presumably necessary in the refolding and reassembly of thermally damaged proteins through multiple cycles of interactions between hsp70 and its targets.

Animals↗
PubMed1995

Ciliary neurotrophic factor promotes the survival of spinal sensory neurons following axotomy but not during the period of programmed cell death.

We have examined the in vivo survival effect of ciliary neurotrophic factor (CNTF) on sensory, i.e., dorsal root ganglion (DRG) neurons during the period of naturally occurring (programmed) cell death and following axotomy in the developing chick and mouse. Administration of CNTF during the period of naturally occurring cell death, from Embryonic Day (E) 6 to E10 in the chick and E14 to E18 in the mouse, had no significant effect in preventing the death of DRG neurons in either species. Axotomy on E12 in the chick or on Postnatal Day (PN) 5 in the mouse resulted in a 60% and a 33% decrease, respectively, in ipsilateral DRG neuron numbers by E16 (chick) or by PN12 (mouse), when compared to contralateral controls. CNTF treatment prevented axotomy-induced cell death of DRG neurons in both the chick and mouse. Daily administration of CNTF following axotomy in E12 chicks significantly increased (72%) DRG neurons by E16. Similarly, CNTF completely rescued mouse DRG neurons from axotomy-induced death. These results show that although CNTF has no effect on naturally occurring death of chick or mouse sensory neurons, this agent has significant ability to rescue sensory neurons following axotomy. These findings suggest that CNTF may be an effective therapeutic agent for the prevention of injury-induced death of vertebrate sensory neurons.

Animals↗
PubMed1995

Generation of human-melanoma-specific T lymphocyte clones defining novel cytolytic targets with panels of newly established melanoma cell lines.

Melanoma is a cancer where the immune system is believed to play an important role in the control of malignant cell growth. To study the variability of the immune response in melanoma patients, we derived melanoma cell lines from several HLA-A2+ and HLA-A2- patients. The melanoma cell lines studied were designated FM3, FM6, FM9, FM28, FM37, FM45, FM55p, FM55M1 and FM55M2 and were established from eight metastatic tumors as well as from one primary tumor from a total of seven different patients. On the basis of the ability of tumor cells to induce specific cytotoxic T lymphocytes (CTL) from peripheral blood lymphocytes (PBL) in mixed lymphocyte/tumor culture with HLA-A2+ melanoma cells, the FM3 cell line was characterized as highly immunogenic. To investigate the expression of different melanoma-associated antigens recognized by CTL on different melanoma cell lines, we selected the cell line FM3 for restimulation and further T cell cloning experiments. The lytic activity of CTL clones with good proliferative activity was examined using a panel of HLA-A2+ and HLA-A2- melanoma cell lines. None of the tested HLA-A2- melanoma cell lines were susceptible to lysis by the CTL clones, whereas allogeneic HLA-A2+ melanoma cell lines were lysed only by a few CTL clones. On the basis of their reactivity with different melanoma cell lines, it was possible to divide the present CTL clones into at least four groups suggesting the recognition of at least four different antigens. Three of these target structures probably are different from already-described HLA-A2-restricted melanoma-associated antigens, because their expression in the different melanoma cell lines do not correlate with the recognition of melanoma cells by these CTL. The results first indicate that poorly immunogenic melanoma cells may express melanoma-associated antigens, and also suggest that, by using CTL clones obtained against different HLA-class-I-matched melanoma cells, it is possible to define such antigens.

Antigens, Neoplasm↗
PubMed1995

Personal and behavioral predictors of automobile crash and injury severity.

The purpose of this paper is to develop a statistical model explaining the relationships between certain driver characteristics and behaviors, crash severity, and injury severity. Applying techniques of categorical data analysis to comprehensive data on crashes in Hawaii during 1990, we build a structural model relating driver characteristics and behaviors to type of crash and injury severity. The structural model helps to clarify the role of driver characteristics and behaviors in the causal sequence leading to more severe injuries. From the model we estimate the effects of various factors in terms of odds multipliers--that is, how much does each factor increase or decrease the odds of more severe crash types and injuries. We found that driver behaviors of alcohol or drug use and lack of seat belt use greatly increase the odds of more severe crashes and injuries. Driver errors are found to have a small effect, while personal characteristics of age and sex are generally insignificant. We conclude with a discussion of our modeling approach and of the implications of our findings for appropriate traffic safety interventions and future research.

Accidents, Traffic↗
PubMed1995

Prostaglandin F2 alpha rises in response to hydroxyl radical generated in vivo.

Free radicals and some free fatty acids, such as arachidonic acid metabolites, have been hypothesized to be contributors to secondary damage to the spinal cord upon injury. These two types of species may form a feedback loop in which generation of one type leads to formation of the other. In this study, to determine whether hydroxyl radical causes generation of arachidonic acid metabolites in vivo, we generated hydroxyl radical, a most reactive oxygen radical, in the rat spinal cord and measured resulting changes in levels of prostaglandin F2 alpha, an arachidonic acid metabolite that rises following traumatic injury. The hydroxyl radical was generated in the rat spinal cord by administering H2O2 through one microdialysis fiber and FeCl2/EDTA through a parallel fiber. The prostaglandin F2 alpha in the collected microdialysates was measured by HPLC as its 3-bromomethyl-6,7-dimethoxy-1-methyl-2-(1H)-quinoxalinone derivative. Prostaglandin F2 alpha dramatically increased in response to hydroxyl radical generation, but declined substantially after 3 h of exposure. Prostaglandin F2 alpha was undetectable when either H2O2 or FeCl2/EDTA was administered alone in control experiments, demonstrating that its formation was caused by generated hydroxyl radical.

Animals↗
PubMed1995

Paraquat--a superoxide generator--kills neurons in the rat spinal cord.

Microdialysis was used to administer paraquat into the spinal cord of the anesthetized rat to determine the effects of the in vivo generation of the superoxide anion (O2.-) on neurons. Exposure to paraquat caused blockage of axonal conduction, destruction of the cell bodies of neurons, and a general release of amino acids. Thus, paraquat is quite harmful to neuronal tissue. Similarities between paraquat-induced damage and that previously observed from the hydroxyl radical are consistent with paraquat, causing damage by generation of reactive oxygen species and the widespread belief that generation of O2.- initiates the formation of destructive reactive oxygen species in a wide variety of traumas and other disorders.

Amino Acids↗
PubMed1995

Antitumor agents, 154. Cytotoxic and antimitotic flavonols from Polanisia dodecandra.

Three flavonols, 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone [1], 5,4'-dihydroxy-3,6,7,8,3'-pentamethoxyflavone [2], and quercetin 3-O-beta-D-glucopyranosyl-7-O-alpha-L-rhamnopyranoside [3], were isolated from Polanisia dodecandra. Compound 1 showed remarkable cytotoxicity in vitro against panels of central nervous system cancer (SF-268, SF-539, SNB-75, U-251), non-small cell lung cancer (HOP-62, NCI-H266, NCI-H460, NCI-H522), small cell lung cancer (DMS-114), ovarian cancer (OVCAR-3, SK-OV-3), colon cancer (HCT-116), renal cancer (UO-31), a melanoma cell line (SK-MEL-5), and two leukemia cell lines (HL-60 [TB], SR), with GI50 values in the low micromolar to nanomolar concentration range. This substance also inhibited rubulin polymerization (IC50 = 0.83 +/- 0.2 microM) and the binding of radiolabeled colchicine to tubulin with 59% inhibition when present in equimolar concentrations with colchicine. Compound 2 also showed cytotoxicity against medulloblastoma (TE-671) tumor cells with an ED50 value of 0.98 microgram/ml. Compound 1 appears to be the first example of a flavonol to exhibit potent inhibition of tubulin polymerization and, therefore, warrants further investigation as an antimitotic agent.

Antineoplastic Agents↗
PubMed1995

Linkage between sexual orientation and chromosome Xq28 in males but not in females.

We have extended our analysis of the role of the long arm of the X chromosome (Xq28) in sexual orientation by DNA linkage analyses of two newly ascertained series of families that contained either two gay brothers or two lesbian sisters as well as heterosexual siblings. Linkage between the Xq28 markers and sexual orientation was detected for the gay male families but not for the lesbian families or for families that failed to meet defined inclusion criteria for the study of sex-linked sexual orientation. Our results corroborate the previously reported linkage between Xq28 and male homosexuality in selected kinships and suggest that this region contains a locus that influences individual variations in sexual orientation in men but not in women.

Base Sequence↗
PubMed1995

The feasibility of targeted selective gene therapy of the hair follicle.

Loss of hair and hair colour is associated with ageing, and when it involves the scalp hair, it can be distressing to both sexes. Hair loss resulting from cancer chemotherapy is particularly distressing. However, safe, effective therapies directed to hair have only just started to be developed. The hair follicle is a complex skin appendage composed of epidermal and dermal tissue, with specialized keratinocytes, the hair matrix cells, forming the hair shaft. Specific therapy of the hair follicle depends on selective targeting of specific cells of the hair follicle. We have developed the histoculture of intact hair-growing skin on sponge-gel matrices. We have recently found in histocultured skin that liposomes can selectively target hair follicles to deliver both small and large molecules. That liposomes can target the hair follicle for delivery has been confirmed independently. Two decades ago we introduced the technique of entrapping DNA in liposomes for use in gene therapy. In this report we describe the selective targeting of the lacZ reporter gene to the hair follicles in mice after topical application of the gene entrapped in liposomes. These results demonstrate that highly selective, safe gene therapy for the hair process is feasible.

Administration, Topical↗