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Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 1,423 records · Page 79Linked to original sources
PubMed1996

Computational studies of human prothrombin fragment 1, the Gla domain of factor IX and several biological interesting mutants.

We have employed molecular dynamics simulations to understand the properties of the gamma-carboxyglutamic acid (Gla) domains of human prothrombin fragment 1 (residues 1-144) and factor IX (residues 1-47). The simulations are based on (1) the crystal structure of bovine prothrombin fragment 1 in the presence of calcium and (2) our subsequent simulation of the solution structure for which we found accommodation of the long range ionic forces critical. In addition, we have estimated the solution structures for key mutant proteins [prothrombin (Gla6 to Asp and Gla16 to Asp) and factor IX (Gly12 to Ala)]. The simulations for the latter two mutants do not stabilize, a result in concert with the known biological data.

1-Carboxyglutamic Acid↗
PubMed1996

SM22 alpha, a marker of adult smooth muscle, is expressed in multiple myogenic lineages during embryogenesis.

SM22 alpha is a calponin-related protein that is expressed specifically in adult smooth muscle. To begin to define the mechanisms that regulate the establishment of the smooth muscle lineage, we analyzed the expression pattern of the SM22 alpha gene during mouse embryogenesis. In situ hybridization demonstrated that SM22 alpha transcripts were first expressed in vascular smooth muscle cells at about embryonic day (E) 9.5 and thereafter continued to be expressed in all smooth muscle cells into adulthood. In contrast to its smooth muscle specificity in adult tissues, SM22 alpha was expressed transiently in the heart between E8.0 and E12.5 and in skeletal muscle cells in the myotomal compartment of the somites between E9.5 and E12.5. The expression of SM22 alpha in smooth muscle cells, as well as early cardiac and skeletal muscle cells, suggests that there may be commonalities between the regulatory programs that direct muscle-specific gene expression in these three myogenic cell types.

Amino Acid Sequence↗
PubMed1996

Effects of FK-506 on contraction and Ca2+ transients in rat cardiac myocytes.

FK-506 binding protein (FKBP) has been reported to be closely associated with the ryanodine receptor in skeletal and cardiac muscle and to modulate sarcoplasmic reticulum (SR) Ca2+ release channel gating in isolated channels. FK-506 can inhibit the activity of FKBP, thereby reversing its effects on SR Ca2+ release. We investigated the function of FKBP during normal contractions and Ca2+ transients in intact rat ventricular myocytes loaded with fluorescent Ca2+ indicators. FK-506 significantly increased steady state twitch Ca2+ transients and contraction amplitudes even under conditions in which the SR Ca2+ load and Ca2+ current were unaltered, suggesting that FK-506 increases the fraction of SR Ca2+ released during excitation-contraction (E-C) coupling. Action potentials were somewhat prolonged, consistent with the larger Ca2+ transients causing greater inward Na(+)-Ca2+ exchange current. FK-506 did not affect SR Ca2+ uptake but modestly decreased Ca2+ extrusion via Na(+)-Ca2+ exchange in intact cells (although no effect on Na(+)-Ca2+ exchange was seen in sarcolemmal vesicles). In most cells, FK-506 caused an increase in SR Ca2+ content during steady state stimulation, as assessed by caffeine-induced contractures. This was probably due to the inhibition of Ca2+ efflux via Na(+)-Ca2+ exchange. FK-506 also accelerated the rest decay of SR Ca2+ content and increased the frequency of resting Ca2+ sparks about fourfold. The increase in frequency of these basic Ca2+ release events was not associated with changes in the amplitude or duration of the Ca2+ sparks. We conclude that FK-506 increases the fraction of SR Ca2+ released during normal twitches and enhances the rate of SR Ca2+ release during rest. FK-506 also inhibits Na(+)-Ca2+ exchange, although this effect may be indirect. These effects are consistent with an important SR-stabilizing effect of FKBP in intact rat ventricular myocytes.

Animals↗
PubMed1996

RtoA links initial cell type choice to the cell cycle in Dictyostelium.

In Dictyostelium, initial cell type choice is correlated with the cell-cycle phase of the cell at the time of starvation. We have isolated a mutant, ratioA (rtoA), with a defect in this mechanism that results in an abnormally high percentage of prestalk cells. The rtoA gene has been cloned and sequenced and codes for a novel protein. The cell cycle is normal in rtoA. In the wild type, prestalk cells differentiate from those cells in S or early G2 phase at starvation and prespore cells from cells in late G2 or M phase at starvation. In rtoA mutants, both prestalk and prespore cells originate randomly from cells in any phase of the cell cycle at starvation.

Amino Acid Sequence↗
PubMed1996

Exogenous heat shock cognate protein Hsc 70 prevents axotomy-induced death of spinal sensory neurons.

Elevation of intracellular heat shock protein (Hsp)70 increases resistance of cells to many physical and metabolic insults. We tested the hypothesis that treatment with Hsc70 can also produce that effect, using the model of axotomy-induced neuronal death in the neonatal mouse. The sciatic nerve was sectioned and in some animals purified bovine brain Hsc70 was applied to the proximal end of the nerve immediately thereafter and again 3 days later. Seven days postaxotomy, the surviving sensory neurons of the lumbar dorsal root ganglion (DRG) and motoneurons of the lumbar ventral spinal cord were counted to assess cell death. Axotomy induced the death of approximately 33% of DRG neurons and 50% of motoneurons, when examined 7 days postinjury. Application of exogenous Hsc70 prevented axotomy-induced death of virtually all sensory neurons, but did not significantly alter motoneuron death. Thus, Hsc70 may prove to be useful in the repair of peripheral sensory nerve damage.

Animals↗
PubMed1996

Effect of transforming growth factor-beta on plasminogen activator production of cultured human uveal melanoma cells.

PURPOSE: Human uveal melanoma cells have been shown to produce plasminogen activator (PA), an enzyme which can enhance tumor metastasis by promoting degradation of extracellular matrix. This study used cultured human uveal melanoma cells to determine whether the PA production of uveal melanoma cells could be modulated by transforming growth factor-beta2 (TGF-beta2), a mitogen present in the uvea. METHODS: Five different cell lines of human uveal melanoma of differing cellular morphology (2 spindle, 2 epithelioid, 1 mixed) derived from tumors from different locations in the eye (3 choroidal, 1 ciliochoroidal, 1 orbital) were grown in serum-free media, in the presence or absence of TGF-beta2 (1ng/ml to 100ng/ml). After 24 hrs, the conditioned media were collected and quantitated for PA activity by measuring the radial diffusion in fibrin-agarose clot and for total PA concentration using an enzyme-linked immunoassay. RESULTS: Among the cell lines studied, all produced PA. Cell lines derived from intraocular tumors secreted tissue-type PA (tPA), and TGF-beta2 stimulated tPA activity and secretion of cell lines containing epithelioid cells but had no effect on spindle cells. In contrast, tumor cells isolated from an orbital tumor secreted urokinase (uPA), activity and secretion of which was inhibited by TGF-beta2. CONCLUSIONS: We conclude that cultured human uveal melanoma cells produce either tPA or uPA, and TGF-beta2 can have a variable effect on PA production of these cells.

Culture Media, Conditioned↗
PubMed1996

Variation of intrarenal angiotensin II and angiotensin II receptors by acute renal ischemia in the aged rat.

The properties of Ang II receptors in the aged kidney and their changes after acute renal ischemia are rarely known. The aim of this study was to examine the expression of Ang II receptor mRNA and characteristics of Ang II receptors in the aged kidney and to compare different responsiveness to 45 min of acute renal ischemia in young (3-4 months) and aged (23-24 months) rats. In the normal condition, AT1 mRNA expression was much lower in the aged than that in the young rats. Maximal binding (Bmax) was also lower in the aged (1315 +/- 48 vs. 2035 +/- 257 fmol/mg, p < 0.05). The dissociation constant (KD) of glomerular Ang II receptors, however, was significantly lower in the aged rats compared to the young (6.8 +/- 1.6 vs. 17.4 +/- 2.5 nM). After acute ischemia, the expression of AT1 mRNA decreased in the young rats but increased in the aged rats. Interestingly, Bmax of glomerular Ang II receptors was significantly increased in the aged ischemic rats (1852 +/- 94 vs. 1315 +/- 48 fmol/mg) with unchanged KD. These results show that: (a) the AT1 mRNA expression and the Ang II receptor binding site are decreased with the aging process in the rat kidney; (b) the acute renal ischemia effect on different age groups has a greatly discrepant pattern in respect of Ang II receptor modulation, which may provide a potential therapeutic future for the receptor antagonists in acute renal ischemia in the aged.

Acute Disease↗
PubMed1996

A greater variability in the 3' flanking region of the IL-6 gene in patients with systemic lupus erythematosus (SLE).

The causes of the aberrant constitutive expression of cytokines in SLE have not been elucidated yet, but alterations in cytokine gene structure could be a contributing factor. By RFLP (Restriction Fragment Length Polymorphism) analysis of genomic DNA, we found a higher incidence of allelic, higher MW XbaI bands in the IL-6 genes of 9/57 SLE patients vs 1/36 unrelated controls (p = 0.05) HLA DR/DQ typing of the polymorphic patients revealed they were all DQ beta 6. The study of one family indicated that the XbaI polymorphic patient and her polymorphic unaffected offspring had higher than normal levels of constitutive IL-6 mRNA. The SLE-associated IL-6 XbaI restriction alleles had duplications of AT-repeat sequences, approximately 500 bp downstream of the 2nd polyadenylation site, in an AT-rich mini-satellite with similarities to Matrix Associated Regions (MARs), that may be important in DNA replication and in gene expression. These are novel observations that suggest that, in SLE, there is increased variability in the 3' flanking region of the IL-6 gene. This variability may be related to the aberrant IL-6 expression that was reported by us and others in this disease.

Deoxyribonucleases, Type II Site-Specific↗
PubMed1996

Effect of orally administered Eubacterium coprostanoligenes ATCC 51222 on plasma cholesterol concentration in laying hens.

Thirty normocholesterolemic laying hens were used to investigate the effect of oral administration of Eubacterium coprostanoligenes on plasma cholesterol concentrations. Hens were divided randomly into three treatment groups (active, inactive, and control) with 10 hens in each group. The active group received 0.5 mL of E. coprostanoligenes suspension (approximately 2 x 10(7) cells per milliliter) daily for 4 wk; the inactive group received the same dosage of killed (boiled) bacterial suspension; and the control group received no supplemental bacteria. After bacterial feeding, the coprostanol to cholesterol ratio in feces of the active group was significantly greater than ratios of the inactive and control groups, indicating that E. coprostanoligenes was colonized in the intestine of hens and was converting intestinal cholesterol to coprostanol. Plasma cholesterol concentrations, however, were not affected by the bacterial treatment.

Administration, Oral↗
PubMed1996

Increased expression of 72-kd type IV collagenase (MMP-2) in human aortic atherosclerotic lesions.

MMP-2, a secreted 72-kd metalloproteinase that specifically degrades type IV collagen as well as denatured collagens, has been implicated in smooth muscle cell migration. To evaluate the possible contribution of this enzyme to the formation and progression of the atherosclerotic lesion, the expression of MMP-2 was studied in human aortic tissue. MMP-2 was visualized in frozen sections of the aortic wall by an immunofluorescent technique with a polyclonal antibody. Expression of MMP-2 in the aortic extracts was also studied by zymography and Western blotting. Our results reveal that a greater amount of MMP-2 is present in fatty streaks and atherosclerotic plaques as compared with normal regions of the aorta. Immunoblotting analysis showed that MMP-2 was expressed in atherosclerotic plaque > fatty streak > normal aortic wall in a ratio of approximately 4:2:1. Zymograms show that both forms (activated and latent) of MMP-2 increased in the atherosclerotic plaques. The presence of macrophages, detected by an immunohistochemical technique in some areas of higher MMP-2 expression suggests that these cells are a possible source of MMP-2. We conclude that MMP-2 collagenase may have a role in the formation and progression of the atherosclerotic lesion and may be involved in clinical complications of atherosclerosis, such as fissure and rupture, leading to thrombosis.

Adolescent↗
PubMed1996

[Investigation on VNTR in intron 40 of vWF gene in Chinese Han population].

The VNTR in the intron 40 of vWF gene was investigated with a method of combination of Amp-FLP and RFLP. Two amplified fragments from a heterozygous person were separated by a non-hydratable polyacrylamide electrolyte gradient electrophoresis. After elution from gel, the preliminary products were amplified again, the amplified fragments were digested with AluI, then the genotype could be directly determined through electrophoresis. For the first time SSCP was used to detect the subtypes of microsatellite DNA. 136 alleles were found from 156 unrelated Hans in Changsha area. There were 153 genotypes in this sample and all of them were heterozygous. The calculated heterozygosity was 0.9884. The distribution of genotypes was in according with the Hardy-Weinberg equilibrium. The polymorphic information content (PIC) was 0.9883. The polymorphism of this VNTR was the highest one in the Amp-FLPs that had been found before. Our data did not show any recombination even in 2 generations of 66 families and 3 generations of 5 families. Aco-dominant segregation was demonstrated.

Base Sequence↗
PubMed1996

[Chemical constituents of Taxillus levinei (Merr.) H.S.Kiu].

Four compounds were isolated from the leaves of Taxillus levinei and identified as protocatechuic acid, isoquercitrin, quercetin-3-O-(6"-galloyl)-beta-D-glucoside and quercetin-3-O-beta-D-glucuronide on the basis of chemical properties and spectral data. These compounds were obtained from T. levinei for the first time.

Drugs, Chinese Herbal↗
PubMed1996

Selective changes in laminin adhesion and alpha 6 beta 4 integrin regulation are associated with the initial steps in keratinocyte maturation.

In skin, the distribution of integrins is compartmentalized. Whereas the alpha 6 beta 4 integrin complex is polarized to the basal portion of proliferating cells in the basal layer juxtaposed to the basement membrane, alpha 3 beta 1 integrin receptors are localized on the cell surface surrounding basal and suprabasal cells, suggesting beta 1 integrins mediate both cell-matrix and cell-cell interactions. As initiation of maturation in skin is associated with the detachment of cells from the basement membrane, the early loss of alpha 6 beta 4, but not alpha 3 beta 1, integrin expression could be a determining factor in the transition from the proliferating to a differentiating keratinocyte. We have studied the regulation of adhesion potential and integrin expression during differentiation of mouse basal keratinocytes culture in 0.05 mM Ca2+ medium and induced to differentiate in 0.12 mM Ca2+ medium. Within 12-24 h after elevation of Ca2+, a selective loss of the alpha 6 beta 4 integrin complex is associated with the induction of the spinous cell marker keratin 1. This early differentiation phenotype coincides with loss of cell attachment mediated by alpha 6 beta 4 to laminins 1 and 5 but not a fibronectin or collagen IV. Selective loss of attachment to laminin is also detected in spinous cells isolated from newborn epidermis in vivo. The loss of alpha 6 and beta 4 protein expression is a consequence of transcriptional and posttranscriptional events, including reduction in mRNA transcripts, reduced synthesis of the alpha 6 protein, and enhanced processing of the alpha 6 and beta 4 chains as determined by Western blots and pulse-chase experiments in metabolically labeled keratinocytes. Selective processing of the beta 4 intracellular domain is detected before loss of beta 4 from the cell surface in basal keratinocytes, and this process is accelerated during differentiation. Whereas early keratinocyte maturation is linked to the selective loss of the alpha 6 beta 4 complex, loss of both beta 1 and beta 4 integrin mRNA and protein occurs as cells proceed to later stages in the differentiation program as induced by 0.5 mM Ca2+ or suspension culture. These conditions are characterized by accelerated expression of transglutaminase; reduced keratin 1 protein; loss of adhesion to fibronectin, laminin 1, laminin 5, and collagen IV; and rapid cell death. Contributing to the down-regulation of beta 1 integrins during terminal differentiation is a selective sensitivity of alpha 3 beta 1 but not alpha 6 beta 4 to down-regulation by transforming growth factors beta 1 and beta 2, factors that are also expressed differentially in normal skin. This study indicates that down-regulation of the alpha 6 beta 4 but not beta 1 integrins occurs during the initial steps of keratinocyte differentiation and is associated with detachment from the laminin matrix. Such changes could contribute an important signal to initiate the process of terminal keratinocyte differentiation.

Animals↗