Biomedical subjects

S H Liu

Publications and source records attributed to S H Liu.

At least 19 recordsLinked to original sources

PubMed1995

Regulation of clathrin assembly and trimerization defined using recombinant triskelion hubs.

Clathrin polymerization into a polyhedral vesicle coat drives receptor sorting at cellular membranes during endocytosis and organelle biogenesis. To study clathrin self-assembly, we expressed the C-terminal third of the clathrin heavy chain in bacteria. The recombinant fragment trimerized, bound clathrin light chains, and morphologically resembled the hub domain of the triskelion-shaped clathrin molecule. Self-assembly of recombinant hubs demonstrated a regulatory role for clathrin light chains and for the distal portions of triskelion legs in clathrin coat formation. Deletion mutagenesis of the hub localized a domain mediating light chain binding and clathrin self-assembly and mapped a transferable trimerization domain. These studies define molecular interactions controlling clathrin self-assembly and establish a recombinant system for future analysis.

Animals↗

PubMed1995

L- and D-enantiomers of 2',3'-dideoxycytidine 5'-triphosphate analogs as substrates for human DNA polymerases. Implications for the mechanism of toxicity.

5'-Triphosphates of beta-D and beta-L-enantiomers of 2',3'-dideoxycytidine (ddC), 2',3'-dideoxy-5-fluorocytidine (FddC), 1,3-dioxolane-cytidine (OddC), and 1,3-dioxolane-5-fluorocytidine (FOddC) were evaluated as inhibitors and substrates for human DNA polymerases alpha, beta, gamma, delta, and epsilon. L-ddCTP was not a substrate or inhibitor for any DNA polymerase studied; L-FddCTP was not an inhibitor or substrate for replicative DNA polymerases and was a less potent inhibitor of DNA polymerases gamma and beta than its D-enantiomer by 2 orders of magnitude. In contrast, all L-dioxolane analogs were potent inhibitors and chain terminators for all cellular DNA polymerases studied. The Ki values of their 5'-triphosphates for DNA polymerase gamma were found to be in the following order: D-ddC < D-FddC L-OddC D-FOddC < L-FOddC << L-FddC. The Ki values of L-OddCTP for the reactions catalyzed by DNA polymerases alpha, delta, epsilon, beta, and gamma were 6.0, 1.9, 0.4, 3.0, and 0.014 microM, respectively, and those of L-FOddCTP were 6.5, 1.9, 0.7, 19, and 0.06 microM, respectively. The Km values for incorporation of L-OddCTP into the standing points of primer extension were also evaluated and determined to be 1.3, 3.5, 1.5, 2.8, and 0.7 microM for DNA polymerases alpha, delta, epsilon, beta, and gamma, respectively. The incorporation of dioxolane analogs into DNA by replicative DNA polymerases could explain their potent cellular toxicity.

Base Sequence↗

PubMed1995

Removal of anti-human immunodeficiency virus 2',3'-dideoxynucleoside monophosphates from DNA by a novel human cytosolic 3'-->5' exonuclease.

A 3'-->5' exonuclease has been highly purified from the cytosol of human acute lymphoblastic leukemia H9 cells. The apparent molecular weight of this enzyme was approximately 50,000, as indicated by its sedimentation in glycerol gradients. The exonuclease did not copurify with DNA polymerase activity, required MgCl2 for its exonucleolytic activity, and was inhibited by KCl above 60 mM. The enzyme was active on single-stranded DNA, DNA duplexes and DNA/RNA duplexes, and it was efficient at removing 3'-terminal mispairs from DNA. The products of the exonucleolytic reaction were deoxynucleoside 5'-monophosphates. The behavior of the exonuclease was examined on DNA terminated at the 3' end with a variety of dideoxynucleosides that are potent against human immunodeficiency virus type 1. The exonuclease has a broad substrate specificity; however, the rate of the enzymatic reaction varied among the D dideoxynucleosides tested (ddAMP = ddCMP > d4TMP > AZTMP). Similarly, the enzyme was examined for its reactivity with DNA terminated by either the D or L enantiomers of ddC, SddC or FddC. The removal of analogs with the native D configuration was at least 6-fold more rapid than that of the L-compounds, and the type of structural modification had an impact on the rate at which the D enantiomers were removed (SddCMP > ddCMP > FddCMP). The monophosphate forms of AZT, D4T, L-FddC and L-ddC were potent inhibitors of the exonuclease at micromolar concentrations, while D-ddCMP partially inhibited the enzyme at millimolar concentrations. Based on its physical and enzymatic properties, this exonuclease represents a novel enzyme that may have an important role in determining the relative potencies of dideoxynucleosides against human immunodeficiency virus type 1.

Antiviral Agents↗

PubMed1995

Anti-AIDS (acquired immune deficiency syndrome) agents. 17. New brominated hexahydroxybiphenyl derivatives as potent anti-HIV agents.

Sixteen biphenyl derivatives were synthesized and evaluated for their inhibitory activity against HIV-1 replication in acutely infected H9 cells. 3-Bromo- (4) and 3,3'-dibromo-4,4'-dimethoxy-5,6,5',6'-bis(methylenedioxy)-2,2'- bis(methoxycarbonyl)biphenyl (5) demonstrated potent anti-HIV activity with EC50 values of 0.52 and 0.23 micrograms/mL and therapeutic index values of > 190 and > 480, respectively. A comparison of the anti-HIV activity of these biphenyl derivatives suggested that the types of substituents on the phenolic hydroxy groups rather than the number of bromine(s) on the aromatic rings are important to the enhanced anti-HIV activity. Compounds 4 and 5 also showed potent inhibitory activity against HIV-1 reverse transcriptase in a template-primer dependent manner. The site of inhibition of HIV could be related to inhibition of this enzyme. Compounds 4 and 5 did not induce virus expression from the chronic HIV-1-infected cell lines ACH-2 and U1. Furthermore, these two agents did not inhibit an increase in virus production from the chronic HIV-1-infected cell lines when the phorbol ester PMA was present.

Antiviral Agents↗

PubMed1995

Anticancer activity of beta-L-dioxolane-cytidine, a novel nucleoside analogue with the unnatural L configuration.

Naturally occurring nucleosides and all anticancer nucleoside analogue drugs are in the beta-D configuration. L-(-)-dioxolane-cytidine [(-)-OddC] is the first L-nucleoside analogue ever shown to have anticancer activity. This compound was converted within cells to its mono-, di-, and triphosphate metabolites and was incorporated into DNA. As with cytosine arabinoside, conversion to the monophosphate was catalyzed by cellular deoxycytidine kinase, which was essential for cytotoxicity. However, unlike cytosine arabinoside, (-)-OddC was not susceptible to degradation by deoxycytidine deaminase. Because (-)-OddC inhibited the growth of hepatocellular and prostate tumors that are generally difficult to treat, it is a promising candidate for additional testing. Our results indicate that there is a great deal of variability in the chiral specificities of cellular enzymes and demonstrate how these differences can be exploited in the design of better anti-viral and anticancer drugs.

Animals↗

PubMed1995

Serum response element associated transcription factors in mouse embryos: serum response factor, YY1, and PEA3 factor.

Many mammalian transcription factors, including human and mouse serum response factors (SRFs), are post-translationally modified with O-linked N-acetylglucosamine monosaccharides on multiple serine and/or threonine residues. Nuclear extracts were prepared from 9.5 to 19 days postcoitum mouse embryos and subsequently were fractionated by wheat germ agglutinin (WGA)-agarose affinity chromatography. SRF binds WGA-agarose and apparently is O-glycosylated. On the other hand, the low molecular weight serum response element (SRE)-binding proteins, including the previously named band I and band II factors, did not bind WGA-agarose. Furthermore, we showed that the fastest migrating complex contains the Yin-Yang 1 (YY1) factor. YY1 binds to the c-fos SRE and skeletal alpha-actin muscle regulatory element (MRE), but not the cardiac alpha-actin MRE. Nuclear extracts from NIH/3T3 fibroblasts contain similar, if not identical, SRE-binding complexes. Besides these SRE-binding factors, mouse PEA3-binding factor, presumably an ETS domain-containing protein, was found to bind SRF protein. This physical interaction, between SRF and ETS domain proteins, was shown to involve the DNA-binding domain-containing region of SRF and not the carboxyl-terminal transactivation domain.

Animals↗

PubMed1995

The effects of thigh soft-tissue stiffness on the control of anterior tibial displacement by functional knee orthoses.

Using three soft-tissue analogs of variable compliances, four custom functional knee orthoses were evaluated for their abilities to control anterior tibial displacement (ATD) using an anterior cruciate ligament (ACL)-deficient surrogate knee model with applied forces from 25 to 250 N. These analogs had stiffnesses (compliance) ranging from 2.18 N/mm to 4.6 N/mm, simulating the range in the thigh soft-tissue compliances found in subjects ranging from sedentary individuals to competitive athletes. Significant differences in the ATDs allowed were observed between the soft-tissue analogs, orthoses, and the force applied. At low forces, soft-tissue compliance did not play an important role in the reduction of ATD; however, at high forces ATD was directly related to the soft-tissue compliance.

Adolescent↗

PubMed1995

Autoimmunity to a cornea-associated stromal antigen in patients with Mooren's ulcer.

PURPOSE: To purify and characterize a cornea-associated antigen (CO-Ag) and to determine antibody levels to CO-Ag in patients with Mooren's ulcer. METHOD: Standard ion exchange and gel filtration chromatographies were used to isolate and purify CO-Ag from crude bovine stromal extracts. The serum of a patient with Mooren's ulcer, containing a high level of antibodies directed against CO-Ag, was used to monitor isolation procedures. Using this newly purified CO-Ag, an enzyme-linked immunoabsorbent assay was used to detect the presence of antibodies to CO-Ag in the sera of other patients with Mooren's ulcer. RESULTS: CO-Ag was purified to apparent homogeneity from bovine corneal stromal extracts by a series of ion exchange chromatographies and gel filtration. Polyacrylamide gel electrophoresis showed that CO-Ag was a tetramer with a molecular weight of 30,000 d that may dissociate under denaturing conditions into a monomer of 7000 d. Strong indirect immunofluorescent staining was demonstrated of the stroma by guinea pig anti-CO-Ag antibody. A statistically significant difference in the level of specific antibodies to CO-Ag between patients with Mooren's ulcer and controls was found (P < 0.001). The antibody level was elevated in patients with Mooren's ulcer (mean antibody level, 0.58 +/- 0.13) compared with the controls (mean antibody level, 0.22 +/- 0.04). CONCLUSION: These results suggest that an autoantigen exists in the corneal stroma that reacts with serum antibodies from patients with Mooren's ulcer. The availability of a purified corneal antigen could facilitate the diagnosis and define the pathogenetic mechanisms in Mooren's ulcer.

Animals↗

PubMed1995

The diagnosis of acute complete tears of the anterior cruciate ligament. Comparison of MRI, arthrometry and clinical examination.

We reviewed 38 patients with arthroscopically-proven complete ACL tears operated on less than three weeks after injury. Their average age was 26 years (16 to 43), with 27 males and 11 females. All patients had had MRI preoperatively. The same examiner performed the Lachman, anterior-drawer, and pivot-shift tests without anaesthesia, recording the differences between the injured and the normal knees. The patients then had KT-1000 arthrometry by the same examiner at 15 lb (6.8 kg) and 20 lb (9 kg), with active displacement, and with maximum manual displacement. All scored positive for differences greater than 3 mm. The results of physical examination, KT-1000 tests and MRI were analysed using McNemar's test for matched data with continuity correction and a 95% confidence interval for each test. The sensitivity of the KT-1000 manual maximum test was 97% for 3 mm and 100% for 2 mm; this was the most useful arthrometric result. The Lachman test gave 95% sensitivity, providing the best simple clinical assessment. MRI was 97% sensitive for the detection of all ACL injuries, but this fell to 82% with respect to complete rupture. We found no significant differences between the results of the Lachman test and the KT-1000 manual maximum test, but these were significantly better than all other tests. In an era of cost-containment, we have shown that inexpensive tests in the clinic can allow treatment to proceed rapidly and in the most economical manner without the routine use of MRI.

Acute Disease↗

PubMed1995

Arthroscopic management of the acromioclavicular joint disorder. A review.

Acromioclavicular joint symptoms may originate from either osteolysis or osteoarthritis. Initial treatment consists of 6 to 12 months of physical therapy, nonsteroidal antiinflammatory drugs, avoidance of exacerbating activities, and other conservative modalities. The majority of patients respond well, but a few remain unable to return to their previous or desired activity levels. Previously this group of patients underwent open resection of the distal clavicle. [The approach violates the deltotrapezial fascia, weakening the surgically treated extremity, which has caused controversy in the literature.] Even without complications, the recovery and time away from work is prolonged. With advances in arthroscopic techniques, resection of the distal clavicle and medial aspect of the acromion has become possible with minimal invasiveness. The arthroscopic technique offers the advantages of rapid rehabilitation with excellent functional results. Several different modifications of 2 basic approaches, the bursal and direct superior, have been described by various authors. The authors sought to examine critically and review the data supporting the choice of arthroscopic surgery rather than an open technique, as well as the advantages of 1 arthroscopic approach over the other.

Acromioclavicular Joint↗

PubMed1995

Current review. Functional knee bracing.

Recent surgical advancements in anterior cruciate ligament reconstructions have led to better results in the treatment of knee injuries. Functional knee braces have been prescribed in greater number, leading to an increased production of commercially available braces. The effectiveness of braces remains controversial because of inconsistency in investigations of functional knee braces. This article reviews the historical background, biomechanics, and static and dynamic testing of knee braces and compares custom and off-the-shelf functional knee braces. Factors such as hinge design and soft tissue compliance, which may affect functional knee bracing, are discussed.

Anterior Cruciate Ligament Injuries↗

PubMed1995

Collagen in tendon, ligament, and bone healing. A current review.

Cells that produce a particular type of collagen under normal physiologic circumstances can be induced by certain local triggers to change the amount and type of collagen synthesized. This has become most apparent during bone, tendon, and ligament healing, where cells that once produced the collagen of normal intact tissue are induced to synthesize different types of collagen at the repair site of injured tissue. For example, Type III collagen, not a major component of the extracellular matrix in normal tendons, is believed to be of great advantage during the healing process because of its ability to form rapid crosslinks and precariously stabilize the repair site. Although much is known about the gross histologic changes occurring during tissue healing, little is known about the specific role of the individual collagen types or what influences their development. This review addresses the role of collagen in normal and healing bone, tendon, and ligament. Much experimental effort is needed to uncover the distribution and function of the collagen types within connective tissue elements and the effect of growth factors on the phenotype of collagen produced in these tissue, with the ultimate goal of developing clinical manipulations that take advantage of the unique properties of each type of collagen.

Anterior Cruciate Ligament↗

PubMed1995

Biomechanics of two types of bone-tendon-bone graft for ACL reconstruction.

We measured the initial fixation strength of a new graft, bone-hamstring-bone (BHB), for reconstruction of the anterior cruciate ligament (ACL) in 79 porcine knees and compared it with that of the normal porcine ACL and of the bone-patellar tendon-bone (BPB) graft. All specimens were subjected to ultimate load to failure and cyclic loading tests to assess the amount of graft slippage. The ultimate load to failure for the intact ACL was 1266 +/- 250 N, for the BPB graft 663 +/- 192 N and for the BHB graft 354 +/- 92 N (p < 0.01). After cycling to 235 N (the maximum load for all groups without failure) the average residual displacements after removal of the load for the ACL, BPB and BHB grafts were 0.031 +/- 0.013 cm, 0.078 +/- 0.033 cm, and 0.322 +/- 0.222 cm, respectively (p < 0.01). For the BHB graft the load to failure was less and the amount of graft slippage was more than for the BPB graft. Neither form of reconstruction was as strong as the intact ACL.

Animals↗

PubMed1995

A new operation for chronic lateral ankle instability.

We have treated 45 patients (47 ankles) for chronic lateral instability by a new reconstructive procedure. The operation includes lateral shift of the entire lateral capsule-ligament complex and proximal advancement of the talocalcaneal ligament and the inferior extensor retinaculum. We reviewed 39 patients (39 ankles) at a mean of 4.6 years (2 to 7) after operation. There were 29 men and 10 women with an average age of 27 years (19 to 43); 11 of them were competitive college-level athletes and 28 were recreational athletes. The functional rating was excellent in 26 patients, good in 8, fair in 3 and poor in 2. Thirty-six patients (92%) were satisfied with the result and 34 (9 of 11 college-level athletes and 25 of 28 recreational athletes) have been able to return to their preinjury level of sport. At the last review, there had been only three episodes of recurrent ankle instability, all in recreational athletes; none had required further surgery. The unsatisfactory results were associated with pre-existing degenerative changes in the ankle.

Adult↗

PubMed1994

Studies on the contracture inducing action of triphenyltin in the mouse diaphragm.

Triphenyltin induces a contracture of the mouse phrenic nerve-diaphragm preparation. This contracture was not inhibited by (+)-tubocurarine, high magnesium or the absence of electrical stimulation. Triphenyltin (0.1 mM) reduced the muscle membrane potential, the amplitude of the muscle action potential and the muscle membrane input resistance. Pretreatment with high K+ (25 mM) or veratridine (1.5 microM; a Na+ channel activator) briefly shortened the onset of the contracture and increased the peak tension of the contracture. Pretreatment with tetrodotoxin (0.3 microM; a Na+ channel blocker) or glycerol (a T tubule uncoupler) however, significantly reduced the triphenyltin-induced contracture. Removing Ca2+ from external solution and prolonged treatment with either caffeine (20 mM) or ryanodine (2 microM) inhibited the triphenyltin-induced contracture. However, a brief treatment with a lower concentration of caffeine (10 mM) potentiated the contracture. 45Ca2+ uptake studies showed that triphenyltin caused the muscle to accumulate Ca2+ which entered from external solution. Pretreatment with trypsin and dithiothreitol (a sulfhydryl-containing reducing agent) blocked the contracture induced by triphenyltin. These results suggest that triphenyltin initially interacts with the sulfhydryl groups of membrane bound proteins (possibly the Na+ channel) to cause depolarization of the muscle fibres. This depolarization triggers the release of Ca2+ from sarcoplasmic reticulum through the mechanism of Ca2+ inducing Ca2+ release, activates the contractile filaments and causes the muscle to contract.

Action Potentials↗

PubMed1994

Serum response factor associated ETS proteins: ternary complex factors and PEA3-binding factor.

An ETS protein binding motif CAGGAT adjoins the 5' side of the Serum Response Element in the c-fos promoter. This sequence is recognized by several ETS proteins which are able to form ternary complexes in the presence of Serum Response Factor. Related sequences, capable of ternary complex formation, are also found in the promoters of immediate early zinc finger proteins. However, similar sequences found in the gamma-actin and c-ets-2 promoters could not bind Ternary Complex Factor. We purified a 60-kDa human ETS protein which could bind the sequence recognized by Ternary Complex Factor, and this protein could bind DNA in the absence of Serum Response Factor. Interestingly, this protein also binds Serum Response Factor in vitro. Therefore the Serum Response Factor DNA-binding/oligomerization domain has affinities for distinct ETS oncoproteins.

Base Sequence↗

PubMed1994

An in vivo comparison of oral 5-iodo-2'-deoxyuridine and 5-iodo-2-pyrimidinone-2'-deoxyribose toxicity, pharmacokinetics, and DNA incorporation in athymic mouse tissues and the human colon cancer xenograft, HCT-116.

5-iodo-2-pyrimidinone-2'-deoxyribose (IPdR) was recently reported to be converted to 5-iodo-2'-deoxyuridine (IUdR) by an aldehyde oxidase, most concentrated in liver tissue. We questioned whether IPdR could be used as a p.o. hepatotropic prodrug to increase the percentage of IUdR-DNA incorporation into liver tumors compared to normal liver with acceptable systemic toxicity. Athymic nude mice with human colon cancer (HCT-116) xenograft tumors as liver metastases and s.c. flank tumors received daily p.o. boluses (via gastric tubes) of IUdR or IPdR for 6 days. The maximum tolerated dose of IUdR was 250 mg/kg/day and was associated with a > 10% weight loss and a high percentage of IUdR-DNA incorporation (> 5%) into normal bone marrow and intestine. In contrast, animals tolerated escalating doses of IPdR to 1 gm/kg/day without weight loss and with less (1.5-4%) IUdR-DNA incorporation in normal tissues. Pharmacokinetic analysis of p.o. IPdR showed peak plasma levels of IPdR and IUdR within 15-45 min, suggesting efficient conversion of IPdR to IUdR. Aldehyde oxidase activity was found in normal liver tissue but not in other normal or tumor tissues. Additionally, we found a 2-3 times greater percentage of IUdR-DNA incorporation in tumor with IPdR than IUdR at the highest doses used. However, no differential effect in the percentage of IUdR-DNA incorporation was noted between liver metastases and s.c. tumors with either IPdR or IUdR. We conclude that p.o. IPdR offers a greater therapeutic index for tumor incorporation (and presumably radiosensitization) than a similar schedule of IUdR.

Administration, Oral↗

PubMed1994

Potentiation by metal ions of ryanodine contracture of the mouse diaphragm.

The aim of this study was to elucidate the possible mechanism of the potentiating action of metal ions (Cu2+, Hg2+, Ag+ and SeO3(2-)) on the ryanodine-induced contracture of the mouse diaphragm. The ryanodine contracture in the quiescent muscle could be augmented by either electrical stimulation or pretreatment with high K+ of the diaphragm. Lowering the external Ca2+ concentration from 2.5 mM to 1 microM or the addition of 7 microM d-tubocurarine, which abolished the muscle excitability by blocking the receptors of acetylcholine, markedly attenuated the ryanodine contracture. Application of Cu2+, Hg2+, Ag+ and SeO3(2-) but not Ni2+ and Co2+, to quiescent muscle restored the ryanodine contracture. The potentiating effects of Hg2+, Ag+ and high K+ were dependent on the presence of external Ca2+ (2.5 mM) and intact transverse tubular systems but the effects of Cu2+ and SeO3(2-) were not. Treatment with 1 mM dithiothreitol 10 min after the application of metal ions and then subsequent addition of ryanodine abolished the potentiating effects of Hg2+ and Ag+ but not those of Cu2+ and SeO3(2-). Although ryanodine by itself had no effect on 45Ca2+ uptake by the mouse diaphragm, it significantly potentiated the increased 45Ca2+ uptake elicited by Cu2+ and Hg2+. Further elucidation of the interaction between metal ions and ryanodine on the outer sarcolemma showed that all of these metal ions, including the inactive Co2+ and Ni2+, not only decreased the membrane potential but also altered the membrane input resistance, effects which were not correlated with the potentiating effects of the metal ions on the ryanodine contracture.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗