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Biomedical subjects

J Liang

Publications and source records attributed to J Liang.

At least 19 recordsLinked to original sources
PubMed1999

Contextual effects of transforming growth factor beta on the tumorigenicity of human colon carcinoma cells.

Transforming growth factor betas (TGF-betas) are a growth factor family with negative autocrine growth functions for most epithelial cells including colon carcinoma cell lines. Both type I (RI) and type II (RII) transmembrane TGF-beta receptors have been shown to be indispensable for TGF-beta-mediated cell growth regulation. Previous studies using different model systems have shown that both overexpression of TGF-beta1 and transfection of antisense TGF-beta1 to reduce TGF-beta1 expression could lead to increased tumorigenicity. These results are seemingly contradictory and suggest that effects of TGF-beta modulation on malignant properties of cancer cells may be contextual. This study addresses this issue using human colon carcinoma cells (CBS and FET) to determine the effects of modulation of the various components of the TGF-beta system on in vitro and in vivo growth properties in two independent isogenic models of colon carcinoma. Cells were stably transfected with a tetracycline-repressible RII expression vector (CBS4-RII), a tetracycline-repressible expression vector containing a truncated RII cDNA lacking the serine/threonine kinase domain (CBS4-deltaRII and FET6-deltaRII), or with a vector containing the TGF-beta1 cDNA (CBS4-beta1S and FET-beta1S). Expression of the truncated RII reduced TGF-beta sensitivity, whereas overexpression of RII increased TGF-beta sensitivity. TGF-beta overexpression did not affect TGF-beta response. In vivo tumorigenicity assays revealed that CBS4-RII cells had lower tumorigenicity than control cells, whereas CBS4-deltaRII and CBS4-beta1S had higher tumorigenicity than controls. The CBS4 cells are poorly tumorigenic in athymic mice, and the wild-type FET6 cells are nontumorigenic. FET6-deltaRII cells formed rapidly growing tumors, and FET-beta1S cells also formed tumors. These data illustrate the paradoxical tumor-promoting and -suppressing effects of TGF-beta signaling activity in two isogenic model systems from human colon carcinomas, thus demonstrating that the effects of modulation of TGF-beta expression or TGF-beta signaling capability affects malignancy in a contextual manner.

Animals↗
PubMed1999

Chloride binding regulates the Schiff base pK in gecko P521 cone-type visual pigment.

The binding of chloride is known to shift the absorption spectrum of most long-wavelength-absorbing cone-type visual pigments roughly 30 nm to the red. We determined that the chloride binding constant for this color shift in the gecko P521 visual pigment is 0.4 mM at pH 6.0. We found an additional effect of chloride on the P521 pigment: the apparent pKa of the Schiff base in P521 is greatly increased as the chloride concentration is increased. The apparent Schiff base pKa shifts from 8.4 for the chloride-free form to >10.4 for the chloride-bound form. We show that this shift is due to chloride binding to the pigment, not to the screening of the membrane surface charges by chloride ions. We also found that at high pH, the absorption maximum of the chloride-free pigment shifts from 495 to 475 nm. We suggest that the chloride-dependent shift of the apparent Schiff base pKa is due to the deprotonation of a residue in the chloride binding site with a pKa of ca. 8.5, roughly that of the Schiff base in the absence of chloride. The deprotonation of this site results in the formation of the 475 nm pigment and a 100-fold decrease in the pigment's ability to bind chloride. Increasing the concentration of chloride results in the stabilization of the protonated state of this residue in the chloride binding site and thus increased chloride binding with an accompanying increase in the Schiff base pK.

Animals↗
PubMed1999

Characterization of a mutant pancreatic eIF-2alpha kinase, PEK, and co-localization with somatostatin in islet delta cells.

Phosphorylation of eukaryotic translation initiation factor-2alpha (eIF-2alpha) is one of the key steps where protein synthesis is regulated in response to changes in environmental conditions. The phosphorylation is carried out in part by three distinct eIF-2alpha kinases including mammalian double-stranded RNA-dependent eIF-2alpha kinase (PKR) and heme-regulated inhibitor kinase (HRI), and yeast GCN2. We report the identification and characterization of a related kinase, PEK, which shares common features with other eIF-2alpha kinases including phosphorylation of eIF-2alpha in vitro. We show that human PEK is regulated by different mechanisms than PKR or HRI. In contrast to PKR or HRI, which are dependent on autophosphorylation for their kinase activity, a point mutation that replaced the conserved Lys-614 with an alanine completely abolished the eIF-2alpha kinase activity, whereas the mutant PEK was still autophosphorylated when expressed in Sf-9 cells. Northern blot analysis indicates that PEK mRNA was predominantly expressed in pancreas, though low expression was also present in several tissues. Consistent with the high levels of mRNA in pancreas, the PEK protein was only detected in human pancreatic islets, and the kinase co-localized with somatostatin, a pancreatic delta cell-specific hormone. Thus PEK is believed to play an important role in regulating protein synthesis in the pancreatic islet, especially in islet delta cells.

Amino Acid Sequence↗
PubMed1999

Electrostatic interactions during activation of coagulation factor IX via the tissue factor pathway: effect of univalent salts.

Interaction between the Gla-domain of coagulation proteins and negatively charged phospholipid membranes is essential for blood coagulation reactions. The interaction is calcium-dependent and mediated both by electrostatic and hydrophobic forces. This report focuses on the electrostatic component of factor IX activation via the extrinsic pathway. Effective charges during the reaction are measured by ionic titration of activity, according to the Debye-Huckel and Gouy-Chapman models. Rates of activation decrease with ionic strength independently of the type of monovalent salt used to control ionic strength. Moreover, the effect of ionic strength decreases at concentrations of charged phospholipid approaching saturation levels, indicating that membrane charges participate directly in the ionic interaction measured. The effective charge on calcium-bound factor IX during activation on phospholipid membranes is 0.95+/-0.1. Possible sites mediating contacts between the Gla-domain and membranes are selected by geometrical criteria in several metal-bound Gla-domain structures. A pocket with a solvent opening-pore of area 24-38 A2 is found in the Gla-domain of factors IX, VII, and prothrombin. The pocket contains atoms with negative partial charges, including carboxylate oxygens from Gla residues, and has a volume of 57-114 A3, sufficient to accommodate additional calcium atoms. These studies demonstrate that electrostatic forces modify the activity coefficient of factor IX during functional interactions and suggest a conserved pocket motif as the contact site between the calcium-bound Gla-domain and charged membranes.

Binding Sites↗
PubMed1999

Single-molecule fluorescence spectroscopy of enzyme conformational dynamics and cleavage mechanism.

Fluorescence resonance energy transfer and fluorescence polarization anisotropy are used to investigate single molecules of the enzyme staphylococcal nuclease. Intramolecular fluorescence resonance energy transfer and fluorescence polarization anisotropy measurements of fluorescently labeled staphylococcal nuclease molecules reveal distinct patterns of fluctuations that may be attributed to protein conformational dynamics on the millisecond time scale. Intermolecular fluorescence resonance energy transfer measurements provide information about the dynamic interactions of staphylococcal nuclease with single substrate molecules. The experimental methods demonstrated here should prove generally useful in studies of protein folding and enzyme catalysis at single-molecule resolution.

Base Sequence↗
PubMed1999

Stereospecific synthesis, structure-activity relationship, and oral bioavailability of tetrahydropyrimidin-2-one HIV protease inhibitors.

The use of tetrahydropyrimidinones as an alternate scaffold for designing HIVPR inhibitors has advantages, over the previously disclosed hexahydro-1,3-diazepin-2-ones, of being more unsymmetrical (different P1/P1'), less crystalline, more soluble, and more lipophilic (mono-ol vs diol). They show a better translation of Ki to IC90 for the more polar P2 groups that in general give the more potent enzyme inhibitors. Structure-activity relationship (SAR) studies of the tetrahydropyrimidinones showed that the phenylethyl P1' substituent, the hydroxyl group, and the urea carbonyl are all critical for good activity. However, there was significant flexibility in the possible P2/P2' substituents that could be used. Many analogues that contained identical or different P2/P2' substituents, or only one P2 substituent, were found to have excellent enzyme potency and several had excellent antiviral potency. Several of these compounds were examined for oral bioavailability in the rat or the dog at 10 mg/kg. However, the oral bioavailability of the tetrahydropyrimidinones was, in general, less than the corresponding hexahydro-1,3-diazepin-2-ones. Unfortunately, when all factors are considered, including potency, protein binding, solubility, bioavailability, and resistance profile, the tetrahydropyrimidinones did not offer any advantage over the previously disclosed hexahydro-1,3-diazepin-2-ones series.

Administration, Oral↗
PubMed1999

Expression of the c-kit proto-oncogene in rat hepatic allografts during acute rejection.

The role of the c-kit proto-oncogene in organ allograft rejection is not known. We investigated the level of c-kit expression following allogeneic transplantation of ACI rat liver grafts into LEW recipients. We studied c-kit mRNA and protein expression in groups of transplant recipients receiving hepatic isografts, hepatic allografts, or hepatic allografts after donor-specific blood transfusion (DST). Pretransplantation DST significantly prolonged survival of hepatic allografts. Infiltrates expressing c-kit were observed in allografts to untreated rats but not in groups receiving isografts or allografts following DST. Northern analysis also demonstrated abundant c-kit mRNA transcripts in the untreated allograft group in contrast to the isograft and the DST-treated groups. In addition, significantly more transcripts for interleukin-12 (IL-12), which is synergistic with c-kit, were present in untreated than in DST-treated allograft groups. In contrast, transforming growth factor beta (TGF-beta), which inhibits c-kit synthesis, was expressed abundantly in hepatic allografts to DST-treated rats but not in allografts to untreated animals. Transcripts for IL-10, which inhibits IL-12 production, were significantly more plentiful in hepatic allografts following DST than in those without DST. The results suggest that c-kit proto-oncogene expression in infiltrating cells is associated with rat hepatic allograft rejection.

Animals↗
PubMed1999

Peroxynitrite formation during rat hepatic allograft rejection.

The role of nitric oxide (NO) on tissue injury of hepatic allografts during rejection remains controversial. We investigated inducible nitric oxide synthase (iNOS) expression and formation of peroxynitrite in ACI rat liver grafts implanted in recipients. Animals were divided into four experimental groups: group I, isografts; group II, untreated hepatic allografts; group III, allografts treated with FK506; and group IV, allografts pretreated with donor-specific blood transfusion (DST). Serum nitrite/nitrate, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) concentrations increased significantly in group II rats after transplantation but were significantly lower in groups I, III, and IV. The numbers of macrophages that reacted with an antimacrophage iNOS monoclonal antibody as well as iNOS messenger RNA (mRNA) levels in liver specimens were also much lower in groups I, III, and IV as compared with group II. Immunostaining and Western blot analysis showed prominent tissue nitrotyrosine expression in untreated hepatic allografts, but not in allografts treated with FK506 or donor-specific blood. These results suggest that one of the mechanisms by which production of NO results in injury in rat hepatic allografts may be because of its reaction with superoxide to form peroxynitrite.

Animals↗
PubMed1999

FGF-19, a novel fibroblast growth factor with unique specificity for FGFR4.

We have identified a novel fibroblast growth factor, FGF-19, the most distant member of the FGF family described to date. FGF-19 is a high affinity, heparin dependent ligand for FGFR4 and is the first member of the FGF family to show exclusive binding to FGFR4. Human FGF-19 maps to chromosome 11 q13.1, a region associated with an osteoporosis-pseudoglioma syndrome of skeletal and retinal defects. FGF-19 message is expressed in several tissues including fetal cartilage, skin, and retina, as well as adult gall bladder and is overexpressed in a colon adenocarcinoma cell line.

Adenocarcinoma↗
PubMed1999

Stress, social relations, and old age mortality in Taiwan.

The research analyzed the relationships among stress, social relations, and mortality in a probability sample of 4,049 Taiwanese adults, aged 60 and over. The baseline survey was conducted in 1989 and the survival status of the respondents was ascertained during the subsequent 4 years. Death of a spouse or a child was found to increase the risk of dying directly and indirectly, whereas major financial difficulty during the past 5 years and current financial strain influenced mortality indirectly through their effects on self-rated health disability. In addition to their direct effect on mortality, martial status and work status lowered the probability of dying through decreased disability and subjective ill health. Finally, no buffering effects of social support were substantiated.

Adaptation, Psychological↗
PubMed1999

Novel carboxamide derivative (IS-741) attenuates lung injury in rats with cerulein-induced pancreatitis complicated by endotoxemia.

The therapeutic effects of an intravenously injected carboxamide derivative (IS-741) on lung injury were studied in rats with cerulein-induced pancreatitis complicated by endotoxemia. Pancreatitis was induced by four intramuscular injections of cerulein (50 microg/kg at 1-hr intervals). Pancreatitis rats were injected intraperitoneally with 10 mg/kg of lipopolysaccharide (LPS) 6 hr following the first cerulein injection as a challenge of endotoxemia. Rats were divided into four groups: group I, pancreatitis with LPS; group II, pancreatitis with LPS treated with a continuous intravenous injection of IS-741 at 0.03 mg/kg/hr); group III, pancreatitis with LPS treated with a continuous intravenous injection of IS-741 at 0.3 mg/kg/hr); and group IV, pancreatitis with LPS treated with a continuous intravenous injection of IS-741 at 3 mg/kg/hr). IS-741 was administered 30 min before the endotoxemia challenge. Intense mononuclear cell infiltration and lung hemorrhage occurred in untreated pancreatitis rats with LPS (group I), but hemorrhage was not seen in group IV rats receiving a continuous injection of IS-741 shortly before the induction of endotoxemia. The IS-741-treated rats (groups II, III, and IV) had lower serum concentrations of cytokine-induced neutrophil chemoattractant (CINC), as well as fewer pulmonary infiltrates immunoreactive for CINC or Mac-1 (CD11b/CD18). The number of neutrophils infiltrating the lung in groups II, III, and IV was significantly lower than that of group I. Conversely, CINC production by bronchoalveolar macrophages in vitro were stimulated by LPS but were reduced by the presence of IS-741. The carboxamide derivative IS-741 effectively prevented pancreatitis-associated lung injury following the challenge of endotoxemia.

Acute Disease↗
PubMed1999

Structure of the PIN/LC8 dimer with a bound peptide.

The structure of the protein known both as neuronal nitric oxide synthase inhibitory protein, PIN (protein inhibitor of nNOS), and also as the 8 kDa dynein light chain (LC8) has been solved by X-ray diffraction. Two PIN/LC8 monomers related by a two-fold axis form a rectangular dimer. Two pairs of alpha-helices cover opposite faces, and each pair of helices packs against a beta-sheet with five antiparallel beta-strands. Each five-stranded beta-sheet contains four strands from one monomer and a fifth strand from the other monomer. A 13-residue peptide from nNOS is bound to the dimer in a deep hydrophobic groove as a sixth antiparallel beta-strand. The structure provides key insights into dimerization of and peptide binding by the multifunctional PIN/LC8 protein.

Amino Acid Sequence↗
PubMed1999

[Epidermoid formation in the pathogenesis of congenital cholesteatoma--a current review].

BACKGROUND: Many theories have been suggested regarding the origin, pathogenesis, diagnosis, and incidence of congenital cholesteatoma. REVIEW OF LITERATURE: An overview on the current literature on congenital cholesteatoma of the middle ear is presented. It comprises the possible etiology and pathogenesis of congenital cholesteatoma. Among other theories, germ scattering, metaplasia, ingrowth of meatal epidermis, and reflux of amniotic fluid have been proposed. Special emphasis is put on the epidermoid formation theory, which has been described by Michaels and others. CONCLUSIONS: It is widely accepted that congenital cholesteatomas may originate from the postpartum persistence of epidermoid formations. Nevertheless, a clear transition from epidermoid formation to congenital cholesteatoma has yet to be confirmed.

Cholesteatoma, Middle Ear↗
PubMed1999

Platelet-activating factor antagonist (TCV-309) attenuates the priming effects of bronchoalveolar macrophages in cerulein-induced pancreatitis rats.

We investigated the role of platelet-activating factor (PAF) as a priming signal for cytokine-induced neutrophil chemoattractant (CINC) expression by bronchoalveolar macrophages in acute pancreatitis. Pancreatitis was induced by four intramuscular injections of cerulein (50 micrograms/kg at 1-h intervals) in Wistar rats. The animals were injected intraperitoneally with 10 micrograms/kg of lipopolysaccharide (LPS) as a septic challenge. Pancreatitis rats were treated with a bolus intravenous injection of TCV-309 (3 or 30 micrograms/kg) 30 min before the septic challenge. Intense mononuclear cell infiltration and lung hemorrhage occurred in pancreatitis rats complicated with sepsis but were not seen in pancreatitis rats receiving a bolus TCV-309. Pancreatitis rats treated with TCV-309 had lower serum concentrations of CINC after septic challenge and lower levels of CINC messenger RNA (mRNA) in the lung, as well as fewer pulmonary infiltrates immunoreactive for CINC or Mac-1 (CD11b/CD18). In vitro CINC production in response to LPS by bronchoalveolar macrophages obtained from pancreatitis rats 6 h after the first cerulein injection, immediately before septic challenge, was enhanced but was significantly reduced in a TCV-309-sensitive manner. LPS-stimulated in vitro CINC production by naive bronchoalveolar macrophages was significantly enhanced by pretreatment with PAF. TMB-8 (an inhibitor of calcium release from endoplasmic reticulum) or W7 (calmodulin antagonist) completely abrogated the chemoattractant production by bronchoalveolar macrophages pretreated with PAF after LPS stimulation. Altered intracellular calcium, due to Ca2+ efflux from intracellular stores, may be involved in the "priming" of bronchoalveolar macrophages to release CINC after triggering with LPS during acute cerulein-induced pancreatitis. The PAF antagonist TCV-309 effectively prevented hyperactivity of bronchoalveolar macrophages and pancreatitis-associated lung injury after the septic challenge.

Animals↗
PubMed1999

Refined structure of the FKBP12-rapamycin-FRB ternary complex at 2.2 A resolution.

The structure of the FKBP12-rapamycin-FRB ternary complex has now been refined at 2.2 A resolution. The cell-cycle arrest agent rapamycin binds FK506-binding protein (FKBP12) and the FKBP12-rapamycin binding (FRB) domain of FKBP12-rapamycin associated protein (FRAP) simultaneously, and the inhibition of FRAP is responsible for rapamycin's biological activity. The conformation of rapamycin in the ternary complex is very similar to that observed in the FKBP12-rapamycin binary complex, with an r.m.s. difference of only 0.30 A. However, a slight (9 degrees ) rotation repositions the FRB-binding face of rapamycin in the ternary complex. There are extensive rapamycin-protein interactions and relatively few interactions between the two protein partners FKBP12 and FRB, these interactions mainly involving residues in the 40s and 80s loops of FKBP12 and alpha1 and alpha4 of FRB. The high-resolution refinement has revealed the crucial role of several buried waters in the formation of the ternary complex.

Amino Acid Sequence↗
PubMed1999

Detection of gastric slow wave propagation from the cutaneous electrogastrogram.

The gastric slow wave is originated in the proximal stomach and propagates distally toward the pylorus. It determines the maximum frequency and propagation of gastric contractions. The aim of this study was to detect the propagation of the gastric slow wave from the surface electrogastrogram (EGG). The study was performed in 11 healthy subjects of normal weight. Gastric myoelectrical activity was recorded for 1 h in the fasting state with the use of a specially designed multichannel recording device that was composed of four identical amplifiers with cutoff frequencies of 1.8 and 16.0 cycles/min. Four active electrodes were placed on the abdomen along the gastric axis and were connected to a common reference electrode placed near the xiphoid process, yielding four-channel bipolar EGG signals. Cross-covariance analysis was performed to compute the time lag among the four channels. There was a time lag in EGG waveform between channels 1 and 4 (9.6 +/- 1.1 s); the average time during which the time lag was observed (>/=3 s) was 89.9 +/- 9.0%. There was a significant difference in the time lag among different adjacent channels (P < 0.04); the time lag observed between channels 3 and 4 was significantly smaller than that between channels 1 and 2 (P < 0.03). No correlation was found between the body mass index and the time lag between channels 1 and 4 (r = -0.31, P = 0.3). It was concluded that, with a multichannel recording device with identical multiamplifiers and an appropriate arrangement of abdominal electrodes, the propagation of the gastric slow wave could be identified from the EGG in healthy subjects. This method may be used to detect the coupling of the gastric slow wave noninvasively.

Adult↗
PubMed1999

The novel carboxamide derivative IS-741 reduces neutrophil chemoattractant production by bronchoalveolar macrophages in rats with cerulein-induced pancreatitis complicated by sepsis.

BACKGROUND/AIMS: The priming mechanism of macrophages to secrete cytokines in acute pancreatitis is important for remote organ failure following septic complication. The effects of novel carboxamide derivative, IS-741, on neutrophil chemoattractant production by bronchoalveolar macrophages were studied in rats with cerulein-induced pancreatitis complicated by sepsis. METHODS: Pancreatitis was induced by four intramuscular injections of cerulein (50 microg/kg at 1-hour intervals). Pancreatitis rats were injected intraperitoneally with 10 mg/kg of lipopolysaccharide (LPS) 6 h following the first cerulein injection as a septic challenge. Pancreatitis rats received a continuous intravenous injection of IS-741 (3 mg/kg/h) 30 min before the septic challenge. RESULTS: Intense mononuclear cell infiltration and lung hemorrhage occurred in untreated pancreatitis rats complicated with sepsis, but hemorrhage was not seen in septic pancreatitis rats receiving a continuous intravenous injection of IS-741 shortly before sepsis induction. The IS-741-treated rats had lower serum concentrations of cytokine-induced neutrophil chemoattractant (CINC), as well as fewer the pulmonary neutrophils and infiltrates immunoreactive for CINC or Mac-1 (CD11b/CD18). CONCLUSION: The novel carboxamide derivative IS-741 reduced CINC production by bronchoalveolar macrophages and effectively prevented pancreatitis-associated lung injury following the septic challenge.

Animals↗