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Biomedical subjects

K Wong

Publications and source records attributed to K Wong.

At least 73 records · Page 4Linked to original sources
PubMed1999

Magnetic resonance imaging of the temporomandibular joint: diagnostic difficulty caused by extensive pneumatization of the mastoid air cells.

OBJECTIVE: During routine MR imaging of temporomandibular joints we have observed that an area of low signal is sometimes identified within the temporal bone overlying the glenoid fossa on proton-density sequences. This finding at times simulates a mass. CT in this situation has demonstrated marked pneumatization of the mastoid air cell extending to that portion of the temporal bone overlying the glenoid fossa. We undertook a clinical study to determine the frequency and appearance of such a finding. DESIGN AND PATIENTS: We reviewed the images of 12 patients who underwent both MR and CT examinations of their temporomandibular joints. The authors, by consensus, graded all 24 joints using a four-point scale for the presence and appearance of a low-signal area overlying the glenoid fossa on the MR images prior to seeing the corresponding CT images. We then compared our grading with the findings on CT to assess for the presence and extent of pneumatization of the temporal bone overlying the glenoid fossa. RESULTS: Of the 24 joints reviewed there was identical extent of low signal on MR imaging and extent of pneumatization on CT in 22 of 24 joints. In two of the 24 joints assessed there was overestimation of pneumatization due to extensive sclerosis secondary to surgery. CONCLUSION: The findings of an area of low signal overlying the glenoid fossa on a T2-weighted scan of a nonoperative temporomandibular joint is often due to extensive temporal bone pneumatization of the mastoid air cells. Recognition of the nature of this finding will avoid mistaking it for a fibrous or osseous lesion. Patients with previous operative history may, however, require further investigation with CT.

Adult↗
PubMed1999

Monoarticular synovial lesions: radiologic pictorial essay with pathologic illustration.

A wide variety of common focal monoarticular synovial lesions may be encountered on imaging studies. A multi-modality approach to these lesions, with appreciation of the differing appearances, can often yield the correct diagnosis. This pictorial essay demonstrates and describes the imaging with illustration of pathologic findings in a spectrum of conditions.

Chondromatosis, Synovial↗
PubMed1999

Mycobacterial spindle cell pseudotumor of the brain: a case report and review of the literature.

Spindle cell pseudotumors found in the skin, lymph nodes, bone marrow, spleen, lungs, and retroperitoneum have been reported recently in immunosuppressed patients, including those with acquired immunodeficiency syndrome. The authors report a similar lesion limited to the brain in a 38-year-old human immunodeficiency virus-negative man receiving steroid therapy for treatment of sarcoidosis. Histopathologically the lesions were composed of spindle and epithelioid histiocytes, small foci of necrosis, and numerous acid-fast bacilli. The acid-fast bacilli were determined by culture and polymerase chain reaction to be Mycobacterium avium intracellulare. Because of the uncommon histologic appearance of this lesion and the potential for treatment if recognized, mycobacterial spindle cell pseudotumors should be included in the differential diagnosis of spindle cell lesions in the brain in immunosuppressed patients.

Adult↗
PubMed1999

Quantal unit populations at the Drosophila larval neuromuscular junction.

Focal extracellular recording at visualized boutons of the Drosophila larval neuromuscular junction was used to determine frequency and time course of the spontaneously occurring quantal events. When simultaneous intracellular recordings from the innervated muscle cell were made, more than one class of quantal event occurred at some of the individual boutons. "True" signals (arising at the bouton within the focal macropatch electrode) were often contaminated by additional signals generated outside the lumen of the focal electrode. Inclusion of these contaminating signals gave spuriously low values for relative amplitude, and spuriously high values for spontaneous quantal emission, for the synapses within the focal electrode. The contaminating signals, which appeared to be conducted along the subsynaptic reticulum surrounding the nerve terminals, generally were characterized by relatively small extracellular signals associated with normal intracellular events in the muscle fiber. From plots of simultaneous extracellular and intracellular recordings, the individual data points were classified according to the angles they subtended with the x axis (extracellular signal axis). Statistical procedures were developed to separate the true signals and contaminants with a high level of confidence. Populations of quantal events were found to be well described by Gaussian mixtures of two or three components, one of which could be characterized as the true signal population. Separation of signals from contaminants provides a basis for improving the estimates of quantal size and spontaneous frequency for the synapses sampled by the focal extracellular electrode.

Animals↗
PubMed1999

Tubing failure during prolonged roller pump use: a laboratory study.

Little is known about the mechanical forces acting on extracorporeal circuit tubing with prolonged roller pump use during extracorporeal membrane oxygenation (ECMO). We examined the time to tubing rupture of three different materials during actual roller pump use, mean and standard deviation (SD) (SD shown in parentheses): Tygon (control) 243.7 h (175.4); LVA 121 h (14.3); and SRT 6.6 h (2.1). Failure times for both LVA and SRT were significantly different from the control (paired t-test, p = 0.02 and p < 0.001, respectively). The minimum failure times for Tygon and LVA were 99 and 101 h, respectively. We then examined Tygon under conditions of pure compression, demonstrating that even after 3.67 million compression cycles at full occlusion crack formation did not occur. If the tubing was over-occluded, cracks appeared within 24 h. Scanning electron microscopy of Tygon, which has been used during clinical ECMO, and the failure pattern during destruction testing demonstrate that shear stress and compression coexist during clinical ECMO. Use of under-occlusive pump settings could improve tubing life.

Equipment Failure Analysis↗
PubMed1999

Receptor binding and biological activity of mammalian expressed sensory and motor neuron-derived factor (SMDF).

Sensory and motor neuron-derived factor (SMDF) is a member of the neuregulin family of proteins. SMDF is structurally characterized by a novel N-terminal domain. Using the signal sequence and N-terminal 28 amino acids (the "epitope") of herpes simplex virus type 1 glycoprotein D (gD), we have expressed SMDF as an epitope-tagged protein (gD-SMDF) in 293 cells, and purified it to > 98% homogeneity on a monoclonal anti-gD column. gD-SMDF stimulates human Schwann cell growth and 3H-thymidine incorporation in MCF-7 and T47D human breast tumor cells in vitro. The biological activity of gD-SMDF is consistent with its ability to compete with 125I-labeled heregulinbeta1 peptide (rHRGbeta1(177-244)) to bind to soluble dimeric ErbB receptor-IgG fusion proteins. gD-SMDF binds with low affinity to homodimeric ErbB3-IgG and ErbB4-IgG but with higher affinity to heterodimeric ErbB2/ErbB3-IgG and ErbB2/ErbB4-IgG. Using a SMDF-IgG(Fc) fusion protein we generated a monoclonal antibody (3G11) which binds SMDF, crossreacts with rHRGbeta1(177-244), and neutralizes the in vitro activities of gD-SMDF and rHRGbeta1(177-244) in human Schwann cells.

Animals↗
PubMed1999

Variable levels of mosaicism for trisomy 21 in a non-immune hydropic infant with chylothorax.

We report the first case of mosaic trisomy 21 with non-immune hydrops fetalis and bilateral chylothoraces. Prenatal fetal blood karyotype analysis of 15 fetal cells revealed a 46,XX karyotype. Aggressive prenatal management, including fetal thoracocentesis and pleuro-amniotic shunt, was performed. A clinical phenotype of Down syndrome was apparent after the gross oedema had subsided. Subsequent chromosome study of neonatal blood lymphocytes showed mosaic trisomy 21 with 23 per cent trisomic cells. Review of the initial fetal blood sample identified trisomy in 5 per cent of 134 cells. Follow-up study at five months showed no trisomy 21 in 100 cells. This case illustrates the variable levels of mosaicism manifest in the peripheral blood of an infant with obvious Down syndrome phenotype, and the limitation of cytogenetic analysis of peripheral lymphocytes alone in prenatal and postnatal detection of low levels of mosaicism.

Adult↗
PubMed1998

Activator-sigma interaction: A hydrophobic segment mediates the interaction of a sigma family promoter recognition protein with a sliding clamp transcription activator.

Activation of transcription at bacteriophage T4 late promoters and coupling of late transcription to concurrent replication requires a peculiar transcriptional activator, the gp45 sliding clamp of the T4 DNA polymerase. In order to activate transcription, the topologically DNA-linked trimeric gp45 must interact with two T4-encoded RNA polymerase-binding proteins, the gp33 co-activator, and the gp55 late sigma factor. The carboxy termini of gp55 and gp33 share a similar sequence, which has been shown to be required for response of late transcription to activation by gp45. Alanine-scanning mutagenesis of the C terminus of gp55 shows that residues within the short hydrophobic sequence L(D/A)FLYE, are necessary for gp55 to bind to gp45, and to respond maximally to transcriptional activation by gp45. When fused to GST, the peptide SLDFLYE suffices for specific gp45 binding. Thus, it constitutes the main gp55 epitope for gp45 interaction.

Alanine↗
PubMed1998

Association of protein kinase Cmu with type II phosphatidylinositol 4-kinase and type I phosphatidylinositol-4-phosphate 5-kinase.

Protein kinase Cmu (PKCmu), also named protein kinase D, is an unusual member of the PKC family that has a putative transmembrane domain and pleckstrin homology domain. This enzyme has a substrate specificity distinct from other PKC isoforms (Nishikawa, K., Toker, A., Johannes, F. J., Songyang, Z., and Cantley, L. C. (1997) J. Biol. Chem. 272, 952-960), and its mechanism of regulation is not yet clear. Here we show that PKCmu forms a complex in vivo with a phosphatidylinositol 4-kinase and a phosphatidylinositol-4-phosphate 5-kinase. A region of PKCmu between the amino-terminal transmembrane domain and the pleckstrin homology domain is shown to be involved in the association with the lipid kinases. Interestingly, a kinase-dead point mutant of PKCmu failed to associate with either lipid kinase activity, indicating that autophosphorylation may be required to expose the lipid kinase interaction domain. Furthermore, the subcellular distribution of the PKCmu-associated lipid kinases to the particulate fraction depends on the presence of the amino-terminal region of PKCmu including the predicted transmembrane region. These results suggest a novel model in which the non-catalytic region of PKCmu acts as a scaffold for assembly of enzymes involved in phosphoinositide synthesis at specific membrane locations.

1-Phosphatidylinositol 4-Kinase↗
PubMed1998

Byr4 and Cdc16 form a two-component GTPase-activating protein for the Spg1 GTPase that controls septation in fission yeast.

BACKGROUND: Spatial and temporal control of cytokinesis ensures the accurate transmission of genetic material and the correct development of multicellular organisms. An excellent model system in which to study cytokinesis is Schizosaccharomyces pombe because there are similarities between cytokinesis in S. pombe and mammals and because genes involved in S. pombe cytokinesis have been characterized. In particular, formation of the septum is positively regulated by the Spg1 GTPase and its effector, the Cdc7 kinase. Septation is negatively regulated by Cdc16, a protein similar to GTPase-activating proteins (GAPs) for Ypt GTPases, and by Byr4, a protein of unknown biochemical function. This study investigates the relationship between Byr4, Cdc16, and Spg1. RESULTS: Genetic interactions were observed between byr4, cdc16, and spg1 mutants. Byr4 bound to Cdc16 and Spg1 in yeast two-hybrid assays and in coprecipitations in vitro and in yeast. Byr4 inhibited the dissociation and hydrolysis of GTP bound to Spg1, but when Byr4 and Cdc16 were combined together they displayed Spg1GAP activity in vitro; Cdc16 alone had no detectable GAP activity. The binding of Byr4 to Spg1 and the Byr4-Cdc16 Spg1GAP activity were specific because Byr4 and Cdc16 did not bind to or affect the GTPase activities of the seven known S pombe Ypt family GTPase. CONCLUSIONS: Byr4 and Cdc16 form a two-component GAP for the Spg1 GTPase. Byr4 and Cdc16 appear to negatively regulate septation in S. pombe by modulating the nucleotide state of Spg1 possibly in a spatially or temporally controlled manner.

Cell Cycle Proteins↗
PubMed1998

Identification of a cAMP-dependent protein kinase catalytic subunit required for virulence and morphogenesis in Ustilago maydis.

Ustilago maydis, a fungal pathogen of maize, alternates between budding and filamentous growth in response to mating and other environmental signals. Defects in components of the cAMP signaling pathway affect this morphological transition and reveal an association of budding growth with elevated cAMP levels and filamentous growth with low cAMP levels. We have identified two genes, adr1 and uka1, encoding catalytic subunits of cAMP-dependent protein kinase (PKA). Disruption of adr1 resulted in a constitutively filamentous growth phenotype similar to that of mutants deficient in adenylyl cyclase. Importantly, adr1 is required for pathogenicity and is responsible for the majority of PKA activity in fungal cells. In contrast, uka1 has little influence on pathogenicity, and deletion of the uka1 gene does not affect cell morphology. These results provide compelling evidence that regulated PKA activity is crucial during infectious development of U. maydis.

Alleles↗
PubMed1998

Core-sigma interaction: probing the interaction of the bacteriophage T4 gene 55 promoter recognition protein with E.coli RNA polymerase core.

The bacterial RNA polymerase sigma subunits are key participants in the early steps of RNA synthesis, conferring specificity of promoter recognition, facilitating promoter opening and promoter clearance, and responding to diverse transcriptional regulators. The T4 gene 55 protein (gp55), the sigma protein of the bacteriophage T4 late genes, is one of the smallest and most divergent members of this family. Protein footprinting was used to identify segments of gp55 that become buried upon binding to RNA polymerase core, and are therefore likely to constitute its interface with the core enzyme. Site-directed mutagenesis in two parts of this contact surface generated gene 55 proteins that are defective in polymerase-binding to different degrees. Alignment with the sequences of the sigma proteins and with a recently determined structure of a large segment of sigma70 suggests that the gp55 counterpart of sigma70 regions 2.1 and 2.2 is involved in RNA polymerase core binding, and that sigma70 and gp55 may be structurally similar in this region. The diverse phenotypes of the mutants implicate this region of gp55 in multiple aspects of sigma function.

Bacteriophage T4↗
PubMed1998

Mortality studies in psoriatic arthritis: results from a single outpatient center. II. Prognostic indicators for death.

OBJECTIVE: To investigate prognostic factors associated with mortality in patients with psoriatic arthritis (PsA). METHODS: Patients followed up at the Toronto PsA Clinic between 1978 and 1994 were included. Patients were reviewed at initial clinic entry and at 6-month intervals using a standard protocol. Data on deaths were collected in a prospective manner, and death certificates were used to identify the primary and antecedent cause(s) of death. All death information was recorded in the clinic's computerized database. Only factors that represented standard clinical measures of disease activity and progression were studied. The relationship between potential prognostic factors recorded at the time of the first clinic visit and the mortality rate was determined using the Cox relative risk regression model. RESULTS: There were 428 patients (234 men and 194 women), of whom 68% were known to be alive on September 1, 1994, 20% were lost to followup but assumed to be alive, and 12% had died. Multivariate analysis revealed that an erythrocyte sedimentation rate (ESR) > 15 mm/hour, medications used prior to initial clinic visit, radiologic damage, and the absence of nail lesions were associated with an increased overall mortality rate. There is some suggestion that prior medication use was least important for deaths associated with the circulatory system, while radiologic damage was particularly important for such deaths. A marked sex-associated effect was noted among deaths caused by injuries/poisoning, since 6 of the deaths occurred in men and only 1 was in a woman. CONCLUSION: Patients with PsA are at an increased risk of death compared with the general population. Evidence of previously active and severe disease, as manifested by the prior use of medications and by radiologic changes as well as an elevated ESR at presentation, are prognostic indicators for death. The presence of nail lesions appears to be a protective factor that has the most clinical importance in the context of previously active and severe disease.

Adolescent↗
PubMed1998

Clenbuterol induces cardiac hypertrophy with normal functional, morphological and molecular features.

OBJECTIVE: Several pharmacological agents have been shown to produce 'physiological' or 'pathological' hypertrophy based on their functional characteristics. The aim of this study was to examine the features of cardiac hypertrophy induced by the selective beta 2-adrenergic agonist, clenbuterol. METHODS: Cardiac hypertrophy was induced in 7-week-old Sprague-Dawley rats by daily injections of clenbuterol for 3 weeks. Thyroxine and isoproterenol were also used to produce cardiac hypertrophy to serve as positive controls for physiological and pathological hypertrophy, respectively. Left ventricular function was determined using an isolated rat heart preparation. Ventricular samples were used for morphological examination while interstitial collagen was measured using high-pressure liquid chromatography. Expression of sarcoplasmic reticulum Ca(2+)-ATPase2a (SERCA2a) and phospholamban (PLB) were measured by dot blot analysis. RESULTS: Clenbuterol treatment induced 26% left ventricular hypertrophy. These hearts demonstrated normal systolic isovolumic parameters and diastolic (active relaxation and passive stiffness) function. In addition, left ventricular concentration of collagen and morphology was normal as were the expression of SERCA2a and PLB mRNA. CONCLUSION: These results suggest that clenbuterol-induced hypertrophy is 'physiological' in terms of its function, extracellular structure and gene expression.

Adenosine Triphosphatases↗
PubMed1998

Protein phosphatase inhibitors exert specific and nonspecific effects on calcium influx in thapsigargin-treated human neutrophils.

C2-ceramide but not inhibitors of phosphatase types 1 and 2A (okadaic acid, calyculin A, tautomycin) blocked store-regulated Ca2+ entry induced in human neutrophils by thapsigargin. This contrasts with previous results showing that both types of compounds inhibit Ca2+ influx in fmet-leu-phe-treated cells. In present studies, phosphatase inhibitors increased the rate of secondary Ca2+ influx in a temperature-dependent manner. Their mechanism of action appeared to be independent of phosphatase inhibition since the inactive congeners, norokadaone and tetraacetyl okadaic acid, also potentiated Ca2+ influx at similar concentrations. When Ca2+ stores were predischarged by thapsigargin, okadaic acid but not norokadaone acted synergistically with fMLP to inhibit subsequent Ca2+ entry. Results suggest that blockade of Ca2+ influx in neutrophils is mediated by a phosphorylation reaction that is prolonged by phosphatase inhibitors. The requisite phosphorylation occurs in fMLP-activated cells but may be absent in cells incubated with thapsigargin.

Calcium↗