Biomedical subjects

M Chow

Publications and source records attributed to M Chow.

At least 55 records · Page 3Linked to original sources

PubMed1995

Myristoyl modification of viral proteins: assays to assess functional roles.

Characterization of the effects of myristoylation on poliovirus function has largely depended on the availability of methods previously characterized to study various aspects of virus biology. Those methods are described here to provide specific examples of how they may be used to analyze the myristoylation mutants and to illustrate general approaches. It is possible that the poliovirus protocols may be directly transferable with little or no modification to analyze other systems. However, it is more likely that the application of specific methods, which have already been developed and characterized for the systems of interest and which utilize the strengths and reagents unique to those experimental systems, may be more efficient and informative.

Capsid↗

PubMed1995

Extrahepatic biliary cystadenomas and cystadenocarcinoma. Report of seven cases and review of the literature.

OBJECTIVE: The aim of this investigation was to describe the clinical features, diagnosis, pathologic characteristics, and optimal surgical management for patients with extrahepatic biliary cystadenomas. SUMMARY BACKGROUND DATA: Extrahepatic biliary cystadenomas are rare epithelial neoplasms. The clinical features and optimal surgical management for these lesions have not been defined clearly. The usual presenting symptom is jaundice. These lesions should be considered premalignant and necessitate resection. Sporadic case studies have reported instances of recurrence with local excision. To the authors' knowledge, this study represents the largest collected single series of extrahepatic biliary cystadenomas and reviews previously reported cases. METHODS: The authors reviewed and reported their institutional experience from 1950 to 1993 in treating seven patients with extrahepatic biliary cystadenomas as well as 19 previously reported cases in the literature. RESULTS: A strong female predominance (96.3% of patients reviewed) was associated with extrahepatic biliary cystadenomas. Obstructive jaundice was the most common presenting symptom (85%). Abdominal pain occurred in 50% of patients; other symptoms included fever and hemobilia. The most common site of occurrence was the common hepatic duct (32%). Papillary cystadenoma with foci of invasive adenocarcinoma, thus supporting the malignant potential of cystadenomas, occurred in one patient. Local excision from the wall of the bile duct was performed in 18 patients and was associated with 50% recurrence within a mean follow-up of 13 months (range, 4-24 months). No recurrence was reported after formal sleeve resection and bilioenteric reconstruction. CONCLUSIONS: Extrahepatic biliary cystadenomas can become malignant, and in this study, local surgical excision was associated with a 50% local recurrence rate. Sleeve resection with negative histologic resection margins followed by bilioenteric reconstruction, therefore, is recommended.

Adenoma, Bile Duct↗

PubMed1995

Mode of spread to and within the central nervous system after oral infection of neonatal mice with the DA strain of Theiler's murine encephalomyelitis virus.

Theiler's murine encephalomyelitis virus is a neurotropic enterovirus known to cause biphasic neural disease after intracerebral inoculation into adult mice. The present study characterizes a neonatal mouse model with a high disease incidence for the study of the acute phase of the pathogenesis of the DA strain of Theiler's murine encephalomyelitis virus after oral infection. The route of viral spread to and within the central nervous system (CNS) was determined by examining the kinetics of viral replication in various organs and by performing histopathological analysis. Viral antigen was detected widely in the neonatal CNS, mainly in the gray matter, and it was asymmetrical and multifocal in its distribution, with considerable variation in lesion distribution from animal to animal. Necrotizing lesions appeared to expand by direct extension from infected cells to their close neighbors, with a general disregard of neuroanatomical boundaries. The diencephalon showed particular susceptibility to viral infection. Other areas of the CNS, including the cerebellum and dentate gyrus of the hippocampus, were consistently spared. Neurons with axons extending peripherally to other organs or receiving direct input from the peripheral nervous system were not preferentially affected. The kinetics of viral replication in the liver, spleen, and CNS and the histopathological findings indicate that viral entry to the CNS is via a direct hematogenous route in orally infected neonatal mice and that the disease then progresses within the CNS mainly by direct extension from initial foci.

Aging↗

PubMed1995

Molecular cloning and characterization of a novel gonadotropin-releasing hormone from the gilthead seabream (Sparus aurata).

A novel form of gonadotropin-releasing hormone (GnRH) had been recently isolated and characterized from the gilthead seabream (Sparus aurata). This novel form, designated sbGnRH, was suggested to be the endogenous stimulator of gonadotropin release. This paper reports on the isolation and characterization of a 360-bp cDNA encoding the complete sbGnRH precursor. This precursor is composed of a 25 amino acid leader sequence, the biologically active sbGnRH, the cleavage site (Gly-Lys-Arg), and a 57 amino acid associated peptide (GAP). Comparison of the nucleotide and amino acid sequence of the sbGnRH precursor with precursors of other GnRH forms places the sbGnRH precursor evolutionarily closer to the mammalian GnRH and chicken GnRH-I, which have also been shown to be the relevant forms for gonadotropin release in mammals and birds, respectively. The characterization of the sbGnRH precursor cDNA lays the foundation for future studies aimed toward understanding the neuroendocrine control of reproduction in seabream and other fish species.

Amino Acid Sequence↗

PubMed1994

Structure of the human gene encoding the associated microfibrillar protein (MFAP1) and localization to chromosome 15q15-q21.

Microfibrils with a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues. To extend our understanding of the proteins composing these microfibrils, the cDNA and gene encoding the human associated microfibril protein (MFAP1) have been cloned and characterized. The coding portion is contained in 9 exons, and the sequence is very homologous to the previously described chick cDNA, but does not appear to share homology or domain motifs with any other known protein. Interestingly, the gene has been localized to chromosome 15q15-q21 by somatic hybrid cell and chromosome in situ analyses. This is the same chromosomal region to which the fibrillin gene, FBN1, known to be defective in the Marfan syndrome, has been mapped. MFAP1 is a candidate gene for heritable diseases affecting microfibrils.

Amino Acid Sequence↗

PubMed1994

Cellular epigenetics: topochronology of progressive "spontaneous" transformation of cells under growth constraint.

Early passages of NIH 3T3 cells yield about 10 transformed foci for every 10(5) cells seeded after the cells multiply to confluence in a standardized 2-week assay. The question arose whether more cells would give rise to foci if given more time for their development. This question could not be answered simply by extending the incubation period, since the original foci spread to cover much of the area of the culture dish. Transformed cells can also detach into the medium from the original foci to initiate new foci by reattaching at a distance. These problems were averted by growing cells in multiwell plates which in effect simulated partitioned culture dishes. All the wells in a given plate were assayed for focus formation at successive intervals up to 14 weeks. The results indicated the spatial pattern and sequence of transformation on different parts of the "partitioned" dish. The number of multiwells containing focus-forming cells increased steadily with time, indicating that all parts of a dish eventually undergo transformation. Also, most of the transformations were recorded long after confluence in the multiwells was reached. Hence such a transformation is much more likely to occur in the nondividing state rather than in the dividing state of the cells and is thus inconsistent with a mutational basis. The results suggest that "spontaneous" transformation is a population-wide, epigenetic phenomenon. This agrees with the results from clonal analysis and other studies and is well described by the concept of progressive state selection, in which "spontaneous" transformation represents a heterogeneous, adaptive response of competent cells to moderate constraints on cell growth.

3T3 Cells↗

PubMed1994

Poliovirus neutralization by antibodies to internal epitopes of VP4 and VP1 results from reversible exposure of these sequences at physiological temperature.

Antisera were raised against peptide sequences that are normally internal in the poliovirus virion. These antisera contain neutralizing activity, but this neutralizing activity is dependent on coincubation of the virus and antisera at 37 degrees C. Immunoprecipitation analyses demonstrate that the neutralization is due to exposure of these normally internal sequences at 37 degrees C and subsequent antibody binding. Exposure of these sequences is reversible. These data demonstrate that the poliovirus particle is a dynamic entity that is capable of undergoing conformational alterations at physiological temperatures. This conformational flexibility provides an explanation for earlier observations of virus neutralization by antibodies to internal epitopes which can be accommodated within the framework of existing models for antibody-mediated neutralization of viral infectivity. Analogies between the sequences which are reversibly exposed at 37 degrees C with those which are irreversibly exposed upon receptor binding suggest that the observed conformational dynamics also may play a role in cell entry.

Antibodies, Viral↗

PubMed1993

Conformal radiotherapy of the pelvis: assessment of acute toxicity.

During the last 3 years the Royal Marsden Hospital (RMH) has conducted a prospective randomised trial of conformal pelvic radiotherapy in which dose/volume data and acute toxicity scores have been determined prospectively. Pending completion of the trial, a preliminary analysis has been undertaken of the volume reductions achieved, and of some of the symptom scores. The average symptom score increased during radiotherapy, more markedly for bowel than bladder symptoms. In comparing total doses of 30-38 Gy with 56-65 Gy, watery bowel motions were more frequent with the higher doses (p = 0.013) but in the high-dose group neither this symptom nor tenesmus correlated with volume of rectum treated to at least 90% of the prescribed dose. We conclude that the assessment of the impact of volume on the level of acute symptoms in pelvic radiotherapy is complex, and requires analysis of a range of symptoms, dose levels and normal-tissue volumes. The degree of symptom reduction from conformal radiotherapy will emerge from the RMH randomised trial within the next 12 months.

Humans↗

PubMed1993

The Royal Marsden Hospital pelvic radiotherapy trial: technical aspects and quality assurance.

Planning and quality control procedures are described for a randomised trial designed to measure the effect on normal tissue toxicity of reducing the volume of normal tissue irradiated through the introduction of Beams-Eye-View designed customised blocks. Consideration is given to the accuracy with which blocks can be designed and to the potential application of multi-leaf collimator technology.

Adult↗

PubMed1993

An unusual case of a retained stone following laparoscopic cholecystectomy.

A patient with gallstone pancreatitis was managed by endoscopic sphincterotomy followed by a laparoscopic cholecystectomy. At the time of surgery, an intraoperative cholangiogram disclosed the presence of a residual calculus, which was erroneously thought to be in the common bile duct. A repeat ERCP showed that the stone was, in fact, in a long cystic duct stump which was fortunately accessible to endoscopic extraction.

Adult↗

PubMed1993

Characterization of poliovirus-specific T lymphocytes in the peripheral blood of Sabin-vaccinated humans.

Poliovirus-specific cellular immune responses were identified in the peripheral blood mononucleocytes of Sabin-immunized human donors by using a proliferation assay. Complement depletion and monoclonal antibody inhibition studies suggest that the effector population is the major histocompatibility complex (MHC) class II-restricted CD4+ T-helper cell. Immune lymphocytes proliferated to polyacrylamide gel purified-capsid proteins VP1, VP2, and VP3 and, in some individuals, to synthetic VP4, indicating the presence of T-cell epitopes in each of these proteins. Using synthetic peptides, T-cell epitopes have been mapped to specific regions in VP1 which lie near previously identified neutralizing antibody recognition sites. Human leukocyte antigen (HLA) typing of the donor individuals indicated that no MHC class II molecule was held in common between all four donor individuals. Thus, the positive responses observed with peptides p182-201 and p244-261 in three of four and four of four donors suggest that these peptides contain epitopes presented by at least two different MHC molecules. Antibody-blocking experiments suggest that an epitope within VP1 residues 244 to 264 is presented by HLA DQ3.

Adult↗

PubMed1993

Efficient analysis of nonviable poliovirus capsid mutants.

Nonviable poliovirus capsid mutants were studied by an efficient infection-transfection system. Phenotypically, nonviable poliovirus capsid mutants appear to segregate into three classes: those that form only protomers, those that can form pentamers, and one that can form completed virions.

Capsid↗

PubMed1993

A mutation in VP4 defines a new step in the late stages of cell entry by poliovirus.

During the entry of poliovirus into cells, a conformational transition occurs within the virion that is dependent upon its binding to the cell surface receptor. This conformational rearrangement generates an altered particle of 135S, results in the extrusion of capsid protein VP4 and the amino terminus of VP1 from the virion interior, and leads to the acquisition of membrane-binding properties by the 135S particle. Although the subsequent fate of VP4 is unknown, its apparent absence from purified 135S particles has long suggested that VP4 is not directly involved during virus entry. We report here the construction by site-specific mutagenesis of a nonviable VP4 mutant that upon transfection of the cDNA appears to form mature virus particles. These particles, upon interaction with the cellular receptor, undergo the 135S conformational transition but are defective at a subsequent stage in virus entry. The results demonstrate that the participation of VP4 is required during cell entry of poliovirus. In addition, these data indicate the existence of additional stages in the cell entry process beyond receptor binding and the transition to 135S particles. These post-135S stages must include the poorly understood processes by which nonenveloped viruses cross the cell membrane, uncoat, and deliver their genomes into the cytoplasm.

Capsid↗

PubMed1992

Myristate modification does not function as a membrane association signal during poliovirus capsid assembly.

The myristate moiety is required for poliovirus assembly. Unlike most other myristoyl-modified proteins, which are membrane associated, no specific membrane association of the poliovirus capsid proteins or assembly intermediates was observed. Furthermore, no apparent differences in membrane association of wild-type and myristoylation deficient mutant viruses could be detected in this analysis. Thus, during poliovirus assembly, the myristate modification is not required as a membrane targeting signal but is more likely involved in structural interactions between protomer subunits.

Capsid↗

PubMed1992

Structure and biological effects of lipid modifications on proteins.

Both the prevalence of lipid modifications of proteins and their importance for protein function and cellular localization have been widely observed. The advances made during the past year in defining the enzymology of lipid addition and in understanding the biological consequences of these modifications on protein function are discussed.

Acyltransferases↗

PubMed1992

Defibrillation energy requirements during moricizine and moricizine-lidocaine therapy.

Defibrillation energy requirements may be altered by antiarrhythmic agents. We investigated the effects of moricizine on the defibrillation threshold (DFT) in 18 pentobarbital-anesthetized pigs. The animals were randomized, in a blinded fashion, to moricizine or control (0.9% saline) treatment groups. Each group underwent three treatment phases: baseline, drug infusion (moricizine or saline), and drug infusion combined with lidocaine. Moricizine (2 mg/kg loading dose, 1.5 mg/kg/h infusion) and lidocaine (5 mg/kg loading dose, 4 mg/kg/h infusion) were dosed to achieve therapeutic concentrations. After 5 s of induced ventricular fibrillation, defibrillation was performed using a cardiac defibrillator interfaced with two epicardial electrode patches. DFTs were determined at baseline, during the drug phase, and during the combination of lidocaine with moricizine or saline. DFT values in the animals randomized to the control group were 15.2 +/- 4.2, 14.0 +/- 3.3, and 17.8 +/- 8.7 J at baseline, saline infusion, and saline combined with lidocaine, respectively. No significant differences were observed among the treatment phases. DFT values in the animals randomized to moricizine group were 12.1 +/- 2.8, 13.8 +/- 5.2, and 22.9 +/- 7.1 J at baseline, moricizine infusion, and moricizine combined with lidocaine, respectively. The DFT values during the lidocaine-moricizine combination treatment phase were significantly greater than baseline and moricizine alone (p < 0.002). The mean change in the DFT from baseline to moricizine (14% increase) was significantly different than the mean change in the DFT from baseline to saline (8% decrease) (p = 0.03). Lidocaine added to moricizine increased the DFT by 84%, which was significantly different from the 27% increase in the DFT when lidocaine was added to saline (p = 0.02). We conclude that moricizine minimally increases the DFT, but the combination of moricizine with lidocaine results in a synergistic rise in the DFT that may have detrimental clinical implications.

Animals↗

PubMed1992

Poliovirus-specific major histocompatibility complex class I-restricted cytolytic T-cell epitopes in mice localize to neutralizing antigenic regions.

A major histocompatibility complex (MHC) class I-restricted cytotoxic T-lymphocyte (CTL) response is induced in BALB/c mice upon immunization with poliovirus serotype 1 (Mahoney strain). A similar class I-restricted response is also induced upon immunization with purified VP1 capsid proteins. Thus, poliovirus-specific MHC class I CTL responses can be induced independently of viral infection in murine hosts. In experiments using recombinant vaccinia virus vectors expressing different segments of the poliovirus capsid proteins and synthetic peptides, two regions of the VP1 capsid protein appear to contain epitopes recognized by this bulk CTL population. These epitope regions contain a Kd-restricted peptide-binding motif. Interestingly, each of these CTL epitopes is located near previously defined neutralizing antigenic sites.

Amino Acid Sequence↗

PubMed1992

Myristate-protein interactions in poliovirus: interactions of VP4 threonine 28 contribute to the structural conformation of assembly intermediates and the stability of assembled virions.

The VP4 capsid protein of poliovirus is N-terminally modified with myristic acid. Within the poliovirus structure, a hydrogen bond is observed between the myristate carbonyl and the hydroxyl side chain of threonine 28 of VP4. This interaction is between two fivefold symmetry-related copies of VP4 and is one of several myristoyl-mediated interactions that appears to structurally link the promoters within the pentamer subunit of the virus particle. Site-specific substitutions of the threonine residue were constructed to investigate the biological relevance of these myristate-protein interactions. Replacement of the threonine with glycine or lysine is lethal, generating nonviable viruses. Substitution with serine or valine led to viable viruses, but these mutants displayed anomalies during virus assembly. In addition, both assembled serine- and valine-substituted virion particles showed reduced infectivity and were more sensitive to thermal inactivation and antibody neutralization. Thus the threonine residue provides interactions necessary for efficient assembly of the virus and for virion stability.

Amino Acid Sequence↗