Search PubMed⌕ Search

Biomedical subjects

C W Chow

Publications and source records attributed to C W Chow.

At least 73 records · Page 4Linked to original sources
PubMed1998

Characterization of a t(8;13)(p11;q11-12) in an atypical myeloproliferative disorder.

Fourteen cases of an atypical myeloproliferative disorder associated with consistent translocations involving 8p11-12 have previously been described. A t(8;13)(p11;q11-12) was the most common, but variant t(8;9)(p11-12;q32-34) and t(6;8)(q27;p12) were also reported. Here we have used a series of yeast artificial chromosomes (YACs) derived from the 8p11 and 13q11-12 regions to analyse one of the t(8;13) cases by fluorescence in situ hybridization (FISH). YACs flanking the 13q11-12 breakpoint and spanning the 8p11 breakpoint have been isolated. These YACs will facilitate characterization of the genes involved in this rearrangement.

Chromosomes, Artificial, Yeast↗
PubMed1997

Nuclear accumulation of NFAT4 opposed by the JNK signal transduction pathway.

The nuclear factor of activated T cells (NFAT) group of transcription factors is retained in the cytoplasm of quiescent cells. NFAT activation is mediated in part by induced nuclear import. This process requires calcium-dependent dephosphorylation of NFAT caused by the phosphatase calcineurin. The c-Jun amino-terminal kinase (JNK) phosphorylates NFAT4 on two sites. Mutational removal of the JNK phosphorylation sites caused constitutive nuclear localization of NFAT4. In contrast, JNK activation in calcineurin-stimulated cells caused nuclear exclusion of NFAT4. These findings show that the nuclear accumulation of NFAT4 promoted by calcineurin is opposed by the JNK signal transduction pathway.

Animals↗
PubMed1997

Sex and test verification bias. Impact on the diagnostic value of exercise echocardiography.

BACKGROUND: The use of exercise echocardiography for the diagnosis of coronary artery disease (CAD) has been validated in pilot studies but is not documented in clinical practice and in women comparatively with men. The objectives of this study were to determine the effects of sex and of test verification bias on the diagnostic performance of exercise echocardiography. METHODS AND RESULTS: Three thousand six hundred seventy-nine consecutive patients (1714 women, 1965 men) who underwent an exercise echocardiographic study were studied; the observed sensitivity, specificity, and correct classification rate were calculated among 340 patients (244 men, 96 women) who underwent angiography; to study the effect of test verification bias, sensitivity and specificity were estimated for all patients who underwent exercise echocardiography including those not referred to angiography. In the angiographic group, the prevalence of CAD was 60% in women and 80% in men. The observed sensitivity and specificity of exercise echocardiography was 78% and 44% in men and 79% and 37% in women. After adjustment for test verification bias, the estimated sensitivity was lower in women (32% versus 42% in men), whereas specificity was similar in both sexes. The positive predictive value was lower in women (66%) compared with men (84%). CONCLUSIONS: In clinical practice, test verification bias results in a lower observed specificity and a higher sensitivity of exercise echocardiography. In women, positive predictive value and adjusted sensitivity are lower compared with that in men.

Aged↗
PubMed1997

Reprogramming the signalling requirement for AP-1 (activator protein-1) activation during differentiation of precursor CD4+ T-cells into effector Th1 and Th2 cells.

Upon antigenic stimulation, precursor CD4+ helper T-cells differentiate into two subsets of effector cells, Th1 and Th2. These two subpopulations are defined by the pattern of cytokine expression that distinguishes these differentiated cells from their precursors. We have used reporter transgenic mice here to show that, during differentiation of precursor T-cells into effector Th1 or Th2 cells, high levels of preformed activator protein (AP)-1 complexes are accumulated. However, upon stimulation, the preformed AP-1 complexes in effector Th2 cells, but not in Th1 cells, are able to induce high levels of AP-1 transcriptional activity. Furthermore, in contrast to precursor T-cells, the induction of AP-1 transcriptional activity is independent of calcium and co-stimulatory signals in effector Th2 cells. This AP-1 transcriptional activity appears to correlate with the presence of JunB complexes, which accumulate differentially in effector Th2 cells, but not in precursor CD4+ T-cells or effector Th1 cells. Unlike precursor cells, the activation of AP-1 does not appear to be mediated by c-Jun N-terminal kinase (JNK) in effector Th2 cells. These results indicate that during differentiation of T-cells, and probably other cell types, the signal requirements for the AP-1 transcription machinery are reprogrammed to enable the differentiated cells to perform their specialized functions.

Amino Acid Sequence↗
PubMed1997

NO3--induced pH changes in mammalian cells. Evidence for an NO3--H+ cotransporter.

The effect of NO3- on intracellular pH (pHi) was assessed microfluorimetrically in mammalian cells in culture. In cells of human, hamster, and murine origin addition of extracellular NO3- induced an intracellular acidification. This acidification was eliminated when the cytosolic pH was clamped using ionophores or by perfusing the cytosol with highly buffered solutions using patch-pipettes, ruling out spectroscopic artifacts. The NO3-- induced pH change was not due to modulation of Na+/H+ exchange, since it was also observed in Na+/H+ antiport-deficient mutants. Though NO3- is known to inhibit vacuolar-type (V) H+-ATPases, this effect was not responsible for the acidification since it persisted in the presence of the potent V-ATPase inhibitor bafilomycin A1. NO3-/HCO3- exchange as the underlying mechanism was ruled out because acidification occurred despite nominal removal of HCO3-, despite inhibition of the anion exchanger with disulfonic stilbenes and in HEK 293 cells, which seemingly lack anion exchangers (Lee, B. S., R.B. Gunn, and R.R. Kopito. 1991. J. Biol. Chem. 266:11448- 11454). Accumulation of intracellular NO3-, measured by the Greiss method after reduction to NO2-, indicated that the anion is translocated into the cells along with the movement of acid equivalents. The simplest model to explain these observations is the cotransport of NO3- with H+ (or the equivalent counter-transport of NO3- for OH-). The transporter appears to be bi-directional, operating in the forward as well as reverse directions. A rough estimate of the fluxes of NO3- and acid equivalents suggests a one-to-one stoichiometry. Accordingly, the rate of transport was unaffected by sizable changes in transmembrane potential. The cytosolic acidification was a saturable function of the extracellular concentration of NO3- and was accentuated by acidification of the extracellular space. The putative NO3--H+ cotransport was inhibited markedly by ethacrynic acid and by alpha-cyano-4-hydroxycinnamate, but only marginally by 4, 4'-diisothiocyanostilbene-2,2' disulfonate or by p-chloromercuribenzene sulfonate. The transporter responsible for NO3--induced pH changes in mammalian cells may be related, though not identical, to the NO3--H+ cotransporter described in Arabidopsis and Aspergillus. The mammalian cotransporter may be important in eliminating the products of NO metabolism, particularly in cells that generate vast amounts of this messenger. By cotransporting NO3- with H+ the cells would additionally eliminate acid equivalents from activated cells that are metabolizing actively, without added energetic investment and with minimal disruption of the transmembrane potential, inasmuch as the cotransporter is likely electroneutral.

Adenosine Triphosphatases↗
PubMed1997

Chronic idiopathic bronchiolitis of infancy.

The clinical and morphological features are presented of eight infants who developed a chronic respiratory illness in the first year of life characterised by tachypnoea and inspiratory crackles on auscultation. The median age at the onset of symptoms was 1 month (range 1 day to 7 months). Five of the infants required supplemental oxygen. Chest radiographs showed only non-specific perihilar alveolar shadowing and generalised hyperinflation. Investigations into the cause of the illness in these infants, including studies for infection, cardiac disease, and gastrooesophageal reflux, were negative, and an open lung biopsy sample was subsequently taken from each infant. Histological examination showed mild lymphocytic bronchiolar infiltration only in six of the eight infants. The other two biopsy samples were normal. Seven of the infants were given a trial of steroids by mouth (mean duration of treatment four months) without any apparent benefit. These infants have now been followed up for a median duration of 21 months (range 1-9 years). All have shown continuous improvement, with either the end of oxygen treatment (three patients) or the use of low flow oxygen only at night (two patients). All have normal development and all but one have normal growth. Chest examination has become normal in four subjects. In the remainder the inspiratory crackles have persisted, although they have decreased markedly in all patients. It is proposed that these infants have a previously unreported respiratory entity and that the clinical and lung biopsy sample findings reported here predict a favourable medium term prognosis.

Bronchiolitis↗
PubMed1997

A maternally transmitted lethal neonatal progeroid syndrome with prominent genitourinary and gastrointestinal features.

Twin brothers and their maternal uncle with a previously undescribed neonatal progeroid syndrome are presented. In addition to progeroid features, they had pseudo-obstruction of the urinary and gastrointestinal tracts, severe leucocytosis, liver dysfunction, and low complex III and IV in muscle but not in liver. Previously described neonatal progeroid syndromes and syndromes featuring pseudo-obstruction are discussed. The two most likely aetiological mechanisms are an X linked single gene disorder or a mitochondrial disorder. The evidence for these possibilities is presented.

Abnormalities, Multiple↗
PubMed1997

Establishment and characterization of conditionally immortalized astrocytes to study their interaction with ts1, a neuropathogenic mutant of Moloney murine leukemia virus.

The cytopathic infection of primary astrocytes with ts1, a neuroimmunopathogenic mutant of Moloney murine leukemia virus (MuLV), has been correlated to intracellular accumulation of viral precursor envelope protein gPr80env. To further study this specific virus-astrocyte interaction in a homogenous population, several immortal astrocyte lines were established from neonatal FVB/N mice using the temperature-sensitive SV40 tsA58 T antigen. These cells expressed glial fibrillary acidic protein, vimentin and T antigen; appeared nontransformed; were star-shape with long processes. They were susceptible to ts1 infection and suffered a cytopathic effect similar to that caused by ts1 infection of primary astrocytes. This cytopathic effect was characterized by growth inhibition, loss of cell processes and syncytium formation. Some cells also rounded up, formed mini cells and became detached from the culture dish. As in primary astrocytes, the processing of gPr80env in the immortalized astrocytes was inefficient. Since the envelope proteins interact with the ecotropic MuLV receptor both intracellularly and on the cell surface and since the receptor has been shown to be an arginine transporter, we attempted to determine the effect of ts1 on arginine uptake by these cells. Our results showed that in both immortalized and primary astrocytes, ts1 infection reduced the uptake of arginine more than did wild-type virus infection. Since arginine localizes predominantly in astrocytes in the CNS and has diverse functions, the decrease of arginine uptake in ts1-infected astrocytes may alter the metabolism of these cells, leading to impairment of their functions.

Animals↗
PubMed1997

Myocarditis in children with dilated cardiomyopathy: incidence and outcome after dual therapy immunosuppression.

BACKGROUND: The true incidence and prognosis of myocarditis in children with acute dilated cardiomyopathy (DCM) at presentation remains uncertain. This study examines the incidence of lymphocytic myocarditis in a consecutive cohort of children with acute DCM at presentation and outcome after dual therapy immunosuppression with cyclosporine and steroids. METHODS: Twenty-nine consecutive children with acute DCM underwent early endomyocardial biopsy. Children with "definite" myocarditis comprised group I (n = 9) and were treated with cyclosporine and prednisolone. Group II (n = 2) had "borderline" myocarditis, and group III (n = 18) nonspecific histologic findings. Outcome was assessed by echocardiographic measurement of left ventricular end-diastolic dimension and fractional shortening, with follow-up endomyocardial biopsy in group I subjects. RESULTS: Myocardial inflammation with or without myocardial necrosis (groups I and II) was present in 38% of all cases. There were no initial clinical, electrocardiographic, or echocardiographic features to distinguish patients in group I from patients in group III. At presentation, the mean +/- SEM left ventricular end-diastolic dimension and fractional score-Z scores of group I patients were 4.6 +/- 1.7 and -5.1 +/- 0.8, respectively, compared with 0.8 +/- 0.3 and -0.9 +/- 0.4, respectively, at withdrawal of immunosuppression (p < 0.001 for both). Both of these parameters did not differ significantly from normal controls at least follow up. Two group I patients had a biopsy-proven relapse after withdrawal of therapy that responded to reinstitution of immunosuppression. At latest follow-up, all nine group I patients had regained normal left ventricular function compared with four of 18 group III patients (p < 0.001). CONCLUSION: Lymphocytic myocarditis is frequent in children with dilated cardiomyopathy and cannot be predicted from noninvasive investigations. The use of cyclosporine and steroids is associated with a favorable outcome, and a controlled trial of dual therapy immunosuppression in children is therefore warranted.

Anti-Inflammatory Agents↗
PubMed1996

In vitro transcription in the presence of DNA oligonucleotides can generate strong anomalous initiation sites.

In the present study, we have explored an unexpected observation in transcription initiation that is mediated by single-stranded oligonucleotides. Initially, our goal was to understand the function of different upstream regulatory elements/initiation sites in the rat xanthine dehydrogenase/oxidase (XDH/XO) promoter. We performed in vitro transcription with HeLa nuclear extracts in the presence of different double-stranded oligonucleotides against upstream elements as competitors. A new and unusual transcription initiation site was detected by primer extension. This new initiation site maps to the downstream region of the corresponding competitor. Subsequent analyses have indicated that the induction of a new transcription initiation site is anomalous which is due to the presence of a small amount of single-stranded oligonucleotide in the competitor. We found that this anomalous initiation site is insensitive to the orientation of the promoter and requires only a small amount of single-stranded oligonucleotide (< 2-fold molar excess relative to template). We surmise that a complementary interaction between the single-stranded oligonucleotide and transiently denatured promoter template may be responsible for this sequence-specific transcription initiation artifact. To study the regulation of transcription initiation by in vitro transcription approaches, we propose that one should probe the effect of removing transacting factors by adding an excess of a cognate oligonucleotide which does not bear exact sequence identity to the template.

Animals↗
PubMed1996

A rare tumor masquerading as an empyema: pleuropulmonary blastoma.

Pleuropulmonary blastoma, although rare, should be considered in the differential diagnosis of children who present with a pleural effusion and symptoms of respiratory tract infection when the empyema fails to respond to medical management. A case of a 2-year-old boy with this rapidly growing tumor is reported. The treatment and outcome of pleuropulmonary blastoma in children is reviewed.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Leigh syndrome: clinical features and biochemical and DNA abnormalities.

We investigated the etiology of Leigh syndrome in 67 Australian cases from 56 pedigrees, 35 with a firm diagnosis and 32 with some atypical features. Biochemical or DNA defects were determined in both groups, ie, 80% in the tightly defined group and 41% in the "Leigh-like" group. Eleven patients had mitochondrial DNA point mutations (nucleotide [nt] 8993 T to G, nt 8993 T to C, or nt 8344 A to G) and 1 Leigh-like patient had a heteroplasmic deletion. Twenty-nine patients had enzyme defects, ie, 13 respiratory chain complex I, 9 complex IV, and 7 pyruvate dehydrogenase complex (PDHC). Complex I deficiency is more common than recognized previously. Six PDHC-deficient patients had mutations in the X-chromosomal gene encoding the E1alpha subunit of PDHC. Parental consanguinity suggested autosomal recessive inheritance in two complex IV-deficient sibships. We found no strong correlation between the clinical features and basic defects. An assumption of autosomal recessive inheritance (frequently made in the past) would have been wrong in nearly one-half (11 of 28 tightly defined and 18 of 41 total patients) of those in whom a cause was found. A specific defect must be identified if reliable genetic counseling is to be provided.

Brain↗
PubMed1996

Intractable constipation with a decrease in substance P-immunoreactive fibres: is it a variant of intestinal neuronal dysplasia?

After Hirschsprung's disease was ruled out for 25 children who had severe chronic constipation, the authors studied the distribution of immunoreactivity for substance P (SP) and vasoactive intestinal peptide (VIP) in the intestinal wall, using immunofluorescence. SP and VIP immunoreactivity identify excitatory and inhibitory nerve fibres, respectively. Full-thickness rectal biopsy specimens were unsatisfactory, so seromuscular biopsies of the caecum, transverse colon, and sigmoid colon were obtained (by laparoscopy and laparotomy; n = 10 patients). SP-immunoreactive fibres were markedly reduced in seven, with concomitant reduction of VIP-immunoreactive fibres in four. In two other patients, there was no obvious reduction in SP- or VIP-immunoreactive fibres. In a patient who subsequently was found to have multiple endocrine neoplasia type 2b, the myenteric plexus was markedly hyperplastic, with an increase in nerve cells and nerve fibres. VIP-immunoreactive fibres were increased, but SP-immunoreactive fibres were markedly decreased. Surgical options included proximal stoma, Malone operation, and subtotal colectomy with preservation of the rectum. Three children with subtotal colectomy have had improvement over short-term follow-up. The combination of seromuscular laparoscopic biopsies and immunofluorescence demonstration of neuropeptides may identify new variants of intestinal neuronal dysplasia than can be treated successfully with surgery.

Adenomatous Polyposis Coli↗
PubMed1996

Rapid diagnosis of germline p53 mutation using the enzyme mismatch cleavage method.

The p53 tumor suppressor gene is the most commonly altered gene in human cancers. Germline mutations in p53 are the genetic alteration underlying predisposition to multiple cancers in Li-Fraumeni syndrome and Li-Fraumeni-like syndrome. We describe a patient who presented with developed adrenocortical carcinoma at age 19 months and a cerebral primitive neuroectodermal tumor at age 5 years. The patient did not have a family history of cancer. We used the enzyme mismatch cleavage (EMC) method to screen for mutations in the p53 gene and found a germline mutation in exon 7 (codon 248). Loss of heterozygosity analysis in one tumor revealed loss of the wild-type p53 allele. In our report we demonstrate the EMC method to be a rapid and sensitive method for mutation detection.

Adrenocortical Carcinoma↗
PubMed1996

The phenotypic features of osteogenesis imperfecta resulting from a mutation of the carboxyl-terminal pro alpha 1 (I) propeptide that impairs the assembly of type I procollagen and formation of the extracellular matrix.

The features of a baby with lethal perinatal osteogenesis imperfecta (OI-II), resulting from the substitution of tryptophan 94 by cysteine in the carboxyl-terminal propeptide of pro alpha 1 (I) chains of type I procollagen, were studied. The limbs and torso were of normal length, shape, and proportion. Similarly, all bones were of relatively normal shape and the long bones showed normal metaphyseal modelling. These clinical and radiographic features were similar to those observed in another baby with OI-II resulting from a mutation of the carboxy-terminal propeptide of pro alpha 1 (I) chains but dissimilar from those reported in babies with OI-II resulting from helical mutations of type I collagen.

Bone and Bones↗