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Biomedical subjects

L Ho

Publications and source records attributed to L Ho.

At least 91 records · Page 5Linked to original sources
PubMed1994

Xenopus laevis cellular retinoic acid-binding protein: temporal and spatial expression pattern during early embryogenesis.

There is increasing evidence that retinoic acid (RA) has a role in establishing normal axial patterns during Xenopus laevis embryo-genesis. Several types of retinoid binding proteins are thought to mediate the effects of RA. We report the isolation of a cDNA, named xCRABP-b, which encodes a X. laevis cellular retinoic acid-binding protein (xCRABP). This cDNA hybridises to a transcript in gastrular stage embryos of approximately 3 kb, much larger than those CRABP transcripts expressed in mice. The expression of the xCRABP mRNA is generally restricted to tissues which are sensitive to the teratogenic effects of excess RA. It is likely, that during normal X. laevis embryogenesis, concentrations of RA in RA-responsive cells are modulated by the xCRABP gene product.

Amino Acid Sequence↗
PubMed1994

Type-specific human papillomavirus DNA in abnormal smears as a predictor of high-grade cervical intraepithelial neoplasia.

Human papillomavirus (HPV) typing and quantitation by polymerase chain reaction was performed on exfoliated cells from 133 women referred for colposcopy because of an abnormal smear. High levels of HPV 16 correctly predicted cervical intraepithelial neoplasia (CIN) grade II-III in 93% of its occurrences, but only 59% of cases of CIN III were associated with high levels of this type. Eighty-four per cent of CIN III lesions contained high levels of at least one of HPV types 16, 18, 31, 33 and 35, but the other types were less specific for CIN III than HPV 16. Overall HPV testing compared favourably with cytology for predicting high-grade CIN lesions, but it would appear that some combination of the two modalities will produce better performance than either alone. In particular, HPV testing appears to be helpful in determining which women with mildly abnormal smears have high-grade underlying lesions in need of immediate referral for colposcopy.

Base Sequence↗
PubMed1994

Inhibition of proliferation of human melanocytes by a KIT antisense oligodeoxynucleotide: implications for human piebaldism and mouse dominant white spotting (W).

KIT constitutes the cell surface transmembrane receptor protein tyrosine kinase for a growth factor variously termed steel factor (SLF), stem cell factor, mast cell growth factor, or Kit ligand. Inherited mutations of the KIT gene result in piebaldism in humans and dominant white spotting (W) in mice. Patches of hypopigmented skin and hair in these disorders represent regions lacking in melanocytes, the result of defective melanoblast differentiation, migration, proliferation, or survival during embryonic development. Here we show that incubation of normal human melanocytes with a KIT antisense oligodeoxynucleotide greatly inhibits cell proliferation in culture, whereas incubation with a KIT sense oligodeoxynucleotide has no effect. The KIT oligodeoxynucleotides also had little or no effect on cell survival.

Animals↗
PubMed1994

Semiautomated detection of human papillomavirus DNA of high and low oncogenic potential in cervical smears.

Detection of DNA from human papillomaviruses (HPV) of high and intermediate oncogenic risk in cervical smears may predict the presence of cervical cancer or may indicate precancerous changes. Here we describe a semiautomated polymerase chain reaction system for the detection and classification of HPV DNA that is present in clinically significant amounts in routine cervical scrapes.

Autoanalysis↗
PubMed1993

Kinetic characterization of Na+/D-mannose cotransport in dog kidney: comparison with Na+/D-glucose cotransport.

Brush-border membrane vesicles (BBMV) prepared from whole dog kidney cortex, or separately from outer cortex (OC) and outer medulla (OM), were used to study the kinetics and inhibition specificity of Na(+)-dependent D-mannose cotransport. In BBMV from whole cortex the measured parameters for Na+/D-mannose uptake were Km = 0.07 +/- 0.01 mM and Vmax = 4.19 +/- 0.24 nmol/mg protein per min (n = 36). In OC BBMV the Km for Na+/D-mannose was 0.04 mM, Vmax = 3.41 nmol/mg per min. In OM the Km was 0.06 +/- 0.02 mM Vmax = 0.18 nmol/mg per min. Thus only about 5% of Na+/D-mannose activity occurs in OM. Both mannoheptulose (Ki = 5.6 mM) and methyl alpha-D-mannoside (Ki = 0.05 mM) are competitive inhibitors of Na+/D-mannose uptake, but at comparable concentrations have little effect on Na+/D-glucose uptake. Phlorizin is a noncompetitive inhibitor of Na+/D-mannose uptake (Ki = 4.45 microM) but a more potent and competitive inhibitor (Ki = 0.58 microM) of Na+/D-glucose uptake. Phloretin (Ki = 104 microM) is a noncompetitive inhibitor of Na+/D-mannose uptake in BBMV. We conclude that Na+/D-mannose uptake is mediated by a unique high-affinity carrier located in the OC presumably at the luminal surface of the proximal convoluted tubule, with strong specificity requirements for sugars with mannose-like structures (i.e., axial C-2 hydroxyl group). Phlorizin is an inhibitor of both Na+/D-mannose and Na+/D-glucose cotransporters but is approx. 10 times less potent for the Na+/D-mannose system and also has a different mode of inhibition (i.e., noncompetitive vs. competitive). The different phlorizin inhibitory mechanisms on the Na+/D-glucose and Na+/D-mannose cotransporters may be mediated by distinct hydrophobic and sugar binding sites that characterize phlorizin-carrier interaction.

Animals↗
PubMed1993

Identification of two unique polypeptides from dog kidney outer cortex and outer medulla that exhibit different Na+/D-glucose cotransport functional properties.

The cloned Na+/D-glucose cotransporter SGLT1 and an additional recently isolated human kidney cDNA Hu14/K15 belong to a family of similar cotransport proteins including the Na(+)-dependent nucleoside and Na(+)-dependent myo-inositol carrier SMIT1. For the present study we used two different polyclonal antibodies raised against the amino acid sequence 402-420 (Ab-E) and 565-574 (Ab-P) of SGLT1 to probe brush-border membrane fractions from different regions (outer cortex-->outer medulla) of dog kidney. In Western blots both Ab-E and Ab-P react specifically (peptide blockable) with two distinct bands migrating on SDS-PAGE under reducing conditions at 75.5 kDa and 72.5 kDa. The higher molecular mass polypeptide is greatly enriched (13:1) in outer cortex and diminishes progressively towards outer medulla, whereas the lower molecular mass band is barely detectable in outer cortex but is enriched in outer medulla (4:1). Brush-border membrane vesicles (BBMV) prepared from the same outer cortical and outer medullary regions that were probed with Ab-E and Ab-P exhibit strikingly different Na+/D-glucose functional transport behavior. The Na+/D-glucose cotransport activity in outer cortical BBMV is a low-affinity system with Km = 5.98 +/- 1.01 mM, Vmax = 13.05 +/- 0.55 nmol/mg protein per min, and with 1:1 Na+:D-glucose stoichiometry. Outer medulla BBMV exhibit high-affinity Km = 0.27 +/- 0.03 mM Vmax = 0.97 +/- 0.04 nmol/mg protein per min and 2:1 Na+:D-glucose stoichiometry. Comparison of SGLT1, Hu14/K15, SNST1 and SMIT indicates that Ab-E could cross react with all four, but Ab-P would recognize SGLT1, Hu14/K15, SNST1 but not SMIT. Also SNST1 is not expressed in outer cortex. Based on currently available sequence data, and its marked enrichment in outer cortex, the 75.5 kDa band is a likely candidate protein responsible for low-affinity and 1:1 Na+:D-glucose stoichiometric Na+/D-glucose cotransport activity (Hu14/K15) while the minor 72.5 kDa band in outer cortex is probably SGLT1. In outer medulla, the predominant band recognized by both Ab-E and Ab-P is the 72.5 kDa protein and this could be either SGLT1 or SNST1.

Antibodies↗
PubMed1993

Multiple protein-binding domains and functional cis-elements in the 5'-flanking region of the human pyruvate dehydrogenase alpha-subunit gene.

We have characterized the 5'-flanking region of the alpha-subunit gene of the human pyruvate dehydrogenase (E1). DNase I footprinting with rat liver nuclear extracts identified 7 major protein-binding domains termed P1 through P7 in a 796 base pair DNA fragment (base pairs -763 to +33). P1 through P4 are clustered in the -221/+33 region. These protein-binding domains contain several known consensus sequences such as a TATA box, CAAT box, Sp1, and CRE, which all have previously been implicated in the constitutive transcription of several genes. Oligonucleotide competition studies indicate that oligonucleotides specific for CTF/NF-1 and Sp1 displaced the nuclear proteins bound to the CAAT box (within P3) and an Sp1 site (within P4), respectively. Several other well-characterized and purified transactivators (c-Fos, c-Jun, C/EBP, AP-2, and Sp1) have been shown to bind to the -221/+33 region. Other elements located upstream of the -221/+33 region, which includes nuclease protection domains P5-P7, are required for enhanced promoter activity of the 796 bp sequence. Promoter activity was measured by transient expression of a chloramphenicol acetyltransferase gene ligated to deletion fragments of the 5'-flanking region. Crucial element(s) for promoter activity and complex DNA-nuclear protein interactions were confined within a region spanning -221/+33. This region also retained more than 75% of the promoter activity of the 796 bp sequence. Additionally, this promoter region shows characteristics of both facultative and housekeeping gene promoters, suggesting complex transcriptional regulation.

Base Sequence↗
PubMed1993

The Xenopus platelet-derived growth factor alpha receptor: cDNA cloning and demonstration that mesoderm induction establishes the lineage-specific pattern of ligand and receptor gene expression.

We have cloned the Xenopus PDGF alpha receptor cDNA and have used this clone, along with cDNA encoding PDGF A, to examine their expression pattern in Xenopus embryos and to determine the factors responsible for lineage specificity. Recombinant Xenopus alpha receptor expressed in COS cells exhibits PDGF-A-dependent tyrosine kinase activity. We find that receptor mRNA is present in cultured marginal zone tissue explants and in animal cap tissue induced to form mesoderm either by grafting to vegetal tissue or by treatment with recombinant activin A. In contrast, PDGF A mRNA is expressed in cultured, untreated animal cap tissue and is suppressed by mesoderm induction. These results suggest that ectodermally produced PDGF A may act on the mesoderm during gastrulation and that mesoderm induction establishes the tissue pattern of ligand and receptor expression.

Amino Acid Sequence↗
PubMed1993

Definition of human papillomavirus type 16 DNA levels in low and high grade cervical lesions by a simple polymerase chain reaction technique.

Human papillomavirus type 16 (HPV 16) is associated with a high proportion of cervical cancers and pre-cancers but has also been reported by some workers to be widely distributed in the normal population. Using a semi-quantitative polymerase chain reaction technique (PCR) operated with carefully regulated sensitivity we have established two distinct levels of HPV 16 DNA which distinguish between high and low grade cervical lesions. The potential use of such an approach in the understanding and management of HPV related cervical disease is discussed.

Biopsy↗
PubMed1993

Sequence variants of human papillomavirus type 16 from couples suggest sexual transmission with low infectivity and polyclonality in genital neoplasia.

Human papillomavirus type 16 (HPV-16) is causally involved in the pathogenesis of genital neoplasia, but important details of the natural history of infection and disease are not yet understood. Many individual HPV-16 DNA isolates differ by characteristic point mutations. In a study of the HPV-16 variants from genital lesions of 32 married couples, HPV-16 was detected in both the husband and the wife in 8 couples. Of these, 4 demonstrated identical HPV-16 variants between husband and wife, and 4 had mismatching HPV-16 variants. Five of 31 biopsies showed simultaneous presence of two different HPV-16 variants. The data suggest that sexual transmission of HPV-16 does occur, but with low infectivity, and that HPV-16-related premalignant lesions are frequently polyclonal.

Adult↗
PubMed1993

The genetic drift of human papillomavirus type 16 is a means of reconstructing prehistoric viral spread and the movement of ancient human populations.

We have investigated the diversity of a hypervariable segment of the human papillomavirus type 16 (HPV-16) genome among 301 virus isolates that were collected from 25 different ethnic groups and geographic locations. Altogether, we distinguished 48 different variants that had diversified from one another along five phylogenetic branches. Variants from two of these branches were nearly completely confined to Africa. Variants from a third branch were the only variants identified in Europeans but occurred at lower frequency in all other ethnic groups. A fourth branch was specific for Japanese and Chinese isolates. A small fraction of all isolates from Asia and from indigenous as well as immigrant populations in the Americas formed a fifth branch. Important patterns of HPV-16 phylogeny suggested coevolution of the virus with people of the three major human races, namely, Africans, Caucasians, and East Asians. But several minor patterns are indicative of smaller bottlenecks of viral evolution and spread, which may correlate with the migration of ethnic groups in prehistoric times. The colonization of the Americas by Europeans and Africans is reflected in the composition of their HPV-16 variants. We discuss arguments that today's HPV-16 genomes represent a degree of diversity that evolved over a large time span, probably exceeding 200,000 years, from a precursor genome that may have originated in Africa. The identification of molecular variants is a powerful epidemiological and phylogenetic tool for revealing the ancient spread of papillomaviruses, whose trace through the world has not yet been completely lost.

Africa↗
PubMed1992

Genomic heterogeneity of DNA repair. Role in aging?

The introduction and repair of DNA lesions are generally heterogeneous with respect to different genomic domains. In particular, the repair of helix-distorting damage, such as the cyclobutane pyrimidine dimers (CPD) induced by ultraviolet light occurs selectively in expressed genes. This is due in large part to the preferential repair of transcribed DNA strands, which is then reflected in a bias toward mutagenesis from persisting lesions in nontranscribed strands. Consequently, determination of overall genomic repair efficiencies may not be a good indicator of cellular sensitivity to agents that damage DNA. Although some studies suggest an age-related accumulation of altered nucleotides in DNA, we do not know the intragenomic distribution of those changes and whether they are relevant to the physiological aspects of aging. Subtle changes in the pattern of preferential repair during maturation could have profound effects on cell and tissue function. DNA repair has been analyzed in differentiating cell systems as possible models for aging. We have observed attenuated overall repair of CPD in differentiated rat myoblasts or PC12 neuron-like cells. In both model systems, several expressed genes have been shown to be repaired relatively efficiently but without strand specificity. In another model system of human HT1080 fibroblasts differentiating in the presence of dexamethasone, we demonstrated enhanced repair in the gene for plasminogen activator inhibitor I whose transcription is induced and, correspondingly, a reduced repair rate in the urokinase plasminogen activator gene whose transcription is suppressed. We conclude that any attempted correlation of the phenomena of aging with DNA repair should focus on the relevant genes in the tissue of interest.

Aging↗
PubMed1992

Human papillomavirus type 16 in cervical smears as predictor of high-grade cervical intraepithelial neoplasia [corrected].

The management of women with mild to moderately dyskaryotic cervical smears would benefit from a non-invasive test that predicts which women have high-grade cervical intraepithelial neoplasia. Detection of human papillomavirus type 16 (HPV16) DNA in cervical smears may be such a test. With the polymerase chain reaction (PCR), we estimated the amount of HPV16 DNA in cervical smears from 85 women referred for colposcopy because of abnormal cytology. An intermediate or high amount of HPV16 DNA predicted the presence of high-grade cervical intraepithelial neoplasia in a subsequent biopsy in almost 90% of patients irrespective of the cytological grade of the referral smear. This technique may allow early identification of those women with low-grade cytological abnormalities who have high-grade underlying cervical disease.

DNA, Viral↗
PubMed1992

Molecular variants of human papillomavirus type 16 from four continents suggest ancient pandemic spread of the virus and its coevolution with humankind.

We have amplified by the polymerase chain reaction, cloned, and sequenced genomic segments of 118 human papillomavirus type 16 (HPV-16) isolates from 76 cervical biopsy, 14 cervical smear, 3 vulval biopsy, 2 penile biopsy, 2 anal biopsy, and 1 vaginal biopsy sample and two cell lines. The specimens were taken from patients in four countries--Singapore, Brazil, Tanzania, and Germany. The sequence of a 364-bp fragment of the long control region of the virus revealed 38 variants, most of which differed by one or several point mutations. Phylogenetic trees were constructed by distance matrix methods and a transformation series approach. The trees based on the long control region were supported by another set based on the complete E5 protein-coding region. Both sets had two main branches. Nearly all of the variants from Tanzania were assigned to one (African) branch, and all of the German and most of the Singaporean variants were assigned to the other (Eurasian) branch. While some German and Singaporean variants were identical, each group also contained variants that formed unique branches. In contrast to the group-internal homogeneity of the Singaporean, German, and Tanzanian variants, the Brazilian variants were clearly divided between the two branches. Exceptions to this were the seven Singaporean isolates with mutational patterns typical of the Tanzanian isolates. The data suggest that HPV-16 evolved separately for a long period in Africa and Eurasia. Representatives of both branches may have been transferred to Brazil via past colonial immigration. The comparable efficiencies of transfer of the African and the Eurasian variants to the New World suggest pandemic spread of HPV-16 in past centuries. Representatives of the African branch were possibly transferred to the Far East along old Arab and Indonesian sailing routes. Our data also support the view that HPV-16 is a well-defined virus type, since the variants show only a maximal genomic divergence of about 5%. The small amount of divergence in any one geographic location and the lack of marked divergence between the Tanzanian and Brazilian African genome variants two centuries after their likely introduction into the New World suggest a very slow rate of viral evolution. The phylogenetic tree therefore probably represents a minimum of several centuries of evolution, if not an age equal to that of the respective human races.

Base Sequence↗
PubMed1992

Characterization of errors detected during central order review.

Characterization of prescribing errors detected by dispensary pharmacists in a tertiary-care teaching hospital is described. During the 25 week study period, 1330 prescribing errors were identified from a total of 237,798 medication orders processed by the pharmacy, representing a rate of 5.6 errors per 1000 orders. Resident physicians wrote more errant medication orders than any other physician class. Errors most often occurred on the general medicine teaching wards. The most common drug classes implicated were non-formulary medications and antibiotics. Approximately 11% of errors were defined as potentially fatal or severe (Type A) errors, 7% were potentially serious (Type B), 21% were potentially significant (Type C) and 61% were problem orders (Type D) based on a classification system of severity. The most common error types were inappropriate dosing of antibiotics and the prescribing of medications for patients who had a potential conflicting allergy history. The acceptance of pharmacists' suggestions was 67%. The study identified three major areas where future educational and corrective measures could be aimed: adherence to the formulary, antibiotic prescribing and allergy validation.

Canada↗