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Biomedical subjects

S C Lo

Publications and source records attributed to S C Lo.

At least 19 recordsLinked to original sources
PubMed2001

Telomerase is regulated by protein kinase C-zeta in human nasopharyngeal cancer cells.

Telomerase, a specialized ribonucleoprotein reverse transcriptase that directs the synthesis of telomeric DNA, is repressed in normal human somatic cells, but is activated in most cancers. Little is known concerning how telomerase activity is activated and maintained in cancer cells. We have shown previously that inhibition of protein kinase C (PKC) decreases the telomerase activity of human nasopharyngeal carcinoma (NPC) cells. Here, we provide evidence that the decrease of telomerase activity by PKC inhibition is not mediated by transcriptional down-regulation of hTERT, the catalytic protein of human telomerase. In vitro phosphorylation studies revealed that exogenous addition of PKC-alpha, -betaI, -delta or -zeta led to restoration of telomerase activity in the crude extracts of PKC-inhibited NPC cells. However, depletion of PKC-alpha and -betaI in vivo had no detectable effect on the telomerase activity of NPC cells. Using antisense oligonucleotides against individual PKC isotypes, we observed that telomerase activity was inhibited only by the antisense oligonucleotide against PKC-zeta but not by those against PKC-alpha, -betaI or -delta. Taken together, these data demonstrate that PKC participates in the regulation of telomerase activity by direct or indirect phosphorylation of telomerase proteins, and that PKC-zeta is the PKC isotype that functions in vivo in the NPC cells.

Base Sequence↗
PubMed2001

Digitized mammography: a clinical trial of postmenopausal women randomly assigned to receive raloxifene, estrogen, or placebo.

BACKGROUND: High mammographic density is associated with increased breast cancer risk. Previous studies have shown that estrogens increase breast density on mammograms, but the effect on mammographic density of selective estrogen receptor modulators, such as raloxifene, is unknown. We assessed changes in mammographic density among women receiving placebo, raloxifene, or conjugated equine estrogens in an osteoporosis prevention trial. METHODS: In a 5-year multicenter, double-blind, randomized, placebo-controlled osteoporosis prevention trial, healthy postmenopausal women who had undergone hysterectomy less than 15 years before the study and had no history of breast cancer received placebo, raloxifene (at one of two doses), or conjugated estrogens (ERT). Women from English-speaking investigative sites who had baseline and 2-year craniocaudal mammograms with comparable positioning (n = 168) were eligible for this analysis. Changes in mammographic density were determined by digital scanning and computer-assisted segmentation of mammograms and were analyzed with the use of analysis of variance. All statistical tests were two-sided. RESULTS: Among the four treatment groups after 2 years on study, the mean breast density (craniocaudal view) was statistically significantly greater in the ERT group than it was in the other three groups (P<0.01 for all three comparisons). Within treatment groups, the mean breast density from baseline to 2 years decreased statistically significantly in women receiving the placebo or either the higher or lower raloxifene dose (P = 0.003, P = 0.002, and P<0.001, respectively) and showed a nonstatistically significant increase in women receiving ERT. CONCLUSIONS: In an osteoporosis prevention trial, raloxifene did not increase breast density after 2 years of treatment. Raloxifene administration should not interfere with, and could even enhance, mammographic detection of new breast cancers.

Breast↗
PubMed2000

Lack of serological evidence for Mycoplasma fermentans infection in army Gulf War veterans: a large scale case-control study.

Mycoplasma firmentans is suspected in the development of 'Gulf War illness' in veterans of Operation Desert Storm. We conducted a matched case-control study for the prevalence of M. firmentans-specific antibodies before and after the operation, as well as seroconversion rates in veterans with and without complaints of 'Gulf War illness'. Cases consisted of Gulf War veterans, who complained of various illnesses and were enrolled in the second phase of the health evaluation by the Army Comprehensive Clinical Examination Program (CCEP). Controls were selected from Gulf War veterans who did not participate in the registry and did not request a health evaluation by the CCEP. Before operation deployment, 34 out of 718 of the cases (48%) and 116 out of 2233 of the controls (5.2%) tested positive for M. fermentans-specific antibodies. There was no difference in rates of seroconversion between cases and controls (1.1 vs. 1.2%) to M. fermentans during Operation Desert Storm. Thus, there is no serological evidence that suggests infectionby M. fermentans is associated with development of 'Gulf War illness'.

Adolescent↗
PubMed2000

Frequency and characterization of platelet-specific antibodies in patients who received multiple platelet transfusions.

BACKGROUND AND PURPOSE: Multiple platelet transfusions may induce alloimmunization. Platelet alloimmunization involves human leukocyte antigen (HLA) antibodies and platelet-specific antibodies, which recognize platelet glycoproteins. No data are available about the frequency and characteristics of platelet-specific antibodies in patients who have received multiple platelet transfusions in Taiwan. METHODS: From June through December 1998, blood samples from 103 patients who had received multiple platelet transfusions were submitted to our laboratory for examination of platelet antibodies. The samples were first screened for HLA antibodies or platelet-specific antibodies using a solid phase method. Positive sera were further tested using an enzyme-linked immunosorbent assay (ELISA) to identify the specificities of the alloantibodies. RESULTS: Forty of the 103 patients who had received multiple platelet transfusions were positive for platelet-reactive antibodies. Further study using ELISA showed that 22 patients had both HLA and platelet-specific antibodies, 12 patients had HLA antibodies alone, and five patients produced platelet-specific antibodies in the absence of HLA antibodies. Most platelet-specific antibodies were found among patients who had HLA antibodies: 81% of platelet-specific antibodies were found in HLA-immunized patients. The most frequently involved platelet glycoprotein antigens were Ia/IIa and IIb/IIIa. CONCLUSIONS: HLA antibodies were the most frequently found platelet-reactive antibodies in Taiwanese patients who had received multiple transfusions, although platelet-specific antibodies were also common. The frequency of platelet-specific antibodies was not as low as previously reported.

Adolescent↗
PubMed1999

Application of image analysis techniques to two-dimensional crossed immunoelectrophoresis study.

Two-dimensional crossed immunoelectrophoresis (2D-CIEP) is a technique widely used for studying composition of protein mixtures in biological and clinical studies. A low cost image analysis system with the use of an optical flatbed scanner and a IBM-compatible PC was set up in this work for capturing 2D-CIEP patterns. A computer package CIEPEASY was developed for modification and analysis of the image acquired to determine various peak parameters such as the migration distance, peak height and peak area of the constituting components for both qualitative and quantitative studies. In this approach, more composition information of the standard and sample gel patterns could be extracted from the proposed image analysis system. The time required for data collection and interpretation of 2D-CIEP images was shortened significantly and the results obtained have a higher accuracy than those obtained by using conventional methods. Moreover, a linear relationship between the peak area and the amount of antigen present in a sample was confirmed accurately and reported for the first time in the literature.

Antigens↗
PubMed1999

Mycoplasma orale has a sequence similar to the insertion-like sequence of M. fermentans.

Polymerase chain reaction (PCR) using the Mycoplasma fermentans insertion sequence-like element (ISLE) RW primer set amplifies DNA from Mycoplasma orale when more than 1 ng is present in the reaction tube. In this study, amplified products from 11 different clinical isolates and the ATCC prototype of M. orale were sequenced and compared to 206 bp amplicons from eight isolates and the ATCC strain of M. fermentans. The nucleotide sequences of the amplified M. orale products had high sequence homology (88-92%) to those from M. fermentans, but differed at several key positions. The M. orale products contained a DraI restriction enzyme site not found in any of the M. fermentans amplified products. Consistent with this finding, the PCR products from M. orale were digested by DraI while the PCR products from M. fermentans were resistant to DraI digestion. The results suggest that M. orale may carry a similar IS-like element that complicates but does not negate using the ISLE PCR assay designed to detect M. fermentans. It appears possible for the RW primers to amplify M. orale if the mycoplasmas are present at higher concentrations. The amplified products can be differentiated from those from M. fermentans by a rapid DraI restriction endonuclease digestion or by Southern blot analysis using the RW006 internal probe under highly stringent conditions.

Base Sequence↗
PubMed1999

cDNA cloning of a sorghum pathogenesis-related protein (PR-10) and differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum.

A sorghum cDNA clone was isolated by differential screening of a cDNA library prepared from mesocotyls (cultivar DK18) inoculated with fungal pathogenes. The deduced translation product shows sequence similarity to a family of intracellular pathogenesis-related proteins (PR-10) with a potential ribonuclease function. We studied the accumulation of PR-10 and chalcone synthase (CHS) transcripts in mesocotyls following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum. CHS is involved in phytoalexin synthesis in sorghum. Coordinate expression of PR-10 and CHS genes was localized in the area of inoculation along with the accumulation of phytoalexins. C. heterostrophus is a nonpathogen of sorghum and cytological studies indicated that cultivar DK18 is resistant to C. sublineolum, a sorghum pathogen. We demonstrated that the two fungi triggered different time courses of plant defense reactions. Inoculation with C. heterostrophus resulted in rapid accumulation of PR-10 and CHS transcripts after appressoria had become mature. Accumulation of these transcripts was delayed in plants inoculated with C. sublineolum until penetration of host tissue had been completed and infection vesicles had formed. Results suggest that different recognition events are involved in the expression of resistance to the two fungi used or that C. sublineolum suppresses the nonspecific induction of defense responses.

Amino Acid Sequence↗
PubMed1999

Lipid extract of Mycoplasma penetrans proteinase K-digested lipid-associated membrane proteins rapidly activates NF-kappaB and activator protein 1.

Lipid-associated membrane proteins (LAMPs) of Mycoplasma penetrans rapidly induced macrophages to produce proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha). Our analysis showed that the macrophage-stimulating activity of TNF-alpha production was mainly attributable to a lipid extractable component(s) in the LAMP preparation. Since induction of gene expression is normally preceded by activation of transcriptional factors that bind to their specific recognition elements located in the upstream promoter region, we examined the activity of transcriptional factors, namely, NF-kappaB and activator protein 1 (AP-1), in thioglycolate exudate peritoneal (TEP) macrophages treated with M. penetrans lipid extract of proteinase K (PK)-digested LAMPs. Initially, in the nuclei of unstimulated TEP cells, there was only a low basal level of active AP-1, and the active form of NF-kappaB could not be detected. M. penetrans lipid extract of PK-digested LAMPs activated both NF-kappaB and AP-1 in TEP macrophages within 15 min. The markedly increased activities of both factors gradually declined and dissipated after 2 h. Parallel to the rapid increase of NF-kappaB and AP-1, the TNF-alpha transcript also increased significantly 15 min after the stimulation. The high-level expression of TNF-alpha persisted over 2 h. Dexamethasone blocked the activation of both NF-kappaB and AP-1 and suppressed the production of TNF-alpha in TEP macrophages stimulated by M. penetrans lipid extract of PK-digested LAMPs. Our study demonstrates that the M. penetrans lipid extract of PK-digested LAMP is a potent activator for NF-kappaB and AP-1 in murine TEP macrophages. Our results also suggest that high-level expression of TNF-alpha in cells induced by M. penetrans lipid extract of PK-digested LAMPs is associated with rapid activation of transcriptional factors NF-kappaB and AP-1.

Animals↗
PubMed1999

Mycoplasmal infections prevent apoptosis and induce malignant transformation of interleukin-3-dependent 32D hematopoietic cells.

32D cells, a murine myeloid cell line, rapidly undergo apoptosis upon withdrawal of interleukin-3 (IL-3) supplement in culture. We found that 32D cells, if infected by several species of human mycoplasmas that rapidly activated NF-kappaB, would live and continue to grow in IL-3-depleted culture. Mycoplasma-infected cells showed no evidence of autocrine production of IL-3. Pyrrolidine dithiocarbamate (PDTC) blocked activation of NF-kappaB and led to prominent cell death. Heat-killed mycoplasmas or mycoplasmal membrane preparations alone could support continued growth of 32D cells in culture without IL-3 supplement for a substantial period of time. However, upon removal of heat-inactivated mycoplasmas, 32D cells quickly became apoptotic. In comparison, live Mycoplasma fermentans or M. penetrans infection for 4 to 5 weeks induced malignant transformation of 32D cells. Transformed 32D cells grew autonomously and no longer required support of growth-stimulating factors including IL-3 and mycoplasmas. The transformed 32D cells quickly formed tumors when injected into nude mice. Karyotyping showed that development of chromosomal changes and trisomy 19 was often associated with malignant transformation and tumorigenicity of 32D cells. Mycoplasmal infections apparently affected the fidelity of genomic transmission in cell division as well as checkpoints coordinating the progression of cell cycle events.

Animals↗
PubMed1998

Refolding of denatured trichosanthin in the presence of GroEL.

The stability of trichosanthin (TCS), a 27-kDa ribosome-inactivating protein, was investigated in the presence of guanidinium chloride (GdnHCl). The process of unfolding was monitored by CD and fluorescence spectroscopy. Both methods show the presence of partially folded intermediates. Unfolding of TCS is attained in 6M GdnHCl, but the inactive species recover a good deal of its DNase activity upon dilution with buffer containing GroEL and ATP. The mechanism of recognition of unfolded TCS by GroEL was studied by fluorescence spectroscopy.

Adenosine Triphosphate↗
PubMed1998

The Arthromitus stage of Bacillus cereus: intestinal symbionts of animals.

In the guts of more than 25 species of arthropods we observed filaments containing refractile inclusions previously discovered and named "Arthromitus" in 1849 by Joseph Leidy [Leidy, J. (1849) Proc. Acad. Nat. Sci. Philadelphia 4, 225-233]. We cultivated these microbes from boiled intestines of 10 different species of surface-cleaned soil insects and isopod crustaceans. Literature review and these observations lead us to conclude that Arthromitus are spore-forming, variably motile, cultivable bacilli. As long rod-shaped bacteria, they lose their flagella, attach by fibers or fuzz to the intestinal epithelium, grow filamentously, and sporulate from their distal ends. When these organisms are incubated in culture, their life history stages are accelerated by light and inhibited by anoxia. Characterization of new Arthromitus isolates from digestive tracts of common sow bugs (Porcellio scaber), roaches (Gromphodorhina portentosa, Blaberus giganteus) and termites (Cryptotermes brevis, Kalotermes flavicollis) identifies these flagellated, spore-forming symbionts as a Bacillus sp. Complete sequencing of the 16S rRNA gene from four isolates (two sow bug, one hissing roach, one death's head roach) confirms these as the low-G+C Gram-positive eubacterium Bacillus cereus. We suggest that B. cereus and its close relatives, easily isolated from soil and grown on nutrient agar, enjoy filamentous growth in moist nutrient-rich intestines of healthy arthropods and similar habitats.

Animals↗
PubMed1998

High-frequency DNA rearrangements in the chromosomes of clinically isolated Mycoplasma fermentans.

Mycoplasma fermentans is currently being examined as an agent potentially associated with human disease. Several strains of M. fermentans were isolated from patients with respiratory tract disease and AIDS. Two of these clinical strains, M64 and SK6, were triple-filter-cloned and designated as the parental clones in this study. Genomic DNA of randomly picked subclones in four and five subsequent generations passed from the parental M64 and SK6 clones were analyzed by using a radiolabeled M. fermentans-specific insertion sequence (IS)-like element as the probe. The hybridization patterns of DNA restriction fragments revealed high frequencies of chromosomal changes accompanied with excision or new insertion of the IS-like element in M. fermentans chromosome. The findings indicate M. fermentans has an effective mechanism(s) to produce a rapid gene rearrangement that may be mediated by one or more copies of the IS-like element.

Blotting, Southern↗
PubMed1998

Porcine pyridoxal kinase c-DNA cloning, expression and confirmation of its primary sequence.

Porcine brain pyridoxal kinase has been cloned. A 1.2 kilo-based cDNA with a 966-base pair open reading frame was determined from a porcine brain cortex cDNA library using PCR technique. The DNA sequence was shown to encode a protein of 322 amino acid residues with a molecular mass of 35.4 kDa. The amino acid sequence deduced from the nucleotide sequence of the cDNA was shown to match the partial primary sequence of pyridoxal kinase. Expression of the cloned cDNA in E. coli has produced a protein which displays both pyridoxal kinase activity and immunoreactivity with monoclonal antibodies raised against natural enzyme from porcine brain. With respect to the physical properties, it is shown that the recombinant protein exhibits identical kinetic parameters with the pure enzyme from porcine brain. Although the primary sequence of porcine pyridoxal kinase has been shown to share 87% homology with the human enzyme, we have shown that the porcine enzyme carries an extra peptide of ten amino acid residues at the N-terminal domain.

Amino Acid Sequence↗
PubMed1998

Partially folded conformations of inositol monophosphatase endowed with catalytic activity.

The stability of porcine brain inositol monophosphatase in the presence of increasing concentrations of urea was investigated at pH 7.5. Exposure of the enzyme to 8 M urea brings about the dissociation of the dimeric species of 58 kDa into monomeric forms as revealed by gel filtration chromatography. Unfolding of the protein by 8 M urea results in a decrease of the ellipticity at 220 nm (20%) together with a perturbation of the near-UV circular dichroism spectrum. Urea-treated inositol monophosphatase binds Co2+ ions with a dissociation constant of 3.3 microM. The enzyme is catalytically competent when assayed with 4-nitrophenyl-phosphate in the presence of the activating ion Co2+ at pH 7.5 in 8 M urea. The apparent activation constant for Co2+ is 2.5 mM. It is postulated that partially folded conformations of monomeric species preserve their catalytic function because the affinity of Co2+ ions for the metal coordination center of the protein is not perturbed by exposure to 8 M urea.

Animals↗
PubMed1998

Reduction of light-induced anthocyanin accumulation in inoculated sorghum mesocotyls. Implications for a compensatory role in the defense response.

Sorghum (Sorghum bicolor L. Moench) accumulates the anthocyanin cyanidin 3-dimalonyl glucoside in etiolated mesocotyls in response to light. Inoculation with the nonpathogenic fungus Cochliobolus heterostrophus drastically reduced the light-induced accumulation of anthocyanin by repressing the transcription of the anthocyanin biosynthesis genes encoding flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase. In contrast to these repression effects, fungal inoculation resulted in the synthesis of the four known 3-deoxyanthocyanidin phytoalexins and a corresponding activation of genes encoding the key branch-point enzymes in the phenylpropanoid pathway, phenylalanine ammonia-lyase and chalcone synthase. In addition, a gene encoding the pathogenesis-related protein PR-10 was strongly induced in response to inoculation. The accumulation of phytoalexins leveled off by 48 h after inoculation and was accompanied by a more rapid increase in the rate of anthocyanin accumulation. The results suggest that the plant represses less essential metabolic activities such as anthocyanin synthesis as a means of compensating for the immediate biochemical and physiological needs for the defense response.

Acyltransferases↗
PubMed1998

Absence of mycoplasmal gene in malignant mammalian cells transformed by chronic persistent infection of mycoplasmas.

Chronic persistent infections by mycoplasmas induced malignant transformation of C3H mouse embryo cells that normally had never been reported to undergo spontaneous transformation. This mycoplasma-mediated oncogenic process had a long latency (more than 7 weeks of continuous mycoplasmal infection) and showed a multistage progression characterized by reversibility (at least up to 11 weeks of mycoplasmal infection) and irreversibility of malignant properties upon removal of the mycoplasma from culture. Further prolonged infections (18 weeks) by Mycoplasma fermentans or M. penetrans resulted in permanent transformation of these C3H cells that no longer required the continued presence of the transformation-inducing mycoplasmas in cultures to retain their malignant properties. Previous studies of viral oncogenesis revealed that virus-transformed cells always had viral gene(s) present. Integration of viral gene(s) apparently played an important role in the process of oncogenesis. In this study, we examined if the continued presence of any mycoplasmal gene(s) in mammalian cells, in whatever form, was also crucial in causing malignant cell transformation. Representational difference analysis (RDA) was a recently developed powerful technique to compare differences between two complex genomes. In the RDA system, subtractive and kinetic enrichment was used to purify and isolate restriction endonuclease gene fragment(s) of mycoplasmal origin, presumably present only in mycoplasma-transformed C3H cells, but not in nonmycoplasma-exposed control C3H cells. After three rounds of subtractive hybridization following PCR enrichment for each of three different restriction enzymes DNA digests, no gene fragment of mycoplasmal origin was amplified or identified in the permanently transformed C3H cells. Differing from tumorigenesis in animal cells induced by most oncogenic viruses or in plant cells induced by Agrobacteria, mycoplasmas evidently did not cause malignant transformation by integrating their gene(s) into the mammalian cell genome.

Animals↗
PubMed1997

Fractal modeling and segmentation for the enhancement of microcalcifications in digital mammograms.

The objective of this research is to model the mammographic parenchymal, ductal patterns and enhance the microcalcifications using deterministic fractal approach. According to the theory of deterministic fractal geometry, images can be modeled by deterministic fractal objects which are attractors of sets of two-dimensional (2-D) affine transformations. The iterated functions systems and the collage theorem are the mathematical foundations of fractal image modeling. In this paper, a methodology based on fractal image modeling is developed to analyze and model breast background structures. We show that general mammographic parenchymal and ductal patterns can be well modeled by a set of parameters of affine transformations. Therefore, microcalcifications can be enhanced by taking the difference between the original image and the modeled image. Our results are compared with those of the partial wavelet reconstruction and morphological operation approaches. The results demonstrate that the fractal modeling method is an effective way to enhance microcalcifications. It may also be able to improve the detection and classification of microcalcifications in a computer-aided diagnosis system.

Algorithms↗