Biomedical subjects

L Ko

Publications and source records attributed to L Ko.

At least 19 recordsLinked to original sources

PubMed2006

Gene amplification and associated loss of 5' regulatory sequences of CoAA in human cancers.

CoAA is an RRM-containing transcriptional coactivator that stimulates transcriptional activation and regulates alternative splicing. We show that the CoAA gene is amplified at the chromosome 11q13 locus in a subset of primary human cancers including non-small cell lung carcinoma, squamous cell skin carcinoma and lymphoma. Analysis of 42 primary tumors suggests that CoAA amplifies independently from the CCND1 locus. Detailed mapping of three CoAA amplicons reveals that the amplified CoAA gene is consistently located at the 5' boundaries of the amplicons. The CoAA coding and basal promoter sequences are retained within the amplicons but upstream silencing sequences are lost. CoAA protein is overexpressed in tumors containing the amplified CoAA gene. RNA dot blot analysis of 100 cases of primary tumors suggests elevated CoAA mRNA expression. CoAA positively regulates its own basal promoter in transfection assays. Thus, gene amplification, loss of silencing sequence and positive feedback regulation may lead to drastic upregulation of CoAA protein. CoAA has transforming activities when tested in soft agar assays, and CoAA is homologous to oncoproteins EWS and TLS, which regulate alternative splicing. These data imply that CoAA may share a similar oncogenic mechanism with oncogene EWS and that CoAA deregulation may alter the alternative splicing of target genes.

Animals↗

PubMed2006

Preserving coherence in Rydberg quantum bits.

The effectiveness of decoherence suppression schemes is explored using quantum bits (qubits) stored in Li np Rydberg states. Following laser excitation, pulsed electric fields coherently control the electronic spin-orbit coupling, facilitating qubit creation, manipulation, and measurement. Spin-orbit coupling creates an approximate decoherence-free subspace for extending qubit storage times. However, sequences of fast NOT operations are found to be substantially more effective for preserving coherence.

Journal Article↗

PubMed2001

Identification and characterization of RRM-containing coactivator activator (CoAA) as TRBP-interacting protein, and its splice variant as a coactivator modulator (CoAM).

We previously cloned and characterized thyroid hormone receptor-binding protein (TRBP) as an LXXLL-containing general coactivator that associates with coactivator complexes through its C terminus. To identify protein cofactors for TRBP action, a Sos-Ras yeast two-hybrid cDNA library was screened using TRBP C terminus as bait. A novel coactivator was isolated, coactivator activator (CoAA), that specifically associates with TRBP. Human CoAA is composed of 669 amino acids with a TRBP-interacting domain and two highly conserved RNA recognition motifs (RRM) commonly found in ribonucleoproteins. A splice variant lacking the entire TRBP-interacting domain was also isolated as a coactivator modulator (CoAM), a 156-amino acid protein containing only the RRM region. Human CoAA and CoAM mRNAs are encoded by a single gene located on chromosome 11q13; alternative splicing in exon 2 of CoAA yields CoAM. CoAA interacts with both TRBP and p300 in vitro. In addition, CoAA potently coactivates transcription mediated by multiple hormone-response elements and acts synergistically with TRBP and CREB-binding protein (CBP). Furthermore, CoAA is associated with the DNA-dependent protein kinase-poly(ADP-ribose) polymerase complex. Strikingly, CoAM, which lacks a TRBP-interacting domain, strongly represses both TRBP and CBP action suggesting that CoAM may modulate endogenous CoAA function. These data suggest that CoAA may serve as a mediator of coactivators such as TRBP in gene activation.

Alternative Splicing↗

PubMed2001

Microwave ionization of an atomic electron wave packet.

A short microwave pulse is used to ionize a lithium Rydberg wave packet launched from the core at a well-defined phase of the field. We observe a strong dependence on the relative phase between the motion of the wave packet and the oscillations of the field. This phase dependent ionization is also studied as a function of the relative frequency. Our experimental observations are in good qualitative agreement with a one-dimensional classical model of wave packet ionization.

Journal Article↗

PubMed2000

Thyroid hormone receptor-binding protein, an LXXLL motif-containing protein, functions as a general coactivator.

Nuclear hormone receptors activate gene transcription through ligand-dependent association with coactivators. Specific LXXLL sequence motifs present in these cofactors are sufficient to mediate these ligand-induced interactions. A thyroid hormone receptor (TR)-binding protein (TRBP) was cloned by a Sos-Ras yeast two-hybrid system using TRbeta1-ligand binding domain as bait. TRBP contains 2063 amino acid residues, associates with TR through a LXXLL motif, and is ubiquitously expressed in a variety of tissues and cells. TRBP strongly transactivates through TRbeta1 and estrogen receptor in a dose-related and ligand-dependent manner, and also exhibits coactivation through AP-1, CRE, and NFkappaB-response elements, similar to the general coactivator CBP/p300. The C terminus of TRBP binds to CBP/p300 and DRIP130, a component of the DRIP/TRAP/ARC complex, which suggests that TRBP may activate transcription by means of such interactions. Further, the association of TRBP with the DNA-dependent protein kinase (DNA-PK) complex and DNA-independent phosphorylation of TRBP C terminus by DNA-PK point to a potential connection between transcriptional control and chromatin architecture regulation.

Amino Acid Motifs↗

PubMed2000

Sensitization of neuronal cells to oxidative stress with mutated human alpha-synuclein.

Linkage of alpha-synuclein (alpha-SN) mutations to familial Parkinson's disease (PD) and presence of alpha-SN as a major constituent of Lewy body in both sporadic and familial PD implicate alpha-SN abnormality in PD pathogenesis. Here we demonstrate that overexpression of wild-type or mutant alpha-SN does not cause any deleterious effect on the growth or continued propagation of transfected human cells, but overproduction of mutant alpha-SN heightens their sensitivity to menadione-induced oxidative injury. Such enhanced vulnerability is more pronounced in neuronal transfectants than in their nonneuronal counterparts and is associated with increased production of reactive oxygen species. The data suggest that mutated alpha-SN, especially with an alanine-to-proline substitution at residue 30, sensitizes neuronal cells to oxidative damage.

Cell Line↗

PubMed1999

Mutations in tau reduce its microtubule binding properties in intact cells and affect its phosphorylation.

In vitro evidence has suggested a change in the ability of tau bearing mutations associated with fronto-temporal dementia to promote microtubule assembly. We have used a cellular assay to quantitate the effect of both isoform differences and mutations on the physiological function of tau. Whilst all variants of tau bind to microtubules, microtubule extension is reduced in cells transfected with 3-relative to 4-repeat tau. Mutations reduce microtubule extension with the P301L mutation having a greater effect than the V337M mutation. The R406W mutation had a small effect on microtubule extension but, surprisingly, tau with this mutation was less phosphorylated in intact cells than the other variants.

Animals↗

PubMed1998

Calcium ionophore-induced degradation of neurofilament and cell death in MSN neuroblastoma cells.

Extensive necrotic death of MSN neuroblastoma cells could be induced after incubation with the calcium ionophore, A23187. The reaction was concentration-dependent and time course-dependent. Levels of the 66 kd/alpha-internexin neurofilament protein (NF-66) and the cognate heat shock protein 70 (Hsc 70) decreased during the Ca2+-activated cell death. Addition of the calcium chelator, ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) restored the normal level of NF-66 and partially that of the Hsc 70. Use of either calpain I or calpain II inhibitor could alleviate the reduction of 66 kd protein during the ionophore treatment whereas only calpain I inhibitor treatment was effective in restoring the normal level of the Hsc 70. Neither of these calpain inhibitors could block the ionophore triggered cell death. EGTA was toxic to cells in a wide range of concentration suggesting a calcium-independent activation of cell death mechanism.

Calcimycin↗

PubMed1997

Menadione-induced tau dephosphorylation in cultured human neuroblastoma cells.

Oxidative stress has been implicated in the mechanism of aging and neurodegenerative disorders such as Alzheimer's disease (AD). Menadione causes oxidative stress by generating reactive oxygen species through its redox cycling and these free radicals are detoxified subsequently at the expense of intracellular thiol homeostasis. In non-neuronal cells, the cytoskeleton is a prime target of menadione-induced thiol oxidation. We used cultured human neuroblastoma MSN cells in this study to determine how tau proteins in neuronal cells are affected by menadione exposure. Menadione caused a dose-dependent thiol oxidation in these cells just like their non-neuronal counterparts. A prominent consequence of such oxidative insult in these neuronal cells was tau dephosphorylation. This dephosphorylation resulted in disappearance of phosphorylated 57-kDa tau with a concomitant emergence of 53-kDa tau whose full-length nature is indicated by its reactivity with antibodies Alz 50, Tau-1 and Tau-46. Immunochemical analyses using phosphorylation-dependent immunoprobes Tau-1 and PHF-1 with the aid of alkaline phosphatase demonstrated that 53-kDa tau was derived from dephosphorylation of 57-kDa tau. Despite its effect on thiol oxidation, menadione treatment did not lead to cytoskeletal changes reminiscent of the neurofibrillary tangles of AD. The data thus indicate that tau dephosphorylation constitutes a major feature of the menadione-induced oxidative injury in these neuronal cells.

Cell Survival↗

PubMed1997

Deletions in Xq26.3-q27.3 including FMR1 result in a severe phenotype in a male and variable phenotypes in females depending upon the X inactivation pattern.

High resolution cytogenetics, microsatellite marker analyses, and fluorescence in situ hybridization were used to define Xq deletions encompassing the fragile X gene, FMR1, detected in individuals from two unrelated families. In Family 1, a 19-year-old male had facial features consistent with fragile X syndrome; however, his profound mental and growth retardation, small testes, and lover limb skeletal defects and contractures demonstrated a more severe phenotype, suggestive of a contiguous gene syndrome. A cytogenetic deletion including Xq26.3-q27.3 was observed in the proband, his phenotypically normal mother, and his learning-disabled non-dysmorphic sister. Methylation analyses at the FMR1 and androgen receptor loci indicated that the deleted X was inactive in > 95% of his mother's white blood cells and 80-85% of the sister's leukocytes. The proximal breakpoint for the deletion was approximately 10 Mb centromeric to FMR1, and the distal breakpoint mapped 1 Mb distal to FMR1. This deletion, encompassing approximately 13 Mb of DNA, is the largest deletion including FMR1 reported to date. In the second family, a slightly smaller deletion was detected. A female with moderate to severe mental retardation, seizures, and hypothyroidism, had a de novo cytogenetic deletion extending from Xq26.3 to q27.3, which removed approximately 12 Mb of DNA around the FMR1 gene. Cytogenetic, and molecular data revealed that approximately 50% of her white blood cells contained an active deleted X. These findings indicate that males with deletions including Xq26.3-q27.3 may exhibit a more severe phenotype than typical fragile X males, and females with similar deletions may have an abnormal phenotype if the deleted X remains active in a significant proportion of the cells. Thus, important genes for intellectual and neurological development, in addition to FMR1, may reside in Xq26.3-q27.3. One candidate gene in this region, SOX3, is thought to be involved in neuronal development and its loss may partly explain the more severe phenotypes of our patients.

Adult↗

PubMed1997

Characterization of in vitro glycation sites of tau.

Tau is a microtubule-associated protein that loses microtubule binding activity and aggregates into paired helical filaments (PHFs) in Alzheimer's disease. Nonenzymic glycation is one of the posttranslational modifications detected in PHF-tau, but not in normal tau. PHF-tau has reduced ability to bind to microtubules. To determine whether glycation of tau occurs in its microtubule binding domains, we have characterized in vitro glycation sites of the longest isoform of tau, which has four microtubule binding domains (Tau-4). The identified glycation sites are Lys-87, 132, 150, 163, 174, 225, 234, 259, 280, 281, 347, 353, and 369. We have also studied glycation of another isoform of tau, which has only three microtubule binding domains (Tau-3). This isoform is modified by glucose 15-20% more slowly than Tau-4. However, the glycation sites appear to be the same in both isoforms, except for Lys-280 and 281; these are located in the second microtubule binding domain, which is missing in Tau-3. Lys-150, 163, and 174 are located within or proximal to the sequence of tau that is involved in the microtubule nucleation activity, and Lys-259, 280, 281, 347, 353, and 369 are located in the microtubule binding domains. Glycation at these sites can affect the functional properties of tau, and advanced glycation at these sites might lead to the formation of insoluble aggregates similar to the ones seen in Alzheimer's disease.

Amino Acid Sequence↗

PubMed1996

The angiogenesis inhibitor AGM-1470 selectively increases E-selectin.

The levels of E-selectin mRNA and protein were analyzed in bovine capillary cells treated with or without the angiogenesis inhibitor AGM-1470 (also known as TNP-470). Cells treated with AGM-1470 had a two- to sevenfold (median fivefold) increase in E-selectin mRNA compared with little or no increase in P-selectin, PECAM-1 and VCAM-1 mRNA. E-selectin protein was also significantly increased after exposure to AGM-1470. In contrast, there was no detectable effect on PECAM-1 protein. The increase in E-selectin mRNA and protein was always greater with subconfluent growing cells than with confluent cells. This apparent resistance of confluent endothelial cells to AGM-1470 may be relevant to its specificity in vivo. The fact that the effect of AGM-1470 on E-selectin is relatively selective for subconfluent growing cells may provide a clue as to how AGM-1470 is able to both reversibly inhibit endothelial cell proliferation in vitro and inhibit tumor growth in vivo without apparent effects to quiescent endothelium.

Adrenal Cortex↗

PubMed1991

Expression of 'Alzheimer antigens' in cultured skin fibroblasts.

When cultured skin fibroblasts were exposed to culture conditions designed to favor the expression of neuronal antigens, cells from each of 19 patients with Alzheimer's disease reacted immunocytochemically with antibodies to paired helical filaments, Alz-50, or both compared with only a small fraction of cells from 19 identically treated age-matched control cultures. Immunoblots confirmed the presence of soluble material reacting with Alz-50 antibody in the Alzheimer fibroblasts. Ultrastructurally, fascicles of 10-nm filaments were seen that occasionally twisted around each other, but no structures were seen that were identical to paired helical filaments. Thus, cultured skin fibroblasts from patients with Alzheimer's disease developed greater immunocytochemical reactivity with antibodies raised to paired helical filaments than did fibroblasts from control subjects, when cultured under the specified conditions.

Aged↗

PubMed1991

Behaviour disorder in pre-school children in Hong Kong. A two-stage epidemiological study.

A representative sample of 855 Hong-Kong Chinese children aged 36-48 months were assessed using the BSQ and the PBCL. Good reliability for both instruments were found. For the BSQ and PBCL, 12.75% and 27.5% were above the cut-off points of 10+ and 12+ respectively and 5.9% were above both cut-off points. In the second stage, 234 subjects were recruited by stratified random sampling according to the results of the screening state. A clinician interviewed the parent, child and teacher before making a diagnosis. The prevalence of behaviour disorder was: nil, 53.7%; dubious, 23.1%; mild, 18.0%; moderate, 4.5%; and severe, 0.7%. There were significantly more boys in the categories mild, moderate and severe.

Adult↗

PubMed1991

Pathology of Alzheimer's disease.

The fundamental pathophysiology of Alzheimer's disease remains poorly understood, but progress has been dramatic in description of the pathology at the molecular level. The characteristic Alzheimer amyloid derives, in part, by action of microglia, from a precursor protein that is well characterized at the protein and gene levels. The characteristic paired helical filaments contain phosphorylated tau proteins and perhaps other constituents. At the neurotransmitter level, Alzheimer's disease involves not only loss of cholinergic cells but of serotonergic and other neurotransmitter systems as well. Damage to mitochondria may play an important role in precipitating the cellular pathophysiology.

Alzheimer Disease↗

PubMed1990

Induction of Alzheimer antigens by an uncoupler of oxidative phosphorylation.

Since previous studies have suggested that the coupling of oxidation to phosphorylation is impaired in Alzheimer brain and fibroblasts, the effects of carbonyl cyanide m-chlorophenylhydrazone, a hydrazone known to uncouple mitochondrial oxidative phosphorylation, were tested on the development of immunoreactivity with antibodies to "Alzheimer antigens" in cultured fibroblasts from cognitively intact subjects. The fibroblasts were exposed for 10 to 14 days to a medium (DMd) modeled on media that favor neuronal differentiation in fetal brain cultures. The addition of a 10-microns concentration of carbonyl cyanide m-chlorophenylhydrazone to the DMd culture medium increased by more than 10-fold the proportion of cells reacting immunocytochemically with antibodies to paired helical filaments and by 157-fold the proportion of cells reacting with the Alz-50 monoclonal antibody. These observations suggest that the oxidative abnormalities previously described in tissues from patients with Alzheimer's disease may contribute to the accumulation of abnormal cytoskeletal materials in this disorder.

Aged↗

PubMed1990

Induction of epitopes associated with neurofibrillary tangles in clonal mouse neuroblastoma (S20Y) cells.

Accumulation of paired helical filaments (PHF) in neurofibrillary tangles is a key neuropathological hallmark in Alzheimer's disease (AD). To date, PHF have been found primarily in humans. Cultured murine cholinergic neuroblastoma (S20Y) cells, following exposure to a serum-free medium or a differentiation medium, developed immunoreactivity to anti-PHF antibodies, and to the Alz-50 by immunocytochemical and immunoblot analyses. Electron microscopic examination revealed abundant fascicles of 10-nm filaments coursing tortuously amongst organelles, such as mitochondria, endoplasmic reticulum and dense-core vesicles, in perikarya and in neuritic extensions. However, subcellular structures identical or similar to PHF could not be found in these non-human cells. This convenient cell culture model may prove to be useful for studying certain aspects of the mechanisms underlying the abnormal cytoskeletal alterations which are characteristic of AD and related neurodegenerative disorders.

Alzheimer Disease↗

PubMed1990

Long-term neurological sequelae following vacuum extractor delivery.

Two hundred and ninety-five children delivered by vacuum extractor (VE) 10 years ago were studied to determine if they had an increased incidence of neurological abnormality; 302 children delivered spontaneously in the same hospital looked after by the same doctors in the same year matched for maternal age, gestational age and birthweight were used as controls. Fine- and gross-motor control, perceptual integration and behavioural maturity were screened by 4 tasks selected from the Quick Neurological Screening Test. Intelligence assessment was based on scholastic performance, speech ability and ability of self-care as commented by teachers and parents. Similar scorings were found between the 2 groups. Mental subnormality or severe neurological abnormality was found in 3 children delivered by VE and in 3 children delivered spontaneously and there was no evidence that it was birth-related.

Child↗