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Biomedical subjects

K Lee

Publications and source records attributed to K Lee.

At least 469 records · Page 26Linked to original sources
PubMed1996

Function of nuclear co-repressor protein on thyroid hormone response elements is regulated by the receptor A/B domain.

Recently, a family of nuclear co-repressor proteins (TRACs) have been identified that interact with thyroid hormone (TR) and retinoic acid receptors to mediate ligand-independent repression of gene transcription. In this report, we have cloned and characterized a human TRAC, which when expressed as a truncated protein lacking its repressing domains, can abolish endogenous cellular TRAC activity. Use of this inhibitor has uncovered a differential function of TRACs on negative versus positive thyroid hormone response elements and has demonstrated the importance of the TR A/B domain in modulating TRAC function. Thus, isoform-specific functions of the TR may be mediated by their functional interaction with co-repressor proteins.

DNA-Binding Proteins↗
PubMed1996

Activity and autophosphorylation of LAMMER protein kinases.

Clk/STY, the murine homologue of the recently described LAMMER family of protein kinases, autophosphorylates on serine/threonine and tyrosine residues in vitro and in vivo. LAMMER kinases are found throughout eukaryotes and possess virtually complete amino acid identity in many domains critical for kinase function, leading to the question of whether other family members also possess dual specificity. We report here that the Drosophila family member DOA, human SK-G1, and the Saccharomyces cerevisiae KNS1, all possess protein kinase activity and autophosphorylate with dual specificity in vitro, suggesting that the entire family possesses this activity. Although the LAMMER kinases are closely related to the mitogen-activated protein kinase family, they possess different substrate specificity in vitro, based on phosphorylation of peptide and protein substrates and sequencing of a phosphorylation site in a common substrate.

Amino Acid Sequence↗
PubMed1996

Inhibition of KATP channel activity by troglitazone in CRI-G1 insulin-secreting cells.

Patch-clamp recording techniques were used to examine the effect of troglitazone on KATP channel activity in Cambridge rat insulinoma-G1 (CRI-G1) insulin-secreting cells. In both inside-out and outside-out patch recordings, bath application of troglitazone reduced KATP channel activity. This inhibition was independent of the membrane voltage and was poorly reversible. In whole-cell studies, troglitazone inhibited KATP channel currents with an IC50 of 697 +/- 92 nM and an associated Hill coefficient of 1.2 +/- 0.2. In current clamp recordings 10 microM troglitazone depolarised the CRI-G1 cell membrane by 36.8 +/- 3.9 mV with a concomitant decrease in membrane conductance. However, in contrast to the rapid depolarisation produced by tolbutamide, the effects of troglitazone developed more slowly, usually taking 15-20 min to develop.

Adenosine Triphosphate↗
PubMed1996

Regulation of rate of cartilage differentiation by Indian hedgehog and PTH-related protein.

Proper regulation of chondrocyte differentiation is necessary for the morphogenesis of skeletal elements, yet little is known about the molecular regulation of this process. A chicken homolog of Indian hedgehog (Ihh), a member of the conserved Hedgehog family of secreted proteins that is expressed during bone formation, has now been isolated. Ihh has biological properties similar to those of Sonic hedgehog (Shh), including the ability to regulate the conserved targets Patched (Ptc) and Gli. Ihh is expressed in the prehypertrophic chondrocytes of cartilage elements, where it regulates the rate of hypertrophic differentiation. Misexpression of Ihh prevents proliferating chondrocytes from initiating the hypertrophic differentiation process. The direct target of Ihh signaling is the perichondrium, where Gli and Ptc flank the expression domain of Ihh. Ihh induces the expression of a second signal, parathyroid hormone-related protein (PTHrP), in the periarticular perichondrium. Analysis of PTHrP (-/-) mutant mice indicated that the PTHrP protein signals to its receptor in the prehypertrophic chondrocytes, thereby blocking hypertrophic differentiation. In vitro application of Hedgehog or PTHrP protein to normal or PTHrP (-/-) limb explants demonstrated that PTHrP mediates the effects of Ihh through the formation of a negative feedback loop that modulates the rate of chondrocyte differentiation.

Animals↗
PubMed1996

PTH/PTHrP receptor in early development and Indian hedgehog-regulated bone growth.

The PTH/PTHrP receptor binds to two ligands with distinct functions: the calcium-regulating hormone, parathyroid hormone (PTH), and the paracrine factor, PTH-related protein (PTHrP). Each ligand, in turn, is likely to activate more than one receptor. The functions of the PTH/PTHrP receptor were investigated by deletion of the murine gene by homologous recombination. Most PTH/PTHrP receptor (-/-) mutant mice died in mid-gestation, a phenotype not observed in PTHrP (-/-) mice, perhaps because of the effects of maternal PTHrP. Mice that survived exhibited accelerated differentiation of chondrocytes in bone, and their bones, grown in explant culture, were resistant to the effects of PTHrP and Sonic hedgehog. These results suggest that the PTH/PTHrP receptor mediates the effects of Indian Hedgehog and PTHrP on chondrocyte differentiation.

Animals↗
PubMed1996

Subunit positional effects revealed by novel heteromeric inwardly rectifying K+ channels.

Kir 4.1 is an inward rectifier potassium channel subunit isolated from rat brain which forms homomeric channels when expressed in Xenopus oocytes; Kir 5.1 is a structurally related subunit which does not. Co-injection of mRNAs encoding Kir 4.1 and Kir 5.1 resulted in potassium currents that (i) were much larger than those seen from expression of Kir 4.1 alone, (ii) increased rather than decreased during several seconds at strongly negative potentials and (iii) had an underlying unitary conductance of 43 pS rather than the 12 pS seen with Kir 4.1 alone. In contrast, the properties of Kir 1.1, 2.1, 2.3, 3.1, 3.2 or 3.4 were not altered by coexpression with Kir 5.1. Expression of a concatenated cDNA encoding two or four linked subunits produced currents with the properties of co-expressed Kir 4.1 and Kir 5.1 when the subunits were connected 4-5 or 4-5-4-5, but not when they were connected 4-4-5-5. The results indicate that Kir 5.1 associates specifically with Kir 4.1 to form heteromeric channels, and suggest that they do so normally in the subunit order 4-5-4-5. Further, the relative order of subunits within the channel contributes to their functional properties.

Animals↗
PubMed1996

Differential sensitivity of human and mouse alkyltransferase to O6-benzylguanine using a transgenic model.

O6-benzlguanine (O6-bG) potentiates nitrosourea cytotoxicity of human tumor xenografts in nude mice by inactivating O6-alkylguanine-DNA alkyltransferase (AGT). Recent reports dispute whether murine AGT, in cell-free systems, is less sensitive to O6-bG than the human AGT protein, raising the possibility that efficacy seen in the mouse host may not predict the therapeutic index observed in clinical trials. To establish whether mouse and human AGT have different sensitivity to O(6)-bG, we evaluated in vitro and in vivo models of O(6)-methylguanine-DNA methyltransferase gene (MGMT) expression in the same genetic background. The 50% inhibitory concentration of O6-bG for inactivation of mouse AGT was >10-fold higher than for the human protein in MGMT-transfected Chinese hamster ovary (CHO) cells. A dose of O6-bG, which inactivated human AGT, markedly sensitized human MGMT-transfected CHO cells to 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU), whereas mouse MGMT-transfected CHO cells were much more resistant. O6-bG inactivation of AGT in vivo was studied in livers of human MGMT-transgenic mice expressing both human and mouse AGT. After a single dose of O6-bG i.p., the 50% inhibitory concentration of AGT was higher for mouse than for human AGT. To reconcile our finding with those of others, we sequenced the mouse MGMT cDNA and found that mutation of amino acid residue Leu180 was associated with O6-bG resistance. These studies provide strong evidence that inactivation of AGT both in vivo and in vitro by O6-bG is species selective and impacts O6-bG-mediated enhancement of BCNU toxicity. This may influence the therapeutic index of O6-bG-BCNU combinations observed in human tumor xenograft-bearing mice.

Animals↗
PubMed1996

Location of the handedness gene on the X and Y chromosomes.

Accumulated data from five handedness surveys show that concordance for sex is slightly but reliably higher among siblings of the same handedness than among those of opposite handedness. This is consistent with Crow's theory that the genetic locus for handedness is in an X-Y homologous region of the sex chromosomes. The small size of the effect is predicted from genetic models in which there is a substantial random component underlying phenotypic left handedness. The findings are relevant to the putative role of cerebral asymmetry in the aetiology of psychosis.

Chromosome Mapping↗
PubMed1996

Expression of c-Fos in subcutaneous adipose tissue of the fetal pig.

Subcutaneous adipose tissue from fetal pigs was examined for c-Fos expression in developing adipocytes. Enhanced c-Fos expression was found in the nuclei of adipocytes and cells closely associated with fat cell clusters from 75 and 105 day old fetuses. 50 day old fetuses which had no adipocytes showed no enhanced c-Fos expression in undifferentiated cells. c-Fos expression in adipocytes was not transient, but persisted through the gestational period from 75 to 105 days. The timing of c-Fos induction appears to be closely related to adipocyte differentiation and was found only in developing adipocytes and cells closely associated with fat cell cluster and was not found in independent stromal-vascular cells.

Adipocytes↗
PubMed1996

Who should be doing what in the international health: a confusion of mandates in the United Nations?

Since 1945 at least five United Nations organisations have become substantially involved in international health activities. This has led to considerable confusion among policy makers, scholars, and UN staff over distinct and appropriate mandates. Interviews with staff an a historical analysis have shown that while formal mandates have been complementary, effective mandates have led to an unclear delineation of activities. The process of translating formal into effective mandates have been influenced by the decentralised nature of the UN, lack of a master plan for its activities, the considerable growth in the policy agenda and the shift towards a multisectoral approach to health. The identification of each organisation's comparative advantage, at both the global and country levels, is one way of understanding what each organisation does best and perhaps should be doing. There is a need for improved mechanisms to define effective mandates, taking into account comparative advantages, if the mandates of UN organisations are appropriate to meet future challenges in international health.

Global Health↗
PubMed1996

Role of DNA repair in resistance to drugs that alkylate O6 of guanine.

The mechanism of cytotoxicity of a number of chemotherapeutic agents involves alkylation at the O6 position of guanine, a site that strongly influences cytotoxicity. Repair of these lesions by the alkyltransferase protects from cytotoxicity and is a major mechanism of resistance to these agents. O6-benzylguanine inhibition of alkyltransferase sensitizes tumor cells, and clinical trials are underway to determine its efficacy. The use of gene therapy to enhance the expression of alkyltransferase in hematopoietic cells may prevent dose-limiting myelosuppression and may enhance the utility of this class of chemotherapeutic agents.

Amino Acid Sequence↗
PubMed1996

Oleosin genes in maize kernels having diverse oil contents are constitutively expressed independent of oil contents. Size and shape of intracellular oil bodies are determined by the oleosins/oils ratio.

In seeds, the subcellular storage oil bodies have a matrix of oils (triacylglycerols) surrounded by a layer of phospholipids embedded with abundant structural proteins called oleosins. We used two maize (Zea mays L.) strains having diverse kernel (seed) oil contents to study the effects of varying the oil and oleosin contents on the structure of the oil bodies. Illinois High Oils (IHO, 15% w/w oils) and Illinois Low Oils (ILO, 0.5%) maize kernels were the products of breeding for diverse oil contents for about 100 generations. In both maize strains, although the genes for oil synthesis had apparently been modified drastically, the genes encoding oleosins appeared to be unaltered, as revealed by Southern blot analyses of the three oleosin genes and sodium dodecyl sulfate-polyacrylamide gel electrophoresis with immunoblotting of the oleosins. In addition, both strains contained the same three oleosin isoforms of a defined proportion, and both accumulated oils and oleosins coordinately. Oleosins in both strains were restricted to the oil bodies, as shown by analyses of the various subcellular fractions separated by sucrose-density-gradient centrifugation. Electron microscopy of the embryos and the isolated organelles revealed that the oil bodies in IHO were larger and had a spherical shape, whereas those in ILO were smaller and had irregular shapes. We conclude that in seeds, oleosin genes are expressed independent of the oil contents, and the size and shape of the oil bodies are dictated by the ratio of oils to oleosins synthesized during seed maturation. The extensive breeding for diverse oil contents has not altered the apparent mechanism of oil-body synthesis and the occurrence of hetero-dimer or -multimer of oleosin isoforms on the oil bodies.

Breeding↗