Biomedical subjects

H G Kim

Publications and source records attributed to H G Kim.

At least 73 records · Page 4Linked to original sources

PubMed1996

The amino terminus of the retinoblastoma (Rb) protein associates with a cyclin-dependent kinase-like kinase via Rb amino acids required for growth suppression.

We have shown previously that a novel cell cycle-regulated histone H1 kinase activity, retinoblastoma kinase (RbK), associates with and phosphorylates the amino terminus of the Rb protein in G2-M. We have shown also that the amino terminus of p107, a Rb-related protein, does not associate with a similar kinase in vitro or in vivo. Here, we report that a RbK-like kinase associates with the amino terminus of p130, another Rb-related protein, only marginally. Moreover, the association of RbK with Rb in vitro is shown to require a discrete portion of the Rb amino terminus, amino acids 89-202. This region has been shown previously to be subject to inactivating mutations in retinoblastoma and to be required for Rb-mediated growth suppression in vitro. Taken together, these data indicate that the formation of Rb-RbK complexes may play an important role in Rb-mediated growth suppression. We have mapped two in vitro sites of Rb phosphorylation by RbK to sites that are phosphorylated in vivo and are targets of cyclin-dependent kinase phosphorylation in vitro. As such, at least some sites of RbK phosphorylation overlap with those of other proline-directed serine and threonine kinases. Consistent with this latter observation, we report that the trans-activation domain of c-myc is phosphorylated specifically by RbK in vitro at a site (serine 62) that is phosphorylated in vivo during G2-M, cell-cycle phases in which RbK activity is maximal.

Base Sequence↗

PubMed1995

Characterization of Mg(2+)-dependent 3'-processing activity for human immunodeficiency virus type 1 integrase in vitro: real-time kinetic studies using fluorescence resonance energy transfer.

Human immunodeficiency virus type 1 integrase (HIV-1 IN) catalyzes the integration of HIV-1 DNA into the host chromosome. In vitro reactions with endogenous viral DNA require Mg2+ as the metal cofactor, whereas in vitro studies performed with short oligonucleotide substrates utilize Mn2+. In this study, we report that the donor processing activity of HIV-1 IN alters depending on the structure and length of the oligonucleotide substrates. Increases in the length of the substrate cause alterations in the efficiency of Mg(2+)-dependent donor processing activity, thereby reconciling this discrepancy between the in vivo and in vitro HIV-1 IN mediated reactions. We have also found that the 3'-processing activity of HIV-IN is responsible for cleaving the junction between the viral and target sequences of the recombination intermediate. Its mechanism differs from the previously described disintegration reaction in that the donor strands are regenerated without a joining reaction of the target strands. Kinetic studies of 3'-processing activity suggest that the kcat (0.24/h) is very low. This implies that HIV-1 IN remains as a complex with the processed DNA prior to the strand transfer reaction.

Base Sequence↗

PubMed1995

Substrate-length-dependent activities of human immunodeficiency virus type 1 integrase in vitro: differential DNA binding affinities associated with different lengths of substrates.

Human immunodeficiency virus type 1 integrase (HIV-IN) is an enzyme essential for the integration of viral DNA into the host chromosome, a process that is an attractive target for drug development. In vitro assays have been developed to study both components of the integration process, the 3'-processing and strand transfer reactions. However, major discrepancies between results obtained from in vivo and in vitro events raise concerns as to the biological relevance of activities observed in vitro. These discrepancies include the size of the substrate and the nature of the divalent cation used. In this study, we characterized activities of HIV-IN with oligonucleotide substrates varying in length. Our previous studies indicate that the preferred cation in vitro for 3'-processing is altered from Mn2+ to Mg2+ by increasing the length of the oligonucleotide substrate. This study demonstrates that HIV-IN efficiently catalyzes Mg(2+)-dependent 3'-processing while repressing the strand transfer reaction. Substrate competition studies indicate that longer substrates preferentially bind to the viral DNA binding site of the integrase, whereas the shorter substrate has much less specificity. In addition, the shorter substrate requires a higher concentration of Mg2+, indicating that there is an alteration in the metal binding affinity associated with the varying substrates. Our results show that substrate-length-dependent differential activities are due to differences in the divalent metal binding and DNA binding affinities associated with the different substrates. These results suggest that the structure of the viral DNA is an important factor in differentiating the donor and target substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1995

Inhibition of in vitro transcription by a triplex-forming oligonucleotide targeted to human c-myc P2 promoter.

Triplex-forming oligonucleotides (TFOs) have been shown to bind in a sequence-specific manner to polypurine/polypyrimidine sequences in several human gene promoters, including the c-myc P1 promoter. TFOs have been shown to inhibit transcription in vitro and the expression of target genes in cell culture. The human c-myc protooncogene contains a 23 base pair purine-pyrimidine-rich motif (-62 to -40) within its predominant promoter, P2, that is a potential target for purine-purine-pyrimidine triplex formation. Using electrophoretic mobility shift analysis (EMSA) and competition experiments, we have demonstrated that a MAZ (myc-associated zinc finger protein) consensus sequence is capable of competing with the purine-pyrimidine motif for the binding of a HeLa nuclear protein. We have shown the formation of an intermolecular triplex using a 23-base purine-rich oligonucleotide antiparallel to the purine-rich target sequence. DNase I footprinting was performed to confirm the exact location of triplex formation. Triplex formation by this oligonucleotide prevents binding of a HeLa nuclear protein (presumably MAZ) to the target site. We have also shown that the P2-targeted TFO is a potent and specific inhibitor of c-myc transcription in vitro. These data demonstrate that this novel TFO inhibits transcription of the c-myc P2 promoter. We propose that the P2-targeted TFO has its effect by blocking the binding of the regulatory factor MAZ.

Base Sequence↗

PubMed1995

Characterization of endonucleolytic activity of HIV-1 integrase using a fluorogenic substrate.

Retroviruses require viral DNA to be synthesized by reverse transcription in the cytoplasm followed by integration of the resulting viral DNA into the host chromosome in the nucleus. Reverse transcription and integration, essential steps in the life cycle of retroviruses, are possible targets in the development of antiviral reagents. One attractive target is the integrase protein, a product of the retroviral pol gene which is solely responsible for the retroviral integration process through cutting and joining reactions. When screening for massive numbers of antiviral agents, a rapid and precise assay is ideal. We report the application of fluorescence resonance energy transfer (FRET) with fluorescein and eosin as the energy transfer pair to characterize HIV-IN-mediated DNA cleavage reactions. Past concerns with applications of FRET to DNA were due to interactions of the fluorophore with the DNA, resulting in quenched fluorescence. However, in this study these concerns have been resolved with the use of a nucleotide analog with a 12-carbon linker arm, 5-amino (12)-2'-deoxyuridine beta-cyanoethyl phosphoramidite. Steady-state fluorescence studies show that cleavage of the fluorogenic substrate by integrase results in enhancement of quenched donor fluorescence intensity. The fluorescence assay was confirmed by autoradiographic analysis of the cleavage reaction with radiolabeled fluorogenic substrate. This fluorescence assay will facilitate both detailed kinetic studies and the rapid screening of novel integrase inhibitors.

Base Sequence↗

PubMed1995

Detection of a novel cell cycle-regulated kinase activity that associates with the amino terminus of the retinoblastoma protein in G2/M phases.

Recent genetic and functional evidence suggests that the amino terminus of the retinoblastoma (Rb) protein plays an important role in Rb-mediated growth suppression. To explore the mechanism(s) by which this portion of Rb may regulate cell growth, we have sought to characterize cellular proteins that associate with the Rb amino terminus using an in vitro protein-binding assay. Here we report that at least one such protein is a cell cycle-regulated Rb/histone H1 kinase (RbK) whose enzymatic and/or Rb association activity is most prevalent in G2/M phases of cells. In contrast to previously characterized cyclin-dependent and Rb-associated kinases, such as cdk1 (cdc2) and cdk2, G2/M RbK 1) is not depleted by incubation with p13suc-beads, 2) is not detected with antisera against several Rb-associated cyclins-cdks, and 3) associated with Rb via the Rb amino terminus, a region that is dispensable for interaction with other Rb-associated kinases. RbK is clearly distinct from previously characterized mitotic cdks since cyclin A-cdc2, cyclin A-cdk2, cyclin B-cdc2, and cyclin B-cdk2 did not associate with the Rb amino terminus. Coprecipitation experiments with Rb antisera confirmed the association of Rb with a RbK-like kinase in metaphase-arrested cells in vivo. Interestingly, G2/M RbK did not appreciably associate with an analogous portion of p107, a Rb-related protein. Taken together, these data indicate that the Rb amino terminus specifically associates with a novel cell cycle-regulated kinase in late cell cycle stages.

Amino Acid Sequence↗

PubMed1995

Locally activated neural networks and stable neural controller design for nonlinear dynamic systems.

A stable neural control scheme using a locally activated neural network has been proposed for a class of nonlinear dynamic systems. The locally activated neural network, for a given input, essentially selects a small subset of the network hidden nodes for output computation using the CMAC-like content addressing mechanism. This network aims to maintain local representations of the system dynamics. Thus, the global control performance in the concerned state space is achieved by the cooperation of many local control efforts and furthermore, real-time control can be facilitated because only a small sized network is involved to control and learn at any given time. The proposed control scheme is composed of two stages: (1) prediction error based learning in which the network attempts to learn the nonlinear basis functions of the plant inverse dynamics by a modified backpropagation learning rule; and (2) tracking error based learning in which the network weights are further fine-tuned using the basis set obtained in (1). This basis set spans the locally partitioned vector space of the system inverse dynamics when the prediction error based learning is achieved within a prescribed error tolerance. For uniform stability, the sliding mode control is introduced as a safety mechanism when the network has not sufficiently learned the plant dynamics yet. With suitable assumptions on the controlled plant, global stability and tracking error convergence proof has been given. Finally, the proposed control scheme is verified with computer simulation.

Adaptation, Physiological↗

PubMed1995

Neural network based dynamic controllers for industrial robots.

The industrial robot's dynamic performance is frequently measured by positioning accuracy at high speeds and a good dynamic controller is essential that can accurately compute robot dynamics at a servo rate high enough to ensure system stability. A real-time dynamic controller for an industrial robot is developed here using neural networks. First, an efficient time-selectable hidden layer architecture has been developed based on system dynamics localized in time, which lends itself to real-time learning and control along with enhanced mapping accuracy. Second, the neural network architecture has also been specially tuned to accommodate servo dynamics. This not only facilitates the system design through reduced sensing requirements for the controller but also enhances the control performance over the control architecture neglecting servo dynamics. Experimental results demonstrate the controller's excellent learning and control performances compared with a conventional controller and thus has good potential for practical use in industrial robots.

Algorithms↗

PubMed1995

Inhibitory control of excitable dendrites in neocortex.

1. Many dendrites of pyramidal cells in mature neocortex express active Na+ and Ca2+ conductances. Dendrites are also the target of numerous inhibitory synapses. We examined the interactions between the intrinsic excitability of dendrites and synaptic inhibition using whole cell recordings from the apical dendrites of layer 5 pyramidal cells. Experiments were performed on slices of somatosensory cortex from mature rats. Slices were bathed in the glutamate receptor antagonists 2-amino-5-phosphonopentanoic acid and 6,7-dinitroquinoxaline-2,3-dione, and maintained at 32-36 degrees C. 2. In agreement with previous findings, intradendritic current injection evoked two distinct types of dendritic firing. Type I dendrites generated monophasic fast spikes, whereas type II dendrites showed more complex firing patterns, consisting of fast and slow spike components. 3. Stimulation of cortical layers 2/3 evoked fast inhibitory postsynaptic potentials (IPSPs) in all dendrites tested. IPSP reversal potentials were bimodally distributed, with means of about -53 and -85 mV when recorded with high-Cl(-)-concentration-filled electrodes. Interestingly, IPSP reversal potentials were correlated with the type of dendritic spiking pattern. 4. IPSPs were able to delay, completely block, or partially block spiking in dendrites, depending on the relative timing between inhibition and dendritic spiking. Slow, Ca(2+)-dependent spike components could be blocked selectively by IPSPs. Furthermore, inhibition could either phase advance or phase delay repetitive patterns of dendritic spiking, depending on the timing of the IPSP.

Animals↗

PubMed1995

Medial medullary syndrome. Report of 18 new patients and a review of the literature.

BACKGROUND AND PURPOSE: With advanced imaging techniques, infarctions occurring in the medulla are now more easily identified. To date, however, only approximately 30 cases of medial medullary infarction syndrome (MMS) have been reported, and the clinical and radiological characteristics of MMS remain to be studied. METHODS: We studied 18 patients (15 men, 3 women; mean age, 62 years) who had compatible clinical and MRI findings of MMS and reviewed the previously reported cases. RESULTS: Seventeen patients had a unilateral lesion usually involving the upper medulla, and 1 had bilateral lesions. Fifteen patients had unilateral sensorimotor stroke, while 2 presented with pure motor stroke. The face was usually but not always spared. The degree of hemiparesis varied, and a tingling sensation with decreased vibration and position sense was the most common sensory manifestation. Two patients had lingual paresis, and none suffered respiratory difficulties. One patient presented with bilateral gait ataxia without sensorimotor dysfunction. Angiography or MR angiography performed in 9 patients showed vertebral artery disease in 6. Three patients had concurrent lateral medullary infarction, and 1 had a previous history of lateral medullary syndrome. The prognosis was generally good, although residual hemiparesis remained in patients with initially severe hemiparesis. Review of 26 previously reported cases showed that they frequently had bilateral lesions, often presenting with quadriplegia, lingual paresis, respiratory symptoms, and a grave prognosis. CONCLUSIONS: Our data illustrate that MMS is most often manifested as benign hemisensorimotor stroke frequently associated with tingling sensation and impaired deep sensation. This benign form of MMS should be much more common than MMS with poor prognosis and may have been frequently misdiagnosed as capsular or pontine stroke before the era of MRI.

Adult↗

PubMed1994

Neurotrophin 3 potentiates neuronal activity and inhibits gamma-aminobutyratergic synaptic transmission in cortical neurons.

Neurotrophins have traditionally been regarded as slowly acting signals essential for neuronal survival and differentiation. However, brain-derived neurotrophic factor and neurotrophin 3 (NT-3) have recently been reported to exert an acute potentiation of synaptic activity at the amphibian neuromuscular junction. Little is known about the role of neurotrophins on functional synapses in the central nervous system. Here we show that NT-3 rapidly increased the frequency of spontaneous action potentials, and it synchronized excitatory synaptic activities in developing cortical neurons. Moreover, the inhibitory synaptic transmission mediated by gamma-aminobutyric acid (GABA) subtype A receptors was found to be reduced by NT-3. Thus, the excitatory effects of NT-3 on spontaneous action potentials were attributable to a reduction of GABAergic transmission. Our findings, together with previous reports of rapid regulation of central nervous system neurotrophin expression by neuronal activity and of the role of GABAergic transmission in cortical plasticity, suggest a mechanism for modulation of synaptic transmission and activity-dependent synaptic modulation in cortical neurons.

Amphibians↗

PubMed1994

Negative regulation of Sp1 trans-activation is correlated with the binding of cellular proteins to the amino terminus of the Sp1 trans-activation domain.

Sp1 is a well characterized and ubiquitously expressed transcription factor that regulates the constitutive and induced expression of a variety of mammalian genes. It is unclear whether Sp1 activity is regulated in vivo; the mechanism by which Sp1 interacts with the basal transcription complex has not been firmly established. We report the identification of a ubiquitously expressed and evolutionarily conserved nuclear protein, p74, that specifically binds Sp1 in vivo and in vitro. p74 interacts with several portions of the Sp1 trans-activation domain in vitro, and we correlate the binding of p74 to the amino-terminal serine/threonine-rich subdomain of Sp1 with the inhibition of Sp1-mediated transcription in vivo.

Binding Sites↗

PubMed1994

Isolated trigeminal sensory change due to pontine hemorrhage.

Isolated trigeminal sensory change has been rarely described as a manifestation of pontine hemorrhage. We report a 31-year-old man who developed sudden and long-lasting trigeminal sensory disturbances. Brain magnetic resonance imaging showed a hemorrhage in the right lateral pontine tegmentum corresponding to the trigeminal sensory nucleus, and the venous phase angiogram demonstrated abnormal vascular structures. Pontine hemorrhage secondary to venous malformation can be one of the causes of isolated trigeminal sensory change.

Adult↗

PubMed1993

Properties of synaptic transmission from photoreceptors to bipolar cells in the mudpuppy retina.

1. Simultaneous, whole-cell recordings were obtained from synaptically coupled photoreceptor/bipolar cell pairs, by the use of direct visualization in a superfused, mudpuppy retinal slice preparation. 2. OFF-bipolar cells (BPs) generated sign-conserving responses when extrinsic current was injected into rods and cones, whereas ON-BPs generated a sign-reversing response. OFF-BPs (n = 24) responded faster than ON-BPs (n = 12), in terms of response latency (27.8 vs. 80.6 ms) and peak response times (50.5 vs. 159.8 ms) when current was injected into photoreceptors. We did not detect any significant difference between rod- versus cone-mediated latency or peak response times in the ON- and OFF-BP subtypes. 3. Rod and cone inputs to OFF-BPs were blocked by kynurenic acid (Kyn), but the doses required were significantly higher for rod inputs: the IC50 (the concentration at which an antagonist blocks 50% of the responses) for Kyn was 0.3 mM for cone inputs and 1 mM for rod inputs. 4. Rod inputs to OFF-BPs showed the same Kyn sensitivity as rod inputs to horizontal cells (HCs). However, cone inputs to HCs (IC50 < 200 microM) were more sensitive to Kyn than those to OFF-BPs. 5. The pharmacological studies presented here, together with previous studies, suggest that the sign-conserving pathway in the outer plexiform layer of the mudpuppy retina involves at least three subtypes of glutamate receptors: 1) cone-activated receptors of HCs; 2) cone-activated receptors of OFF-BPs; and 3) rod-activated receptors found in HCs and BPs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminobutyrates↗

PubMed1993

Consequences of rapid fertility decline in the Republic of Korea: issues and solutions.

During the last 3 decades, efforts to deal with population problems in Korea have focused largely on reducing population growth. The national population control program has been a major means of achieving this goal. Between the early 1960s and 1990, evidence from a national survey indicates that the percent of current use of contraception rose from about 12% to 80% and the total fertility rate fell to 1.6. representing 1 of the most rapid fertility transitions in the developing world. In conjunction with this rapid reduction in fertility, mortality also improved significantly during this period. Thus, Korea has virtually completed the demographic transition from high birth and death rates to low birth and death rates during the same period. It is widely recognized that Korea has reached demographic maturity and has also achieved remarkable economic development at the same time. The world's demographic history shows that the demographic transition which almost every industrialized country has gone through from a predominantly rural, illiterate society with high birth and death rates, to a predominantly rural, illiterate society with high birth and death rates, to a predominantly urban, educated society with low birth and death rates usually takes well over a century, but in Korea, that process has taken only a few decades. On the other hand, the consequences of a rapid fertility decline bring about various demographic and social issues which we have to take into consideration for future socioeconomic development policy concerning the well-being of the Korean people. Some of issues for policy consideration can be broadly summarized as follows: 1) gradual imbalance of sex ratio at birth due to traditional son preference behavior; 2) latent effect of inevitable population aging and increasing dependency burden on behalf of the elderly for the public sector; 3) changes in family life cycle and rapid transformation form a large to a small family; 4) increasing demand for now social roles for women, supported by easing of child care burdens within households.

Asia↗

PubMed1993

Apical dendrites of the neocortex: correlation between sodium- and calcium-dependent spiking and pyramidal cell morphology.

Apical dendrites and somata of layer V pyramidal neurons were recorded with tight-seal patch electrodes in a slice preparation of rat somatosensory cortex. Recording sites were confirmed by measurements of the electrode location and by staining with biocytin. Dendritic recordings were made along the main trunk of the apical dendrite, usually within layer IV, at distances from 100 to 500 microns from the soma. Most cells recorded through the dendrite had a distinct enlargement of the apical trunk around the presumed recording site. The electrical properties of apical dendrites were readily distinguishable from those of somata. Dendrites generated two types of response when injected with depolarizing current. Group I responses were relatively small and broad Na(+)-dependent action potentials whose amplitude and rate-of-rise were negatively correlated with recording distance from the soma. Group II responses were complex, clustered firing patterns of Na(+)-dependent spikes together with higher-threshold slow spikes or plateaus; in these dendrites spike parameters were not correlated with distance from the soma. These two response groups were correlated with dendritic morphology: group I had significantly fewer oblique branches on the apical dendrite (5.5 vs 12.0) and a thinner apical trunk (2.0 vs 2.5 microns) than group II. TTX (1-2 microM) selectively blocked fast dendritic spikes, but not slow spikes and plateaus. Blocking Ca2+ currents reduced complex firing patterns and suppressed high-threshold slow spikes. Physiological and pharmacological studies imply that slow spikes and plateau potentials were primarily generated by high-threshold Ca2+ channels in the apical dendrite. Stimulating axons of layer I elicited EPSPs on distal apical dendrites of layer V cells. Recordings from both groups of apical dendrites revealed that EPSPs triggered a variety of distally generated, all-or-nothing depolarizations. The results show that voltage-dependent Na+ and Ca2+ currents are present in distal apical dendrites, in variable densities. These currents significantly modify distal synaptic events. The prevalence and character of active dendritic spiking (and presumably of Na+ and Ca2+ channel densities) correlate with the morphology of the apical dendritic tree.

Action Potentials↗

PubMed1992

Physiological and morphological correlations of horizontal cells in the mudpuppy retina.

1. Horizontal cells (HCs) of the mudpuppy (Necturus maculosus) retina were physiologically characterized with the use of intracellular recordings in a superfused, dark-adapted, retina-eyecup preparation. 2. Physiological analysis included an evaluation of rod versus cone input and a determination of the receptive field size with the use of a displaced slit of light. 3. The morphology of HCs was established through intracellular staining with horseradish peroxidase (HRP) and Lucifer yellow mixed in a single electrode. 4. Three types of horizontal cells were identified, each associated with a distinct morphology. Physiological subtypes included luminosity (L) and chromaticity (C) cells. Morphological diversities included single axon-bearing, multiple axon-bearing and, nonaxon-bearing cells. All C-type HCs lacked axons. 5. Approximately 90% of HCs encountered in this study were L-type cells, which received sign-conserving inputs from both rods and cones. These cell types contained one or more long axons that often stretched greater than 500 microns. This group was morphologically diverse, particularly with respect to variations in the number of axons, but we were unable to correlate this diversity with any unique set of physiological properties. 6. Several C-type HCs were identified (n = 8). These cells depolarized to a low-intensity, short-wavelength (SW) stimulus, whereas they hyperpolarized to high-intensity, long-wavelength stimuli. Morphologically, these cells were axonless (n = 4), with relatively small dendritic fields. 7. A third group of HCs were classified as "short wavelength preferring" HCs (n = 7). These cells responded better to a SW stimulus at all intensity levels. They were thus dissimilar to the common L-type HCs, which showed an apparent rod to cone transition as the stimulus intensity increased, suggestive of a shift from rod to cone preference. Morphologically, these cells were axonless (n = 2), but had broader dendritic fields than the C-type HCs. 8. Our observations indicate that the horizontal cell population of the mudpuppy retina is considerably more complex than previously supposed. The existence of both axon-bearing and axonless HCs, which could be correlated with L- and C-type physiology, implies that HCs may support more than one function in outer retina processing.

Animals↗

PubMed1992

PRAD1 (cyclin D1): a parathyroid neoplasia gene on 11q13.

Hyperparathyroidism is a central component of multiple endocrine neoplasia type 1 (MEN 1), and both sporadic and familial forms of parathyroid disease may share certain pathogenetic features. We recently identified a gene that is clonally rearranged with the PTH locus in a subset of sporadic parathyroid adenomas. This candidate oncogene, PRAD1 (previously D11S287), appears to contribute to parathyroid tumorigenesis in a fashion analogous to activation of C-MYC or BCL-2 by rearrangement with tissue-specific enhancers of the immunoglobulin genes in B-lymphoid neoplasia. The PRAD1 gene maps to 11q13 and has been linked to the BCL-1 breakpoint locus, although not to the most tightly linked MEN 1 markers, by pulsed field gel electrophoresis. PRAD1 may, in fact, be the long-sought BCL-1 lymphoma oncogene. PRAD1 encodes a novel type of cyclin protein and thus may normally function in controlling the cell cycle, perhaps through direct interaction with cdc2 or a related kinase. PRAD1's possible primary, or more likely secondary, involvement in the pathogenesis of MEN 1-related tumors is unknown and under investigation.

Amino Acid Sequence↗