PubMed Health⌕ Search

Biomedical subjects

A Cho

Publications and source records attributed to A Cho.

At least 19 recordsLinked to original sources
PubMed2001

Increased GTP-binding to dynamin II does not stimulate receptor-mediated endocytosis.

Regarding the molecular mechanism of dynamin in receptor-mediated endocytosis, GTPase activity of dynamin has been thought to have a critical role in endocytic vesicle internalization. However, a recent report suggested that GTP-binding to dynamin itself activates the dynamin to recruit molecular machinery necessary for endocytosis. In this study, to investigate the role of GTP binding to dynamin II, we generated two mutant dynamin II constructs: G38V and K44E. G38V, its GTP binding site might be mainly occupied by GTP caused by reduced GTPase activity, and K44E mutant, its GTP binding site might be vacant, caused by its decreased affinity for GTP and GDP. From the analysis of the ratio of GTP vs GDP bound to dynamin, we confirmed these properties. To test the effect of these mutant dynamins on endocytosis, we performed flow cytometry and confocal immunofluorescence analysis and found that these two mutants have inhibitory effect on transferrin-induced endocytosis. Whereas fluorescent transferrin was completely internalized in wild-type (WT) dynamin II expressing cells, no intracellular accumulation of fluorescent transferrin was found in the cells overexpressing K44E and G38V mutant. Interestingly, the amount of GTP bound to K44E was increased when endocytosis was induced than that bound to WT. The present results suggested that the GTPase activity of dynamin II is required for formation of endocytic vesicle and GTP-binding to dynamin II per se is not sufficient for stimulating endocytosis.

3T3 Cells↗
PubMed2001

Neuronal cyclin-dependent kinase 5 activity is critical for survival.

Cyclin-dependent kinase 5 (Cdk5) null mice exhibit a unique phenotype characterized by perinatal mortality, disrupted cerebral cortical layering attributable to abnormal neuronal migration, lack of cerebellar foliation, and chromatolytic changes of neurons in the brainstem and the spinal cord. Because Cdk5 is expressed in both neurons and astrocytes, it has been unclear whether this phenotype is primarily attributable to defects in neurons or in astrocytes. Herein we report reconstitution of Cdk5 expression in neurons in Cdk5 null mice and its effect on the null phenotype. Unlike the Cdk5 null mice, the reconstituted Cdk5 null mice that express the Cdk5 transgene under the p35 promoter (TgKO mice) were viable and fertile. Because Cdk5 expression is mainly limited to neurons in these mice and rescues the defects in the nervous system of the Cdk5 null phenotype, it clearly demonstrates that Cdk5 activity is necessary for normal development and survival of p35-expressing neurons.

Animals↗
PubMed2001

Neuron-specific expression of Cre recombinase during the late phase of brain development.

Gene targeting to disrupt gene expression in a temporal and spatial manner in a specific tissue using Cre recombinase-mediated gene inactivation has been proven to be useful to study in vivo gene function. To delete genes specifically in neurons during the late phase of brain development, we have generated transgenic mouse lines that express Cre recombinase under the control of the murine neurofilament-H (mNF-H) gene promoter. In this study, we report that one of these mouse lines expresses Cre recombinase specifically in the neurons of the brain and spinal cord during the late stage of their development. The transgenic line displays specific excision of the loxP-flanked gene in the neurons just after embryonic day 18.5 (E.18.5), which coincides with the later phase of brain maturation including spinal cord and olfactory bulb area. This mNF-H-cre transgenic mouse line will be valuable for studying in vivo functions of neuron-specific genes, particularly, defining their precise roles in the mature nervous system using conditional gene targeting strategies.

Age Factors↗
PubMed2000

Reduced expression of dentin sialophosphoprotein is associated with dysplastic dentin in mice overexpressing transforming growth factor-beta 1 in teeth.

Transforming growth factor (TGF)-beta1 is expressed in developing tooth from the initiation stage through adulthood. Odontoblast-specific expression of TGF-beta1 in the tooth continues throughout life; however, the precise biological functions of this growth factor in the odontoblasts are not clearly understood. Herein, we describe the generation of transgenic mice that overexpress active TGF-beta1 predominantly in the odontoblasts. Teeth of these mice show a significant reduction in the tooth mineralization, defective dentin formation, and a relatively high branching of dentinal tubules. Dentin extracellular matrix components such as type I and III collagens are increased and deposited abnormally in the dental pulp, similar to the hereditary human tooth disorders such as dentin dysplasia and dentinogenesis imperfecta. Calcium, one of the crucial inorganic components of mineralization, is also apparently increased in the transgenic mouse teeth. Most importantly, the expression of dentin sialophosphoprotein (dspp), a candidate gene implicated in dentinogenesis imperfecta II (MIM 125420), is significantly down-regulated in the transgenic teeth. Our results provide in vivo evidence suggesting that TGF-beta1 mediated expression of dspp is crucial for dentin mineralization. These findings also provide for the first time a direct experimental evidence indicating that decreased dspp gene expression along with the other cellular changes in odontoblasts may result in human hereditary dental disorders like dentinogenesis imperfecta II (MIM 125420) and dentin dysplasia (MIM 125400 and 125420).

Animals↗
PubMed2000

Biophysics. What's shakin' in the ear?

Auditory researchers agree that hair cells are the ear's miniature amplifiers. They just don't agree about how the curious devices work. The two most popular ideas--one involving chemically activated trapdoors, the other cells that pump like pistons--both have been boosted by recent research.

Animals↗
PubMed2000

Phosphatase-triggered guest release from a cyclodextrin complex.

[reaction: see text] A synthetic supramolecular system is described that models the effect of phosphoryl transfer in molecular recognition. beta-Cyclodextrin-6A-phosphate (pCD), which is shown to be a substrate of alkaline phosphatase, binds cationic aromatic guests, including anticancer agents, up to 100-fold better than native beta-CD. The above observations demonstrate that pCD is capable of releasing the guests from its cavity upon hydrolysis with the phosphatase, as also confirmed by monitoring the hydrolysis in the presence of a guest.

Alkaline Phosphatase↗
PubMed2000

Anatomy of the right anterosuperior area (segment 8) of the liver: evaluation with helical CT during arterial portography.

PURPOSE: To evaluate the segmental anatomy of the right anterosuperior area (segment 8) of the liver by using helical computed tomography during arterial portography (CTAP). MATERIALS AND METHODS: Twenty-seven patients without lesions at segment 8 underwent helical CTAP. Three-dimensional portograms were reconstructed to verify the course of the portal veins. The number of subsegmental branches, in addition to the branching point and the distribution in segment 8, was assessed. RESULTS: In 25 (93%) patients, the dorsal branch of segment 8 gave rise to dorsally directed branches posterior to the right hepatic vein. In only four (25%) of 16 patients in whom the medial branch of segment 8 arose near the porta hepatis, the long paracaval portal branch of the caudate lobe extended upward above the interval between the middle and right hepatic veins. CONCLUSION: In most of the patients, the dorsal branches of segment 8 supplied the dorsocranial area of the right lobe posterior to the right hepatic vein. The paracaval portion of the caudate lobe was limited to below the interval between the middle and right hepatic veins in the majority of patients who showed medial branches of segment 8 arising near the porta hepatis. Recognition of this vascular anatomy is clinically important for preoperative evaluation of hepatic tumors in segment 8 because it may contribute to a safer surgical approach.

Adult↗
PubMed2000

Phosphatidylinositol 3-kinase signaling is important for smooth muscle cell replication after arterial injury.

The phosphoinositide 3-kinase [PI(3)K] pathway is a key signaling pathway important for replication of mammalian cells. In this study, we examined the role of PI(3)K in smooth muscle cell (SMC) replication after balloon catheter injury of rat carotid arteries. Protein kinase B (PKB), a downstream target of PI(3)K, was phosphorylated at 30 and 60 minutes after injury and to a lesser degree after 6 hours and 1 and 2 days but not after 7 days. Wortmannin (10 microgram per rat), a PI(3)K inhibitor, given to rats 60 and 5 minutes before and 11 hours after balloon injury, reduced the levels of phosphorylated PKB. SMC replication quantified between 24 to 48 hours was significantly reduced compared with control replication, as were the levels of cyclin D(1). Wortmannin was also administered to rats between days 7 and 8 and between days 7 and 9 after balloon catheter injury. A reduction in levels of phosphorylated PKB was detected, but no decrease in the replication of intimal SMCs was observed in either experiment. These data demonstrate that the PI(3)K signal transduction pathway plays an important role in medial but not intimal SMC replication.

Androstadienes↗
PubMed2000

Mitogen-activated protein kinases mediate matrix metalloproteinase-9 expression in vascular smooth muscle cells.

Expression of matrix metalloproteinase (MMP)-9 has been linked to the progression of plaque rupture and intimal formation in arterial lesions. In this study, we determined which factors and signaling pathways are involved in regulating the MMP-9 gene. Rat carotid arterial smooth muscle cells treated with tumor necrosis factor (TNF)-alpha showed a marked increase in MMP-9 activity and mRNA level, whereas platelet-derived growth factor (PDGF) showed a slight induction of the MMP-9 mRNA level. TNF-alpha treatment caused an increase in c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38 MAPK), and extracellular signal-regulated kinase (ERK) activities, whereas PDGF treatment caused an increase in ERKs and p38 MAPK activities without any effect on JNK activity. Treatment with either SB203580 (inhibitor of p38 MAPK) or U0126 (inhibitor of the ERK pathway) downregulated the TNF-alpha-induced MMP-9 expression in a dose-dependent manner. Treatment of cells with TNF-alpha and PDGF together stimulated the MMP-9 expression at a level higher than that observed with either factor alone, suggesting that TNF-alpha and PDGF have a synergistic effect on MMP-9 expression in arterial smooth muscle cells. Furthermore, suboptimal inhibitory concentrations of SB203580 and U0126 together almost completely inhibited the MMP-9 expression. These results suggest that p38 MAPK and ERK pathways contribute to the transcriptional regulation of MMP-9 in arterial smooth muscle cells.

Animals↗
PubMed2000

SAR studies of anti-MRSA non-zwitterionic 3-heteroarylthiocephems.

SAR studies in a series of 3-heteroarylthio substituted cephalosporins established that high activity against methicillin-resistant Staphylococcus aureus (MRSA) can be achieved with various heteroaryl substituents. Early results showed that highly lipophilic 3-heteroarylthio substituents, which were necessary for anti-MRSA activity, caused high affinity of such cephems toward serum proteins. Our earlier published efforts described discovery of zwitterionic cephems MC-02,331 and RWJ-54428 (MC-02,479), where serum binding was reduced by employing basic, positively charged functionalities attached to the 3-heteroarylthio substituent. In order to avoid low solubility problems associated with most such zwitterionic cephalosporins a wide variety of non-basic heteroaryl substituents was tested (non-zwitterionic cephems are more easily formulated as water soluble sodium salts for intravenous administration). Considerable reduction in serum binding was obtained in some analogs while maintaining high anti-MRSA potency.

Animals↗
PubMed2000

Discovery of RWJ-54428 (MC-02,479), a new cephalosporin active against resistant gram-positive bacteria.

The discovery of RWJ-54428 (MC-02,479), a new cephalosporin displaying promising activity against sensitive and resistant Gram-positive bacteria, is described. Progressive structural modification from the previously reported 3-phenylthiocephem MC-02,331 afforded an overall increase in potency against MRSA while retaining other key properties such as acceptable solubility and serum binding. Evaluation of the in vitro potency and in vivo efficacy of a series of closely related compounds resulted in selection of RWJ-54428 (MC-02,479) for further studies.

Cephalosporins↗
PubMed1999

Spatial and temporal activity of the dentin sialophosphoprotein gene promoter: differential regulation in odontoblasts and ameloblasts.

Dentin sialoprotein and dentin phosphoprotein are non-collagenous proteins that are cleavage products of dentin sialophosphoprotein (DSPP). Although these two protein products are believed to have a crucial role in the process of tooth mineralization, their precise biological functions and the molecular mechanisms of gene regulation are not clearly understood. To understand such functions, we have developed a transgenic mouse model expressing a reporter gene (lacZ) under the control of approximately 6 kb upstream sequences of Dspp. The transgenic fusion protein was designed to reside within the cells to facilitate the precise identification of cell type and developmental stages at which the Dspp-lacZ gene is expressed. The results presented in this report demonstrate: (a) the 6 kb upstream sequences of Dspp have the necessary regulatory elements to direct the tissue specific expression of the transgene similar to endogenous Dspp, (b) both odontoblasts and ameloblasts exhibit transgene expression in a differentiation dependent manner, and (c) a differential regulation of the transgene in odontoblasts and ameloblasts occurs during tooth development and mineralization.

Ameloblasts↗
PubMed1998

Endothelin-1-induced vasoconstriction causes a significant increase in portal pressure of rat liver: localized constrictive effect on the distal segment of preterminal portal venules as revealed by light and electron microscopy and serial reconstruction.

Intraportal infusion of endothelin-1 (ET-1), a potent vasoconstrictor, significantly elevates portal venous pressure. To determine the major site of vascular constriction in the intrahepatic porto-sinusoidal system, we performed an in situ perfusion of rat livers with 1 nmol/L ET-1 at a flow rate of 20 mL/min. Portal pressure rose from 22 cm H2O to 54 cm H2O within 25 minutes. Specimens were prepared for light-microscopic serial reconstruction and electron microscopy. The distal segment of preterminal portal venules (DS/PPV) with an inner diameter of 40 to 80 microm showed complete obliteration of the lumen over a 300-microm distance caused by the intense contraction of perivascular smooth muscle cells and protruding of endothelial cells into the lumen. The proximal segment of preterminal portal venules (PS/PPV) with a larger diameter up to 150 microm also underwent strong constriction, but still had luminal space for the flow, while the PS/PPV with a diameter of 150 to 400 microm showed moderate or mild constriction and retained a wide lumen. Neither terminal portal venules, inlet venules, sinusoids, nor central veins, however, exhibited demonstrable constriction. Liver parenchyma fed by the inlet venules that emerged from the PS/PPV exhibited a wide sinusoidal lumen and vacuolated hepatocytes caused by the influx of excess portal perfusate that escaped from the occlusive areas. The present study has revealed that the DS/PPV functions as a presinusoidal quasi-sphincter mechanism and is involved in the redistribution of intrahepatic portal flow under increased portal pressure.

Animals↗
PubMed1998

Eliminating arterial pulsatile strain by external banding induces medial but not neointimal atrophy and apoptosis in the rabbit.

We have examined the role of vessel pulsation and wall tension on remodeling and intimal proliferation in the rabbit infrarenal abdominal aorta. A rigid perivascular polyethylene cuff was used to reduce vessel systolic diameter by 25%, producing a region of reduced circumferential strain. At 6 weeks postoperatively, reduced circumferential strain caused medial atrophy, with 45% reduction of medial area and 30% loss of medial smooth muscle cells. Apoptotic cell death was indicated by DNA fragmentation, propidium iodide staining, and cell morphology. Cuffing the aorta after balloon denudation produced medial atrophy but did not inhibit neointimal growth. At 1 week postoperatively, intimal thickness was slightly decreased in regions with reduced strain; however, intimal thickening in regions of reduced strain was not different from control segments at 3 weeks postoperatively (intimal area was 0.37 +/- 0.05 mm2 with reduced strain and 0.50 +/- 0.08 for controls, mean +/- SEM). We conclude that circumferential strain is a major factor controlling medial structure and cell number, whereas growth of the neointima after injury is not significantly affected by either reduced strain or extensive medial cell death. Vessel cuffing represents a new model of blood vessel remodeling in vivo that involves extensive smooth muscle cell apoptosis.

Animals↗