Search PubMed⌕ Search

Biomedical subjects

A Nakano

Publications and source records attributed to A Nakano.

At least 91 records · Page 5Linked to original sources
PubMed1999

Identification of SEC12, SED4, truncated SEC16, and EKS1/HRD3 as multicopy suppressors of ts mutants of Sar1 GTPase.

The yeast SAR1 gene encodes a low-molecular-weight GTPase which is essential for the formation of transport vesicles from the endoplasmic reticulum (ER). To understand how the Sar1p function is regulated in its GTPase cycle, we searched for multicopy suppressors of sar1 temperature-sensitive mutants and identified SEC12, SED4, truncated SEC16, and EKS1. EKS1 turns out to be identical to HRD3, which was independently isolated as a gene implicated in the degradation of an HMG-CoA reductase isozyme, Hmg2p. In this paper, we show that the product of EKS1/HRD3 is a type-I transmembrane glycoprotein and resides in the ER. The eks1/hrd3 disrupted cells are normal in growth and transport of cargo proteins, but missecrete BiP (Kar2p). The overexpression of EKS1/HRD3, which stabilizes Hmg2p, did not affect the stability of wild-type or mutant Sar1p or any early Sec proteins we examined. These results suggest that the role of Eks1p/Hrd3p is not involved in the ER protein degradation in general but rather required for the maintenance of the ER membrane functions. The novel genetic interactions unveiled between SAR1, SEC12, SEC16, and SED4 will provide useful information as to how the complex machinery of vesicle budding operates.

Endoplasmic Reticulum↗
PubMed1999

The Escherichia coli homologue of yeast RER2, a key enzyme of dolichol synthesis, is essential for carrier lipid formation in bacterial cell wall synthesis.

We found in the Escherichia coli genome sequence a homologue of RER2, a Saccharomyces cerevisiae gene required for proper localization of an endoplasmic reticulum protein, and designated it rth (RER2 homologue). The disruption of this gene was lethal for E. coli. To reveal its biological function, we isolated temperature-sensitive mutants of the rth gene. The mutant cells became swollen and burst at the nonpermissive temperature, indicating that their cell wall integrity was defective. Further analysis showed that the mutant cells were deficient in the activity of cis-prenyltransferase, namely, undecaprenyl diphosphate synthase, a key enzyme of the carrier lipid formation of peptidoglycan synthesis. The cellular level of undecaprenyl phosphate was in fact markedly decreased in the mutants. These results are consistent with the fact that the Rer2 homologue of Micrococcus luteus shows undecaprenyl diphosphate synthase activity (N. Shimizu, T. Koyama, and K. Ogura, J. Biol. Chem. 273:19476-19481, 1998) and demonstrate that E. coli Rth is indeed responsible for the maintenance of cell wall rigidity. Our work on the yeast rer2 mutants shows that they are defective in the activity of cis-prenyltransferase, namely, dehydrodolichyl diphosphate synthase, a key enzyme of dolichol synthesis. Taking these data together, we conclude that the RER2 gene family encodes cis-prenyltransferase, which plays an essential role in cell wall biosynthesis in bacteria and in dolichol synthesis in eukaryotic cells and has been well conserved during evolution.

Alkyl and Aryl Transferases↗
PubMed1999

The yeast RER2 gene, identified by endoplasmic reticulum protein localization mutations, encodes cis-prenyltransferase, a key enzyme in dolichol synthesis.

As an approach to understand the molecular mechanisms of endoplasmic reticulum (ER) protein sorting, we have isolated yeast rer mutants that mislocalize a Sec12-Mfalpha1p fusion protein from the ER to later compartments of the secretory pathway (S. Nishikawa and A. Nakano, Proc. Natl. Acad. Sci. USA 90:8179-8183, 1993). The temperature-sensitive rer2 mutant mislocalizes different types of ER membrane proteins, suggesting that RER2 is involved in correct localization of ER proteins in general. The rer2 mutant shows several other characteristic phenotypes: slow growth, defects in N and O glycosylation, sensitivity to hygromycin B, and abnormal accumulation of membranes, including the ER and the Golgi membranes. RER2 and SRT1, a gene whose overexpression suppresses rer2, encode novel proteins similar to each other, and their double disruption is lethal. RER2 homologues are found not only in eukaryotes but also in many prokaryote species and thus constitute a large gene family which has been well conserved during evolution. Taking a hint from the phenotype of newly established mutants of the Rer2p homologue of Escherichia coli, we discovered that the rer2 mutant is deficient in the activity of cis-prenyltransferase, a key enzyme of dolichol synthesis. This and other lines of evidence let us conclude that members of the RER2 family of genes encode cis-prenyltransferase itself. The difference in phenotypes between the rer2 mutant and previously obtained glycosylation mutants suggests a novel, as-yet-unknown role of dolichol.

Alkyl and Aryl Transferases↗
PubMed1999

Endovascular treatment of ruptured dissecting aneurysms aimed at occlusion of the dissected site by using Guglielmi detachable coils.

OBJECT: Surgical or endovascular occlusion of the parent artery proximal to an aneurysm has been recommended for treatment of dissecting aneurysms of the intracranial posterior circulation. However, dissecting aneurysms may rupture even after proximal occlusion because distal progression of thrombus is necessary to occlude the dissecting aneurysm completely, and this may be delayed by the presence of retrograde flow. In this article the authors present their experience in treating six patients with ruptured dissecting aneurysms. METHODS: The authors report on six patients with a ruptured dissecting aneurysm in the posterior fossa who were successfully treated by endovascular occlusion of the aneurysm by using Guglielmi detachable coils. The procedure was particularly aimed at occluding the dissected site. CONCLUSIONS: At the present time, endovascular occlusion of the dissected site is a safe, minimally invasive, and reliable treatment for dissecting aneurysms when a test occlusion is tolerated and adequate collateral circulation is present.

Adult↗
PubMed1999

[Expression of reactive oxygen-related enzymes in human umbilical vein endothelial cells (HUVEC) cultured with high concentrations of glucose].

We examined the levels of reactive oxygen-related enzymes in human umbilical vein endothelial cells cultured with high concentrations of glucose, in vitro. From the results, elevated levels of catalase mRNA and its protein were exhibited in the presence of higher glucose. In addition, the message level of p22-phox as the active center of NADPH oxidase, was slightly increased. Taken together, the endothelial injury induced by diabetes may associated to the elevated level of O2- production. However, the level of catalase as .OH scavenger was mainly increased, cooperatively.

Cells, Cultured↗
PubMed1999

[Oxidized LDL in patients with coronary heart disease and normal subjects].

Basic research has provided strong evidence that oxidation of LDL plays an important role in the progression of atherosclerotic vascular disease. The levels of plasma oxidized two-density lipoprotein (ox-LDL) were measured by sandwich ELISA using the monoclonal antibody (DLH3) recognized oxidatively modified lipoproteins and the anti-human apolipoprotein B monoclonal antibody in healthy subjects and patients with coronary heart disease (CHD). Plasma ox-LDL could be detected in normal subjects and patients with CHD. No sex-related difference was observed in normal subjects. The levels of ox-LDL in the forties and fifties were higher than those in the thirties and twenties. The levels of plasma ox-LDL were significantly higher in patients with CHD than in controls. There was no difference between the levels of ox-LDL of patients with single vessel disease and those with multivessel disease. These results suggest that elevated levels of oxidized LDL may be a marker for CHD.

Adult↗
PubMed1998

Widespread neuronal degeneration in rats following oral administration of methylmercury during the postnatal developing phase: a model of fetal-type minamata disease.

The neurotoxicity of methylmercury (MeHg) treatment during the postnatal developing phase in rats was studied. Rats on postnatal day 1 were orally administered 5 mg/kg/day methylmercury chloride (MMC) for more than 30 consecutive days. Body weight loss began 26 days after MMC was administered, and severe paralysis of the hind-limbs and unsteadiness appeared subsequently. Histopathologically, the widespread neuronal degeneration was observed in the cerebral neocortex, neostriatum, red nucleus, brainstem, cerebellum and spinal dorsal root ganglia on day 32. The widespread distribution of the lesions was quite similar to that in fetal cases of MeHg intoxication in Minamata, Japan. These findings suggest that MMC treatment during the postnatal development phase in rats produce a good model of fetal-type Minamata disease.

Animals↗
PubMed1998

AtGDI2, a novel Arabidopsis gene encoding a Rab GDP dissociation inhibitor.

The GTPase cycle of Rab/Ypt proteins is strictly controlled by several classes of regulators to ensure their proper roles in membrane traffic. GDP dissociation inhibitor (GDI) is known to play essential roles in regulating nucleotide states and subcellular localizations of Rab/Ypt proteins. To obtain further knowledge on this regulator molecule in plants, we isolated and characterized two genes of Arabidopsis thaliana that encode different GDIs. AtGDI1 has been identified by a novel functional cloning in yeast [Ueda et al. (1996) Plant Cell, 8, 2079-2091] and AtGDI2 was isolated by cross-hybridization in this study. AtGDI2, as well as AtGDI1, complements the yeast sec19/gdi1 mutant, indicating that they can replace the function of yeast GDI. Evidence is shown that both AtGDI1 and AtGDI2 can interact with Ara4, an Arabidopsis Rab protein, in the yeast ypt1 mutant cells. AtGDI2 is ubiquitously expressed in Arabidopsis tissues with some difference from AtGDI1 in expression level. Genomic DNA hybridization using specific probes reveals the presence of one more GDI gene in Arabidopsis. This may imply differentiated roles of GDI in higher plants.

Amino Acid Sequence↗
PubMed1998

Induction by mercury compounds of brain metallothionein in rats: Hg0 exposure induces long-lived brain metallothionein.

Metallothionein (MT) is one of the stress proteins which can easily be induced by various kind of heavy metals. However, MT in the brain is difficult to induce because of blood-brain barrier impermeability to most heavy metals. In this paper, we have attempted to induce brain MT in rats by exposure to methylmercury (MeHg) or metallic mercury vapor, both of which are known to penetrate the blood-brain barrier and cause neurological damage. Rats treated with MeHg (40 micromol/kg per day x 5 days, p.o.) showed brain Hg levels as high as 18 microg/g with slight neurological signs 10 days after final administration, but brain MT levels remained unchanged. However, rats exposed to Hg vapor for 7 days showed 7-8 microg Hg/g brain tissue 24 h after cessation of exposure. At that time brain MT levels were about twice the control levels. Although brain Hg levels fell gradually with a half-life of 26 days, MT levels induced by Hg exposure remained unchanged for > 2 weeks. Gel fractionation revealed that most Hg was in the brain cytosol fraction and thus bound to MT. Hybridization analysis showed that, despite a significant increase in MT-I and -II mRNA in brain, MT-III mRNA was less affected. Although significant Hg accumulation and MT induction were observed also in kidney and liver of Hg vapor-exposed rats, these decreased more quickly than in brain. The long-lived MT in brain might at least partly be accounted for by longer half-life of Hg accumulated there. The present results showed that exposure to Hg vapor might be a suitable procedure to provide an in vivo model with enhanced brain MT.

Animals↗
PubMed1998

Long term follow-up in a case of anomalous origin of the left coronary artery from the pulmonary artery.

An adult patient with anomalous origin of the left coronary artery from the pulmonary artery had no serious cardiac event for 19 years after closing the shunt from the aorta to the pulmonary trunk by ligation of the left main coronary artery. Although one-coronary arterial perfusion is considered to have worse prognosis than two-coronary arterial system, this patient proved to have an unexpectedly good long-term prognosis.

Adult↗
PubMed1998

Assessment of "microvascular no-reflow phenomenon" using technetium-99m macroaggregated albumin scintigraphy in patients with acute myocardial infarction.

OBJECTIVES: The aim of this study was the scintigraphic evaluation of clinical no-reflow phenomenon. BACKGROUND: In patients with acute myocardial infarction, the relationship of the severity of reduction of microvascular reflow to the ischemia time or to the secondary extension of myocardial necrosis is poorly understood, and we accordingly conducted a scintigraphic evaluation of clinical no-reflow phenomenon. METHODS: The group studied consisted of 25 consecutive patients with their first acute myocardial infarction. After recanalization, each patient received intracoronary injections of technetium-99m macroaggregated albumin (MAA). RESULTS: Eight patients (32%) had absent tracer uptake (scintigraphic no-reflow phenomenon). Fourteen patients showed absent or moderately reduced MAA uptake (group 1) and 11 showed slightly reduced or normal uptake (group 2). The time to recanalization was significantly longer in group 1 than in group 2 (290.4+/-130.6 min vs. 1773+/-93.5 min; p=0.0238). In chronic phase, the thallium-201 (TI-201) defect score index was significantly larger (p < 0.01) and regional ejection fraction was significantly lower (p < 0.01) in group 1 compared with corresponding values in group 2. No significant deterioration from acute phase to chronic phase in either TI-201 defect score index or regional ejection fraction was found in either group (two-way repeated measures analysis of variance). CONCLUSIONS: These findings suggest that scintigraphic noreflow phenomenon occurs in a subgroup of patients without angiographic no-reflow phenomenon, that the myocardial damage depends on the severity of microvascular damage and that prolonged ischemia time may increase the likelihood of "microvascular no-reflow phenomenon."

Aged↗
PubMed1998

Expansion of the oral end of free revascularised jejunum with a jejunal patch flap rotated like a folding fan.

We have devised a new expansion process for the reconstruction of the cervical oesophagus with free revascularised jejunum in cases of hypopharyngeal cancer. The jejunal island flap is divided into three subislands and the major island of the caudal end is split partially at its oral end. The middle island is split, trimmed triangularly, and inserted into opened major island to expand the diameter of the oral end of the conduit for the cervical oesophagus and to make it funnel-shaped. The smallest island on the oral side is used as a circulation monitor for the transferred jejunum. Because the jejunal island patch is rotated around the root of mesentery like a folding fan and joined to the major island, there is neither shortening of the pedicle nor distortion. This method allows expansion of the oral end by up to 180% to facilitate end to end anastomosis in proximal pharyngeal defects.

Aged↗
PubMed1998

Differential expression of multidrug resistance (mdr) and canalicular multispecific organic anion transporter (cMOAT) genes following extrahepatic biliary obstruction in rats.

The hepatic canalicular membrane has transporters that play an important role as efflux pumps in the excretion of endogenous bile constituents or xenobiotics into bile canaliculi. To elucidate functional significance of canalicular transporters in the mechanism of cholestasis, mRNA expression levels of multidrug resistance (mdr) 1b, mdr2 and canalicular multispecific organic anion transporter (cMOAT) genes were analyzed by Southern blotting of reverse-transcribed PCR products of liver mRNA obtained from cholestatic rats that had been subjected to bile duct ligation. Both mdr1b and mdr2 mRNA expression increased after ligation. Immunohistochemical study revealed that the products of both mdr1b and mdr2 were present on the canaliculi, and that their levels increased after ligation. In contrast, cMOAT mRNA expression was not increased, but rather attenuated by ligation. The expression of canalicular transporters was differentially regulated in extrahepatic biliary obstruction, indicating the different roles are played by mdr and cMOAT in the pathogenesis of cholestasis.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1998

Identification of potential regulatory elements for the transport of Emp24p.

To examine the possibility of active recycling of Emp24p between the endoplasmic reticulum (ER) and the Golgi, we sought to identify transport signal(s) in the carboxyl-terminal region of Emp24p. Reporter molecules were constructed by replacing parts of a control invertase-Wbp1p chimera with those of Emp24p, and their transport rates were assessed. The transport of the reporter was found to be accelerated by the presence of the cytoplasmic domain of Emp24p. Mutational analyses revealed that the two carboxyl-terminal residues, leucine and valine (LV), were necessary and sufficient to accelerate the transport. The acceleration was sequence specific, and the terminal valine appeared to be more important. The LV residues accelerated not only the overall transport to the vacuole but also the ER to cis-Golgi transport, suggesting its function in the ER export. Hence the LV residues are a novel anterograde transport signal. The double-phenylalanine residues did not affect the transport by itself but attenuated the effect of the anterograde transport signal. On the other hand, the transmembrane domain significantly slowed down the ER to cis-Golgi transport and effectively counteracted the anterograde transport signal at this step. It may also take part in the retrieval of the protein, because the overall transport to the vacuole was more evidently slowed down. Consistently, the mutation of a conserved glutamine residue in the transmembrane domain further slowed down the transport in a step after arriving at the cis-Golgi. Taken together, the existence of the anterograde transport signal and the elements that regulate its function support the active recycling of Emp24p.

Amino Acid Sequence↗
PubMed1998

Activities of mutant Sar1 proteins in guanine nucleotide binding, GTP hydrolysis, and cell-free transport from the endoplasmic reticulum to the Golgi apparatus.

Sar1p belongs to a unique subfamily of the small GTPase superfamily and is essential for the formation of vesicles that transport proteins from the endoplasmic reticulum to the Golgi apparatus. We have obtained mutants of the yeast SAR1 gene, which show several different phenotypes in cell growth and protein transport [Nakano, A. , Otsuka, H., Yamagishi, M., Yamamoto, E., Kimura, K., Nishikawa, S., and Oka, T. (1994) J. Biochem. 116, 243-247; Yamanushi, T., Hirata, A., Oka, T., and Nakano, A. (1996) ibid. 120, 452-458]. In this study, we have purified five mutant Sar1 proteins using an Escherichia coli expression system and characterized their biochemical properties in detail. Three of them prefer GDP binding to GTP binding and are thus regarded as GDP-form mutants, and one is insensitive to the GTPase-activating protein and is almost fixed in the GTP-bound state. The GDP mutants are defective in vesicle formation in vitro, whereas the GTP mutant can drive vesicle formation but not the overall transport to the Golgi. These mutants will be useful for further understanding of the regulation of the GTPase cycle of Sar1p.

Amino Acid Substitution↗
PubMed1998

RMA1, an Arabidopsis thaliana gene whose cDNA suppresses the yeast sec15 mutation, encodes a novel protein with a RING finger motif and a membrane anchor.

To identify molecules that function in the plant secretory pathway, we screened for Arabidopsis thaliana cDNA clones that complement the temperature-sensitive (ts), secretion-deficient sec15 mutation of yeast Saccharomyces cerevisiae. RMA1, one of the genes obtained in this screening, suppressed not only the ts growth of sec15 but also its secretory defect. RMA1 is not a structural homologue of SEC15 but encodes a novel 28 kDa protein with a RING finger motif and a C-terminal membrane-anchoring domain. Mutational analysis indicates that the RING finger motif of RMA1 is important for its suppression activity. In Arabidopsis plant, RMA1 is ubiquitously expressed. A search for homologous proteins in the database revealed that Arabidopsis, nematode, mouse and human possess close homologues of RMA1.

Amino Acid Sequence↗
PubMed1998

Isolation of a tobacco cDNA encoding Sar1 GTPase and analysis of its dominant mutations in vesicular traffic using a yeast complementation system.

The cDNA clone of NtSAR1, a gene encoding the small GTPase Sar1p which is essential for vesicle formation from the endoplasmic reticulum (ER) membrane in yeast, has been isolated from Nicotiana tabacum BY-2 cells. NtSAR1 as well as AtSAR1 cDNA isolated from Arabidopsis thaliana [d'Enfert et al. (1992) EMBO J. 11: 4205] could complement the lethality of the disruption of SAR1 in yeast cells in a temperature-sensitive fashion. They also suppressed yeast sec12 and sec16 temperature-sensitive mutations as yeast SAR1 does. Using this complementation system, we analyzed the phenotypes of several mutations in plant SAR1 cDNAs in yeast cells. The expression of NtSAR1 H74L and AtSAR1 N129I showed dominant negative effect in growth over the wild-type SAR1, which was accompanied by the arrest of ER-to-Golgi transport. Such dominant mutations will be useful to analyze the role of membrane trafficking in plant cells, if their expression can be regulated conditionally.

Amino Acid Sequence↗