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A Ichihara

Publications and source records attributed to A Ichihara.

At least 55 records · Page 3Linked to original sources
PubMed1996

Newly identified pair of proteasomal subunits regulated reciprocally by interferon gamma.

Interferon (IFN) gamma induces replacements of the proteasomal subunits X and Y by LMP7 and LMP2, respectively, resulting in an alteration of the proteolytic specificity. We found a third pair of proteasome subunits expressed reciprocally in response to IFN-gamma. Molecular cloning of a cDNA encoding one subunit designated as Z, downregulated by IFN-gamma, showed that it is a novel proteasomal subunit with high homology to MECL1, which is markedly induced by IFN-gamma. Thus, IFN-gamma induces subunit replacements of not only X and Y by LMP7 and LMP2, respectively, but also of Z by MECL1, producing proteasomes responsible for immunological processing of endogenous antigens. When processed from their precursors, three pairs of the 10 homologous, but distinct, beta-type subunits of eukaryotic proteasomes, that is, X/LMP7, Y/LMP2, and Z/MECL1, have an NH2-terminal threonine residue, assumed to be part of a catalytic center. These findings suggest that the altered molecular organization of the proteasome induced by IFN-gamma may be responsible for acquisition of its functional change.

Amino Acid Sequence↗
PubMed1996

Role of adenosine in the renal responses to contrast medium.

Despite the development of non-ionic radiographic contrast media (CM), CM-induced nephropathy is a clinically important problem in patients with pre-existing renal insufficiency. We examined the effects of non-ionic CM (iohexol) on renal function in conscious dogs with and without renal insufficiency, and evaluated the effects of a non-selective (theophylline), an A1 selective (KW-3902), and an A2 selective adenosine antagonist (KF17837) on the renal responses to CM. In sham-operated group, iohexol (2 ml/kg/min for 3 min) increased effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), whereas in renal insufficiency group (with subtotal nephrectomy), following transient increases in ERPF and GFR, CM markedly decreased ERPF (-46.5 +/- 6.7%) and GFR (-51.2 +/- 7.1%). In sham-operated group, theophylline and KF17837 markedly attenuated CM-induced increases in ERPF and GFR, while KW-3902 had no effects on CM-induced increases in ERPF or GFR. In renal insufficiency group, initial increases in ERPF and GFR were blunted by theophylline and KF17837. In contrast, the subsequent decreases in ERPF and GFR were attenuated by theophylline (% delta ERPF, -12.2 +/- 3.2% vs. -46.6 +/- 6.7%, P < 0.01; % delta GFR, 4.3 +/- 2.5% vs. -51.0 +/- 7.1%, P < 0.01), and were completely prevented by KW-3902 (% delta ERPF, 10.8 +/- 2.9%; % delta GFR, 23.8 +/- 4.4%), whereas KF17837 aggravated ERPF (-73.3 +/- 5.3%) and GFR (-78.4 +/- 5.3%). These data indicate that in normal renal function, iohexol elicits renal vasodilation by activating mainly the adenosine A2 receptors. In contrast, in impaired renal function, CM induces both A2 and A1 activation; the former is associated with the initial renal vasodilation, while the latter is responsible for the sustained aggravation of renal hemodynamics.

Adenosine↗
PubMed1995

Molecular cloning of two types of cDNA encoding subunit RC6-I of rat proteasomes.

A new subunit, named RC6-I, of the rat 20 S proteasome was purified and the partial amino acid sequences of several peptide fragments obtained by digestion with lysyl-endopeptidase were determined by Edman degradation. Amplification of cDNAs encoding RC6-I by the polymerase chain reaction (PCR) technique revealed two types of cDNA, tentatively designated as RC6-IL and RC6-IS in order of size. The nucleotide sequences of the two cDNAs are identical except that RC6-IL contains an insertion of 18 nucleotides in the coding region compared with RC6-IS. The polypeptide predicted from the open reading frame of RC6-IS cDNA consists of 248 amino acid residues with a calculated molecular weight of 27,783. These values are consistent with those obtained by protein chemical analyses. Computer-assisted homology analysis showed that RC6-I belongs to the alpha-type subfamily of the proteasome gene family, which shows similarity to the alpha-subunit of the archaebacterium Thermoplasma acidophilum proteasome, and that the 18 nucleotide insert, encoding six amino acid residues, VVASVS, appears to be unique to RC6-IL, because this motif has not been conserved in any other alpha-type subunit. By reverse transcription (RT)-PCR analysis, the mRNAs for both RC6-IL and RC6-IS were found in all the rat tissues examined. These results suggest that proteasomes are present as a heterogeneous population, possibly for acquisition of diversity of functions.

Amino Acid Sequence↗
PubMed1995

Long-term maintenance of functional rat hepatocytes in primary culture by additions of pyruvate and various hormones.

Mature adult rat hepatocytes were cultured as monolayers in serum-free Williams medium E containing 10(-7) M each of insulin (Ins), dexamethasone (Dex) and triiodothyronine (T3) and 30 mM pyruvate. The hepatocytes remained morphologically intact for at least 14 days, during which period they maintained normal liver functions such as the expressions of cytochrome P-450 mRNA and glucokinase and secretion of albumin. They also retained the ability to resume proliferation. Cells cultured with pyruvate had a much higher ATP level than those without pyruvate, suggesting that pyruvate can sustain functional hepatocytes for a long period in culture in the presence of Ins, Dex and T3, probably by producing enough energy for their maintenance.

Adenosine Triphosphate↗
PubMed1995

Roles of proteasomes in cell growth.

Proteasomes are large, unique protein complexes catalyzing energy- and ubiquitin-dependent proteolysis. Recent studies have revealed that these complexes are involved in two important cellular functions. One is to make antigen fragments for major histo-compatibility complex (MHC) class I-restricted antigen presentation and the other is to regulate the cell cycle by proteolysis. Here we review only the latter function of proteasomes. Proteasomes are widely distributed in eukaryotic cells, but their levels have been shown to be particularly high in various immature cells, such as cancerous, fetal and lymphoblastic cells, and agents including cell differentiation were found to suppress their expression. These conditions also regulate the expression of ubiquitin genes in a similar way, suggesting that proteasomes act ubiquitin-dependently in their 26S form in immature cells. High levels of proteasomes were found immunochemically in the nuclei of rapidly growing cells, indicating that proteasomes are important for eukaryotic cell growth. Indeed, gene disruptions of most subunits of proteasomes in yeast resulted in total suppression of cell growth and cell death. Short-lived regulatory factors of the cell cycle, such as Fos, p53, Mos, and cyclins are degraded by the proteasome-ubiquitin pathway under phosphorylated or dephosphorylated conditions. Ornithine decarboxylase, which is also a short-lived enzyme and is involved in the early phase of cell growth, is quickly degraded by proteasomes with antizyme, but without ubiquitination. Recently, we found that one of the regulatory factors of 26S proteasomes, p31, is a homologue of Nin1p, whose mutation caused inhibition of the cell cycle in yeast. These results indicate that proteasomes play important roles in regulation of the cell cycle in eukaryotes.

Amino Acid Sequence↗
PubMed1995

Status of patients who underwent uninephrectomy in adulthood more than 20 years ago.

We investigated the status of patients without systemic diseases who had undergone uninephrectomy for unilateral renal diseases in adulthood more than 20 years ago at Tokyo Denryoku Hospital. There were 21 participants (mean age +/- SD, 58.6 +/- 8.0 years) who fulfilled these criteria. The average interval since nephrectomy was 27.9 +/- 6.2 years. The mean current creatinine clearance was 88.5 +/- 21.2 mL/min/1.73 m2, which is 92.9% of that in healthy age- and sex-matched controls with two kidneys. The 24-hour urine protein excretion in these patients was only slightly higher than in the controls (214 +/- 190 mg v 119 +/- 62 mg, P = NS). Age at nephrectomy, length of time with a single kidney, or sex had little effect on the remnant renal functions. There was a positive correlation between current mean arterial pressure and serum creatinine (r = 0.44, P < 0.05). Patients who developed hypertension after uninephrectomy had a family history of hypertension more frequently than those with normotension (86% v 29%, P < 0.05). We conclude that (1) renal function after compensatory hyperfiltration of more than 20 years due to uninephrectomy for unilateral renal diseases in adulthood is well maintained, although hypertension has a considerable effect on the renal functions, and that (2) family history of hypertension plays a key role in determining the incidence of hypertension even in the uninephrectomized patients.

Adult↗
PubMed1995

Ordered structure of the crystallized bovine 20S proteasome.

Eukaryotic proteasomes are multicatalytic proteinase complexes with a molecular weight of 750 kDa, containing, respectively, two copies of a hetero-heptamer of alpha-type subunits and one of beta-type subunits, (alpha 1-7 beta 1-7)2. Proteasome was purified from bovine liver and crystallized into a hexagonal system with cell dimensions of a = b = 121.83(2) A, c = 930.68(6) A. A cylindrical particle size of 122 A diameter and 155 A height was determined from the molecular packing in a unit cell. The crystal gave diffraction spots up to at least 4.4 A resolution, which was the minimum spacing of the camera used. The overall temperature factor of the enzyme was estimated to be in the range of 36.2 to 25.8 A2. These results imply that the enzyme complex has a unique ordered structure comprising multisubunits with two types of hetero-heptamer. This ordered structure may facilitate highly organized cooperation of individual functions of subunits within the enzyme complex.

Amino Acid Sequence↗
PubMed1995

Isolation and characterization of the IS3-like element from Thermus aquaticus.

We have cloned and characterized a genetic element (1187 bp) that is responsible for the induction of thermotolerance as well as ompC expression in E. coli. This element (ISLtaq1) was isolated from Thermus aquaticus. DNA and protein data bases were searched with this element (ISLtaq1), which suggested it to be very similar to IS150 belonging to the IS3 family. ORF1, found on ISLtaq1, which encodes 100 amino acids (aa), had a DNA-binding motif: a helix-turn-helix and a leucine zipper. In fact, when the ORF1 protein was overproduced in E. coli, thermotolerance as well as ompC expression was induced.

Adaptation, Biological↗
PubMed1995

Modulation of angiotensin II type 1 receptor mRNA expression in human blood cells: comparison of platelets and mononuclear leucocytes.

The objective of the present study was to quantify the expression of angiotensin II type 1 (AT1) receptor transcripts in human blood cells--platelets and mononuclear leukocytes--from 10 normal healthy volunteers during the alterations in the renin-angiotensin system. A quantitative assay employing reverse transcription-polymerase chain reaction (RT-PCR) was utilized. Oral administration of furosemide, 40 mg for 2 days, under mild salt restriction (50 mEq NaCl/day) for 6 days stimulated the renin-angiotensin system resulting in significant increases in plasma renin activity (PRA) (1.84 +/- 0.12 vs. 1.05 +/- 0.17 ng/l/s; P < 0.01), plasma angiotensin II concentration, and plasma aldosterone concentration (PAC). The ratio of AT1 receptor mRNA to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA expression in mononuclear leucocytes was significantly (P < 0.05) increased from the basal level (0.49 +/- 0.05 vs. 0.29 +/- 0.03) (P < 0.01), while in platelets these changes were opposite (0.11 +/- 0.05 vs. 0.25 +/- 0.05) (P < 0.01). Compared to these significant changes, salt loading (200 mEq NaCl/day) for 6 days decreased PRA(0.49 +/- 0.10 vs. 1.05 +/- 0.17 ng/l/s; P < 0.01) and induced the opposite changes in the ratio of AT1 receptor/GAPDH mRNA. These data suggest that AT1 receptors in human blood cells may be of two different types--platelets and mononuclear leucocytes.

Adult↗
PubMed1995

Interactions between angiotensin II and norepinephrine on renin release by juxtaglomerular cells.

While the interactions between angiotensin II (Ang II) and norepinephrine (NE) on cardiovascular responses are well known, their effects on renin responses are not. We determined the renin secretion rate (RSR) and intracellular calcium level in juxtaglomerular cells harvested from Sprague-Dawley rats using a radioimmunoassay and a two-dimensional calcium analyzer. The effect of Ang II and NE was inhibitory on RSR and stimulatory on intracellular calcium. The NE-induced RSR response was amplified in the presence of Ang II (20 nmol/l). The NE-induced intracellular calcium response was also potentiated by the Ang II. There was a significant correlation (r = 0.994, p < 0.0001) between the changes in the RSR and those in intracellular calcium levels. Losartan (0.1 mumol/l). an Ang II type 1 receptor antagonist, blocked the Ang II threshold RSR responses and completely abolished the Ang II-related enhancements. The exclusion of calcium from the buffer reduced the maximal RSR response to NE but did not prevent the enhancement, suggesting the importance of the mobilization of intracellular calcium in the mechanism. The Ang II-induced RSR was amplified in the presence of NE (0.2 mumol/l). The Ang II-induced intracellular calcium response was also potentiated by the NE. A significant correlation (r = 0.996, p < 0.0001) between the changes in the RSR and the changes in intracellular calcium levels was also noted. Prazosin (1 mumol/l), an alpha 1-adrenoceptor antagonist, blocked the NE threshold RSR responses and abolished the agonist-related enhancements. The calcium-free buffer diminished this amplication with a slight decrease in the maximum RSR response to Ang II.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-1 Receptor Antagonists↗
PubMed1994

Isolation and characterization of alpha-type HC3 and beta-type HC5 subunit genes of human proteasomes.

Eukaryotic proteasomes from an evolutionarily conserved multi-gene family and are thought to have originated from a common ancestral gene and diverged into alpha-type and beta-type subgroups. To understand the molecular basis of the proteasome genes, we isolated and characterized two human proteasome genes econding the alpha-type HC3 and beta-type HC5 subunit. The functional genes for HC3 and HC5 are similar in being approximately 15 kb in length, but differ in having exon numbers of 9 and 6, respectively. Analyses of about 2.5 to 3.0 kb of the 5'-flanking regions of these two genes revealed the absence of TATA and CAAT promoter elements. However, two or three GC boxes were found. By analysis of the transcriptional regulatory activities in the 5'-flanking regions of the two genes, these GC boxes were found to function coordinately as promoters of the two genes. Interestingly, the HC3 gene possesses an additional silencer element in the 5'-upstream region near the first exon. This element is also able to repress the promoter activities of other genes, such as the HC5 and the type 1 glucose transporter genes, irrespective of whether it has a sense or antisense orientation, indicating that it acts as a general transcriptional silencer. The HC5 gene does not have this silence element, and its promoter activity is five to ten times that of HC3. These results show that the human proteasomal HC3 and HC5 genes differ not only in their genomic structures, such as their numbers of exons and their exon-intron organizations, but also in the mechanisms regulating their transcription, suggesting that they diverged at an early stage of evolution.

Animals↗
PubMed1994

Expression of GATA-binding transcription factors in rat hepatocytes.

Recently, we demonstrated that a DNA-binding protein(s) is involved in transcriptional repression of the rat serine dehydratase gene in fetal liver. Here, we report that a GAT(A/T) motif is the target sequence for the DNA-binding protein. By screening a fetal liver cDNA library, we isolated a rat homolog of GATA-1. Rat GATA-1 expressed as a GST-fusion protein in E. coli bound to the GAT(A/T) motif in the serine dehydratase gene. Northern analysis show that GATA-1 and GATA-4 mRNAs are expressed in fetal hepatocytes.

Amino Acid Sequence↗