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T Hanabusa

Publications and source records attributed to T Hanabusa.

15 recordsLinked to original sources
PubMed1998

Organization of the human carboxypeptidase E gene and molecular scanning for mutations in Japanese subjects with NIDDM or obesity.

Insulin is synthesized in the pancreatic beta cell as a larger precursor molecule proinsulin which is converted to insulin and C-peptide by the concerted action of prohormone convertase 2 (PC2), prohormone convertase 3 (PC3) and carboxypeptidase E (CPE). One of the features of non-insulin-dependent diabetes mellitus (NIDDM) is an elevation in the proinsulin level and/or proinsulin/insulin molar ratio suggesting that mutations in these three proinsulin processing enzymes might contribute to the development of NIDDM. The identification of a mutation in the CPE gene of the fat/fat mouse which leads to marked hyperproinsulinaemia and late-onset obesity and diabetes is consistent with a possible role for mutations in CPE in the development of diabetes and obesity in humans. In order to test this hypothesis, we have isolated and characterized the human CPE gene and screened it for mutations in a group of Japanese subjects with NIDDM and obesity. The human CPE gene consists of 9 exons spanning more than 60 kb. Primer extension analysis identified the transcriptional start site at -141 bp from the translational start site. Single strand conformational polymorphism analysis and nucleotide sequencing of the promoter and entire coding region of the CPE gene in 269 Japanese subjects with NIDDM, 28 nondiabetic obese subjects and 104 nonobese and nondiabetic controls revealed three nucleotide changes, a G-to-T substitution at nucleotide -53, a G-to-A substitution at nucleotide -144 (relative to start of transcription) in the promoter region and a silent G-to-A substitution in codon 219. None of the nucleotide substitutions were associated with NIDDM or obesity. Thus, genetic variation in the CPE gene does not appear to play a major role in the pathogenesis of NIDDM or obesity in Japanese subjects.

Base Sequence↗
PubMed1998

Characterization of the promoter of the mouse prohormone convertase PC2 gene.

Prohormone convertase 2 (PC2) is a member of a family of mammalian subtilisin-like endoproteases that are involved in the processing of prohormones, neuropeptides and many other precursor derived proteins. The expression of PC2 is restricted to neuroendocrine tissues such as pancreatic islets, the pituitary and the brain. To understand the regulation of the PC2 gene, we cloned and characterized the promoter region of the mouse PC2 gene. The transcriptional start site of the mouse PC2 gene is identical to that of the human. There is 79% identity in the sequences of the promoter regions between the mouse and human PC2 genes. The mouse PC2 gene, like the human, does not have a TATA-like motif in the region just upstream of the start of the transcription. Studies with promoter-reporter gene, chloramphenicol acetyltransferase (CAT), constructs showed that the region from -400 to -170 bp was necessary for high level expression of the mouse PC2 gene in the betaTC-3 insulinoma cells.

Animals↗
PubMed1997

A missense mutation of the muscle glycogen synthase gene (M416V) is associated with insulin resistance in the Japanese population.

Muscle glycogen synthase (GYS1) is a key enzyme of non-oxidative pathway of glucose metabolism that has been reported to be related to insulin resistance in non-insulin-dependent diabetic (NIDDM) patients. We scanned the GYS1 gene for mutation by single strand conformational polymorphism in 244 non-obese Japanese NIDDM patients and 181 non-diabetic control subjects, and found two missense mutations; Met to Val at position 416 in the exon 10 (M416V) and Pro to Ala at position 442 in the exon 11 (P442A). The P442A mutation was found in only one NIDDM patient treated with sulfonylureas. On the other hand, the M416V mutation was widely found in the Japanese population. The mutant allele frequency in the NIDDM patients (13.7%) was slightly higher but not statistically significant compared with that in non-diabetic subjects (9.7%). However, the insulin sensitivity index [SI: x 10(-4) x min(-1) x (microU/ml)(-1)] estimated by Minimal Model analysis in the NIDDM patients carrying the M416V mutation was significantly lower than that in those without the mutation (1.18 +/- 0.27, n = 21 vs 2.20 +/- 0.20, n = 60, mean +/- SEM, p < 0.01). Glucose effectiveness, age, body mass index, and levels of glycated haemoglobin and serum lipids were not significantly different between the two groups. The same trend could be seen in non-diabetic subjects (SI: 3.70 +/- 0.46, 9 subjects with the mutation vs 5.94 +/- 0.66, 19 subjects without the mutation, p < 0.05). These findings indicate that the M416V mutation of the GYS1 gene is one of the factors contributing to the insulin resistance in the Japanese population and may play some role in the pathogenesis of NIDDM.

Adult↗
PubMed1996

Human prohormone convertase 3 gene: exon-intron organization and molecular scanning for mutations in Japanese subjects with NIDDM.

Proinsulin is converted to insulin by the concerted action of two sequence-specific subtilisin-like proteases termed prohormone convertase 2 (PC2) and prohormone convertase 3 (PC3). PC3 is a type I proinsulin-processing enzyme that initiates the sequential processing of proinsulin to insulin by cleaving the proinsulin molecule on the COOH-terminal side of the dibasic peptide, Arg31-Arg32, joining the B-chain and C-peptide. Thus, PC3 plays a key role in regulating insulin biosynthesis. Expressions of insulin and PC3, but not PC2, are coordinately regulated by glucose, consistent with the important role of PC3 in regulating proinsulin processing. NIDDM is associated with increased secretion of proinsulin and proinsulin-like molecules, suggesting that mutations in the PC3 gene may be involved in the development of this disorder. To examine this hypothesis, we have isolated and characterized the human PC3 gene and screened it for mutations in a group of Japanese subjects with NIDDM. The PC3 gene consists of 14 exons spanning more than 35 kb. The exon-intron organization of PC2 and PC3 genes are conserved, consistent with a common evolutionary origin for the prohormone convertase gene family. Single-strand conformational analysis and nucleotide sequencing of the entire coding region of the PC3 gene in 102 Japanese subjects with NIDDM revealed missense mutations in exons 2 (Arg/Gln53) and 14 (Gln/Glu638), neither of which was associated with NIDDM in this population. These data suggest that genetic variation in the PC3 gene is unlikely to be a major contributor to NIDDM susceptibility in Japanese.

Animals↗
PubMed1996

Missense mutation of amylin gene (S20G) in Japanese NIDDM patients.

Many studies suggest that amylin, which is cosecreted with insulin from islet beta-cells, is a biologically active peptide and modulates plasma glucose levels. We therefore scanned the amylin gene for mutations in 294 Japanese NIDDM patients by single-strand conformational polymorphism, and we found a single heterozygous missense mutation (Ser-->Gly at position 20: S20G mutation) in 12 NIDDM patients (frequency 4.1%). None of the 187 nondiabetic subjects or 59 IDDM patients had the mutation. Of 12 patients carrying the mutation, 8 were diagnosed as having NIDDM at a relatively early age (< or = 35 years), and they had severe diabetes and strong family histories of late-onset NIDDM. On the other hand, the remaining four patients were diagnosed as having NIDDM after age 51, and they had mild diabetes without family histories of diabetes. In high-performance liquid chromatography analysis, a small amount (16%) of amylin immunoreactivity appeared in the position corresponding to normal amylin and a much larger amount (84%) appeared in the position corresponding to mutant amylin. These findings suggest that the S20G mutation of the amylin gene may play a partial role in the pathogenesis of early-onset NIDDM in the Japanese population and may also provide an important model to investigate the true physiological action of amylin.

Adult↗
PubMed1994

Nucleotide sequence and analysis of the mouse SPC3 promoter region.

Insulin is converted from the higher molecular weight proprotein, proinsulin by highly specific proteolytic cleavage at two dibasic amino acid sites. SPC3 and SPC2, two recently identified prohormone convertase that are specifically expressed in beta cells and other neuroendocrine cells, appear to be responsible for those cleavages. We have sequenced the 5'-upstream region of the SPC3 gene and examined its promotor/enhancer activity and most of several deletion mutants in several cell lines. This region contains no CAAT box but has several non-functional TATA-like sequences and several putative transcriptional regulatory elements, including AP-1, Sp1 and cAMP response elements. These features are not unlike those of the human SPC2 upstream region. In beta TC3 insulinoma cells, the sequence between the EcoRI (620 bp) and NsiI (702 bp) sites seems to be important for gene expression, while the sequence between the NsiI and DraI (775 bp) sites may contain strong enhancer element(s).

Amino Acid Sequence↗
PubMed1992

Lack of effect of islet amyloid polypeptide on hepatic glucose output in the in situ-perfused rat liver.

Islet amyloid polypeptide (IAPP), a novel peptide isolated from islet amyloid deposits in patients with insulinoma and non-insulin-dependent diabetes mellitus (NIDDM), has been reported to be cosecreted with insulin from pancreatic beta cells and to inhibit glucose uptake and glycogen synthesis in muscle tissue in vitro. We investigated the effects of the synthesized, rat-amidated form of IAPP on hepatic glucose output, and IAPP extraction, using an in situ flow-through perfusion system in rats to elucidate the actions of IAPP on the liver. The IAPP (10(-8) mol/L) alone had no effects on the hepatic glucose release. Infusion of 6 x 10(-11) mol/L glucagon alone resulted in an expected elevation in glucose production (30.0 +/- 1.7 mumol/35 min/g liver). Insulin (3 x 10(-10) mol/L) submaximally decreased the glucagon-stimulated glucose production to 73% (from 30.0 +/- 1.7 to 22.0 +/- 1.4 mumol/35 min/g liver; n = 7, P less than .01). A simultaneous infusion of 10(-8) mol/L IAPP did not influence the glucagon-stimulated glucose production (27.6 +/- 1.2 mumol/35 min/g liver) or the insulin-dependent inhibition of glucagon-stimulated glucose production (22.6 +/- 1.3 mumol/35 min/g liver). IAPP extraction by the liver in a single passage was minimal, in contrast to approximately 50% hepatic insulin extraction. These results indicate that IAPP does not play any important role in modulating glycogen metabolism in the liver.

Amyloid↗
PubMed1992

Islet amyloid polypeptide (IAPP) secretion from islet cells and its plasma concentration in patients with non-insulin-dependent diabetes mellitus.

Islet amyloid polypeptide (IAPP/Amylin) is a novel peptide which was extracted from islet amyloid deposits in patients with non-insulin-dependent diabetes mellitus (NIDDM). However, its pattern of secretions and plasma concentrations under various conditions has not yet been made clear enough. In this study, we examined IAPP secretion from islet beta-cells in vitro using cultured islet cells of neonatal rat pancreas and plasma IAPP responses under various conditions in vivo in normal control subjects and patients with glucose intolerance. Our data revealed that (1) IAPP is co-secreted with insulin from islet cells of the rat pancreas by glucose and non-glucose stimuli; (2) fasting plasma IAPP levels in normal control subjects are 24.9 +/- 2.0 pg/ml and the molar ratio of IAPP/insulin is approximately 1/7; (3) fasting IAPP levels are high in obese patients and low in insulin-dependent diabetic patients, and the molar ratio of IAPP/C-peptide in NIDDM patients is lower than that in normal control subjects, suggesting the basal hyposecretion of IAPP relative to insulin in NIDDM; and (4) the obese patients who had a hyperresponsiveness of insulin relative to C-peptide had the hyperresponsiveness of IAPP relative to C-peptide during an oral glucose load, suggesting that IAPP may have some physiological effect in glucose metabolism.

Adult↗
PubMed1991

Plasma islet amyloid polypeptide (Amylin) levels and their responses to oral glucose in type 2 (non-insulin-dependent) diabetic patients.

Fasting plasma islet amyloid polypeptide concentrations and their responses to an oral glucose load were determined in non-diabetic control subjects and patients with abnormal glucose tolerance in relation to the responses of insulin or C-peptide. Plasma islet amyloid polypeptide was measured by radioimmunoassay. In the non-diabetic control subjects, fasting plasma islet amyloid polypeptide was 6.4 +/- 0.5 fmol/ml (mean +/- SEM) and was about 1/7 less in molar basis than in insulin. The fasting islet amyloid polypeptide level rose in obese patients and fell in patients with Type 1 (insulin-dependent) diabetes mellitus. In non-obese patients with impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetic patients without insulin therapy, the level was equal to that of the control subjects, but a low concentration of islet amyloid polypeptide relative to insulin or C-peptide was observed in the non-obese Type 2 diabetic group. The patterns of plasma islet amyloid polypeptide responses after oral glucose were similar to those of insulin or C-peptide. However, compared to non-obese patients, a hyper-response of islet amyloid polypeptide relative to C-peptide was noted in obese patients who had a hyper-response of insulin relative to C-peptide. This study suggests that basal hypo-secretion of islet amyloid polypeptide relative to insulin exists in non-obese Type 2 diabetes and that circulating islet amyloid polypeptide may act physiologically with insulin to modulate the glucose metabolism.

Adult↗