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M Kasuga

Publications and source records attributed to M Kasuga.

At least 289 records · Page 16Linked to original sources
PubMed1991

[Difference in effects of sodium fluoride and cholecystokinin on pepsinogen secretion from isolated guinea pig gastric chief cells].

In order to further investigate the precise mechanisms of cholecystokinin(CCK)-induced pepsinogen secretion from gastric chief cells, we compared the signal transducing mechanisms activated by CCK with those activated by sodium fluoride (NaF) in isolated guinea pig gastric chief cells. NaF stimulated a monophasic increase in diacylglycerol accumulation with a peak value observed at 15 sec, while CCK strongly stimulated its biphasic accumulation. NaF evoked an increase in initial Ca2+ influx rate with a slow and smooth increase in intracellular free Ca2+ concentration [( Ca2+]i) monitored by fura-2, while CCK stimulated a rapid increase in [Ca2+]i followed by a late sustained phase of [Ca2+]i increase. Lanthanum chloride (La3+) effectively (unlike either nifedipine or verapamil) blocked NaF-stimulated increase in [Ca2+], but it blocked only CCK-stimulated late sustained phase of [Ca2+]i increase. La3+ reduced NaF-or CCK-stimulated maximal pepsinogen secretion to 57.0 +/- 2.5% and 73.1 +/- 3.1% of control, respectively. These results suggest that NaF activates a signal transducing mechanism which seems to be distinct from that activated by CCK, thereby inducing an increase in diacylglycerol accumulation, Ca3+ influx and pepsinogen secretion in guinea pig gastric chief cells.

Animals↗
PubMed1991

Characterization of cholecystokinin receptors on guinea pig gastric chief cell membranes.

The binding of cholecystokinin (CCK) to its receptors on guinea pig gastric chief cell membranes were characterized by the use of 125I-CCK-octapeptide (CCK8). At 30 degrees C optimal binding was obtained at acidic pH in the presence of Mg2+, while Na+ reduced the binding. In contrast to reports on pancreatic and brain CCK receptors, scatchard analysis of CCK binding to chief cell membranes revealed two classes of binding sites. Whereas, in the presence of a non-hydrolyzable GTP analog, GTP gamma S, only a low affinity site of CCK binding was observed. Chief cell receptors recognized CCK analogs, with an order of potency of: CCK8 greater than gastrin-I greater than CCK4. Although all CCK receptor antagonists tested (dibutyryl cyclic GMP, L-364718 and CR1409) inhibited labeled CCK binding to chief cell membranes, the relative potencies of these antagonists in terms of inhibiting labeled CCK binding were different from those observed in either pancreatic membranes or brain membranes. The results indicate, therefore, that on gastric chief cell membranes there exist specific CCK receptors, which are coupled to G protein. Furthermore, chief cell CCK receptors may be distinct from pancreatic or brain type CCK receptors.

Animals↗
PubMed1991

The inhibitory effect of anti-tumor drugs on phosphatidylcholine synthesis and its reversal by geranylgeranylacetone in the isolated guinea pig gastric glands.

To clarify the mechanism by which the administration of anti-tumor drugs, antibiotics or hypoglycemic agents causes gastric mucosal injury, the effects of these drugs on phosphatidylcholine synthesis in isolated guinea pig gastric glands were examined in vitro. Anti-tumor drugs such as tegafur, cyclophosphamide, and mitomycin C decreased [3H]choline incorporation into phosphatidylcholine. Furthermore, tegafur at 0.4 mg/ml decreased [3H]choline incorporation in the glands that had been pulsed with [3H]choline incorporation, suggesting that tegafur exerts its effect by inhibiting late step of phosphatidylcholine synthesis in the stomach. On the other hand, cefaclor and glibenclamide had no effect on [3H]choline incorporation. Geranylgeranylacetone, an anti-ulcer drug partially restored tegafur-induced reduction of [3H]choline incorporation into phosphatidylcholine. These results suggest that the anti-tumor drug-induced gastric mucosal injury may be due to drug-induced decrease in phosphatidylcholine synthesis, which the restoration of phosphatidylcholine synthesis by geranylgeranylacetone may explain its anti-ulcer action on drug-induced gastric mucosal lesions in vivo.

Animals↗
PubMed1991

Activation of MAP kinase and enhanced phosphorylation of the 350-kDa protein by mitogenic stimuli in quiescent Balb/c 3T3 cells.

In quiescent Balb/c 3T3 cells, competence factors such as platelet-derived growth factor and 12-O-tetradecanoylphorbol-13-acetate (TPA) activated MAP kinase, whereas progression factors such as insulin did not. Insulin was, however, capable of activating MAP kinase in cells pretreated with TPA. Moreover, TPA plus insulin activated MAP kinase more strongly and for a longer time period than did TPA alone. Treatment of Balb/c 3T3 cells with competence factors stimulated phosphorylation of the 350-kDa protein which was immunoprecipitated with antibodies against brain high-molecular-weight microtubule-associated protein MAP1, whereas insulin treatment did not stimulate the phosphorylation. Insulin could induce, however, further increase in the phosphorylation of the 350-kDa protein, when added simultaneously with TPA or added to the TPA-treated cells. The enhanced phosphorylation of the 350-kDa protein thus correlated with the MAP kinase activation. As insulin acts synergistically with TPA to induce initiation of DNA synthesis in the quiescent Balb/c 3T3 cells, it seems that activation of MAP kinase and enhanced phosphorylation of the 350-kDa protein are accompanied by the initiation of DNA synthesis.

Animals↗
PubMed1991

A pilot clinical trial of a new oral hypoglycemic agent, CS-045, in patients with non-insulin dependent diabetes mellitus.

CS-045, (+/-)-5-[4-(6-hydroxy-2,5,7,8-tetramkethylchroman-2- ylmethoxy)benzyl]-2,4-thiazolidinedione, lowers plasma glucose in several animal models of non-insulin dependent diabetes mellitus (NIDDM) presumably by increasing insulin sensitivity. Little adverse effect was found in a phase 1 study on healthy male subjects. In order to test its efficacy in lowering plasma glucose in NIDDM in man, a pilot multi-center clinical trial of CS-045 was carried out in 146 patients with NIDDM whose glycemic control was inadequate (FPG greater than 140 mg/dl) on diet and/or other oral hypoglycemic agents. CS-045 was given orally in a daily dose of 200 mg or 400 mg for 12 weeks in addition to the previous treatment. The mean fasting plasma glucose (FPG) and fructosamine began to decrease within 2 weeks and the mean HbA1c within 8 weeks. After 12 weeks, the FPG fell from 192 +/- 41 to 155 +/- 45 mg/dl (P less than 0.01), fructosamine from 3.7 +/- 0.6 to 3.3 +/- 0.6 (P less than 0.01), and HbA1c from 8.9 +/- 1.5 to 8.1 +/- 1.5% (P less than 0.01). The drug was effective in 39% of patients in that FPG fell by more than 20% of the initial value. This rate of efficacy was the same when CS-045 was given alone or together with other oral hypoglycemic agents. The drug was more effective in a dosage of 400 mg than with 200 mg (the rate of efficacy 46% vs 25%) and more effective in obese patients than in lean patients (46% vs 25%).(ABSTRACT TRUNCATED AT 250 WORDS)

Biomarkers↗
PubMed1991

Brain peptide YY receptors: highly conserved characteristics throughout vertebrate evolution.

We have shown previously that peptide YY (PYY) receptors are uniquely distributed in various mammalian brains and also have identified the receptor from porcine hippocampal membranes as a protein of 50,000 mol wt. To extend these observations, both the characteristics of PYY-receptor interaction and the structure of the receptor have been examined and compared with those of its sister peptide, neuropeptide Y (NPY), in the brains of various vertebrates including mammals (human, dog, guinea pig, rat, and mouse), birds (chicken), reptiles (snapping turtle), amphibians (bullfrog), and fish (yellowtail fish). The affinities and relative potencies of PYY as well as NPY receptors for pancreatic polypeptide (PP) family peptides were about the same in all species examined except for chickens. PYY and NPY bound to both the PYY and NPY receptors with high affinities, but porcine and avian PPs did not. In chicken brain, however, PYY, NPY, porcine PP, and avian PP all bound to the receptors with high affinity. Analysis of the equilibrium binding data for PYY receptors produced curvilinear Scatchard plots in all of the species, suggesting the existence of high and low affinity binding sites. Affinity cross-linking using disuccinimidyl suberate followed by electrophoretic analysis of ligand-receptor complexes characterized the molecular size of PYY and NPY receptors. [125I]PYY was cross-linked to a protein of 50,000 mol wt without sulfhydryl-bonded subunits on mammalian hippocampal membranes. A receptor protein with the same mol wt was identified in other brain areas, including hypothalamus and pituitary, PYY receptors in other vertebrate brains were similar in size to those of mammalian species except in chicken brain, where a receptor protein of 67,000 mol wt was observed. In addition, we also have demonstrated that the NPY receptor is a monomeric 50,000 and 55,000 mol wt protein in mammalian and fish brains, respectively. These findings indicate that brain PYY and NPY receptors in most vertebrate species from fish to man are pharmacologically and structurally similar and have been well conserved over a period of evolution of 400 million yr. The divergence of the receptors observed in chicken brain may reflect some change in their function.

Animals↗
PubMed1991

[Diabetes mellitus and molecular biology].

There are two approaches to identify diabetes-susceptibility genes. One approach is to isolate and characterize genes expressed in the beta-cell and in insulin target tissues whose mutation or altered expression may contribute to the development of diabetes mellitus. Another approach is to clone a diabetes-susceptibility gene by a reverse genetic strategy. The first step for this strategy is to identify a DNA polymorphism that is linked to the disease locus. Using the strategy of the first approach, several candidate genes were examined. Among these genes, the mutation of insulin genes and insulin receptor genes was found in the patient with diabetes. By cDNA cloning or PCR-direct sequencing methods, we identified several mutations in the insulin receptor genes of four insulin-resistant diabetic patients. At least two mutants of insulin receptor genes were expressed in Chinese hamster ovary cells and these mutated receptors showed impaired ability to transduce insulin action in these cultured cells. The expression of these mutant genes in animals such as transgenic mice will be indispensable to establish the relationship between the gene mutation and the abnormality found in the patient. Using the strategy of the second approach, Bell et al. recently reported that the gene responsible for MODY (maturity-onset diabetes of the young) is tightly linked to the adenosine deaminase gene on chromosome 20q. However, this strategy will not be applicable for identification of diabetes-susceptibility genes of NIDDM, since this disorder is likely to be genetically heterogenous, with mutations in several different genes able to cause hyperglycemia, and this heterogeneity could confound the linkage analysis.

Diabetes Mellitus↗
PubMed1991

[The inhibitory effect of cholecystokinin on phosphatidylcholine synthesis in isolated rat pancreatic acini].

The effects of cholecystokinin (CCK) and other pancreatic secretagogues on phosphatidylcholine (PC) synthesis were studied in isolated rat pancreatic acini. When acini were incubated with [3H] choline in the presence of 1 nM CCK-octapeptide (CCK8) for 60 min, the incorporations of [3H] choline to both water soluble choline metabolites and PC in acini were reduced by CCK8 to 74% and 41% of control, respectively. Pulse-chase study revealed that CCK reduced both the disappearance of phosphocholine and the synthesis of PC. Ca(2+)-mobilizing secretagogues such as carbamylcholine and Ca2+ ionophore A23187 also reduced PC synthesis to the same extent as CCK8. By contrast, neither cAMP-dependent secretagogues such as secretin and dibutyryl cAMP nor a phorbol ester had any effect on PC synthesis in acini. These results suggest that CCK inhibits PC synthesis by inducing both the reduction of choline uptake into acini and the inhibition of CTP: phosphocholine cytidylyltransferase activity. This hormonal regulation of PC synthesis via CDP-choline pathway appears to be mediated by Ca(2+)-dependent pathway but not by cAMP- or protein kinase C-dependent pathway.

Animals↗
PubMed1990

Phosphorylation state and biological function of a mutant human insulin receptor Val996.

Chinese hamster ovary (CHO) cell transfectants that expressed human insulin receptors whose glycine 996 was substituted by valine were studied. Receptor processing and insulin binding were unaffected by this mutation; however, this mutant insulin receptor had little or no tyrosine kinase activity. Nevertheless, the Val996 mutant exhibited seryl and threonyl phosphorylation in both the basal and insulin-stimulated state in intact cells. This is in contrast to the Lys----Ala1018 tyrosine kinase deficient mutant (Russell, D. S., Gherzi, R., Johnson, E. L., Chou, C-K., and Rosen, O. M. (1987) J. Biol. Chem. 262, 11833-11840). Cells expressing the normal human receptor were 10-fold more sensitive to insulin than the untransfected CHO cells with respect to phosphorylation of a cellular substrate (pp 185) on tyrosyl residues, glucose incorporation into glycogen, thymidine incorporation into DNA, and phosphorylation of ribosomal protein S6. Cells expressing the mutant receptor exhibited the same insulin sensitivity as the untransfected CHO cells. Insulin was rapidly internalized in cells expressing the normal human receptor and the number of receptors expressed on the cell surface was decreased in response to exposure to insulin. However, little insulin was internalized in cells expressing the mutant receptor, and the number of receptors on the cell surface was not significantly diminished in response to exposure to insulin. It is concluded that despite the occurrence of seryl and threonyl phosphorylations, post-receptor effects of insulin described above are not mediated by the tyrosine kinase-deficient receptor, Val996.

Amino Acid Sequence↗
PubMed1990

Natural regulatory mechanisms of insulin degradation by insulin degrading enzyme.

Insulin-degrading enzyme (IDE) accounts for most of the insulin degrading activity in extracts of several tissues and plays an important role in the intracellular degradation of insulin. Using newly developed sandwich radioimmunoassay for rat IDE, this enzyme was detectable in all tissues we examined and liver had the highest level of IDE. The ratio of insulin degrading activity to IDE concentration was roughly the same in liver, brain and muscle, however, twice as high in kidney as compared with other tissues. On the contrary, its degrading activity in these tissue extracts, including kidney, was completely lost after immunoprecipitation of IDE. These results suggest that IDE degrades insulin in the initial step of cleavage and that there are some mechanisms to regulate insulin degrading activity by IDE in the tissues.

Animals↗
PubMed1990

Insulin enhancer binding protein has helix-loop-helix structure.

Insulin gene expression is restricted to pancreatic B cells and the 5' flanking region is responsible for the tissue specificity. The GCCATCTG motif in this region of the rat insulin 1 gene functions as an enhancer for insulin transcription. A cDNA coding for a GCCATCTG motif-binding protein (IEBP1) was isolated from a rat pancreatic B cell tumor lambda gt11 library. The IEBP1 protein was found to be the rat counterpart of the immunoglobulin (Ig) enhancer binding protein E12/47 having a helix-loop-helix domain. This result indicates that the Ig gene and insulin gene employ the same (or a similar) binding protein as a part of their transcriptional apparatus.

Amino Acid Sequence↗
PubMed1990

Immunological detection of phosphotyrosine-containing proteins in rat livers after insulin injection.

Tyrosine-phosphorylated proteins in Triton X-100-solubilized fractions of rat livers were examined by immunoblotting with anti-phosphotyrosine antibodies. After 2 min of insulin injection via the portal vein into livers, three major bands of 170,000, 140,000, and 95,000 Mr were stimulated. Because the incubation of nitrocellulose membrane with anti-phosphotyrosine antibodies in the presence of 40 mM phosphotyrosine completely abolished these bands, the anti-phosphotyrosine antibodies appear to recognize the phosphotyrosine residues of these proteins. Insulin injection (2-2000 micrograms) very quickly stimulated the tyrosine phosphorylation of these proteins in a dose-dependent fashion. In contrast, insulinlike growth factor I or epidermal growth factor injection had little effect in stimulating the tyrosine phosphorylation of these proteins. Because anti-insulin-receptor antibodies immunoprecipitated a tyrosine-phosphorylated 95,000-Mr protein, this protein must be the beta-subunit of the insulin receptor; i.e., the beta-subunit of the insulin receptor and two other proteins were phosphorylated at tyrosine residues in vivo by insulin injection. These data suggest that the tyrosine phosphorylation and tyrosine kinase activity of the insulin receptor may have important roles in in vivo insulin action.

Animals↗
PubMed1990

Substrates for insulin-receptor kinase.

Several studies suggest that the tyrosine-specific protein kinase activity of the beta-subunit of the insulin receptor is necessary to mediate the biological effects of insulin. This conclusion leads to the hypothesis that the effect of insulin is mediated through the tyrosine phosphorylation of cellular substrates by the insulin-receptor tyrosine kinase. In this review, the experimental evidence regarding insulin-stimulated phosphorylation of proteins both in vitro and in vivo is evaluated. In a cell-free system, tubulin, microtubule-associated protein 2, tau, fodrin, calmodulin-dependent kinase, calmodulin, and lipocortins 1 and 2 were reported to be good substrates for insulin-receptor kinase. However, none were found to be tyrosine phosphorylated in an intact-cell system. In intact-cell systems, proteins of Mr 185,000 (pp185), 120,000 (pp120), 240,000 (pp240), 15,000 (pp15), 60,000 (pp60), and 62,000 (pp62) as well as several others were reported to be tyrosine phosphorylated in an insulin-dependent fashion. However, the function or functional alteration of these proteins induced by insulin-stimulated tyrosine phosphorylation is not clear. Therefore, physiologically relevant substrates for the insulin-receptor kinase have not been established, and more work is necessary to verify the phosphorylation cascade hypothesis of insulin action.

Animals↗
PubMed1989

Identification of a phosphorylation site of the rat insulin receptor catalyzed by protein kinase C in an intact cell.

In two-dimensional tryptic phosphopeptide mapping, the beta-subunit of the insulin receptor phosphorylated by 12-O-tetradecanoylphorbol-13-acetate in rat hepatoma cells (H-35) was separated into one phosphothreonine-containing peptide and several phosphoserine-containing peptides. The synthetic peptide coding residues 1327-1343 in the C-terminal region of the rat insulin receptor was phosphorylated at the threonine residue by protein kinase C in a phosphatidylserine and oleoylacetylglycerol dependent manner. Tryptic digest of this phosphopeptide migrated to the same position as the phosphothreonine containing peptide obtained from the beta-subunit in two-dimensional phosphopeptide mapping. These data suggested that Thr 1336 of the insulin receptor is the site of phosphorylation by protein kinase C in intact cells.

Animals↗