| Project/Area Number |
06670134
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
General medical chemistry
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| Research Institution | Yamagata University |
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Principal Investigator |
ISHIKAWA Kiichi Yamagata Univ.School of Medicine Prof., 医学部, 教授 (40018312)
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| Co-Investigator(Kenkyū-buntansha) |
OTSU Kaoru Yamagata Univ.School of Research Associate, 医学部, 助手 (80185305)
KUZUMAKI Takejiro Yamagata Univ.School of Assoc.Prof., 医学部, 助教授 (70211208)
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| Project Period (FY) |
1994 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1994: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Aldolase B / Carbohydrate intake / gene expression control / Insulin / Glucagon / Primary cultured hepatocyte / hormone action / signal transduction / B形アルドラーゼ / アルドラーゼB遺伝子 / 遺伝子発現誘導 / ホルモン協調的作用 / プロモーター活性 / run-on assay / G-free cassette |
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| Research Abstract |
Aldolase B is a liver-specific enzyme of glycolysis pathway, and its gene expression in the liver was significantly induced by the intake of carbohydrate. Interestingly, the mRNA level of serum albumin which is also specifically synthesized in the liver did not elevated when that of aldolase B was much elevated. We confirmed by run-on assay that this induction of aldolase B gene expression is the induction at the transcriptional level. By measuring the concentrations of several hormones in the blood during the induction by carbohydrate food intake, we found that insulin level increased, while glucagon level decreased reciprocally, in parallel to the induction. Corticosterone level did not change as much as other formones. These results suggested that the carbordhyate intake increases insulin secretion and suppresses glucagon secretio in the rat and the change of both hormone concentration in the blood is the cause of aldolase gene induction.
To verify above idea, we employed primary cultured hepatocytes and assessed direct dffects of above hormones on the isolated hepatocytes. The result showed that insulin and dexamethazone stimulated aldolase B gene transcription by a concentration-dependent manner and glucagon suppressed it. The suppressive effect of glucagon on aldolase B gene transcription did not change in the presence or absence of insulin and dexamethazone. This, we realized that glucagon is the most important factor to aldolase B gene transcription.
In order to understand how glucagon exerts its effect, we added forskolin or dibutyryl-cAMP to primary cultured hepatocytes. Both of them suppressed aldolase B gene transcription dose-dependently. H-7, a specific inhibitor of protein-kinase A,canceled the effect of glucagon also dose-dependently. Thus, it is certain that glucagon exerts its effect on sldolase B gene transcription by the activation of protein-kinase A.
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