1999 Fiscal Year Final Research Report Summary
Molecular Mechanism of Glucagon for Suppression of Aldolase B Gene Transcription
| Project/Area Number |
10671055
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Metabolomics
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| Research Institution | YAMAGATA UNIVERSITY |
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Principal Investigator |
KAZUMAKI Takejiro School of Medicine, Yamagata Univ. Associate Professor, 医学部, 助教授 (70211208)
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| Co-Investigator(Kenkyū-buntansha) |
IUCHI Yoshihito School of Medicine, Yamagata Univ. Instructor, 医学部, 助手 (60272069)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Aldolase / Gene Expression / Glucagon / Hepatocytes / Glucose Metabolism |
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| Research Abstract |
Transcription of the aldolase B gene, AldB, in the liver is regulated by hormones such as insulin and glucagon. We investigated the molecular mechanism of glucagon for suppression of aldolase B gene expression since glucagon is a potent suppressor for aldolase B gene transcription. In this research project, we clarified the signal transduction pathway triggered by glucagon and identified the glucagon-responsive element and insulin-responsive region in aldolase B gene promoter. Glucagon binds to the specific receptor located on the surface of hepatocytes. We examined the signal transduction pathway using H-7 (protein kinase A inhibitor), forskolin and dbcAMP (cAMP agonist) in rat primary cultured hepatocytes. By the experiments, we concluded that glucagon suppresses the aldolase B gene expression through the cAMP/protein kinase A pathway. To characterize the elements which are responsive to glucagon in the upstream region of AldB, plasmids carrying various length of the upstream region
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of this gene were constructed and transfected to primary cultured rat hepatocytes. The transcription activities of the mutants containing the sequences between -764 and +25 bp were suppressed by glucagon. Within this region, the sequence element similar to the cAMP-responsive element (CRE) was found between -89 and -82bp (designated CRE-89). The deletion of the CRE-89 element diminished the responsiveness to glucagon. A gel retardation assay showed that the nuclear factors bind to the CRE-89 element. These results suggest that the CRE-89 element in the promoter region is prerequisite for suppression of the gene by glucagon in hepatocytes. On the other hand, insulin enhanced the transcription activity of aldolase B gene. The transcription activities of the mutants containing the sequences between -228 and -85 bp were enhanced by insulin. Within this region, the known insulin-responsive elements (IRE) was not found. Novel IRE is suggested to involve in the activation of aldolase B gene expression Less
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